JP2019133773A - Nonaqueous electrolyte and nonaqueous electrolyte power storage component - Google Patents

Abstract

To provide nonaqueous electrolyte capable of improving capacity maintenance rate of nonaqueous electrolyte power storage component after charge discharge cycle where the maximum arrival potential of positive electrode reaches high potential, and to provide a nonaqueous electrolyte power storage component including the same.SOLUTION: Nonaqueous electrolyte for power storage component contains electrolyte salt and nonaqueous solvent, where the nonaqueous solvent contains fluorination cyclic carbonate, fluorination chain carbonate, and fluorination non-carbonate compound having viscosity of 4 mPa s or less at 25°C. In another aspect, the nonaqueous electrolyte power storage component includes a positive electrode containing a positive electrode active material actuating under such charging conditions that the maximum arrival potential goes above 4.5 V (vs.Li/Li), and the nonaqueous electrolyte mentioned above.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nonaqueous electrolyte and a nonaqueous electrolyte storage element.

  Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte (electrolytic solution) interposed between the electrodes, and an ion is interposed between the electrodes. It is comprised so that it may charge / discharge by performing delivery. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are widely used as nonaqueous electrolyte storage elements other than nonaqueous electrolyte secondary batteries.

In a nonaqueous electrolyte storage element, it is desired that good performance is maintained even by repeated charge and discharge. However, the non-aqueous electrolyte storage element is operated under charging conditions in which the maximum potential of the positive electrode is a high potential of, for example, 4.5 V (vs. Li ^/ Li ⁺ ) or more, so that the capacity retention rate is reduced. Become prominent. Such a decrease in the capacity retention rate is attributed to oxidative decomposition of the nonaqueous electrolyte that occurs at a high potential. On the other hand, in order to improve oxidation resistance, an electrolytic solution containing a fluorinated saturated cyclic carbonate and a fluorinated chain carbonate has been proposed (see Patent Document 1).

Japanese Patent Laying-Open No. 2015-191737

  However, even in a nonaqueous electrolyte storage element using a nonaqueous solvent containing a fluorinated carbonate as described above, the capacity retention rate after a charge / discharge cycle in which the maximum potential reached by the positive electrode reaches a high potential can be said to be sufficiently high. It is not a thing.

  The present invention has been made based on the circumstances as described above, and its object is to improve the capacity retention rate of the nonaqueous electrolyte storage element after a charge / discharge cycle in which the maximum potential reached by the positive electrode reaches a high potential. It is providing the nonaqueous electrolyte which can be manufactured, and a nonaqueous electrolyte electrical storage element provided with the same.

  One embodiment of the present invention made to solve the above problems includes an electrolyte salt and a nonaqueous solvent, wherein the nonaqueous solvent has a fluorinated cyclic carbonate, a fluorinated chain carbonate, and a viscosity at 25 ° C. of 4 mPa · It is a non-aqueous electrolyte for an electricity storage device containing a fluorinated non-carbonate compound that is s or less.

Another embodiment of the present invention is a non-aqueous device including a positive electrode including a positive electrode active material that operates under a charging condition in which a maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or more, and the non-aqueous electrolyte. It is an electrolyte storage element.

Another embodiment of the present invention is a nonaqueous electrolyte storage element that includes a positive electrode and the nonaqueous electrolyte, and has a maximum ultimate potential of 4.5 V (vs. Li ^/ Li ⁺ ) or more.

  According to the present invention, a nonaqueous electrolyte capable of improving the capacity retention rate of a nonaqueous electrolyte storage element after a charge / discharge cycle in which the maximum potential of the positive electrode reaches a high potential, and a nonaqueous electrolyte storage element including the nonaqueous electrolyte are provided. Can be provided.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte storage element according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of nonaqueous electrolyte power storage elements according to an embodiment of the present invention.

  The non-aqueous electrolyte according to an embodiment of the present invention includes an electrolyte salt and a non-aqueous solvent, and the non-aqueous solvent has a viscosity of 4 mPa · s or less at 25 ° C. and a fluorinated cyclic carbonate, a fluorinated chain carbonate, and 25 ° C. It is a nonaqueous electrolyte for an electricity storage device containing a certain fluorinated noncarbonate compound.

The nonaqueous electrolyte can improve the capacity retention rate of the nonaqueous electrolyte storage element after a charge / discharge cycle in which the maximum potential of the positive electrode reaches a high potential of, for example, 4.5 V (vs. Li ^/ Li ⁺ ) or higher. . Although this reason is not certain, the following reason is guessed. As a cause of a decrease in capacity retention rate in a conventional nonaqueous electrolyte using a fluorinated carbonate, for example, under a high potential condition in which the maximum ultimate potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more, Side reactions occur continuously and complexly. On the other hand, in the nonaqueous solvent of the nonaqueous electrolyte, in addition to the fluorinated cyclic carbonate and the fluorinated chain carbonate, a fluorinated noncarbonate compound is contained so that the cation and the anion that constitute the electrolyte salt can interact with each other. The action becomes stronger. In this way, when the interaction between the cation and the anion is strengthened, the HOMO-LUMO level of the anion changes, and it is presumed that the capacity retention rate is improved by improving the oxidation resistance. Further, since the fluorinated non-carbonate compound has a viscosity at 25 ° C. of 4 mPa · s or less, the non-aqueous electrolyte containing the fluorinated non-carbonate compound is not too high in viscosity and ensures good ionic conductivity. Is done. For this reason, according to the nonaqueous electrolyte, the capacity retention rate after the charge / discharge cycle of the nonaqueous electrolyte storage element operated under the charging condition in which the maximum potential of the positive electrode reaches a high potential can be improved. It is guessed.

  In the present specification, the viscosity is measured using a falling ball viscometer (Lovis 2000 M manufactured by Anton Paar GmbH (Anton Paar GmbH)) in an Ar atmosphere with an electrolytic solution enclosed in a test cell and at 25 ° C. It shall be.

  The electrolyte salt preferably contains an imide salt. When the electrolyte salt contains an imide salt, the capacity retention rate of the nonaqueous electrolyte storage element can be further increased. This is presumed to be because the imide salt has more remarkable effects than the other lithium salts, such as the improvement in oxidation resistance of the anion caused by the stronger interaction between the cation and the anion. Conventionally, when an imide salt is used as an electrolyte salt, oxidative dissolution of aluminum or the like used as a positive electrode base material or the like occurs, which adversely affects the life of the nonaqueous electrolyte storage element. In order to suppress the oxidative dissolution of aluminum or the like, it is necessary to increase the concentration of the imide salt. This is because the imide salt is brought close to the saturated state to suppress the oxidative dissolution of aluminum or the like in the non-aqueous electrolyte at a high potential. However, when the concentration of the imide salt is increased until it approaches a saturated state, there is a problem that the viscosity of the non-aqueous electrolyte increases and the high-rate discharge performance of the non-aqueous electrolyte storage element decreases. On the other hand, according to the non-aqueous electrolyte, by using a fluorinated non-carbonate compound having a viscosity at 25 ° C. of 4 mPa · s or less, oxidative dissolution of aluminum or the like is suppressed without increasing the viscosity of the non-aqueous electrolyte. It is speculated that the capacity maintenance rate of the nonaqueous electrolyte storage element can be improved. Specifically, for example, the viscosity at 25 ° C. is 4 mPa · s or less and the solubility of the imide salt is low with respect to a saturated solution of an imide salt using a fluorinated cyclic carbonate and a fluorinated chain carbonate as a solvent. By diluting by adding a fluorinated non-carbonate compound, it is possible to form a state in which aluminum or the like is hardly oxidized and dissolved while reducing the viscosity. Therefore, according to the non-aqueous electrolyte, it is possible to improve the capacity retention rate of the non-aqueous electrolyte storage element that operates under a charging condition in which the maximum potential of the positive electrode reaches a high potential while avoiding the increase in viscosity. In addition, a decrease in high rate discharge performance can be suppressed.

  The content of the imide salt in the electrolyte salt is preferably 90 mol% or more. By setting the content of the imide salt in the electrolyte salt to 90 mol% or more, the capacity retention rate of the nonaqueous electrolyte storage element that is operated under a charging condition in which the maximum potential of the positive electrode reaches a high potential is further improved. It is possible to improve the capacity retention rate after a charge / discharge cycle at a relatively high temperature (for example, 45 ° C.) and when the maximum potential of the positive electrode reaches a high potential.

  The concentration of the electrolyte salt is preferably 0.5 mol / kg or more and 3 mol / kg or less. According to the non-aqueous electrolyte, the non-aqueous electrolyte is operated under a charging condition in which the maximum ultimate potential of the positive electrode reaches a high potential without increasing the concentration of the electrolyte salt until it reaches a saturated state exceeding 3 mol / kg, for example. The capacity maintenance rate after the charge / discharge cycle of the electrolyte storage element can be improved. Further, when the concentration of the electrolyte salt is 0.5 mol / kg or more and 3 mol / kg or less, it is possible to avoid the increase in viscosity of the non-aqueous electrolyte, and as a result, it is possible to suppress a decrease in high rate discharge performance. .

A nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode including a positive electrode active material that operates under a charging condition in which a maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or more, and the nonaqueous electrolyte. A nonaqueous electrolyte electricity storage element (A) comprising an electrolyte. Since the nonaqueous electrolyte storage element (A) includes the nonaqueous electrolyte, the capacity retention rate after the charge / discharge cycle is improved. Moreover, since the maximum potential of the positive electrode can be 4.5 V (vs. Li ^/ Li ⁺ ) or more, the non-aqueous electrolyte storage element (A) can be a non-aqueous electrolyte storage element with a high voltage, Has high energy density.

Note that “a positive electrode active material that operates under a charging condition in which the maximum potential reached 4.5 V (vs. Li ^/ Li ⁺ ) or higher” also means a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher. It is a substance that operates, that is, a substance that causes a reversible charge / discharge reaction as a positive electrode active material. The positive electrode active material, 4.5V (vs.Li/Li ⁺⁾ may be also operated in the following potential at the charging conditions the maximum achieved potential is less than 4.5V (vs.Li/Li ⁺⁾ It may be activated.

A non-aqueous electrolyte electricity storage device according to an embodiment of the present invention includes a positive electrode and the non-aqueous electrolyte, and the maximum ultimate potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or higher. It is an electrolyte electrical storage element (B). Since the nonaqueous electrolyte storage element (B) includes the nonaqueous electrolyte, the capacity retention rate after the charge / discharge cycle is improved. In addition, the nonaqueous electrolyte electricity storage element (B) has a high energy density because the maximum ultimate potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more.

  Hereinafter, a nonaqueous electrolyte and a nonaqueous electrolyte storage element according to an embodiment of the present invention will be described in detail.

<Nonaqueous electrolyte>
The nonaqueous electrolyte according to an embodiment of the present invention includes an electrolyte salt and a nonaqueous solvent. The nonaqueous electrolyte is used as an electrolyte of a nonaqueous electrolyte storage element such as a nonaqueous electrolyte secondary battery.

(Electrolyte salt)
As said electrolyte salt, the well-known electrolyte salt normally used as an electrolyte salt of the general nonaqueous electrolyte for electrical storage elements can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, and the like, and lithium salt is preferable. Examples of the electrolyte salt include inorganic salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , and LiClO ₄ , and organic salts such as imide salts. 1 type or 2 types or more can be used for electrolyte salt.

  As the electrolyte salt, an organic salt is preferable, an imide salt is more preferable, and a lithium imide salt is more preferable. In the present invention, the imide salt is not only an imide salt having a structure in which two carbonyl groups are bonded to a nitrogen atom, but also having a structure in which two sulfonyl groups are bonded to a nitrogen atom. Also included are those having a structure in which two phosphonyl groups are bonded, and those having a structure in which a nitrogen atom is bonded to two types selected from a carbonyl group, a sulfonyl group and a phosphonyl group.

As the lithium imide salt,
LiN (SO ₂ F) ₂ (lithium bis (fluorosulfonyl) imide: LiFSI), LiN (SO ₂ CF ₃ ) ₂ (lithium bis (trifluoromethanesulfonyl) imide: LiTFSI), LiN (SO ₂ C ₂ F ₅ ) ₂ (Lithium bis (pentafluoroethanesulfonyl) imide: LiBETI), LiN (SO ₂ C ₄ F ₉ ) ₂ (lithium bis (nonafluorobutanesulfonyl) imide), CF ₃ —SO ₂ —N—SO ₂ —N—SO ₂ CF ₃ Li ₂ , FSO ₂ —N—SO ₂ —C ₄ F ₉ Li, CF ₃ —SO ₂ —N—SO ₂ —CF ₂ —SO ₂ —N—SO ₂ —CF ₃ Li ₂ , CF ₃ — _{SO 2 -N-SO 2 -CF 2} -SO 3 Li 2, CF 3 -SO 2 -N-SO 2 -CF 2 -SO 2 -C (- Lithium imide salts such as _{O 2 CF 3) 2 Li 2} ;
Examples thereof include lithium phosphonilimide salts such as LiN (POF ₂ ) ₂ (lithium bis (difluorophosphonyl) imide: LiDFPI).

The lithium imide salt preferably has a fluorine atom, and specifically, for example, preferably has a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, or the like. Among the lithium imide salts, lithium sulfonylimide salts are preferable, LiFSI, LiTFSI, and LiBETI are more preferable, and LiFSI is more preferable. These imide salts are imide salts that are relatively easy to cause oxidative dissolution of aluminum or the like during charging up to a high potential (for example, the maximum potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more). . Therefore, when such an imide salt is used, it is possible to improve the capacity retention rate after a charge / discharge cycle of a nonaqueous electrolyte storage element that operates under a charging condition in which the maximum potential of the positive electrode reaches a high potential. The effects of the invention can be obtained particularly effectively.

  The lower limit of the content of the imide salt in the electrolyte salt may be, for example, 50 mol% or 80 mol%, preferably 90 mol%, more preferably 95 mol%, further preferably 99 mol%. In addition, the upper limit of the content of the imide salt in the electrolyte salt may be 100 mol%.

  The lower limit of the electrolyte salt concentration (electrolyte salt content) in the nonaqueous electrolyte is preferably 0.5 mol / kg, more preferably 0.8 mol / kg, still more preferably 1.0 mol / kg, and 1.5 mol. / Kg is even more preferable. By setting the concentration of the electrolyte salt to the above lower limit or more, as described later, the interaction between the cation and the anion of the electrolyte salt mainly dissolved in the fluorinated cyclic carbonate and the fluorinated chain carbonate increases the anion. The capacity retention rate of the nonaqueous electrolyte electricity storage element can be further increased by changing the HOMO-LUMO level of the material and improving oxidation resistance. On the other hand, the upper limit of the concentration of the electrolyte salt is preferably 3 mol / kg, more preferably 2.5 mol / kg, and even more preferably 1.5 mol / kg. By making the concentration of the electrolyte salt not more than the above upper limit, it is possible to suppress the increase in viscosity of the nonaqueous electrolyte, and as a result, it is possible to improve the high rate discharge performance and the like of the nonaqueous electrolyte electricity storage element. In addition, the discharge capacity of the nonaqueous electrolyte storage element tends to be increased by setting the concentration of the electrolyte salt to the upper limit or less.

(Non-aqueous solvent)
The non-aqueous solvent includes a fluorinated cyclic carbonate, a fluorinated chain carbonate, and a fluorinated non-carbonate compound. The fluorinated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated non-carbonate compound can be used singly or in combination of two or more. The solubility of the electrolyte salt in the fluorinated cyclic carbonate and fluorinated chain carbonate constituting the nonaqueous electrolyte is usually higher than that of the fluorinated noncarbonate compound. Therefore, in the non-aqueous electrolyte, it is considered that the electrolyte salt is mainly dissolved in the fluorinated cyclic carbonate and the fluorinated chain carbonate.

(Fluorinated cyclic carbonate)
The fluorinated cyclic carbonate is a compound in which part or all of the hydrogen atoms of the cyclic carbonate are substituted with fluorine atoms. The fluorinated cyclic carbonate forms a good film on the negative electrode surface and contributes to an improvement in capacity retention.

  Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, (fluoromethyl) ethylene carbonate, (difluoromethyl) ethylene carbonate, (trifluoromethyl) ethylene carbonate, bis ( Fluoromethyl) ethylene carbonate, bis (difluoromethyl) ethylene carbonate, bis (trifluoromethyl) ethylene carbonate, (fluoroethyl) ethylene carbonate, (difluoroethyl) ethylene carbonate, (trifluoroethyl) ethylene carbonate, 4-fluoro-4 -Methylethylene carbonate, 4,4-difluoro-5-methylethylene carbonate, 4,5- Fluoro-4,5-dimethylethylene carbonate, and the like. As the fluorinated cyclic carbonate, fluoroethylene carbonate is preferred.

  The lower limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent is preferably 1% by volume and more preferably 5% by volume. By setting the content of the fluorinated cyclic carbonate to be not less than the above lower limit, a sufficient amount of a film can be formed on the negative electrode surface, and the capacity retention rate can be further increased. On the other hand, the upper limit of the content of the fluorinated cyclic carbonate is preferably 30% by volume, more preferably 20% by volume, and still more preferably 15% by volume. By making the content of the fluorinated cyclic carbonate not more than the above upper limit, a sufficient amount of the fluorinated chain carbonate and the fluorinated non-carbonate compound, which are other non-aqueous solvents, can be contained. The capacity maintenance rate can be further increased.

(Fluorinated chain carbonate)
The fluorinated chain carbonate is a compound in which some or all of the hydrogen atoms of the chain carbonate are substituted with fluorine atoms. The fluorinated chain carbonate is a solvent having a relatively low viscosity, can suppress the increase in viscosity, and can enhance the high rate discharge performance and the like of the nonaqueous electrolyte electricity storage device.

The fluorinated chain carbonate is represented by, for example, R ^a —O—CO—O—R ^b (R ^a is a fluorinated alkyl group. R ^b is an alkyl group or a fluorinated alkyl group). Can be mentioned. R ^b is preferably an alkyl group. Moreover, it is preferable that it is 1-3, respectively, and, as for carbon number of R ^<a> and R ^<b >, it is more preferable that it is 1 or 2.

  Examples of the fluorinated chain carbonate include methyl fluoromethyl carbonate, methyl fluoroethyl carbonate, methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, bis (trifluoroethyl) carbonate, methyl fluoropropyl carbonate, methyl difluoropropyl carbonate, methyl trifluoride. Fluoropropyl carbonate, methyltetrafluoropropyl carbonate, methylpentafluoropropyl carbonate, bis (trifluoropropyl) carbonate, bis (tetrafluoropropyl) carbonate, bis (pentafluoropropyl) carbonate and the like can be mentioned. As the fluorinated chain carbonate, methyl trifluoroethyl carbonate is preferred.

  The lower limit of the content of the fluorinated chain carbonate in the non-aqueous solvent is preferably 30% by volume, more preferably 40% by volume, and even more preferably 45% by volume. By setting the content of the fluorinated chain carbonate to the above lower limit or more, a sufficient amount of the electrolyte salt can be dissolved. The content of the fluorinated chain carbonate is preferably larger than the respective contents of the fluorinated cyclic carbonate and the fluorinated non-carbonate compound. On the other hand, the upper limit of the content of the fluorinated chain carbonate is preferably 80% by volume, more preferably 65% by volume, and still more preferably 55% by volume. By setting the content of the fluorinated chain carbonate below the above upper limit, the interaction between the cation and the anion of the electrolyte salt becomes stronger, the HOMO-LUMO level of the anion changes, and the oxidation resistance of the anion is improved. And the capacity retention rate of the nonaqueous electrolyte storage element can be further increased.

(Fluorinated non-carbonate compound)
The fluorinated non-carbonate compound is a fluorinated non-carbonate compound having a viscosity at 25 ° C. of 4 mPa · s or less. The fluorinated non-carbonate compound is a non-aqueous solvent having a fluorine atom other than carbonate. The fluorinated non-carbonate compound is not limited to a liquid compound at room temperature except at 25 ° C. A fluorinated non-carbonate compound is a fluorinated compound and has good oxidation resistance. As described above, this fluorinated non-carbonate compound functions as a diluting solvent that suppresses the increase in viscosity of the non-aqueous electrolyte while forming a strong interaction between the cation and anion of the electrolyte salt. it is conceivable that.

  It is assumed that the above function is exhibited when the solubility of the electrolyte salt in the fluorinated non-carbonate compound is lower than the solubility in other solvents (fluorinated cyclic carbonate and fluorinated chain carbonate) constituting the non-aqueous electrolyte. Is done. In order to effectively express such a function, the fluorinated non-carbonate compound is preferably a compound having a relatively low polarity. Specifically, examples of the fluorinated non-carbonate compound include fluorinated hydrocarbons, fluorinated ethers, fluorinated esters, etc. Among these, fluorinated hydrocarbons and fluorinated ethers are preferred, and fluorinated ethers. Is more preferable. Further, among the fluorinated ethers, chain fluorinated ethers are preferable.

The fluorinated ether is a compound in which some or all of the hydrogen atoms of the ether are substituted with fluorine atoms. Examples of the fluorinated ether include R ^c —O—R ^d (R ^c is a fluorinated hydrocarbon group having 1 to 8 carbon atoms. R ^d is a hydrocarbon group having 1 to 8 carbon atoms or a carbon number. 1 to 8 fluorinated hydrocarbon groups).

R ^c is preferably a fluorinated alkyl group. The upper limit of the carbon number of R ^c is preferably 5, and more preferably 3. The lower limit of the carbon number of R ^c is preferably 2. R ^d is preferably a fluorinated hydrocarbon group, more preferably a fluorinated alkyl group. The upper limit of the number of carbon atoms in R ^d is preferably 5, 3 is more preferable. The lower limit of the number of carbon atoms of R ^d is 2 is preferred.

As a specific example of a fluorinated non-carbonate compound,
1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE: viscosity at 25 ° C .: 0.65 mPa · s),
1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE: viscosity 1.6 mPa · s at 25 ° C.),
Ethyl-1,1,2,2-tetrafluoroethyl ether (viscosity of 0.486 mPa · s at 23 ° C.),
Hexafluoroisopropyl methyl ether (viscosity of 0.498 mPa · s at 23 ° C.) can be exemplified.

  The upper limit of the viscosity of the fluorinated non-carbonate compound at 25 ° C. is preferably 2 mPa · s, and more preferably 1 mPa · s. By making the viscosity of the fluorinated non-carbonate not more than the above upper limit, the capacity retention rate of the non-aqueous electrolyte electricity storage element can be further increased. On the other hand, the lower limit of the viscosity may be, for example, 0.1 mPa · s, 0.3 mPa · s, or 0.5 mPa · s.

  The lower limit of the content of the fluorinated non-carbonate compound in the non-aqueous solvent is preferably 5% by volume, more preferably 15% by volume, even more preferably 25% by volume, and still more preferably 35% by volume. By setting the content of the fluorinated non-carbonate compound to the above lower limit or more, the electrolyte salt can be brought into a preferable state where the interaction between the cation and the anion is strong. On the other hand, the upper limit of the content of the fluorinated non-carbonate compound is preferably 60% by volume, more preferably 50% by volume, and still more preferably 45% by volume. By setting the content of the fluorinated non-carbonate compound to the above upper limit or less, the content of fluorinated carbonate, which is another non-aqueous solvent, can be increased, and a sufficient amount of electrolyte salt is dissolved in the non-aqueous electrolyte. be able to.

(Other solvents)
The non-aqueous solvent may further contain a solvent other than the fluorinated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated non-carbonate compound having a viscosity at 25 ° C. of 4 mPa · s or less. Examples of the other solvent include a fluorinated non-carbonate compound having a viscosity at 25 ° C. of more than 4 mPa · s, a non-fluorinated carbonate, an ester, an ether, an amide, a sulfone, a lactone, and a nitrile.

  However, the upper limit of the content of the other solvent in the non-aqueous solvent is preferably 10% by volume, more preferably 1% by volume, and still more preferably 0.1% by volume. Thus, when the other solvent is not substantially contained, the capacity retention rate of the nonaqueous electrolyte electricity storage element can be further increased due to the increased oxidation resistance.

(Other ingredients)
The nonaqueous electrolyte may contain components other than the electrolyte salt and the nonaqueous solvent as long as the effects of the present invention are not impaired. As said other component, the various additives contained in the general nonaqueous electrolyte for electrical storage elements can be mentioned. However, as an upper limit of content of said other component, 10 mass% may be preferable, 1 mass% may be more preferable, and 0.1 mass% may be further more preferable. When the content of other components is large, these components may affect the solubility, viscosity, oxidation resistance and the like of the electrolyte salt, and may affect the capacity retention rate of the nonaqueous electrolyte electricity storage device including the same.

  The method for preparing the nonaqueous electrolyte is not particularly limited, and can be obtained by mixing each component at a predetermined ratio.

<Nonaqueous electrolyte storage element>
A nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superposed by stacking or winding via a separator. The electrode body is housed in a case, and the case is filled with the nonaqueous electrolyte. In the nonaqueous electrolyte secondary battery, the nonaqueous electrolyte described above is used as the nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the case, a known metal case, a resin case, or the like that is usually used as a case of a nonaqueous electrolyte secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed on the positive electrode base material directly or via an intermediate layer.

  The positive electrode base material has conductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and an aluminum alloy are preferable from the balance of high conductivity and cost. Examples of the form of forming the positive electrode base material include foil, vapor-deposited film and the like, and foil is preferable from the viewpoint of cost. That is, an aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

An intermediate | middle layer is a coating layer of the surface of a positive electrode base material, and reduces the contact resistance of a positive electrode base material and a positive electrode active material layer by including electroconductive particles, such as a carbon particle. The structure of an intermediate | middle layer is not specifically limited, For example, it can form with the composition containing a resin binder and electroconductive particle. “Conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “nonconductive” Means that the volume resistivity is more than 10 ⁷ Ω · cm.

  The positive electrode active material layer is formed from a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture for forming the positive electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler as necessary.

Examples of the positive electrode active material include composite oxides represented by, for example, Li _x MeO _y (Me represents at least one transition metal) (complex oxides having a layered α-NaFeO ₂ type crystal structure, other spinel types) Li _x Mn ₂ O ₄ having a crystal structure, Li _x Ni _α Mn _(2-α) O _4, etc.), Li _w Me _x (XO _y ) _z (Me represents at least one kind of transition metal, and X represents, for example, P , Si, B, V, etc.) represented by polyanion compounds (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc. ) And the like. The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one kind of these compounds may be used alone, or two or more kinds may be mixed and used.

As one embodiment of the present invention, the positive electrode preferably includes a positive electrode active material that operates under a charging condition in which the maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or higher. The non-aqueous electrolyte secondary battery has a high capacity retention rate even in use where the maximum potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more. Therefore, by using a positive electrode active material that operates under a charging condition in which the maximum potential reaches 4.5 V (vs. Li ^/ Li ⁺ ) or higher, the energy density increases and the capacity retention rate after the charge / discharge cycle is high. A non-aqueous electrolyte secondary battery can be obtained.

A positive electrode active material that operates under a charging condition in which the maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or higher is a reversible lithium ion at a potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher. It may be a positive electrode active material capable of insertion and desorption. As such a positive electrode active material, for example, Li _{1 + α} Me _1-α O ₂ having a layered α-NaFeO ₂ type crystal structure (Me is a metal element containing Mn, Mn / Me> 0.5, 0 <α <0.5) or Li _x Ni _α Mn _(2-α) O ₄ having a spinel crystal structure (0 <x <1, 0 <α <1), LiNi _0.5 Mn _1.5 O _4, LiNiPO ₄ is an example of a polyanionic _{compound, LiCoPO 4, Li 2 CoPO 4} F, can be mentioned Li 2 MnSiO _4, and the like.

  As content of the positive electrode active material in the said positive electrode active material layer, it can be set as 80 to 98 mass%, for example, and it is preferable that it is 90 mass% or more.

  The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect battery performance. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, ketjen black and other carbon blacks, metals, conductive ceramics, and the like. Examples of the shape of the conductive agent include powder and fiber.

  Examples of the binder include thermoplastic resins such as fluororesin (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene Examples thereof include elastomers such as butadiene rubber (SBR) and fluororubber; polysaccharide polymers.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

  The filler is not particularly limited as long as it does not adversely affect battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

(Negative electrode)
The negative electrode includes a negative electrode base material and a negative electrode active material layer disposed on the negative electrode base material directly or via an intermediate layer. The intermediate layer can have the same configuration as the positive electrode intermediate layer.

  The negative electrode base material can have the same configuration as the positive electrode base material, but as a material, a metal such as copper, nickel, stainless steel, nickel-plated steel or an alloy thereof is used, and copper or a copper alloy is used. preferable. That is, copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

  The negative electrode active material layer is formed from a so-called negative electrode mixture containing a negative electrode active material. Moreover, the negative electrode composite material which forms a negative electrode active material layer contains arbitrary components, such as a electrically conductive agent, a binder, a thickener, and a filler as needed. The same components as those for the positive electrode active material layer can be used as optional components such as a conductive agent, a binder, a thickener, and a filler.

  As the negative electrode active material, a material that can occlude and release lithium ions is usually used. Specific negative electrode active materials include, for example, metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide and Sn oxide; polyphosphate compounds; graphite (graphite), non-graphitic Examples thereof include carbon materials such as carbon (easily graphitizable carbon or non-graphitizable carbon).

  Furthermore, the negative electrode mixture (negative electrode active material layer) includes typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, and Ge. Typical metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W may be contained.

(Separator)
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of liquid retention of the nonaqueous electrolyte. The main component of the separator is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength, and is preferably polyimide or aramid from the viewpoint of resistance to oxidative degradation. These resins may be combined.

An inorganic insulating layer may be disposed between the separator and the electrode (usually a positive electrode). This inorganic insulating layer is a porous layer called a heat-resistant layer. A separator in which an inorganic insulating layer is formed on one or both surfaces of the porous resin film can also be used. The inorganic insulator layer is usually composed of inorganic insulator particles and a binder, and may contain other components. As the inorganic insulating particles, Al ₂ O ₃ , SiO ₂ , aluminosilicate and the like are preferable.

(Maximum potential)
Since the non-aqueous electrolyte secondary battery uses the non-aqueous electrolyte, even when the maximum ultimate potential of the positive electrode reaches a high potential of 4.5 V (vs. Li ^/ Li ⁺ ) or higher, Capacity maintenance rate is high. Therefore, the nonaqueous electrolyte secondary battery can be suitably used under charging conditions that reach a high end-of-charge voltage. For example, the maximum ultimate potential of the positive electrode of the nonaqueous electrolyte secondary battery can be used by being charged to 4.5 V (vs. Li ^/ Li ⁺ ) or more, and the maximum ultimate potential of this positive electrode is 4.7 V. It may be (vs. Li ^/ Li ⁺ ) or more. Thus, high energy density can be achieved because the maximum ultimate potential of the positive electrode is high. The upper limit of the maximum achieved potential of the positive electrode can be, for example, 5.4V (vs.Li/Li ^+), may be ^{5.2V (vs.Li/Li +), 5.0V (} vs Li / Li ⁺ ). The maximum potential reached by the positive electrode may be the positive electrode potential at the end-of-charge voltage of the nonaqueous electrolyte secondary battery during normal use. Here, the time of normal use means the case where the nonaqueous electrolyte secondary battery is used under the charge / discharge conditions recommended or specified in the nonaqueous electrolyte secondary battery. Regarding a charging condition, when a charger for the non-aqueous electrolyte secondary battery is prepared, the case of using the non-aqueous electrolyte secondary battery by applying the charger is referred to as a normal use.

(Method for producing non-aqueous electrolyte secondary battery)
The manufacturing method of the nonaqueous electrolyte secondary battery is not particularly limited. The non-aqueous electrolyte secondary battery can be manufactured by using the non-aqueous electrolyte. The manufacturing method includes, for example, a step of producing a positive electrode, a step of producing a negative electrode, a step of preparing a non-aqueous electrolyte, and stacking or winding the positive electrode and the negative electrode through a separator to alternately overlap electrode bodies. Forming the positive electrode and the negative electrode (electrode body) in a container, and injecting the nonaqueous electrolyte into the container. After the injection, the non-aqueous electrolyte secondary battery can be obtained by sealing the injection port.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode. For example, in the positive electrode and the negative electrode, the intermediate layer may not be provided, and the clear layer structure may not be provided. For example, the positive electrode and the negative electrode may have a structure in which an active material is supported on a mesh substrate. In the above embodiment, the non-aqueous electrolyte storage element is mainly described as a non-aqueous electrolyte secondary battery. However, other non-aqueous electrolyte storage elements may be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

  FIG. 1 shows a schematic diagram of a rectangular nonaqueous electrolyte storage element 1 (nonaqueous electrolyte secondary battery) which is an embodiment of the nonaqueous electrolyte storage element according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, an electrode body 2 is accommodated in a container 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′. In addition, a nonaqueous electrolyte according to an embodiment of the present invention is injected into the container 3.

  The configuration of the nonaqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical storage element, a rectangular storage element (rectangular storage element), a flat storage element, and the like. The present invention can also be realized as a power storage device including a plurality of the above nonaqueous electrolyte power storage elements. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and 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.

The electrolyte salt and non-aqueous solvent used in Examples and Comparative Examples are shown below.
(Electrolyte salt)
LiFSI: lithium bis (fluorosulfonyl) imide LiPF ₆
(Fluorinated cyclic carbonates and other cyclic carbonates: solvent A)
-FEC: fluoroethylene carbonate-EC: ethylene carbonate (fluorinated chain carbonates and other chain carbonates: solvent B)
MFEC: methyl trifluoroethyl carbonate EMC: ethyl methyl carbonate (fluorinated non-carbonate compound: solvent C)
TFEE: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (viscosity 0.65 mPa · s at 25 ° C.)
HFE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (viscosity at 25 ° C. 1.6 mPa · s)
TFEP: Tris phosphate (2,2,2-trifluoroethyl) (viscosity at 25 ° C. 4.6 mPa · s)

[Example 1]
(Preparation of non-aqueous electrolyte)
Fluorinated cyclic carbonate (solvent A), FEC, fluorinated chain carbonate (solvent B), MFEC, and fluorinated non-carbonate compound (solvent C), TFEE, were mixed at a volume ratio of 10:70:20. . Subsequently, LiFSI which is electrolyte salt was added in the ratio of 1.00 mol with respect to 1 kg of this mixed solvent, LiFSI was dissolved, and the nonaqueous electrolyte of Example 1 was obtained.

(Preparation of nonaqueous electrolyte storage element)
LiNi _0.5 Mn _1.5 O ₄ is used as a positive electrode active material that operates under a charging condition in which the maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or more, and an aluminum foil is used as a positive electrode substrate. Thus, a positive electrode plate was produced. Moreover, the negative electrode plate was produced using graphite as a negative electrode active material. An electrode body was fabricated by laminating the positive electrode plate and the negative electrode plate through a separator that is a polyolefin microporous film. The electrode body is housed in a container made of a metal resin composite film, and the nonaqueous electrolyte is injected into the container, which is then sealed by thermal welding. The nonaqueous electrolyte storage element of Example 1 (laminate-type nonaqueous electrolyte secondary) Battery).

[Examples 2-8, Comparative Examples 1-22]
Each of Examples 2 to 8 and Comparative Examples 1 to 22 was the same as Example 1 except that the type and concentration of the electrolyte salt, the type and volume ratio of the nonaqueous solvent were as shown in Tables 1 and 2. A non-aqueous electrolyte was prepared and a non-aqueous electrolyte electricity storage device was produced.

In Examples 8 of Table 2, at a rate of 1.00mol the LiFSI the mixed solvent 1 kg, the LiPF ₆ at a rate of 0.2 mol, it was added respectively. In Example 8, the content of imide salt (LIFSI) in the electrolyte salt is about 83 mol%.

  In Comparative Examples 12, 13, 15, 16, 20, and 21, the added electrolyte salt was not completely dissolved in the solvent, and a non-aqueous electrolyte could not be prepared. Therefore, for these comparative examples, no non-aqueous electrolyte storage element is produced.

(Measurement of initial charge / discharge and discharge capacity)
About each obtained nonaqueous electrolyte electrical storage element, initial charge / discharge was performed on condition of the following. After charging at a constant current of 0.1 C with a charging current of 0.1 C up to 4.8 V at 25 ° C., the battery was charged at a constant voltage of 4.8 V. The positive electrode potential at the end of charging (maximum potential of the positive electrode) was 4.9 V (vs. Li ^/ Li ⁺ ). The charge termination conditions were until the charge current reached 0.02C. After a 10-minute rest after charging, the battery was discharged at a constant current of 0.1 C up to 3.5 V at 25 ° C. The second cycle after a 10-minute rest after discharging is performed at a constant current of 0.2C for the charging current and the discharging current, and the charging end condition is 0.02C as in the first cycle. Until then. Table 1 shows the discharge capacity per positive electrode active material in the second cycle.

(Measurement of charge / discharge cycle test and capacity maintenance rate at 25 ° C)
Following the measurement of the discharge capacity, a charge / discharge cycle test was performed under the following conditions. After charging at a constant current of 0.25 C with a charging current of 0.25 C up to 4.8 V at 25 ° C., the battery was charged at a constant voltage of 4.8 V. The charge termination conditions were until the charge current reached 0.02C. After a 10-minute rest after charging, the battery was discharged at a constant current of 0.25 C to 3.5 V at 25 ° C. A 10-minute pause was provided after the discharge. This charge / discharge cycle was carried out 50 cycles. The discharge capacity at the 50th cycle relative to the discharge capacity at the 1st cycle was determined as a capacity retention rate (%). The results are shown in Table 1.

  In Comparative Examples 18 and 19, 50 cycles of charge / discharge could not be performed. Moreover, about the comparative example 22, this measurement was not implemented.

(Measurement of charge / discharge cycle test and capacity retention at 45 ° C)
Using each of the nonaqueous electrolyte electricity storage devices of Examples 3, 5 and 8, a charge / discharge cycle test at 45 ° C. and a capacity retention rate were measured. The measurement conditions other than those performed under the environment of 45 ° C. are the same as the above “measurement of charge / discharge cycle test and capacity maintenance rate at 25 ° C.”. The results are shown in Table 2.

  As shown in Table 1 above, a fluorinated non-carbonate compound (solvent C) having a viscosity at 25 ° C. of 4 mPa · s or less is added to the fluorinated cyclic carbonate (solvent A) and the fluorinated chain carbonate (solvent B). It can be seen that Examples 1 to 7 using the added nonaqueous electrolyte have a high capacity retention rate in a charge / discharge cycle test employing a charging condition where the maximum potential of the positive electrode reaches a high potential. Comparing Examples 1 to 3, it can be seen that increasing the content ratio of the solvent C and decreasing the content ratio of the solvent B further increases the capacity retention rate. This is because by reducing the amount of solvents A and B that are highly soluble in the electrolyte salt, the interaction between lithium ions and anions of the electrolyte salt dissolved in these solvents becomes stronger, and the HOMO-LUMO level of the anion Is presumed to be due to a change in oxidation resistance and the like. Moreover, when Example 3 and 4 and Example 5 and 6 are compared, it turns out that a capacity | capacitance maintenance factor increases more by using TFEE with a lower viscosity as a fluorinated non-carbonate compound (solvent C). In addition, when Examples 3 and 5 and Examples 4 and 6 are compared, increasing the content of the electrolyte salt increases the capacity retention rate, while reducing the content of the electrolyte salt, It can be seen that the capacity increases. Furthermore, when Examples 1-6 and 7 are compared, when LiFSI which is an imide salt is used as electrolyte salt, it turns out that a capacity | capacitance maintenance factor increases.

  On the other hand, as in Comparative Examples 1 to 6, in the case of a mixed solvent containing only the fluorinated cyclic carbonate (solvent A) and the fluorinated chain carbonate (solvent B), the capacity retention rate is not sufficient. In Comparative Examples 7 and 8, in which TFEP having a viscosity at 25 ° C. exceeding 4 mPa · s was used as the fluorinated non-carbonate compound (solvent C), the capacity retention rate was decreased. Furthermore, in any of Comparative Examples 9 to 22 using nonaqueous electrolytes having other compositions, the capacity retention rate could not be sufficiently improved.

  In addition, as shown in Table 2, Examples 3 and 5 having a high content of imide salt (LIFSI) in the electrolyte salt are positive electrodes even under relatively high temperatures, which is an environment in which the capacity retention rate is likely to decrease. It can be seen that the capacity retention rate is high even after the charge / discharge cycle in which the maximum potential reached becomes high.

  The present invention can be applied to a non-aqueous electrolyte storage element used as a power source for personal computers, electronic devices such as communication terminals, automobiles, and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte electrical storage element 2 Electrode body 3 Container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 The electrical storage unit 30 The electrical storage apparatus

Claims (6)

Including an electrolyte salt and a non-aqueous solvent,
A nonaqueous electrolyte for a storage element, wherein the nonaqueous solvent includes a fluorinated cyclic carbonate, a fluorinated chain carbonate, and a fluorinated noncarbonate compound having a viscosity at 25 ° C. of 4 mPa · s or less.   The nonaqueous electrolyte according to claim 1, wherein the electrolyte salt includes an imide salt.   The non-aqueous electrolyte according to claim 2, wherein a content of the imide salt in the electrolyte salt is 90 mol% or more.   The nonaqueous electrolyte according to claim 1, wherein the concentration of the electrolyte salt is 0.5 mol / kg or more and 3 mol / kg or less. A positive electrode including a positive electrode active material that operates under a charging condition in which a maximum ultimate potential is 4.5 V (vs. Li ^/ Li ⁺ ) or more;
A nonaqueous electrolyte storage element comprising: the nonaqueous electrolyte according to any one of claims 1 to 4. A positive electrode;
A non-aqueous electrolyte according to any one of claims 1 to 4, and
The non-aqueous electrolyte electricity storage element whose maximum potential of the positive electrode is 4.5 V (vs. Li ^/ Li ⁺ ) or more.

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