JP2021077608A - Nonaqueous electrolyte, nonaqueous electrolyte power storage element and method for manufacturing nonaqueous electrolyte power storage element - Google Patents

Abstract

To provide: a nonaqueous electrolyte capable of increasing the capacity retention rate of a nonaqueous electrolyte power storage element after charge/discharge cycles and capable of suppressing an increase in thickness thereof, and a nonaqueous electrolyte power storage element using the same; and a method for manufacturing a nonaqueous electrolyte power storage element.SOLUTION: There are provided: a nonaqueous electrolyte for power storage elements which does not substantially include hexafluorophosphate, includes an imide salt, tetrafluoroborate and a phosphate ester, and further includes chain carbonate and fluorinated cyclic carbonate, and a nonaqueous electrolyte power storage element using the same; and a method for manufacturing a nonaqueous electrolyte power storage element.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a non-aqueous electrolyte, a non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. A non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge with. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

Generally, the non-aqueous electrolyte of the non-aqueous electrolyte storage element includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the electrolyte salt _{, hexafluorophosphates such as LiPF 6} and imide salts such as lithium bis (fluorosulfonyl) imide (LiFSI) are widely used (see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2015-128052 JP-A-2018-101612

A non-aqueous electrolyte storage element having a non-aqueous electrolyte in which hexafluorophosphate is used as an electrolyte salt does not have a sufficient capacity retention rate after a charge / discharge cycle. On the other hand, the non-aqueous electrolyte power storage element having a non-aqueous electrolyte in which an imide salt is used as the electrolyte salt tends to increase in thickness due to gas generation with charging and discharging.

The present invention has been made based on the above circumstances, and an object of the present invention is to increase the capacity retention rate of a non-aqueous electrolyte power storage element after a charge / discharge cycle and to suppress an increase in thickness. It is an object of the present invention to provide a water electrolyte, a non-aqueous electrolyte storage element having a high capacity retention rate after a charge / discharge cycle and suppressing an increase in thickness, and a method for manufacturing such a non-aqueous electrolyte storage element.

The non-aqueous electrolyte according to one aspect of the present invention is a non-aqueous electrolyte for a power storage element, which contains an imide salt, a tetrafluoroborate, and a phosphoric acid ester.

The non-aqueous electrolyte storage element according to another aspect of the present invention is a non-aqueous electrolyte storage element including the non-aqueous electrolyte according to one aspect of the present invention.

A method for producing a non-aqueous electrolyte storage element according to another aspect of the present invention comprises preparing a non-aqueous electrolyte containing an imide salt, a tetrafluoroborate, and a phosphoric acid ester. It is a manufacturing method.

According to the non-aqueous electrolyte according to one aspect of the present invention, it is possible to increase the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle and suppress the increase in thickness.
According to the non-aqueous electrolyte power storage device according to another aspect of the present invention, the capacity retention rate after the charge / discharge cycle is high, and the increase in thickness is suppressed.
According to the method for producing a non-aqueous electrolyte storage element according to another aspect of the present invention, it is possible to produce a non-aqueous electrolyte storage element having a high capacity retention rate after a charge / discharge cycle and suppressing an increase in thickness. it can.

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

First, an outline of a method for manufacturing a non-aqueous electrolyte, a non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element disclosed by the present specification will be described.

The non-aqueous electrolyte according to one aspect of the present invention is a non-aqueous electrolyte for a power storage element, which contains an imide salt, a tetrafluoroborate, and a phosphoric acid ester.

According to the non-aqueous electrolyte, it is possible to increase the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle and suppress the increase in thickness. The reason why the above effect occurs in the non-aqueous electrolyte is not clear, but the following reasons are presumed. In the non-aqueous electrolyte, by using an imide salt as the electrolyte salt, it is possible to increase the capacity retention rate of the non-aqueous electrolyte storage element after the charge / discharge cycle. It is presumed that the reason for this is that the imide salt is unlikely to cause a side reaction that causes a decrease in the capacity of the non-aqueous electrolyte power storage element during charging. On the other hand, in a non-aqueous electrolyte power storage device using a conventional non-aqueous electrolyte containing an imide salt, the cause of the increase in thickness due to gas generation is that a film capable of suppressing gas generation is not formed on the electrode surface. Conceivable. For example, when a conventional non-aqueous electrolyte containing hexafluorophosphate is used, a film containing a phosphorus atom derived from hexafluorophosphate is formed on the electrode surface, thereby suppressing gas generation and non-water. It is considered that the increase in the thickness of the electrolyte storage element is suppressed. On the other hand, in the non-aqueous electrolyte, by containing tetrafluoroborate and a phosphoric acid ester in addition to the imide salt, a film derived from these that can suppress gas generation is formed, and the non-aqueous electrolyte is non-aqueous. It is presumed that the increase in the thickness of the electrolyte storage element is suppressed.

The non-aqueous electrolyte preferably contains substantially no hexafluorophosphate. Hexafluorophosphates are prone to side reactions that cause a decrease in capacity, especially when the positive electrode potential reaches a high potential (for example, 4.0 V vs. Li ^/ Li + or higher) and the non-aqueous electrolyte storage element is charged. Therefore, when the non-aqueous electrolyte contains substantially no hexafluorophosphate, the capacity retention rate of the non-aqueous electrolyte storage element after the charge / discharge cycle is further increased, and particularly after the charge / discharge cycle in which the positive electrode potential reaches a high potential. Can also suppress the decrease in capacity.

In the present invention, the term "substantially free of hexafluorophosphate" of the non-aqueous electrolyte means that the content of hexafluorophosphate is less than 0.15 mol / kg.

The non-aqueous electrolyte may further contain a chain carbonate. Since chain carbonate is a solvent having a relatively low boiling point, it usually tends to be a factor of gas generation. However, in the non-aqueous electrolyte, even when the chain carbonate is further contained, gas generation can be suppressed and an increase in the thickness of the non-aqueous electrolyte power storage element can be suppressed. Therefore, as the non-aqueous electrolyte according to one embodiment of the present invention, a form containing a chain carbonate is also suitable.

The non-aqueous electrolyte may further contain a fluorinated cyclic carbonate. Since the fluorinated cyclic carbonate is easily reduced and decomposed at the negative electrode, it is usually likely to be a factor of gas generation. However, in the non-aqueous electrolyte, even when the fluorinated cyclic carbonate is further contained, gas generation can be suppressed and an increase in the thickness of the non-aqueous electrolyte power storage element can be suppressed. Therefore, as the non-aqueous electrolyte according to the embodiment of the present invention, a form containing a fluorinated cyclic carbonate is also suitable.

The non-aqueous electrolyte storage element according to another aspect of the present invention is a non-aqueous electrolyte storage element including the non-aqueous electrolyte according to one aspect of the present invention. Since the non-aqueous electrolyte power storage element uses the non-aqueous electrolyte, the capacity retention rate after the charge / discharge cycle is high, and the increase in thickness is suppressed.

The non-aqueous electrolyte storage element further includes a positive electrode having a positive electrode mixture containing a phosphorus atom, and the maximum value of the peak attributable to P2p is located at a position of 134 eV or less in the X-ray photoelectron spectroscopic spectrum of the surface of the positive electrode mixture. It is preferable to be present. By providing such a positive electrode, the capacity retention rate after the charge / discharge cycle can be further increased. The reason for this is not clear, but the following can be inferred. When the positive electrode mixture is formed by the positive electrode mixture paste containing phosphorus oxoacid, the maximum value of the peak attributed to P2p in the X-ray photoelectron spectroscopy spectrum derived from this phosphorus oxoacid is formed on the surface of the positive electrode mixture. A film containing a component present at a position of 134 eV or less is formed. Since this coating suppresses oxidative corrosion of aluminum normally used as a positive electrode base material or the like, it is presumed that the capacity retention rate after the charge / discharge cycle is increased.

A sample (positive electrode mixture) used for measuring the X-ray photoelectron spectroscopic spectrum is prepared by the following method. The non-aqueous electrolyte power storage element is discharged to a discharge end voltage at the time of normal use with a current of 0.1 C to bring it into a completely discharged state. The non-aqueous electrolyte power storage element in a completely discharged state is disassembled, the positive electrode is taken out, the positive electrode is thoroughly washed with dimethyl carbonate, and then dried under reduced pressure at room temperature. The dried positive electrode is cut out to a predetermined size (for example, 2 × 2 cm) and used as a sample for the measurement of the X-ray photoelectron spectral spectrum. The work from disassembling the non-aqueous electrolyte power storage element to preparing the sample in the measurement of the X-ray photoelectron spectrum is performed in an argon atmosphere with a dew point of -60 ° C or lower, and the prepared sample is enclosed in a transfer vessel and the dew point is -60. It is kept in an argon atmosphere below ° C. and introduced into the sample chamber of the measuring device for the X-ray photoelectron spectrum. The equipment and measurement conditions used in the measurement of the X-ray photoelectron spectroscopic spectrum are as follows.
Equipment: "AXIS NOVA" from KRATOS ANALYTICAL
X-ray source: Monochromatic AlKα
Acceleration voltage: 15kV
Analytical area: 700 μm x 300 μm
Measurement range: P2p = 145-128eV, C1s = 300-272eV
Measurement interval: 0.1 eV
Measurement time: P2p = 72.3 seconds / time, C1s = 70.0 seconds / time Accumulation number: P2p = 15 times, C1s = 8 times

Further, the position of the maximum value of the peak in the above spectrum is a value obtained as follows. First, the position of the peak of C1s attributed to sp2 carbon is set to 284.8 eV, and the binding energies of all the obtained spectra are corrected. Next, the corrected spectrum is leveled by removing the background using the linear method. In the spectrum after the leveling treatment, the slope of the tangent line of the peak of the spectrum in the range of 128 eV to 144 eV of the binding energy becomes 0, and the binding energy showing the maximum value is set as the position of the maximum value of the peak attributed to P2p.

A method for producing a non-aqueous electrolyte storage element according to another aspect of the present invention comprises preparing a non-aqueous electrolyte containing an imide salt, a tetrafluoroborate, and a phosphoric acid ester. It is a manufacturing method. According to this manufacturing method, it is possible to manufacture a non-aqueous electrolyte power storage element having a high capacity retention rate after a charge / discharge cycle and suppressing an increase in thickness.

The production method further preferably comprises producing a positive electrode using a positive electrode mixture paste containing an oxo acid of phosphorus. By producing the positive electrode in this way, as described above, in the X-ray photoelectron spectroscopic spectrum derived from the oxo acid of phosphorus, the component existing at the position where the maximum value of the peak assigned to P2p is 134 eV or less is contained. Since the film to be formed is formed on the surface of the positive electrode mixture, the capacity retention rate of the obtained non-aqueous electrolyte power storage element after the charge / discharge cycle becomes higher.

Hereinafter, the non-aqueous electrolyte, the non-aqueous electrolyte power storage element, the method for manufacturing the non-aqueous electrolyte power storage element, and other embodiments according to the embodiment of the present invention will be described in detail. The name of each component (each component) used in each embodiment may be different from the name of each component (each component) used in the background technology.

<Non-aqueous electrolyte>
The non-aqueous electrolyte according to one embodiment of the present invention contains an imide salt, a tetrafluoroborate, and a phosphoric acid ester. The imide salt and tetrafluoroborate are contained in the non-aqueous electrolyte as electrolyte salts. The non-aqueous electrolyte usually contains an imide salt, a tetrafluoroborate, a phosphoric acid ester, a non-aqueous solvent, and the like. The non-aqueous electrolyte is used as a non-aqueous electrolyte (non-aqueous electrolyte solution) for a power storage element.

(Imid salt)
The imide salt is contained in the non-aqueous electrolyte as the first electrolyte salt. Examples of the imide salt include lithium imide salt, sodium imide salt, potassium imide salt, magnesium imide salt, and imide salt having onium ion, but lithium imide salt is preferable.

As the lithium imide salt,
LiN (SO ₂ F) ₂ (Lithium bis (fluorosulfonyl) imide: LiFSI), LiN (CF ₃ SO ₂ ) ₂ (Lithium bis (trifluoromethanesulfonyl) imide: LiTFSI), LiN (C ₂ F ₅ SO ₂ ) ₂ (lithium bis (pentafluoroethane sulfonyl) _{imide: LiBETI), LiN (C 4} F 9 SO 2) 2 ( lithium bis (nonafluorobutanesulfonyl) _{imide), CF 3 -SO 2 -N-} SO 2 -N-SO _{2 CF 3 Li, FSO 2 -N} -SO 2 -C 4 F 9 Li, CF 3 -SO 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 (-SO ₂ CF ₃ ) Lithium sulfonylimide salt such as ₂ Li _2;
Examples thereof include lithium phosphonylimide salts such as LiN (POF ₂ ) ₂ (lithium bis (difluorophosphonyl) imide: LiDFPI). As the lithium imide salt, one kind or two or more kinds can be used.

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.

Further, as the imide salt, a bis (fluorosulfonyl) imide salt such as LiFSI is preferable. The bis (fluorosulfonyl) imide salt has a higher corrosion potential of aluminum used as a material for a general positive electrode base material than, for example, LiTFSI. Therefore, by using the bis (fluorosulfonyl) imide salt, corrosion of the positive electrode base material and the like can be suppressed, and the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle can be further increased.

The content of the imide salt in the non-aqueous electrolyte is preferably 0.2 mol / kg or more and 5.0 mol / kg or less, and more preferably 0.4 mol / kg or more and 3.0 mol / kg or less. The lower limit of the content of the imide salt may be more preferably 0.6 mol / kg. Further, the upper limit of the content of the imide salt is more preferably 2.0 mol / kg and even more preferably 1.2 mol / kg. By setting the content of the imide salt to the above lower limit or more, the capacity retention rate of the non-aqueous electrolyte power storage device after the charge / discharge cycle can be further increased. On the other hand, by setting the content of the imide salt to the above upper limit or less, the increase in the thickness of the non-aqueous electrolyte power storage element tends to be suppressed.

Further, in the non-aqueous electrolyte according to the embodiment of the present invention, the capacity retention rate after the charge / discharge cycle of the non-aqueous electrolyte power storage element is not required to have a high concentration such that the imide salt is much higher than 1.0 mol / kg, for example. The effect of the present invention can be exhibited. Therefore, the non-aqueous electrolyte has a high concentration of the imide salt, which can improve the unfavorable points of the non-aqueous electrolyte or the non-aqueous electrolyte power storage element using the imide salt having a high concentration such as high viscosity and high internal resistance. It can also be suitably used as a design having a concentration range other than that.

On the other hand, in the non-aqueous electrolyte according to the embodiment of the present invention, the present invention increases the capacity retention rate after the charge / discharge cycle of the non-aqueous electrolyte power storage element even if the concentration of the imide salt exceeds, for example, 2.0 mol / kg. Can exert the effect of. Therefore, the non-aqueous electrolyte can be in a state in which the content of the non-aqueous solvent that is not solvated with the electrolyte salt containing the imide salt is very small or absent, so that the corrosion potential of aluminum is low and the concentration is low. It can also be suitably used as a design in which the concentration range of the imide salt is high, which can improve the unfavorable points of the non-aqueous electrolyte or the non-aqueous electrolyte power storage element using the imide salt.

(Tetrafluoroborate)
The tetrafluoroborate is contained in the non-aqueous electrolyte as a second electrolyte salt. Although it is not clear, in the non-aqueous electrolyte, it is presumed that a film containing a phosphorus atom capable of suppressing gas generation is formed by containing tetrafluoroborate together with a phosphoric acid ester.

Examples of the _{tetrafluoroborate include alkali metal salts of tetrafluoroboric acid such as LiBF 4} (lithium tetrafluoroborate), NaBF ₄ (sodium tetrafluoroborate) and KBF ₄ (potassium tetrafluoroborate), and Mg (BF). ₄ ) ₂ (magnesium tetrafluoroborate), tetrafluoroborate having onium ion and the like can be mentioned, and LIBF ₄ is preferable. As the tetrafluoroborate, one kind or two or more kinds can be used.

The content of tetrafluoroborate in the non-aqueous electrolyte is preferably 0.05 mol / kg or more and 1.50 mol / kg or less, and more preferably 0.10 mol / kg or more and 1.00 mol / kg or less. The lower limit of the content of tetrafluoroborate may be more preferably 0.15 mol / kg or 0.25 mol / kg. The upper limit of the content of tetrafluoroborate may be more preferably 0.75 mol / kg or 0.50 mol / kg. By setting the content of tetrafluoroborate to be equal to or higher than the above lower limit, it is possible to more sufficiently suppress an increase in the thickness of the non-aqueous electrolyte power storage element. On the other hand, when the content of tetrafluoroborate is not more than the above upper limit, the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle tends to increase.

(Hexafluorophosphate)
It is preferable that the non-aqueous electrolyte does not substantially contain _{hexafluorophosphate (LiPF 6,} etc.), which is a kind of electrolyte salt. In this case, the non-aqueous electrolyte can increase the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle in which the positive electrode potential reaches a high potential. The content of hexafluorophosphate in the non-aqueous electrolyte is preferably less than 0.15 mol / kg, more preferably less than 0.10 mol / kg, further preferably less than 0.05 mol / kg, and less than 0.01 mol / kg. Is even more preferable. Furthermore, it may be substantially 0 mol / kg or 0 mol / kg.

(Other electrolyte salts, etc.)
The non-aqueous electrolyte may or may not further contain other electrolyte salts. Examples of such an electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts and the like other than imide salts and tetrafluoroborate salts.

The total content of the imide salt and the tetrafluoroborate in the total electrolyte salt in the non-aqueous electrolyte is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 99 mol% or more. When the electrolyte salt in the non-aqueous electrolyte is composed substantially only of the imide salt and the tetrafluoroborate, the effect of the present invention may be more sufficiently exhibited. The molar ratio of the imide salt of the electrolyte to the tetrafluoroborate (imide salt: tetrafluoroborate) in the non-aqueous electrolyte is not particularly limited, but is preferably 10:90 or more and 90:10 or less, for example. It is more preferably 20:80 or more and 80:20 or less, and further preferably 50:50 or more and 75:25 or less.

The content of the total electrolyte salt in the non-aqueous electrolyte is preferably 0.5 mol / kg or more and 5.0 mol / kg or less, more preferably 0.7 mol / kg or more and 2.0 mol / kg or less, and 0.9 mol / kg or more. More preferably 1.2 mol / kg or less.

(Phosphate ester)
The non-aqueous electrolyte contains a phosphate ester. When a non-aqueous electrolyte containing a phosphoric acid ester is used, it is presumed that a phosphorus-containing film derived from the phosphoric acid ester is formed on the electrode surface. It is presumed that this coating can suppress gas generation and suppress an increase in the thickness of the non-aqueous electrolyte power storage element.

The phosphoric acid ester is O = P (OR ¹ ) (OR ² ) (OR ³ ) (R ¹ , R ² and R ³ are independently hydrocarbon groups or fluorinated hydrocarbon groups, respectively). It is preferably the compound represented.

The ^{hydrocarbon group represented by R 1} , R ² and R ³ may be any of an aliphatic hydrocarbon group and an aromatic hydrocarbon group. Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group and n-pentyl group, ethenyl group (vinyl group) and 1-propenyl group. Examples thereof include an alkenyl group such as a 2-propenyl group (allyl group), an alkynyl group such as an ethynyl group and a propynyl group, and a cycloalkyl group such as a cyclohexyl group. Examples of the aromatic hydrocarbon group include a phenyl group and a tolyl group.

Examples of the fluorinated hydrocarbon group represented by R ¹ , R ² and R ³ include a group in which a part or all of the hydrogen atoms of the above-mentioned hydrocarbon group are substituted with a fluorine atom.

R ^1, R ² and R ^3, preferably an aliphatic hydrocarbon group and a fluorinated aliphatic hydrocarbon group, an alkyl group, an alkenyl group, fluoroalkyl group and fluoroalkyl alkenyl group is more preferable.

The carbon number of R ¹ , R ² and R ³ may be, for example, 1 or more and 12 or less, but is preferably 1 or more and 6 or less, and more preferably 2 or more and 4 or less.

When R ¹ , R ² and R ³ are fluorinated hydrocarbon groups, the ^{number of fluorines of R 1} , R ² and R ³ is preferably 1 or more and 12 or less, and more preferably 2 or more and 8 or less.

Examples of the phosphoric acid ester include O = P (OCH ₃ ) ₃ , O = P (OCH ₂ CH ₃ ) ₃ , O = P (OCH ₂ CFH ₂ ) ₃ , O = P (OCH ₂ CF ₂ H) ₃ , O = P (OCH ₂ CF ₃ ) ₃ , O = P (OCH ₃ ) ₂ (OCH ₂ CF ₃ ), O = P (OCH ₃ ) (OCH ₂ CF ₃ ) ₂ , O = P (OCH ₂ CH ₃ ) ₂ (OCH ₂ CF ₃ ), O = P (OCH ₂ CH ₃ ) (OCH ₂ CF ₃ ) ₂ , O = P (OCH ₂ CH ₂ CH ₃ ) ₃ , O = P (OCH ₂ CF ₂ CF ₂ H) ₃ , O = P (OCH ₂ CF ₂ CF ₃ ) ₃ , O = P (OCH ₂ CH = CH ₂ ) ₃ , O = P (OCH (CH ₃ ) ₂ ) ₃ , O = P (OCH (CF ₃ )) ₂ ) ₃ , O = P (OC (CH ₃ ) ₃ ) _{3 and the} like can be mentioned.

The content of the phosphoric acid ester with respect to all the components other than the electrolyte salt in the non-aqueous electrolyte is preferably 1% by volume or more and 60% by volume or less, more preferably 3% by volume or more and 50% by volume or less, and 5% by volume or more and 40% by volume or less. Is even more preferable. The lower limit of the phosphate ester content may be even more preferably 10% by volume, 15% by volume or 20% by volume. The upper limit of the content of the phosphoric acid ester may be more preferably 30% by volume, 25% by volume or 20% by volume. Further, the content of the phosphoric acid ester with respect to the total of the phosphoric acid ester and the non-aqueous solvent in the non-aqueous electrolyte is also preferably within the above numerical range. By setting the content of the phosphoric acid ester to the above lower limit or more, a sufficient film is formed, and an increase in the thickness of the non-aqueous electrolyte power storage element can be more sufficiently suppressed. On the other hand, by setting the content of the phosphoric acid ester to the above upper limit or less, the capacity retention rate of the non-aqueous electrolyte power storage element after the charge / discharge cycle tends to increase.

(Non-aqueous solvent)
As the non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a non-aqueous electrolyte for a general non-aqueous electrolyte power storage element can be used. Examples of the non-aqueous solvent include carbonates (cyclic carbonates and chain carbonates), esters, ethers, amides, sulfones, lactones, nitriles and the like. Of these, carbonate is preferable. The carbonate may be a carbonate having no substituent or a carbonate having a substituent. Examples of this substituent include a hydroxy group and a halogen atom. As the non-aqueous solvent, one kind or two or more kinds can be used.

As a non-aqueous solvent, chain carbonate may be contained. Even when the non-aqueous electrolyte contains a chain carbonate, which is generally considered to be a factor of gas generation, gas generation is suppressed and an increase in the thickness of the non-aqueous electrolyte power storage element is suppressed. Can be done.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, methyltrifluoroethyl carbonate (MFEC), bis (trifluoroethyl) carbonate (FDEC) and the like. be able to.

As the chain carbonate, a fluorinated chain carbonate such as MFEC or FDEC is preferable because it can suppress side reactions during charging and discharging when the positive electrode potential reaches a high potential.

The content of the chain carbonate with respect to all the components other than the electrolyte salt in the non-aqueous electrolyte is preferably 20% by volume or more and 80% by volume or less, and more preferably 30% by volume or more and 70% by volume or less. The content of the chain carbonate with respect to the total of the phosphoric acid ester and the non-aqueous solvent in the non-aqueous electrolyte is also preferably within the above numerical range. The content of the chain carbonate in the non-aqueous solvent is preferably 20% by volume or more and 90% by volume or less, and more preferably 50% by volume or more and 90% by volume or less.

Cyclic carbonate may be included as the non-aqueous solvent. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), fluoromethylethylene carbonate, trifluoroethylethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned.

As the cyclic carbonate, a fluorinated cyclic carbonate such as FEC or DFEC is preferable because it can suppress side reactions during charging and discharging when the positive electrode potential reaches a high potential. On the other hand, even when the non-aqueous electrolyte contains fluorinated cyclic carbonate, which is generally considered to be a factor of gas generation, gas generation is suppressed and the thickness of the non-aqueous electrolyte power storage element is increased. Can be suppressed.

The content of the cyclic carbonate with respect to all the components other than the electrolyte salt in the non-aqueous electrolyte is preferably 5% by volume or more and 50% by volume or less, and more preferably 10% by volume or more and 40% by volume or less. The content of the cyclic carbonate with respect to the total of the phosphoric acid ester and the non-aqueous solvent in the non-aqueous electrolyte is also preferably within the above numerical range. The content of cyclic carbonate in the non-aqueous solvent is preferably 10% by volume or more and 60% by volume or less, and more preferably 15% by volume or more and 45% by volume or less.

The non-aqueous solvent preferably contains a chain carbonate and a cyclic carbonate. When the chain carbonate and the cyclic carbonate are used in combination, the volume ratio of the chain carbonate to the cyclic carbonate (chain carbonate: cyclic carbonate) is not particularly limited, but is, for example, 50:50 or more and 90:10 or less. Is preferable.

The content of carbonate in the non-aqueous solvent (total content of chain carbonate and cyclic carbonate) may be preferably 50% by volume or more, more preferably 90% by volume or more, 99% by volume or more, or Substantially 100% by volume may be even more preferred. As described above, when carbonate becomes the main non-aqueous solvent, the effect of the present invention may be more sufficiently exhibited.

The lower limit of the total content of the fluorinated solvent in the non-aqueous solvent is preferably 50% by volume, more preferably 90% by volume, still more preferably 99% by volume. The fluorinated solvent refers to a solvent (non-aqueous solvent) having a fluorine atom in the molecule, such as a fluorinated carbonate (fluorinated chain carbonate and fluorinated cyclic carbonate). By setting the total content of the fluorinated solvent to the above lower limit or more in this way, it is possible to further increase the capacity retention rate after the charge / discharge cycle in which the positive electrode potential reaches a high potential.

Other additives may be added to the non-aqueous electrolyte. However, as the upper limit of the content of the components other than the electrolyte salt, the phosphoric acid ester and the non-aqueous solvent in the non-aqueous electrolyte, 20% by mass may be preferable, 5% by mass may be more preferable, and 2% by mass is used. In some cases, 1% by mass or 0.1% by mass is even more preferable.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte power storage element may further have a separator. Hereinafter, as an example of the non-aqueous electrolyte power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. That is, the normal electrode body is usually composed of a positive electrode, a negative electrode, and a separator. The electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the container, a known metal container, resin container, or the like that is usually used as a container for a secondary battery can be used.

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

The positive electrode base material has conductivity. Incidentally, to have a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, and "non-conductive" means that the volume resistivity is 10 ⁷ Ω · cm greater. As the material of the base material, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of high conductivity and cost balance. Further, when the positive electrode base material is aluminum or an aluminum alloy, the addition of phosphorus oxoacid to the positive electrode mixture can suppress a decrease in the capacity retention rate due to oxidative corrosion of aluminum of the positive electrode base material. Examples of the form of the positive electrode base material include foils and vapor-deposited films, and foils are preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The average thickness of the positive electrode base material is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material within the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material. The "average thickness" means a value obtained by dividing the punching mass when punching a base material having a predetermined area by the true density of the base material and the punching area. The same definition applies when the "average thickness" is used for other members and the like.

The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles.

The positive electrode active material layer is a layer formed of a positive electrode mixture. This positive electrode mixture contains a positive electrode active material. The positive electrode mixture preferably contains a phosphorus atom, and further contains an optional component such as a conductive agent, a binder, a thickener, a filler, and a dispersant, if necessary. When the positive electrode mixture contains a phosphorus atom, the maximum value of the peak assigned to P2p is preferably located at a position of 134 eV or less in the X-ray photoelectron spectrum of the surface of the positive electrode mixture (positive electrode active material layer). The positive electrode active material layer is usually formed on the surface of the positive electrode base material by coating and drying the positive electrode mixture paste containing the positive electrode active material and the like. The positive electrode mixture paste preferably contains phosphorus oxoacid. In the secondary battery, a part or all of the oxo acid of phosphorus may be denatured. Further, it is presumed that the phosphorus atom is present in the coating film formed on the surface of the positive electrode active material layer. The phosphorus atom derived from the oxo acid of phosphorus is assigned to P2p in the X-ray photoelectron spectroscopy spectrum of the surface of the positive electrode mixture (positive electrode active material layer) due to the presence of the phosphorus atom derived from the positive electrode active material layer in the film formed on the surface of the positive electrode active material layer. It is presumed that the maximum value of the peak is located at a position of 134 eV or less.

Examples of the positive electrode active material include a lithium transition metal composite oxide and a polyanion compound. Examples of the lithium transition metal composite oxide include composite oxides represented by Li _x MO _y (M represents at least one transition metal) ( _{Li x} CoO ₂ and Li _{having a layered α-NaFeO type 2} crystal structure). _x NiO ₂ , Li _x MnO ₃ , Li _x Ni _α Co _1-α O ₂ , Li _x Ni _α Co _β Al _1-α-β O ₂ , Li _x Ni _α Mn _β Co _1-α-β O ₂ , Examples _{thereof include Li 1 + x} (Ni _α Mn _β Co _1-α-β ) _1-x O _{2 , Li x} Mn ₂ O ₄ having a spinel-type crystal structure, Li _x Ni _α Mn _2-α O _4, etc.). Further, as the polyanion compound, _{a polyanion compound (LiFePO 4 ) represented by 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.). , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.). 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 of these compounds may be used alone, or two or more of these compounds may be mixed and used.

The positive electrode active material has a positive electrode potential of 4.0 V vs. the final charge voltage during normal use of the secondary battery. Li / Li ⁺ or higher, and even 4.2V vs. Li / Li ⁺ or higher or 4.4V vs. It is preferable to contain a positive electrode active material which can be Li / Li ^{+ or more.} In the secondary battery, the maximum potential of the positive electrode is 4.0 V vs. Even in the case of use of Li / Li ⁺ or more, the capacity retention rate after the charge / discharge cycle is high, and the increase in thickness can be suppressed. Therefore, the positive electrode potential at the end-of-charge voltage during normal use of the secondary battery is 4.0 V vs. By using a positive electrode active material that can be Li / Li ⁺ or higher, it is possible to obtain a secondary battery in which the energy density is increased, the capacity retention rate after the charge / discharge cycle is high, and the increase in thickness is suppressed.

The positive electrode potential at the end-of-charge voltage during normal use is 4.0 V vs. Examples of the positive electrode active material that can be Li / Li ⁺ or higher include lithium transition metal composite oxide, which has an α-NaFeO _{type 2} crystal structure and contains at least one of nickel, manganese, and cobalt. Metal composite oxides are preferred. Specifically, the formula Li _{1 + x} (Ni _α Mn _β Co _1-α-β ) _1-x O ₂ (0 ≦ x <1, 0 ≦ α ≦ 1, 0 ≦ β ≦ 1, 0 ≦ 1-α- Examples thereof include compounds represented by β ≦ 1). It is preferable that x in the above formula is more than 0 and 0.5 or less.

Here, the term "normal use" refers to the case where the secondary battery is used by adopting the charge / discharge conditions recommended or specified for the secondary battery. Regarding the charging conditions, when a charger for the secondary battery is prepared, the case where the charger is applied and the secondary battery is used is referred to as normal use.

The lower limit of the content ratio of the lithium transition metal composite oxide in the total positive electrode active material is preferably 50% by mass, more preferably 90% by mass, and even more preferably 99% by mass. The positive electrode active material may be composed substantially only of the lithium transition metal composite oxide. By increasing the content ratio of the lithium transition metal composite oxide in this way, the energy density can be increased.

The positive electrode active material is usually particles (powder). The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. When a complex of a positive electrode active material and another material is used, the average particle size of the complex is taken as the average particle size of the positive electrode active material. The "average particle size" is based on JIS-Z-8825 (2013) and is based on the particle size distribution measured by the laser diffraction / scattering method for a diluted solution obtained by diluting the particles with a solvent. -2 (2001) means a value at which the volume-based integrated distribution calculated in accordance with (2001) is 50%.

A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The content of the positive electrode active material in the positive electrode active material layer can be, for example, 80% by mass or more and 98% by mass or less, and is preferably 90% by mass or more.

In the X-ray photoelectron spectroscopy spectrum of the surface of the positive electrode mixture (positive electrode active material layer), the upper limit of the position of the maximum value of the peak attributed to P2p is preferably 134.0 eV, more preferably 133.5 eV. preferable. On the other hand, the lower limit of the position of the maximum value of this peak may be 130 eV or 132 eV.

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

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

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

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

The positive electrode active material layer (positive electrode mixture) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn. , Sr, Ba and other typical metal elements, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, etc. It may be contained as a component other than the thickener and the filler.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer arranged directly on the negative electrode base material or via an intermediate layer. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.

The negative electrode base material may have the same structure as the positive electrode base material, but as the material, metals such as copper, nickel, stainless steel, nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. .. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode base material is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the negative electrode base material.

The negative electrode active material layer is formed from a negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, a filler, and a dispersant, if necessary. Any component such as a conductive agent, a binder, a thickener, a filler, and a dispersant can be the same as that of the positive electrode active material layer.

The negative electrode active material layer (negative electrode mixture) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn. , Sr, Ba and other typical metal elements, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as negative electrode active materials, conductive agents, binders, etc. It may be contained as a component other than the thickener and the filler.

The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the negative electrode active material include metal Li; metal or semi-metal such as Si and Sn; metal oxide or semi-metal oxide such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTIO ₂ and TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite (graphite) and non-graphitizable carbon (graphitizable carbon or non-graphitizable carbon). Be done. Among these materials, graphite and non-graphitic carbon are preferable. In the negative electrode active material layer, one of these materials may be used alone, or two or more thereof may be mixed and used.

_{“Graphite” refers to a carbon material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material having stable physical properties can be obtained.

_{“Non-graphitic carbon” refers to a carbon material having an average lattice spacing (d 002} ) of (002) planes determined by X-ray diffraction before charging / discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. Say. Examples of non-graphitizable carbon include non-graphitizable carbon and easily graphitizable carbon. Examples of the non-graphitic carbon include a resin-derived material, a petroleum pitch or a petroleum pitch-derived material, a petroleum coke or a petroleum coke-derived material, a plant-derived material, an alcohol-derived material, and the like.

Here, the "discharged state" refers to a state in which the open circuit voltage is 0.7 V or more in a unipolar battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode. Since the potential of the metal Li counter electrode in the open circuit state is substantially equal to the oxidation-reduction potential of Li, the open circuit voltage in the single-pole battery is substantially equal to the potential of the negative electrode containing the carbon material with respect to the oxidation-reduction potential of Li. .. That is, the fact that the open circuit voltage in the single-pole battery is 0.7 V or more means that lithium ions that can be occluded and discharged are sufficiently released from the carbon material that is the negative electrode active material during charging and discharging. ..

The “non-graphitizable carbon” _{refers to a carbon material having d 002} of 0.36 nm or more and 0.42 nm or less.

The “graphitizable carbon” _{refers to a carbon material having d 002} of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 μnm or more and 100 μm or less. When the negative electrode active material is, for example, a carbon material, the average particle size thereof may be preferably 1 μm or more and 100 μm or less. When the negative electrode active material is a metal, a semi-metal, a metal oxide, a semi-metal oxide, a titanium-containing oxide, a polyphosphate compound or the like, the average particle size thereof may be preferably 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or higher than the above lower limit, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the active material layer is improved. A crusher, a classifier, or the like is used to obtain a powder having a predetermined particle size. The pulverization method and the powder grade method can be selected from, for example, the methods exemplified for the positive electrode.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

(Separator)
As the material of the separator, for example, a woven fabric, a non-woven 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 non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the main component of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. Moreover, you may combine these resins.

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

(Non-aqueous electrolyte)
The non-aqueous electrolyte used in the secondary battery is the non-aqueous electrolyte according to the above-described embodiment of the present invention.

(Maximum ultimate potential of positive electrode, etc.)
In the secondary battery, the maximum potential of the positive electrode is 4.0 V vs. Since the capacity retention rate is high and the increase in thickness is suppressed even after the charge / discharge cycle of Li / Li ^{+ or more, the positive electrode is set to 4.0 V vs.} It can be used at an operating potential of Li / Li ^{+ or higher.} The lower limit of the maximum ultimate potential of the positive electrode of the secondary battery is 4.0 V vs. Li / Li ⁺ is preferred, 4.2 V vs. Li / Li ⁺ is more preferred, 4.4 V vs. Li / Li ⁺ is more preferred, 4.6 V vs. Li / Li ⁺ is even more preferred. Since the maximum potential of the positive electrode is high in this way, it is possible to increase the energy density. The upper limit of the maximum ultimate potential of this positive electrode is, for example, 5.4 V vs. It may be Li / Li ⁺ , 5.0 V vs. It may be Li / Li ^+.

The maximum potential of the positive electrode is preferably the positive electrode potential at the end-of-charge voltage of the secondary battery during normal use. In general, when the positive electrode potential frequently reaches a high potential due to repeated charging and discharging, the capacity tends to decrease and the thickness tends to increase. Therefore, the maximum potential of the positive electrode is frequently increased by repeating charging and discharging, for example, 4.0 V vs. When it becomes Li / Li ⁺ or more, the effect of improving the capacity retention rate after the charge / discharge cycle of the secondary battery and the effect of suppressing the increase in thickness are more remarkably exhibited.

<Manufacturing method of non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage element is preferably manufactured by the following method. That is, the method for producing a non-aqueous electrolyte power storage element according to an embodiment of the present invention is to prepare a non-aqueous electrolyte containing an imide salt, a tetrafluoroborate, and a phosphoric acid ester (non-aqueous electrolyte preparation step). Be prepared.

It is preferable that the production method further includes producing a positive electrode using a positive electrode mixture paste (positive electrode production step). At this time, the positive electrode mixture paste preferably contains phosphorus oxoacid.

(Non-aqueous electrolyte preparation process)
In this step, a non-aqueous electrolyte can be prepared by mixing an imide salt, a tetrafluoroborate, and a phosphoric acid ester, and if necessary, other components. At this time, it is preferable that the hexafluorophosphate is not substantially mixed.

(Positive electrode manufacturing process)
The positive electrode mixture paste usually contains a positive electrode active material and a binder in addition to the oxo acid of phosphorus, which is a preferable component, and further contains other components if necessary. The positive electrode mixture paste can be obtained by mixing these components. By applying this positive electrode mixture paste to the surface of the positive electrode base material and drying it, a positive electrode having a maximum value of the peak attributable to P2p at a position of 134 eV or less can be obtained in the X-ray photoelectron spectroscopic spectrum of the positive electrode mixture. Be done.

The phosphorus oxo acid refers to a compound having a structure in which a hydroxy group (-OH) and an oxy group (= O) are bonded to a phosphorus atom. Examples of the phosphorus oxo acid include phosphoric acid (H ₃ PO ₄ ), phosphoric acid (H ₃ PO ₃ ), phosphinic acid (H ₃ PO ₂ ), pyrophosphoric acid (H ₄ P ₂ O ₇ ), polyphosphoric acid and the like. Can be mentioned. Among these, phosphoric acid and phosphonic acid are preferable, and phosphonic acid is more preferable. The oxo acid of phosphorus forms a film containing a phosphorus atom on the positive electrode.

The content (addition amount) of phosphorus oxo acid in the positive electrode mixture paste is preferably 0.05 parts by mass or more and 5 parts by mass or less, and 0.1 parts by mass or more and 3 parts by mass with respect to 100 parts by mass of the positive electrode active material. More preferably, it is 0.3 parts by mass or more and 2 parts by mass or less. By setting the phosphorus oxoacid content in the above range, the capacity retention rate of the non-aqueous electrolyte power storage device after the charge / discharge cycle can be further increased.

An organic solvent is usually used as the dispersion medium in the positive electrode mixture paste. Examples of this organic solvent include polar solvents such as N-methyl-2-pyrrolidone (NMP), acetone and ethanol, and non-polar solvents such as xylene, toluene and cyclohexane.

The method for applying the positive electrode mixture paste is not particularly limited, and a known method such as roller coating, screen coating, or spin coating can be used.

The manufacturing method may include, in addition to the non-aqueous electrolyte preparation step and the positive electrode manufacturing step, other steps provided in the usual manufacturing method of the non-aqueous electrolyte power storage element. The manufacturing method is, for example, manufacturing a negative electrode, forming an electrode body in which positive electrodes and negative electrodes are alternately superposed by laminating or winding through a separator, and containerizing a positive electrode and a negative electrode (electrode body). It can be provided to be housed in a container and to inject a non-aqueous electrolyte into a container. Normally, the electrode body is housed in a container, and then the non-aqueous electrolyte is injected into the container, but the order may be reversed. After these steps, a non-aqueous electrolyte power storage element can be obtained by sealing the injection port.

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. For example, it is not necessary to provide an intermediate layer in the positive electrode or the negative electrode. Further, in the positive electrode of the non-aqueous electrolyte power storage element, the positive electrode mixture does not have to form a clear layer. For example, the positive electrode may have a structure in which a positive electrode mixture is supported on a mesh-shaped positive electrode base material.

Further, in the above-described embodiment, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Examples of other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte storage element 1 which is an embodiment of the non-aqueous electrolyte storage element according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte power storage element 1 shown in FIG. 1, the electrode body 2 is housed in the container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode mixture and a negative electrode having a negative electrode mixture through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51. Further, a non-aqueous electrolyte is injected into the container 3.

The configuration of the non-aqueous electrolyte power storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte power storage elements. An embodiment of the 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 non-aqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

(Preparation of lithium excess positive electrode active material)
17.7 g of nickel sulfate hexahydrate and 32.5 g of manganese sulfate pentahydrate were weighed and all of them were dissolved in 200 mL of ion-exchanged water, and the molar ratio of Ni: Mn was 33.3: 66.7. A 1.0 mol / L sulfate aqueous solution was prepared. _{On the other hand, CO 2} was dissolved in the ion-exchanged water by pouring 750 mL of ion-exchanged water into a ₂ L reaction vessel and bubbling CO 2 gas for 30 minutes. The temperature of the reaction tank is set to 50 ° C. (± 2 ° C.), and the sulfate aqueous solution is stirred at a speed of 2 mL / min while stirring the inside of the reaction tank at a rotation speed of 700 rpm using a paddle blade equipped with a stirring motor. Dropped. Here, the pH in the reaction vessel is controlled to always be maintained at 7.9 (± 0.05) by appropriately dropping an aqueous solution containing 1.0 M sodium carbonate from the start to the end of the dropping. did. After completion of the dropping, stirring in the reaction vessel was continued for another 5 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.
Next, the particles of coprecipitated carbonate generated in the reaction vessel are separated using a suction filtration device, and the sodium ions adhering to the particles are washed and removed using ion-exchanged water, and an electric furnace is used. Then, it was dried at 80 ° C. for 20 hours under normal pressure in an air atmosphere. Then, in order to make the particle size uniform, it was crushed in an agate mortar for several minutes. In this way, a coprecipitated carbonate precursor was prepared.

To 2.8 g of the coprecipitated carbonate precursor, 1.2 g of lithium carbonate was added and mixed well using an agate mortar to obtain a mixed powder having a Li: (Ni, Mn) molar ratio of 1.35: 1. The body was prepared. It was molded at a pressure of 40 MPa using a pellet molding machine to obtain pellets having a diameter of 25 mm. The amount of the mixed powder used for pellet molding was determined by converting so that the assumed mass of the final product was 2.5 g. One of the pellets is placed on the lid of an alumina crucible having a total length of about 50 mm, installed in a box-type electric furnace (model number: AMF20), and raised in an air atmosphere under normal pressure from room temperature to a temperature of 890 ° C. over 10 hours. After warming, the temperature was increased and the mixture was baked for 9 hours. The internal dimensions of the box-type electric furnace are 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was switched off, and the lid of the alumina crucible was left in the furnace to allow it to cool naturally. As a result, the temperature of the furnace dropped to about 200 ° C. after 5 hours, but the rate of temperature decrease thereafter was rather slow. After a day and night, after confirming that the temperature of the furnace was 100 ° C. or lower, the pellets were taken out and crushed in an agate mortar for several minutes in order to make the particle size uniform. In this way, the lithium excess type positive electrode active material Li _1.35 Ni _0.315 Mn _0.685 O ₂ was prepared.

(Aluminum treatment of lithium excess positive electrode active material)
Aluminum sulfate hydrate and ion-exchanged water were mixed in a 300 mL Erlenmeyer flask to prepare an aqueous aluminum sulfate solution having an aluminum sulfate content of 0.5 mol / L. 5.0 g of the above-mentioned lithium excess type positive electrode active material was added to the place where the above-mentioned aluminum sulfate aqueous solution was stirred at 25 ° C. and 400 rpm using a stirrer. The lithium-rich positive electrode active material was charged, and then suction filtration was performed 30 seconds later to recover the lithium-rich positive electrode active material on the filter paper.
This lithium-rich positive electrode active material was dried in air at normal pressure at 80 ° C. for 20 hours using a dryer to obtain an aluminum-treated lithium-rich positive electrode active material.

(Heat treatment to aluminum-treated lithium excess positive electrode active material)
The above aluminum-treated lithium excess type positive electrode active material is placed on the lid of an alumina crucible and installed in a box-type electric furnace (model number: AMF20). By heat-treating under the conditions of 400 ° C. and a holding time of 4 hours, an aluminum-coated lithium-rich positive electrode active material was obtained.

(Preparation of positive electrode)
The above-mentioned aluminum-coated lithium-rich positive electrode active material: acetylene black (AB): polyvinylidene fluoride (PVDF): phosphonic acid (H ₃ PO ₃ ) = 93.5: 4.5: 1.5: 0. A positive electrode mixture paste containing 5 (in terms of solid matter) and using N-methylpyrrolidone (NMP) as a dispersion medium was prepared. This positive electrode paste was applied to one side of an aluminum foil which is a positive electrode base material. Then, it was dried at 100 ° C. for 1 hour to remove NMP in the positive electrode mixture paste to form a positive electrode active material layer. Further, the positive electrode mixture paste was similarly applied to the opposite surface of the aluminum foil and dried. The positive electrode active material layer formed on the opposite surface was peeled off after drying. In this way, a positive electrode was obtained.

(Preparation of negative electrode)
A negative electrode using graphite as the negative electrode active material was produced.

[Example 1]
(Preparation of non-aqueous electrolyte)
Fluoroethylene carbonate (FEC), methyltrifluoroethyl carbonate (MFEC) and tris phosphate (2,2,2-trifluoroethyl) (TFEP: O = P (OCH ₂ CF ₃ ) ₃ ) in a volume ratio of 30: The mixture was mixed at a ratio of 65: 5. Further, lithium bis (fluorosulfonyl) imide (LiFSI) as an electrolyte salt was dissolved at a concentration of 0.75 _{mol / kg, and lithium tetrafluoroborate (LiBF 4} ) was dissolved at a concentration of 0.25 mol / kg, and Example 1 Non-aqueous electrolyte was prepared.

(Manufacturing of non-aqueous electrolyte power storage element)
An electrode body was produced by laminating the positive electrode and the negative electrode via a separator which is a microporous polyolefin film. This electrode body is housed in a container made of a metal resin composite film, and after injecting the non-aqueous electrolyte of Example 1 into the inside, the electrode body is sealed by heat welding, and the non-aqueous electrolyte power storage element of Example 1 (laminated non-water). Electrolyte secondary battery) was obtained.

[Examples 2 to 9, Comparative Examples 1 to 8]
Each non-aqueous electrolyte and each non-aqueous electrolyte power storage element of Examples 2 to 9 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1 except that the composition of the non-aqueous electrolyte was as shown in Table 1. It was.

The non-aqueous solvent, phosphoric acid ester, etc. in the table indicate the following compounds.
FEC: Fluoroethylene carbonate MFEC: Methyltrifluoroethyl carbonate TFEP: Tris phosphate (2,2,2-trifluoroethyl) (O = P (OCH ₂ CF ₃ ) ₃ )
TEP: Triethyl phosphate (O = P (OCH ₂ CH ₃ ) ₃ )
TAP: Triallyl phosphate (O = P (OCH ₂ CH = CH ₂ ) ₃ )
HFiP: Tris phosphate (1,1,1,3,3,3-hexafluoro-2-propyl) (O = P (OCH (CF ₃ ) ₂ ) ₃ )
BTP: Bisphosphite (2,2,2-trifluoroethyl) (O = PH (OCH ₂ CF ₃ ) ₂ )

[Evaluation]
(Initial charge / discharge)
Each of the obtained non-aqueous electrolyte power storage elements was initially charged and discharged under the following conditions. After charging at 25 ° C. to 4.6 V with a constant current of 0.1 C, the battery was charged with a constant voltage of 4.6 V. The charging end condition was until the charging current reached 0.05C. After a 10-minute rest after charging, the battery was discharged at a constant current of 0.1 C up to 2.0 V at 25 ° C.

(X-ray photoelectron spectroscopy)
The non-aqueous electrolyte storage elements of Example 1 and Comparative Example 8 in a completely discharged state after the initial charge and discharge were disassembled in an argon atmosphere having a dew point of -60 ° C. or lower to take out a positive electrode, and the positive electrode was washed with dimethyl carbonate. Then, it was dried under reduced pressure at room temperature. The obtained positive electrode is sealed in a transfer vessel in an argon atmosphere, introduced into the sample chamber of an X-ray photoelectron spectroscopy measurement device, and X on the surface of the positive electrode mixture (positive electrode active material layer) of the positive electrode under the above conditions. X-ray photoelectron spectroscopy was performed. From the obtained spectrum, the position of the maximum value of the peak attributed to P2p was determined by the above method. In the positive electrode mixture of Example 1 and Comparative Example 8, the maximum value of the peak attributed to P2p was between 133 eV and 134 eV. Further, in the positive electrode mixture of Example 1 containing the phosphoric acid ester, the maximum value of the peak attributed to P2p derived from the phosphoric acid ester was confirmed also in the vicinity of 134.5 eV. On the other hand, in the positive electrode mixture of Comparative Example 8 in which _{LiPF 6} was used as the electrolyte salt, the maximum value of the peak attributed to P2p derived from _{LiPF 6 was confirmed also in the vicinity of 136 eV.}

(Charge / discharge cycle test)
After the initial charge and discharge, each non-aqueous electrolyte power storage element is stored in a constant temperature bath at 45 ° C. for 2 hours, charged to 4.6 V with a constant current of 0.25 C, and then set to 4.6 V. It was charged with voltage. The charging end condition was until the charging current reached 0.05C. The positive electrode potential (= maximum potential of the positive electrode) at the end of charging is 4.7 V vs. It was Li / Li ^+. After a 10-minute rest after charging, the battery was discharged to 2.0 V at a constant current of 0.25 C. A 10-minute rest was provided after the discharge. This cycle was repeated 25 cycles, with these charging, discharging, and resting steps as one cycle. Charging, discharging and pausing were performed in a constant temperature bath at 45 ° C.

(Capacity maintenance rate)
For each non-aqueous electrolyte power storage element, the discharge capacity at the 25th cycle with respect to the discharge capacity at the first cycle of the charge / discharge cycle test is shown in Table 1 as a capacity retention rate (%). A capacity retention rate of 93.0% or more was evaluated as "A", and a capacity retention rate of less than 93.0% was evaluated as "B".

(Thickness increase)
Before and after the charge / discharge cycle test, the thickness of the gas pool portion (the end portion excluding the heat-welded portion of the container in which the electrode body does not exist) in each non-aqueous electrolyte power storage element was measured with a caliper. Table 1 shows the amount of increase (mm) in the thickness of the gas reservoir after the charge / discharge cycle test with respect to the thickness of the gas reservoir before the charge / discharge cycle test. A thickness increase of less than 1.50 mm was evaluated as "A", and a thickness increase of 1.50 mm or more was evaluated as "B".

As shown in Table 1, each non-aqueous electrolyte storage element of Examples 1 to 9 using a non-aqueous electrolyte containing an imide salt, a tetrafluoroborate, and a phosphoric acid ester has a high capacity retention rate and is thick. The amount of increase is also small.

On the other hand, the non-aqueous electrolyte storage element of Comparative Example 1 using a non-aqueous electrolyte containing _{LiPF 6 as an electrolyte salt and not containing an imide salt and tetrafluoroborate has a capacity retention rate.} Is low. Each of the non-aqueous electrolyte power storage elements of Comparative Examples 2 to 6 using the non-aqueous electrolyte containing an imide salt as the electrolyte salt has a higher capacity retention rate than that of Comparative Example 1. However, Comparative Example 2 in which the non-aqueous electrolyte does not contain the tetrafluoroborate and the phosphoric acid ester, and Comparative Examples 3 to 6 in which the non-aqueous electrolyte contains the phosphoric acid ester but does not contain the tetrafluoroborate are any of the above. The amount of thickness increase is large. Each of the non-aqueous electrolyte storage elements of Comparative Examples 2 to 6 does not contain a phosphoric acid ester or a tetrafluoroborate, although gas is likely to be generated by using an imide salt as the electrolyte salt. Therefore, it is considered that a film capable of suppressing the generation of such gas is not formed. Further, the non-aqueous electrolyte storage element of Comparative Example 7 in which BTP, which is a phosphite ester, is used instead of the phosphoric acid ester, has a low capacity retention rate and a large increase in thickness. Further, each non-aqueous electrolyte storage element of Comparative Example 8 in which _{LiPF 6} containing a phosphorus atom is used instead of the phosphoric acid ester has a low capacity retention rate and a large amount of thickness increase due to the use of _{LiPF 6.} large. _{In Comparative Example 8, LiPF 6} having an amount containing a phosphorus atom in an amount substantially equal to that of the phosphorus atom of the phosphoric acid ester of Example 1 was used. From these results, the presence of both the phosphate ester and the tetrafluoroborate in the non-aqueous electrolyte suppresses the generation of gas that is likely to occur when the imide salt is used for the first time, thereby storing the non-aqueous electrolyte. It can be seen that the effect of suppressing the increase in the thickness of the element is exhibited.

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

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims (8)

A non-aqueous electrolyte for a power storage device, including an imide salt, a tetrafluoroborate, and a phosphate ester. The non-aqueous electrolyte for a power storage device according to claim 1, which is substantially free of hexafluorophosphate. The non-aqueous electrolyte according to claim 1 or 2, further comprising a chain carbonate. The non-aqueous electrolyte according to claim 1, claim 2 or claim 3, further comprising a fluorinated cyclic carbonate. A non-aqueous electrolyte power storage device comprising the non-aqueous electrolyte according to any one of claims 1 to 4. Further provided with a positive electrode having a positive electrode mixture containing a phosphorus atom,
The non-aqueous electrolyte storage element according to claim 5, wherein the maximum value of the peak attributable to P2p exists at a position of 134 eV or less in the X-ray photoelectron spectroscopic spectrum of the surface of the positive electrode mixture. A method for producing a non-aqueous electrolyte storage element, which comprises preparing a non-aqueous electrolyte containing an imide salt, a tetrafluoroborate, and a phosphoric acid ester. The method for producing a non-aqueous electrolyte power storage element according to claim 7, further comprising producing a positive electrode using a positive electrode mixture paste containing an oxo acid of phosphorus.

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