JP2019145343A - Nonaqueous electrolyte, nonaqueous electrolyte power storage element, and method for manufacturing nonaqueous electrolyte power storage element - Google Patents

Abstract

To provide: a nonaqueous electrolyte containing fluorinated cyclic carbonate, which can reduce an increase rate of DC resistance after a nonaqueous electrolyte power storage element is stored in a high temperature environment; and a nonaqueous electrolyte power storage element including such a nonaqueous electrolyte and a method of manufacturing the same.SOLUTION: One embodiment of the present invention is a nonaqueous electrolyte for a power storage element which contains fluorinated cyclic carbonate and a cyclic boron compound. The cyclic boron compound is a boron compound with a six-membered ring structure or a boron compound with a five-membered ring structure in which the number of atoms is 2 or less, the atoms being bonded to one boron atom and having electronegativity of equal to or more than the electronegativity of oxygen atoms.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte, a non-aqueous electrolyte storage element, and a method for manufacturing a non-aqueous 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 nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is comprised so that it may charge / discharge. 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.

  Generally, the nonaqueous electrolyte of the nonaqueous electrolyte electricity storage element includes a nonaqueous solvent and an electrolyte salt that dissolves in the nonaqueous solvent. In this non-aqueous electrolyte, various additives and solvents are selected and used for performance improvement. For example, a secondary battery using a nonaqueous electrolyte containing a fluorinated cyclic carbonate such as fluorinated ethylene carbonate is known (see Patent Documents 1 and 2).

JP 2008-243810 A International Publication No. 2013/100081

A storage element using a non-aqueous electrolyte containing a fluorinated cyclic carbonate as described above has a high voltage (for example, 4.4 V (vs. The capacity retention rate in the charge / discharge cycle of Li / Li ⁺ )) is improved. However, a power storage device using a non-aqueous electrolyte containing a fluorinated cyclic carbonate has a disadvantage that the rate of increase in DC resistance after storage in a high temperature environment is high.

  The present invention has been made based on the circumstances as described above, and an object thereof is a nonaqueous electrolyte containing a fluorinated cyclic carbonate, and a direct current after storing the nonaqueous electrolyte storage element in a high temperature environment. A non-aqueous electrolyte capable of reducing the rate of increase in resistance, a non-aqueous electrolyte electricity storage device including such a non-aqueous electrolyte, and a method for manufacturing the same.

  One embodiment of the present invention made to solve the above problems includes a fluorinated cyclic carbonate and a cyclic boron compound, and the cyclic boron compound has a boron compound having a six-membered ring structure or a five-membered ring structure. And a non-aqueous electrolyte for a power storage element, which is a boron compound having two or less atoms having an electronegativity equal to or greater than the electronegativity of an oxygen atom, bonded to one boron atom.

  Another embodiment of the present invention is a nonaqueous electrolyte storage element including the nonaqueous electrolyte.

  Another aspect of the present invention is a method for manufacturing a nonaqueous electrolyte storage element comprising injecting the nonaqueous electrolyte into a container.

  According to the present invention, a nonaqueous electrolyte containing a fluorinated cyclic carbonate, which can reduce the rate of increase in DC resistance after storing the nonaqueous electrolyte storage element in a high-temperature environment, and such a nonaqueous electrolyte A non-aqueous electrolyte electricity storage device including a water electrolyte and a method for producing the same 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 nonaqueous electrolyte according to one embodiment of the present invention contains a fluorinated cyclic carbonate and a cyclic boron compound, and the cyclic boron compound has a boron compound (a) having a six-membered ring structure or a five-membered ring structure. 1 is a non-aqueous electrolyte for a storage element, which is a boron compound (b) having two or less atoms having an electronegativity of not less than the electronegativity of an oxygen atom and bonded to one boron atom.

  Although the non-aqueous electrolyte is a non-aqueous electrolyte containing a fluorinated cyclic carbonate, it can reduce the rate of increase in DC resistance after storing the non-aqueous electrolyte storage element in a high temperature environment. Although this reason is not certain, the following reason is guessed. The cyclic boron compound contained in the nonaqueous electrolyte has a six-membered ring or a five-membered ring structure. When the cyclic boron compound has such a cyclic structure, film formation on the electrode surface is likely to proceed by a reaction such as polymerization accompanying decomposition of the cyclic structure. In addition, when the said cyclic boron compound has a five-membered ring structure, stability is low compared with what has a six-membered ring structure. In such a cyclic boron compound having a five-membered ring structure, when the number of atoms bonded to one boron atom and having an electronegativity equal to or greater than the electronegativity of an oxygen atom is more than 2, the boron atom is large and has an electron. It becomes more unstable because it is in a solicited state. In the case of such a low stability cyclic boron compound, it is presumed that an excessive film is formed. That is, in the non-aqueous electrolyte, the boron compound (a) having a six-membered ring structure or the boron compound (b) having a five-membered ring structure and a specific structure causes a film to be appropriately formed on the electrode surface. It is presumed that the rate of increase in DC resistance after the nonaqueous electrolyte storage element is stored in a high-temperature environment is reduced by this film formed. Moreover, since the non-aqueous electrolyte contains a fluorinated cyclic carbonate, the capacity retention rate in a high-voltage charge / discharge cycle in a high-temperature environment of the non-aqueous electrolyte storage element is increased by using the non-aqueous electrolyte. The cyclic boron compound is presumed to be difficult to inhibit the action of the fluorinated cyclic carbonate to improve the capacity retention rate.

  The electronegativity is based on the electronegativity of all red locomotive.

  It is preferable that the number of boron atoms contained in one ring structure of the cyclic boron compound is 1 or less. In such a case, the rate of increase in DC resistance after storing the nonaqueous electrolyte storage element in a high temperature environment can be further reduced. The reason for this is not clear, but when the cyclic boron compound has such a ring structure, the stability of the ring structure, that is, the reactivity is more appropriate, and the state of the film to be formed is optimized. It is guessed.

  The ring structure of the cyclic boron compound preferably contains a boron atom and two oxygen atoms bonded to the boron atom. In such a case, the rate of increase in DC resistance after storing the nonaqueous electrolyte storage element in a high temperature environment can be further reduced. The reason for this is not clear, but when the cyclic boron compound has such a ring structure, the stability of the ring structure, that is, the reactivity is more appropriate, and the state of the film to be formed is optimized. It is guessed.

  A nonaqueous electrolyte storage element according to an embodiment of the present invention is a nonaqueous electrolyte storage element (hereinafter, also simply referred to as “storage element”) including a nonaqueous electrolyte. The power storage element has a high capacity retention rate in a high-voltage charge / discharge cycle under a high temperature environment and a low increase rate of DC resistance after storage in a high temperature environment.

The positive electrode potential at the end-of-charge voltage during normal use of the power storage element is preferably 4.4 V (vs. Li ^/ Li ⁺ ) or higher. Since the storage element has a high capacity retention rate in a charge / discharge cycle at a high voltage under a high temperature environment, the storage element is used in a charge condition in which the positive electrode potential at the end-of-charge voltage during normal use is relatively high. In some cases, this effect can be exerted particularly well. Here, the normal use is a case where the power storage element is used under the recommended or specified charging conditions for the power storage element, and a charger for the power storage element is prepared Refers to the case where the battery element is used and the power storage element is used. Note that, for example, in a power storage element using graphite as a negative electrode active material, the positive electrode potential is about 5.1 V (vs. Li ^/ Li ⁺ ) when the charge end voltage is 5.0 V, depending on the design.

  The manufacturing method of the nonaqueous electrolyte electrical storage element which concerns on one Embodiment of this invention is a manufacturing method of a nonaqueous electrolyte electrical storage element provided with inject | pouring the said nonaqueous electrolyte into a container.

  According to the manufacturing method, a non-aqueous electrolyte storage element having a high capacity retention rate in a high-voltage charge / discharge cycle under a high-temperature environment and a low increase rate of direct current resistance after storage under a high-temperature environment is manufactured. be able to.

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

<Nonaqueous electrolyte>
The non-aqueous electrolyte according to one embodiment of the present invention is used as a non-aqueous electrolyte for a power storage element. The non-aqueous electrolyte contains a fluorinated cyclic carbonate and a cyclic boron compound.

(Fluorinated cyclic carbonate)
The fluorinated cyclic carbonate is a nonaqueous solvent in the nonaqueous electrolyte. The fluorinated cyclic carbonate refers to a compound in which part or all of the hydrogen atoms of the cyclic carbonate are substituted with fluorine atoms.

  Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate (FEC), difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, (fluoromethyl) ethylene carbonate, (difluoromethyl) ethylene carbonate, and (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-difluoro-4,5-dimethylethylene carbonate, and the like. As the fluorinated cyclic carbonate, FEC is preferred. The said fluorinated cyclic carbonate can be used individually by 1 type or in mixture of 2 or more types.

  The lower limit of the content of the fluorinated cyclic carbonate in the nonaqueous solvent of the nonaqueous electrolyte is preferably 1% by volume, more preferably 3% by volume, and even more preferably 5% by volume. By setting the content of the fluorinated cyclic carbonate to be equal to or higher than the above lower limit, the capacity retention rate in a high-voltage charge / discharge cycle in a high-temperature environment of the energy storage device can be further increased. On the other hand, the upper limit of the content is preferably 50% by volume, more preferably 30% by volume, still 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, the charge / discharge cycle performance of the nonaqueous electrolyte electricity storage device can be made more sufficient, and the amount of expensive fluorinated cyclic carbonate used is suppressed, An increase in the cost of the nonaqueous electrolyte itself can also be suppressed.

(Other non-aqueous solvents)
The non-aqueous electrolyte may include a non-aqueous solvent other than the fluorinated cyclic carbonate. As the other non-aqueous solvent, a known non-aqueous solvent that is usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a storage element is used. A solvent can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, fluorinated chain carbonate, ester, ether, amide, sulfone, lactone, and nitrile. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination.

  Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), styrene carbonate, 1-phenyl vinylene carbonate, 1,2- Examples thereof include diphenyl vinylene carbonate. The cyclic carbonate may be one in which some or all of the hydrogen atoms are substituted with atoms or substituents other than fluorine atoms, but those that are not substituted are preferred. As the cyclic carbonate, EC, PC and BC are preferable, PC and BC are more preferable, and PC is more preferable.

  As a minimum of content of the cyclic carbonate which occupies for the above-mentioned nonaqueous solvent, 1 volume% is preferred and 5 volume% is more preferred. On the other hand, as an upper limit of this content, 40 volume% is preferable and 20 volume% is more preferable.

  Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diphenyl carbonate. The chain carbonate may be one in which some or all of the hydrogen atoms are substituted with other atoms or substituents, but is preferably not substituted. As the chain carbonate, DEC, DMC and EMC are preferable, and EMC is more preferable.

  As a minimum of content of the chain carbonate which occupies for the above-mentioned nonaqueous solvent, 50 volume% is preferred and 70 volume% is more preferred. On the other hand, as an upper limit of this content, 95 volume% is preferable and 90 volume% is more preferable.

  The lower limit of the total content of the fluorinated cyclic carbonate, cyclic carbonate and chain carbonate in the non-aqueous solvent is preferably 80% by volume, more preferably 95% by volume, and more preferably 99% by volume. The upper limit of this total content may be 100% by volume.

  By setting the composition of the non-aqueous solvent as described above, the capacity retention rate of the power storage element can be further improved due to the appropriate dielectric constant, viscosity, and the like.

(Cyclic boron compound)
The cyclic boron compound is a boron compound (a) having a six-membered ring structure or a boron compound (b) having a five-membered ring structure. However, in the boron compound (b) having a five-membered ring structure, the number of atoms bonded to one boron atom and having an electronegativity equal to or higher than that of an oxygen atom is 2 or less. Examples of the atom bonded to the boron atom of the boron compound (b) include carbon, oxygen, and boron. In the boron compound (b), the number of oxygen bonded to one boron atom is preferably 2 or less, and more preferably 2.

  A cyclic boron compound is a compound having a ring structure and containing a boron atom. In the cyclic boron compound, the boron atom may or may not be contained in the ring structure, but the boron atom is preferably contained in the ring structure. Among the cyclic boron compounds, examples of the compound in which the ring structure does not contain a boron atom include cyclohexyl boronic acid and triphenyl borate. The number of boron atoms contained in one ring structure of the cyclic boron compound is preferably 1 or less, and more preferably 1.

  The ring structure of the cyclic boron compound preferably includes a boron atom and two oxygen atoms bonded to the boron atom. Examples of the compound having such a ring structure include boric acid esters, boronic acid esters, and diboronic acid esters. Moreover, as such a suitable cyclic boron compound, the compound represented by following formula (1) or formula (2) can be mentioned.

In formula (1), R ¹ is a hydrocarbon group, an alkoxy group or a group represented by —B (OR ^a ) ₂ . Part or all of the hydrogen atoms of the hydrocarbon group and the alkoxy group may be substituted with a group represented by the above -B (OR ^a ) ₂ . Each R ^a is independently a hydrocarbon group. Two R ^a may be bonded to each other to form a five-membered or six-membered ring structure together with atoms linked to these.
R ^{2 to} R ⁷ are each independently a hydrogen atom or an alkyl group.
In formula (2), R ⁸ is a hydrocarbon group or a group represented by —B (OR ^b ) ₂ . Part or all of the hydrogen atoms of the hydrocarbon group may be substituted with a group represented by the above -B (OR ^b ) ₂ . Each R ^b is independently a hydrocarbon group. Two R ^{b s} may be bonded to each other to form a five-membered or six-membered ring structure together with the atoms connected to them.
R ^{9 to} R ¹² are each independently a hydrogen atom or an alkyl group.

(Compound represented by the above formula (1))
The compound represented by the above formula (1) is a preferred form of the boron compound (a) having a six-membered ring structure. When R ¹ in the above formula (1) is a hydrocarbon group, this compound is a boronic ester. When R ¹ is an alkoxy group, this compound is a borate ester. When R ¹ is a group represented by —B (OR ^a ) ₂ , this compound is a diboronic acid ester.

As the hydrocarbon group for R ¹ ,
Alkyl groups such as methyl, ethyl, propyl, butyl, propyl, butyl,
Alkenyl groups such as ethenyl group, propenyl group, butenyl group,
Monovalent aliphatic chain hydrocarbon group such as alkynyl group such as ethynyl group, propynyl group, butynyl group;
A cycloalkyl group such as a cyclohexyl group,
And monovalent alicyclic hydrocarbon groups such as cycloalkenyl groups such as cyclohexenyl groups; and monovalent aromatic hydrocarbon groups such as phenyl groups, naphthyl groups, biphenyl groups, and benzyl.

  As an upper limit of the carbon number of the said hydrocarbon group, it is 12, for example, 6 is preferable and 3 is more preferable. The lower limit of this carbon number is 1.

The alkoxy group in R ¹ has a structure in which a hydrocarbon group is bonded to an oxygen atom. Examples of the hydrocarbon group possessed by the alkoxy group include those described above as the hydrocarbon group for R ¹ .

Examples of the hydrocarbon group for R ^a include those described above as the hydrocarbon group for R ¹ .

In the group represented by -B (OR ^a ) ₂ above, as the group in which two R ^a are bonded to each other and together with the atoms linked to these, a 5-membered or 6-membered ring structure is formed, A group represented by the following formula (3) can be exemplified.

In formula (3), R < ¹³ > -R < ¹⁸ > is a hydrogen atom or an alkyl group each independently. n is 0 or 1. * Indicates a bonding point.

As an alkyl group in said R < ¹³ > -R < ¹⁸ >, what was mentioned above as an alkyl group in R < ¹ > can be mentioned.

As said R < ¹ >, the group represented by an alkoxy group and -B (OR ^<a> ) ₂ is preferable. As the alkoxy group, a group having a structure in which an alkyl group is bonded to an oxygen atom is preferable. As an upper limit of the carbon number of this alkyl group, 6 is preferable and 3 is more preferable. Among the alkoxy groups, a methoxy group, an ethoxy group, and a propoxy group are preferable, and an ethoxy group is more preferable. Of the groups represented by —B (OR ^a ) ₂ , the group represented by the above formula (3) is preferable. At this time, as R < ¹³ > -R < ¹⁸ > of Formula (3), a hydrogen atom and a C1-C3 alkyl group are preferable. Moreover, it is preferable that at least one of R ¹³ , R ¹⁴ , R ¹⁷ and R ¹⁸ is an alkyl group. n is preferably 1.

Examples of the R ² to R ^7, preferably an alkyl group having a hydrogen atom and 1 to 3 carbon atoms, more preferably a hydrogen atom or a methyl group. Moreover, it is preferable that at least one of R ² , R ³ , R ⁶ and R ⁷ is an alkyl group.

(Compound represented by the above formula (2))
The compound represented by the above formula (2) is a preferred form of the boron compound (b) having a five-membered ring structure. When R ⁸ in the above formula (2) is a hydrocarbon group, this compound is a boronic ester. When R ⁸ is a group represented by —B (OR ^b ) ₂ , this compound is a diboronic acid ester.

Examples of the hydrocarbon group in R ⁸ and R ^b include those described above as the hydrocarbon group in R ¹ .

In the group represented by -B (OR ^b ) ₂ above, as the group in which two R ^b are bonded to each other and together with the atoms linked to these, a 5-membered ring structure or a 6-membered ring structure is formed, A group represented by the above formula (3) can be exemplified.

Above the upper limit of the carbon number of the hydrocarbon group represented by R ⁸ is preferably 6, 3 is more preferable. Moreover, as this hydrocarbon group, an alkyl group is preferable, a methyl group, an ethyl group, and a propyl group are preferable, and an ethyl group is more preferable. Of the groups represented by —B (OR ^b ) ₂ , the group represented by the above formula (3) is preferable. At this time, as R < ¹³ > -R < ¹⁸ > of Formula (3), a hydrogen atom and a C1-C3 alkyl group are preferable. Moreover, it is preferable that at least one of R ¹³ , R ¹⁴ , R ¹⁷ and R ¹⁸ is an alkyl group, and it is more preferable that all of these are alkyl groups. n is preferably 0.

Examples of the ^R 9 ^{to R 12,} preferably an alkyl group having a hydrogen atom and 1 to 3 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, more preferably methyl group.

  The lower limit of the content of the cyclic boron compound in the non-aqueous electrolyte is preferably 0.01% by mass, more preferably 0.05% by mass, further preferably 0.1% by mass, and more preferably 0.3% by mass. More preferably, 0.7% by mass may be even more preferable. By making content of a cyclic boron compound more than the said minimum, the increase rate of direct-current resistance after preserve | saving an electrical storage element in a high temperature environment can be made lower. On the other hand, the upper limit of the content is preferably 5% by mass, more preferably 3% by mass, further preferably 2% by mass, still more preferably 1% by mass, and particularly preferably 0.8% by mass. By setting the content of the cyclic boron compound to be equal to or lower than the above upper limit, the capacity retention rate in a high-voltage charge / discharge cycle in a high-temperature environment of the power storage element tends to be further increased.

(Electrolyte salt)
The non-aqueous electrolyte usually contains an electrolyte salt dissolved in a non-aqueous solvent. 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 lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiPF ₂ (C ₂ O ₄ ) ₂ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN ( _{SO 2 CF 3) 2, LiN} (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) (SO 2 C 4 F 9), LiC (SO 2 CF 3) 3, LiC (SO 2 C 2 F ₅ ) A lithium salt having a fluorinated hydrocarbon group such as ₃ can be mentioned.

Among the lithium salts, inorganic lithium salts are preferable, and LiPF ₆ is more preferable.

The lower limit of the content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol / dm ^3, more preferably 0.3 mol / dm ^3, more preferably 0.5mol / dm ^3, 0.8mol / dm ³ is particularly preferred. On the other hand, the upper limit is not particularly limited, but is preferably 2.5 mol / dm ^3, more preferably 2 mol / dm ^3, more preferably 1.5 mol / dm ^3.

  Other additives may be added to the non-aqueous electrolyte. However, the upper limit of the content of components other than nonaqueous solvents (including fluorinated cyclic carbonates), cyclic boron compounds and electrolyte salts in the nonaqueous electrolyte may be preferably 5% by mass, and more preferably 1% by mass. In some cases, 0.1% by mass may be more preferable.

<Nonaqueous electrolyte storage element>
The electrical storage element which concerns on one Embodiment of this invention has a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a secondary battery will be described as an example of a power 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 container, and the container is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as said container, the well-known metal container normally used as a container of a secondary battery, a resin container, etc. can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture 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 aluminum alloys are preferable from the balance of potential resistance, high conductivity and cost. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a positive electrode base material, and foil is preferable from the surface 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).

The said 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 compound material layer by including electroconductive particles, such as a carbon particle. The configuration of the intermediate layer is not particularly limited, and can be formed of a composition containing a resin binder and conductive particles, for example. “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 mixture layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary.

As the positive electrode active material, a metal oxide is usually used. As a specific positive electrode active material, for example, a complex oxide represented by Li _x MO _y (M represents at least one transition metal) (Li _x CoO ₂ , Li having a layered α-NaFeO ₂ type crystal structure) _{x NiO 2, Li x MnO 3} , Li x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 , etc., _Li x Mn ₂ having a spinel type crystal structure O ₄ , Li _x Ni _α Mn _(2-α) O ₄ ), Li _w Me _x (XO _y ) _z (Me represents at least one transition metal, and X represents, for example, P, Si, B, V, etc. 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.) The The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode mixture layer, one kind of these compounds may be used alone, or two or more kinds may be mixed and used.

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

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

  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 mixture 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 mixture 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 composite material layer contains arbitrary components, such as a electrically conductive agent, a binder, a thickener, and a filler, as needed. Arbitrary components such as a conductive agent, a binder, a thickener, and a filler can be the same as those for the positive electrode mixture layer.

  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).

  Further, the negative electrode mixture (negative electrode mixture 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 layer may be provided between the separator and the electrode (usually a positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer. Moreover, the separator by which the inorganic layer was formed in one surface of the porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and may contain other components. As the inorganic particles, Al ₂ O ₃ , SiO ₂ , aluminosilicate and the like are preferable.

(Nonaqueous electrolyte)
The nonaqueous electrolyte used for the secondary battery (storage element) is the nonaqueous electrolyte according to the embodiment of the present invention described above.

Since the secondary battery (storage element) has a high capacity retention rate in a high-voltage charge / discharge cycle under a high-temperature environment, it can be used at a high operating voltage. For example, the positive electrode potential at the end-of-charge voltage during normal use of the secondary battery may be, for example, 4.0 V (vs. Li ^/ Li ⁺ ) or higher, but 4.4 V (vs. Li ^/ Li ⁺ ). The above is preferable. On the other hand, the upper limit of the positive electrode potential at the charge voltage at the time of normal use, for example, 5.1V (vs.Li/Li ^+), may be 5.0V (vs.Li/Li ^+).

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The power storage element is preferably manufactured by the following method. That is, the manufacturing method of the nonaqueous electrolyte electrical storage element which concerns on one Embodiment of this invention comprises inject | pouring a nonaqueous electrolyte into a container (nonaqueous electrolyte injection | pouring process).

(Nonaqueous electrolyte injection process)
The non-aqueous electrolyte injection step can be performed by a known method except that the non-aqueous electrolyte according to the embodiment of the present invention described above is used as the non-aqueous electrolyte. That is, the nonaqueous electrolyte may be prepared and the prepared nonaqueous electrolyte may be poured into a container.

  The manufacturing method may include the following steps in addition to the nonaqueous electrolyte injection step. That is, the manufacturing method includes, for example, a step of producing a positive electrode, a step of producing a negative electrode, a step of forming an electrode body alternately superimposed by laminating or winding the positive electrode and the negative electrode via a separator, and The process of accommodating a positive electrode and a negative electrode (electrode body) in a container can be provided. Usually, after the electrode body is accommodated in the container, the nonaqueous electrolyte is injected into the container, but this order may be reversed. After these steps, a secondary battery (nonaqueous electrolyte storage element) can be obtained by sealing the inlet.

<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, the intermediate layer may not be provided in the positive electrode or the negative electrode. Further, the positive electrode and the negative electrode of the nonaqueous electrolyte electricity storage element may not have a clear layer structure. For example, the positive electrode may have a structure in which a positive electrode mixture is supported on a mesh-like positive electrode base material.

  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 mixture and a negative electrode including a negative electrode mixture 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 ′. The container 3 is injected with a nonaqueous electrolyte according to an embodiment of the present invention.

  The configuration of the nonaqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, 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.

  Abbreviations for non-aqueous solvents and boron compounds used in Examples, Comparative Examples and Reference Examples are shown below.

EC: ethylene carbonate EMC: ethyl methyl carbonate FEC: fluoroethylene carbonate PC: propylene carbonate

[Example 1]
(Preparation of non-aqueous electrolyte)
FEC, PC, and EMC were mixed at a volume ratio of 10:10:80 to obtain a non-aqueous solvent. In this non-aqueous solvent, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt has a content of 1.2 mol / dm ³ , and the compound represented by the above formula (A1) as an additive (A1) ) Were each dissolved to a content of 0.2% by mass to prepare a non-aqueous electrolyte.

(Preparation of positive electrode)
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material. A positive electrode paste containing a positive electrode active material: polyvinylidene fluoride (PVdF): acetylene black (AB) = 94: 3: 3 (in terms of solids) in mass ratio and using N-methylpyrrolidone as a dispersion medium was prepared. . This positive electrode paste was applied to both surfaces of a strip-shaped aluminum foil as a positive electrode substrate so that the positive electrode active material was contained at 18.6 mg / cm ² per unit electrode area. This was pressed with a roller press to form a positive electrode mixture layer, and then dried under reduced pressure at 100 ° C. for 14 hours to remove the liquid in the electrode plate. In this way, a positive electrode was obtained.

(Preparation of negative electrode)
Graphite was used as the negative electrode active material. Negative electrode active material (graphite): styrene butadiene rubber (SBR): carboxymethyl cellulose (CMC) = 97: 2: 1 in a mass ratio (solid content conversion), and a negative electrode paste using water as a dispersion medium was prepared. . This negative electrode paste was applied to both sides of a strip-shaped copper foil current collector as a negative electrode base material so that the negative electrode active material was contained at 9.9 mg / cm ² per unit electrode area. This was pressed with a roller press to form a negative electrode mixture layer, and then dried under reduced pressure at 100 ° C. for 12 hours to remove moisture in the electrode plate. In this way, a negative electrode was obtained.

(Preparation of nonaqueous electrolyte storage element)
A polyolefin microporous film coated with an inorganic layer was used as a separator. An electrode body was produced by laminating the positive electrode and the negative electrode through this separator. This electrode body was accommodated in an aluminum rectangular battery case, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the container (rectangular battery case), the container was sealed to obtain the non-aqueous electrolyte storage element (secondary battery) of Example 1.

[Examples 2-8, Comparative Examples 1-3, Reference Examples 1-2]
Examples 2 to 8 are the same as Example 1 except that the type and volume ratio of the nonaqueous solvent, the content of the electrolyte salt, and the type and content of the additive are as shown in Tables 1 and 2. The nonaqueous electrolytes and nonaqueous electrolyte electricity storage devices of Comparative Examples 1 to 3 and Reference Examples 1 to 2 were obtained. In addition, "-" in the column of the additive of a table | surface shows that the corresponding additive is not used. Comparative Example 1 is described in both Tables 1 and 2.

[Evaluation]
(Initial charge / discharge)
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 0.2 C to a charging current of 0.2C at 25 ° C., constant voltage charging (CCCV) was performed at 4.30 V. The charging termination condition was 8 hours. Thereafter, the battery was discharged at a constant current of 0.2 C to 2.75 V at 25 ° C. In the second cycle, a constant current of 1 C was charged at 25 ° C. to 4.30 V, and then a constant voltage was charged at 4.30 V. The charging termination condition was 3 hours. Then, it discharged at 25 degreeC with the constant current of 1C to 2.75V. In all cycles, a 10 minute rest period was set after charging and discharging.

(45 ° C charge / discharge cycle test: capacity retention rate)
Each non-aqueous electrolyte storage element after initial charge / discharge is stored in a constant temperature bath at 45 ° C. for 5 hours, then charged to 4.30V at a constant current of 1C, and then charged at a constant voltage of 4.30V. did. The charging termination condition was 3 hours. Thereafter, the battery was discharged at a constant current of 1.0 C up to 2.75V. In all cycles, a 10 minute rest period was set after charging and discharging. These steps of charging and discharging were regarded as one cycle, and this cycle was repeated 200 cycles. Charging, discharging, and rest were all performed in a constant temperature bath at 45 ° C. The discharge capacity at the 200th cycle relative to the discharge capacity at the first cycle is shown in Tables 1 and 2 as the capacity retention rate (%). In addition, when the capacity maintenance rate in this test is 80% or more, it can be judged that the capacity maintenance rate in the high voltage charging / discharging cycle in a high temperature environment is high. Reference Example 1 is evaluated by 180 cycles.

(DCR increase rate)
About each obtained nonaqueous electrolyte electrical storage element, initial charge / discharge was performed similarly to the above. Thereafter, constant current charging with a current of 1 C is performed at 25 ° C., and SOC (State of Charge) is set to 50%. Then, at 25 ° C., the current is 0.2 C, 0.5 C, and 1.0 C in this order. Discharged every second. The relationship between the current at each discharge current and the voltage at 10 seconds after the start of discharge was plotted, and the direct current resistance was obtained as the initial DCR from the slope of the straight line obtained from the three-point plot.
Next, constant current / constant voltage charging was performed at 25 ° C. with a current of 1.0 C and a voltage of 4.30 V for 3 hours. Next, the battery was placed in an open circuit state and stored in a 45 ° C. constant temperature bath for 15 days. Then, the direct current resistance (DCR) after 15 days was calculated | required by the method similar to initial stage DCR. Tables 1 and 2 show the DCR increase rate obtained from the initial DCR and the DCR after storage at 45 ° C. for 15 days. In addition, when the DCR increase rate in this test is 18.0% or less, it can be determined that the DC resistance increase rate after storage in a high temperature environment is low.

(ACR increase rate)
As a reference evaluation, the 1 kHz AC resistance (initial ACR) after the initial charge / discharge and the 1 kHz ACR after 15 days storage in a 45 ° C. thermostat were obtained in the same manner as the DCR increase rate test. Tables 1 and 2 show the ACR increase rate obtained from the initial ACR and the ACR after 15 days storage at 45 ° C.

  From Table 1 above, the following can be understood. Comparing Reference Example 1 and Comparative Example 1, using FEC, which is a fluorinated cyclic carbonate, as a non-aqueous solvent improves the capacity retention rate after charge / discharge cycles at high voltage, but it is stored at high temperatures. The subsequent DCR increase rate becomes high. Even in Comparative Example 2 in which a boron compound (x) having no ring structure is added to a non-aqueous solvent containing a fluorinated cyclic carbonate, the DCR increase rate is not improved. On the other hand, in Examples 1-5 in which boron compounds (A1, A2, A3) having a five-membered ring structure were added to a non-aqueous solvent containing a fluorinated cyclic carbonate, a sufficiently high capacity retention rate was maintained. It can be seen that the DCR increase rate is decreasing. In addition, as shown in Reference Example 2, when a boron compound (A3) having a five-membered ring structure is added to a non-aqueous solvent not containing a fluorinated cyclic carbonate, the effect of reducing the DCR increase rate does not appear. I understand. Further, when attention is paid to the ACR increase rate of Comparative Example 1 and Examples 1 to 5, it can be seen that the effect of improving the ACR increase rate by the addition of the boron compound having a five-membered ring structure does not necessarily occur. It can be said that there is no relation between the suppression of the DCR increase rate and the suppression of the ACR increase rate.

  In addition, the following can be seen from Table 2 above. A boron compound having a five-membered ring structure in a non-aqueous solvent containing a fluorinated cyclic carbonate and having an electronegativity equal to or greater than the oxygenegativity of an oxygen atom and having two or less atoms. In Examples 6 to 8 to which (B1, B2) was added, the DCR increase rate decreased while maintaining a sufficiently high capacity maintenance rate. On the other hand, a comparative example in which a boron compound (y) having a five-membered ring structure and binding to one boron atom and having an electronegativity equal to or greater than the electronegativity of an oxygen atom is 3 In the case of 3, it turns out that the effect of reducing a DCR increase rate does not appear. Also from Table 2, it can be said that there is no relationship between the suppression of the DCR increase rate and the suppression of the ACR increase rate.

  The present invention can be applied to electronic devices such as personal computers and communication terminals, nonaqueous electrolyte storage elements used as power sources for 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)

Containing a fluorinated cyclic carbonate and a cyclic boron compound,
The cyclic boron compound is
A boron compound having a six-membered ring structure, or a boron compound having a five-membered ring structure and binding to one boron atom, wherein the number of atoms having an electronegativity equal to or greater than the electronegativity of an oxygen atom is 2 or less. A non-aqueous electrolyte for a storage element.   The nonaqueous electrolyte according to claim 1, wherein the number of boron atoms contained in one ring structure of the cyclic boron compound is 1 or less.   The nonaqueous electrolyte according to claim 1 or 2, wherein the ring structure of the cyclic boron compound includes a boron atom and two oxygen atoms bonded to the boron atom.   A nonaqueous electrolyte storage element comprising the nonaqueous electrolyte according to claim 1, 2 or 3. The nonaqueous electrolyte storage element according to claim 4, wherein the positive electrode potential at the end-of-charge voltage during normal use is 4.4 V (vs. Li ^/ Li ⁺ ) or more.   A method for producing a nonaqueous electrolyte storage element comprising injecting the nonaqueous electrolyte according to claim 1, 2 or 3 into a container.

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