JP2018049821A - Nonaqueous electrolyte for power storage element, nonaqueous electrolyte power storage element, and method for manufacturing nonaqueous electrolyte power storage element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte for a power storage element, which enables the improvement of a nonaqueous electrolyte power storage element in charge/discharge cycles performance; a nonaqueous electrolyte power storage element including the nonaqueous electrolyte; and a method for manufacturing the nonaqueous electrolyte power storage element.SOLUTION: A nonaqueous electrolyte for a power storage element according to the present invention comprises: a nonaqueous solvent containing a propylene carbonate; and a sulfate ester compound. In the nonaqueous solvent, the content of the propylene carbonate is 2-25 vol.%. The sulfate ester compound is represented by the formula (1) below. In the formula (1), Rand Rindependently represent a hydrogen atom or a hydrocarbon group with 1-3 carbon atoms.SELECTED DRAWING: None

Description

  The present invention relates to a nonaqueous electrolyte for a storage element, a nonaqueous electrolyte storage element, and a method for manufacturing a nonaqueous electrolyte storage element.

  Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The 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 non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt that dissolves in the non-aqueous solvent, and other components are added as necessary. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). May be used together (see Patent Documents 1 and 2).

International Publication No. 2012/032700 JP 2009-164053 A

  One of the performances required for such a non-aqueous electrolyte storage element is charge / discharge cycle performance. In particular, the non-aqueous electrolyte storage element has the disadvantage that the charge / discharge cycle capacity retention rate is reduced when operated at a high voltage. This decrease in capacity retention rate is presumed to be due to the positive electrode surface being attacked by a small amount of hydrogen fluoride (HF) present in the vicinity of the positive electrode. By this erosion, the positive electrode active material component is eluted from the positive electrode surface and diffuses to the negative electrode side, and the positive electrode active material component is deposited on the negative electrode. As a result, it is estimated that the irreversible capacity and resistance of the negative electrode increase, and the charge / discharge cycle capacity retention rate decreases. This reaction is triggered by oxidative decomposition of a non-aqueous solvent, and particularly when a non-aqueous electrolyte containing EC, which is a high dielectric constant solvent, is used, the capacity retention rate is significantly reduced.

  Here, it is conceivable to use fluorinated cyclic carbonate or PC as an alternative solvent for EC. However, since fluorinated cyclic carbonate is expensive, it is difficult to use a large amount as a main solvent. On the other hand, when a large amount of PC is used, the charge / discharge cycle performance is significantly reduced. For example, when graphite is used for the negative electrode, it is presumed that PC is co-inserted between the graphite layers.

  The present invention has been made based on the circumstances as described above, and an object of the present invention is to provide a nonaqueous electrolyte for a storage element that can improve the charge / discharge cycle performance of the nonaqueous electrolyte storage element, and a nonaqueous electrolyte equipped with the same. It is to provide an electrolyte storage element and a method for manufacturing the nonaqueous electrolyte storage element.

（式（１）中、Ｒ^１及びＲ^２は、それぞれ独立して、水素原子又は炭素数１〜３の炭化水素基である。） One embodiment of the present invention made to solve the above-described problems contains a non-aqueous solvent containing propylene carbonate and a sulfate ester compound, and the content of propylene carbonate in the non-aqueous solvent is 2% by volume or more and 25% by volume. The sulfuric acid ester compound is a non-aqueous electrolyte for a storage element represented by the following formula (1).

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.)

  Another embodiment of the present invention is a nonaqueous electrolyte storage element including the above nonaqueous electrolyte for a storage element and a negative electrode containing graphite.

  Another embodiment of the present invention is a method for producing a non-aqueous electrolyte storage element using the non-aqueous electrolyte for a storage element and a negative electrode containing graphite.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte for electrical storage elements which can improve the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element, a nonaqueous electrolyte electrical storage element provided with the same, and the manufacturing method of this nonaqueous electrolyte electrical storage element are provided. can do.

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.

  A nonaqueous electrolyte for a storage element according to an embodiment of the present invention contains a nonaqueous solvent containing propylene carbonate (PC) and a sulfate ester compound, and the content of PC in the nonaqueous solvent is 2% by volume or more and 25%. The sulfuric acid ester compound is a non-aqueous electrolyte for power storage elements represented by the following formula (1) (hereinafter also simply referred to as “non-aqueous electrolyte”).

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.

  According to the non-aqueous electrolyte, first, since 2% by volume to 25% by volume of PC is contained in the non-aqueous solvent, the charge / discharge cycle performance of the non-aqueous electrolyte storage element can be improved. The reason for this is not clear, but since the oxidation potential of PC is higher than that of EC, the oxidative decomposition of the entire non-aqueous solvent is suppressed, and the PC content is reduced to 25% by volume or less. It is estimated that the influence which can have on the negative electrode can be reduced. Furthermore, the said nonaqueous electrolyte can improve the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element by containing the sulfate ester compound represented by the said Formula (1). Although the reason for this is not clear, it is presumed that the above compound has a sulfate ester structure and a sulfonate ester structure. That is, by having the above structure, a decomposition reaction occurs at an appropriate potential, and a coating film is effectively formed on the surface of the positive electrode by the decomposition product generated by this reaction, thereby suppressing erosion by the HF on the surface of the positive electrode. Etc. are guessed.

In particular, the non-aqueous electrolyte includes a non-aqueous electrolyte storage element in which a charging condition in which a positive electrode potential at a charge end voltage during normal use is relatively noble and a positive electrode active material that can have a relatively noble potential. When applied to a non-aqueous electrolyte electricity storage device having the above, it is possible to effectively exhibit the ability to suppress oxidative decomposition of a non-aqueous solvent or the like. The charging condition in which the positive electrode potential at the end-of-charge voltage in normal use is relatively noble is, for example, charging in which the positive-electrode potential at the end-of-charge voltage in normal use is more noble than 4.35 V (vs. Li / Li ⁺ ). It is a condition. Here, the normal use is a case where the nonaqueous electrolyte storage element is used by adopting the recommended charging condition or the specified charging condition for the nonaqueous electrolyte storage element. When the battery charger is prepared, the battery charger is applied to use the nonaqueous electrolyte storage element. Further, the positive electrode active material that can be a relatively noble potential is, for example, a positive electrode active material that can be a specific potential nobler than 4.35 V (vs. Li / Li ⁺ ), and is a positive electrode active material for a lithium ion secondary battery. The material is a positive electrode active material capable of reversible insertion and desorption of lithium ions reaching a specific potential nobler than 4.35 V (vs. Li / Li ⁺ ). For example, in a nonaqueous electrolyte storage element using graphite as a negative electrode active material, the positive electrode potential is about 5.1 V (vs. Li ^/ Li ⁺ ) when the end-of-charge voltage is 5.0 V, depending on the design. is there.

  The nonaqueous electrolyte preferably further contains a fluorinated cyclic carbonate. The fluorinated cyclic carbonate has high oxidation resistance, and can suppress side reactions (oxidative decomposition of a nonaqueous solvent, etc.) that may occur during charging / discharging of the nonaqueous electrolyte storage element. For this reason, the charge / discharge cycle performance of the nonaqueous electrolyte storage element, particularly the charge / discharge cycle performance of the nonaqueous electrolyte storage element operating at a high voltage can be further improved.

  The content of the fluorinated cyclic carbonate is preferably 0.05% by mass or more and 3% by mass or less of the nonaqueous electrolyte. By making content of a fluorinated cyclic carbonate into the said range, the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element can be improved more.

  The content of the sulfate ester compound is preferably 0.05% by mass or more and 3% by mass or less of the nonaqueous electrolyte. By making content of a sulfate ester compound into the said range, the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element can be improved more.

  The non-aqueous electrolyte preferably further contains a lithium oxalate compound. By using the sulfate compound and the lithium oxalate compound together as an additive, the charge / discharge cycle performance of the nonaqueous electrolyte storage element can be further improved.

  A nonaqueous electrolyte storage element according to an embodiment of the present invention is a nonaqueous electrolyte storage element including the nonaqueous electrolyte and a negative electrode including graphite.

  Since the nonaqueous electrolyte storage element uses the nonaqueous electrolyte according to an embodiment of the present invention, the charge / discharge cycle performance is improved. In particular, in the non-aqueous electrolyte, since the content of PC in the non-aqueous solvent is relatively low at 25% by volume or less, the charge / discharge cycle capacity retention rate due to insertion of PC between the graphite layers of the negative electrode is reduced. The decrease can be suppressed. “Graphite” refers to a carbon material having an average lattice spacing d002 of 002 planes determined by a wide-angle X-ray diffraction method of less than 0.340 nm.

In the nonaqueous electrolyte storage element, it is preferable that the positive electrode potential at the end-of-charge voltage during normal use is nobler than 4.35 V (vs. Li / Li ⁺ ). Since the non-aqueous electrolyte storage element uses the non-aqueous electrolyte according to one embodiment of the present invention, even when operating at a high voltage, a decrease in the cycle capacity maintenance rate is suppressed. Therefore, the non-aqueous electrolyte storage element has the effect of improving the charge / discharge cycle performance when the positive electrode potential at the end-of-charge voltage during normal use is more noble than 4.35 V (vs. Li / Li ⁺ ). Can fully demonstrate.

  The manufacturing method of the nonaqueous electrolyte electrical storage element which concerns on one Embodiment of this invention is a manufacturing method of the nonaqueous electrolyte electrical storage element using the said nonaqueous electrolyte and the negative electrode containing graphite.

  According to the manufacturing method, it is possible to manufacture a non-aqueous electrolyte storage element with improved charge / discharge cycle performance.

  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 for power storage element>
A nonaqueous electrolyte according to an embodiment of the present invention includes a nonaqueous solvent, and a sulfate ester compound and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte preferably further contains a fluorinated cyclic carbonate. The non-aqueous electrolyte preferably further contains a lithium oxalate compound. The non-aqueous electrolyte is not limited to a liquid. That is, the nonaqueous electrolyte is not limited to a liquid form, and includes a solid form or a gel form.

(Non-aqueous solvent)
The non-aqueous solvent includes PC. The lower limit of the PC content in the non-aqueous solvent is 2% by volume, preferably 5% by volume, and more preferably 8% by volume. On the other hand, the upper limit of the content is 25% by volume, preferably 20% by volume, more preferably 15% by volume, and still more preferably 12% by volume. The charge / discharge cycle performance of the nonaqueous electrolyte storage element can be enhanced by setting the PC content to the above lower limit or more and the upper limit or less.

  The non-aqueous solvent contains an organic solvent other than PC. Examples of other organic solvents include cyclic carbonates other than PC, chain carbonates, esters, ethers, amides, sulfones, lactones, and nitriles. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use chain carbonate.

  Examples of the cyclic carbonate include EC, butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenyl vinylene carbonate, and 1,2-diphenyl vinylene carbonate. Etc.

  Among the cyclic carbonates, it is particularly preferable that the content of EC, which is a high dielectric constant solvent, is small. The upper limit of the EC content in the non-aqueous solvent is preferably 20% by volume, more preferably 10% by volume, further preferably 5% by volume, still more preferably 2% by volume, and particularly preferably 1% by volume. , EC may not be substantially contained.

  The lower limit of the content of PC in the total cyclic carbonate including PC in the non-aqueous solvent is preferably 50% by volume, more preferably 80% by volume, still more preferably 95% by volume, and still more preferably 99% by volume. The upper limit of this content may be 100% by volume. Thus, by reducing the content of cyclic carbonate other than PC, the dielectric constant of the entire nonaqueous solvent becomes appropriate, and thus the charge / discharge cycle performance of the nonaqueous electrolyte storage element can be further improved. it can.

  The chain carbonate has an effect of lowering viscosity by being mixed with PC or the like. Examples of the chain carbonate include DEC, EMC, dimethyl carbonate (DMC), diphenyl carbonate and the like. Among these, EMC is preferable.

  The lower limit of the content of the chain carbonate in the non-aqueous solvent is preferably 70% by volume, more preferably 80% by volume, still more preferably 85% by volume, and still more preferably 88% by volume. On the other hand, as this upper limit, 95 volume% is preferable and 92 volume% is more preferable. By setting the content of the chain carbonate in the above range, the charge / discharge cycle performance of the nonaqueous electrolyte storage element can be further improved.

  In the above non-aqueous solvent, the lower limit of the total content of cyclic carbonate and chain carbonate containing PC is preferably 80% by volume, more preferably 95% by volume, and more preferably 99% by volume or more. The upper limit of this total content may be 100% by volume. Thus, by increasing the total content of the cyclic carbonate and the chain carbonate in the non-aqueous solvent, the dielectric constant of the entire non-aqueous solvent becomes appropriate. Further improvements can be made.

  In addition, the said non-aqueous solvent may be comprised only from 1 type of PC and the said organic solvent, and may mix and use 2 types or more of PC and the said organic solvent. The content rate of each organic solvent which comprises the said nonaqueous solvent can be 5 volume% or more with respect to the whole nonaqueous solvent, respectively. The non-aqueous solvent may be composed only of a compound not containing a fluorine atom.

(Sulfate ester compound)
The sulfate ester compound is a compound represented by the following formula (1).

In formula (1), R ¹ and R ² are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.

  As said C1-C3 hydrocarbon group, the alkyl group which is a methyl group, an ethyl group, n-propyl group, or i-propyl group, alkenyl groups, such as a vinyl group, etc. can be mentioned.

R ¹ is preferably a hydrogen atom.

R ² is preferably a hydrocarbon group having 1 to 3 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and further preferably a methyl group.

  As a minimum of content of the above-mentioned sulfate ester in the nonaqueous electrolyte, 0.05 mass% is preferred, 0.1 mass% is more preferred, 0.5 mass% is still more preferred, and 1 mass% is still more preferred. On the other hand, the upper limit of the content may be, for example, 5% by mass, but is preferably 3% by mass, and more preferably 2.5% by mass. By making content of the said sulfate ester compound more than the said minimum and below the said upper limit, the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element can be improved more.

(Lithium oxalate compound)
The lithium oxalate compound is usually a salt containing lithium ions and oxalate ions ((C ₂ O ₄ ) ²⁻ : oxalate) or anions having an oxalate group.

Examples of the lithium oxalate compound include lithium bisoxalate borate (Li [B (C ₂ O ₄ ) ₂ ]), lithium difluorooxalate borate (Li [BF ₂ (C ₂ O ₄ )]), lithium difluorobisoxa Rate phosphate (Li [PF ₂ (C ₂ O ₄ ) ₂ ]) and the like. Among these, compounds containing an anion in which at least one oxalic acid group is bonded to boron (B) as a central atom, such as lithium bisoxalate borate and lithium difluorooxalate borate are preferable, and lithium bisoxalate borate is more preferable. .

  As a minimum of content of the said lithium oxalate compound in the said nonaqueous electrolyte, 0.05 mass% is preferable, 0.1 mass% is more preferable, 0.5 mass% is further more preferable, 1 mass% is still more preferable. On the other hand, the upper limit of the content may be, for example, 5% by mass, but is preferably 3% by mass, and more preferably 2.5% by mass. By making content of the said lithium oxalate compound more than the said minimum and below the said upper limit, the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element can be improved more.

(Electrolyte salt)
As said electrolyte salt, the well-known electrolyte salt normally used as an electrolyte salt of the general nonaqueous electrolyte for electrical storage elements can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, and the like, and lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO Fluorohydrocarbon groups such as 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 ) ₃ A lithium salt having Among these, inorganic lithium salts are preferable, and LiPF ₆ is more preferable.

  In addition, when the non-aqueous electrolyte contains the lithium oxalate compound, the lithium oxalate compound can also function as an electrolyte salt. In the non-aqueous electrolyte, only the lithium oxalate compound may be contained as an electrolyte salt, but when the lithium oxalate compound is contained, an electrolyte salt different from the lithium oxalate compound is further contained. It is preferable that

The lower limit of the content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1 mol ^{dm -3,} and more preferably 0.3 mol ^{dm -3,} more preferably 0.5 mol ^{dm -3,} 0. mol dm ⁻³ M is particularly preferred. On the other hand, the upper limit is not particularly limited, but is preferably 2.5 mol ^{dm -3,} and more preferably 2 mol ^{dm -3,} more preferably 1.5 mol ^{dm -3.}

As a minimum of content of electrolyte salts other than the above-mentioned lithium oxalate compound in the nonaqueous electrolyte, 0.1 mol dm ^-3 is preferred, 0.3 mol dm ^-3 is more preferred, and 0.5 mol dm ^-3 is still more preferred. 0.7 mol dm ^-3 is particularly preferred. On the other hand, the upper limit is not particularly limited, but is preferably 2.5 mol ^{dm -3,} and more preferably 2 mol ^{dm -3,} more preferably 1.5 mol ^{dm -3.}

(Additive)
The nonaqueous electrolyte contains additives other than the nonaqueous solvent, the sulfate ester compound represented by the formula (1), the lithium oxalate compound, and the electrolyte salt as long as the effects of the present invention are not impaired. May be. Examples of the additive include a fluorinated cyclic carbonate and other additives. Here, the content of each additive is usually less than 5% by volume with respect to the whole non-aqueous solvent.

(Fluorinated cyclic carbonate)
The fluorinated cyclic carbonate refers to a compound in which part or all of the hydrogen atoms of a cyclic carbonate such as EC, PC, BC are substituted with fluorine atoms. This fluorinated cyclic carbonate does not correspond to the non-aqueous solvent.

  Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonate such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonate, and fluorinated butylene carbonate. Fluorinated ethylene carbonate is preferred, and FEC Is more preferable. The said fluorinated cyclic carbonate can be used individually by 1 type or in mixture of 2 or more types.

  The content of the fluorinated cyclic carbonate is not particularly limited, but the lower limit of the content with respect to the nonaqueous electrolyte is preferably 0.05% by mass, more preferably 0.1% by mass, and 0.3% by mass. More preferably, 0.5 mass% is still more preferable. By making content of a fluorinated cyclic carbonate more than the said minimum, the charge / discharge cycle performance of a nonaqueous electrolyte electrical storage element can be improved more. On the other hand, the upper limit of the content is usually less than 5% by mass, preferably 3% by mass, more preferably 2% by mass, and still more preferably 1.5% by mass. 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 additives)
Examples of additives other than the fluorinated cyclic carbonate include various additives contained in a general non-aqueous electrolyte for power storage elements. The total content of additives other than the fluorinated cyclic carbonate in the non-aqueous electrolyte is preferably 5% by mass or less, and more preferably 1% by mass or less.

  The non-aqueous electrolyte can be usually obtained by adding and dissolving each component such as a sulfate ester compound, a lithium oxalate compound, and an electrolyte salt in the non-aqueous solvent.

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

The nonaqueous electrolyte secondary battery (storage element) can be used at a high operating voltage. For example, it the positive electrode potential in the normal charge voltage at the time of use is preferably nobler than 4.35V (vs.Li/Li ^+), which is nobler than 4.4V (vs.Li/Li ⁺⁾ More preferred. 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 ^+).

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

  The positive electrode base material has conductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and 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 active material layer by including electroconductive particles, such as a carbon particle. The structure of an intermediate | middle layer is not specifically limited, For example, it can form with the composition containing a resin binder and electroconductive particle. “Conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “nonconductive” Means that the volume resistivity is more than 10 ⁷ Ω · cm.

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

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

The positive electrode active material has a positive electrode potential of 4.35 V (vs. Li ^/ Li ⁺ ), more preferably 4.4 V (vs. Li ^/ Li ⁺ ) at the end-of-charge voltage during normal use of the nonaqueous electrolyte secondary battery. It is preferable to include a positive electrode active material that can be more noble. The non-aqueous electrolyte contained in the non-aqueous electrolyte secondary battery (storage element) has high oxidation and decomposition resistance. Therefore, even when such a positive electrode active material that can be a noble potential is included, the decomposition of the nonaqueous electrolyte is satisfactorily suppressed. Therefore, by using a positive electrode active material that can be a specific potential nobler than 4.35 V (vs. Li / Li ⁺ ), it has high energy density, excellent high rate discharge performance, and charge / discharge cycle performance. It can be set as the improved nonaqueous electrolyte electrical storage element.

As a positive electrode active material capable of reversible insertion and desorption of lithium ions reaching a noble potential from 4.35 V (vs. Li / Li ⁺ ), for example, Li _x Ni _α Mn ₍₂ can be cited an example and _LiNi 0.5 _Mn 1.5 _{O 4} which is a _{-α) O 4, LiNiPO 4,} LiCoPO 4 is an example of a polyanionic _{compound, Li} 2 CoPO ₄ F, the Li 2 MnSiO _4, and the like.

  The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect battery performance. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, 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 active material layer disposed on the negative electrode base material directly or via an intermediate layer. The intermediate layer can have the same configuration as the positive electrode intermediate layer.

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

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

  The negative electrode active material includes graphite. Note that graphite and other negative electrode active materials may be used in combination. Other negative electrode active materials include, for example, metals and semimetals such as Si and Sn; metal oxides and semimetal oxides such as Si oxide and Sn oxide; polyphosphate compounds; non-graphitic carbon (easily graphitizable) Carbon or non-graphitizable carbon).

  The lower limit of the graphite content in the negative electrode active material is preferably 50% by mass, more preferably 80% by mass, still more preferably 95% by mass, and even more preferably 99% by mass. On the other hand, the upper limit of this content may be 100 mass%.

  As a minimum of content of a negative electrode active material in the above-mentioned negative electrode active material layer, 50 mass% is preferred, 80 mass% is more preferred, and 90 mass% is still more preferred. By setting the content of the negative electrode active material to the above lower limit or more, the discharge capacity can be increased. On the other hand, as an upper limit of this content, 99 mass% is preferable, for example, and 97 mass% is more preferable.

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

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

  An inorganic 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.

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
The manufacturing method of the nonaqueous electrolyte electrical storage element which concerns on one Embodiment of this invention is a manufacturing method of the nonaqueous electrolyte electrical storage element using the said nonaqueous electrolyte and the negative electrode containing graphite. In the manufacturing method, for example, a step of producing a positive electrode, a step of producing a negative electrode containing graphite, a step of preparing a nonaqueous electrolyte, and laminating or winding the positive electrode and the negative electrode through a separator are alternately superimposed. A step of forming an electrode body, a step of accommodating a positive electrode and a negative electrode (electrode body) in a battery container, and a step of injecting the nonaqueous electrolyte into the battery container. After the injection, the nonaqueous electrolyte storage element can be obtained by sealing the injection port.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode. For example, the intermediate layer may not be provided in the positive electrode or the negative electrode. In addition, the nonaqueous solvent for a power storage element can also be applied to a nonaqueous electrolyte power storage element having a negative electrode that does not contain graphite.

  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 housed in a battery container 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material containing graphite 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 ′. Moreover, the nonaqueous electrolyte which concerns on one Embodiment of this invention is inject | poured into the battery container 3. FIG.

  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.

Each additive used in Examples and Comparative Examples is shown below.
Compound A: sulfate compound represented by the following formula (A)

化合物ａ：下記式（ａ）で表されるプロペンスルトン

Compound a: propene sultone represented by the following formula (a)

化合物ｂ：下記式（ｂ）で表される硫酸エステル化合物

Compound b: sulfate compound represented by the following formula (b)

[Example 1]
(Preparation of non-aqueous electrolyte)
LiPF ₆ as an electrolyte salt was dissolved at a concentration of 1.2 mol dm ⁻³ in a non-aqueous solvent in which PC: EMC was mixed at a volume ratio of 15:85, and 2% by mass of the above compounds A and 1 as additives were added thereto. The non-aqueous electrolyte of Example 1 was obtained by adding mass% FEC.

(Preparation of positive electrode plate)
Li _1.18 Ni _0.10 Co _0.17 Mn _0.55 O ₂ was used as the positive electrode active material. In a mass ratio, the positive electrode active material: polyvinylidene fluoride (PVdF): acetylene black (AB) = 94: 1.5: 4.5 (in terms of solids), and containing N-methylpyrrolidone as a dispersion medium A positive electrode paste 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 13.5 mg / cm ² per unit electrode area. This was pressed with a roller press to form a positive electrode active material layer, and then dried under reduced pressure at 100 ° C. for 10 hours to remove the liquid in the electrode plate. In this way, a positive electrode plate was obtained.

(Preparation of negative electrode plate)
Graphite was used as the negative electrode active material. A negative electrode paste containing water as a dispersion medium was prepared in a mass ratio of graphite: styrene butadiene rubber (SBR): carboxymethyl cellulose (CMC) = 97: 2: 1 (in terms of solid content). This negative electrode paste was applied to both surfaces of a strip-shaped copper foil current collector as a negative electrode substrate so that the negative electrode active material was contained at 11.5 mg / cm ² per unit electrode area. This was pressed with a roller press to form a negative electrode active material 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 plate was obtained.

(Preparation of nonaqueous electrolyte storage element)
As the separator, a polyolefin microporous film having an inorganic layer formed on the surface thereof was used. The electrode body was produced by laminating the positive electrode plate and the negative electrode plate with the separator interposed therebetween. The electrode body is housed in a case made of a metal resin composite film, and the nonaqueous electrolyte is injected into the case, and then sealed by thermal welding. The laminated cell type nonaqueous electrolyte storage element (secondary battery) of Example 1 Got.

[Examples 2 to 5, Comparative Examples 1 to 10]
The nonaqueous electrolytes of Examples 2 to 5 and Comparative Examples 1 to 10 were the same as Example 1 except that the types and amounts of the solvents and additives used were as shown in Tables 1 and 2. A nonaqueous electrolyte storage element was obtained. In the table, “-” indicates that the corresponding additive is not used. Further, Example 1 and Comparative Example 1 are described in both Table 1 and Table 2 for comparison.

[Evaluation]
(Initialization)
About each obtained nonaqueous electrolyte electrical storage element, initialization was performed on condition of the following. The battery was charged at a constant current of 0.1 C to 4.50 V at 25 ° C. and then charged at a constant voltage of 4.50 V. The charge termination conditions were until the charge current reached 0.02C. After a 10-minute pause after charging, the battery was discharged at a constant current of 0.1 C up to 2.00 V at 25 ° C.

(Initial capacity confirmation test)
After the initialization, an initial capacity confirmation test was performed under the following conditions. The battery was charged at a constant current of 0.1 C to 4.35 V at 25 ° C. and then charged at a constant voltage of 4.35 V. The charge termination conditions were until the charge current reached 0.02C. After a 10-minute rest after charging, the battery was discharged at a constant current of 1.0 C up to 2.00 V at 25 ° C. Thereby, the initial discharge capacity (initial capacity) was measured.

(Charge / discharge cycle test)
Next, the following cycle test was performed. At 45 ° C., the battery was charged at a constant current and a constant voltage with a charge current of 1.0 C and a charge end voltage of 4.35 V. The charge termination conditions were until the charge current reached 0.02C. A 10 minute rest period was then provided. Thereafter, a constant current discharge was performed with a discharge current of 1.0 C and a discharge end voltage of 2.00 V, and then a 10-minute rest period was provided. This charging / discharging was performed 100 cycles. The positive electrode potential at the end-of-charge voltage in the charge / discharge cycle test using graphite as the negative electrode is about 4.45 V (vs. Li / Li ⁺ ).

  Thereafter, a discharge capacity confirmation test at 25 ° C. was performed in the same manner as the initial capacity confirmation test. Tables 1 and 2 show the discharge capacity after the cycle test with respect to the initial discharge capacity as a percentage.

  As shown in Table 1 above, in Examples 1 and 2 to which Compound A, which is a sulfate ester compound represented by the above formula (1), was added, Comparative Examples 1 and 2 to which other ester compounds were added and It can be seen that the capacity retention rate is high, that is, the charge / discharge cycle performance is improved as compared with Comparative Example 3 in which no ester compound is added. In addition, although the compound a of the comparative example 1 has a sulfonate structure, it does not have a sulfate structure. Compound b of Comparative Example 2 has two cyclic sulfate structures, but does not have a sulfonate structure. On the other hand, Compound A used in Examples has both a cyclic sulfate structure and a sulfonate structure. Therefore, it is presumed that the effect that the nonaqueous electrolyte electricity storage device of this example has a high capacity retention rate is a unique effect caused by using a compound having the above structure.

  Moreover, as Table 2 shows, it turns out that a high capacity | capacitance maintenance factor is shown by making content of PC into the predetermined range. On the other hand, from the results of Comparative Examples 5 to 10, when other ester compounds are added, even if the solvent ratio is changed or the amount of FEC added is increased, the charge / discharge cycle performance is not improved as much as each Example. I understand.

[Examples 6 to 7, Comparative Example 11]
Examples and amounts of solvents and additives used are as shown in Table 3, and the examples are the same as in Example 1 except that the electrode body is housed in a small rectangular case and the rated capacity is different. The nonaqueous electrolytes of 6 to 7 and Comparative Example 11 and the small rectangular nonaqueous electrolyte storage element were obtained. In Table 3, LiBOB represents lithium bisoxalate borate. Further, “-” indicates that the corresponding additive is not used.

[Evaluation]
(Initialization)
About each obtained nonaqueous electrolyte electrical storage element, initialization was performed on condition of the following. The battery was charged at a constant current of 0.1 C to 4.475 V at 25 ° C., and then charged at a constant voltage of 4.475 V. The charge termination condition was set until the charge current reached 0.05C. After a 10-minute pause after charging, the battery was discharged at a constant current of 0.1 C up to 2.00 V at 25 ° C.

(Initial capacity confirmation test)
After the initialization, an initial capacity confirmation test was performed under the following conditions. The battery was charged at a constant current of 0.1 C to 4.35 V at 25 ° C. and then charged at a constant voltage of 4.35 V. The charge termination condition was set until the charge 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 2.00 V at 25 ° C. A 10-minute pause was provided after the discharge. Next, the battery was charged at a constant current of 0.1 C to 4.35 V again at 25 ° C., and then charged at a constant voltage of 4.35 V. The charge termination condition was set until the charge current reached 0.05C. After a 10-minute rest after charging, the battery was discharged at a constant current of 1.0 C up to 2.00 V at 25 ° C. Thereby, the initial discharge capacity (initial capacity) was measured.

(Charge / discharge cycle test)
Next, the following cycle test was performed. At 45 ° C., the battery was charged at a constant current and a constant voltage with a charge current of 1.0 C and a charge end voltage of 4.35 V. The charge termination condition was set until the charge current reached 0.1C. A 10 minute rest period was then provided. Thereafter, a constant current discharge was performed with a discharge current of 0.1 C and a discharge end voltage of 2.00 V, and then a 10-minute rest period was provided. This charging / discharging was performed 300 cycles. The positive electrode potential at the end-of-charge voltage in the charge / discharge cycle test using graphite as the negative electrode is about 4.45 V (vs. Li / Li ⁺ ).

  Thereafter, a discharge capacity confirmation test at 25 ° C. was performed in the same manner as the initial capacity confirmation test. Table 3 shows the discharge capacity after the cycle test with respect to the initial discharge capacity as a percentage.

  As shown in Table 3, Example 6 in which Compound A, which is a sulfate ester compound represented by Formula (1), was added to Example 6 in which Compound A and LiBOB, which is a lithium oxalate compound, were added. Example 7 shows that the capacity retention is improved even though the total amount of additives is the same. On the other hand, the capacity retention rate of Comparative Example 11 in which only the same amount of LiBOB was added is not so high, and the effect of Example 7 can be said to be an effect produced when two additives are combined.

  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 nonaqueous electrolytes for storage elements provided therein.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte electrical storage element 2 Electrode body 3 Battery 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 non-aqueous solvent containing propylene carbonate and a sulfate ester compound,
The propylene carbonate content in the non-aqueous solvent is 2% by volume or more and 25% by volume or less,
The nonaqueous electrolyte for electrical storage elements in which the said sulfate ester compound is represented by following formula (1).

(In Formula (1), R ¹ and R ² are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.)   The nonaqueous electrolyte for an electricity storage device according to claim 1, further comprising a fluorinated cyclic carbonate.   The nonaqueous electrolyte for an electricity storage device according to claim 1, further comprising a lithium oxalate compound. A non-aqueous electrolyte for a storage element according to claim 1, claim 2 or claim 3,
A non-aqueous electrolyte electricity storage device comprising: a negative electrode containing graphite. The nonaqueous electrolyte storage element according to claim 4, wherein the positive electrode potential at the end-of-charge voltage during normal use is nobler than 4.35 V (vs. Li / Li ⁺ ).   The manufacturing method of the nonaqueous electrolyte electrical storage element using the nonaqueous electrolyte for electrical storage elements of Claim 1, Claim 2, or Claim 3 and the negative electrode containing graphite.

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