JP2017208215A - Nonaqueous electrolyte for power storage device, nonaqueous electrolyte power storage device, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nonaqueous electrolyte for a power storage device, in which lithium tetrafluoroborate is dissolved as an electrolyte salt, and which enables the enhancement in high-rate discharge performance of a nonaqueous electrolyte power storage device; a nonaqueous electrolyte power storage device including the nonaqueous electrolyte; and a method for manufacturing the nonaqueous electrolyte power storage device.SOLUTION: A nonaqueous electrolyte for a power storage device according to the present invention comprises: a nonaqueous solvent; and lithium tetrafluoroborate dissolving in the nonaqueous solvent. The nonaqueous solvent includes a first nonaqueous solvent of which the number of donors is 15 or more, and fluorinated phosphoric ester; and a content of the first nonaqueous solvent to a content of the lithium tetrafluoroborate is 4 or less by molar ratio.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 the same.

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

In such a non-aqueous electrolyte electricity storage element, it is known that side reactions such as oxidative decomposition of an electrolytic solution occur due to repeated charge and discharge, and charge / discharge performance gradually decreases. On the other hand, it has been reported that the oxidative decomposition of the electrolytic solution is suppressed by increasing the salt concentration in the electrolytic solution (see Non-Patent Documents 1 and 2). In Non-Patent Document 2, a high concentration electrolytic solution using LiBF ₄ (lithium tetrafluoroborate) is applied as compared with a high concentration electrolytic solution using LiPF ₆ (lithium hexafluorophosphate). It is also described that the initial coulombic efficiency of the non-aqueous electrolyte secondary battery is excellent, and overvoltage (the difference between the voltage when the charge state is 50% and the voltage when the discharge depth is 50%) is suppressed.

Satoshi Masuhara and 7 others, “Design of Oxidation-resistant Electrolyte for 5V-Class Positive Electrode”, Proceedings of the 55th Battery Conference, Electrochemical Society, November 19, 2014, p386 Yusuke Shimizu and 7 others, “Design of oxidation-resistant electrolyte for 5V spinel positive electrode”, Proceedings of the 56th Battery Conference, Electrochemical Society of Japan, November 10, 2015, p368

As described above, the high-concentration electrolytic solution using LiBF ₄ has an effect of improving initial coulomb efficiency and an effect of suppressing overvoltage when applied to a non-aqueous electrolyte electricity storage device as compared with the case of using LiPF _6. It has been confirmed that there is. On the other hand, non-aqueous electrolyte storage elements are required to have not only these performances but also high rate discharge performance. However, a nonaqueous electrolyte storage element to which a high concentration electrolytic solution using LiBF ₄ is applied is not sufficient for this high rate discharge performance, and there is room for improvement.

The present invention has been made based on the circumstances as described above, and its purpose is to improve the high rate discharge performance of a nonaqueous electrolyte storage element in a nonaqueous electrolyte in which LiBF ₄ is dissolved as an electrolyte salt. A nonaqueous electrolyte for a storage element, a nonaqueous electrolyte storage element including the nonaqueous electrolyte, and a method for manufacturing the nonaqueous electrolyte storage element are provided.

  A nonaqueous electrolyte for an electricity storage device according to one embodiment of the present invention made to solve the above problems is a nonaqueous electrolyte for an electricity storage device containing a nonaqueous solvent and lithium tetrafluoroborate dissolved in the nonaqueous solvent. A water electrolyte, wherein the non-aqueous solvent includes a first non-aqueous solvent having a donor number of 15 or more, and a fluorinated phosphate ester, and the first non-aqueous solvent with respect to the lithium tetrafluoroborate content. Content is 4 or less by molar ratio, It is characterized by the above-mentioned.

  A nonaqueous electrolyte storage element according to another embodiment of the present invention is a nonaqueous electrolyte storage element including the above nonaqueous electrolyte for a storage element.

  A method for producing a non-aqueous electrolyte electricity storage device according to another aspect of the present invention is a method for producing a non-aqueous electrolyte electricity storage device having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is used for the electricity storage device. A non-aqueous electrolyte is used.

According to the present invention, in a non-aqueous electrolyte in which LiBF ₄ is dissolved as an electrolyte salt, a non-aqueous electrolyte for a power storage element capable of enhancing the high rate discharge performance of the non-aqueous electrolyte power storage element, and a non-aqueous electrolyte power storage element including the same And the manufacturing method of this nonaqueous electrolyte electrical storage element can be provided.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte secondary battery 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 secondary batteries according to an embodiment of the present invention.

  Hereinafter, a nonaqueous electrolyte for a storage element, 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 for a storage element according to an embodiment of the present invention (hereinafter sometimes simply referred to as “nonaqueous electrolyte”) contains a nonaqueous solvent and LiBF ₄ dissolved in the nonaqueous solvent. The nonaqueous electrolyte for a storage element, wherein the nonaqueous solvent includes a first nonaqueous solvent having a donor number of 15 or more, and a fluorinated phosphate ester, and the first nonaqueous solvent with respect to the content of LiBF ₄ Is 4 or less in molar ratio. 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.

  The number of donors is a parameter that represents the electron-donating ability of a solvent, and is defined by the negative value of the enthalpy of formation of a 1: 1 addition compound between antimony pentachloride in 1,2-dichloroethane and the solvent of interest. Is done. In this specification, the number of donors is determined by the method described in Victor Gutmann, “The Donor-Acceptor Approach to Molecular Interactions”, Springer, 1978 (ISBN-13: 978-0306310645).

The non-aqueous electrolyte can enhance the high-rate discharge performance of the nonaqueous electrolyte electricity storage device in the case of using LiBF ₄ as an electrolyte salt. The reason for this is not clear, but the following can be inferred. In the non-aqueous electrolyte, the first non-aqueous solvent having a large donor number is used, and the content of the first non-aqueous solvent with respect to the content of the electrolyte salt LiBF ₄ is 4 or less in terms of molar ratio. In contrast, it contains a high concentration of LiBF ₄ . This suppresses oxidative decomposition of a non-aqueous solvent or the like, improves the initial coulomb efficiency of the non-aqueous electrolyte storage element, and suppresses overvoltage. These effects are presumed to be caused by the fact that most of the first nonaqueous solvent is solvated with lithium ions. However, in this case, since the movement of lithium ions is suppressed due to an increase in the interaction between LiBF ₄ and the first nonaqueous solvent, and the conductivity of the lithium ions is reduced, the high rate discharge performance of the nonaqueous electrolyte storage element Decreases. On the other hand, the solvation of the first nonaqueous solvent to LiBF ₄ is inhibited by further containing a fluorinated phosphate ester having a low solvation ability with respect to lithium ions as the second nonaqueous solvent in the nonaqueous electrolyte. Without dissociation, it is presumed that the dissociation of LiBF ₄ is promoted, the conductivity of lithium ions is increased, and the high-rate discharge performance of the nonaqueous electrolyte storage element is improved. That is, it is speculated that the high rate discharge performance of the nonaqueous electrolyte electricity storage device can be enhanced by the combination of LiBF ₄ , the first solvent, and the fluorinated phosphate ester. Non-Patent Document 2 describes that a high-concentration electrolytic solution using LiBF ₄ suppresses overvoltage of a non-aqueous electrolyte secondary battery even though the viscosity is high. Therefore, it is presumed that by containing a fluorinated phosphate ester having a high viscosity but a low solvating ability, the overvoltage of the nonaqueous electrolyte storage element is suppressed even when the viscosity of the nonaqueous electrolyte remains high.

In addition, since the non-aqueous electrolyte contains LiBF ₄ at a high concentration relative to the first non-aqueous solvent as described above, the non-aqueous electrolyte is subjected to oxidative decomposition such as non-aqueous solvent due to repeated charge / discharge of the non-aqueous electrolyte storage element. Occurrence can be suppressed. For this reason, in particular, the non-aqueous electrolyte is a non-aqueous electrolyte storage element that adopts a charging condition in which the positive electrode potential at the end-of-charge voltage during normal use is relatively noble, or a positive electrode active material that can have a relatively noble potential. When applied to a non-aqueous electrolyte electricity storage device having a positive electrode containing, the ability to suppress oxidative decomposition of a non-aqueous solvent or the like can be effectively exhibited. 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 4.4 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 a positive electrode active material that can be a specific potential nobler than 4.4 V (vs. Li ^/ Li ⁺ ), for example, 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 4.4 V (vs. Li ^/ Li ⁺ ).

For example, in a non-aqueous electrolyte secondary battery 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 battery design. ).

(Electrolyte salt)
The non-aqueous electrolyte contains LiBF ₄ as an electrolyte salt dissolved in a non-aqueous solvent. When LiBF ₄ is used at a high concentration as the electrolyte salt, the oxidation resistance of the non-aqueous electrolyte and the initial coulomb efficiency of the non-aqueous electrolyte storage element to which the non-aqueous electrolyte is applied are increased, and overvoltage is also suppressed.

The nonaqueous electrolyte may contain other electrolyte salt other than LiBF _{4 as long} as the effect of the present invention is not affected. Other electrolyte salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F 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 , a fluorinated hydrocarbon group such as 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 Examples thereof include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, and the like.

The lower limit of the content of LiBF ₄ to the total electrolyte salts, for example, preferably 80 wt%, more preferably 95 wt%, more preferably 99% by mass. By setting the content of LiBF ₄ to be equal to or higher than the above lower limit, a favorable solvation state of lithium ions can be achieved more suitably.

The lower limit of the molar concentration of LiBF ₄ in the non-aqueous electrolyte (the number of moles of LiBF ₄ with respect to the mass of the non-aqueous solvent) is preferably 1 mol / kg, more preferably 1.5 mol / kg, and even more preferably 2 mol / kg. . On the other hand, the upper limit is, for example, 5 mol / kg. By making the salt concentration high in this way, it is possible to demonstrate good oxidative decomposition resistance of the nonaqueous electrolyte, and it is possible to further improve the initial coulomb efficiency and overvoltage suppression capability of the nonaqueous electrolyte storage element to which this is applied. it can.

(Non-aqueous solvent)
The non-aqueous solvent includes a first non-aqueous solvent having a donor number of 15 or more and a fluorinated phosphate ester. The non-aqueous solvent preferably further contains a fluorinated cyclic carbonate. Moreover, the said nonaqueous solvent may contain the other nonaqueous solvent in the range which does not inhibit the effect of this invention.

(First non-aqueous solvent)
The first nonaqueous solvent is a nonaqueous solvent having a donor number of 15 or more.

  Examples of the first non-aqueous solvent include propylene carbonate (donor number: 15.1), ethylene carbonate (16.4), diethyl carbonate (16.4), dimethyl carbonate (15.2), γ-butyrolactone (18 ), Ethyl acetate (17.1), tetrahydrofuran (20), 1,2-dimethoxyethane (20), diglyme (19.2), tetraglyme (16.6), and the like. The said 1st non-aqueous solvent can be used individually by 1 type or in mixture of 2 or more types.

  As the first nonaqueous solvent, it is preferable to select and use a nonaqueous solvent having a donor number that is not too large. By selecting and using a non-aqueous solvent having a donor number that is not too large, it is possible to reduce the fact that the first non-aqueous solvent has too strong a coordination force to solvate to lithium ions. That is, it is possible to reduce the energy required for the desolvation of lithium ions on the active material surface from becoming too large, and the electrode reaction can proceed more efficiently. From such a viewpoint, the upper limit of the number of donors in the first nonaqueous solvent is preferably 17, more preferably 16.5, still more preferably 16, and particularly preferably 15.5. As a specific first non-aqueous solvent, propylene carbonate (PC) is preferable. That is, the first non-aqueous solvent preferably contains PC. The content of PC in the first non-aqueous solvent is preferably 80% by mass, more preferably 90% by mass, and the first non-aqueous solvent may consist essentially of PC.

The upper limit of the content of the first nonaqueous solvent relative to LiBF ₄ (first nonaqueous solvent / LiBF ₄ ) is 4 in molar ratio, and 2.5 is preferable. Thus, by reducing the content of the first non-aqueous solvent relative to LiBF ₄ , the first non-aqueous solvent that is not solvated is reduced, and the oxidative decomposition resistance of the non-aqueous electrolyte can be improved.

On the other hand, the lower limit of the content of the first non-aqueous solvent for LiBF ₄ (first non-aqueous solvent / LiBF ₄₎ is preferably 0.5 molar ratio, more preferably 1, more preferably 1.5, 2 Is particularly preferred. By setting this ratio to be equal to or higher than the above lower limit, the state of solvation of the first nonaqueous solvent with respect to LiBF ₄ can be more suitably achieved, and the discharge capacity and high rate discharge performance of the nonaqueous electrolyte storage element can be further increased. .

  The lower limit of the content of the first nonaqueous solvent in the total nonaqueous solvent is preferably 30% by volume, more preferably 40% by volume, still more preferably 50% by volume, and particularly preferably 60% by volume. On the other hand, as this upper limit, 80 volume% is preferable and 70 volume% is more preferable. By setting the content of the first nonaqueous solvent in the total nonaqueous solvent in the above range, the high rate discharge performance of the nonaqueous electrolyte electricity storage element can be further enhanced.

(Fluorinated phosphate ester)
The non-aqueous solvent contains a fluorinated phosphate ester as the second non-aqueous solvent. Since the fluorinated phosphate ester is fluorinated and has low solvability with respect to lithium ions, the state in which the movement of lithium ions is suppressed can be relaxed. The non-aqueous solvent may contain a fluorinated phosphate ester having a donor number of 15 or more. In that case, the fluorinated phosphate ester is contained in the fluorinated phosphate ester, and the first non-aqueous solvent is used. It is not included in the solvent. The number of donors in the fluorinated phosphate is preferably smaller than the number of donors in the first non-aqueous solvent, and more preferably less than 15.

The fluorinated phosphate ester refers to a compound in which part or all of hydrogen contained in phosphoric acid (O = P (OH) ₃ ) is substituted with an organic group having a fluorine atom. The organic group having a fluorine atom is usually a fluorinated hydrocarbon group, preferably a fluorinated alkyl group. That is, as the fluorinated phosphate ester, a fluoroalkyl phosphate ester (fluoroalkyl phosphate) is preferable, and a trisfluoroalkyl phosphate ester (trisfluoroalkyl phosphate) is more preferable.

  Examples of the fluorinated phosphate ester include tris phosphate (2,2-difluoroethyl), tris phosphate (2,2,3,3-tetrafluoropropyl), and tris phosphate (2,2,3,3). , 4,4-hexafluorobutyl), tris phosphate (1H, 1H, 5H-octafluoropentyl), tris phosphate (1H, 1H, 7H-dodecafluoroheptyl), tris phosphate (1H, 1H, 3H) , 7H-perfluoroheptyl), tris phosphate (1H, 1H, 9H-hexadecafluorononyl), tris phosphate (2,2,2-trifluoroethyl), tris phosphate (2,2,3,3) 3,3-pentafluoropropyl), tris phosphate (1H, 1H-perfluorobutyl), tris phosphate (1H, 1H-perfluoropentyl), tris phosphate (1H, H-perfluoroheptyl), tris phosphate (1H, 1H-perfluorononyl), tris (1,1-difluoroethyl) phosphate tris (1,1,2,2-tetrafluoropropyl), etc. Can be mentioned. As the fluorinated phosphate ester, tris (2,2,2-trifluoroethyl) phosphate (TFEP) is preferable. The said fluorinated phosphate ester can be used individually by 1 type or in mixture of 2 or more types.

  The lower limit of the value of the first nonaqueous solvent in the volume ratio of the first nonaqueous solvent to the fluorinated phosphate ester (first nonaqueous solvent: fluorinated phosphate ester) is, for example, 30:70, However, 50:50 is preferable, and 60:40 is more preferable. On the other hand, the upper limit may be 99: 1, for example, but is preferably 90:10, more preferably 80:20, and even more preferably 70:30. By setting the volume ratio of the first non-aqueous solvent and the fluorinated phosphate ester to the above lower limit and / or the upper limit, the high rate discharge performance of the non-aqueous electrolyte storage element can be further enhanced. Moreover, the discharge capacity of the nonaqueous electrolyte storage element can be increased by setting the volume ratio to be equal to or higher than the lower limit. This is because, by setting the volume ratio of the first non-aqueous solvent to the fluorinated phosphate ester within the above range, the solvation state of the non-aqueous electrolyte is more suitably achieved, and the viscosity and the conductivity of lithium ions are improved. Is presumed to be optimized.

  The lower limit of the content of the fluorinated phosphate in the total non-aqueous solvent is preferably 10% by volume, more preferably 20% by volume, and still more preferably 30% by volume. On the other hand, the upper limit is preferably 70% by volume, more preferably 50% by volume, still more preferably 40% by volume, and particularly preferably 35% by volume. By setting the content of the fluorinated phosphate in the entire nonaqueous solvent within the above range, the high rate discharge performance of the nonaqueous electrolyte electricity storage element can be further enhanced.

(Fluorinated cyclic carbonate)
The non-aqueous solvent preferably contains a fluorinated cyclic carbonate as a third non-aqueous solvent. When the non-aqueous solvent contains a fluorinated cyclic carbonate, side reactions (such as oxidative decomposition of a non-aqueous solvent) that may occur during charging / discharging of the non-aqueous electrolyte storage element can be suppressed. The non-aqueous solvent may contain a fluorinated cyclic carbonate having a donor number of 15 or more. In that case, the fluorinated cyclic carbonate is contained in the fluorinated cyclic carbonate, and the first non-aqueous solvent includes Not included. The number of donors in the fluorinated cyclic carbonate is preferably smaller than the number of donors in the first non-aqueous solvent, and more preferably less than 15.

  Examples of the fluorinated cyclic carbonate include fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, and the like, and fluoroethylene carbonate (FEC) is preferable. The said fluorinated cyclic carbonate can be used individually by 1 type or in mixture of 2 or more types.

  Although it does not restrict | limit especially as content of the said fluorinated cyclic carbonate, As a minimum with respect to the total mass of the said 1st non-aqueous solvent and the said fluorinated phosphate ester, 1 mass% is preferable and 3 mass% is more preferable. On the other hand, as this upper limit, 20 mass% is preferable and 10 mass% is more preferable. Moreover, as a minimum of content of the said 1st nonaqueous solvent which occupies for all the nonaqueous solvents, 1 volume% is preferable and 3 volume% is more preferable. On the other hand, as this upper limit, 20 volume% is preferable and 10 volume% is more preferable. By setting the content of the fluorinated cyclic carbonate to the above lower limit or more, side reactions that can occur during charging and discharging of the nonaqueous electrolyte storage element can be more effectively suppressed. On the other hand, by setting the content of the fluorinated cyclic carbonate below the upper limit, the viscosity of the non-aqueous electrolyte, the conductivity of lithium ions, and the like can be optimized.

(Other solvents, etc.)
The non-aqueous solvent may contain other non-aqueous solvents other than the first non-aqueous solvent, the fluorinated phosphate ester, and the fluorinated cyclic carbonate. However, the content of the other nonaqueous solvent in the total nonaqueous solvent is preferably 10% by volume or less, and sometimes 1% by volume or less. When the content of the other non-aqueous solvent is large, the solvation state of the non-aqueous electrolyte, lithium ion conductivity, viscosity, and the like may be affected.

  Moreover, the said nonaqueous electrolyte may contain other components other than electrolyte salt and a nonaqueous solvent, unless the effect of this invention is inhibited. As said other component, the various additives contained in the general nonaqueous electrolyte for electrical storage elements can be mentioned. However, the content of the other components in the nonaqueous electrolyte is preferably 5% by mass or less, and more preferably 1% by mass or less.

The non-aqueous electrolyte can be obtained by adding LiBF ₄ or the like to the non-aqueous solvent and dissolving it.

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

According to the non-aqueous electrolyte secondary battery, although it has a non-aqueous electrolyte using LiBF ₄ as an electrolyte salt, the high-rate discharge performance of the non-aqueous electrolyte secondary battery to which this is applied is improved. Can do. In addition, the nonaqueous electrolyte secondary battery is excellent in the oxidative decomposition resistance of the nonaqueous electrolyte. Therefore, the nonaqueous electrolyte secondary battery (storage element) can be used at a high operating voltage. For example, the positive electrode potential in the fully charged nonaqueous electrolyte secondary battery can be made nobler than 4.4 V (vs. Li ^/ Li ⁺ ). On the other hand, the upper limit of the positive electrode potential in the fully charged nonaqueous electrolyte secondary battery is, for example, 5.1 V (vs. Li ^/ Li ⁺ ), and 5.0 V (vs. Li ^/ Li ⁺ ). Also good.

(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).

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

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

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.

It is preferable that the positive electrode includes a positive electrode active material in which the positive electrode potential at the end-of-charge voltage during normal use of the nonaqueous electrolyte secondary battery can be nobler than 4.4 V (vs. Li ^/ Li ⁺ ). The non-aqueous electrolyte secondary battery has high discharge performance as described above, and the non-aqueous electrolyte has high oxidative 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 have a specific potential nobler than 4.4 V (vs. Li ^/ Li ⁺ ), a non-aqueous electrolyte storage element having high energy density and excellent high-rate discharge performance can be obtained. be able to.

As a positive electrode active material capable of reversible insertion / extraction of lithium ions reaching a specific potential nobler than 4.4 V (vs. Li ^/ Li ⁺ ), for example, Li _x Ni _α Mn having a spinel crystal structure LiNi _0.5 Mn _1.5 O ₄ which is an example of _(2-α) O ₄ , LiCoPO ₄ which is an example of a polyanion compound Li _w Co _x (PO ₄ ) _y X _{z and} the like can be mentioned.

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

  Examples of the binder (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, glass, and carbon.

(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.

  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) and amorphous Examples thereof include carbon materials such as carbon (easily graphitizable carbon or non-graphitizable carbon).

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

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

<Method for Manufacturing Nonaqueous Electrolyte Storage Element>
A method for producing a nonaqueous electrolyte storage element according to an embodiment of the present invention is a method for producing a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the nonaqueous electrolyte is used for the storage element. A non-aqueous electrolyte is used. The manufacturing method includes, for example, a step of housing a positive electrode and a negative electrode (electrode body) in a case, and a step of injecting the nonaqueous electrolyte into the case.

  The injection can be performed by a known method. After the injection, the non-aqueous electrolyte secondary battery (non-aqueous electrolyte storage element) can be obtained by sealing the injection port. The details of each element constituting the nonaqueous electrolyte secondary battery obtained by the manufacturing method are as described above. According to the manufacturing method, by using the non-aqueous electrolyte for a storage element, a non-aqueous electrolyte storage element having high high-rate discharge performance can be obtained.

<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, for example, when a polymer solid electrolyte is used as the non-aqueous electrolyte, the above-described injection step may not be provided in the method for manufacturing a non-aqueous electrolyte electricity storage device of the present invention.

  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 view of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of a nonaqueous electrolyte storage element according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode body 2 is accommodated 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 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 configuration of the nonaqueous electrolyte secondary battery 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 non-aqueous electrolyte secondary batteries. 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 secondary batteries 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.

[Example 1]
(Preparation of non-aqueous electrolyte)
Propylene carbonate (PC) as a first nonaqueous solvent and tris (2,2,2-trifluoroethyl) phosphate (TFEP) were mixed at a volume ratio of 1: 0.5. Next, fluoroethylene carbonate (FEC) was added to the two mixed solvents at a ratio of 4.9% by mass to obtain a nonaqueous solvent composed of the three mixed solvents. LiBF ₄ as an electrolyte salt was added at a rate of 2.5 mol with respect to 1 kg of this non-aqueous solvent and dissolved to obtain the non-aqueous electrolyte of Example 1. The number of moles of PC relative to the number of moles of LiBF ₄ (same as the number of moles of Li) is calculated to be 2.2.

(Preparation of nonaqueous electrolyte storage element)
A positive electrode plate using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material was produced. Moreover, the negative electrode plate which uses a graphite as a negative electrode active material was produced. Subsequently, the said positive electrode plate and the said negative electrode plate were laminated | stacked through the separator which consists of a polyimide nonwoven fabric, and the electrode body was produced. The electrode body was housed in a case made of a metal resin composite film, and the nonaqueous electrolyte was injected into the inside, and then sealed by thermal welding to obtain a nonaqueous electrolyte storage element (lithium ion secondary battery).

[Examples 2-3, Comparative Examples 1-5, Reference Examples 1-4]
Except that the type and concentration of the electrolyte salt, the amount of TFEP used (volume ratio with PC), and the amount of FEC added (added to the mixed solvent of PC or PC and TFEP) are as shown in Table 1. In the same manner as in Example 1, the nonaqueous electrolyte electricity storage elements of Examples 2 to 3, Comparative Examples 1 to 5, and Reference Examples 1 to 4 were obtained. Table 1 also shows the molar ratio of PC and Li and the volume ratio of each solvent.

[Evaluation]
(0.2 CmA discharge capacity confirmation test)
About each obtained nonaqueous electrolyte storage element, constant current constant voltage charging was performed at 25 ° C. with a constant current process charge current of 0.2 CmA, a charge end voltage of 5.0 V, and a constant voltage process charge end current of 0.02 CmA, A 10 minute rest period was then provided. Thereafter, a constant current discharge was performed with a discharge current of 0.2 CmA and a discharge end voltage of 3.0 V, and then a 10-minute rest period was provided. This charging / discharging was performed for 2 cycles, and the discharge capacity at the second cycle was set to “0.2 CmA discharge capacity (mAh)”.

(1.0 CmA discharge capacity confirmation test)
Next, constant current and constant voltage charge is performed at 25 ° C. with a constant current process charge current of 0.2 CmA, a charge end voltage of 5.0 V, and a constant voltage process charge end current of 0.02 CmA, and then a 10-minute rest period is provided. It was. Thereafter, constant current discharge was performed with a discharge current of 1.0 CmA and a discharge end voltage of 3.0 V, and the discharge capacity at this time was defined as “1.0 CmA discharge capacity (mAh)”.

  The percentage of the “1.0 CmA discharge capacity (mAh)” relative to the “0.2 CmA discharge capacity (mAh)” was defined as “high rate discharge performance (%)”. The results are shown in Table 1.

As shown in Table 1 above, the nonaqueous electrolyte electricity storage devices of Examples 1 to 3 are fluorinated phosphate esters despite using high concentration LiBF ₄ as the electrolyte salt in the nonaqueous electrolyte. It turns out that it has the outstanding high-rate discharge performance by containing TFEP. This is presumably because TFEP does not inhibit the solvation of PC to LiBF ₄ and functions so as to promote the dissociation of LiBF ₄ .

On the other hand, in Comparative Example 1, since the concentration of LiBF _{4 in the} non-aqueous electrolyte solution is low and there are many unsolvated PCs, side reactions (oxidative decomposition reactions such as non-aqueous solvents and negative electrode active materials into the graphite layer) In other words, the non-aqueous electrolyte storage element could not be charged / discharged during the test. Furthermore, in Comparative Examples 2-5, since the LiBF ₄ concentration of the nonaqueous electrolyte was increased as compared with Comparative Example 1, the amount of PC that was not solvated was reduced, and charging / discharging of the nonaqueous electrolyte storage element was performed. However, the solvation of PC with LiBF ₄ increases the interaction between molecules or ions in the electrolyte and prevents the movement of lithium ions, resulting in a low rate discharge performance of the nonaqueous electrolyte storage element. It was.

In addition, from the results of Reference Examples 1 to 4 using LiPF ₆ as the electrolyte salt, it is shown that the high rate discharge performance of the nonaqueous electrolyte electricity storage element is decreased by mixing TFEP. This is because the viscosity of the non-aqueous electrolyte is increased by mixing TFEP (viscosity at 25 ° C. of 4.6 mPa · s) with PC (viscosity of 2.5 mPa · s at 25 ° C.). It is presumed that the conductivity decreased. That is, it can be said that the effect of increasing the high rate discharge performance of the nonaqueous electrolyte electricity storage element by mixing TFEP is a unique effect when LiBF ₄ is used as the electrolyte salt. This is presumably because the behavior (interaction etc.) in the non-aqueous electrolyte differs depending on the degree of dissociation between LIBF ₄ and LiPF ₆ and the size of the anion. In the nonaqueous electrolytes of Examples 1 to 3, the solvation state of the nonaqueous electrolyte is more suitably formed by the combination of LiBF ₄ , the first nonaqueous solvent (PC) and the fluorinated phosphate ester (TFEP). It is presumed that the viscosity and the conductivity of lithium ions are optimized.

  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 secondary battery 2 Electrode body 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (8)

A non-aqueous electrolyte for a storage element containing a non-aqueous solvent and lithium tetrafluoroborate dissolved in the non-aqueous solvent,
The non-aqueous solvent includes a first non-aqueous solvent having a donor number of 15 or more, and a fluorinated phosphate ester,
The nonaqueous electrolyte for a storage element, wherein the content of the first nonaqueous solvent with respect to the content of lithium tetrafluoroborate is 4 or less in terms of molar ratio.   2. The nonaqueous electrolyte for a storage element according to claim 1, wherein a volume ratio of the first nonaqueous solvent to the fluorinated phosphate ester is 50:50 or more and 90:10 or less.   The nonaqueous electrolyte for a storage element according to claim 1 or 2, wherein the first nonaqueous solvent contains propylene carbonate.   The nonaqueous electrolyte for a storage element according to claim 1, wherein the nonaqueous solvent further contains a fluorinated cyclic carbonate.   A nonaqueous electrolyte electricity storage element provided with the nonaqueous electrolyte for electricity storage elements of any one of Claims 1-4. The nonaqueous electrolyte storage element according to claim 5, comprising a positive electrode and a negative electrode, wherein the positive electrode includes a positive electrode active material that can be nobler than 4.4 V (vs. Li ^/ Li ⁺ ). The nonaqueous electrolyte storage element according to claim 5 or 6, wherein the positive electrode potential at the end-of-charge voltage during normal use is nobler than 4.4 V (vs. Li ^/ Li ⁺ ). A method for producing a nonaqueous electrolyte storage element having a positive electrode, a negative electrode, and a nonaqueous electrolyte,
The manufacturing method of the nonaqueous electrolyte electrical storage element which uses the nonaqueous electrolyte for electrical storage elements of any one of Claim 1 to 4 as said nonaqueous electrolyte.

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