JP6794658B2 - Non-aqueous electrolyte for power storage element, non-aqueous electrolyte power storage element and its manufacturing method - Google Patents

Description

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

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

It is known that in such a non-aqueous electrolyte power storage element, repeated charging / discharging causes side reactions such as oxidative decomposition of the electrolytic solution, and the charging / discharging performance gradually deteriorates. On the other hand, it has been reported that oxidative decomposition of the electrolytic solution is suppressed by increasing the salt concentration in the electrolytic solution (see Non-Patent Documents 1 and 2). Further, 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 Coulomb efficiency of the non-aqueous electrolyte secondary battery is excellent, and the overvoltage (the difference between the voltage when the charging state is 50% and the voltage when the discharging depth is 50%) is suppressed.

Rin Masuhara, 7 outsiders, "Design of oxidation-resistant electrolyte for 5V class positive electrode", Proceedings of the 55th Battery Discussion Meeting, Denki Kagakkai, November 19, 2014, p386 Yusuke Shimizu, 7 outsiders, "Design of oxidation-resistant electrolyte for 5V class spinel positive electrode", Proceedings of the 56th Battery Discussion Meeting, Denki Kagakkai, November 10, 2015, p368

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

The present invention has been made based on the above circumstances, and an object of the present invention is to improve the high rate discharge performance of the non-aqueous electrolyte power storage element in a non-aqueous electrolyte in which LiBF ₄ is dissolved as an electrolyte salt. It is an object of the present invention to provide a non-aqueous electrolyte for a power storage element, a non-aqueous electrolyte power storage element provided with the same, and a method for manufacturing the non-aqueous electrolyte power storage element.

The non-aqueous electrolyte for a power storage element according to one aspect of the present invention made to solve the above problems is a non-aqueous solvent and a non-aqueous electrolyte for a power storage element containing lithium tetrafluoroborate dissolved in the non-aqueous solvent. The water electrolyte, wherein the non-aqueous solvent contains a first non-aqueous solvent having 15 or more donors and a fluorinated phosphate ester of the first non-aqueous solvent with respect to the content of the lithium tetrafluoroborate. The content is characterized by having a molar ratio of 4 or less.

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

The method for manufacturing a non-aqueous electrolyte power storage element according to another aspect of the present invention is a method for manufacturing a non-aqueous electrolyte power storage element having a positive electrode, a negative electrode and a non-aqueous electrolyte, and the non-aqueous electrolyte is used for the power storage element. Use a non-aqueous electrolyte.

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 storage element capable of enhancing the high rate discharge performance of the non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element including the non-aqueous electrolyte. , And a method for manufacturing the non-aqueous electrolyte power storage element.

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

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

<Non-aqueous electrolyte for power storage elements>
The non-aqueous electrolyte for a power storage element according to an embodiment of the present invention (hereinafter, may be simply referred to as “non-aqueous electrolyte”) contains a non-aqueous solvent and LiBF ₄ dissolved in the non-aqueous solvent. A non-aqueous electrolyte for a power storage element, wherein the non-aqueous solvent contains a first non-aqueous solvent having 15 or more donors and a fluorinated phosphate ester, and the first non-aqueous solvent with respect to the content of LiBF _4. The content of is 4 or less in terms of molar ratio. The non-aqueous electrolyte is not limited to a liquid. That is, the non-aqueous electrolyte is not limited to a liquid electrolyte, but also includes a solid electrolyte, a gel electrolyte, and the like.

The number of donors is a parameter representing the electron pair 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 trichloride in 1,2-dichloroethane and the solvent of interest. Will be done. In the present specification, the number of donors is determined by the method described in Viktor Gutmann, “The Donor-Accessor Approach to Molecular Interactions”, Springer, 1978 (ISBN-13: 978-0306330645).

The non-aqueous electrolyte can enhance the high rate discharge performance of the non-aqueous electrolyte power storage element when LiBF ₄ is used as the electrolyte salt. The reason for this is not clear, but the following can be inferred. In the non-aqueous electrolyte, a first non-aqueous solvent having a large number of donors was used, and the content of the first non-aqueous solvent with respect to the content of the electrolyte salt LiBF ₄ was 4 or less in terms of molar ratio, and the first non-aqueous solvent. It contains a high concentration of LiBF ₄ . As a result, oxidative decomposition of the non-aqueous solvent and the like is suppressed, the initial Coulomb efficiency of the non-aqueous electrolyte power storage element is improved, and overvoltage is suppressed. It is presumed that these effects are caused by the fact that most of the first non-aqueous solvent is solvated with lithium ions. However, in this case, the increase in the interaction between LiBF ₄ and the first non-aqueous solvent suppresses the movement of lithium ions and reduces the conductivity of lithium ions, so that the high rate discharge performance of the non-aqueous electrolyte storage element is reduced. Decreases. On the other hand, the non-aqueous electrolyte further contains a fluorinated phosphate ester having a low solvation ability for lithium ions as the second non-aqueous solvent, thereby inhibiting the solvation of the first non-aqueous solvent to LiBF ₄ . It is presumed that the dissociation of LiBF ₄ is promoted, the conductivity of lithium ions is enhanced, and the high rate discharge performance of the non-aqueous electrolyte storage element is improved. That is, it is presumed that the combination of LiBF ₄ , the first solvent, and the fluorinated phosphate ester can enhance the high rate discharge performance of the non-aqueous electrolyte power storage element. In addition, Non-Patent Document 2 describes that the high-concentration electrolytic solution using LiBF ₄ suppresses the overvoltage of the non-aqueous electrolyte secondary battery even though it has a high viscosity. Therefore, it is presumed that the overvoltage of the non-aqueous electrolyte power storage element is suppressed even if the viscosity of the non-aqueous electrolyte remains high by containing the fluorinated phosphate ester having a high viscosity but a low solvation ability.

Further, as described above, since the non-aqueous electrolyte contains LiBF ₄ having a high concentration with respect to the first non-aqueous solvent, oxidative decomposition of the non-aqueous solvent and the like due to repeated charging and discharging of the non-aqueous electrolyte storage element The occurrence can be suppressed. Therefore, in particular, the non-aqueous electrolyte is a non-aqueous electrolyte storage element that employs charging conditions 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 power storage element provided with a positive electrode containing the above, 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 during normal use is relatively noble is, for example, charging at which the positive electrode potential at the end-of-charge voltage during normal use is 4.4 V (vs. Li ^/ Li ⁺ ). It is a condition. Here, the normal use is a case where the non-aqueous electrolyte storage element is used by adopting the charging conditions recommended or specified for the non-aqueous electrolyte storage element, and for the non-aqueous electrolyte storage element. When the charger is prepared, it means the case where the charger is applied to use the non-aqueous electrolyte power storage element. The positive electrode active material that can have a relatively noble potential is, for example, a positive electrode active material that can have a specific potential that is noble than 4.4 V (vs. Li ^/ Li ⁺ ), and is a positive electrode active material for a lithium ion secondary battery. In terms of material, it is a positive electrode active material capable of reversible insertion and desorption of lithium ions up to a specific potential noble 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 charge termination voltage is 5.0 V, although it depends 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 oxidative decomposition 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 enhanced, and overvoltage is also suppressed.

The non-aqueous electrolyte may contain other electrolyte salts other than LiBF _{4 as long} as the effects of the present invention are 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). _It has fluorinated hydrocarbon groups such as 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. Examples thereof include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like.

As the lower limit of the content of LiBF _{4 in} the total electrolyte salt, for example, 80% by mass is preferable, 95% by mass is more preferable, and 99% by mass is further preferable. By setting the content of LiBF ₄ to the above lower limit or more, a good solvation state of lithium ions can be more preferably achieved.

The lower limit of the mass molar concentration of LiBF ₄ (the number of moles of LiBF ₄ with respect to the mass of the non-aqueous solvent) in the non-aqueous electrolyte is preferably 1 mol / kg, more preferably 1.5 mol / kg, still more preferably 2 mol / kg. .. On the other hand, the upper limit is, for example, 5 mol / kg. By increasing the salt concentration in this way, the good oxidative decomposition resistance of the non-aqueous electrolyte can be exhibited, and the initial Coulomb efficiency and overvoltage suppression ability of the non-aqueous electrolyte power storage element to which this is applied can be further enhanced. it can.

(Non-aqueous solvent)
The non-aqueous solvent includes a first non-aqueous solvent having 15 or more donors and a fluorinated phosphate ester. The non-aqueous solvent preferably further contains a fluorinated cyclic carbonate. In addition, the non-aqueous solvent may further contain other non-aqueous solvents as long as the effects of the present invention are not impaired.

(First non-aqueous solvent)
The first non-aqueous solvent is a non-aqueous solvent having 15 or more donors.

Examples of the first non-aqueous solvent include propylene carbonate (number of donors: 15.1), ethylene carbonate (16.4), diethyl carbonate (16.4), dimethyl carbonate (15.2), and γ-butyrolactone (18). ), Ethyl acetate (17.1), tetrahydrofuran (20), 1,2-dimethoxyethane (20), diglime (19.2), tetraglime (16.6) and the like. The first non-aqueous solvent may be used alone or in combination of two or more.

As the first non-aqueous solvent, it is preferable to select and use a non-aqueous solvent in which the number of donors is not too large. By selecting and using a non-aqueous solvent in which the number of donors is not too large, it is possible to reduce that the coordinating force of the first non-aqueous solvent to solvate lithium ions becomes too strong. That is, it is possible to reduce that the energy required for desolvation of lithium ions on the surface of the active material becomes too large, and the electrode reaction can proceed more efficiently. From this point of view, the upper limit of the number of donors of the first non-aqueous solvent is preferably 17, more preferably 16.5, further 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 be substantially composed of only PC.

The upper limit of the content of the first non-aqueous solvent (first non-aqueous solvent / LiBF ₄ ) with respect to LiBF _{4 is 4 in} terms of molar ratio, preferably 2.5. By reducing the content of the first non-aqueous solvent with respect to LiBF _{4 in} this way, the amount of the first non-aqueous solvent that is not solvated can be reduced, and the oxidative decomposition resistance of the non-aqueous electrolyte can be enhanced.

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

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

(Fluorinated phosphate ester)
The non-aqueous solvent contains a fluorinated phosphate ester as a second non-aqueous solvent. Since the fluorinated phosphate ester is fluorinated and has low solvation with respect to lithium ions, it is possible to alleviate the state in which the movement of lithium ions is suppressed. The non-aqueous solvent may contain a fluorinated phosphoric acid ester having 15 or more donors. In that case, the fluorinated phosphoric acid ester is contained in the fluorinated phosphoric acid ester, and the first non-aqueous solvent is used. Not included in the solvent. The number of donors of the fluorinated phosphate ester is preferably smaller than the number of donors of the first non-aqueous solvent, and more preferably less than 15.

The fluorinated phosphoric acid ester refers to a compound in which part or all of the hydrogen contained in phosphoric acid (O = P (OH) ₃ ) is replaced with an organic group having a fluorine atom. The organic group having a fluorine atom is usually a fluorinated hydrocarbon group, and an alkyl fluorinated group is preferable. That is, as the fluorinated phosphoric acid ester, a fluoroalkyl phosphoric acid ester (fluoroalkyl phosphate) is preferable, and a trisfluoroalkyl phosphoric acid 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-Pentafluoropropyl), Tris phosphate (1H, 1H-perfluorobutyl), Tris phosphate (1H, 1H-perfluoropentyl), Tris phosphate (1H, 1H-perfluoroheptyl), Phosphate Examples thereof include tris phosphate (1H, 1H-perfluorononyl), tris phosphate (1,1-difluoroethyl) and tris phosphate (1,1,2,2-tetrafluoropropyl). As the fluorinated phosphate ester, tris phosphate (2,2,2-trifluoroethyl) (TFEP) is preferable. The above-mentioned fluorinated phosphate ester can be used alone or in combination of two or more.

The lower limit of the value of the first non-aqueous solvent in the volume ratio of the first non-aqueous solvent to the fluorinated phosphoric acid ester (first non-aqueous solvent: fluorinated phosphoric acid ester) is, for example, 30:70. Although it may be preferable, 50:50 is preferable, and 60:40 is more preferable. On the other hand, the upper limit may be, for example, 99: 1, but 90:10 is preferable, 80:20 is more preferable, and 70:30 is further preferable. By setting the volume ratio of the first non-aqueous solvent to the fluorinated phosphate ester to the above lower limit or more and / or the upper limit or less, the high rate discharge performance of the non-aqueous electrolyte power storage element can be further improved. Further, by setting this volume ratio to the above lower limit or more, the discharge capacity of the non-aqueous electrolyte power storage element can be increased. By setting the volume ratio of the first non-aqueous solvent to the fluorinated phosphate in the above range, the solvated state of the non-aqueous electrolyte is more preferably achieved, and the viscosity and the conductivity of lithium ions are achieved. Is presumed to be due to the preference.

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

(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, it is possible to suppress side reactions (oxidative decomposition of the non-aqueous solvent or the like) that may occur during charging / discharging of the non-aqueous electrolyte power storage device. The non-aqueous solvent may contain a fluorinated cyclic carbonate having 15 or more donors. In that case, the fluorinated cyclic carbonate is contained in the fluorinated cyclic carbonate, and the first non-aqueous solvent contains. Not included. The number of donors of the fluorinated cyclic carbonate is preferably smaller than the number of donors of 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, but fluoroethylene carbonate (FEC) is preferable. The above-mentioned fluorinated cyclic carbonate can be used alone or in combination of two or more.

The content of the fluorinated cyclic carbonate is not particularly limited, but the lower limit of the total mass of the first non-aqueous solvent and the fluorinated phosphoric acid ester is preferably 1% by mass, more preferably 3% by mass. On the other hand, as the upper limit, 20% by mass is preferable, and 10% by mass is more preferable. The lower limit of the content of the first non-aqueous solvent in the total non-aqueous solvent is preferably 1% by volume, more preferably 3% by volume. On the other hand, as the upper limit, 20% by volume is preferable, and 10% by volume is more preferable. By setting the content of the fluorinated cyclic carbonate to be equal to or higher than the above lower limit, side reactions that may occur during charging / discharging of the non-aqueous electrolyte power storage device can be more effectively suppressed. On the other hand, by setting the content of the fluorinated cyclic carbonate to the above upper limit or less, 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 can contain the first non-aqueous solvent, the fluorinated phosphoric acid ester, and other non-aqueous solvents other than the fluorinated cyclic carbonate. However, the content of the other non-aqueous solvent in the total non-aqueous solvent is preferably 10% by volume or less, and may be preferably 1% by volume or less. If the content of the other non-aqueous solvent is high, it may affect the solvation state of the non-aqueous electrolyte, the conductivity of lithium ions, the viscosity, and the like.

In addition, the non-aqueous electrolyte may contain components other than the electrolyte salt and the non-aqueous solvent as long as the effects of the present invention are not impaired. Examples of the other components include various additives contained in a general non-aqueous electrolyte for a power storage device. However, the content of the other components 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 obtained by adding LiBF ₄ or the like to the non-aqueous solvent and dissolving it.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example of the non-aqueous electrolyte power storage element. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a case, and the case is filled with the non-aqueous electrolyte. In the non-aqueous electrolyte secondary battery, the above-mentioned non-aqueous electrolyte for a power storage element is used as the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known aluminum case or the like which is usually used as a case of a non-aqueous 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 to be improved. Can be done. Further, the non-aqueous electrolyte secondary battery is excellent in oxidative decomposition resistance of the non-aqueous electrolyte. Therefore, the non-aqueous electrolyte secondary battery (storage element) can be used at a high operating voltage. For example, the positive electrode potential of the non-aqueous electrolyte secondary battery in a fully charged state can be made more noble than 4.4 V (vs. Li ^/ Li ⁺ ). On the other hand, the upper limit of the positive electrode potential in the non-aqueous electrolyte secondary battery of the fully charged state is, for example, 5.1V (vs.Li/Li ^+), a 5.0V (vs.Li/Li ⁺⁾ May be good.

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

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

The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles. Incidentally, to have a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, and "non-conductive" means that the volume resistivity is 10 ⁷ Ω · cm greater.

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

Examples of the positive electrode active material include composite oxides represented by Li _x MO _y (M represents at least one kind of transition metal) (Li _x CoO ₂ and Li _x NiO having a layered α-NaFeO type ₂ crystal structure). 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 etc.), Li _w Me _x (XO _y ) _z (Me represents at least one kind of transition metal, and X represents, for example, P, Si, B, V, etc.) Examples thereof include polyanionic compounds represented by (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 of these compounds may be used alone, or two or more of these compounds may be mixed and used.

The positive electrode preferably contains a positive electrode active material having a positive electrode potential of 4.4 V (vs. Li ^/ Li ⁺ ) at the end-of-charge voltage of the non-aqueous electrolyte secondary battery during normal use. As described above, the non-aqueous electrolyte secondary battery has high high rate discharge performance and high oxidative decomposition resistance of the non-aqueous electrolyte. Therefore, even when a positive electrode active material that can have such a noble potential is contained, the decomposition of the non-aqueous electrolyte is satisfactorily suppressed. Therefore, by using a positive electrode active material that can have a specific potential noble 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.

Examples of the positive electrode active material capable of reversible insertion and desorption of lithium ions reaching a specific potential noble than 4.4 V (vs. Li ^/ Li ⁺ ) include Li _x Ni _α Mn having a spinel-type crystal structure. _{(2-α) O} or _LiNi 0.5 _Mn 1.5 _{O 4,} which is an example of _4, can be cited LiCoPO ₄ or the like which is an example of a polyanionic compound _{Li w Co x (PO 4)} y X z.

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

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

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

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

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

The negative electrode base material may have the same structure as the positive electrode base material, but as the material, 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 base material. 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. Further, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. As the optional component such as the conductive agent, the binder, the thickener, and the filler, the same one as that of the positive electrode active material layer can be used.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is usually used. Specific negative electrode active materials include, for example, metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide and Sn oxide; polyphosphoric acid compounds; graphite and amorphous. Examples thereof include carbon materials such as carbon (graphitizable carbon or graphitizable carbon).

Further, the negative electrode mixture (negative electrode active material layer) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge. It may contain a typical metal element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and the like.

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

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing a non-aqueous electrolyte power storage element according to an embodiment of the present invention is a method for manufacturing a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte, and the non-aqueous electrolyte is used for the power storage element. It is characterized by using a non-aqueous electrolyte. The manufacturing method includes, for example, a step of accommodating a positive electrode and a negative electrode (electrode body) in a case, and a step of injecting the non-aqueous electrolyte into the case.

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

<Other Embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in various modifications and improvements in addition to the above-described embodiment. For example, it is not necessary to provide an intermediate layer 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-mentioned injection step may not be provided in the method for producing the non-aqueous electrolyte power storage element of the present invention.

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

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte secondary battery 1 which is an embodiment of the non-aqueous electrolyte power storage element according to the present invention. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte secondary battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through 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 non-aqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte secondary batteries. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

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

[Example 1]
(Preparation of non-aqueous electrolyte)
Propylene carbonate (PC) as the first non-aqueous solvent and tris (2,2,2-trifluoroethyl) (TFEP) phosphate were mixed in a volume ratio of 1: 0.5. Next, fluoroethylene carbonate (FEC) was added at a ratio of 4.9% by mass to the two mixed solvents to obtain a non-aqueous solvent composed of the three mixed solvents. LiBF ₄ as an electrolyte salt was added at a ratio of 2.5 mol 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.

(Manufacturing of non-aqueous electrolyte power storage element)
A positive electrode plate using LiNi _0.5 Mn _1.5 O ₄ as a positive electrode active material was produced. In addition, a negative electrode plate using graphite as a negative electrode active material was produced. Next, an electrode body was produced by laminating the positive electrode plate and the negative electrode plate via a separator made of a polyimide non-woven fabric. This electrode body was housed in a case made of a metal resin composite film, the non-aqueous electrolyte was injected into the case, and then sealed by heat welding to obtain a non-aqueous electrolyte storage element (lithium ion secondary battery).

[Examples 2 to 3, Comparative Examples 1 to 5, Reference Examples 1 to 4]
Examples 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 (amount added to PC or a mixed solvent of PC and TFEP) are as shown in Table 1. In the same manner as in No. 1, each non-aqueous electrolyte power storage element of Examples 2 to 3, Comparative Examples 1 to 5, and Reference Examples 1 to 4 was 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)
Each of the obtained non-aqueous electrolyte power storage elements was subjected to constant current constant voltage charging at 25 ° C. with a constant current process charging current of 0.2 CmA, a charging end voltage of 5.0 V, and a constant voltage process of charging end current of 0.02 CmA. After that, a rest period of 10 minutes was provided. Then, 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 rest period of 10 minutes was provided. This charge / discharge was carried out for two cycles, and the discharge capacity in the second cycle was set to "0.2 CmA discharge capacity (mAh)".

(1.0 CmA discharge capacity confirmation test)
Next, constant current constant voltage charging is performed at 25 ° C. with a constant current process charging current of 0.2 CmA, a charging end voltage of 5.0 V, and a constant voltage process of charging end current of 0.02 CmA, followed by a 10-minute rest period. It was. After that, 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 set to "1.0 CmA discharge capacity (mAh)".

The percentage of the "1.0 CmA discharge capacity (mAh)" with respect to the "0.2 CmA discharge capacity (mAh)" was defined as "high rate discharge performance (%)". The above results are shown in Table 1.

As shown in Table 1 above, the non-aqueous electrolyte storage elements of Examples 1 to 3 are fluorinated phosphoric acid esters even though a high concentration of LiBF ₄ is used as the electrolyte salt for the non-aqueous electrolyte. It can be seen that the inclusion of TFEP has excellent high rate discharge performance. It is presumed that this is because TFEP functions so as not to inhibit the solvation of PC to LiBF _{4 and} to promote the dissociation of LiBF ₄ .

On the other hand, in Comparative Example 1, since the LiBF ₄ concentration of the non-aqueous electrolyte solution was low and there were many PCs that were not solvated, side reactions (oxidative decomposition reactions of non-aqueous solvents and the like and the graphite layers as the negative electrode active material) (Co-insertion of PC, etc.) occurred, and the non-aqueous electrolyte power storage element could not be charged and discharged during the test. Further, in Comparative Examples 2 to 5, since the LiBF ₄ concentration of the non-aqueous electrolyte solution was increased as compared with Comparative Example 1, the amount of unsolvated PC was reduced, and the non-aqueous electrolyte power storage element could be charged and discharged. However, solvation of PC to LiBF ₄ increases the interaction between molecules or ions in the electrolyte and hinders the movement of lithium ions, resulting in low high-rate discharge performance of the non-aqueous electrolyte storage element. It was.

From the results of Reference Examples 1 to 4 in which LiPF ₆ was used as the electrolyte salt, it is shown that the high rate discharge performance of the non-aqueous electrolyte power storage element is conversely lowered by mixing TFEP. This is because the viscosity of the non-aqueous electrolyte is increased by mixing TFEP (viscosity at 25 ° C. 4.6 mPa · s) with PC (viscosity 2.5 mPa · s at 25 ° C.), and lithium ions It is presumed that this is due to the decrease in conductivity. That is, it can be said that the effect of enhancing the high rate discharge performance of the non-aqueous electrolyte power storage element by mixing TFEP is a peculiar effect when LiBF ₄ is used as the electrolyte salt. It is presumed that this is 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 non-aqueous electrolytes of Examples 1 to 3, the solvation state of the non-aqueous electrolyte was more preferably formed by the combination of LiBF ₄ , the first non-aqueous solvent (PC) and the fluorinated phosphate ester (TFEP). It is presumed that the viscosity and the conductivity of lithium ions have been optimized.

The present invention can be applied to a non-aqueous electrolyte power storage element used as a power source for a personal computer, an electronic device such as a communication terminal, an automobile, etc., and a non-water electrolyte for a power storage element provided therein.

1 Non-aqueous electrolyte secondary battery 2 Electrode body 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (8)

A non-aqueous electrolyte for a power storage device containing a non-aqueous solvent and lithium tetrafluoroborate dissolved in the non-aqueous solvent.
The non-aqueous solvent contains a first non-aqueous solvent having 15 or more donors and a fluorinated phosphate ester.
The number of donors of the fluorinated phosphate ester is smaller than the number of donors of the first non-aqueous solvent.
The content of the first non-aqueous solvent to the content of the lithium tetrafluoroborate is state, and are 4 or less in terms of the molar ratio,
The content of the non-aqueous solvent other than the main solvent composed of the first non-aqueous solvent, the fluorinated phosphate ester and the optional component fluorinated cyclic carbonate in the non-aqueous solvent is 10% by volume or less. non-aqueous electrolyte for an electricity storage device according to claim Rukoto Oh. The non-aqueous electrolyte for a power storage element according to claim 1, wherein the volume ratio of the first non-aqueous solvent to the fluorinated phosphoric acid ester is 50:50 or more and 90:10 or less. The non-aqueous electrolyte for a power storage element according to claim 1 or 2, wherein the first non-aqueous solvent contains propylene carbonate. The non-aqueous electrolyte for a power storage element according to claim 1, 2, or 3, wherein the non-aqueous solvent further contains a fluorinated cyclic carbonate. A non-aqueous electrolyte power storage element comprising the non-water electrolyte for a power storage element according to any one of claims 1 to 4 . The non-aqueous electrolyte power storage element according to claim 5 , further comprising a positive electrode and a negative electrode, wherein the positive electrode contains a positive electrode active material having a potential higher than 4.4 V (vs. Li ^/ Li ⁺ ). The non-aqueous electrolyte power storage element according to claim 5 or 6 , wherein the positive electrode potential at the end-of-charge voltage during normal use is noble than 4.4 V (vs. Li ^/ Li ⁺ ). A method for manufacturing a non-aqueous electrolyte power storage element having a positive electrode, a negative electrode, and a non-aqueous electrolyte.
A method for producing a non-aqueous electrolyte power storage element, wherein the non-water electrolyte for a power storage element according to any one of claims 1 to 4 is used as the non-water electrolyte.

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