TECHNICAL FIELD

The present invention relates to an additive for nonaqueous electrolyte solutions. The present invention also relates to a nonaqueous electrolyte solution containing the additive for nonaqueous electrolyte solutions and an electricity storage device using the nonaqueous electrolyte solution.

BACKGROUND ART

In recent years, along with an increase in attention to solving environmental problems and establishing a sustainable recycling-based society, nonaqueous electrolyte solution secondary batteries typified by lithium ion batteries and electricity storage devices such as an electric double layer capacitor have been widely studied. The lithium ion batteries are used as power sources for electronic equipment such as laptops, or for electric motives or power storage from the viewpoint that they have high working voltages and energy densities. These lithium ion batteries are increasingly demanded as a battery having a high output and a high energy density with a high capacity from the viewpoint that they have higher energy densities than lead batteries and nickel-cadmium batteries and an increase of the capacity is realized.

In particular, automotive lithium ion batteries have been required to suppress battery swelling due to a long lifespan and deterioration among battery performance required for the lithium ion batteries. That is, it has become a significant task to sufficiently meet suppression of battery swelling by maintaining the capacity of a battery, reducing the resistance of a battery, and suppressing gas generation inside a battery.

As a method for obtaining a battery having a long lifespan, a method in which various additives are added to an electrolyte solution has been studied. The additives are decomposed during a first charge/discharge to form a film called a solid electrolyte interface (SEI) on a surface of an electrode. Since the SEI is formed during the first cycle of the charge/discharge cycles, electricity is suppressed from being consumed for the decomposition of a solvent and the like in the electrolyte solution and the lithium ions can be transferred between electrodes through the SEI. That is, formation of the SEI prevents the deterioration of electricity storage devices such as a nonaqueous electrolyte solution secondary battery in a case where the charge/discharge cycles are repeated, and contributes to an improvement of battery characteristics, storage characteristics, load characteristics, or the like.

As for a compound that forms the SEI, for example, Patent Literature 1 discloses that charge/discharge cycle characteristics of a lithium secondary battery are improved by incorporating 1,3-propanesultone (PS) into an electrolyte solution. Patent Literature 2 discloses that discharge characteristics and the like of a lithium secondary battery are improved by the addition of a derivative of vinylene carbonate (VC) as an additive. Patent Literature 3 discloses that gas generation in a battery is suppressed by incorporating a phosphoric acid ester-based compound into an electrolyte solution. Further, Patent Literatures 4 and 5 disclose that battery performance such as cycle characteristics is improved by adding a cyclic disulfonic acid ester as an additive. In addition, Patent Literature 6 discloses that charge/discharge efficiency, storage characteristics, and cycle characteristics are improved by incorporating a vinylene carbonate compound and/or a vinyl ethylene carbonate compound, and an acid anhydride into an electrolyte solution.

CITATION LIST

Patent Literature

[Patent Literature 1] Japanese Unexamined Patent Publication No. S63-102173

[Patent Literature 2] Japanese Unexamined Patent Publication No. H5-74486

[Patent Literature 3]. Japanese Unexamined Patent Publication No. 2012-84384

[Patent Literature 4] Japanese Unexamined Patent Publication No. 2004-281368

[Patent Literature 5] Japanese Unexamined Patent Publication No. 2015-138597

[Patent Literature 6] Japanese Unexamined Patent Publication No. 2002-352852

SUMMARY OF INVENTION

Technical Problem

However, nonaqueous electrolyte solutions using the additives in the related art were still not sufficient in satisfying both extension of a lifespan and suppression of gas generation.

An object of the present invention is to provide an additive for nonaqueous electrolyte solutions to obtain an electricity storage device having a long lifespan and suppressed gas generation. Another object of the present invention is to provide a nonaqueous electrolyte solution containing the additive for nonaqueous electrolyte solutions and an electricity storage device using the nonaqueous electrolyte solution.

Solution to Problem

As a result of extensive studies to solve the problems, the present inventors have found that it is possible to extend a lifespan and suppress gas generation in an electricity storage device with an additive for nonaqueous electrolyte solutions, including a combination of: a specific cyclic sulfone compound; and at least one compound selected from the group consisting of a specific ethylene carbonate compound, a specific vinyl ethylene carbonate compound, a specific cyclic sulfonic acid ester compound, and a specific cyclic disulfonic acid ester compound, thereby completing the present invention.

The present invention provides an additive for nonaqueous electrolyte solutions, containing a first compound represented by the following formula (1) and at least one second compound selected from the group consisting of a compound represented by the following formula (2-1), a compound represented by the following formula (2-2), a compound represented by the following formula (2-3), and a compound represented by the following formula (2-4).



In the formula (1), X represents a sulfonyl group or a carbonyl group, and R1represents an optionally substituted alkyl group having 1 to 4 carbon atoms, an optionally substituted alkenyl group having 2 to 4 carbon atoms, an optionally substituted alkynyl group having 2 to 4 carbon atoms, an optionally substituted aryl group, an optionally substituted alkoxy group having 1 to 4 carbon atoms, an optionally substituted alkenyloxy group having 2 to 4 carbon atoms, an optionally substituted alkynyloxy group having 2 to 4 carbon atoms, or an optionally substituted aryloxy group.



In the formula (2-1), X1, X2, X3, and X4each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, a vinyl group, an allyl group, or an alkyl group having 1 to 3 carbon atoms and optionally substituted with a halogen atom.



In the formula (2-2), Y1and Y2each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 3 carbon atoms and optionally substituted with a halogen atom.



In the formula (2-3), Z1, Z2, Z3, Z4, Z5, and Z6each independently represent a hydrogen atom, a fluorine atom, a chlorine atom, or an alkyl group having 1 to 3 carbon atoms and optionally substituted with a halogen atom, and n represents 0 or 1.



In the formula (2-4), W1and W2each independently represent an optionally branched, and substituted or unsubstituted alkylene group having 1 to 3 carbon atoms, an optionally branched, and substituted or unsubstituted perfluoroalkylene group having 1 to 3 carbon atoms, an optionally branched, and substituted or unsubstituted fluoroalkylene group having 1 to 3 carbon atoms.

Advantageous Effects of Invention

According to the present invention, provided is an additive for nonaqueous electrolyte solutions to obtain an electricity storage device having a long lifespan and suppressed gas generation. The additive for nonaqueous electrolyte solutions according to the present invention can form a stable solid electrolyte interface (SEI) on the surface of an electrode to improve a capacity retention rate upon a cycle test and suppress a resistance increase upon the cycle test, and suppress gas generation in a case where the additive for nonaqueous electrolyte solutions is used in an electricity storage device such as a nonaqueous electrolyte solution secondary battery and an electric double layer capacitor. The additive for nonaqueous electrolyte solutions according to the present invention can exhibit a more remarkable effect, as compared with the related art, particularly in a case where a lithium-containing composite oxide having a high Ni ratio is used as a positive electrode.

