JP2022076996A - Electrolytic solution for non-aqueous secondary battery, and non-aqueous secondary battery using the same - Google Patents

Abstract

To provide an electrolytic solution capable of improving charge and discharge cycle characteristics in a non-aqueous secondary battery in which lithium-free transition metal sulfide is used as a positive electrode active material.SOLUTION: Provided is an electrolytic solution used for a non-aqueous secondary battery in which lithium-free transition metal sulfide is used as a positive electrode active material. The electrolytic solution contains: an organic solvent containing a cyclic carbonate compound; and an additive agent.SELECTED DRAWING: None

Description

The present invention relates to an electrolytic solution for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

Due to the recent improvement in the performance of portable electronic devices, hybrid vehicles, etc., the lithium ion secondary batteries used in them are required to have higher capacities. However, in the current lithium ion secondary battery, the capacity of the positive electrode is insufficiently increased as compared with the negative electrode, and the capacity of the lithium nickelate material, which is said to have a relatively high capacity, is only about 190 to 220 mAh / g. not.

On the other hand, sulfur has a high theoretical capacity of about 1670 mAh / g and is expected to be used as a positive electrode active material. However, in general, the capacity of a sulfur-based positive electrode active material may decrease as the charge / discharge cycle is repeated. Are known. This is because it elutes into the organic electrolytic solution as lithium polysulfide during charging and discharging, and a technique for suppressing elution into the organic electrolytic solution is indispensable.

Lithium-free transition metal sulfides (lithium-free transition metal sulfides) have electron conductivity and are less likely to elute into organic electrolytes, but are not sufficient. Taking vanadium sulfide as an example of a lithium-free transition metal sulfide, for example, when crystalline vanadium ( _{III) sulfide (V2 S 3 )} sold as a reagent is used as a positive electrode active material, Since the reaction with the organic electrolytic solution cannot be suppressed, the measured capacity is only about 23 mAh / g for the charge capacity and about 52 mAh / g for the discharge capacity. On the other hand, the present inventors show a high capacity when a low crystalline vanadium sulfide having a specific composition is used as an electrode active material for a lithium ion secondary battery, and also have charge / discharge cycle characteristics. Also reported to be excellent (see, for example, Patent Document 1).

International Publication No. 2018/181698

As described above, the present inventors have developed a material that exhibits high capacity when used as an electrode active material for a lithium ion secondary battery and also has excellent charge / discharge cycle characteristics. However, the lithium ion secondary battery has been developed. There is no end to the demand for higher performance, and further improvements are required for charge / discharge cycle characteristics.

Causes of cycle deterioration include accumulation of by-products due to the reaction between lithium-free transition metal sulfide and electrolytic solution and reduction of electrode active material components, and suppression of these leads to improvement of charge / discharge cycle characteristics. it is conceivable that. As a method of suppressing the reaction between the two, for example, an electrolytic solution having low reactivity can be used.

The present invention has been made in view of the above-mentioned current state of the prior art, and a main object thereof is a charge / discharge cycle characteristic in a non-aqueous secondary battery using a lithium-free transition metal sulfide as a positive electrode active material. Is to provide an electrolytic solution that can improve.

The present inventors have carried out diligent research to achieve the above-mentioned object. As a result, the charge / discharge cycle characteristics are further improved in the non-aqueous secondary battery using the lithium-free transition metal sulfide as the positive electrode active material by containing the organic solvent containing the cyclic carbonate compound and the additive. I found that I could do it. The present invention has been completed as a result of further research based on such findings. That is, the present invention includes the following configurations.

Item 1. An electrolytic solution for a non-aqueous secondary battery used in a non-aqueous secondary battery that uses a lithium-free transition metal sulfide as a positive electrode active material.
The electrolytic solution is an electrolytic solution for a non-aqueous secondary battery containing an organic solvent containing a cyclic carbonate compound and an additive.

Item 2. The additive is the general formula (1) :.

[In the formula, R ¹ and R ² are the same or different and indicate a hydrogen atom or a halogen atom. Bonds shown by solid and dashed lines indicate single or double bonds. ]
The compound represented by, or the general formula (2) :.

[In the formula, R ³ is the same or different and represents a halogen atom. M indicates a counter cation. ]
The electrolytic solution for a non-aqueous secondary battery according to claim 1, which is a compound represented by.

Item 3. The compound represented by the general formula (1) contains at least one selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), trifluoromethylethylene carbonate and vinylethylene carbonate.
Item 2. The electrolytic solution for a non-aqueous secondary battery according to Item 2, wherein the compound represented by the general formula (2) contains difluoro (oxalate) lithium borate (DFOB).

Item 4. Item 2. The electrolytic solution for a non-aqueous secondary battery according to any one of Items 1 to 3, wherein the content of the additive is 0.5 to 20 parts by mass with respect to 100 parts by mass of the organic solvent.

Item 5. Any of Items 1 to 4, wherein the total amount of the organic solvent is 100% by volume, the content of the cyclic carbonate compound is 80 to 100% by volume, and the content of the chain carbonate compound is 0 to 20% by volume. The electrolytic solution for a non-aqueous secondary battery according to item 1.

Item 6. Item 5. The non-aqueous secondary according to Item 5, wherein the chain carbonate compound is at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and methyl propyl carbonate. Electrolyte for batteries.

Item 7. Item 2. The non-aqueous secondary battery according to any one of Items 1 to 6, wherein the cyclic carbonate compound is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate. Electrolyte.

Item 8. Item 2. The non-aqueous secondary battery according to any one of Items 1 to 7, wherein the lithium-free transition metal sulfide is at least one selected from the group consisting of vanadium sulfide, molybdenum sulfide, and iron sulfide. Electrolyte.

Item 9. Item 2. The electrolytic solution for a non-aqueous secondary battery according to any one of Items 1 to 8, further comprising a lithium salt.

Item 10. Item 9. The electrolytic solution for a non-aqueous secondary battery according to Item 9, wherein the lithium salt is at least one selected from the group consisting of an organic lithium salt having a sulfonyl group and an organic lithium salt having a boron atom.

Item 11. The lithium salt is lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N). , Lithium Hexafluorophosphate (LiPF ₆ ), Lithium Tetrafluoroborate (LiBF ₄ ), Lithium Hexafluoroarsenate (LiAsF ₆ ), Lithium Perchlorate (LiClO ₄ ), Lithium Bis (oxalate) Borate (LiBOB), Lithium Item 9 or 10 which is at least one selected from the group consisting of oxalate difluoroborate (LiBF ₂ (C ₂ O ₄ )) and lithium bis (malonate) bolate (LiB (C ₃ O ₄ H ₂ ) ₂ ). The electrolyte for non-aqueous secondary batteries described in 1.

Item 12. Item 2. The electrolytic solution for a non-aqueous secondary battery according to any one of Items 9 to 11, wherein the concentration of the lithium salt is 0.3 to 2.5 mol / L.

Item 13. Item 2. The electrolytic solution for a non-aqueous secondary battery according to any one of Items 1 to 12, which is an electrolytic solution for a lithium ion secondary battery.

Item 14. A non-aqueous secondary battery comprising the electrolytic solution for a non-aqueous secondary battery according to any one of Items 1 to 13.

Item 15. Item 2. The non-aqueous secondary battery according to Item 14, which is a lithium ion secondary battery.

According to the present invention, in a non-aqueous secondary battery using a lithium-free transition metal sulfide as a positive electrode active material, the charge / discharge cycle characteristics can be further improved.

As used herein, "contains" is a concept that includes any of "comprise," "consist essentially of," and "consist of." Further, in the present specification, when the numerical range is indicated by "A to B", it means A or more and B or less.

In the present specification, the concentration (mol / L) of each component means that a desired number of moles is contained with respect to 1 L of the organic solvent.

1. 1. Electrolyte for non-aqueous secondary battery The electrolytic solution for non-aqueous secondary battery of the present invention is an electrolysis for non-aqueous secondary battery used in a non-aqueous secondary battery using a lithium-free transition metal sulfide as a positive electrode active material. The electrolytic solution is a liquid and contains an organic solvent containing a cyclic carbonate compound and an additive.

(1-1) Lithium-Free Transition Metal Sulfide In the present invention, the transition metal sulfide containing lithium needs to be handled in an inert atmosphere such as an argon gas atmosphere, and therefore lithium-free. Use transition metal sulfides contained. As such a lithium-free transition metal sulfide, a lithium-free transition metal sulfide used as a positive electrode active material in a non-aqueous secondary battery in which the electrolytic solution for a non-aqueous secondary battery of the present invention is used. The above is not particularly limited as long as it is a lithium-free transition metal sulfide known as a positive electrode active material of a lithium ion secondary battery. Specifically, vanadium sulfide (lithium-free vanadium sulfide; International Publication No. 2018/181698), niobium sulfide and titanium niobium sulfide (lithium-free niobium sulfide and lithium-free titanium niobium sulfide; International Publication No. 2015/049986), molybdenum sulfide (molybdenum-free molybdenum sulfide), iron sulfide (lithium-free iron sulfide), and the like. The descriptions of International Publication No. 2018/181698 and International Publication No. 2015/049986 are cited by reference (incorporate by reference). These lithium-free transition metal sulfides can be used alone or in combination of two or more. Among these, vanadium sulfide (lithium-free vanadium sulfide; International Publication No. 2018/181698), molybdenum sulfide (lithium-free molybdenum sulfide), from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, etc. Iron sulfide (molybdenum-free iron sulfide) and the like are preferable, and vanadium sulfide (molybdenum-free vanadium sulfide; International Publication No. 2018/181698) is more preferable.

As such a lithium-free transition metal sulfide, both a crystalline material and a low crystalline material (or an amorphous material) can be adopted. Among them, a low crystalline material (or amorphous material) is particularly excellent in charge / discharge capacity, charge / discharge cycle characteristics, etc., and from the viewpoint of easily suppressing the reaction with the organic electrolytic solution when in contact with the organic electrolytic solution. Is preferable.

In the present invention, as the lithium-free transition metal sulfide, the composition ratio (S / M ¹ ) of sulfur and the transition metal is particularly excellent in charge / discharge capacity, charge / discharge cycle characteristics, etc., easy to synthesize, and tentatively organic electrolysis. From the viewpoint of easily suppressing the reaction with the organic electrolytic solution when in contact with the liquid, the molar ratio is preferably 2.1 to 10.

More specifically, the lithium-free transition metal sulfide is described in the general formula (2) :.
M ¹ S _x (2)
[In the equation, M ¹ represents a transition metal. x indicates 2.1 to 10. ]
It is preferable to have a composition represented by. When a plurality of transition metals are contained as M ¹ , the composition ratio (S / M ¹ ) of sulfur and the total amount of the transition metals is preferably 2.1 to 10 in terms of molar ratio.

As described above, in the present invention, the lithium-free metal sulfide has a high elemental ratio of sulfur to the transition metal (M ¹ ). Therefore, in the present invention, by using the lithium-free metal sulfide, it is possible to have a high charge / discharge capacity and excellent charge / discharge cycle characteristics. In the present invention, the higher the sulfur content (the larger x), the higher the charge / discharge capacity tends to be, and the lower the sulfur content (the smaller x), the more difficult it is to contain elemental sulfur. The charge / discharge cycle characteristics tend to be high. In the present invention, even if a sulfide having inferior charge / discharge cycle characteristics is used, the charge / discharge cycle characteristics can be improved by using an electrolytic solution having a composition described later, so that the charge / discharge capacity tends to be high. It is particularly useful for applying polysulfides whose charge / discharge cycle characteristics tend to be inadequate. Therefore, x is preferably 2.1 to 10, and more preferably 3 to 8.

Hereinafter, vanadium sulfide (lithium-free vanadium sulfide), which is a preferable lithium-free transition metal sulfide, will be described as an example.

In the present invention, the vanadium sulfide preferably has a crystal structure similar to that of crystalline vanadium tetrasulfide (IV) (VS ₄ ) (hereinafter, may be referred to as “VS ₄ type crystal structure”).

More specifically, the vanadium sulfide is 15.4 °, 35. In the range of the diffraction angle 2θ = 10 ° to 80 ° in the X-ray diffraction pattern by CuKα ray, within the allowable range of ± 1.0 °. It is preferable to have peaks at 3 ° and 45.0 °. That is, it is preferable to have peaks in the ranges of 14.4 ° to 16.4 °, 34.3 ° to 36.3 ° and 44.0 ° to 46.0 °.

In the present invention, the X-ray diffraction pattern is obtained by the powder X-ray diffraction measurement method (θ-2θ method), and the following measurement conditions are:
Measuring device: D8ADVANCE (BrookerAXS)
X-ray source: CuKα40kV / 40mA
Measurement conditions: Measure at 2θ = 10 ° to 80 °, 0.1 ° step, scanning speed 0.02 ° / sec.

In the present invention, the vanadium sulfide preferably has a peak at the above-mentioned 2θ position, but in the range of the diffraction angle 2θ = 10 ° to 80 °, within the allowable range of ± 1.0 °, 54.0 °. And it is preferable to have a peak at at least one point (particularly all) at 56.0 °.

In the present invention, vanadium sulfide is a sulfide having a high proportion of sulfur as an average composition, but sulfur hardly exists as elemental sulfur as described later, and is combined with vanadium to have low crystallinity. It is preferable that the sulfide is formed. As described above, in the present invention, the vanadium sulfide has more sites into which lithium ions can be inserted and desorbed by lowering the crystallinity, and a gap that can be a three-dimensional conductive path of lithium. Can be structurally easy to hold. In addition, it has many advantages such as easy three-dimensional volume change during charging and discharging. Therefore, the charge / discharge capacity and the charge / discharge cycle characteristics can be further improved. Further, it is preferable that vanadium sulfide ₍ V2 _S3 or the like) used as a raw material is almost absent. In the present specification, the average composition of sulfide indicates the elemental ratio of each element constituting the whole of sulfide.

Hereinafter, "low crystallinity" in the present invention will be described. In the present invention, in vanadium sulfide, there is no peak at 2θ = 15.4 °, 35.3 ° and 45.0 °, or even if a peak appears, the full width at half maximum of the peak is 0. It is preferably 8 to 2.0 ° (particularly 1.0 to 2.0 °). This is because the full width at half maximum of the X-ray diffraction peak is inversely proportional to the crystallinity size, that is, the large full width at half maximum of the peak indicates that the crystal grain size is relatively small, and the crystalline vanadium sulfide (IV). In (VS ₄ ), it is based on the fact that the full width at half maximum of the peaks of 2θ = 15.4 °, 35.3 ° and 45.0 ° is 0.2 to 0.6 °. Thus, in the present invention, the vanadium sulfide has no peak at 2θ = 15.4 °, 35.3 ° and 45.0 °, or even if a peak appears, the full width at half maximum of the peak is crystallized. It is preferably larger than the full width at half maximum of the peak of vanadium (IV) sulfide (VS ₄ ). As described above, since the low crystallinity in the present invention tends to increase the number of sites where Li can stably exist, when a low crystallinity lithium-free metal sulfide is used as a positive electrode active material, the charge / discharge capacity is increased. And it is easy to improve the charge / discharge cycle characteristics.

Further, when a material containing a large amount of elemental sulfur or the like is used as the positive electrode active material, the cyclic carbonate compound contained in the electrolytic solution for a non-aqueous secondary battery of the present invention is compared with the fact that it easily reacts with elemental sulfur. In the present invention, for example, when the mechanical milling treatment is performed for a sufficient time, the vanadium sulfide described above contains almost no elemental sulfur or the like, and therefore, when used as a positive electrode active material, a cyclic carbonate. Even when a compound is used, these problems do not occur, and it is easy to dramatically improve the charge / discharge capacity and charge / discharge cycle characteristics.

More specifically, the strongest peak of sulfur (S ₈ ) exists at 2θ = 23.0 ° with a tolerance of ± 1.0 °. From this, in the X-ray diffraction diagram using CuKα rays, is there a peak having a maximum near 2θ = 23.0 °, which is a peak characteristic of simple sulfur within the allowable range of ± 1.0 °? The area of the peak having the maximum in the vicinity of 2θ = 23.0 ° is preferably 0 to 20%, particularly 0.1 to 19% of the area of the peak having the maximum in the vicinity of 2θ = 35.3 °. .. Thereby, in the present invention, the vanadium sulfide can be used as a material containing almost no elemental sulfur, the concern of causing a reaction with the electrolytic solution as described above is further reduced, and the charge / discharge capacity and charge / discharge cycle characteristics are reduced. Can be further improved.

In the present invention, the vanadium sulfide also has a permissible range of ± 1.0 ° at positions near 2θ = 25.8 ° and 27.8 °, which are characteristic peaks of elemental sulfur. The area of the peak having no peak or having a maximum at the position is 0 to 10%, particularly 0.1 to 8% of the area of the peak having a maximum in the vicinity of 2θ = 35.3 °. preferable. As a result, the vanadium sulfide can be made into a material containing almost no elemental sulfur, the concern of causing a reaction with the electrolytic solution as described above is reduced, and the charge / discharge capacity and charge / discharge cycle characteristics are further improved. be able to.

The vanadium sulfide that satisfies these conditions is within the allowable range of ± 0.1 Å in the X-ray / neutron atom pair correlation function analysis (PDF analysis), and g (r) = 2.4 Å (g (r)). It is preferable to have a strong peak at the position (which shows a peak at the distance between each atom in the two-atom distribution function), but for sulfides with better charge / discharge capacity and charge / discharge cycle characteristics, ± 0.1 Å. It is more preferable to have a shoulder peak at g (r) = 2.0 Å within the allowable range of ± 0.1 Å, and also have a peak at the position of g (r) = 3.3 Å within the allowable range of ± 0.1 Å. Is more preferable. In other words, the vanadium sulfide preferably has not only a VS bond but also an SS bond (disulfide bond). This is because in VS ₄ , g (r) derived from VS bond has a peak at 2.4 Å, and g (r) derived from SS bond has a peak at 2.0 and 3.3 Å. To do.

In the present invention, the above-mentioned vanadium sulfide can be obtained, for example, by using vanadium sulfide and sulfur as raw materials or intermediates and using a production method comprising a step of subjecting to a mechanical milling method.

The mechanical milling treatment is a method of grinding and mixing raw materials while applying mechanical energy. According to this method, vanadium sulfide and vanadium sulfide and are mixed by applying mechanical impact and friction to the raw materials. Sulfur comes into close contact and becomes finer, causing a reaction of the raw materials. That is, at this time, mixing, pulverization and reaction occur at the same time. Therefore, it is possible to react the raw material more reliably without heating the raw material to a high temperature. By using the mechanical milling treatment, a metastable crystal structure that cannot be obtained by ordinary heat treatment may be obtained.

Specifically, as the mechanical milling process, mixed pulverization can be performed using a mechanical pulverizer such as a ball mill, a bead mill, a rod mill, a vibration mill, a disc mill, a hammer mill, or a jet mill.

All of these raw materials or intermediates can be mixed at the same time and subjected to mechanical milling treatment. Some materials or intermediates are first subjected to mechanical milling treatment, and then the remaining materials are added for mechanical milling treatment. It can also be offered to.

In particular, in the case of producing vanadium sulfide having a high sulfur content (the composition ratio (S / V) of sulfur and vanadium is 3.3 or more in terms of molar ratio), crystalline vanadium sulfide may be produced depending on the charged mass. Things may be obtained. Therefore, in order to facilitate the acquisition of low-crystalline vanadium sulfide having excellent charge / discharge capacity and charge / discharge cycle characteristics, first, vanadium sulfide and a part of sulfur are subjected to mechanical milling treatment, which is desired as an intermediate. After obtaining the low crystalline sulfide, it is preferable to subject the obtained low crystalline sulfide and the remaining sulfur to a mechanical milling treatment.

As a specific raw material, it is preferable to use crystalline vanadium sulfide (III) (V ₂ S ₃ ) as the vanadium sulfide. The vanadium sulfide is not particularly limited, and any commercially available vanadium sulfide can be used. In particular, it is preferable to use a high-purity one. Further, since the vanadium sulfide is mixed and pulverized by a mechanical milling treatment, the particle size of the vanadium sulfide to be used is not limited, and a commercially available powdered vanadium sulfide can be usually used.

Further, as sulfur, it is possible to use elemental sulfur (S ₈ ) in an amount necessary for forming a sulfide having a desired composition. The sulfur used as a raw material is not particularly limited, and any sulfur can be used. In particular, it is preferable to use a high-purity one. Further, since sulfur is mixed and pulverized by a mechanical milling treatment, the particle size of sulfur used is not limited, and commercially available powdered sulfur can be usually used.

Further, as described above, when subjected to a plurality of (particularly two-step) mechanical milling treatments, a low crystalline vanadium sulfide (low crystalline VS _2.5 , etc.) having a desired composition should be used as the intermediate. You can also.

As for the mixing ratio of the raw materials, since the charging ratio of the raw materials is almost the same as the ratio of each element of the product, the ratio can be the same as the element ratio of vanadium and sulfur in the target vanadium sulfide. For example, 1.2 mol or more (particularly 1.2 to 17.0 mol, further 3.0 to 13.0 mol) of sulfur is preferable with respect to 1 mol of vanadium sulfide.

The temperature at which the mechanical milling treatment is performed is not particularly limited, and is preferably 300 ° C. or lower, more preferably -10 to 200 ° C., because sulfur is less likely to volatilize and the previously reported crystal phase is less likely to be formed.

The time of the mechanical milling treatment is not particularly limited, and the mechanical milling treatment can be performed for any time until the desired vanadium sulfide is precipitated.

The atmosphere when performing the mechanical milling treatment is not particularly limited, but an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere can be adopted.

For example, the mechanical milling process can be performed within a processing time range of 0.1 to 100 hours (particularly 15 to 80 hours). It should be noted that this mechanical milling process can be performed in a plurality of times with a pause in the middle, if necessary.

When the mechanical milling process is repeated a plurality of times, the above conditions can be satisfied in the mechanical milling process of each step.

By the above-mentioned mechanical milling treatment, the desired vanadium sulfide can be obtained as a fine powder.

(1-2) Organic Solvent As described above, the electrolytic solution for a non-aqueous secondary battery of the present invention is a non-aqueous secondary used in a non-aqueous secondary battery using a lithium-free transition metal sulfide as a positive electrode active material. It is an electrolytic solution for batteries. As described above, in the present invention, although it is used for a non-aqueous secondary battery using a lithium-free transition metal sulfide, by adding an additive described later, a carbonate compound and a lithium-free transition metal sulfide are added. It is possible to suppress the reaction with objects and dramatically improve the charge / discharge cycle characteristics.

The cyclic carbonate compound is not particularly limited as long as it can be used as an organic solvent in the electrolytic solution of the lithium ion secondary battery, and examples thereof include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate and the like. .. These cyclic carbonate compounds may be used alone or in combination of two or more.

The content of the cyclic carbonate compound described above is 80, with the total amount of the organic solvent as 100% by volume, from the viewpoint of easily suppressing the reaction between the carbonate compound and the lithium-free transition metal sulfide and easily improving the charge / discharge cycle characteristics. It is preferably ~ 100% by volume, more preferably 85-100% by volume, still more preferably 90-100% by volume. In the present invention, only the cyclic carbonate compound may be used as the organic solvent (the content of the cyclic carbonate compound is 100% by volume), or other organic such as a chain carbonate compound other than the cyclic carbonate compound. Solvents can also be used (the content of the cyclic carbonate compound is 80-99.9% by volume, particularly 85-99.8% by volume, even 90-99.5% by volume). However, from the viewpoint of charge / discharge cycle characteristics, it is preferable to use only the cyclic carbonate compound as the organic solvent (the content of the cyclic carbonate compound is 100% by volume).

The chain carbonate compound is not particularly limited as long as it can be used as an organic solvent in the electrolytic solution of a lithium ion secondary battery, and is, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). ), Methylpropyl carbonate and the like. These chain carbonate compounds may be used alone or in combination of two or more.

The content of the above-mentioned chain carbonate compound is such that the total amount of the organic solvent is 100% by volume from the viewpoint that the reaction between the carbonate compound and the lithium-free transition metal sulfide is easily suppressed and the charge / discharge cycle characteristics are easily improved. 0 to 20% by volume is preferable, 0 to 15% by volume is more preferable, and 0 to 10% by volume is further preferable. As described above, in the present invention, only the cyclic carbonate compound can be used as the organic solvent (the content of the chain carbonate compound is 0% by volume), or the chain carbonate compound is used (chain carbonate compound). The content of the compound can be 0.1 to 20% by volume, particularly 0.2 to 15% by volume, and even 0.5 to 10% by volume). From the viewpoint of easily suppressing the decomposition of the organic solvent, the content of the chain carbonate compound is preferably small, and only the cyclic carbonate compound is used as the organic solvent (the content of the chain carbonate compound is 0% by volume). ) Is particularly preferable.

In the present invention, the organic solvent constituting the electrolytic solution for a non-aqueous secondary battery may be composed of only the above-mentioned cyclic carbonate compound and, if necessary, a chain carbonate compound, and in addition to these, lithium. It is also possible to include a compound known as an organic solvent in the electrolytic solution of the ion secondary battery.

Examples of the organic solvent as such a third component include cyclic carboxylic acid ester compounds such as γ-butyrolactone; chain carboxylic acid ester compounds such as methyl acetate, methyl propionate and ethyl acetate; and sulforane and diethyl sulfone. Sulfone compounds; ether compounds such as tetrahydrofuran, 2-methyltetrachloride, 1,2-dimethoxyethane and the like can be mentioned. These organic solvents as the third component may be used alone or in combination of two or more.

When the above-mentioned organic solvent as the third component is contained, the content of the organic solvent as the third component is 0.1 to 10 volumes, where the total amount of the organic solvent is 100% by volume from the viewpoint of charge / discharge cycle characteristics. % Is preferable, and 0.2 to 5% by volume is more preferable.

(1-3) Additives As described above, in the electrolytic solution for non-aqueous secondary batteries of the present invention, the reaction between the carbonate compound and the lithium-free transition metal sulfide is suppressed by containing the additive. It is possible to dramatically improve the charge / discharge cycle characteristics.

As such an additive, the general formula (1): from the viewpoint that the reaction between the carbonate compound and the lithium-free transition metal sulfide is easily suppressed and the charge / discharge cycle characteristics are easily improved.

[In the formula, R ¹ and R ² are the same or different and indicate a hydrogen atom or a halogen atom. Bonds shown by solid and dashed lines indicate single or double bonds. ]
The compound represented by, and the general formula (2) :.

[In the formula, R ³ is the same or different and represents a halogen atom. M indicates a counter cation. ]
The compound represented by is preferable.

The compound represented by the above general formula (1) is the general formula (1A) :.

[In the formula, R ¹ and R ² are the same or different and indicate a hydrogen atom or a halogen atom. ]
The compound represented by and the general formula (1B) :.

[In the formula, R ¹ and R ² are the same or different and indicate a hydrogen atom or a halogen atom. ]
The compound represented by is included.

In the general formulas (1), (1A) and (1B), the halogen atom represented by R ¹ and R ² is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. .. Among them, from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, etc., a fluorine atom, a chlorine atom, a bromine atom and the like are preferable, a fluorine atom, a chlorine atom and the like are more preferable, and a fluorine atom is further preferable.

In the general formula (2), the halogen atom represented by R ³ is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among them, from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, etc., a fluorine atom, a chlorine atom, a bromine atom and the like are preferable, a fluorine atom, a chlorine atom and the like are more preferable, and a fluorine atom is further preferable.

In the general formula (2), the counter cation represented by M is not particularly limited, and examples thereof include alkali metal ions such as lithium ion, sodium ion, and potassium ion. Among them, lithium ion is preferable from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, and the like.

Examples of the additive satisfying the above conditions include vinylene carbonate (VC), fluoroethylene carbonate (FEC), trifluoromethylethylene carbonate, vinylethylene carbonate and the like as the compound represented by the general formula (1). Examples of the compound represented by the general formula (2) include difluoro (oxalat) lithium borate (DFOB) and the like. These compounds represented by the general formula (1) may be used alone or in combination of two or more, and the compounds represented by the general formula (2) may be used alone. Alternatively, two or more kinds may be used in combination.

The above-mentioned additive is not particularly limited, but a compound represented by the general formula (1) is preferable from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, and the like.

The above-mentioned additives can be used alone or in combination of two or more. When two or more kinds of additives are used in combination, for example, even when an additive having a preferable small amount of addition such as vinylene carbonate (VC) is used, the total content of the additives can be adjusted. It is possible to improve the charge / discharge cycle characteristics at most.

The content of the above-mentioned additive is preferably 0.5 to 20.0 parts by mass and 0.7 to 20.0 parts by mass with respect to 100 parts by mass of the organic solvent from the viewpoint of charge / discharge capacity, charge / discharge cycle characteristics, energy density and the like. 15.0 parts by mass is more preferable, and 1.0 to 10.0 parts by mass is further preferable. However, when only one kind of vinylene carbonate (VC) or the compound represented by the general formula (2) is used as an additive, it is easier to improve the charge / discharge cycle characteristics by using a small amount, so 100 parts by mass of the organic solvent. On the other hand, 0.5 to 5.0 parts by mass is preferable, 0.7 to 3.0 parts by mass is more preferable, and 1.0 to 2.0 parts by mass is further preferable. Even when only one type of additive is used, when only one type of fluoroethylene carbonate (FEC), trifluoromethylethylene carbonate, vinylethylene carbonate, etc. is used, it is better to increase the amount of charge / discharge. Since it is easy to improve the cycle characteristics, 0.5 to 20.0 parts by mass is preferable, 0.7 to 15.0 parts by mass is more preferable, and 1.0 to 10.0 parts by mass is preferable with respect to 100 parts by mass of the organic solvent. The unit is more preferable. Further, when two or more kinds of additives are used, for example, even when an additive having a preferable small amount of addition such as vinylene carbonate (VC) is used, the total content is increased. Since it is easy to improve the charge / discharge cycle characteristics and the energy density, the total content of the additives is preferably 1.0 to 20.0 parts by mass with respect to 100 parts by mass of the organic solvent, and is preferably 1.5. ~ 15.0 parts by mass is more preferable, and 2.0 to 10.0 parts by mass is further preferable.

(1-4) Lithium Salt The electrolytic solution for a non-aqueous secondary battery of the present invention preferably further contains a lithium salt. The lithium salt is not particularly limited, and examples thereof include an organic lithium salt having a sulfonyl group and an organic lithium salt having a boron atom. From the viewpoint of the charge / discharge cycle characteristics described above, when a lithium salt is contained, it is not an inorganic lithium salt (LiPF ₆ , LiBF ₄ , etc.) but an organic lithium salt having a sulfonyl group and an organic lithium salt having a boron atom. Is preferable.

The organic lithium salt having a sulfonyl group is not particularly limited as long as it is conventionally used in an electrolytic solution for a non-aqueous secondary battery, and is, for example, lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ); perfluoroalkane sulfonyl. Organic lithium salts with groups (lithium bis (trifluoromethanesulfonyl) imide (LiTFSI; Li (CF ₃ SO ₂ ) ₂ N), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N) Etc.), etc. Among them, an organic lithium salt having a perfluoroalkanesulfonyl group is preferable from the viewpoint of withstanding charging at a higher voltage and further improving charge / discharge cycle characteristics, and lithium bis (trifluoromethanesulfonyl). _Iimide (LiTFSI; Li (CF ₃ SO ₂ ) 2N) is more preferable. The organic lithium salt having these sulfonyl groups may be used alone or in combination of two or more.

The organic lithium salt having a boron atom is not particularly limited as long as it is conventionally used in an electrolytic solution for a non-aqueous secondary battery, and is, for example, lithium bis (oxalate) borate (LiBOB; LiB (C ₂ O ₄ ). ) ₂ ), lithium oxalate difluoroborate (LiBF ₂ (C ₂ O ₄ )), lithium bis (malonate) bolate (LiB (C ₃ O ₄ H ₂ ) ₂ ) and the like. Among them, lithium bis (oxalate) borate (LiBOB; LiB (C ₂ O ₄ ) ₂ ) is preferable from the viewpoint of withstanding charging at a higher voltage and further improving charge / discharge cycle characteristics. These organolithium salts having a boron atom may be used alone or in combination of two or more.

As the above-mentioned lithium salt, since the non-aqueous secondary battery of the present invention uses a lithium-free metal sulfide as the positive electrode active material, the influence on the charge / discharge cycle characteristics due to the reactivity with sulfur is taken into consideration. From the viewpoint of charge / discharge cycle characteristics, an organic lithium salt having a sulfonyl group is preferable, and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI; Li (CF ₃ SO ₂ ) 2N) is _more preferable.

In the electrolytic solution for a non-aqueous secondary battery of the present invention, the concentration of the above-mentioned lithium salt is not particularly limited, and is preferably 0.3 to 2.5 mol / L, preferably 1.0 to 2.5 mol / L, from the viewpoint of charge / discharge cycle characteristics. 2.0 mol / L is more preferable.

(1-5) Others In the electrolytic solution for a non-aqueous secondary battery of the present invention, the effect of the present invention is not impaired (for example, 0.01 to 0.2 mol / L, particularly 0.02 to 0.1 mol / L). If it is L), components other than the above, for example, other additives may be included. Examples of such other additives include tetrabutylammonium hexafluorophosphate, tetrabutylammonium perchlorate, tetramethylammonium tetrafluoroborate, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, and tetra bromide. Examples thereof include methylammonium, tetraethylammonium bromide, tetrabutylammonium bromide, biphenyl, trialkyl phosphate (trimethyl phosphate and the like). These other additives may be used alone or in combination of two or more.

The electrolytic solution for a non-aqueous secondary battery of the present invention is usually liquid, but a gel-like electrolyte gelled with a gelling agent made of a polymer or the like can also be used.

2. 2. Non-water secondary battery The non-water secondary battery of the present invention includes the above-mentioned electrolyte for a non-water secondary battery. For other configurations and structures, the configurations and structures employed in conventionally known non-aqueous secondary batteries may be applied. Usually, the non-aqueous secondary battery of the present invention may include a positive electrode, a negative electrode and a separator in addition to the above-mentioned electrolytic solution for a non-aqueous secondary battery.

(2-1) Positive Electrode As the positive electrode, a configuration in which a positive electrode mixture layer containing a positive electrode active material, a binder, and the like is formed on one side or both sides of a positive electrode current collector can be adopted.

In this positive electrode mixture layer, a binder is added to the positive electrode active material and the conductive auxiliary agent added as needed, and this is dispersed in an organic solvent to prepare a paste for forming the positive electrode mixture layer (in this case, in this case). The binder may be dissolved or dispersed in an organic solvent in advance), applied to the surface (one side or both sides) of the positive electrode current collector made of a metal foil or the like, and dried to form a positive electrode mixture layer. It can be manufactured through a process of processing as needed.

As the positive electrode active material, the above-mentioned lithium-free metal sulfide is adopted. The details of the lithium-free metal sulfide follow those described above.

As the conductive auxiliary agent, as in the case of a normal non-aqueous secondary battery, graphite; carbon black (acetylene black, Ketjen black, etc.); an amorphous carbon material such as a carbon material having amorphous carbon generated on the surface. Fibrous carbon (gas-phase grown carbon fiber, carbon fiber obtained by carbonizing after spinning pitch); carbon nanotube (various multi-layered or single-layer carbon nanotubes) and the like can be used. As the conductive auxiliary agent for the positive electrode, it may be used alone or in combination of two or more.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, styrene butadiene rubber, polyimide, polyvinyl alcohol, water-soluble carboxymethyl cellulose and the like.

The organic solvent used in producing the positive electrode mixture is not particularly limited, and examples thereof include N-methylpyrrolidone (NMP), which is used in the form of a paste using a positive electrode active material, a binder and the like. Can be done.

Regarding the composition of the positive electrode mixture layer, for example, the above-mentioned positive electrode active material is preferably about 70 to 95% by weight, and the binder is preferably about 1 to 30% by weight. When a conductive auxiliary agent is used, the positive electrode active material is about 50 to 90% by weight, the binder is about 1 to 20% by weight, and the conductive auxiliary agent is about 1 to 40% by weight. preferable. Further, the thickness of the positive electrode mixture layer is preferably about 1 to 100 μm per one side of the current collector.

As the positive electrode current collector, for example, a foil made of aluminum, stainless steel, nickel, titanium or an alloy thereof, punched metal, expanded metal, mesh or the like can be used, and aluminum having a thickness of about 10 to 30 μm is usually used. Foil is preferably used.

(2-2) Negative electrode As the negative electrode, a configuration in which a negative electrode mixture layer containing a negative electrode active material, a binder, and the like is formed on one side or both sides of a negative electrode current collector can be adopted.

This negative electrode mixture layer is formed into a sheet by mixing a binder with a negative electrode active material and a conductive auxiliary agent added as needed, and this is formed on the surface (one side) of a negative electrode current collector made of a metal foil or the like. Alternatively, it can be manufactured through a process of crimping to (both sides).

The negative electrode active material is not particularly limited, and for example, graphite (natural graphite, artificial graphite, etc.), difficult-to-sinter carbon, lithium metal, tin, silicon, alloys containing these, and SiO can be used. Preferably, a lithium metal, a lithium alloy, or the like can be used in the metallic lithium primary battery and the metallic lithium secondary battery, and in the lithium ion secondary battery, a material capable of doping and dedoping lithium ions (graphite (natural graphite, artificial)). Graphite, etc.), difficult-to-saturate carbon, etc.) can be used as the active material. These negative electrode active materials may be used alone or in combination of two or more.

As the conductive auxiliary agent, as in the case of a normal non-aqueous secondary battery, graphite; carbon black (acetylene black, Ketjen black, etc.); an amorphous carbon material such as a carbon material having amorphous carbon generated on the surface. Fibrous carbon (gas-phase grown carbon fiber, carbon fiber obtained by carbonizing after spinning pitch); carbon nanotube (various multi-layered or single-layer carbon nanotubes) and the like can be used. As the conductive auxiliary agent for the negative electrode, it may be used alone, or may be used in combination of two or more, or may not be used when the negative electrode active material has high conductivity.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, styrene butadiene rubber, polyimide, polyvinyl alcohol, water-soluble carboxymethyl cellulose and the like.

Regarding the composition of the negative electrode mixture layer, for example, it is preferable that the negative electrode active material is about 70 to 95% by weight and the binder is about 1 to 30% by weight. When a conductive auxiliary agent is used, the negative electrode active material is about 50 to 90% by weight, the binder is about 1 to 20% by weight, and the conductive auxiliary agent is about 1 to 40% by weight. preferable. Further, the thickness of the negative electrode mixture layer is preferably about 1 to 100 μm per one side of the current collector.

As the negative electrode current collector, for example, a foil made of aluminum, copper, stainless steel, nickel, titanium or an alloy thereof, punched metal, expanded metal, mesh, net or the like can be used, and the thickness is usually 5 to 5 or more. A copper foil of about 30 μm is preferably used.

(2-3) Separator The positive electrode and the negative electrode described above can be used, for example, in the form of a laminated electrode body laminated with a separator interposed therebetween, or a wound electrode body obtained by winding the same in a spiral shape.

The separator preferably has sufficient strength and can hold a large amount of electrolytic solution. From such a viewpoint, polyethylene, polypropylene, and ethylene-propylene copolymer weight having a thickness of 10 to 50 μm and an aperture ratio of 30 to 70%. Microporous films and non-woven fabrics containing one or more coalesced products are preferable.

Further, as the form of the non-aqueous secondary battery of the present invention, a tubular shape (square tubular shape, cylindrical shape, etc.) using a stainless steel can, an aluminum can, or the like as an outer can can be adopted. Further, a soft package battery having a laminated film integrated with a metal foil as an exterior body can also be adopted.

Hereinafter, the present invention will be described in detail based on examples, but it goes without saying that the present invention is not limited to the following examples.

Synthesis Example 1: Synthesis of vanadium sulfide (positive electrode active material) Commercially available vanadium sulfide ( _{III) (V2 S 3 ;} manufactured by High Purity Chemical Laboratory Co., Ltd.) and sulfur (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) Weighed in a glove box (dew point −80 ° C.) in an argon gas atmosphere so that the molar ratio was 1: 6, and sealed in a glass tube in vacuum. The vacuum-sealed sample was calcined at 400 ° C. for 5 hours in a tube furnace. The calcined sample was calcined in vacuum at 200 ° C. for 8 hours to desulfurize excess sulfur and synthesize crystalline vanadium sulfide VS ₄ (c-VS ₄ ).

Next, the obtained crystalline VS ₄ (c-VS ₄ ) was mechanically milled (balls) in a glove box (dew point -80 ° C) in an argon gas atmosphere with a ball mill device (PL-7 manufactured by Fritsch) for 40 hours. A low crystalline vanadium sulfide VS ₄ (a-VS ₄ ) was synthesized by carrying out a diameter of 4 mm and a rotation speed of 270 rpm), and used as a positive electrode active material. Regarding the obtained a-VS ₄ , no clear peak was observed other than the extremely small peak of V ₂ O ₃ which is a very small amount of impurities from the powder XRD measurement, and it was found that the a-VS 4 was completely amorphous. Do you get it.

Example 1: VC1.0 mass% / EC + PC (50:50) / LiTFSI1.0M
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 50: 50 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Was added so as to be the solvent standard), and 1.0 part by volume of vinylene carbonate (VC) was further added to 100 parts by volume of the mixed solvent to obtain an electrolytic solution for a non-aqueous secondary battery of Example 1. ..

Example 2: VC2.0 mass% / EC + PC (50:50) / LiTFSI1.0M
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 50: 50 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Was added so as to be the solvent standard), and 2.0 parts by volume of vinylene carbonate (VC) was further added to 100 parts by volume of the mixed solvent to obtain an electrolytic solution for a non-aqueous secondary battery of Example 2. ..

Example 3: VC5.0 mass% / EC + PC (50:50) / LiTFSI1.0M
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 50: 50 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Was added so as to be the solvent standard), and 5.0 parts by volume of vinylene carbonate (VC) was added to 100 parts by volume of the mixed solvent to obtain an electrolytic solution for a non-aqueous secondary battery of Example 3. ..

Example 4: FEC3.0% by mass / EC + PC (50:50) / LiTFSI1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. 2. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) so that the concentration is 1.0 mol / L (volume is based on the solvent), and further add fluoroethylene carbonate (FEC) to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 4.

Example 5: FEC 1.0% by mass / EC + PC (50:50) / LiTFSI1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. Bis (trifluoromethanesulfonyl) imide (LiTFSI) was added so that the concentration was 1.0 mol / L (volume is based on the solvent), and fluoroethylene carbonate (FEC) was further added to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 5.

Example 6: FEC 5.0% by mass / EC + PC (50:50) / LiTFSI1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. 5. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) so that the concentration is 1.0 mol / L (volume is based on the solvent), and further add fluoroethylene carbonate (FEC) to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 6.

Example 7: DFOB 2.0% by mass / EC + PC (50:50) / LiTFSI1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) to a concentration of 1.0 mol / L (volume is based on the solvent), and add difluoro (oxalate) lithium borate (DFOB) to 100 parts by mass of the mixed solvent. 2.0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 7.

Example 8: FEC 10.0% by mass / EC + PC (50:50) / LiTFSI 1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. Bis (trifluoromethanesulfonyl) imide (LiTFSI) was added so that the concentration was 1.0 mol / L (volume is based on the solvent), and fluoroethylene carbonate (FEC) was further added to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 6.

Example 9: FEC 10.0% by mass / EC + PC (50:50) / LiTFSI2.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. Bis (trifluoromethanesulfonyl) imide (LiTFSI) was added so that the concentration was 2.0 mol / L (volume is based on the solvent), and fluoroethylene carbonate (FEC) was further added to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 9.

Example 10: FEC 5.0% by mass / EC + PC (50:50) / LiTFSI2.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. 5. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) so that the concentration is 2.0 mol / L (volume is based on the solvent), and further add fluoroethylene carbonate (FEC) to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 10.

Example 11: FEC3.0% by mass / EC + PC (50:50) / LiTFSI2.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 50: 50 (volume ratio)) and lithium. 2. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) so that the concentration is 2.0 mol / L (volume is based on the solvent), and further add fluoroethylene carbonate (FEC) to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 11.

Example 12: FEC8.0 mass% / EC + PC (50:50) / LiTFSI1.0M Ethylene carbonate (EC) and propylene carbonate (PC) mixed solvent (EC: PC = 50: 50 (volume ratio)) and lithium 3. Add bis (trifluoromethanesulfonyl) imide (LiTFSI) so that the concentration is 1.0 mol / L (volume is based on the solvent), and further add fluoroethylene carbonate (FEC) to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 12.

Example 13: FEC 1.0% by mass / EC + PC (10:90) / LiTFSI1.0M A mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 10: 90 (volume ratio)) and lithium. Bis (trifluoromethanesulfonyl) imide (LiTFSI) was added so that the concentration was 1.0 mol / L (volume is based on the solvent), and fluoroethylene carbonate (FEC) was further added to 100 parts by mass of the mixed solvent. 0 parts by volume was added to obtain an electrolytic solution for a non-aqueous secondary battery of Example 13.

Example 14: FEC 5.0% by mass + VC 5.0% by mass / EC + PC (50:50) / LiTFSI 1.0M
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 50: 50 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Is added so as to be the solvent standard), and 5.0 parts by volume of fluoroethylene carbonate (FEC) and 5.0 parts by mass of vinylene carbonate (VC) are added to 100 parts by mass of the mixed solvent. An electrolytic solution for a non-aqueous secondary battery of Example 14 was obtained.

Comparative Example 1: No additive / EC + PC (50:50) / LiTFSI 1.0M
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 50: 50 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Was added so as to be the solvent standard) to obtain an electrolytic solution for a non-aqueous secondary battery of Comparative Example 1.

Comparative Example 2: No additive / EC + PC (10:90)
Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) at a concentration of 1.0 mol / L (volume) in a mixed solvent (EC: PC = 10: 90 (volume ratio)) of ethylene carbonate (EC) and propylene carbonate (PC). Was added so as to be based on the solvent), and an electrolytic solution for a non-aqueous secondary battery of Comparative Example 2 was obtained.

Test Example 1: Charging / discharging test The _VS4 powder obtained in Synthesis Example 1 was used as the positive electrode active material, and the electrolytic solutions for non-aqueous secondary batteries obtained in Examples 1 to 13 and Comparative Examples 1 and 2 were used as follows. A test electrochemical cell (lithium secondary battery) was prepared by the above method, and at 25 ° C., the charge / discharge rate was 0.1 C (1C = 747 mAh / g), and the voltage was in the range of 2.6 to 1.5 V. The constant current charge / discharge measurement was performed for 100 cycles with a pause time of 10 minutes between cycles.

As a method for producing a test electrochemical cell, first, the working electrode (positive electrode) is 1 mg of Ketjen black and polytetrafluoroethylene (PTFE) as a binder with respect to 10 mg of VS ₄ powder obtained in Synthesis Example 1. ) 1 mg was added, mixed in a mortar for 8 minutes, and then attached to an aluminum mesh to prepare the product. Lithium metal was used as the counter electrode (negative electrode). Polypropylene was used as the separator. Table 1 shows the results of charge / discharge cycle characteristics (capacity retention rate at 100 cycles). The capacity retention rate is the ratio of the capacity measured after 100 cycles when the capacity at the start of the cycle test (first cycle) is 100. The higher the capacity retention rate, the better the battery life characteristics. Show that.

The capacity retention rate is not determined based on a threshold value, but considering that an average charge / discharge efficiency of 99.5% or more in at least each cycle is a good life characteristic, after 100 cycles. Is 0.995 ¹⁰⁰ = 0.606, and after 100 cycles, all the examples show a capacity retention rate of more than 60%, while all the comparative examples show a capacity retention rate of less than 60%. Therefore, the embodiment of the present invention has excellent life characteristics.

The electrolytic solution for a non-aqueous secondary battery of the present invention and the non-aqueous secondary battery using the same can be used for various known applications. Specific examples include notebook computers, mobile phones, electric vehicles, load leveling power supplies, renewable energy storage power supplies, and the like.

Claims (15)

An electrolytic solution for a non-aqueous secondary battery used in a non-aqueous secondary battery that uses a lithium-free transition metal sulfide as a positive electrode active material.
The electrolytic solution is an electrolytic solution for a non-aqueous secondary battery containing an organic solvent containing a cyclic carbonate compound and an additive. The additive is the general formula (1) :.

[In the formula, R ¹ and R ² are the same or different and indicate a hydrogen atom or a halogen atom. Bonds shown by solid and dashed lines indicate single or double bonds. ]
The compound represented by, or the general formula (2) :.

[In the formula, R ³ is the same or different and represents a halogen atom. M indicates a counter cation. ]
The electrolytic solution for a non-aqueous secondary battery according to claim 1, which is a compound represented by. The compound represented by the general formula (1) contains at least one selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), trifluoromethylethylene carbonate and vinylethylene carbonate.
The electrolytic solution for a non-aqueous secondary battery according to claim 2, wherein the compound represented by the general formula (2) contains lithium difluoro (oxalate) borate (DFOB). The electrolytic solution for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the content of the additive is 0.5 to 20 parts by mass with respect to 100 parts by mass of the organic solvent. Any of claims 1 to 4, wherein the total amount of the organic solvent is 100% by volume, the content of the cyclic carbonate compound is 80 to 100% by volume, and the content of the chain carbonate compound is 0 to 20% by volume. The electrolytic solution for a non-aqueous secondary battery according to item 1. The non-aqueous battery according to claim 5, wherein the chain carbonate compound is at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and methyl propyl carbonate. Electrolyte for next battery. The non-aqueous secondary battery according to any one of claims 1 to 6, wherein the cyclic carbonate compound is at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate. Electrolyte. The non-aqueous secondary according to any one of claims 1 to 7, wherein the lithium-free transition metal sulfide is at least one selected from the group consisting of vanadium sulfide, molybdenum sulfide, and iron sulfide. Electrolyte for batteries. The electrolytic solution for a non-aqueous secondary battery according to any one of claims 1 to 8, further comprising a lithium salt. The electrolytic solution for a non-aqueous secondary battery according to claim 9, wherein the lithium salt is at least one selected from the group consisting of an organic lithium salt having a sulfonyl group and an organic lithium salt having a boron atom. The lithium salt is lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N). , Lithium Hexafluorophosphate (LiPF ₆ ), Lithium Tetrafluoroborate (LiBF ₄ ), Lithium Hexafluoroarsenate (LiAsF ₆ ), Lithium Perchlorate (LiClO ₄ ), Lithium Bis (oxalate) Borate (LiBOB), Lithium Claim 9 or at least one selected from the group consisting of oxalate difluoroborate (LiBF ₂ (C ₂ O ₄ )) and lithium bis (malonate) bolate (LiB (C ₃ O ₄ H ₂ ) ₂ ). 10. The electrolytic solution for a non-aqueous secondary battery according to 10. The electrolytic solution for a non-aqueous secondary battery according to any one of claims 9 to 11, wherein the concentration of the lithium salt is 0.3 to 2.5 mol / L. The electrolytic solution for a non-aqueous secondary battery according to any one of claims 1 to 12, which is an electrolytic solution for a lithium ion secondary battery. A non-aqueous secondary battery comprising the electrolytic solution for a non-aqueous secondary battery according to any one of claims 1 to 13. The non-aqueous secondary battery according to claim 14, which is a lithium ion secondary battery.