WO2014156110A1

WO2014156110A1 - Non-aqueous electrolyte secondary cell

Info

Publication number: WO2014156110A1
Application number: PCT/JP2014/001678
Authority: WO
Inventors: 顕岸本
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2013-03-27
Filing date: 2014-03-24
Publication date: 2014-10-02
Also published as: CN105190983A

Abstract

A non-aqueous electrolyte secondary cell provided with a non-aqueous electrolyte containing boric acid and one or more types of substances selected from a group consisting of: calcium oxide, magnesium oxide, sodium sulfate, phosphorus pentoxide, activated alumina, activated carbon, a compound having an oxalato borate structure, a cyclic carbonate ester having an unsaturated structure, and a cyclic sulfonic acid compound.

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte.

Non-aqueous electrolyte batteries typified by lithium ion secondary batteries are widely used as power supplies for mobile devices typified by mobile phones because of their high energy density. In the future, non-aqueous electrolyte batteries are expected to be used for power storage, electric vehicles, hybrid vehicles, and the like.

In recent years, application of nonaqueous electrolyte batteries to the automotive field such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles has been studied, and some have been put into practical use. These automobile batteries are required to have high energy density and excellent charge / discharge cycle performance. In other words, when a vehicle battery such as an electric vehicle, a hybrid vehicle, or a plug-in hybrid is charged, it is expected that a certain travelable distance is secured. In general, the discharge capacity of a nonaqueous electrolyte secondary battery gradually decreases when charging and discharging are repeated. When the battery is repeatedly charged, the extent to which the travelable distance becomes shorter increases as the degree of decrease in the discharge capacity increases. For this reason, it becomes difficult to predict the next time when charging is required, and there is a possibility that the car stops while traveling due to a lack of charging time.

Patent Document 1 describes a lithium battery containing a boron compound in an electrolytic solution containing a fluorine compound (Claim 1), a lithium battery containing a dehydrating agent in the electrolytic solution (Claim 2), and boron. As the compound, “for example, B ₂ O ₃ , H ₃ BO ₃ , (CH ₃ O) ₃ B, (C ₂ H ₅ O) ₃ B, (CH ₃ O) ₃ B—B ₂ O _{3 and the} like can be used. Among them, B ₂ O ₃ is particularly desirable ”(paragraph 0037), and the dehydrating agent includes“ activated alumina, zeolite, sodium sulfate, activated carbon, silica gel, magnesium oxide, calcium oxide, etc. ”(paragraph 0040). It is described. In addition, there is a description that “when an electrolytic solution containing a boron compound and a dehydrating agent is used, the effect becomes even more remarkable” (paragraph 0072). Further, in “Example 1”, EC / PC / DME (2/2/1) -1MLiPF ₆ is used as a non-aqueous electrolyte of a non-aqueous electrolyte lithium secondary battery using LiCoO ₂ for the positive electrode. It is specifically described that an electrolytic solution to which 8 wt% B ₂ O ₃ was added was used. In “Example 3”, 0.8 wt% in EC / PC / DME (2/2/1) -1MLiPF ₆ was used as a nonaqueous electrolyte for a lithium secondary battery using LiCoO ₂ as a positive electrode. Specifically, it was described that an electrolyte solution containing 5 wt% magnesium oxide as a dehydrating agent and B ₂ O ₃ was used. In addition, the inclusion of the boron compound in the electrolytic solution can greatly reduce the acidic substance produced by the water contained in the electrolysis solution. This is due to the deterioration of the electrolytic solution and the container structure due to the corrosion of the battery container. This results in preventing the negative electrode activity from being reduced due to metal ions ”(paragraph 0039),“ By including these dehydrating agents, the electrolyte is prevented from being decomposed by water, and thus the electrolyte is deteriorated, and the acidic substance. Can be suppressed ”(paragraph 0041).

Patent Document 2 includes a substance that generates water by increasing the temperature inside the nonaqueous electrolyte secondary battery (Claim 1), and a substance that generates water by increasing temperature is included in the nonaqueous electrolyte ( (Claim 3), it is described that the substance which produces | generates water by a temperature rise is a boric acid (Claim 7). In addition, “Example 1” describes a nonaqueous electrolyte secondary battery in which a positive electrode paste containing LiNiO ₂ and H ₃ BO ₃ is applied to a titanium core, dried at 95 ° C., and rolled to form a positive electrode. “Example 2” describes a non-aqueous electrolyte secondary battery in which a negative electrode paste containing a carbon material and H ₃ BO ₃ is applied to a copper core, dried at 95 ° C., and rolled to form a negative electrode. Yes. In addition, there is a description that “a non-aqueous electrolyte is an equal volume mixed solution of ethylene carbonate and dimethoxyethane in which 1 mol / l lithium perchlorate is dissolved” (paragraph 0013).

Patent Document 3 discloses “a lithium secondary battery using a lithium-containing manganese oxide as a positive electrode, wherein the positive electrode contains a boron compound that can be dissolved in an electrolytic solution” (claim). Item 1), “The boron compound is a boron compound containing at least one selected from B ₂ O ₃ , H ₃ BO ₃ , HBO ₂ , and H ₂ B ₄ O _7. The lithium secondary battery according to claim 2 ”(Claim 2),“ However, when LiMn ₂ O ₄ is used for the positive electrode and a halogen-containing lithium salt such as LiPF ₄ is used for the electrolyte, the lithium salt reacts with a trace amount of moisture. and, generating a hydrohalic acid such as hydrofluoric acid. the hydrohalic acid can be prepared by dissolving the LiMn ₂ O ₄ positive electrode, the form of the high resistance coating such as MnF ₂ on the carbon surface of the negative electrode And has been a cause of reducing the cycle performance. "(Paragraph 0003), a method of adding a" boron compound cathode, a mixture of H ₃ BO ₃ in the lithium-containing manganese oxide as a positive electrode active material However, since H ₃ BO ₃ contains many hydrogen atoms that react with lithium and may cause irreversible side reactions in the battery, the positive electrode is heated to 100 ° C. to 140 ° C. Alternatively, it is preferable to perform heat treatment at a temperature higher than that.It is considered that H ₃ BO ₃ is changed to HBO ₂ , H ₂ B ₄ O _7, etc. by the heat treatment ”(paragraph 0009). . In the “Example”, a positive electrode obtained by heat-treating a polytetrafluoroethylene sheet electrode containing spinel manganese and H ₃ BO ₃ at 90 to 300 ° C. for 40 hours under reduced pressure was used, and EC / DEC (1/1 It is described that, as a result of charging a battery combined with -1MLiPF ₆ electrolyte at a constant current and a constant voltage at 4.4 V, the cycle life was superior to that of a boron compound-free product. It is also described that it is estimated that H ₃ BO _{3 in the} positive electrode is changed to H ₃ BO ₄ by heat treatment at 90 ° C. for 40 hours under reduced pressure (paragraphs 0033 to 0034).

The abstract of patent document 4 and claim 1 include: “a non-aqueous electrolyte that suppresses an increase in electrode interface resistance, gives the battery excellent load characteristics and low-temperature characteristics, and provides excellent life characteristics; For the purpose of “providing a secondary battery having excellent life characteristics using a non-aqueous electrolytic solution containing a boric acid ester represented by the formula (1), a non-aqueous solvent and an electrolyte, and a battery using the same. The invention consisting of “secondary battery” is described, B (OR ¹ ) (OR ² ) (OR ³ ) is described as formula (1), and “R ¹ to R ³ may be the same or different. , Represents a hydrogen, metal, or organic group, and may be bonded to each other. However, there is no description about using boric acid. Further, in the column of Examples of Patent Document 4, in order to evaluate the characteristics of the non-aqueous electrolyte secondary battery using LiCoO ₂ for the positive electrode, and the charge condition and 4.2V constant voltage or 4.1V constant voltage It is described.

JP-A-9-139232 Japanese Patent Laid-Open No. 11-191417 JP 2001-257003 A JP 2003-132946 A

An object of the present invention is to provide a high-performance nonaqueous electrolyte battery.

The present invention is from the group consisting of calcium oxide, magnesium oxide, sodium sulfate, diphosphorus pentoxide, activated alumina, activated carbon, a compound having an oxalate borate structure, a cyclic carbonate having an unsaturated structure, and a cyclic sulfonic acid compound. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing one or two or more selected substances and boric acid.

The present invention can be realized not only as such a non-aqueous electrolyte secondary battery, but also as a battery module including a plurality of such non-aqueous electrolyte secondary batteries. Further, it can be realized as an electric vehicle (EV), a hybrid vehicle (HEV), or a plug-in hybrid vehicle (PHEV) equipped with the battery module.

According to the present invention, a high-performance nonaqueous electrolyte battery can be provided.

The figure which shows the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery which relates to the preliminary test The figure which shows the charge / discharge cycle performance of the nonaqueous electrolyte secondary battery which relates to the preliminary test The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example The figure which shows the charging / discharging cycle performance of the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example External perspective view showing one embodiment of a nonaqueous electrolyte secondary battery Schematic showing a power storage device comprising a plurality of non-aqueous electrolyte secondary batteries Schematic showing an automobile equipped with a power storage device

(Knowledge that became the basis of the present invention)
The inventors examined various boric acid compounds as additives to be added to the non-aqueous electrolyte as described later as a preliminary test. As a result, it was found that by selecting boric acid, the charge / discharge cycle performance of a non-aqueous electrolyte secondary battery using the boric acid, particularly the charge / discharge cycle performance under high voltage operation, can be improved. Based on this knowledge, the present inventor wanted to further improve the battery performance.

The configuration and operational effects of the present invention will be described with a technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

Since boric acid is an extremely inexpensive material, selecting boric acid not only provides an effect superior to that of other boron compounds, but can also provide a nonaqueous electrolyte battery at low cost.

The non-aqueous electrolyte secondary battery contains one or more substances selected from the group consisting of calcium oxide, magnesium oxide, sodium sulfate, diphosphorus pentoxide, activated alumina, and activated carbon, and boric acid. By providing the non-aqueous electrolyte, it is possible to provide a non-aqueous electrolyte secondary battery that is excellent in charge / discharge cycle performance and in which battery swelling is suppressed.

A nonaqueous electrolyte secondary battery is provided with a nonaqueous electrolyte containing a compound having an oxalate borate structure and boric acid, thereby providing a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle performance. can do.

The non-aqueous electrolyte secondary battery is provided with a non-aqueous electrolyte containing a cyclic carbonate or cyclic sulfonic acid compound having an unsaturated structure and boric acid, thereby providing excellent charge / discharge cycle performance and storage performance. In addition, an excellent non-aqueous electrolyte secondary battery can be provided.

The non-aqueous electrolyte can contain 0.03 mol / l or less of boric acid.

As will be described later, the present inventors have found that the amount of boric acid contained in the nonaqueous electrolyte to which boric acid is added may be reduced compared to the amount of boric acid added when adjusting the nonaqueous electrolyte. Even if it exists, it discovered that the nonaqueous electrolyte to which at least 0.5 mass% or more boric acid was added contains boric acid. Moreover, the nonaqueous electrolyte battery using the nonaqueous electrolyte to which 0.5% by mass or more of boric acid was added was found to exhibit excellent battery performance. In addition, a non-aqueous electrolyte battery manufactured using a non-aqueous electrolyte to which 0.5% by mass or more of boric acid is added can be used in the non-aqueous electrolyte even if it is used with charge / discharge. It was found to contain.

The method for adjusting the nonaqueous electrolyte according to the present invention is not limited at all. For example, a general electrolytic solution using LiPF ₆ as an electrolyte salt has calcium oxide, magnesium oxide, sodium sulfate, diphosphorus pentoxide, activated alumina, activated carbon, a compound having an oxalate borate structure, and an unsaturated structure. It can be obtained by adding one or two or more substances selected from the group consisting of cyclic carbonates and cyclic sulfonic acid compounds and boric acid. The boric acid is represented by the chemical formula H ₃ BO ₃ or B (OH) ₃ and can be obtained as a reagent or the like. In addition, the boric acid ester whose H part of the above chemical formula is a hydrocarbon group is inferior to boric acid.

The amount of boric acid added in the case of adding boric acid to the electrolyte solution containing the electrolyte salt is preferably 0.2% by mass or more, more preferably 0.5% by mass or more in order to sufficiently exhibit the effects of the present invention. . Moreover, 2 mass% or less is preferable and 1.5 mass% or less is more preferable in order to reduce the possibility that the discharge capacity will decrease.

The calcium compound or magnesium compound that can be used in the present invention is not particularly limited. In the present invention, it is not always clear about the action mechanism that suppresses the swelling of the battery during production by using boric acid and calcium oxide and / or magnesium oxide together, but calcium oxide and / or magnesium oxide is non-aqueous. The present inventor speculates that the fluorine ions are inactivated by reacting with fluorine ions in the electrolyte to produce a compound having a Ca—F bond or an Mg—F bond. In Examples to be described later, the effect of CaO and MgO was confirmed. However, the effect of the present invention is exhibited as long as the compound can react with fluorine ions to form a compound having a Ca—F bond or an Mg—F bond. It is thought.

It is preferable that the amount of calcium oxide and / or magnesium oxide added to the non-aqueous electrolyte is not too small because the effects of the present invention can be reliably achieved. The total amount of calcium oxide and / or magnesium oxide added to the non-aqueous electrolyte may not necessarily be dissolved in the non-aqueous electrolyte. Fluorine ions may be generated in the electrolyte solution not only during the battery manufacturing process but also during battery use. Therefore, even in such a case, calcium oxide and / or part of magnesium oxide added to the nonaqueous electrolyte is not dissolved as a sufficient source of Ca or Mg to inactivate the generated fluorine ions. The aspect which contains in the state of is preferable. However, the amount of calcium oxide and / or magnesium oxide added to the non-aqueous electrolyte is preferable because it can be easily handled during production by making it not too much. In this respect, the amount of calcium oxide and / or magnesium oxide added to the nonaqueous electrolyte is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. . Moreover, less than 5 mass% is preferable, 3 mass% or less is more preferable, and 2 mass% or less is further more preferable.

The amount of sodium sulfate added to the non-aqueous electrolyte is preferably not too small because the effects of the present invention can be reliably achieved. On the other hand, the total amount of sodium sulfate added to the non-aqueous electrolyte does not necessarily have to be dissolved in the non-aqueous electrolyte. Fluorine ions may be generated in the electrolytic solution not only during the battery manufacturing process but also during battery use. Therefore, even in such a case, a part of sodium sulfate added to the non-aqueous electrolyte is contained in an undissolved state as a sufficient source of Na for inactivating the generated fluorine ions. Embodiments are preferred. However, the amount of sodium sulfate added to the non-aqueous electrolyte is preferable because it can be easily handled during production by making the amount not too large. From this viewpoint, the amount of sodium sulfate added to the nonaqueous electrolyte is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. Moreover, less than 5 mass% is preferable, 3 mass% or less is more preferable, and 2 mass% or less is further more preferable.

Diphosphorus pentoxide is also called phosphorus pentoxide and is a compound represented by the chemical formula P ₂ O ₅ . The amount of diphosphorus pentoxide added to the non-aqueous electrolyte is preferably not too small because the effects of the present invention can be reliably exhibited. On the other hand, the total amount of diphosphorus pentoxide added to the non-aqueous electrolyte does not necessarily have to be dissolved in the non-aqueous electrolyte. Although the mechanism of action of diphosphorus pentoxide in the present invention is not clear, the effect of the present invention is exhibited by capturing or inactivating diphosphorus pentoxide on a substance remaining or generated in the non-aqueous electrolyte. Assuming that, such a substance cannot be denied or generated even during the use of the battery as well as during the battery manufacturing process. Therefore, even in such a case, in order to make diphosphorus pentoxide act effectively, an embodiment in which a part of diphosphorus pentoxide added to the nonaqueous electrolyte is contained in an undissolved state is preferable. However, the amount of diphosphorus pentoxide added to the non-aqueous electrolyte is preferable because it can be easily handled during production by making the amount not too large. In this respect, the amount of diphosphorus pentoxide added to the nonaqueous electrolyte is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. Moreover, less than 5 mass% is preferable, 3 mass% or less is more preferable, and 2 mass% or less is further more preferable.

Activated carbon (Activated Charcoal, Activated Carbon) is a kind of amorphous carbon that is obtained by activating carbon and other carbon materials as raw materials with gas and chemicals at high temperatures. Examples of activated carbon materials include coconut shell, sawdust, and bituminous coal. The methylene blue adsorption amount is preferably 120 ml / g or more, and more preferably 170 ml / g or more. The amount of the activated carbon added to the non-aqueous electrolyte is preferably not too small because the effects of the present invention can be reliably achieved. Further, the amount of activated carbon added to the non-aqueous electrolyte is preferable because it can be handled easily during production and the insulation between the positive and negative electrodes can be reliably maintained by making the amount not too large. In this respect, the amount of activated carbon added to the nonaqueous electrolyte is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. Moreover, less than 5 mass% is preferable, 3 mass% or less is more preferable, and 2 mass% or less is further more preferable.

Activated alumina is a compound represented by the chemical formula Al ₂ O ₃ containing aluminum oxide having a spinel crystal structure called γ-alumina. Active alumina often contains α-alumina in addition to the main component γ-alumina. The specific surface area is preferably 120 m ² / g or more, and more preferably 300 m ² / g or more. The amount of the activated alumina added to the non-aqueous electrolyte is preferably not too small because the effects of the present invention can be reliably achieved. On the other hand, the activated alumina added to the non-aqueous electrolyte does not necessarily have to be completely dissolved in the non-aqueous electrolyte. Although it is not clear about the action mechanism of the activated alumina in the present invention, it is assumed that the activated alumina captures or inactivates a substance remaining or generated in the non-aqueous electrolyte so that the effect of the present invention is exhibited. In such a case, there is an undeniable possibility that such a substance remains or is generated not only during the manufacturing process of the battery but also during the use of the battery. Therefore, even in such a case, in order to make activated alumina act effectively, an embodiment in which a part of activated alumina added to the nonaqueous electrolyte is contained in an undissolved state is preferable. However, the amount of activated alumina added to the non-aqueous electrolyte is preferable because it can be easily handled during production by making the amount not too large. From this viewpoint, the amount of activated alumina added to the nonaqueous electrolyte is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1.0% by mass or more. Moreover, less than 5 mass% is preferable, 3 mass% or less is more preferable, and 2 mass% or less is further more preferable.

Examples of the compound having an oxalate borate structure include a compound having a bisoxalate borate structure. For example, lithium bisoxalate borate (hereinafter also referred to as “LiBOB”) represented by LiC ₄ BO ₈ is preferable. Alkali metal compounds such as sodium bisoxalate borate and potassium bisoxalate borate may be used. _Further, it may be an alkali metal compound difluoro oxalate borate represented by LiC 2 _BF 2 _{O 4.}

The addition amount of the compound having an oxalate borate structure is preferably 0.2% by mass or more, more preferably 0.5% by mass or more in terms of lithium bisoxalate borate in order to sufficiently exhibit the effects of the present invention. . Moreover, 2 mass% or less is preferable and 1.5 mass% or less is more preferable in order to reduce the possibility that the discharge capacity will decrease.

Examples of the cyclic carbonate having an unsaturated bond include vinylene carbonate, styrene carbonate, catechol carbonate, vinyl ethylene carbonate, 1-phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate and the like. These may be used alone or in combination of two or more.

Here, when the non-aqueous solvent contains a cyclic carbonate such as ethylene carbonate and a chain carbonate such as ethyl methyl carbonate and diethyl carbonate, the cyclic carbonate occupies the total volume of the cyclic carbonate and the chain carbonate. The volume ratio is preferably 10% by volume or more, and more preferably 20% by volume or more. Moreover, 40 volume% or less is preferable and 30 volume% or less is more preferable.

Examples of the cyclic sulfonic acid compound include compounds represented by the following general formula.

[In Chemical Formula 1, R ₁ to R ₄ are each a hydrogen atom or the same or different alkyl group, alkoxy group, halogen, alkyl group having halogen, or aryl group, and n is 1 or 2. ]

Among these, unsaturated sultone in which n = 1 and R ₁ to R ₄ are both hydrogen atoms, that is, 1,3-propene sultone is preferable.

[In General Formula (1), R ¹ and R ² represent a group bonded to each other represented by Formula (2), or one of them is represented by General Formula (3), Formula (4) or Formula ( 5) (the part of * is bonded to either R ¹ or R ² ) and the other is a hydrogen atom. R ³ is an alkyl group having 1 to 3 carbon atoms which may contain halogen. ]

Among the cyclic sulfonic acid compounds represented by the general formula (1), there are compounds having two or more asymmetric carbons and having stereoisomers (diastereomers). In the present specification, the cyclic sulfonic acid compound represented by the general formula (1) includes a mixture of such diastereomers.

In the general formula (1), the cyclic sulfonic acid compound in which ^one of R ¹ and R ² is a group represented by the formula (4) and the other is a hydrogen atom corresponds to diglycol sulfate (DGLST).

Cyclic sulfonic acid compounds in which R ¹ and R ² represent a group bonded to each other represented by the formula (2) are erythritol (erythritol) or a quaternary alcohol similar to threitol, and are combined with sulfonic acid. It is a compound similar to DGLST. A cyclic sulfonic acid compound in which either ^one of R ¹ and R ² is a group represented by the formula (5) and the other is a hydrogen atom also has two rings combined with a sulfonic acid. A compound.

The cyclic sulfonic acid compound in which either ^one of R ¹ and R ² is a group represented by the general formula (3) and the other is a hydrogen atom uses a tertiary alcohol as a raw material and has one ring. This compound combines with the sulfonic acid, and has the same effect as DGLST. When R ³ is a methyl group, it is 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, and when R ³ is an ethyl group, 4-ethylsulfonyloxymethyl-2, 2-dioxo-1,3,2-dioxathiolane.

Among these, DGLST having a small molecular weight is preferable because the content in the non-aqueous electrolyte is small.

The action mechanism of the cyclic sulfonic acid compound is not always clear. Hereinafter, an estimation mechanism of charge / discharge cycle performance improvement in the case of using a non-aqueous electrolyte containing 1,3-propene sultone or diglycol sulfate (DGLST) is described.

Generally, in a nonaqueous electrolyte battery, it is considered that continuous reductive decomposition of an organic solvent in an electrolyte solution causes a decrease in battery life such as cycle characteristics on the negative electrode. Here, the reductive decomposition potential of 1,3-propene sultone or DGLST is about 1.1 V (vs. Li ^/ Li ⁺ ), which is relatively higher than other common solvents, and therefore, a non-aqueous electrolyte secondary battery In the first charge, a film derived from 1,3-propene sultone or DGLST is formed on the negative electrode prior to other solvents. It is estimated that the continuous reductive decomposition of the organic solvent is suppressed by this coating. Therefore, it is considered that the life of the non-aqueous electrolyte secondary battery such as cycle characteristics is improved by including 1,3-propene sultone or DGLST in the non-aqueous electrolyte.

The content of the cyclic sulfonic acid compound is preferably included to the extent that the cyclic sulfonic acid compound is detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery. Thus, when the cyclic sulfonic acid compound is contained to the extent that it is detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery, the charge / discharge cycle performance can be improved. In addition, when the non-aqueous electrolyte secondary battery is in the state after initial activation (before use, at the time of shipment), when the cyclic sulfonic acid compound is detected from the non-aqueous electrolyte, the battery is used. Is particularly preferable because the cycle characteristics can be sufficiently improved.

The amount of the cyclic sulfonic acid compound detected from the nonaqueous electrolyte in the nonaqueous electrolyte secondary battery is preferably 0.01% by mass or more and less than 5% by mass. If the detected cyclic sulfonic acid compound is 0.01% by mass or more, it is preferable because cycle characteristics can be sufficiently improved. Moreover, it is preferable to make the detected cyclic sulfonic acid compound less than 5% by mass because the cost of the non-aqueous electrolyte secondary battery can be suppressed while maintaining the effects of the present invention. Especially preferably, it is 0.05 mass% or more and 4 mass% or less.

The detection (qualitative and quantitative) of the cyclic sulfonic acid compound contained in the non-aqueous electrolyte can be performed by GC-MS measurement or LC-MS measurement.

In preparing a non-aqueous electrolyte containing a cyclic sulfonic acid compound, the order of mixing the electrolyte salt, non-aqueous solvent and cyclic sulfonic acid compound constituting the non-aqueous electrolyte is arbitrary. In the examples described later, after dissolving an electrolyte salt in a non-aqueous solvent, a non-aqueous electrolyte containing a cyclic sulfonic acid compound is prepared by a procedure of adding a cyclic sulfonic acid compound. Even if a non-aqueous electrolyte containing the prepared cyclic sulfonic acid compound is used, the effect of the present invention is exhibited. Similarly, when the nonaqueous electrolyte contains a compound other than the cyclic sulfonic acid compound, the mixing order is arbitrary.

The non-aqueous solvent contained in the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the present invention is not limited, and non-aqueous solvents generally proposed for use in lithium batteries and the like can be used. For example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain forms such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate Carbonates; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, Ethers such as methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof alone or in combination thereof Although the above mixture etc. can be mentioned, it is not limited to these.

When the non-aqueous solvent contains a cyclic carbonate such as ethylene carbonate and a chain carbonate such as ethyl methyl carbonate and diethyl carbonate, the volume ratio of the cyclic carbonate in the total volume of the cyclic carbonate and the chain carbonate is 10 volume% or more is preferable and 20 volume% or more is more preferable. Moreover, 40 volume% or less is preferable and 30 volume% or less is more preferable.

Examples of the electrolyte salt used for the non-aqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ (SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ , NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate Organic ion salts such as lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, and the like, and these ionic compounds can be used alone or in admixture of two or more.

There is no restriction | limiting in particular as a positive electrode active material used for the positive electrode of the nonaqueous electrolyte secondary battery which concerns on this invention, A various material can be used suitably. For example, lithium transition metal complex oxide is mentioned. Examples of the lithium transition metal composite oxide include spinel type lithium manganese oxide represented by LiMn ₂ O _{4 and the} like, spinel type lithium nickel manganese oxide represented by LiNi _1.5 Mn ₀₅ O _{4 and the} like. Lithium transition metal oxide having a spinel crystal structure, LiCoO ₂ , LiNiO ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li _1.1 Co _2/3 Ni _1/6 Mn _1/6 Examples include LiMeO ₂ type (Me is a transition metal) lithium transition metal composite oxide having an α-NaFeO ₂ structure typified by O ₂ and the like.

Further, a so-called “lithium-excess type” lithium transition metal composite oxide that can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0) may be used. Here, the Li / Me ratio is preferably 1.25 to 1.6. If the Li / Me ratio is β, β = (1 + α) / (1−α). For example, when Li / Me is 1.5, α = 0.2. The ratio of elements such as Co, Ni and Mn constituting the transition metal element constituting the lithium transition metal composite oxide can be arbitrarily selected according to the required characteristics, but the discharge capacity is large and the initial charge is high. The molar ratio Co / Me of Co to the transition metal element Me is preferably 0.02 to 0.23, and preferably 0.04 to 0. 0, in that a nonaqueous electrolyte secondary battery having excellent discharge efficiency can be obtained. 21 is more preferable, and 0.06 to 0.17 is most preferable. In addition, the molar ratio Mn / Mn of the transition metal element Me is 0.63 to 0.72 in that a nonaqueous electrolyte secondary battery having a large discharge capacity and excellent initial charge / discharge efficiency can be obtained. Preferably, 0.65 to 0.71 is more preferable.

The negative electrode material used for the negative electrode of the non-aqueous electrolyte secondary battery according to the present invention is not limited, and any negative electrode material that can deposit or occlude lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure typified by Li [Li _1/3 Ti _5/3 ] O ₄ ; alloy-based materials such as Si, Sb, and Sn; lithium metal; lithium -Lithium alloys such as silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as wood alloys; lithium composite oxides such as lithium-titanium; oxidation Silicon; alloys capable of inserting and extracting lithium; carbon materials such as graphite, hard carbon, low-temperature fired carbon, and amorphous carbon.

It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite such as scaly graphite, scaly graphite, and earth graphite; artificial graphite; carbon black; acetylene black; Carbon black; Carbon fiber; Metal powder such as copper, nickel, aluminum, silver, and gold; Metal fiber; Conductive material such as conductive ceramic material may be included as one kind or a mixture thereof.

Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black after pulverizing it into ultrafine particles of 0.1 to 0.5 μm because the required amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

Examples of the binder include thermoplastic resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethylene, and polypropylene; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The amount of the binder added is preferably 1 to 50% by weight, particularly 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

As the filler, any material that does not adversely affect battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

For the positive and negative electrodes, the main constituents (positive electrode active material for the positive electrode, negative electrode material for the negative electrode) and other materials are kneaded to form a mixture and mixed in an organic solvent such as N-methylpyrrolidone and toluene or water Then, the obtained liquid mixture is applied or pressure-bonded onto a current collector described in detail below, and is heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours, so that it is suitably produced. . About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for non-aqueous electrolyte batteries include polyolefin resins typified by polyethylene and polypropylene; polyester resins typified by polyethylene terephthalate and polybutylene terephthalate; polyvinylidene fluoride; vinylidene fluoride-hexa Fluoropropylene copolymer; vinylidene fluoride-perfluorovinyl ether copolymer; vinylidene fluoride-tetrafluoroethylene copolymer; vinylidene fluoride-trifluoroethylene copolymer; vinylidene fluoride-fluoroethylene copolymer; Vinylidene fluoride-hexafluoroacetone copolymer; vinylidene fluoride-ethylene copolymer; vinylidene fluoride-propylene copolymer; vinylidene fluoride-trifluoropropylene copolymer; vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer; a vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

Furthermore, it is desirable that the separator is used in combination with the above-described porous film, nonwoven fabric or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

The configuration of the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. FIG. 10 shows a schematic diagram of a rectangular nonaqueous electrolyte secondary battery 1 which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte secondary battery 1 shown in FIG. 10, the electrode group 2 is accommodated in a battery container 3. The electrode group 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

The present invention can also be realized as a power storage device including a plurality of the above non-aqueous electrolyte secondary batteries. One embodiment of a power storage device is shown in FIG. In FIG. 11, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV). FIG. 12 is a conceptual diagram of the automobile 100 on which the power storage device 30 is mounted. Here, the automobile 100 includes a power storage device 30 and a vehicle body 40 that houses the power storage device 30.

The nonaqueous electrolyte secondary battery 1, the power storage unit 20, or the power storage device 30 according to the embodiment preferably includes charge / discharge control means. The charge / discharge control means may be provided for each nonaqueous electrolyte secondary battery 1, or may be provided for each power storage unit 20 or each power storage device 30. The charge / discharge control means includes charge control means for controlling the inter-terminal voltage of the secondary battery so that it does not rise above the set charge upper limit voltage during charging. The charge control means may be charge control means including control for charging the nonaqueous electrolyte secondary battery according to the embodiment to a positive electrode potential of 4.4 V (vs. Li ^/ Li ⁺ ) or higher. In this specification, when the positive electrode potential of the secondary battery when the inter-terminal voltage of the secondary battery reaches the set charge upper limit voltage is 4.4 V (vs. Li ^/ Li ⁺ ) or more, charge / discharge control is performed. The means includes charge control means including control for charging the secondary battery to a positive electrode potential of 4.4 V (vs. Li ^/ Li ⁺ ) or higher. According to such an embodiment, the non-aqueous electrolyte secondary battery according to the present invention repeats charging and discharging even when charging conditions reaching a positive electrode potential of 4.4 V (vs. Li ^/ Li ⁺ ) or higher are adopted. Therefore, the non-aqueous electrolyte secondary battery or power storage device with high energy density and long life can be provided.

(Preliminary test)
The contents of the preliminary test on which the present invention was based are as follows.

(Preparation of positive electrode active material)
A sodium hydroxide aqueous solution is added to an aqueous solution containing cobalt nitrate, nickel nitrate and manganese nitrate at a Co: Ni: Mn atomic ratio of 1: 1: 1, and the mixture is coprecipitated and heated in air at 110 ° C. and dried. Thus, a coprecipitation precursor containing Co, Ni and Mn was produced. Lithium hydroxide was added to the coprecipitation precursor and mixed well using a smoked automatic mortar to prepare a mixed powder having a Li: (Co, Ni, Mn) molar ratio of 102: 100. This is filled in an alumina sagger, heated to 1000 ° C. at 100 ° C./h using an electric furnace, and calcined at 1000 ° C. for 5 hours in the air atmosphere, whereby the composition formula LiCo _1/3 A lithium transition metal composite oxide represented by Ni _1/3 Mn _1/3 O ₂ was produced and used as a positive electrode active material. The BET specific surface area measured by the nitrogen adsorption method was 1.0 m ² / g, and the value of D50 using a laser diffraction scattering method particle size distribution measuring device was 12.1 μm. In this way, a positive electrode active material was produced.

(Preparation of positive electrode plate)
A positive electrode paste containing the positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) in a mass ratio of 93: 3: 4 (in terms of solid content) and N-methylpyrrolidone (NMP) as a solvent. It produced and apply | coated on both surfaces of the 15-micrometer-thick strip | belt-shaped aluminum foil electrical power collector. The electrode plate was pressure-molded with a roller press to form a positive electrode active material layer, and then dried under reduced pressure at 150 ° C. for 14 hours to remove moisture in the electrode plate. In this way, a positive electrode plate was produced.

(Preparation of negative electrode plate)
A negative electrode paste containing graphite, styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) in a mass ratio of 97: 2: 1 (in terms of solid content) and water as a solvent was prepared. A negative electrode paste was applied to both surfaces of a strip-shaped copper foil current collector having a thickness of 10 μm. The electrode plate was pressure-molded with a roller press to form a negative electrode active material layer, and then dried under reduced pressure at 25 ° C. (room temperature) for 14 hours to remove moisture in the electrode plate. In this way, a negative electrode plate was produced.

(Nonaqueous electrolyte 1)
An electrolyte solution in which LiPF ₆ is dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 is referred to as nonaqueous electrolyte 1.

(Nonaqueous electrolyte 2)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. .5% by weight boric acid was added and dissolved. This is designated as non-aqueous electrolyte 2.

(Nonaqueous electrolyte 3)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. .5 mass% lithium bisoxalate borate (LiBOB) was added and dissolved. This is designated as non-aqueous electrolyte 3.

(Nonaqueous electrolyte 4)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 5% by mass of the boroxine ring compound (TiPBx) represented by (Chemical Formula 3) was added and dissolved. This is designated as non-aqueous electrolyte 4.

(Nonaqueous electrolyte 5)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. .5% by weight tributyl borate (TBB) was added and dissolved. This is designated as non-aqueous electrolyte 5.

(Nonaqueous electrolyte 6)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 5% by mass of tripropyl borate (TPB) was added and dissolved. This is designated as non-aqueous electrolyte 6.

(Nonaqueous electrolyte 7)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 5% by weight of tris (trimethylsilyl) borate (TMSB) was added and dissolved. This is designated as non-aqueous electrolyte 7.

Using the above nonaqueous electrolytes 1 to 7, nonaqueous electrolyte secondary batteries were produced in the following procedure.

(Preparation of non-aqueous electrolyte secondary battery)
<Assembly process>
The positive electrode plate and the negative electrode plate are laminated through a separator made of a polyethylene microporous membrane, wound in a flat shape to produce a power generation element, housed in an aluminum square battery case, and positive and negative electrode terminals Attached. The container was sealed after injecting a nonaqueous electrolyte into the container. The outer dimensions of the battery case can are 49.3 mm (height) × 33.7 mm (width) × 5.17 mm (thickness). In this way, a non-aqueous electrolyte battery was assembled.

<Initial charge / discharge process>
Next, it was subjected to an initial charge / discharge process of 2 cycles at 25 ° C. All voltage control was performed on the voltage between the positive and negative terminals. Charging in the first cycle was constant current constant voltage charging with a current of 0.2 CmA and a voltage of 4.35 V for 8 hours, and discharging was constant current discharging with a current of 0.2 CmA and a final voltage of 2.75 V. The second cycle charge was a constant current constant voltage charge with a current of 1.0 CmA and a voltage of 4.35 V for 3 hours, and the discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging. In this way, a nonaqueous electrolyte battery was produced.

<Charge / discharge cycle test (condition 1)>
About the produced nonaqueous electrolyte secondary battery, the charging / discharging cycle test was done and the transition of discharge capacity was investigated. All voltage control was performed on the voltage between the positive and negative terminals. Charging was performed at a constant current and constant voltage with a current of 1.0 CmA and a voltage of 4.20 V for 3 hours, and discharging was performed at a constant current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging. Here, it is known that when the voltage between the positive and negative terminals is 4.20 V, the positive electrode potential is 4.30 V (vs. Li / Li ⁺ ). The result is shown in FIG.

As can be seen from the results of the charge / discharge cycle test employing the above “Condition 1”, among the non-aqueous electrolyte secondary batteries using non-aqueous electrolytes to which various boron compounds are added, “non-aqueous electrolyte 2 to which boric acid is added” is shown. ”And when“ Nonaqueous Electrolyte 4 ”added with TiPBx was used, particularly excellent results were obtained. Of these, boric acid is an extremely inexpensive material compared to TiPBx, and it can be seen that using boric acid can provide a nonaqueous electrolyte battery with excellent charge / discharge cycle performance at low cost.

<Charge / discharge cycle test (Condition 2)>
About the produced nonaqueous electrolyte secondary battery, the conditions were changed and the charging / discharging cycle test was done, and transition of the discharge capacity was investigated. All voltage control was performed on the voltage between the positive and negative terminals. Charging was performed at a constant current and constant voltage with a current of 1.0 CmA and a voltage of 4.35 V for 3 hours, and discharging was performed at a constant current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging. Here, it is known that when the voltage between the positive and negative terminals is 4.35 V, the positive electrode potential is 4.45 V (vs. Li / Li ⁺ ). The percentage of the discharge capacity at the 50th cycle or the 150th cycle with respect to the discharge capacity at the second cycle in the initial charge / discharge process was determined and was defined as “discharge capacity retention rate (%)”. The results are shown in Table 1. In the table, “x” marks indicate that the test was terminated before reaching 150 cycles because the discharge capacity significantly decreased with the progress of the charge / discharge cycles.

As can be seen from the results of the charge / discharge cycle test employing the above “Condition 2”, among the nonaqueous electrolyte secondary batteries using the nonaqueous electrolyte to which various boron compounds are added, “nonaqueous electrolyte 2 to which boric acid is added” is shown. Only when "" was used, outstanding results were obtained.

Next, the suitable addition amount of boric acid was examined. The amount of boric acid added to the electrolytic solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 according to the nonaqueous electrolyte 2 described above. A non-aqueous electrolyte with 0% by mass, 0.1% by mass, 0.2% by mass, 0.5% by mass, 1.0% by mass, and 1.5% by mass was prepared. A non-aqueous electrolyte battery was prepared in the same procedure, and a charge / discharge cycle test employing the above “condition 2” was performed up to 250 cycles. As a result, the initial charge / discharge efficiency was 88.9% when the addition amount of boric acid was 0% by mass, 90.8% at 0.1% by mass, 92.4% at 0.2% by mass, and 0.5% by mass. Was 91.5%, 1.0% by mass was 88.8%, and 1.5% by mass was 82.7%. As shown in FIG. 2, the charge / discharge cycle performance is improved as the amount of boric acid added increases to 0 mass%, 0.1 mass%, 0.2 mass%, and 0.5 mass%. It was the best when it was ˜1.0% by mass and decreased again at 1.5% by mass. From the above results, the amount of boric acid added is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and most preferably 0.5% by mass or more. Moreover, 1.5 mass% or less is preferable and 1.0 mass% or less is more preferable.

(Analysis of non-aqueous electrolyte)
The boric acid is 0.2% by mass with respect to the electrolytic solution in which LiPF ₆ is dissolved at a concentration of 1.0 mol / l in the above mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7. Electric power is generated by disassembling the added nonaqueous electrolyte (sample 1), the nonaqueous electrolyte added with 0.5% by mass (sample 2), and the nonaqueous electrolyte battery at the stage where the initial charge / discharge is completed. The non-aqueous electrolyte (sample 3) taken out from the element by centrifugation, the non-aqueous electrolyte added with 1.5% by mass (sample 4), and the non-aqueous electrolyte at the stage where the initial charge / discharge was completed using this An ion chromatography analysis was performed on the nonaqueous electrolyte (sample 5) that was disassembled from the electrolyte battery and removed from the power generation element by centrifugation. As a result, the concentration of PF ₆ ⁻ was 0.9 mol / l for sample 2 and sample 3, and 0.6 mol / l for sample 4 and sample 5. The concentrations of boric acid were 0.01 mol / l (0.05 mass%) for sample 2 and sample 3, 0.05 mol / l (0.25 mass%) for sample 4, and 0.03 mol / l for sample 5. l (0.15% by mass). No boric acid was detected from Sample 1.

In the ion chromatography analysis, the columns and detectors used for the quantification of PF ₆ ⁻ are as follows.
IonPac AS16 (4x250mm) + Precolumn AG16 manufactured by Nippon Dionex
Eluent: 35 mmol / l KOH aqueous solution Volume: 1.0 ml / ml
Detector: Electrical conductivity

In the ion chromatography analysis, the columns and detectors used for boric acid quantification are as follows, and the detection limit is 0.001 mol / l. In the analysis, since the sample is diluted with water for measurement, the ion species detected by the column is BO ₃ ^3- .
Nippon Dionex IonPac ICE-AS1 (9 x 250mm)
Eluent: 1.0 mol / l octanesulfonic acid + 2% 2-propanol aqueous solution Volume: 0.8 ml / ml
Detector: Electrical conductivity

From the above results, it is suggested that a part of boric acid added to the electrolytic solution is changed to another compound. Further, a non-aqueous electrolyte in which 0.5% by mass or more of boric acid is added to an electrolytic solution in which 1.0 mol / l LiPF ₆ is dissolved in a non-aqueous solvent is 0.01 mol / l or more boric acid. It can be seen that it contains 0.9 mol / l or less of LiPF ₆ . Moreover, it turns out that it contains similarly about the nonaqueous electrolyte with which the nonaqueous electrolyte battery produced using this nonaqueous electrolyte is provided.

(Reference example)
1% by mass of boric acid was added to the positive electrode paste with respect to the positive electrode active material. Using this positive electrode paste, a non-aqueous electrolyte battery was prepared according to the same formulation as the preliminary test except that “non-aqueous electrolyte 1” to which boric acid was not added was used, and “condition 1” was adopted. The charge / discharge cycle test was performed. As a result, compared with all the reference examples to which boric acid was added, the discharge capacity decreased and the internal resistance increased under various temperature conditions, and no advantageous effect was observed. In addition, the positive electrode paste to which boric acid was added agglomerated the active material only by leaving it for only a few hours after kneading, and the resulting agglomerate caused coating unevenness during coating, resulting in a greatly inferior productivity. Further, when the battery after the evaluation test was disassembled and the nonaqueous electrolyte was taken out and subjected to ion chromatography analysis, boric acid was not detected. Assuming that the amount of boric acid taken into the battery from the positive electrode paste by the above formulation is added to the non-aqueous electrolyte and injected, the electrolyte containing 1.2% by mass of boric acid is added. It corresponds to the case of using. From this, when boric acid is added to the positive electrode paste, it is changed to another compound during the manufacturing process of the nonaqueous electrolyte, and is not contained as boric acid in the nonaqueous electrolyte. It turns out that there is no effect either.

(Example 1)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added, and the mixture was gently stirred. Next, 2% by mass of calcium oxide (manufactured by Junsei Co., Ltd.) was added to the mass of the solution and mixed with stirring. This was designated as the nonaqueous electrolyte according to Example 1.

(Example 2)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and stirred gently. Subsequently, 2 mass% magnesium oxide (made by Wako Pure Chemical Industries, Ltd.) was added with respect to the mass of this solution, and it stirred and mixed. This was designated as the nonaqueous electrolyte according to Example 2.

(Comparative Example 1)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 1.

(Comparative Example 2)
The “non-aqueous electrolyte 1” was a non-aqueous electrolyte according to Comparative Example 2.

(Comparative Example 3)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. The calcium oxide of the mass% was added and stirred and mixed. This was used as the nonaqueous electrolyte according to Comparative Example 3.

(Comparative Example 4)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% of the magnesium oxide was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 4.

(Comparative Example 5)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and stirred gently. Subsequently, 2% by weight of barium oxide (manufactured by Aldrich) was added to the weight of the solution, and the mixture was stirred and mixed. This was used as the nonaqueous electrolyte according to Comparative Example 5.

(Comparative Example 6)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and stirred gently. Next, 2% by mass of magnesium sulfate (manufactured by Nacalai Tesque, anhydrous) with respect to the mass of the solution was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 6.

(Example 3)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added, and the mixture was gently stirred. Next, 2% by mass of sodium sulfate (manufactured by Nacalai Tesque, anhydrous) was added to the mass of the solution, and the mixture was stirred and mixed. As a result, a cloudy solution in which undissolved sodium sulfate was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Example 3.

(Comparative Example 7)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. The sodium sulfate of the mass% was added and mixed with stirring. As a result, a cloudy solution in which undissolved sodium sulfate was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Comparative Example 7.

(Comparative Example 8)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% magnesium sulfate (manufactured by Nacalai Tesque, anhydrous) was added and mixed with stirring. As a result, a cloudy solution in which undissolved magnesium sulfate was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Comparative Example 8.

(Comparative Example 9)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and stirred gently. Next, 2% by mass of lithium sulfate monohydrate (manufactured by Nacalai Tesque) with respect to the mass of this solution was added after drying at 150 ° C. for 12 hours, and mixed by stirring. As a result, a cloudy solution in which undissolved lithium sulfate was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Comparative Example 9.

Example 4
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added, and the mixture was gently stirred. Next, 2% by mass of diphosphorus pentoxide (manufactured by Nacalai Tesque, product name “phosphorous oxide (V) (diphosphorus pentoxide)”, 98%) with respect to the mass of the solution was added and mixed with stirring. As a result, a cloudy solution in which undissolved diphosphorus pentoxide was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Example 4.

(Comparative Example 10)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. A mass% of the diphosphorus pentoxide was added and mixed with stirring. As a result, a white gel-like substance was separated and produced, and a uniform solution could not be obtained. Such an electrolyte was not used because it could not be injected into the battery.

(Example 5)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added, and the mixture was gently stirred. Next, 2% by mass of activated carbon (produced by Nacalai Tesque, product name: activated carbon (powder, sawdust, treated with hydrochloric acid, methylene blue adsorbed amount: 180 ml / g)) is added to the mass of the solution, and mixed with stirring. did. As a result, a black solution in which activated carbon was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Example 5.

(Comparative Example 11)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. A mass% of the activated carbon was added and mixed with stirring. As a result, a black solution in which activated carbon was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Comparative Example 11.

(Example 6)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added, and the mixture was gently stirred. Next, 2% by mass of activated alumina (product name: activated alumina 200, manufactured by Nacalai Tesque Co., Ltd.) was added to the mass of the solution and mixed with stirring. As a result, a cloudy solution in which activated alumina was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Example 6.

(Comparative Example 12)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. A mass% of the activated alumina was added and stirred and mixed. As a result, a cloudy solution in which activated alumina was dispersed was obtained. This was designated as the nonaqueous electrolyte according to Comparative Example 12.

(Comparative Example 13)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.0% by mass of the boric acid was added and stirred gently. Next, 2% by mass of silica gel (manufactured by Nacalai Tesque, product name: silica gel 60, particle size: 70 to 230 mesh) was added to the mass of the solution, and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 13.

Except that the nonaqueous electrolytes according to Examples 1 to 6 and Comparative Examples 1 to 13 were used, respectively, the power generation element was housed in a rectangular battery case and the nonaqueous electrolyte was injected in the same manner as the preliminary test. . Next, a current of 0.2 CmA was applied for 90 minutes in the charging direction. At this time, the closed circuit voltage between the terminals after energization reached about 3.8V. After energization, it was allowed to stand for 1 hour and then sealed. In this way, a non-aqueous electrolyte battery was assembled.

However, in the case of using the nonaqueous electrolyte according to Comparative Example 13 to which boric acid and silica gel were added, when the nonaqueous electrolyte was injected, the injected electrolyte solution with a large amount of bubbles was blown out violently. From this, it was found that the nonaqueous electrolyte according to Comparative Example 13 has a large manufacturing problem.

<Initial charge / discharge process>
These nonaqueous electrolyte batteries assembled using the nonaqueous electrolytes according to Examples 1 to 6 and Comparative Examples 1 to 12, respectively, were subjected to an initial charge / discharge process of 2 cycles at 25 ° C. All voltage control was performed on the voltage between the positive and negative terminals. Charging in the first cycle was constant current constant voltage charging with a current of 0.2 CmA and a voltage of 4.35 V for 8 hours, and discharging was constant current discharging with a current of 0.2 CmA and a final voltage of 2.75 V. The second cycle charge was a constant current constant voltage charge with a current of 1.0 CmA and a voltage of 4.35 V for 3 hours, and the discharge was a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V. In all cycles, a 10 minute rest period was set after charging and discharging. As in the case of the preliminary test, it is known that when the voltage between the positive and negative terminals is 4.35 V, the positive electrode potential is 4.45 V (vs. Li / Li ⁺ ).

For the nonaqueous electrolyte batteries according to all examples and comparative examples, at the stage where the initial charge and discharge were completed, the thickness of the battery was measured with calipers, and the battery case at the time when the power generation element was stored in the battery case can The increment (mm) relative to the thickness (5.17 mm) was recorded.

The above results are shown in Tables 2-6.

From Table 2, compared with the nonaqueous electrolyte battery according to Comparative Example 1 in which only boric acid was added, the nonaqueous electrolyte batteries according to Examples 1 and 2 in which boric acid and calcium oxide or magnesium oxide were used together had a battery thickness. It can be seen that the increase in is suppressed. On the other hand, the non-aqueous electrolyte battery according to Comparative Example 5 using barium oxide instead of calcium oxide or magnesium oxide is deteriorated in terms of an increase in battery thickness. In addition, the non-aqueous electrolyte battery according to Comparative Example 6 using magnesium sulfate instead of calcium oxide or magnesium oxide was also not effective in increasing the battery thickness.

From Table 3, compared with the nonaqueous electrolyte battery according to Comparative Example 1 in which only boric acid was added, the nonaqueous electrolyte battery according to Example 3 in which boric acid and sodium sulfate were used in combination was suppressed from increasing in battery thickness. You can see that On the other hand, the effect was not recognized in the nonaqueous electrolyte battery which concerns on the comparative example 8 which used boric acid and magnesium sulfate together, and the nonaqueous electrolyte battery which concerns on the comparative example 9 which used boric acid and lithium sulfate together.

From Table 4, the nonaqueous electrolyte battery according to Example 4 using boric acid and diphosphorus pentoxide in combination with the nonaqueous electrolyte battery according to Comparative Example 1 to which only boric acid was added had an increase in battery thickness. It turns out that it is suppressed.

From Table 5, compared with the nonaqueous electrolyte battery according to Comparative Example 1 in which only boric acid was added, the nonaqueous electrolyte battery according to Example 5 using both boric acid and activated carbon had an increase in battery thickness suppressed. I understand that.

From Table 6, compared with the nonaqueous electrolyte battery according to Comparative Example 1 in which only boric acid was added, the nonaqueous electrolyte battery according to Example 6 in which boric acid and activated alumina were used together was suppressed from increasing in battery thickness. You can see that

<Charge / discharge cycle test>
Next, the nonaqueous electrolyte batteries according to Examples 1 to 6 and Comparative Examples 1 and 12 were subjected to a charge / discharge cycle test employing the above “Condition 2”. The results are shown in FIGS.

As can be seen from FIG. 3, the nonaqueous electrolyte battery according to Examples 1 and 2 in which boric acid and calcium oxide or magnesium oxide are used in combination is compared with the nonaqueous electrolyte battery cage according to Comparative Example 1 in which only boric acid is added. Equivalent or better charge / discharge cycle performance was shown. Therefore, it can be seen that the effect of improving the charge / discharge cycle performance, which is achieved by adding boric acid to the electrolytic solution, is not impaired even when calcium oxide or magnesium oxide is used in combination. Especially, it turns out that there exists an effect which further improves the charging / discharging cycling performance of the nonaqueous electrolyte battery using the nonaqueous electrolyte which added boric acid by using boric acid and calcium oxide together.

As can be seen from FIG. 4, the nonaqueous electrolyte battery according to Example 3 using both boric acid and sodium sulfate exhibits better charge / discharge cycle performance than the nonaqueous electrolyte battery according to Comparative Example 1 to which only boric acid is added. It was. Therefore, the combined use of sodium sulfate does not impair the effect of improving the charge / discharge cycle performance, which is exhibited by adding boric acid to the electrolytic solution, and also uses a nonaqueous electrolyte to which boric acid is added. It turns out that there exists an effect which further improves the charge / discharge cycle performance of a nonaqueous electrolyte battery.

As can be seen from FIG. 5, the non-aqueous electrolyte battery according to Example 4 using boric acid and diphosphorus pentoxide in combination is equivalent to or better than the non-aqueous electrolyte battery according to Comparative Example 1 to which only boric acid is added. The discharge cycle performance is shown. Therefore, the combined use of diphosphorus pentoxide does not impair the effect of improving the charge / discharge cycle performance, which is achieved by adding boric acid to the electrolyte, and also includes a nonaqueous electrolyte to which boric acid is added. It can be seen that the charge / discharge cycle performance of the used nonaqueous electrolyte battery may be further improved.

As can be seen from FIG. 6, the nonaqueous electrolyte battery according to Example 5 using both boric acid and activated carbon has a charge / discharge cycle performance comparable to that of the nonaqueous electrolyte battery according to Comparative Example 1 to which only boric acid is added. showed that. Therefore, it can be seen that the effect of improving the charge / discharge cycle performance, which is exhibited by adding boric acid to the electrolytic solution, is substantially maintained even when activated carbon is used in combination.

As can be seen from FIG. 7, the nonaqueous electrolyte battery according to Example 6 using boric acid and activated alumina in combination is equal to or more than the nonaqueous electrolyte battery cell according to Comparative Example 1 to which only boric acid is added. Cycle performance was shown. Accordingly, the combined use of activated alumina does not impair the effect of improving the charge / discharge cycle performance, which is achieved by adding boric acid to the electrolytic solution, and also uses a nonaqueous electrolyte to which boric acid is added. It can be seen that there is a possibility of further improving the charge / discharge cycle performance of the nonaqueous electrolyte battery.

(Example 7)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. .5% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) was added and stirred gently. Next, 0.5% by mass of lithium bisoxalate borate (LiBOB) with respect to the mass of the solution was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Example 7.

(Comparative Example 14)
The “nonaqueous electrolyte 2” was used as the nonaqueous electrolyte according to Comparative Example 14.

(Comparative Example 15)
The “nonaqueous electrolyte 3” was used as the nonaqueous electrolyte according to Comparative Example 15.

A nonaqueous electrolyte battery was assembled in the same manner as in the preliminary test except that the nonaqueous electrolytes according to Example 7 and Comparative Examples 14 and 15 were used.

<Charge / discharge cycle test>
A nonaqueous electrolyte battery was assembled using the nonaqueous electrolytes according to Example 7 and Comparative Examples 2, 14, and 15 in the same manner as in the preliminary test. Next, it was subjected to an initial charge / discharge process under the same conditions as in Example 1. Furthermore, a charge / discharge cycle test employing the above "condition 2" was performed. The result is shown in FIG. As can be seen from FIG. 8, the nonaqueous electrolyte battery according to Example 7 to which boric acid and lithium bisoxalate borate were added was more charged than the nonaqueous electrolyte battery according to Comparative Example 14 to which only boric acid was added. The discharge cycle performance was further improved. On the other hand, the nonaqueous electrolyte battery according to Comparative Example 15 to which only lithium bisoxalate borate was added was comparable to the nonaqueous electrolyte battery according to Comparative Example 2 to which neither boric acid nor lithium bisoxalate borate was added. Only showed performance.

(Example 8)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. .5% by weight boric acid (Nacalai Tesque, purity 99.5% or more) was added and stirred gently, then 2% by weight vinylene carbonate (VC) was added to the weight of the solution and stirred. Mixed. This was designated as the nonaqueous electrolyte according to Example 8.

Example 9
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Add 0.5% by weight boric acid (Nacalai Tesque, purity 99.5% or more), stir gently, then add 2% by weight vinyl ethylene carbonate (VEC) to the weight of this solution, Stir and mix. This was designated as the nonaqueous electrolyte according to Example 9.

(Comparative Example 16)
The “nonaqueous electrolyte 1” was used as the nonaqueous electrolyte according to Comparative Example 16.

(Comparative Example 17)
The “nonaqueous electrolyte 2” was used as the nonaqueous electrolyte according to Comparative Example 17.

(Comparative Example 18)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% vinylene carbonate (VC) was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 18.

A nonaqueous electrolyte battery was assembled in the same manner as in the preliminary test except that the nonaqueous electrolytes according to Examples 8 and 9 and Comparative Examples 16 to 18 were used. Next, it was subjected to an initial charge / discharge process under the same conditions as in Example 1. A nonaqueous electrolyte battery was manufactured through the initial charge / discharge process.

<45 ° C repeated storage test (measurement of recovery capacity)>
A 45 ° C. repeated storage test was performed using the non-aqueous electrolyte battery thus produced. The conditions and procedure of the 45 ° C. repeated storage test are as follows. Constant current and constant voltage charging was performed at a current of 1.0 CmA and a voltage of 4.35 V for 3 hours. Next, the battery was placed in an open circuit state and stored in a 45 ° C. constant temperature bath for 15 days. Next, constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V was performed at 25 ° C., and the discharge capacity was measured. Again, after charging at a constant current and a constant voltage for 3 hours at a current of 1.0 CmA and a voltage of 4.35 V, it was further stored in a 45 ° C. thermostat for 15 days. Thus, after storing for a total of 30 days in a 45 degreeC thermostat, the constant current discharge of electric current 1.0CmA and final voltage 2.75V was performed at 25 degreeC. Again, at 25 ° C., after carrying out constant current / constant voltage charging for 3 hours with a current of 1.0 CmA and a voltage of 4.35 V, a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V was performed to reduce the discharge capacity. It was measured. The discharge capacity at this time is defined as a recovery capacity. The percentage of the recovery capacity with respect to the discharge capacity at the second cycle in the initial charge / discharge process was determined and was defined as “capacity retention ratio (%)”. The results are shown in Table 7.

As can be seen from Table 7, the nonaqueous electrolyte battery cages according to Examples 8 and 9 to which boric acid and a cyclic carbonate having an unsaturated bond were added were the nonaqueous electrolyte battery cage according to Comparative Example 17 to which only boric acid was added. Compared with storage performance improved. In addition, in the battery according to Comparative Example 17 to which only boric acid was added and the battery according to Comparative Example 18 to which only the cyclic carbonate having an unsaturated bond was added, boric acid and a cyclic carbonate having an unsaturated bond were also added. It was found that the storage performance was worse than that of the battery according to Comparative Example 16 that was not.

<Charge / discharge cycle test>
Moreover, the charge / discharge cycle test was done using the nonaqueous electrolyte battery produced by the same prescription and procedure. The above-mentioned “Condition 2” was adopted as the condition for the charge / discharge cycle test. The result is shown in FIG.

As can be seen from FIG. 3, the nonaqueous electrolyte battery cages according to Examples 8 and 9 to which boric acid and a cyclic carbonate having an unsaturated bond were added were the nonaqueous electrolyte battery cage according to Comparative Example 17 to which only boric acid was added. Equivalent or better charge / discharge cycle performance was shown. Therefore, it can be seen that the effect of improving charge / discharge cycle performance, which is achieved by adding boric acid to the electrolytic solution, is not impaired even when a cyclic carbonate having an unsaturated bond is used in combination. Especially, in Example 9 using vinyl ethylene carbonate as a cyclic carbonate having an unsaturated bond, performance exceeding Comparative Example 17 was shown. On the other hand, the nonaqueous electrolyte battery cage according to Comparative Example 18 to which only the cyclic carbonate having an unsaturated bond was added was the nonaqueous electrolyte battery according to Comparative Example 16 to which neither boric acid nor a cyclic carbonate having an unsaturated bond was added. It showed only the same level of performance.

(Example 10)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.5% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) and 2% by mass of 1,3-propene sultone were added and mixed with stirring. This was designated as the non-aqueous electrolyte according to Example 10.

(Example 11)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. 0.5% by mass of boric acid (manufactured by Nacalai Tesque, purity 99.5% or more) and 2% by mass of diglycol sulfate (DGLST) were added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Example 11.

(Comparative Example 19)
The “nonaqueous electrolyte 1” was used as the nonaqueous electrolyte according to Comparative Example 19.

(Comparative Example 20)
The “nonaqueous electrolyte 2” was used as the nonaqueous electrolyte according to Comparative Example 20.

(Comparative Example 21)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% 1,3-propene sultone was added and mixed with stirring. This was designated as the nonaqueous electrolyte according to Comparative Example 21.

(Comparative Example 22)
An electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / l in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was prepared. Mass% of diglycol sulfate (DGLST) was added and stirred and mixed. This was designated as the nonaqueous electrolyte according to Comparative Example 22.

A nonaqueous electrolyte battery was assembled in the same manner as in the preliminary test except that the nonaqueous electrolytes according to Examples 10 and 11 and Comparative Examples 19 to 22 were used. Next, it was subjected to an initial charge / discharge process under the same conditions as in Example 1. A nonaqueous electrolyte battery was manufactured through the initial charge / discharge process.

<45 ° C repeated storage test (measurement of remaining capacity)>
A 45 ° C. repeated storage test was performed using the non-aqueous electrolyte battery thus produced. The conditions and procedure of the 45 ° C. repeated storage test are as follows. Constant current and constant voltage charging was performed at a current of 1.0 CmA, a voltage of 4.35 V, and 3 hours. Next, the battery was placed in an open circuit state and stored in a 45 ° C. constant temperature bath for 15 days. Next, at 25 ° C., a constant current discharge with a current of 1.0 CmA and a final voltage of 2.75 V, a current of 1.0 CmA, a voltage of 4.35 V, and a constant current and constant voltage charge for 3 hours were performed. It was further stored for 15 days in a thermostatic bath. Thus, after storing for a total of 30 days in a 45 degreeC thermostat, at 25 degreeC, the constant current discharge of the electric current 1.0CmA and the end voltage 2.75V was performed, and the discharge capacity was measured. The discharge capacity at this time is defined as the remaining capacity. The percentage of the remaining capacity with respect to the discharge capacity at the second cycle in the initial charge / discharge process was determined and was defined as “capacity maintenance ratio (%)”. The results are shown in Tables 8 and 9.

As can be seen from Tables 8 and 9, in the battery according to Comparative Example 20 to which only boric acid was added and the batteries according to Comparative Examples 21 and 22 to which only cyclic sulfonic acid compounds were added, both boric acid and cyclic sulfonic acid compounds were added. The storage performance was the same or decreased as compared with the battery according to Comparative Example 19 which was not. In contrast, the nonaqueous electrolyte battery case according to Examples 10 and 11 to which boric acid and a cyclic sulfonic acid compound were added had improved storage performance.

<Charge / discharge cycle test>
Moreover, the charge / discharge cycle test was done using the nonaqueous electrolyte battery produced by the same prescription and procedure. The above-mentioned “Condition 2” was adopted as the condition for the charge / discharge cycle test. The number of cycles in which the discharge capacity was maintained at 60% or more with respect to the discharge capacity at the second cycle in the initial charge / discharge process was counted and shown in Tables 10 and 11.

As can be seen from Tables 10 and 11, the nonaqueous electrolyte battery cages according to Examples 10 and 11 to which boric acid and a cyclic sulfonic acid compound were added were compared with the nonaqueous electrolyte battery cage according to Comparative Example 20 to which only boric acid was added. The charge / discharge cycle performance was significantly improved.

Since the nonaqueous electrolyte secondary battery according to the present invention has excellent charge / discharge cycle performance, it is useful as a power source for automobiles such as electric cars, hybrid cars, plug-in hybrid cars and the like.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 Power storage unit 30 Power storage device 40 Body body 100 Automobile

Claims

One selected from the group consisting of calcium oxide, magnesium oxide, sodium sulfate, diphosphorus pentoxide, activated alumina, activated carbon, a compound having an oxalate borate structure, a cyclic carbonate having an unsaturated structure, and a cyclic sulfonic acid compound Alternatively, a nonaqueous electrolyte secondary battery comprising a nonaqueous electrolyte containing two or more substances and boric acid.
The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte contains 0.03 mol / l or less of boric acid.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic sulfonic acid compound is represented by Chemical Formula 1 or Chemical Formula 2.

[In the general formula (1), R 1 to R 4 are each a hydrogen atom or the same or different alkyl group, alkoxy group, halogen, alkyl group having halogen, or aryl group, and n is 1 or 2. is there. ]

[In General Formula (1), R 1 and R 2 represent a group bonded to each other represented by Formula (2), or one of them is represented by General Formula (3), Formula (4) or Formula ( 5) (the part of * is bonded to either R 1 or R 2 ) and the other is a hydrogen atom. R 3 is an alkyl group having 1 to 3 carbon atoms which may contain halogen. ]
The non-aqueous electrolyte secondary battery further includes charge / discharge control means, and the charge / discharge control means includes charge control means including control for charging to a positive electrode potential of 4.4 V (vs. Li / Li + ) or higher. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, comprising:
A power storage device comprising a plurality of the nonaqueous electrolyte secondary batteries according to claims 1 to 4.
An automobile equipped with the power storage device according to claim 5.