JP5499359B2 - Nonaqueous electrolyte and nonaqueous electrolyte secondary battery including the nonaqueous electrolyte - Google Patents

Description

  The present invention relates to a nonaqueous electrolyte and a chargeable / dischargeable nonaqueous electrolyte secondary battery including the nonaqueous electrolyte and used mainly as a power source for portable electronic devices such as a video camera, a mobile computer, and a mobile phone.

A battery containing a non-aqueous electrolyte is widely used as a power source for consumer electronic devices because it has a high voltage, a high energy density, and high reliability such as storage stability.
As a typical example of a battery containing a nonaqueous electrolyte, a lithium battery and a lithium ion secondary battery can be given. These batteries include a negative electrode made of metal lithium or an active material capable of occluding and releasing lithium, a positive electrode made of transition metal oxide, fluorinated graphite, a composite oxide of lithium and transition metal, and the like. A water electrolyte.
The non-aqueous electrolyte is a solution obtained by mixing a Li electrolyte such as LiBF ₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , and Li ₂ SiF ₆ in an aprotic organic solvent.

In a non-aqueous electrolyte secondary battery (hereinafter referred to as a battery) such as a lithium ion secondary battery, the non-aqueous electrolyte transfers ions between a positive electrode and a negative electrode. In order to improve the charge / discharge characteristics of the battery, it is necessary to increase the ion transfer speed between the positive electrode and the negative electrode as much as possible, to increase the ionic conductivity of the nonaqueous electrolyte or to lower the viscosity of the nonaqueous electrolyte. For example, it is necessary to facilitate mass transfer by diffusion. In addition, non-aqueous electrolytes are used for positive and negative electrodes that are chemically and electrochemically highly reactive in order to improve the storage stability of batteries (such as storage characteristics) and cycle stability when charging and discharging are repeated. It needs to be stable.
Lithium salt such as LiPF ₆ was dissolved in a high dielectric constant carbonate solvent such as propylene carbonate and ethylene carbonate, and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate as a non-aqueous electrolyte for stabilizing the electrode. Things are known.

However, the battery containing the nonaqueous electrolyte described above has a problem that the discharge capacity after the test is lowered when the battery is left in a charged state at a high temperature or repeatedly charged and discharged at a low temperature.
As described above, the discharge capacity of the battery decreases because the decomposition reaction of the nonaqueous electrolyte proceeds on the positive electrode and the negative electrode, the reaction resistance of the electrode increases, the electrical conductivity of the nonaqueous electrolyte decreases, This is because the internal resistance of the battery increases due to clogging or the like.
Moreover, patent documents 1-11 are mentioned as a well-known example of a boron compound.

Japanese Patent Laid-Open No. 09-120825 JP-A-10-223258 Japanese Patent Application Laid-Open No. 11-054133 JP-A-11-121033 Japanese Patent Laid-Open No. 11-100409 JP 2002-025609 A JP 2002-216844 A JP 2003-132946 A JP 2003-168476 A JP 2008-198542 A JP 2009-245829 A

In the above-mentioned patent document, a non-aqueous electrolyte in which various boron compounds are added to the non-aqueous electrolyte is proposed. However, it has been confirmed that when these nonaqueous electrolytes are used, the charge / discharge cycle life characteristics are improved, but the charge / discharge efficiency is reduced when charging / discharging at a low temperature. The boron compound in the above-mentioned patent document forms a film on the negative electrode due to the reaction with the negative electrode, and when charged at a low temperature, it becomes a lithium ion migration resistance and metal lithium is likely to be deposited on the negative electrode. The cause is.
In order to solve these problems, there is a demand for the development of an additive that satisfactorily suppresses the decomposition of the nonaqueous electrolyte on the surfaces of the positive electrode and the negative electrode and does not increase the lithium ion migration resistance of the film on the negative electrode. .
Further, boronic acid compounds such as JP2009-245829 have been studied. However, when an electrolytic solution to which these boronic acids are added is left as it is, the electrolytic solution is colored or gas is generated by reductive decomposition of hydroxyl groups contained in the boronic acid. Has occurred and the battery swelled.

  The present invention has been made in view of such circumstances, and when a non-aqueous electrolyte secondary battery is produced by containing a specific vinyl boronic acid compound, the discharge capacity after the charge / discharge cycle life test is reduced. An object of the present invention is to provide a non-aqueous electrolyte that is small, has a good discharge capacity during low-temperature charge / discharge, and has a small battery swelling.

  In addition, the present invention provides a non-aqueous electrolyte secondary battery that includes the non-aqueous electrolyte so that a decrease in discharge capacity after a charge / discharge cycle life test is small and discharge capacity during low-temperature charge / discharge is good. The purpose is to do.

In order to solve the above-mentioned problems, the present inventor has paid attention to the boronic acid compound and conducted intensive studies. As a result, it has been found that the above problem can be solved by constituting a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing the following vinylboronic acid compound, and the present invention has been completed.
That is, the non-aqueous electrolyte according to the first invention is used in a non-aqueous electrolyte secondary batteries, non-aqueous solvent, and a lithium salt and further contains represented by the following general formula (1) ruby Niruboron acid compound an electrolyte solution, the content of the vinyl boronic acid compound, characterized in der Rukoto less 0.001 wt% to 5 wt%.

In the general formula (1), R _{1 to} R ₂ are alkyl groups having 1 to 5 carbon atoms, which may be the same or different.

Here, the nonaqueous electrolyte refers to an electrolytic solution in which a supporting salt is dissolved in a nonaqueous solvent.
In the present invention, since the vinyl boronic acid compound is added to the non-aqueous electrolyte, when a non-aqueous electrolyte secondary battery is produced using this non-aqueous electrolyte, the discharge capacity decreases after the charge / discharge cycle life test. And has a good discharge capacity at low temperature charge / discharge.
Accordingly, it is possible to suppress the battery life from being shortened.

  Although the detailed reason why such an effect is obtained is unknown, the vinyl boronic acid compound acts on the surface of the electrode (active material) to form a protective film that is stable even at high temperatures at the interface between the electrode and the non-aqueous electrolyte. Since the decomposition of the non-aqueous electrolyte (non-aqueous solvent) in the positive electrode and the negative electrode is suppressed, the capacity retention when charging / discharging is repeated at a high temperature is good, and the lithium ion conductivity of the negative electrode protective film is good This is probably because of this. This effect is manifested only by the addition of the vinyl boronic acid compound.

  The non-aqueous electrolyte secondary battery according to the second invention includes the non-aqueous electrolyte according to the first invention.

  In this invention, since the nonaqueous electrolyte of 1st invention is included, it can suppress that the discharge capacity at the time of low-temperature charge / discharge is favorable, and the lifetime of a battery becomes short.

  According to the non-aqueous electrolyte of the present invention, when a non-aqueous electrolyte secondary battery is produced using this non-aqueous electrolyte, initial battery swelling is small, and charge / discharge cycle life characteristics and low-temperature charge characteristics are good. A nonaqueous electrolyte secondary battery is obtained.

  According to the nonaqueous electrolyte secondary battery of the present invention, the initial battery thickness is small, and charge / discharge cycle life characteristics and low-temperature charge characteristics are good.

It is sectional drawing which shows the nonaqueous electrolyte secondary battery which concerns on this invention.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
The battery (nonaqueous electrolyte secondary battery) of the present invention has a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte.

(1) Nonaqueous Electrolyte The nonaqueous electrolyte according to the present invention comprises a vinylboronic acid compound represented by the general formula (1) in a nonaqueous solvent and a lithium salt described later.
In said general formula (1), R < ₁ > -R < ₂ > is a C1-C5 alkyl group, and may be same or different.

Specific examples of the alkyl group having 1 to 5 carbon atoms represented by R _{1 to} R ₂ include a methyl group, an ethyl group, a propyl group (including isomers), a butyl group (including isomers), and a pentyl group. (Including isomers).

  Specific examples of the vinyl boronic acid compound represented by the general formula (1) include dimethyl vinyl boronate, diethyl vinyl boronate, dinormal propyl vinyl boronate, diisopropyl vinyl boronate, dinormal butyl vinyl boronate, diisobutyl vinyl boronate, vinyl boron. Examples include ditertiary butyl acid, diisobutyl vinylboronate, disecondary butyl vinylboronate, dinormalpentyl vinylboronate, diisopentyl vinylboronate, ditertiary amyl vinylboronate.

  The content of the vinyl boronic acid compound represented by the general formula (1) is 0.001% by mass or more and 5% by mass or less, preferably 0.05% by mass with respect to the total weight of the nonaqueous electrolyte. The content is 3% by mass or less, more preferably 0.1% by mass or more and 2% by mass or less. This range is preferable for achieving the object of the present invention.

The nonaqueous solvent used in the nonaqueous electrolyte of the present invention preferably contains at least a cyclic aprotic solvent and / or a chain aprotic solvent.
Examples of the cyclic aprotic solvent include cyclic carbonates such as ethylene carbonate, cyclic esters such as γ-butyrolactone, cyclic sulfones such as sulfolane, and cyclic ethers such as dioxolane.
Examples of the chain aprotic solvent include chain carbonates such as dimethyl carbonate, chain carboxylic acid esters such as methyl propionate, and chain ethers such as dimethoxyethane.

In particular, when the load characteristics and low temperature characteristics of the battery are intended to be improved, the non-aqueous solvent is preferably a mixture of a cyclic aprotic solvent and a chain aprotic solvent. Furthermore, when importance is attached to the electrochemical stability of the non-aqueous electrolyte, it is preferable to use a cyclic carbonate as the cyclic aprotic solvent and a chain carbonate as the chain aprotic solvent.
Specific examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans Examples include -2,3-pentylene carbonate, cis-2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and the like.
Of these, ethylene carbonate and propylene carbonate having a high dielectric constant are preferable. When graphite is used for the negative electrode active material, it is more preferable to use ethylene carbonate. Moreover, you may use these cyclic carbonates in mixture of 2 or more types.

Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl trifluoroethyl carbonate. Can be mentioned.
Of these, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate are preferred because of their low viscosity. These chain carbonates may be used in combination of two or more.

  As for the mixing ratio of the cyclic carbonate and the chain carbonate, the cyclic carbonate: chain carbonate (volume ratio) is preferably 5:95 to 70:30, more preferably 10:90 to 60:40. By setting such a ratio, the increase in the viscosity of the nonaqueous electrolyte can be suppressed and the dissociation degree of the nonaqueous electrolyte can be increased, so that the conductivity of the nonaqueous electrolyte contributing to the charge / discharge characteristics of the battery can be increased. it can.

  In the non-aqueous electrolyte according to the present invention, a compound other than the above-described boron-containing compound may be included as an additive in the non-aqueous solvent as long as the object of the present invention is not hindered. Specific examples of other compounds include carbonates having a carbon-carbon unsaturated bond such as vinylene carbonate, dimethyl vinylene carbonate, and divinyl carbonate; amides such as dimethylformamide; and chain-like compounds such as methyl-N, N-dimethylcarbamate. Carbamates; Cyclic amides such as N-methylpyrrolidone; Cyclic ureas such as N, N-dimethylimidazolidinone; Trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, tri (trimethylsilyl) borate, etc. Boric acid esters; trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tri (trimethylsilyl) phosphate, triphenyl phosphate, etc .; ethylene glycol dimethyl ether, diethylene glycol dimethyl ester Ethylene glycol derivatives such as tellurium and polyethylene glycol dimethyl ether; aromatic hydrocarbons such as biphenyl, fluorobiphenyl, o-terphenyl, toluene, ethylbenzene, fluorobenzene, cyclohexylbenzene, 2-fluoroanisole and 4-fluoroanisole; 3-propane sultone, 1,4-butane sultone, 1,3-prop-1-ene sultone, 1-methyl-1,3-prop-1-ene sultone, 2-methyl-1,3-prop-1-ene sultone, 3 -Sulfur systems such as methyl-1,3-prop-1-ene sultone, ethylene sulfite, propylene sulfite, ethylene sulfate, propylene sulfate, butene sulfate, hexene sulfate, vinylene sulfate, 3-sulfolene, divinyl sulfone, dimethyl sulfate, diethyl sulfate Compound As well as maleic anhydride, a carboxylic acid anhydride having a carbon-carbon unsaturated compounds such as dicarboxylic acid anhydride.

  These compounds may be added alone or in combination of two or more. Among these, use of vinylene carbonate, 1,3-prop-1-ene sultone, ethylene sulfate, propylene sulfate, butene sulfate, and hexene sulfate is preferable. The content of these compounds is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass with respect to the total mass of the nonaqueous electrolyte.

As the lithium salt contained in the non-aqueous electrolyte of the present invention, any lithium salt that is used as a normal non-aqueous electrolyte can be used.
Specific examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiN (SO ₂ C _{k F (2k + 1)) 2} (k = 1~8 _{integer), LiPF n (C k F} (2k + 1)) (6-n) (n = 1~5,
k = 1 to 8), LiBF _n C _k F _{(2k + 1)} (n = 1 to 3, k = 1 to 8), LiB (C ₂ O ₄ ) ₂ (lithium bisoxalyl borate) ), LiBF ₂ (C ₂ O ₄ ) (lithium difluorooxalyl borate), LiPF ₃ (C ₂ O ₄ ) (lithium trifluorooxalyl phosphate).
Moreover, the lithium salt shown by the following general formula can also be used.
LiC (SO ₂ R ¹¹ ) (SO ₂ R ¹² ) (SO ₂ R ¹³ )
LiN (SO ₂ OR ¹⁴ ) (SO ₂ OR ¹⁵ )
LiN (SO ₂ R ¹⁶ ) (SO ₂ OR ¹⁷ )
(In formula, R < ¹¹ > -R < ¹⁷ > may mutually be same or different, and is a C1-C8 perfluoroalkyl group).
These lithium salts may be used alone or in combination of two or more.
Of these, LiPF ₆ , LiBF ₄ , and LiN (SO ₂ C _k F _{(2k + 1)} ) ₂ (k = 1 to 8) are particularly preferable.
The above lithium salt is preferably contained in the non-aqueous electrolyte at a concentration of 0.1 to 3 mol / liter, more preferably 0.5 to 2 mol / liter.

(2) Positive electrode As the positive electrode active material used in the battery of the present invention, a composition formula Li _x MO ₂ , Li _y M ₂ O ₄ (where M is selected from transition metals), which is a compound capable of inserting and extracting lithium. Or a composite oxide represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), a metal chalcogenide or a metal oxide having a tunnel structure and a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiCo _x Ni _1-x O ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS. ₂ etc. are mentioned.
Examples of the organic compound include conductive polymers such as polyaniline.
Furthermore, the above-mentioned various active materials may be mixed and used regardless of an inorganic compound or an organic compound.
When a granular positive electrode active material is used, the positive electrode is produced, for example, by forming a mixture of positive electrode active material particles, a conductive additive and a binder on a metal current collector such as aluminum. .

(3) Negative electrode As the negative electrode active material of the present invention, all generally known materials such as metallic lithium, lithium alloys, and carbon materials capable of occluding and releasing lithium can be used. Examples of the negative electrode active material include alloys of lithium such as Al, Si, Pb, Sn, Zn, and Cd, metal oxides such as LiFe ₂ O ₃ , WO ₂ , MoO ₂ , SiO, and CuO, graphite, and carbon. A carbonaceous material, lithium nitride such as Li ₃ N, metallic lithium, or a mixture thereof can be used.

(4) Separator As the separator of the present invention, a woven fabric, a nonwoven fabric, a synthetic resin microporous membrane, or the like can be used, and a synthetic resin microporous membrane can be suitably used. Among these, a microporous membrane made of polyethylene and polypropylene, or a polyolefin microporous membrane such as a microporous membrane composed of these is preferably used in terms of thickness, membrane strength, membrane resistance, and the like.
Moreover, it can also serve as a separator by using solid electrolytes, such as a polymer solid electrolyte.
Further, a synthetic resin microporous membrane and a polymer solid electrolyte may be used in combination. In this case, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and the polymer solid electrolyte may further contain a nonaqueous electrolyte.

  The shape of the battery of the present invention is not particularly limited, and can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a square, a long cylinder, a coin, a button, a sheet, and a cylindrical battery. Although it is possible, the effect is satisfactorily exhibited in a battery in which the battery case is easily deformed, such as a rectangular shape, a long cylindrical shape, a coin shape, a button shape, and a sheet shape.

  Hereinafter, the present invention will be described with reference to preferred embodiments. However, the present invention is not limited to the embodiments in any way, and can be implemented with appropriate modifications within a range not changing the gist thereof. .

Example 1
FIG. 1 is a cross-sectional view showing a nonaqueous electrolyte secondary battery according to the present invention. In FIG. 1, 1 is a square nonaqueous electrolyte secondary battery (hereinafter referred to as a battery), 2 is an electrode group, 3 is a negative electrode, 4 is a positive electrode, 5 is a separator, 6 is a battery case, 7 is a case lid, 8 Is a safety valve, 9 is a negative electrode terminal, and 10 is a negative electrode lead. The electrode group 2 is obtained by winding the negative electrode 3 and the positive electrode 4 in a flat shape with the separator 5 interposed therebetween. The electrode group 2 and the nonaqueous electrolyte are housed in a battery case 6, and the opening of the battery case 6 is sealed by laser welding a case lid 7 provided with a safety valve 8. The negative electrode terminal 9 is connected to the negative electrode 3 via the negative electrode lead 10, and the positive electrode 4 is connected to the inner surface of the battery case 6.

The positive electrode 4 was produced as follows.
90% by mass of LiCoO ₂ as a positive electrode active material, 5% by mass of acetylene black as a conductive additive, and 5% by mass of polyvinylidene fluoride (PVDF) as a binder are mixed to form a positive electrode mixture. A paste was obtained by dispersing in N-methyl-2-pyrrolidone. This paste was uniformly applied to an aluminum current collector with a thickness of 20 μm and dried, and then compression molding was performed with a roll press to obtain the positive electrode 4.

The negative electrode 3 was produced as follows.
A slurry was prepared by mixing 97% by mass of graphite as a negative electrode active material, 1.5% by mass of carboxymethyl cellulose and 1.5% by mass of styrene butadiene rubber as a binder, and adding and dispersing distilled water as appropriate. . This slurry was uniformly applied to a 15 μm thick copper current collector, dried, dried at 100 ° C. for 5 hours, and then the density of the negative electrode active material layer composed of the binder and the active material was 1.40 g / cm ³ . Thus, the negative electrode 3 was obtained by compression molding with a roll press.

As the separator, a microporous polyethylene film having a thickness of 20 μm was used.
As a non-aqueous electrolyte, 1.1 mol / L of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1 to obtain vinylene. 1% by mass of carbonate is added with respect to the total mass of the non-aqueous electrolyte, and 0.001% by mass of dinormal butyl vinylboronate represented by the general formula (1) with respect to the total mass of the non-aqueous electrolyte. What was added was used.

(Example 2)
A battery was fabricated in the same manner as in Example 1 except that 0.05% by mass of vinyl normal acid di-normal butyl was added to the total mass of the nonaqueous electrolyte.

(Example 3)
A battery was fabricated in the same manner as in Example 1 except that 0.1% by mass of vinyl normal dianol butyl was added to the total mass of the nonaqueous electrolyte.

(Example 4)
A battery was fabricated in the same manner as in Example 1 except that 0.2% by mass of vinyl normal acid di-normal butyl was added to the total mass of the nonaqueous electrolyte.

(Example 5)
A battery was produced in the same manner as in Example 1 except that 0.5% by mass of vinyl normal dianol butyl was added to the total mass of the nonaqueous electrolyte.

(Example 6)
A battery was fabricated in the same manner as in Example 1 except that 1.0% by mass of vinyl normal dianol butyl was added to the total mass of the nonaqueous electrolyte.

(Example 7)
A battery was produced in the same manner as in Example 1 except that 2.0% by mass of vinyl normal acid di-normal butyl was added to the total mass of the nonaqueous electrolyte.

(Example 8)
A battery was fabricated in the same manner as in Example 1 except that 3.0% by mass of vinyl normal acid di-normal butyl was added to the total mass of the nonaqueous electrolyte.

Example 9
A battery was fabricated in the same manner as in Example 1 except that 5.0% by mass of vinyl normal dianol butyl was added to the total mass of the nonaqueous electrolyte.

(Example 10)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of dimethylvinylboronate was added to the total mass of the nonaqueous electrolyte.

(Example 11)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of diethyl vinylboronate was added relative to the total mass of the nonaqueous electrolyte.

(Example 12)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of vinylboronate dinormalpropyl was added to the total mass of the nonaqueous electrolyte.

(Example 13)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of vinyl normal dianpentylpentyl was added to the total mass of the nonaqueous electrolyte.

(Example 14)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of vinyl tert-butyl vinylboronate was added to the total mass of the nonaqueous electrolyte.

(Example 15)
A battery was fabricated in the same manner as in Example 1 except that 0.5% by mass of dinormalbutyl was added and 2.0% by mass of vinylene carbonate was added to the total mass of the nonaqueous electrolyte.

(Comparative Example 1)
A battery was fabricated in the same manner as in Example 1 except that the vinylboronic acid compound represented by the general formula (1) was not added to the nonaqueous electrolyte.

(Comparative Example 2)
A battery was fabricated in the same manner as in Example 1 except that 0.2% by mass of vinyl boronic acid was added instead of the vinyl boronic acid compound represented by the general formula (1) with respect to the total mass of the nonaqueous electrolyte. .

(Comparative Example 3)
A battery was produced in the same manner as in Example 1 except that 0.2% by mass of ethyl ethylboronate was added instead of the vinylboronic acid compound represented by the general formula (1) with respect to the total mass of the nonaqueous electrolyte. did.

(Comparative Example 4)
A battery was produced in the same manner as in Example 1 except that 0.2% by mass of dimethyl ethylboronate was added instead of the vinylboronic acid compound represented by the general formula (1) with respect to the total mass of the nonaqueous electrolyte. did.

(Comparative Example 5)
0.2 mass% of n-propyl boronic acid di-n-propyl is added instead of the vinyl boronic acid compound represented by the general formula (1) with respect to the total mass of the non-aqueous electrolyte, and Example 1 is otherwise performed. A battery was produced in the same manner as described above.

(Comparative Example 6)
A battery was fabricated in the same manner as in Example 1 except that 2.0% by mass of vinylene carbonate was added instead of the vinylboronic acid compound represented by the general formula (1) with respect to the total mass of the nonaqueous electrolyte. .

  The following performance evaluation was performed on the batteries of the above-described examples and comparative examples.

[Electrolytic solution storage test]
The electrolyte solution to which various additives were added was placed in a sealed solution, and APHA after being left in a 45 ° C. constant temperature bath for 2 weeks was measured according to ASTM D1209 to evaluate the coloring state of the electrolyte solution.
APHA is a Hazen number, which is an index indicating the strength of the color tone, and the larger the value, the greater the coloring.

[Initial capacity check test]
The initial capacity (mAh) was measured for the batteries of each Example and each Comparative Example. The batteries of each Example and each Comparative Example were prepared in 5 cells, and each battery was charged at a constant current and a constant voltage for 3 hours up to 4.2 V at a current of 800 mA, and then discharged to 3 V at a current of 800 mA. The discharge capacity (initial capacity) and the thickness of the battery were measured, and the average value of 5 cells was determined.

[Charge / discharge cycle life test]
The charge / discharge cycle life test was performed under the following conditions.
The battery after the initial capacity confirmation test was repeated for 500 cycles of charge / discharge cycles under the same conditions as the initial capacity measurement in a 45 ° C. thermostat, and then the capacity retention rate at the 500th cycle relative to the initial capacity (= 500 cycles). The discharge capacity of the eye ÷ initial capacity × 100) was determined.

[Low temperature cycle test]
The low temperature charge / discharge test was carried out under the following conditions.
The battery after the initial capacity confirmation test was charged in a constant temperature bath at −5 ° C. under the same conditions as the measurement of the initial capacity. The charged battery was left at 25 ° C. for 5 hours, and the discharge capacity was measured under the same conditions as the initial capacity measurement. The capacity retention ratio with respect to the initial capacity (= measured discharge capacity ÷ initial capacity × 100) was determined.

  Table 1 below shows the results of the initial capacity confirmation test, the high temperature storage test, and the low temperature charge / discharge cycle test.

〔Test results〕
Below, the result of an Example and a comparative example is considered.
[Differences between Examples and Comparative Examples]
In Examples 1 to 15, the vinyl boronic acid compound of the present invention was added. These show that the initial capacity is large and the battery thickness is small with respect to the non-addition of Comparative Example 1, and the charge / discharge cycle life characteristics and the low temperature charge characteristics are excellent. It is considered that the electrode film formed by the vinyl boronic acid compound of the present invention suppresses the reactivity of the electrolytic solution on the electrode and has good lithium ion conductivity even at a low temperature.
In Examples 1 to 9, the test was conducted by changing the addition amount of the vinyl boronic acid compound of the present invention from 0.001% by mass to 5% by mass. The low temperature charge characteristics are sufficiently effective even with an extremely small addition amount of 0.001% by mass, but in order to obtain good cycle life characteristics, the addition amount is preferably 0.05% or more, and better cycle life characteristics are obtained. In order to obtain it, the addition amount is preferably 0.1% by mass or more.
Furthermore, when the addition amount of the vinyl boronic acid compound is more than 3% by mass, the initial discharge capacity becomes small due to the improvement of the viscosity of the electrolytic solution. Therefore, the preferable addition amount of the vinyl boronic acid compound of the present invention is 2% by mass. It is as follows.
Examples 5 and 10 to 14 are obtained by adding 0.5% by mass of vinyl boronic acid compounds having different numbers of carbon atoms. When the number of carbon atoms is large, the molecular weight becomes large, and when added to the electrolytic solution, the viscosity becomes high and the discharge characteristics may be lowered. Therefore, the more preferable number of carbon atoms is 4 or less.

[Comparison with vinylboronic acid of Comparative Example 2]
When 0.2% by mass of the vinyl boronic acid of Comparative Example 2 was added, the charge / discharge cycle life characteristics and low-temperature charge acceptance were improved, but the electrolyte after the storage test was colored brown and the initial battery was swollen. Became larger. As a cause of coloring, it is considered that a hydroxyl group of vinyl boronic acid decomposes the electrolytic solution to generate a colored component. The initial swelling of the battery is considered to be due to the generation of hydrogen by the reduction of the hydroxyl group of vinylboronic acid on the negative electrode during the initial charge.

(Comparison with boronic acids of Comparative Examples 3 to 5)
In the batteries of Comparative Examples 3 to 5 in which 0.2% by mass of various boronic acid compounds were added, the high-temperature cycle characteristics were improved, but the charge / discharge efficiency at the time of low-temperature charge was lowered.
This is because the boronic acid compounds of Comparative Examples 3 to 5 formed a film having high resistance at low temperatures, whereas the film formed by the vinyl boronic acid compound of the present invention exhibited good lithium ion conductivity even at low temperatures. It is thought that it is because it has.

(Mixing effect with vinylene carbonate)
As in Comparative Example 6, when vinylene carbonate is added to the electrolytic solution, the charge / discharge cycle life characteristics at high temperature are improved, but the film resistance on the negative electrode is increased, so the charge / discharge efficiency at low temperature is reduced. It was. However, as in Example 15, by further adding the vinyl boronic acid compound of the present invention to the electrolyte solution added with vinylene carbonate, the cycle life characteristics are further improved and the charge acceptance at a low temperature is good. I found out. The negative electrode film formed by adding both the vinyl boronic acid compound of the present invention and vinylene carbonate further suppresses the decomposition of the electrolyte during charge and discharge at high temperatures and has low resistance at low temperatures. I found out.
A synergistic effect was obtained by mixing vinylene carbonate and the vinyl boronic acid compound of the present invention.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 3 Negative electrode plate 4 Positive electrode plate 5 Separator 6 Battery case 7 Case cover 8 Safety valve 9 Negative electrode terminal 10 Negative electrode lead

Claims (2)

Used in non-aqueous electrolyte secondary batteries, non-aqueous solvent, and a lithium salt, and an electrolytic solution comprising a represented by the following general formula (1) ruby Niruboron acid compound, the content of the vinyl boronic acid compound There nonaqueous electrolyte, characterized in der Rukoto than 5 mass% 0.001 mass% or more.

In the general formula (1), R _{1 to} R ₂ are alkyl groups having 1 to 5 carbon atoms, which may be the same or different. Non-aqueous electrolyte secondary battery which comprises a non-aqueous electrolyte according to claim 1.

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