JP2000243437A - Solute for nonaqueous electrolyte battery and nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a capacitance from reducing when stored under the high temperature with a battery charged and to provide a battery with excellent storage characteristics under the high temperature by using lithium borate bonded with one kind of group selected from an alkoxy group, phenoxy group and their derivative group. SOLUTION: A solute of lithium borate bonded with an alkoxy group and phenoxy group is lithium tetraphenoxyborates or lithium tetraalkoxyborates such as lithium tetramethoxyborate and lithium tetraethoxyborate. When the solute that a part of hydrogen is substituted with fluorine is used, the solute is hardly reduced so that the reaction of the solute to a negative electrode in a charging condition is further suppressed. As the solute substituted with the fluorine, the solute in which the hydrogen of the alkoxy group or phenoxy group of lithium tetrakis (trifluoromethoxy) borate, etc., is substituted with the fluorine is named.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a solute used for the non-aqueous electrolyte in the non-aqueous electrolyte battery. It is characterized by improving the solute used for, especially, suppressing the dissociation of this solute at high temperature and reacting with the electrode, and improving the storage characteristics of the nonaqueous electrolyte battery at high temperature. is there.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries having a high electromotive force using a non-aqueous electrolyte and utilizing oxidation and reduction of lithium have been used as new batteries having a high output and a high energy density.

Here, in such a non-aqueous electrolyte battery, as a non-aqueous electrolyte, a solvent such as propylene carbonate or dimethyl carbonate is generally added to lithium hexafluorophosphate LiPF ₆ or lithium perchlorate Lithium.
Solutes such as ClO ₄ have been used, but solutes such as lithium perchlorate LiClO ₄ have problems in safety, etc., and at high temperatures such solutes react with the electrodes. As a result, self-discharge occurs and the capacity is reduced when the nonaqueous electrolyte battery is charged and stored at a high temperature.

In recent years, Japanese Patent Application Laid-Open No. 61-21 / 1986
As disclosed in Japanese Patent No. 4375, there has been proposed a method in which lithium tetraphenylborate purified by recrystallization in an organic solvent is used as a solute of a nonaqueous electrolyte.

[0005] However, even when lithium tetraphenylborate is used as the solute of the non-aqueous electrolyte,
This solute is easily dissociated in the non-aqueous electrolyte,
This solute is dissociated at a high temperature and reacts with the electrode to cause self-discharge, and there is a problem that the capacity is reduced when the nonaqueous electrolyte battery is stored at a high temperature while being charged.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in a non-aqueous electrolyte battery provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte.
As a solute used for the non-aqueous electrolyte, a solute that does not dissociate and react with the electrode at high temperatures is provided, and such a solute is used in a non-aqueous electrolyte battery, and the non-aqueous electrolyte battery is charged. It is an object of the present invention to prevent the capacity of the nonaqueous electrolyte battery from lowering when stored at a high temperature in order to obtain a nonaqueous electrolyte battery having excellent storage characteristics at a high temperature. .

[0007]

According to the first aspect of the present invention, there is provided a solute for a non-aqueous electrolyte battery, wherein at least one selected from an alkoxy group, a phenoxy group and a derivative group thereof is used in order to solve the above-mentioned problems. That is, one in which one type of group was bonded to lithium borate was used.

In the solute for a non-aqueous electrolyte battery according to the first aspect, a group selected from an alkoxy group, a phenoxy group and a derivative group thereof is firmly bonded to boron, whereby the solute becomes non-aqueous. Dissociation in the electrolytic solution is suppressed, and this solute is stably present in the non-aqueous electrolytic solution even at a high temperature, and it is less likely to react with the electrode.

The solute for a non-aqueous electrolyte battery in which at least one group selected from an alkoxy group, a phenoxy group and a derivative group thereof is bonded to lithium borate as described above includes, for example, tetramethoxy Lithium tetraalkoxy borate such as lithium borate, lithium tetraethoxy borate, lithium tetrapropoxy borate, lithium tetrabutoxy borate and the like; lithium tetraphenoxy borate, tetrakis (3-methylphenoxy)
Lithium tetraphenoxyborates such as lithium borate and lithium tetrakis (3,5-dimethylphenoxy) borate.

In a solute for a non-aqueous electrolyte battery according to a second aspect of the present invention, in a group selected from the above-mentioned alkoxy group, phenoxy group and these derived groups, at least a part of hydrogen is replaced by fluorine. When the solute is used, the solute is less likely to be reduced, and the solute is further suppressed from reacting with the negative electrode in a charged state.

The solute for a non-aqueous electrolyte battery in which at least a part of the hydrogen in the alkoxy group, the phenoxy group, and the derivative group bonded to lithium borate is substituted with fluorine as described above includes, for example, Lithium tetrakis (trifluoromethoxy) borate, lithium tetrakis (2,2,2-trifluoroethoxy) borate, lithium tetrakis (pentafluoroethoxy) borate, bis (trifluoromethoxy) bis (pentafluoroethoxy) borate At least part of hydrogen in an alkoxy group such as lithium is substituted with fluorine,
Lithium tetrakis (pentafluorophenoxy) borate, tetrakis (3-trifluoromethylphenoxy)
Phenoxy groups such as lithium borate and lithium tetrakis (3,5-bis (trifluoromethyl) phenoxy) borate in which part of hydrogen in a phenoxy group is substituted with fluorine are mentioned.

Further, in the non-aqueous electrolyte battery according to claim 3 of the present invention, the solute for a non-aqueous electrolyte battery described in claim 1 or 2 is used as the solute in the non-aqueous electrolyte. .

Here, as in the non-aqueous electrolyte battery according to claim 3 of the present invention, the solute in the non-aqueous electrolyte is
When the solute for a non-aqueous electrolyte battery according to claim 1 or 2 is used, dissociation of the solute in the non-aqueous electrolyte is suppressed as described above. It is stably present in the electrolyte, preventing the solute from reacting with the electrode and self-discharging, and suppressing a decrease in capacity when the nonaqueous electrolyte battery is stored at a high temperature in a charged state. The storage characteristics at high temperatures are improved.

The non-aqueous electrolyte battery of the present invention is characterized by the solute used for the non-aqueous electrolyte as described above. Is not particularly limited, and those generally used in nonaqueous electrolyte batteries can be used.

The solvent used for the non-aqueous electrolyte is, for example, a cyclic carbonate such as ethylene carbonate, propylene carbonate, vinylene carbonate or butylene carbonate, dimethyl carbonate, or the like.
Acyclic carbonates such as diethyl carbonate and methyl ethyl carbonate, 1,2-diethoxyethane,
Solvents such as 1,2-dimethoxyethane and ethoxymethoxyethane can be used alone or as a mixture of two or more. In particular, when a mixed solvent obtained by mixing the cyclic carbonate and the non-cyclic carbonate described above is used as the solvent in the non-aqueous electrolyte, the ionic conductivity of the non-aqueous electrolyte is improved, and , The dissociation of the solute is further suppressed, and the storage characteristics at high temperatures are further improved.

In the non-aqueous electrolyte battery according to the present invention, a non-aqueous electrolyte obtained by dissolving the above-mentioned solute in the above-mentioned solvent can be impregnated into a polymer to be used as a gel polymer electrolyte. is there.

In the non-aqueous electrolyte battery of the present invention, the positive electrode material constituting the positive electrode includes, for example, manganese dioxide, lithium-containing manganese oxide, lithium-containing cobalt oxide, lithium-containing vanadium oxide,
Lithium-containing nickel oxide, lithium-containing iron oxide,
Lithium-containing chromium oxide, lithium-containing titanium oxide and the like are used.

In the nonaqueous electrolyte battery according to the present invention, the negative electrode constituting the negative electrode may be lithium metal, Li-Al, Li-In, Li-Sn, Li-P.
b, Li-Bi, Li-Ga, Li-Sr, Li-S
i, Li-Zn, Li-Cd, Li-Ca, Li-Ba
Materials containing carbon, such as lithium alloys such as graphite, graphite, coke, and organic materials that can store and release lithium ions,
Metal oxides such as SnO ₂ , SnO, TiO, and Nb ₂ O ₃ having a lower potential than the positive electrode material can be used. In particular, when a carbon material is used as the negative electrode material, A film having excellent ion conductivity is formed on the surface of the carbon material by the non-aqueous electrolyte containing the solute, and the reaction of the negative electrode with the non-aqueous electrolyte is further suppressed by this film,
High-temperature storage characteristics of a nonaqueous electrolyte battery using a carbon material as a negative electrode material are significantly improved.

[0019]

EXAMPLES Hereinafter, a solute for a non-aqueous electrolyte battery according to the present invention and a non-aqueous electrolyte battery using the solute will be specifically described with reference to examples, and in the non-aqueous electrolyte battery in this example, It will be clarified that a decrease in capacity when stored at a high temperature is reduced and storage characteristics under a high temperature are improved by using a comparative example. In addition,
The solute for a non-aqueous electrolyte battery and the non-aqueous electrolyte battery according to the present invention are not limited to those shown in the following examples, and can be appropriately modified and implemented without changing the gist thereof.

Example 1 In Example 1, a positive electrode and a negative electrode were prepared as described below, and a non-aqueous electrolyte was prepared as described below. As shown in FIG. 14mm, height 50mm, battery capacity 400mA
h, a cylindrical lithium secondary battery was manufactured.

[Preparation of Positive Electrode] In preparing a positive electrode, LiCoO ₂ powder was used as a positive electrode material.
O ₂ powder and acetylene black powder as a conductive agent were mixed at a weight ratio of 90: 6 to prepare a positive electrode mixture.

Then, a solution prepared by dissolving polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is added to the positive electrode mixture. The above positive electrode mixture and PVdF are 9
A slurry was prepared by kneading them so as to have a weight ratio of 6: 4, and this slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil by a doctor blade method,
This was vacuum-dried at 150 ° C. for 2 hours to produce a positive electrode.

[Preparation of Negative Electrode] In preparing the negative electrode, a natural graphite powder was used as a negative electrode material, and a solution of PVdF as a binder dissolved in NMP was added to the natural graphite powder. PVdF was adjusted to a weight ratio of 96: 4, and the mixture was kneaded to prepare a slurry. The slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method. Vacuum drying was performed for 2 hours to produce a negative electrode.

[Preparation of Non-Aqueous Electrolyte] In preparing a non-aqueous electrolyte, ethylene carbonate (hereinafter abbreviated as EC) which is a cyclic carbonate and diethyl carbonate (hereinafter abbreviated as DEC) which is a non-cyclic carbonate are used. Abbreviated.)
And 1 mol of lithium tetramethoxyborate LiB (OCH ₃ ) ₄ in a mixed solvent in which
/ L to prepare a non-aqueous electrolyte.

[Preparation of Battery] In preparing the battery, as shown in FIG. 1, a microporous polyethylene film as a separator 3 was interposed between the positive electrode 1 and the negative electrode 2 prepared as described above. These are wound in a spiral shape and accommodated in a battery can 4, and the above-mentioned non-aqueous electrolyte is poured into the battery can 4 and sealed.
a, the negative electrode 2 is connected to the battery can 4 via the negative electrode lead 2a.
The positive electrode cover 5 and the positive electrode cover 5 were electrically insulated by an insulating packing 6 to obtain a lithium secondary battery.

(Examples 2 to 17) In the lithium secondary batteries of Examples 2 to 17, only the solute used in the preparation of the non-aqueous electrolyte was changed from that of the lithium secondary battery of Example 1 described above. Otherwise, a cylindrical lithium secondary battery was fabricated in the same manner as in Example 1 above.

Here, in Examples 2 to 17, LiB (CH ₃ ) (OCH ₃ ) ₃ was added to the solute in the non-aqueous electrolyte as shown in Table 1 below. In No. 3, LiB (CH ₃ ) ₂ (OCH ₃ )
₂ and LiB (CH ₃ ) ₃ (OCH
₃ ) is replaced by LiB (OC ₂ H ₅ ) in Example 5.
₄ and LiB (OC ₃ H ₇ ) ₄ in Example 6.
Example 7 uses LiB (OC ₄ H ₉ ) ₄ , Example 8 uses LiB (OCF ₃ ) ₄ , Example 9 uses LiB (OCH ₂ CF ₃ ) ₄ , and Example 10 uses LiB ( OC ₂ F ₅ ) ₄ , LiB (OCF ₃ ) ₂ (OC ₂ F ₅ ) ₂ in Example 11, and Example 12
In Example 13, LiB (OC ₆ H ₅ ) ₄ was used. In Example 13, LiB (OC ₆ H ₄ CH ₃ ) ₄ was used. In Example 14, LiB (OC ₆ H ₃ (CH ₃ ) ₂ ) ₄ was used. In Example 15, LiB (OC ₆ F ₅ ) ₄ was used.
In Example 6, LiB (OC ₆ H ₄ CF ₃ ) ₄ was used, and in Example 17, LiB (OC ₆ H ₃ (CF ₃ ) ₂ ) ₄ was used.

(Comparative Examples 1 to 3) In the lithium secondary batteries of Comparative Examples 1 to 3, only the solute used in the preparation of the non-aqueous electrolyte was changed from that of the lithium secondary battery of Example 1 described above. Otherwise, a cylindrical lithium secondary battery was fabricated in the same manner as in Example 1 above.

Here, in Comparative Examples 1 to 3, as shown in Table 1 below, LiPF ₆ in Comparative Example 1 and LiB ₆ in Comparative Example 2
(CH ₃ ) ₄ and LiB (C
₆ H ₅ ) ₄ was used.

Then, each of the lithium secondary batteries of Examples 1 to 17 and Comparative Examples 1 to 3 was charged at 1 mA / cm ^2.
After charging to a charging end voltage of 4.2 V with a charging current of
A discharge current of 3 mA was discharged at a discharge current of mA / cm ² to measure a discharge capacity Q0 before storage. Each of the above-mentioned lithium secondary batteries was charged at a charge current of 1 mA / cm ^{2 and had} a discharge voltage of 4.2 V. After charging, each lithium secondary battery was stored for 1 month in a temperature atmosphere of 60 ° C., and then discharged at a discharge current of 1 mA / cm ² to a discharge termination voltage of 3 V, and a discharge capacity Q1 after storage was measured. The rate of decrease in discharge capacity after storage (capacity decrease rate) was determined by the following equation, and the results are shown in Table 1 below. Capacity reduction rate (%) = [(Q0−Q1) / Q0] × 100

[0031]

[Table 1]

As is apparent from the results, an embodiment using a solute in which lithium borate is bonded to lithium alkoxylate, a phenoxy group and one group selected from these derived groups as the solute in the non-aqueous electrolyte. Each of the lithium secondary batteries of Nos. 1 to 17 had a temperature of 60 ° C. as compared with the lithium secondary batteries of Comparative Examples 1 to 5 using a solute that did not satisfy the requirements of the present invention.
At a temperature of 1 month, the capacity reduction rate after storage for one month was low, and the storage characteristics at high temperatures were improved. Further, each of the lithium secondary batteries of Examples 8 to 11 and 15 to 17 in which at least a part of hydrogen in the above-mentioned alkoxy group, phenoxy group and these derived groups bonded to lithium borate was substituted with fluorine, The storage characteristics at high temperatures were further improved as compared with those in which the hydrogen in the corresponding alkoxy group, phenoxy group and these derived groups was not substituted with fluorine.

(Examples 18 to 27) In the lithium secondary batteries of Examples 18 to 27, in the preparation of the nonaqueous electrolyte in Example 1 described above, the solute in Example 8 was used.
The same LiB (OCF ₃ ) ₄ as in Example 1 was used, and the solvent in the non-aqueous electrolyte was changed as shown in Table 2 below. Was manufactured.

Here, as a solvent in the non-aqueous electrolyte,
In Examples 18 to 21, a mixed solvent of cyclic carbonate and acyclic carbonate was used.
In Example 8, a mixed solvent obtained by mixing propylene carbonate (hereinafter abbreviated as PC) and DEC at a volume ratio of 1: 1 was used. In Example 19, butylene carbonate (hereinafter abbreviated as BC) and DEC were mixed in a ratio of 1 to 1. In Example 20, a mixed solvent obtained by mixing EC and dimethyl carbonate (hereinafter abbreviated as DMC) at a volume ratio of 1: 1 was used.
And ethyl methyl carbonate (hereinafter abbreviated as EMC)
And a mixed solvent obtained by mixing at a 1: 1 volume ratio. On the other hand, in Example 22, only EC, in Example 23, only DEC, in Example 24, only 1,2-dimethoxyethane (hereinafter abbreviated as DME), and in Example 25, EC and DME were used. In a 1: 1 volume ratio, and in Example 26
In Example 27, a mixed solvent obtained by mixing C and tetrahydrofuran (hereinafter abbreviated as THF) at a volume ratio of 1: 1 was used. In Example 27, γ-butyrolactone (hereinafter abbreviated as γ-BL) was used.
And DEC in a 1: 1 volume ratio.

Each of the lithium secondary batteries of Examples 18 to 27 is also similar to the lithium secondary batteries of Examples 1 to 17 and Comparative Examples 1 to 3 before storage. The discharge capacity Q0 and the discharge capacity Q1 after each lithium secondary battery was stored for one month in a 60 ° C. temperature atmosphere were measured to determine the above-mentioned capacity reduction rate, and the results were combined with Example 8 above. The results are shown in Table 2 below.

[0036]

[Table 2]

As is evident from the results, the solute of the non-aqueous electrolytic solution is made of LiB (OCF ₃ ) satisfying the requirements of the present invention.
₄ with use of, Example 8,18～21 using a mixed solvent of a cyclic carbonate and a non-cyclic carbonate in the solvent
Example 2 using a solvent other than a mixed solvent of a cyclic carbonate and an acyclic carbonate in each of the lithium secondary batteries of Example 2
Compared with each of the lithium secondary batteries of Nos. 2 to 27, the rate of decrease in capacity when stored for one month in a 60 ° C temperature atmosphere was further reduced, and the storage characteristics at high temperatures were further improved.

(Examples 28 and 29 and Comparative Examples 4 and 5) In Examples 28 and 29, the same solute as LiB (OCF ₃ ) ₄ in Example 8 was used for the solute in the non-aqueous electrolyte. As shown in Table 3 below, as the negative electrode material for the negative electrode, lithium metal was used in Example 28, and a Li-Al alloy was used in Example 29, and the other cases were the same as those in Example 1 above. In the same manner as in the above, a cylindrical lithium secondary battery was produced.

In Comparative Examples 4 and 5, the solute in the non-aqueous electrolyte was the same LiPF as in Comparative Example 1 described above.
_6, and as a negative electrode material in the negative electrode, as shown in Table 3 below, lithium metal was used in Comparative Example 4;
In Comparative Example 5, a Li-Al alloy was used,
Otherwise, a cylindrical lithium secondary battery was manufactured in the same manner as in Example 1 described above.

The lithium secondary batteries of Examples 28 and 29 and Comparative Examples 4 and 5 are the same as those of the lithium secondary batteries of Examples 1 to 17 and Comparative Examples 1 to 3 described above. Then, the discharge capacity Q0 before storage and the discharge capacity Q1 after storage of each lithium secondary battery for one month in a temperature atmosphere of 60 ° C. were measured to obtain the above-mentioned rate of capacity reduction, and the results were obtained as described above. The results are shown in Table 3 below together with Example 8 and Comparative Example 1.

[0041]

[Table 3]

As is evident from the results, Example 2
As shown in Examples 8 and 29 and Comparative Examples 4 and 5, when a lithium metal other than graphite or a Li-Al alloy is used as the negative electrode material, LiB (OCF ₃ ) satisfying the requirements of the present invention is used as the solute in the non-aqueous electrolyte. each lithium secondary batteries of examples 28 and 29 using _4, as compared to the lithium secondary batteries of Comparative examples 4 and 5 using LIPF ₆ solute and 1 month storage at an ambient temperature of 60 ° C. In this case, the capacity reduction rate was low, and the storage characteristics at high temperatures were improved.

When comparing the lithium secondary batteries of Examples 8, 28 and 29 with each other, the lithium secondary battery of Example 8 using graphite as the negative electrode material was more suitable for lithium metal and Li other than graphite. The improvement in storage characteristics at high temperatures was greater than those of the lithium secondary batteries of Examples 28 and 29 using -Al alloy.

[0044]

As described in detail above, the solute for a nonaqueous electrolyte battery according to the present invention, in which a group selected from an alkoxy group, a phenoxy group and a derivative thereof is bonded to lithium borate, is used. When used, this solute is suppressed from dissociating in the non-aqueous electrolyte, and this solute is stably present in the non-aqueous electrolyte, especially at high temperatures,
Reaction with the electrode is reduced.

When the above-mentioned solute for a non-aqueous electrolyte battery is used as a solute for a non-aqueous electrolyte battery, dissociation of the solute in the non-aqueous electrolyte is suppressed as described above, In this case, the solute stably exists in the non-aqueous electrolyte, preventing the solute from reacting with the electrode and self-discharging, and storing the non-aqueous electrolyte battery at a high temperature in a charged state. In this case, the capacity did not decrease much, and the storage characteristics at high temperatures were improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an internal structure of a lithium secondary battery produced in an example of the present invention and a comparative example.

[Explanation of symbols]

 1 positive electrode 2 negative electrode

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Ikuo Yonezu 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 5H029 AJ04 AK02 AK03 AL02 AL06 AL07 AL12 AM00 AM01 AM02 AM03 AM06 BJ02 BJ14 DJ09

Claims (4)

[Claims] 1. A solute for a non-aqueous electrolyte battery, wherein at least one group selected from an alkoxy group, a phenoxy group and a derivative group thereof is bonded to lithium borate. 2. The solute for a non-aqueous electrolyte battery according to claim 1, wherein at least a part of the hydrogen in the alkoxy group, the phenoxy group, and the derivative group thereof is replaced with fluorine. Solute for non-aqueous electrolyte batteries. 3. A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the solute for the non-aqueous electrolyte battery according to claim 1 or 2 is used as the solute in the non-aqueous electrolyte. Non-aqueous electrolyte battery characterized by the above-mentioned. 4. The non-aqueous electrolyte battery according to claim 3, wherein a carbon material is used as a negative electrode material in the negative electrode.