JPH08301879A - Lithium salt, electrolyte using the same and lithium battery - Google Patents

Abstract

PURPOSE: To obtain a lithium salt having a large transference number of lithium ion, not having ignition property, combustion accelerating property nor toxicity and not generating toxic substance by decomposition, an electrolyte using the lithium salt and a lithium battery using the electrolyte CONSTITUTION: This lithium salt is expressed by the formula, (RX)4 Al<-> Li<+> [R are individually independent a linear or cyclic <=20C alkyl group, a <=20C alkenyl group, a methoxy oligoethyleneoxy group at a chain end (repeating number of the ethyleneoxy is 1-21), a phenyl group, a substituted phenyl group substituted with a <=4C group, a <=20C aryl group, a furfuryl group or a tetrahydrofurfuryl group and X are individually independent O-atom or S-atom bonding R with Al].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel lithium salt, an electrolyte using the same, and a lithium battery using the electrolyte.

[0002]

2. Description of the Related Art Lithium batteries, which have a high energy density, have been widely used in a wide range of applications in accordance with the recent trend toward light, thin, short and small cordless in the electronics field. Since lithium has a property of reacting violently with water or the like, the electrolyte of these lithium batteries is usually used in an aprotic organic solvent such as lithium perchlorate, lithium trifluoromethanesulfonate, LiBF ₄ , LiPF ₆ ,
A liquid in which a lithium salt such as LiAsF ₆ is dissolved is used.

[0003]

A lithium battery using metallic lithium has a problem that acicular deposition (dendrites) of lithium occurs with repeated charging and discharging.
That is, there is a problem in that needle-like precipitated lithium crystals pierce the separator and reach the positive electrode, causing an internal short circuit and significantly reducing battery performance. Also,
If an internal short circuit occurs, an excessive current will flow, causing an abnormal temperature rise and the accompanying volatilization of the organic electrolyte, which will increase the internal pressure of the battery, and in the worst case, extremely serious safety that could lead to a rupture or explosion of the battery. Have problems in terms of.

In particular, the electrolyte using lithium perchlorate is
Since dendrites are easily generated and it is an oxygen-supplying substance, there is a high risk of ignition and explosion. A triflate-based lithium fluoride salt has been proposed to avoid such a risk, but this also decomposes when liquid leaks or an abnormal rise in temperature produces a highly toxic fluorine compound. In addition, there is a problem in that there is a possibility of producing poisonous substances such as hydrofluoric acid and phosphorus pentafluoride by hydrolysis.

Further, when the transport number of lithium ions is high, the polarization of lithium ions is small and stable conduction of lithium ions is obtained, so that a lithium battery capable of extracting a stable current can be obtained. Therefore, there has been a demand for a lithium salt having a high lithium ion transport number.

The object of the present invention is to provide a large transport number of lithium ions, and to have no ignitability, combustion promoting property and toxicity.
It is to provide a lithium salt that does not generate a toxic substance by decomposition, an electrolyte using the lithium salt, and a lithium battery using the electrolyte.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the above-mentioned conventional problems, and as a result, have a large lithium ion transport number, and have a high ignitability, a combustion promoting property, and a toxicity. The present invention has been completed by finding a lithium salt that does not have a toxic substance due to decomposition.

That is, the present invention relates to general formulas (I) and (I
It is a lithium salt represented by I) and (III).

[0009]

[Chemical 4]

(In the formula, each R independently has 20 carbon atoms.
Substitution substituted with the following chain or cyclic alkyl group, alkenyl group having 20 or less carbon atoms, terminal methoxyoligoethyleneoxy group (repeating number of ethyleneoxy is 1 to 21), phenyl group, group having 4 or less carbon atoms A phenyl group, an aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group, wherein X is independently R
Represents an O atom or an S atom connecting Al to Al. )

[0011]

Embedded image

(In the formula, each R ¹ independently has 2 carbon atoms.
Substituted with a chain or cyclic alkyl group having 0 or less, an alkenyl group having 20 or less carbon atoms, a terminal methoxyoligoethyleneoxy group (the repeating number of ethyleneoxy is 1 to 21), a phenyl group, and a group having 4 or less carbon atoms. A substituted phenyl group,
An aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group is shown. R ² is alkylene having 20 or less carbon atoms, phenyldialkylene and phenylene having 20 or less carbon atoms, alkenylene having 20 or less carbon atoms,
_{(CH 2 CH 2 O) n} -CH 2 CH 2 - (n is 0 to 20
Indicates the number of. ), Arylene having 30 or less carbon atoms, aralkylene having 30 or less carbon atoms, and alkylenediphenylene having 30 or less carbon atoms. X represents an O atom or an S atom which independently connects R ¹ or R ² and Al. )

[0013]

[Chemical 6]

(In the formula, each R ¹ independently has 2 carbon atoms.
Substituted with a chain or cyclic alkyl group having 0 or less, an alkenyl group having 20 or less carbon atoms, a terminal methoxyoligoethyleneoxy group (the repeating number of ethyleneoxy is 1 to 21), a phenyl group, and a group having 4 or less carbon atoms. A substituted phenyl group,
An aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group is shown. R ³ represents a trivalent aliphatic or aromatic hydrocarbon group. X's each independently represent an O atom or an S atom connecting R ¹ or R ³ and Al. )

Examples of the phenyl group substituted with a group having 4 or less carbon atoms include a methylphenyl group, an ethylphenyl group, an isopropylphenyl group and a t-butylphenyl group.

The electrolyte of the present invention has the general formula (I):
An electrolyte obtained by dissolving the lithium salt of (II) or (III) in an aqueous solvent or polymer. A lithium battery of the present invention is a lithium battery comprising the electrolyte of the present invention, a positive electrode capable of occluding or releasing lithium ions, and a negative electrode capable of occluding or releasing lithium ions.

The lithium salt represented by the general formula (I) of the present invention can be produced by reacting LiAlH ₄ with stoichiometric amounts of alcohols, thiols, phenols, thiophenols and the like.

The lithium salt represented by the general formula (II) of the present invention comprises LiAlH ₄ in addition to the above alcohols, thiols, phenols and thiophenols, dihydric alcohols and / or dihydric alcohols. It can be produced by reacting a stoichiometric amount using thiols.

The lithium salt represented by the general formula (III) of the present invention comprises LiAlH ₄ in addition to the above alcohols, thiols, phenols and thiophenols, and three hydroxyl groups or mercapto groups in one molecule. It can be produced by reacting a compound having

The above-mentioned alcohols, thiols, phenols and thiophenols include furfuryl alcohol, tetrahydrofurfuryl alcohol, methylfurfuryl alcohol, methyltetrahydrofurfuryl alcohol, phenol, cresol and methoxyphenol.
Furfuryl mercaptan, tetrahydrofurfuryl mercaptan, methylfurfuryl mercaptan, methyltetrahydrofurfuryl mercaptan, thiophenol, methylthiophenol, methoxythiophenol, xylenol, ethylphenol, isopropylphenol,
Examples thereof include t-butylphenol and isopropylthiophenol.

Examples of the above divalent alcohols and divalent thiols include oligoethylene glycol, 1,2-ethanedithiol, 1,4-butanedithiol, dimer thiols such as 2-mercaptoethyl ether, and bisphenol A. , Hydroquinone, benzenedithiol, ethylene oxide adduct of hydroquinone, bisphenol A
Examples thereof include ethylene oxide adducts thereof. Examples of the compound having three hydroxyl groups or mercapto groups include glycerin and thioglycerin.

In the reaction for synthesizing the lithium salt of the present invention, the water content 1 equipped with both cooling and heating baths is preferable.
It is carried out in an inert gas such as argon at a level of ppm or less. The reaction can be carried out in a solvent, for example dehydrated TH
Ether solvents such as F, diethyl ether and dimethoxyethane are preferably used. It is also possible to use excess alcohol as the solvent. The reaction is preferably started under cooling, and a method of completing the reaction by successively heating and heating at 40 to 120 ° C., preferably 60 to 80 ° C. for 1 to 2 hours can be adopted.

When the lithium salt of the present invention is used as an electrolyte for a lithium battery, it is used by dissolving it in a non-aqueous solvent or a non-aqueous polymer. When the lithium salt is produced in an ether solvent, it may be directly dissolved in a non-aqueous solvent or polymer. After removing the solvent, the solvent may be newly dissolved in a non-aqueous solvent or a non-aqueous polymer.

Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-propiolactone, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, sulfolane, N-methylpyrrolidone, Examples thereof include N-cyclohexylpyrrolidone.

As the non-aqueous polymer, MEP-7 (phosphazene polymer; manufactured by Otsuka Chemical Co., Ltd.), polyethylene oxide dimethyl ether, methacrylic acid ester polymer of polyethylene oxide monomethyl ether, etc. can be widely used. Further, the lithium salt of the present invention can be mixed with several kinds of salts to form a molten salt electrolyte.

The lithium battery of the present invention comprises a positive electrode capable of storing or releasing lithium ions, an electrolyte containing the lithium salt of the present invention, and a negative electrode capable of storing or releasing lithium ions. The lithium battery of the present invention is a battery in which the positive electrode and the negative electrode are in contact with each other via the electrolyte containing the lithium salt of the present invention and are electrically separated by the electrolyte. Therefore, for example, a combination of two electrodes that generate electromotive force due to the overall redox reaction between electrodes, such as a normal alkaline battery, or two electrodes that are arranged so that their properties change when energy is applied to the battery It can be a battery.

[0027]

INDUSTRIAL APPLICABILITY The lithium salt of the present invention has a large lithium ion transport number and a high ion mobility, and can be suitably used as an electrolyte of a lithium battery. Further, since the lithium salt of the present invention has no ignitability, combustion promoting property, and toxicity, and does not generate a toxic substance by decomposition, the lithium battery using the lithium salt of the present invention is extremely safe. It can be a battery.

[0028]

Example 1 In a 200 ml glass reaction vessel equipped with a reflux condenser, a dropping funnel and a stirrer in an argon box equipped with both cooling / heating baths and having a water content kept at 1 ppm or less,
50 ml of a THF solution in which LiAlH ₄ was diluted to a concentration of 1 M / l was charged, and 2,6-dimethylphenol 27.
What melt | dissolved 6 g in 80 ml THF was dripped in the reaction container by a dropping funnel at -5 degreeC, stirring. After that, the temperature was raised to 70 ° C over 1 hour, and then at
Allowed to react for hours. When a part of the reaction solution was collected and THF was completely removed, a colorless transparent solid having a melting point of 80 ° C. was obtained.

The product obtained has (1) no IR absorption at 3250 cm ^{-1 in} its IR spectrum,
(2) The peak observed in the proton NMR spectrum is only the peak derived from the 2,6-dimethylphenoxy group, and (3) the Li content by flame photometry is 1.2.
Since it was 0%, lithium tetrakis (2,6-
It was confirmed to be dimethylphenoxy) aluminate. ^{The 1} H-NMR spectrum is shown in FIG. 1.

This compound was pelletized by a pressure molding method, an electrode was attached, and the AC conductivity (ionic conductivity) was measured and found to be 4.2 × 10 ^-7 S / cm. This indicates that lithium is ionically dissociated in the solid state, and this lithium salt is very easily dissociated, and it can be a supporting electrolyte having high ion conductivity.

0.8 parts by weight of ethylene carbonate was added to 1.0 part by weight of the reaction solution obtained by the above reaction. The ionic conductivity of this solution is 2 × 10 ^-2 S / cm
It was a high value.

A predetermined amount of MEP is added to the above reaction solution.
-7 (Otsuka Chemical Co., Ltd., oligoethyleneoxypolyphosphazene) was added and made compatible. This solution was cast on an electrode and the solvent was removed to prepare a biionic polymer solid electrolyte having salt concentrations shown in Table 1. The ionic conductivity values of the obtained polymer solid electrolyte are shown in Table 1.

[0033]

[Table 1]

The AC conductivity (ionic conductivity) is H
Using P4192A (manufactured by Hewlett Packard), amplitude 0.1 V, measurement range 5 to 13 MHz, temperature 25
It is a value measured at ° C.

Examples 2 to 17 In the same manner as in Example 1, lithium salts having an anion structure shown in Table 2 were synthesized. Appearance of the obtained lithium salt
The properties and ionic conductivity are shown in Table 2. In Table 2, E
O is an ethyleneoxy group, Me is a methyl group, Ph is a phenyl group or a substituted phenyl group, and tBu is a tertiary butyl group.

[0036]

[Table 2]

The structure of the lithium salt shown in Table 2 was confirmed by
As in Example 1, IR spectrum, ¹H-NMR spectrum
Tor, and¹³It was performed using C-NMR. Conversion of Example 4
The IR spectrum of the compound is shown in FIG. In Figure 2, the actual
The wire is the raw material triethylene glycol monomethyl ether
And the dotted line shows the reaction product lithium salt.
are doing.

[0038]Example 18 LiAlH_FourEthylene oxide based on 0.05 mol
The number of repetitions of m is the value shown in Table 3.
Recall 0.025 mol and repeat of ethylene oxide
The number n is the value shown in Table 3 oligoethylene glycol
0.15 mol of monomethyl ether was added in the same manner as in Example 1.
To react, Li⁺[H₃C- (OCH₂CH₂)_n
O-]₃Al^--(OCH₂CH₂)_mO-Al^-[-
O (CH ₂CH₂O)_n-CH₃]₃Li⁺Of salt
did. Appearance, properties and ionic conductivity of the obtained lithium salt
The degrees are shown in Table 3.

[0039]

[Table 3]

Example 19 0.05 mol of LiAlH _{4 to} 0.0 mol of glycerin
17 mol and 0.15 mol of triethylene glycol monomethyl ether were reacted according to Example 1 to give Li
⁺ _{[H 3 C- (OCH 2 CH 2} ) 3 O- ] ₃ Al ^- -O
CH {CH ₂ OAl ^- _{[-O (CH 2 CH 2 O)} 3 -C
Yield of H _{3] 3} Li ^+} ₂ salt. This salt is a very viscous liquid and its ionic conductivity is 9.7 × 10 ^-6 S / c
It was m.

Example 20 0.025 mol of ethanediol and 0.15 mol of diethylene glycol monomethyl ether were reacted according to Example 1 with respect to 0.05 mol of LiAlH ₄ ,
Li ⁺ _{[H 3 C- (OCH 2 CH 2} ) 2 O- ] ₃ Al ^-
-SCH ₂ CH ₂ S-Al ^- [-O (CH ₂ CH ₂ O)
It was obtained ₂ -CH _{3] 3} Li ⁺ salts. This salt is a very viscous liquid and its ionic conductivity is 9.7 × 10 ^-6 S /
It was cm.

[Preparation of Lithium Battery] In Example 1, a lithium battery was prepared using the polymer solid electrolyte with MEP-7 having a salt concentration of 5% by weight.

The positive electrode was manufactured as follows. LiC
The oO ₂ powder and acetylene black were mixed at a ratio of 85:15 (% by weight), vacuum-dried, and then the dry weight ratio was 30% with respect to the LiCoO ₂ powder and acetylene black. The polymer solid electrolyte solution was mixed in a dry box. After volatilizing THF, EPDM (ethylene propylene dimonomer) was added so as to be 5% by weight and kneaded, and this was stuck in a sheet form on a stainless steel foil by a roll press. In addition,
A sealing material made of polyolefin resin is heat-sealed around the stainless steel foil. The above solid polymer electrolyte solution was applied onto the positive electrode obtained as described above, and TH
F is volatilized to form a polymer solid electrolyte layer.

The negative electrode was formed as follows. Graphite powder (JPS: manufactured by Nippon Graphite Co., Ltd.), which is a carbon material used as the negative electrode active material, and the above-mentioned polymer solid electrolyte solution were mixed with the above polymer solid electrolyte solution so that the ratio was 70:30 (% by weight). Mixed with graphite powder. After volatilizing THF, EP
DM was added so as to be 5% by weight and kneaded. This was attached to a stainless foil with a roll press in a sheet form.
A sealing material made of polyolefin resin is heat-sealed around the stainless steel foil. On the negative electrode thus formed, apply the above-mentioned polymer solid electrolyte solution,
THF was volatilized to form a polymer solid electrolyte layer.

The positive electrode and the negative electrode formed as described above were manufactured so as to secure a capacity of 15 mAh. The positive electrode and the negative electrode produced as described above were pasted together to produce an all-solid lithium secondary battery. FIG. 3 is a sectional view showing the battery structure thus obtained. FIG.
As shown in FIG. 2, the positive electrode mixture material 1 and the negative electrode mixture material 2 are pasted together so as to sandwich the solid polymer electrolyte 3, and the stainless steel foil 4 is provided outside the positive electrode mixture material 1 and the negative electrode mixture material 2, respectively. It is provided. An insulating encapsulant 5 is provided between the stainless steel foils 4 around the polymer solid electrolyte 3, the positive electrode mixture 1, and the negative electrode mixture 2.

Charging the prepared all-solid-state lithium secondary battery
The discharge cycle characteristics were evaluated. The cycle of charging to 4.2 V at a current density of 25 μA / cm ² and discharging to 2.8 V at the same current density was repeated, and the charge / discharge capacity at that time was measured. The cycle characteristics of the obtained charge / discharge capacity are shown in FIG. As shown in FIG. 4, excellent battery characteristics are exhibited even though the battery is charged / discharged at a current twice as high as usual.

With respect to the electrolytes containing lithium salts of Examples 2 to 20 other than the above Example 1, lithium secondary batteries were prepared in the same manner as above, and the charge / discharge cycle characteristics were evaluated. As a result, in each case, similarly excellent battery characteristics were exhibited.

The positive electrode active material is not limited to those of the above examples as long as it can react as a lithium battery, and the negative electrode active material may be other than graphite such as Li metal. The electrolyte is not limited to the solid electrolyte, and may be an aprotic liquid electrolyte or a solvent-free molten salt electrolyte.

The lithium salt of the present invention becomes a safe aluminum oxide or aluminate and a raw material alcohol, thiol or phenols, or thiophenols upon hydrolysis due to atmospheric exposure or thermal decomposition under abnormal conditions. Therefore, there is no danger of producing toxic substances. Also, fire
It does not cause an explosion. Therefore, the battery using the electrolyte containing the lithium salt of the present invention is an extremely safe battery.

[Brief description of drawings]

FIG. 1 is a diagram showing a proton NMR spectrum of an example of the lithium salt of the present invention.

FIG. 2 is a diagram showing an IR spectrum of another example of the lithium salt of the present invention.

FIG. 3 is a cross-sectional view showing the structure of a lithium secondary battery manufactured in an example of the present invention.

FIG. 4 is a diagram showing charge / discharge cycle characteristics of a lithium secondary battery manufactured in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode mixture material 2 ... Negative electrode mixture material 3 ... Polymer solid electrolyte 4 ... Stainless steel foil 5 ... Insulation sealing material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Kameshima 463 Kagasuno, Kawauchi Town, Tokushima City, Tokushima Prefecture Otsuka Chemical Co., Ltd.

Claims (5)

[Claims] 1. A lithium salt represented by the general formula (I). Embedded image (In the formula, each R is independently a chain or cyclic alkyl group having 20 or less carbon atoms, an alkenyl group having 20 or less carbon atoms, a terminal methoxyoligoethyleneoxy group (the repeating number of ethyleneoxy is 1 to 21), phenyl Base, carbon number 4
A substituted phenyl group substituted with the following groups, an aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group is shown, and each X independently represents an O atom or an S atom connecting R and Al. ) 2. A lithium salt represented by the general formula (II). Embedded image (In the formula, each R ¹ is independently a chain or cyclic alkyl group having 20 or less carbon atoms, an alkenyl group having 20 or less carbon atoms, a terminal methoxyoligoethyleneoxy group (the repeating number of ethyleneoxy is 1 to 21), A phenyl group, a substituted phenyl group substituted with a group having 4 or less carbon atoms, an aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group, R ² represents alkylene having 20 or less carbon atoms, and 20 carbon atoms The following phenyldialkylene and phenylene, alkenylene having 20 or less carbon atoms,-(CH ₂ CH
₂ O) _n —CH ₂ CH ₂ — (n represents a number of 0 to 20), arylene having 30 or less carbon atoms, aralkylene having 30 or less carbon atoms, and alkylenediphenylene having 30 or less carbon atoms. X represents an O atom or an S atom which independently connects R ¹ or R ² and Al. ) 3. A lithium salt represented by the general formula (III). Embedded image (In the formula, each R ¹ is independently a chain or cyclic alkyl group having 20 or less carbon atoms, an alkenyl group having 20 or less carbon atoms, a terminal methoxyoligoethyleneoxy group (the repeating number of ethyleneoxy is 1 to 21), A phenyl group, a substituted phenyl group substituted by a group having 4 or less carbon atoms, an aryl group having 20 or less carbon atoms, a furfuryl group, or a tetrahydrofurfuryl group, R ³ is a trivalent aliphatic or aromatic hydrocarbon X represents each independently R ¹ or R
Indicates an O atom or an S atom connecting ³ and Al. ) 4. An electrolyte obtained by dissolving the lithium salt according to claim 1 in a non-aqueous solvent or polymer. 5. A lithium battery comprising a positive electrode capable of occluding or releasing lithium ions, the electrolyte according to claim 4, and a negative electrode capable of occluding or releasing lithium ions.