JP3433446B2 - Electrolyte for non-aqueous batteries and non-aqueous batteries - Google Patents

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 for use in a non-aqueous battery and a lithium-based non-aqueous battery.

[0002]

2. Description of the Related Art Lithium hexafluorophosphate (LiPF ₆ ) is used as a solute of an electrolytic solution used in a lithium secondary battery.
Lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), (Li
N (CF ₃ SO ₂ ) ₂ ) or lithium perchlorate (LiC
10 ₄ ) and the like, all of which are biionic electrolyte salts in which both cations (cations) and anions (anions) move in the electrolyte during charge and discharge. In such a biionic electrolyte salt, not only cations but also anions that do not participate in the battery reaction move. The transport number showing ionic conductivity due to migration of cations (here, lithium ions) in the electrolytic solution obtained by dissolving these in a non-aqueous solvent is generally low at 0.3 to 0.5, which is not satisfactory. It was

Further, since the electrode of the lithium battery is a blocking electrode (inert electrode) with respect to anions in the electrolytic solution, uneven distribution of the anions near the electrodes causes polarization of the electrolytic solution, resulting in difficulty in flowing current. There was a problem to say. Further, at this time, when the battery was charged and discharged, anions were unevenly distributed in the vicinity of one of the electrodes, which could adversely affect the electrodes. That is, when aluminum is used for the positive electrode current collector and LIN (CF ₃ SO ₂ ) ₂ is used for the electrolyte salt,
It is known that adverse effects such as corrosion of aluminum, which is a current collector, occur during charging.

[0004]

The present invention solves the above-mentioned problems of the prior art, that is, an electrolytic solution for a non-aqueous battery having a high transport number, which exhibits ionic conductivity due to the movement of cations (here, lithium ions). The purpose is to provide.

[0005]

In order to solve the above problems, the electrolytic solution for a non-aqueous battery according to the present invention has the following features.
It has a constitution composed of a lithium siloxyaluminate polymer and an aprotic solvent.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the lithium siloxyaluminate polymer has a structure represented by the chemical formula (I).

[0007]

[Chemical 1]

As the above lithium siloxyaluminate polymer, it is desirable that its terminal group is protected by an aromatic hydrocarbon such as a phenyl group or an alkyl group because it is chemically stable. Here, an ethyl, propyl, butyl, or phenyl group is easy to synthesize and obtain. When the above-mentioned terminal group is a methyl group, the raw material has some difficulty in storage stability and stability.
Such a lithium siloxyaluminate polymer can be obtained, for example, by reacting a dialkylsilanediol with lithium aluminum hydride. It is also possible to select appropriately different functional groups instead of the alkyl group.

Further, the solvent in the present invention is required to have an aprotic property. Examples of such an aprotic solvent include various cyclic carbonates, chain carbonates, chain or cyclic ethers, and the like.
Specifically, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2
-Methyltetrahydrofuran, 1,3-dioxolane,
4-methyl-1,3-dioxolane, diethyl ether, sulfolane, acetonitrile, propionitrile,
Anisole, dimethyl carbonate, diethyl carbonate, butylene carbonate, methyl acetate, ethyl methyl carbonate, N-methyl-2-pyrrolidone and mixtures thereof can be used. A solvent such as organophosphazene can also be used. Although a study has been made to obtain a solid electrolyte by adding a plasticizer such as polyethylene glycol in order to impart plasticity to the lithium siloxyaluminate polymer,
With this method, it was not possible to obtain a sufficient transport number and a satisfactory conductivity.

The non-aqueous battery electrolyte of the present invention can be obtained by dissolving the lithium siloxyaluminate polymer in the aprotic solvent. At this time, it is possible to accelerate dissolution by commonly using a general means such as heating or ultrasonic shaking. A third component, for example, a component that increases the degree of dissociation of the electrolyte or a component that suppresses dendrite precipitation may be added during the dissolution.

The nonaqueous battery electrolyte of the present invention obtained as described above can be used in the production of a lithium battery together with other components such as a cathode, an anode and a separator. Use lithium cobalt oxide, lithium nickel oxide, etc. as the positive electrode, and coke-based / graphite-based carbon material for the negative electrode, or tin amorphous oxide and other materials commonly used in lithium secondary batteries. You can

The electrolytic solution for a non-aqueous battery of the present invention exhibits high ionic conductivity and selective cation conductivity. In the lithium battery using this electrolyte for non-aqueous batteries, the action of this electrolyte eliminates the bias of ions that are not involved in the electrode reaction, and the potential between the electrodes does not rise, so an extremely stable current is obtained. . At the same time, the adverse effect on the electrodes is eliminated, and as a result, a good cycle life is exhibited.

Although the electrolytic solution for a non-aqueous battery of the present invention is excellent as described above, a secondary battery can be produced by handling it in the same manner as the conventional electrolytic solution for a non-aqueous battery. Requires almost no changes to the battery assembly line. An aprotic solvent is used in the electrolytic solution for a non-aqueous battery of the present invention. Due to this, unlike the addition of a plasticizer such as polyethylene glycol, excellent conductivity and a high transport number can be obtained.

[0014]

EXAMPLES Examples of the nonaqueous battery electrolytic solution of the present invention and the secondary battery using the same are shown below. [Synthesis of Lithium Siloxyaluminate Polymer: See Chemical Formula II (wherein Ph represents a phenyl group)] A lithium diphenylsiloxyaluminate polymer having a phenyl substituent is selected as the alkali siloxyaluminate polymer and synthesized as shown below. did.

[0015]

[Chemical 2]

That is, 300 ml under an argon atmosphere
8.66 g (40.03 mmol) of dried diphenylsilanediol and 75 ml of tetrahydrofuran were placed in the three-necked flask described in (1), and the mixture was cooled to -78 ° C, and 1 mol / l-hydrogen was added so that lithium aluminum hydride became 20.01 mmol while stirring. After slowly adding a lithium aluminum chloride / tetrahydrofuran solution, the temperature was gradually returned to room temperature and the reaction was carried out by stirring for 2 hours. The solution after the reaction had neither precipitate nor precipitate.

After the above reaction, vacuum drying was performed. The obtained reaction product was 12.655 g, and the yield was 137%, because the solvent tetrahydrofuran could not be completely removed. The infrared absorption spectrum of this product is shown in Fig. 1.
^{The 1} H-NMR spectrum is shown in FIG. In addition, FIG. 2 is a result of measurement using a deuterium-substituted C ₃ D ₇ NO of dimethylformamide (hereinafter referred to as “DMF-d ₇ ”) as a solvent. In the figure, ppm is tetramethylsilane (as an internal standard). It is a value when TMS) is used. 1 in FIG.
420 cm ^-1 and 1120cm aromatic absorption of around ^-1,
Absorption due to Si-O bond at 900-1100 cm ^-1 ,
Absorption of monosubstituted aromatics near 700 cm ^-1 520 cm ^-1
Absorption derived from Si (C ₆ H ₅ ) ₂ is seen in the vicinity. Further, in FIG. 2, a peak derived from the proton of the aromatic ring is seen around 6.8 to 7.6 ppm. The other peaks are impurities.

Further, in FIGS. 3, 4 and 5, carbon ( ¹³ C, solvent CDCl ₃ ) and aluminum ( ²⁷ A
1, solvent CD ₃ OD), silicon ( ²⁹ Si solvent, CD ₃ O
The NMR measurement spectrum about D) is shown. In FIG. 3, C ₆ H ₅ - a number of peaks derived from the structure is to appear. In addition, in the ²⁷ Al-NMR spectrum of FIG.
Since a peak is observed in the vicinity of 0 to 70 ppm, the aluminum atom may have a tetracoordinate tetrahedral structure, and in the ²⁹ Si-NMR spectrum of FIG. 5, the peaks near −47 ppm and −50 ppm show Ph ₂ SiO in the structure. ₂ A
It is due to l. In addition, in FIG. 4 and FIG. 5, peaks other than these peaks are considered to be derived from impurities. Furthermore, ICP (inductively coupled plasma) analysis, C
HNS / O elemental analysis was performed. The results are shown in Table 1 together with theoretical values.

[0019]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━               Al Li Si C H O ──────────────────────────────────── Measured value (%) 6.0 1.5 11.7 61.0 4.4 15.4 Theoretical value (%) 5.9 1.5 12.2 62.3 4.3 13.8 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

When the molecular weight was separately measured by GPC chromatography (Tosoh HLC802A), it was found that this had a peak at a molecular weight of around 8100.

[Example] [Example 1] A mixed system of a cyclic carbonate and a chain carbonate was examined. That is, the above-mentioned lithium diphenylsiloxyaluminate polymer was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate in an equal volume ratio, and the transport number was measured by the electromotive force method. Based on.

That is, a concentration of 0.1 mol was provided in one chamber of an H-type electrolytic cell (having a glass filter in the liquid junction).
A dm ^-3 (hereinafter, this concentration is referred to as C ₁ ; the molar concentration at this time represents the number of moles of aluminum in the polymer; the same applies hereinafter) solution of lithium diphenylsiloxyaluminate polymer is put into the other chamber. Is 1 / of the concentration C ₁
Concentration of 2, 1/4, 1/8, 1/16
₂ ) lithium diphenylsiloxyaluminate polymer solution was added, and the electromotive force generated between the electrodes composed of a pair of lithium metal wires provided in both chambers at this time was measured, and the natural logarithm of the concentration ratio (ln (ln ( C ₂ / C ₁ ))
The transport number (t ₊ ) was calculated by fitting the following equation (1) (Nernst equation) from the slope when plotted against. Where R is gas constant, T is absolute temperature (K), F
Represents the Faraday constant.

[0023]

[Equation 1]

As a result, in this mixed solvent system, 0.85
It was found that a high transport number could be obtained. Also, ethylene car
On top of a mixed solvent such as Bonate and dimethyl carbonate in the same volume ratio.
Lithium diphenylsiloxy aluminate polymer 1
1.14 g was dissolved and 50 ml (lithium concentration was 0.1.
4 mol / l) electrolyte with conductivity of 7.7 × 10 ^-Four
It was also found to be as high as S / cm. In addition, lithium diphe
Nylsiloxyaluminate polymer 5.57g mixed solution
Electrolyte solution (50% lithium)
2 mol / l) and used as the negative electrode of a lithium secondary battery
When a charge / discharge test was performed using a graphite electrode
A sufficient reversible capacity should be obtained as shown in Fig. 6.
Was confirmed.

Similarly, except that a secondary battery was formed by using an aluminum current collector, charging and discharging were repeated 100 times, and then the aluminum current collector was taken out and examined. There wasn't.

Example 2 Next, the ionic conductivity of five electrolytes (lithium concentration of 0.4 mol / l, obtained by dissolving the lithium diphenylsiloxyaluminate polymer used in Example 1 in various solvents) was used. Ionic conductivity) and their transport numbers were measured. The results are shown in Table 2. A charge / discharge experiment using a secondary battery using an aluminum current collector was carried out in the same manner as in Example 1 using these five types of electrolytic solutions. In any case, no corrosion occurred in the aluminum current collector. There wasn't.

[0027]

[Table 2]

Table 2 shows that the electrolytic solution according to the present invention is an excellent electrolytic solution having high ionic conductivity and high transport number.

[0029]

EFFECT OF THE INVENTION The electrolytic solution of the present invention has a high conductivity while having a sufficient conductivity, and is excellent in electrolysis without causing a trouble even when an inexpensive and lightweight aluminum current collector is used. It is a liquid.

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum of a lithium diphenylsiloxyaluminate polymer synthesized in an example of the present invention.

FIG. 2 ¹ H-NMR of lithium diphenylsiloxyaluminate polymer synthesized in an example of the present invention.
It is a spectrum.

¹³ C-NMR of [3] Lithium diphenylsiloxy aluminate polymer synthesized in an embodiment of the present invention
It is a spectrum.

FIG. 4 ²⁷ Al-NM of lithium diphenylsiloxyaluminate polymer synthesized in an example of the present invention.
It is an R spectrum.

FIG. 5: ²⁹ Si-NM of lithium diphenylsiloxyaluminate polymer synthesized in an example of the present invention
It is an R spectrum.

FIG. 6 is a diagram showing the result of a charge / discharge test of a graphite negative electrode for a lithium secondary battery formed in an example of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-11-140318 (JP, A) JP-A-10-74418 (JP, A) JP-A-10-241460 (JP, A) JP-A-11- 111049 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 6/16 H01M 10/40

Claims (2)

(57) [Claims] 1. An electrolytic solution for a non-aqueous battery comprising a lithium siloxyaluminate polymer and an aprotic solvent. 2. A non-aqueous battery comprising a non-aqueous battery electrolyte comprising a lithium siloxyaluminate polymer and an aprotic solvent.