JPH1097869A - Rocking chair type lithium secondary battery incombustible electrolyte and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To individually precipitate Li by adding a Li metal to a LiCl saturation bath because Al is far more precious than Li. SOLUTION: A Li metal with reduction capability is added to a LiCl saturation AlCl3 -EMIC bath (50mol%<AlCl3 ). Thus Al2 Cl7 <-> is deposited as Al on the Li metal, and local cell reaction is caused to dissolve the Li metal acting as Li in the bath. As a result, the remaining Al2 Cl<-> can be removed from the bath in order to provide the electrolytic bath where the Al cannot be deposited during cathode (charging) reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is the presence of Li ⁺ in the flammable and pyrophoric no AlCl ₃ -EMIC molten salts, by only Li ⁺ was set to carry catcher over ion, rocking chair type This is realized as a nonflammable electrolyte for a lithium secondary battery.

[0002]

2. Description of the Related Art In lithium secondary batteries, research and development have been actively conducted mainly on those using an organic solvent system as an electrolytic solution. However, in a lithium secondary battery using an organic solvent system as an electrolyte, lithium perchlorate (LiClO ₄ ) used as an electrolyte has a danger of explosion, and an organic solvent system used as a battery electrolyte ignites and ignites. There are problems such as having properties.

[0003]

In order to be used as an electrolyte for a lithium secondary battery, an AlCl ₃ -EMIC bath (50 mol% <AlCl ₃ , hereinafter referred to as an acidic bath).
Need to be made Li ⁺ . LiCl in this bath
Is mainly dissolved It is believed to be due to the reaction Therefore, L
solubility iCl is, _Al 2 Cl ₇ in the bath ^- will depend on the amount of. However, in the formula [1], since the equilibrium does not completely tilt to the right, it is conceivable that some Al ₂ Cl ₇ ⁻ remains in the bath. For this reason, there is a problem that a slight eutectoid reaction between Li and Al may occur during charging (cathode polarization).

[0004]

SUMMARY OF THE INVENTION The present invention eliminates this drawback by adding Li metal, which is much lower than Al, to a LiCl saturated bath, whereby 4Al ₂ Cl ₇ ⁻ +3 Li → Al + ₇ AlCl ₄ ⁻ +3 Li ⁺ [2] The reaction succeeded in completely removing Al ₂ Cl ₇ ⁻ from the bath by the following reaction.
Al ₂ C of carrier ion of Al precipitation reaction from bath
l ₇ ⁻ disappears, and Li and A during charging (cathode polarization).
No eutectoid reaction with 1 occurs, and Li can be precipitated alone.

[0005]

Next, an embodiment of the present invention will be described with reference to experimental results. First example the present invention is not flammable and pyrophoric LiCl saturated AlCl ₃
-In order to realize an EMIC bath as a non-combustible electrolyte for a lithium secondary battery, the problem was solved by the following method. (B) The molar ratio between anhydrous AlCl ₃ and EMIC is 1.
The solution mixed at 5: 1 was purified overnight by the Al substitution method. The anhydrous LiCl was dried under reduced pressure at 200 ° C. and about 1 Torr for 1 week to sufficiently remove water. This is the above AlC
It was added to l ₃ -EMIC based bath, overnight, and the electrolytic bath and stirred at 50 ° C.. (B) LiCl saturated AlCl ₃ -EMIC bath (50
mol% <AlCl ₃ ), Li metal having a reducing ability was added. As described above, as shown in the equation [2], Al ₂
It is considered that a local cell reaction occurs in which Cl ₇ ⁻ precipitates on the Li metal as Al and the Li metal dissolves in the bath as Li ⁺ . As a result, the remaining Al ₂ Cl ₇ ⁻ can be removed from the bath, and an electrolytic bath in which Al does not precipitate during a cathode (charge) reaction is obtained. As an example of adding LiCl to the acidic bath at a saturation solubility or higher, LiCl saturated 60.6 mol% Al
Cl ₃ -39.4 mol% C.I. of tungsten (W) electrode in EMIC bath. V. Is shown in FIG. FIG. 1 (a)
C. of the LiCl-free bath shown in FIG. V. Compared to (b)
Then -0.1Vvs. The redox peak near Al became smaller. These slight peaks are considered to be related to the precipitation and dissolution reaction of Al. This is because the dissolution of LiCl is due to the equilibrium reaction shown in equation [1], and the equilibrium does not completely tilt to the right. This is probably because Al ₂ Cl ₇ ⁻ remained in the bath. In addition, the C.I. V. Is shown in FIG. −2.0 V vs. A
1 and a reduction peak near −1.4 V vs. An oxidation peak appeared near Al. This peak indicates that the use of Al for the substrate enables the precipitation and dissolution reaction of Li. The reversibility of this reaction was stable even after repeating the scanning for 80 cycles. Here, -1.2V
vs. A very small reduction peak was observed near Al, and this peak is considered to be the peak of the precipitation reaction of Al. From the above, it can be considered that a carrier in which LiCl is added to an acidic bath at a saturation solubility or higher contains carrier ions for the Li deposition reaction, and thus it can be said that there is a possibility as an electrolyte for a lithium secondary battery. However, since a small amount of Al ₂ Cl ₇ ⁻ remained in the bath, it was suggested that some eutectoid of Al occurs during charging (cathode polarization).

Second Example Here, in order to confirm that Al ₂ Cl ₇ ⁻ existing in the bath can be completely removed by adding Li metal, 60.6 mol% of LiCl saturated after adding Li metal was used.
AlCl ₃ -39.4 mol% W in EMIC bath
C. of electrode V. Was measured. As shown in FIG.
-1.0 V vs. observed in (b). Al and a reduction peak near -0.2 Vvs. The oxidation peak near Al disappeared, indicating that Al ₂ Cl ₇ ⁻ had completely disappeared. The potential window at this time was about 4.4V. In addition, the C.I. V. (FIG. 4), it can be seen from FIG. 2 that -1.2 V vs. Al
The nearby small reduction peak disappeared, and only the Li ⁺ reduction peak appeared. Therefore, from now on, Al
₂ Cl ₇ ^- is lost, it can be said that Li has become possible precipitation alone.

[0007]

According to the present invention, the following effects are expected. (1) A non-flammable electrolyte for a rocking chair type lithium secondary battery can be obtained using an AlCl ₃ -EMIC molten salt having no ignitability or ignition property. (2) It can replace the organic solvent system used as a conventional electrolyte for lithium secondary batteries.

[Brief description of the drawings]

FIG. 1: LiCl saturated AlCl ₃ -E before adding Li metal
Cyclic voltammogram of W electrode in MIC bath

FIG. 2: LiCl saturated AlCl ₃ -E before adding Li metal
Cyclic voltammogram of Al electrode in MIC bath

FIG. 3: LiCl saturated AlCl ₃ -E after addition of Li metal
Cyclic voltammogram of W electrode in MIC bath

FIG. 4: LiCl saturated AlCl ₃ -E after addition of Li metal
Cyclic voltammogram of Al electrode in MIC bath

Claims (3)

[Claims] 1. An aluminum chloride (AlCl ₃ ) -1.
-Ethyl-3-methylimidazolium chloride (EMI
C) -containing electrolytic solution (AlCl ₃ ratio is 50 mol)
% <AlCl ₃ ), lithium ion (LCl) is added at a saturation solubility or higher.
i ⁺ ) A method for producing an electrolytic solution in which the electrolytic solution exists. 2. A negative electrode substrate capable of performing a cathode reaction (a negative electrode charging reaction) by using the electrolytic solution according to claim 1 and using a metal substrate (such as aluminum) alloyed with electrodeposited lithium. 3. The method according to claim 1, wherein the electrolyte is lithium (Li).
A method of removing carrier ions in an aluminum (Al) deposition reaction by adding a metal.