JPS62217578A - Lithium battery - Google Patents

Abstract

PURPOSE:To enhance the heat stability of an electrolyte, and to increase storage life and charge-discharge performance when used as a secondary battery by using dicyclic tertiary amine as an additive. CONSTITUTION:A battery has a positive electrode and a negative electrode comprising lithium or lithium alloy and uses a lithium salt of Lewis acid indicated in the formula I as a solute and an organic solvent. An organic electrolyte added with dicyclic tertiary amine indicated in the formula II is used. Since increase in the content of the additive more stabilizes the electrolyte, the larger content of the additive is preferable. However, the larger content of the additive causes decrease in conductivity and in charge-discharge performance preferable content of the additive is 0.05-2 times in mol based on the lithium salt of Lewis acid indicated in the formula I.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to lithium batteries, and more particularly to improvements in their electrolytes.

[Conventional technology]

In recent years, the general formula (LiMFn (1) (where M is P, As, Sb or B, n is M is P,
An organic electrolyte using a Lewis acid lithium salt (6 when As or Sb is 4 when M is B) as a solute has high conductivity and is safer than a perchlorate-based one. Due to its excellent properties, electrolyte for lithium batteries,
In particular, it has come to be widely used as an electrolyte for lithium secondary batteries.

However, electrolytes containing Lewis acid lithium salts as solutes have problems with thermal stability, causing decomposition and polymerization of the electrolyte solvent during high-temperature storage, increasing the internal resistance of the battery and impairing battery performance. There was a problem of lowering the

Therefore, it has been proposed to add hexamethylphosphoric triamide to the electrolytic solution to improve the thermal stability of the electrolytic solution (for example, JP-A-60-175380).

[Problem that the invention seeks to solve]

However, when the electrolytic solution to which hexamethylphosphoric triamide is added as described above is used as an electrolytic solution for a secondary battery, the P=O bond contained in its molecular structure becomes active during charging. There was a problem in that it reacted with lithium and deteriorated charge/discharge characteristics.

[Means for solving problems]

The present invention provides an organic electrolyte having a Lewis acid lithium salt represented by the general formula (I) as a solute, and an organic electrolyte having the general formula (II) (where ρ is 3 to 6, m is 0 to 2, and n is 3). ~6,
R is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms)
By adding the bicyclic tertiary amine represented by the above, even when applied to secondary batteries, there is no deterioration in charge/discharge characteristics, and the electrolytic performance is better than when adding the hexamethylphosphoric triamide. This improves the thermal stability of the liquid.

Examples of the bicyclic tertiary amine represented by the above general formula (U) include pyrrolizidine, pyrocollidine, quinolidinone, and flurvinan B110-methylquinolizidine as shown in the following structural formula.

Pyrrolizidine: Virocollidine: Quinolidinone: 10-methylquinolizidine: The bicyclic tertiary amine represented by the above general formula (II) is
It is an oily liquid with a high boiling point and dissolves in the electrolyte solvent. These bicyclic tertiary amines represented by general formula (n) include the above-mentioned pyrrolizidine, pyrocollidine, quinolidinone,
As is clear from the structural formula of norrubinane B, 10-methylquinolizidine, it has a sterically large tertiary amine in its molecular structure.

Therefore, when the bicyclic tertiary amine represented by the general formula (II) is added to the electrolyte, the sterically large tertiary amine will react with the ionized Lewis acid lithium salt such as LiPF6 in the electrolyte. It coordinates with Li+ ion to form a stable complex, and Li+ ion and F- ion (this F- ion is
The electrolytic solution is stabilized by suppressing the reaction with PF5 (produced by decomposition of PF5- ions generated by ionization from iPF6) and suppressing the decomposition of Lewis acid lithium salts such as LiSbF6. In addition, since these bicyclic tertiary amines represented by general formula (II) are large molecules, they appear between the eyebrows of the crystal structure of titanium disulfide, which is commonly used as a positive electrode active material for secondary batteries. , efficiently stabilizes the electrolyte even in small amounts.It also has a basicity that can neutralize the acidity of HF (hydrogen fluoride) generated by the decomposition of 1PFB, etc.
The generation of HF is suppressed, thereby suppressing the decomposition of 1,1PF6, and the electrolyte is stabilized from this aspect as well.

In addition, the bicyclic tertiary amine represented by the above general formula (II) has a functional group that easily reacts with electrodeposited lithium, such as the P=◯ bond of hexamethylphosphoryl 7-cutotriamide, in its molecular structure. Therefore, even when an electrolytic solution to which this is added is used as an electrolytic solution for a secondary battery, no trouble will occur.

The bicyclic tertiary amine represented by the above general formula (11) is
The larger the amount added, the greater the effect of stabilizing the electrolyte, and from that point of view, the larger the amount added, the better, but if it is too large, the conductivity at low temperatures may decrease, and when applied to secondary batteries. Since it causes a deterioration in charge/discharge characteristics, the amount added is preferably 0.05 to 2 times the mole of the Lewis acid lithium salt represented by the general formula (1).

In the present invention, the general formula (1
), M is P(
LiPF5 (lithium hexafluorophosphate) which is phosphorus), LiSbF6 where M is Sb (antimony)
(lithium hexafluoroantimonate), M is As (arsenic)
1-iAsF6 (lithium hexafluoroarsenate)
, is LiBF4 (lithium tetrafluoroborate) in which M is B (boron).

The electrolytic solution is a Lewis acid lithium salt represented by the general formula CI), for example, propylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,2-dimethoxyethane, 1,2-jethoxyethane, 1.3-dioxolane, 4-methyl - Dissolve 1 g in an organic solvent such as 1,3-dioxolane alone or in a mixture of two or more, and add thereto the bicyclic tertiary amine represented by the general formula (II), or After adding the bicyclic tertiary amine represented by the general formula (II) to the general formula (
It is prepared by dissolving the Lewis acid lithium salt shown below. In short, in the present invention, it is sufficient that the electrolytic solution contains a bicyclic tertiary amine represented by the general formula ('), and a bicyclic tertiary amine represented by the general formula (n). The order of addition of the amine and the Lewis acid lithium salt represented by the general formula (1) does not matter.The amount of the Lewis acid lithium salt represented by the general formula (1) is usually 0.
It is preferable to set it to 1-3 not/da3.

In the battery of the present invention, lithium or a lithium alloy is used for the negative electrode. As the lithium alloy, for example, lithium alloys such as lithium-aluminum, lithium-lead, lithium-gallium, lithium-indium, lithium-gallium-indium, lithium-magnesium, and lithium-zinc are used. Examples of the active material of the positive electrode include titanium disulfide (TiSz), molybdenum disulfide (MoS2), and molybdenum trisulfide (M.

S3), zirconium sulfide (ZrS2), niobium disulfide (NbS2), phosphorous nickel trisulfide (NiPS3), vanadium selenide (VSez), iron sulfide, copper oxide, carbon fluoride, etc. are used.

Particularly in the production of secondary batteries, titanium disulfide is preferably used because it has a layered crystal structure and has a large diffusion constant for lithium.

[Example] Next, the present invention will be explained in more detail by giving examples.

Example 1 4-methyl-! as the electrolyte! , 3-dioxolane 58
．． 1% by volume, 1,2-dimethoxyethane 38.7% by volume
and 3.2% by volume of pyrrolizidine.
Using an organic electrolyte in which iPF6 was dissolved at a concentration of 1.0 mol/dm3, a lithium-aluminum alloy containing 36 at% lithium was used as the negative electrode, and a molding mixture containing titanium disulfide as the positive electrode active material was used as the positive electrode. A lithium battery as shown in FIG. 1 was assembled. In the above electrolytic solution, pyrrolizidine is equivalent to about 0.3 times the mole of LiPF5.

In Fig. 1, 1 is a negative electrode can, this negative electrode can l is made of stainless steel, and the surface is nickel plated, and 2
is a current collector on the negative electrode side made of a stainless steel mesh, and is spot welded to the inner surface of the negative electrode can 1. 3 is a negative electrode made of the aforementioned lithium-aluminum alloy. 4 is a separator made of microporous polypropylene film;
is an electrolyte absorber made of polypropylene nonwoven fabric,
45 μl of the electrolytic solution is injected into the battery, but most of it is occluded by the electrolytic solution absorber 5 and the separator 4. 6 is a positive electrode formed by pressure molding a mixture containing titanium disulfide as a positive electrode active material into a pellet shape, and 7 is a current collector on the positive electrode side made of a stainless steel mesh. 8 is stainless steel tI
The positive electrode can has a nickel-plated surface, and 9 is a polypropylene annular gas get. The theoretical amount of electricity of the negative electrode of this battery is about 20 mAh, and the theoretical amount of electricity of the positive electrode is about 8 mAh.

Example 2 4-methyl-1,3-dioxolane 57.
Li was added to a mixed solvent consisting of 8% by volume, 38.6% by volume of 1,2-dimethoxyethane, and 3.6% by volume of cocolidine.
A lithium battery was assembled in the same manner as in Example 1, except that an organic electrolyte in which PF6 was dissolved at a concentration of 1.0 01/dm3 was used. In the above electrolyte, pyrocollidine is Li
It corresponds to about 0.3 times the mole of PF6.

Example 3 An electrolytic solution containing 57.6% by volume of 4-methyl-1,3-dioxolane, 38.4% by volume of 1,2-dimethoxyethane, and 4.0% by volume of quinolinodine was mixed with 1 liter of PF6,
A lithium battery was assembled in the same manner as in Example 1, except that an organic electrolyte dissolved in Omol/da3 was used. In the above electrolytic solution, quinolidinone is about 0.3 times mole of 1.1PF6.

Comparative Example 1 An organic electrolyte in which 1PFs was dissolved at 1.0 mol/c1w3 in a mixed solvent consisting of 60% by volume of 4-methyl-1,3-dioxolane and 40% by volume of 1,2-dimethoxyethane. A lithium battery similar to that in Example 1 was assembled except that an electrolytic solution was used.

Comparative Example 2 In a mixed solvent consisting of 60% by volume of 4-methyl-1,3-dioxolane, 34.8% by volume of 1,2-dimethoxyethane and 5.2% by volume of hexamethylphosphoric triamide as an electrolytic solution, 1PF6 was added. 1. Omol/d+e3
A lithium battery was assembled in the same manner as in Example 1, except that an organic electrolyte was used which was melted so as to be as follows. In the above electrolyte, hexamethylphosphoric triamide is 1-iPF
This corresponds to about 0.3 times the mole of 6.

The batteries of Examples 1 to 3 and the batteries of Comparative Examples 1 to 2 were
It was stored at 0°C, and the change in internal resistance at 10 kHz due to storage was examined. The results are shown in Figure 2.For the batteries of Examples 1 to 3 and the battery of Comparative Example 2, charging and discharging of 0.5mAh at a constant current of 1.0mA was performed at a voltage of 1.5 to 2.5μ. FIG. 3 shows the relationship between the end-of-discharge voltage at the end of 0.5 mAh discharge and the number of cycles when cycled within the range.

As shown in FIG. 2, in the battery of Comparative Example 1 to which no additives were added, the internal resistance significantly increased as the number of days of storage increased, but in the batteries of Examples 1 to 3 of the present invention, No such large increase in internal resistance was observed, and the storage property was excellent. This seems to be due to the fact that the thermal stability of the electrolyte was greatly improved by the addition of pyrrolizidine, pyrocollidine, quinolidinone, etc. to the electrolyte. Furthermore, the batteries of Examples 1 to 3 of the present invention showed less increase in internal resistance due to storage than the battery of Comparative Example 2 in which hexamethylphosphoric triamide was added.

As for the charge/discharge characteristics, as shown in Figure 3,
0.5 mA in each cycle compared to the battery of Comparative Example 2 with hexamethylphosphoric triamide added.
The final discharge voltage at the end of h discharge was high, and the number of cycles capable of 0.5 mA h discharge was large when viewed from ■, 5V end, and the charge/discharge characteristics were excellent.

In the above Examples, LiPF5 was used as an example of the Lewis acid lithium salt represented by the general formula (+), but the effect of the present invention is that LiAs
Even when F6, LiSbF6, LiBF4, etc. are used, the performance is similar to that of LiPF6.

〔Effect of the invention〕

As explained above, in the present invention, by adding a bicyclic tertiary amine such as pyrrolizidine, pyrocollidine, or quinolidinone, the thermal stability of the electrolytic solution is increased, the storage property is improved, and the storage capacity is improved. We were able to improve the charge/discharge characteristics when

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a lithium battery according to the present invention. FIG. 2 is a diagram showing the 10 kHz internal resistance change during storage of the batteries of Examples 1 to 3 of the present invention and the batteries of Comparative Examples 1 to 2, and FIG. and 0.0 when the battery of Comparative Example 2 was repeatedly charged and discharged.
It is a figure which shows the relationship between the end-of-discharge voltage at the end of 5mAh discharge, and the number of charging/discharging cycles. 3...Pledge, 4...Separator, 5...Electrolyte absorber, 6...Positive electrode No. 1 Figure 3 - Teiyu Figure 2 Piezodiarrhea (day)

Claims (3)

[Claims] (1) It has a positive electrode and a negative electrode made of lithium or a lithium alloy, and the solute has the general formula (I) LiMFn(I) (wherein M is P, As, Sb or B, n is M,
6 when As or Sb, 4 when M is B), the solvent is an organic solvent, and the additive is general formula (II) ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, l is 3 to 6, m is 0 to 2, n is 3 to 6,
R is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms)
A lithium battery characterized by using an organic electrolyte to which a bicyclic tertiary amine represented by: (2) The lithium battery according to claim 1, wherein the bicyclic tertiary amine represented by general formula (II) is pyrrolizidine, pyrocollidine or quinolizidine. (3) The lithium battery according to claim 1 or 2, wherein the positive electrode active material is titanium disulfide.