JPH07282845A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To increase conductivity and suppress generation of dendrites on a negative electrode to enhance reliability by selecting an electrolyte from the group containing a dioxaspiro compound and comprising ethylene carbonate as the main solvent. CONSTITUTION:By containing a dioxaspiro compound in an electrolyte, a lithium atom deposited on a metallic substrate is not fixed in the deposition portion, diffuses on the surface of the substrate, and is caught at a thermodinamically stable crystal lattice point. When a crystal nucleus having many defects is formed immediately after deposition starts, deposited atoms gather around the crystal nucleous, crystallinity is increased, and the crystal nucleous globularly grows to prevent the generation of dendrites. When the main solvent of the electrolyte is ethylene carbonate and/or propylene carbonate, the solubility of the dioxaspiro compound is increased even at low temperature, and battery performance is increased. Conductivity is enhanced, generation of dendrites is suppressed, internal short circuit is prevented, and reliability is enhanced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
Particularly, it relates to improvement of the electrolytic solution.

[0002]

2. Description of the Related Art Today, organic solvents such as propylene carbonate, γ-butyrolactone, dimethoxyethane, tetrahydrofuran and dioxolane are mixed with LiClO ₄ , Li
A non-aqueous electrolyte battery having a combination of an electrolyte obtained by dissolving a solute such as BF ₄ , LiAsF ₆ , LiPF ₆ , and LiCF ₃ SO ₃ and a negative electrode using an alkali metal such as lithium as an active material has a high energy density. Therefore, it has come to be widely used in small electronic devices such as electronic timepieces and cameras. One of the problems in enabling this type of non-aqueous electrolyte battery to be charged is that the form of the alkali metal deposited on the negative electrode during the charging process becomes so-called dendrite, which is dendritic, fibrillar, or acicular. When this dendrite grows significantly, not only the risk of internal short circuit between the negative electrode and the positive electrode and ignition increases, but even if the dendrite is dissolved in the subsequent discharge process, local dissolution of the dendrite proceeds and part of it is electrically Not all dendrites can be melted out because they are more liberated. That is, the amount of discharge (dissolution) with respect to the amount of charge (deposition) becomes small (reduction of charge / discharge efficiency), and the cycle life becomes short.

As a method for solving such a problem,
There is an attempt to suppress the generation of dendrites by including a hydrocarbon compound as an additive in a solvent of propylene carbonate having a high dielectric constant, which dissolves a large amount of electrolyte salt, and protecting the surface of the precipitated lithium (3rd International
Meeting on Lithium Batteries, Abstract, 34th
Page 6 (1986)).

[0004]

Even when the above-mentioned solvent in which propylene carbonate contains hydrocarbon as an additive is used in the electrolytic solution, charging (precipitation) occurs as described in the above cited document. ) There has been a problem that the corrosion of lithium on the electrode that has been left for a long period of time afterward progresses, and the charge / discharge efficiency decreases. Further, it has been found that when a hydrocarbon compound is added to the electrolytic solution, the electric conductivity of the electrolytic solution is lowered, so that there is an inconvenience that polarization at the time of charging and discharging at a high current density becomes large. The present invention eliminates such conventional defects, while suppressing the progress of corrosion of alkali metals such as lithium deposited by charging (deposition),
It is an object of the present invention to provide a highly reliable non-aqueous electrolyte secondary battery by obtaining an electrolytic solution having a high electric conductivity and suppressing generation of dendrites on the negative electrode even when charging and discharging are repeated.

[0005]

A non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, an alkali ion conductive non-aqueous electrolytic solution, and a negative electrode using an alkali metal as an active material. Is 1,3-dioxaspiro [4,5] decane represented by the formula 1, 1,4-dioxaspiro [4,5] decane represented by the formula 2, and 1,3-dioxaspiro [4,4 represented by the formula 3 ] Nonane and 1,4 shown in Formula 4
-Containing at least one member selected from the group consisting of dioxaspiro [4,4] nonane.

[0006]

[Chemical 1]

Here, the main solvent of the electrolytic solution is preferably at least one selected from the group consisting of ethylene carbonate and propylene carbonate.

[0008]

According to various investigations by the present inventors, in the electrolyte solution containing the dioxaspiro compound, the lithium atoms (strictly speaking, adsorbed ions) deposited on the metal substrate are not fixed on the spot where they are deposited, and the substrate surface It has been found that after being diffused, it is easily trapped at thermodynamically stable crystal lattice points.
Therefore, when crystal nuclei with many defects are generated immediately after the start of precipitation, the precipitated atoms gather in the crystal nuclei to enhance their crystallinity and prevent the crystal nuclei from growing spherically to become so-called dendrites. The dioxaspiro compound is
As is clear from the structural formula, one of the molecular structures is a hydrophobic structure containing only carbon and hydrogen atoms, and the other is a hydrophilic structure containing oxygen atoms. Therefore, it is easy to be compatible with a solvent having a high dielectric constant such as ethylene carbonate or propylene carbonate, and also contributes to the dissociation of the electrolyte salt by coordinating with ions such as lithium, so that the conductivity of the electrolytic solution is not impaired. .

As a result of the analysis, the dioxaspiro compound is adsorbed on the surface of the electrode made of an alkali metal such as lithium, and is present at the boundary with a solvent having a high dielectric constant such as ethylene carbonate or propylene carbonate. It was found that the high dielectric constant solvent of the above prevents the direct reaction with the alkali metal. From such a thing,
It is considered that the alkali metal deposited in the electrolytic solution containing the dioxaspiro compound does not undergo corrosion even when left standing for a long time and the charge / discharge efficiency is improved.

When the main solvent of the electrolytic solution is ethylene carbonate and / or propylene carbonate,
The solubility of the dioxaspiro compound is large even at a low temperature, and a battery having excellent characteristics is provided.

[0011]

EXAMPLES Examples of the present invention will be described below. All the batteries in the examples were assembled under an argon gas atmosphere. Example 1 Ethylene carbonate and propylene carbonate were mixed in a volume ratio of 1/1, and LiClO ₄ was dissolved in this mixed solvent at a ratio of 1 mol / l to prepare an electrolytic solution. Various dioxaspiro compounds were added to this electrolytic solution in a proportion of 1 wt% in total, and the conductivity thereof was measured at 25 ° C. using an AC bipolar method. Comparative Example 1 An electrolytic solution prepared in the same manner as in Example 1 except that 1% by weight of decalin was mixed with the electrolytic solution will be used as a comparative example.

Table 1 shows the electric conductivities of the electrolytic solutions of these Examples and Comparative Examples. Here, D13 represents 1,3-dioxaspiro [4,5] decane, D14 is 1,4-dioxaspiro [4,5] decane, and N13 is 1,3-dioxaspiro [4,5] decane. Nonane and N14 represent 1,4-dioxaspiro [4,4] nonane, respectively. From Table 1, the conductivity of the electrolytic solution containing the dioxaspiro compound, which is an example of the present invention, is about 1 as compared with the comparative example.
It can be seen that it is improved by 5%. This is because the dioxaspiro compound itself contributes to the dissociation of the electrolyte salt and does not impair the conductivity.

[0013]

[Table 1]

[Example 2] As in Example 1, ethylene carbonate and propylene carbonate were mixed in a volume ratio of 1 /
The mixture was mixed at a ratio of 1 and LiClO ₄ was dissolved in this mixed solvent at a ratio of 1 mol / l to prepare an electrolytic solution. Various dioxaspiro compounds were added to this electrolytic solution in a proportion of 1 wt% in total. A flat-type battery as shown in FIG. 1 was constructed using the electrolytic solution thus prepared. The structure of this battery will be described with reference to FIG. The positive electrode 1 is LiMn ₂ O ₄ powder,
The carbon black and the tetrafluoroethylene resin powder were mixed, and the current collector 2 made of expanded metal of titanium was spot-welded and pressed into a positive electrode can 3. The negative electrode 4 is obtained by crimping a lithium sheet punched into a disc shape onto a sealing plate 6 obtained by spot welding an expanded metal 5 of nickel. A polypropylene porous film is used for the separator 7. After injecting the electrolytic solution into the positive electrode can,
A flat battery was constructed by combining a sealing plate with a gasket 8 interposed therebetween.

COMPARATIVE EXAMPLE 2 An electrolytic solution prepared by dissolving LiClO ₄ at a ratio of 1 mol / l in a solvent prepared by mixing propylene carbonate and ethylene carbonate at a ratio of 1/1 by volume, and adding 1 wt% of decalin thereto. A battery configured in the same manner as in Example 2 except for the use is used as a comparative battery. The batteries of Example 2 and Comparative Example 2 configured as described above were used as 25
At a temperature of ² ° C, the charge / discharge cycle was repeated at a current density of ² mA / cm ² , a discharge lower limit voltage of 2.0 V, and a charge upper limit voltage of 3.5 V, and the number of cycles (cycle life) until the discharge capacity became half of the first cycle I asked. Table 2 compares the cycle lives of the batteries of Examples and Comparative Examples. From Table 2, it can be seen that the battery using the electrolyte solution containing the dioxaspiro compound of the present invention has a significantly improved charge / discharge cycle life. This is because the electrolytic solution of the present invention reduces the corrosion of the negative electrode and suppresses the generation of dendrites, thereby improving the charge / discharge efficiency of the negative electrode.

[0016]

[Table 2]

Example 3 LiClO ₄ was dissolved at a ratio of 1 mol / l in a solvent prepared by mixing propylene carbonate and ethylene carbonate at a ratio of 1/1 by volume. 1,3-Dioxaspiro [4,5] decane was added to this electrolyte at a ratio of 5 wt%. A flat-type battery similar to that of Example 2 was constructed using this electrolytic solution. [Comparative Example 3] Propylene carbonate, ethylene carbonate and dimethoxyethane in a volume ratio of 0.5 / 0.5 / 2
LiClO ₄ was dissolved in a solvent mixed at a ratio of 1 mol / l at a ratio of 1 mol / l, and 1,3-dioxaspiro [4,5]
A battery manufactured in the same manner as the example except that the electrolytic solution added with decane at a ratio of 5 wt% was used as a comparative example. The internal resistances of the batteries of Example 3 and Comparative Example 3 configured as described above were measured at various temperatures and plotted in FIG. It can be seen from FIG. 2 that the battery of Comparative Example 3 has a sharp increase in internal resistance at a temperature of −15 ° C. or lower. This is Comparative Example 3
This is because the battery of No. 1 does not use propylene carbonate or ethylene carbonate as a main solvent, and the electrolyte has a phase separation due to the low solubility of the dioxaspiro compound at low temperature.

[0018]

As described above, when the electrolytic solution containing the dioxaspiro compound of the present invention is adopted, the electric conductivity is high,
Further, by suppressing the generation of dendrites on the negative electrode during charging, it is possible to obtain a highly reliable non-aqueous electrolyte secondary battery having a long charge / discharge cycle life without internal short circuit.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a flat battery used in an example of the present invention.

FIG. 2 is a diagram in which internal resistances at respective temperatures of the batteries of Examples of the present invention and Comparative Examples are plotted.

[Explanation of symbols]

 1 Positive Electrode 2 Positive Electrode Current Collector 3 Positive Electrode Can 4 Negative Electrode 5 Negative Current Collector 6 Sealing Plate 7 Separator 8 Gasket

Claims (2)

[Claims] 1. A positive electrode, an alkali ion conductive non-aqueous electrolytic solution, and a negative electrode having an alkali metal as an active material.
The electrolytic solution is 1,3-dioxaspiro [4,5] decane, 1,4-dioxaspiro [4,5] decane, 1,3
-A non-aqueous electrolyte secondary battery comprising at least one selected from the group consisting of dioxaspiro [4,4] nonane and 1,4-dioxaspiro [4,4] nonane. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the main solvent of the electrolytic solution is at least one selected from the group consisting of ethylene carbonate and propylene carbonate.