JP3223035B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery,
In particular, it relates to improvement of the electrolyte.

[0002]

Nowadays, propylene carbonate, .gamma.-butyrolactone, dimethoxyethane, tetrahydrofuran, in organic solvent dioxolane, LiClO _4, Li
A non-aqueous electrolyte battery in which an electrolyte obtained by dissolving a solute such as BF ₄ , LiAsF ₆ , LiPF ₆ , or 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 been widely used for small electronic devices such as electronic watches and cameras. One of the problems that make this type of nonaqueous electrolyte battery chargeable is that the form of alkali metal deposited on the negative electrode during the charging process is a so-called dendrite such as a dendrite, fibril or needle. If the dendrite grows remarkably, the danger of internal short circuit between the negative electrode and the positive electrode and the risk of ignition increase, and even if the dendrite is melted in the subsequent discharge process, local melting of the dendrite progresses and part of the dendrite becomes electrically Not all dendrites can be dissolved because they are more liberated. In other words, the amount of discharge (dissolution) relative to the amount of charge (precipitation) is reduced (decrease in charge and discharge efficiency), and the cycle life is shortened.

[0003] As a method of solving such a problem,
Attempts have been made to suppress the generation of dendrites by adding a hydrocarbon compound as an additive to a high dielectric constant propylene carbonate solvent that dissolves a large amount of electrolyte salt to protect the surface of the deposited lithium (3rd International
Meeting on Lithium Batteries, Abstract, 34
6 (1986)).

[0004]

As described in the above cited document, even if a solvent in which propylene carbonate contains a hydrocarbon as an additive is used as an electrolyte as described above, the charge (deposition) There is a problem in that the corrosion of lithium on the electrode left for a long time after the progress proceeds, and the charge / discharge efficiency decreases. In addition, it has been found that when a hydrocarbon compound is added to the electrolytic solution, the conductivity of the electrolytic solution is reduced, so that there is a disadvantage that polarization during charging and discharging at a high current density increases. The present invention is intended to eliminate such conventional disadvantages, and suppresses the progress of corrosion of alkali metals such as lithium deposited by charging (deposition).
An object of the present invention is to provide a highly reliable nonaqueous electrolyte secondary battery by obtaining an electrolytic solution having high conductivity and suppressing generation of dendrites on a negative electrode even when charge and discharge are repeated.

[0005]

A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a non-aqueous electrolyte having alkali ion conductivity, and a negative electrode having an alkali metal as an active material. Are 1,3-dioxaspiro [4,5] decane represented by Formula 1, 1,4-dioxaspiro [4,5] decane represented by Formula 2, 1,3-dioxaspiro [4,4] represented by Formula 3 Nonane and 1,4 represented by formula 4
-Dioxaspiro [4,4] nonane, wherein at least one member selected from the group consisting of:

[0006]

Embedded image

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 considerations by the present inventors, in an electrolytic solution containing a dioxaspiro compound, lithium atoms (to be exact, adsorbed ions) deposited on a metal substrate are not fixed in situ when deposited, and the surface of the substrate is not fixed. Has been found to be easily trapped at thermodynamically stable crystal lattice points after diffusion.
Therefore, when a crystal nucleus with many defects is generated immediately after the start of the precipitation, the precipitated atoms gather in the crystal nucleus to enhance its crystallinity, and the crystal nucleus grows in a spherical shape, thereby preventing so-called dendrite. The dioxaspiro compound is
As is clear from the structural formula, one of the molecular structures is a hydrophobic structure consisting of only carbon and hydrogen atoms, and the other is a hydrophilic structure containing oxygen atoms. Therefore, it is easily compatible with a solvent having a high dielectric constant, such as ethylene carbonate or propylene carbonate, and also coordinates itself with ions such as lithium and contributes to dissociation of the electrolyte salt, 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 an electrode made of an alkali metal such as lithium, and at the boundary with a solvent having a high dielectric constant such as ethylene carbonate or propylene carbonate. It has been found that the high dielectric constant solvent prevents direct reaction with alkali metals. From such a thing,
It is considered that the alkali metal precipitated in the electrolytic solution containing the dioxaspiro compound does not progress corrosion even when left for a long period of time, and improves the charge / discharge efficiency.

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

[0011]

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

Table 1 shows the conductivity of the electrolyte solutions of these examples and comparative examples. Here, D13 represents 1,3-dioxaspiro [4,5] decane, D14 represents 1,4-dioxaspiro [4,5] decane, and N13 represents 1,3-dioxaspiro [4,4]. Nonane, and N14 represents 1,4-dioxaspiro [4,4] nonane, respectively. From Table 1, it is found that the conductivity of the electrolytic solution to which the dioxaspiro compound according to the example of the present invention is added is about 1 times that of the comparative example.
It turns out that it improves 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 at a volume ratio of 1 /
The mixture was mixed at a ratio of 1 and LiClO ₄ was dissolved at a ratio of 1 mol / l in this mixed solvent to prepare an electrolytic solution. Various dioxaspiro compounds were added to this electrolyte at a total of 1 wt%. A flat battery as shown in FIG. 1 was constructed using the electrolyte solution thus prepared. The configuration of this battery will be described with reference to FIG. Positive electrode 1 is made of LiMn ₂ O ₄ powder,
It is obtained by mixing carbon black and ethylene tetrafluoride resin powder and press-molding a current collector 2 made of expanded metal of titanium into a positive electrode can 3 spot-welded. The negative electrode 4 is formed by pressing a disc-shaped punched lithium sheet onto a sealing plate 6 to which nickel expanded metal 5 is spot-welded. A porous film made of polypropylene is used for the separator 7. After injecting the above electrolyte 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 electrolyte obtained by dissolving LiClO ₄ at a ratio of 1 mol / l in a solvent in which propylene carbonate and ethylene carbonate were mixed at a ratio of 1/1 was added with 1% by weight of decalin. A battery configured in the same manner as in Example 2 except for the use was used as a battery of Comparative Example. The batteries of Example 2 and Comparative Example 2 configured as described above
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 was determined. I asked. Table 2 compares the cycle life of the batteries of the example and the comparative example. Table 2 shows that the battery using the electrolytic solution to which the dioxaspiro compound of the present invention was added has significantly improved charge / discharge cycle life. This is because in the electrolyte of the present invention, the corrosion of the negative electrode was reduced, and the generation of dendrites was suppressed, so that the charge and discharge efficiency of the negative electrode was improved.

[0016]

[Table 2]

Example 3 LiClO ₄ was dissolved at a rate of 1 mol / l in a solvent in which propylene carbonate and ethylene carbonate were mixed at a volume ratio of 1/1. 1,3-Dioxaspiro [4,5] decane was added to the electrolyte at a ratio of 5 wt%. Using this electrolyte solution, a flat battery similar to that in Example 2 was formed. [Comparative Example 3] Propylene carbonate, ethylene carbonate and dimethoxyethane in a volume ratio of 0.5 / 0.5 / 2.
LiClO ₄ is dissolved at a rate of 1 mol / l in a solvent mixed at a ratio of 1,3-dioxaspiro [4,5].
A comparative example is a battery manufactured in the same manner as in the example except that an electrolytic solution to which decane was added at a ratio of 5 wt% was used. 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. 2 that the internal resistance of the battery of Comparative Example 3 sharply increases at a temperature of −15 ° C. or lower. This is Comparative Example 3
This is because battery No. did not use propylene carbonate or ethylene carbonate as the main solvent, and the electrolytic solution phase-separated due to low solubility of the dioxaspiro compound at low temperatures.

[0018]

As described above, the use of the electrolytic solution to which the dioxaspiro compound of the present invention has been added provides high conductivity,
In addition, since the generation of dendrites on the negative electrode during charging is suppressed, a highly reliable nonaqueous electrolyte secondary battery having a long charge-discharge cycle life without internal short circuit can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a flat type battery used in an example of the present invention.

FIG. 2 is a diagram in which the internal resistance at each temperature of the batteries of Examples and Comparative Examples of the present invention is plotted.

[Explanation of symbols]

 Reference Signs List 1 positive electrode 2 positive electrode current collector 3 positive electrode can 4 negative electrode 5 negative electrode current collector 6 sealing plate 7 separator 8 gasket

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (2)

(57) [Claims] Claims 1. A positive electrode, a non-aqueous electrolyte having an alkali ion conductivity, and a negative electrode containing an alkali metal as an active material,
The electrolytic solution comprises 1,3-dioxaspiro [4,5] decane, 1,4-dioxaspiro [4,5] decane,
-A non-aqueous electrolyte secondary battery comprising at least one member 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.