JPH05335033A - Non-aqueous solvent for battery electrolyte - Google Patents

Abstract

PURPOSE:To provide a non-aqueous solvent for electrolytic solution which is hard to be reduced and satisfies perfectly other physical and chemical characteristics by mixing a 1,3-dioxane-2-on derivative given by a specific structural expression with other non-aqueous solvent. CONSTITUTION:A 1,3-dioxane-2-on derivative given by the expression in attached illustration is mixed with a non-aqueous solvent such as ester, ether, etc. In expression, R1, R6 are alkyl radical given by general expression CnH2n+1 (n=1-4) or alkoxyl radical given by general expression OCnH2n+1 (n=1-4), and R2-R5 are H or alkyl radical given by general expression CnH2n+1 (n=1-4) or alkoxyl radical given by general expression OCnH2n+1 (n=1-4) O<1>-C<6>, O<3>-C<4> of this compound are hard to be cleaved, i.e., not likely to be reduced. Further, it has a high specific dielectric factor and is not likely reduced by other non-aqueous electrolyte PC, BC, to provide a favorable non-aqueous solvent for electrolyte to be used in a battery. As positive electrode active material is used a metal oxide or sulfide, while metal Li, Li alloy, or a carbonaceous material capable of occluding and releasing Li ions is used to the negative electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolytic solution secondary battery such as a lithium secondary battery or a non-aqueous solvent for an electrolytic solution used in a lithium primary battery.

[0002]

2. Description of the Related Art As a non-aqueous electrolyte secondary battery, MnO ₂ , V ₂ O ₅ , MoO ₃ , V ₆ O ₁₃ and Ti are used as positive electrode active materials.
A secondary battery is known in which a metal oxide such as S ₂ or MoS ₂ or a transition metal oxide or a sulfide is used, and metal lithium or an alloy thereof such as a wood alloy or a lithium aluminum alloy is used for a negative electrode.

[0003] To achieve the recent high energy density in batteries of this type, and material generating a higher voltage is studied, for example, the general _{formula: Li x M y O 2 (} M is C
O or Ni, x is 0.8 or less, and y is almost 1).
It is disclosed in Japanese Patent Publication No. 9507.

The open circuit voltage of a battery constructed by using this active material for the negative electrode of lithium and the electrolyte of LiBF ₄ (1M) / propylene carbonate reaches 4 V or more. Further, the actual operating voltage range can be about 3.4 to 4.6V.

A battery having such a high battery voltage characteristic is suitable as a power source for various electronic devices, which have been remarkably developed in recent years, as a high energy density battery, and the device is lightweight, compact, and highly functional. Further promote

However, in these secondary battery systems,
The low charge and discharge efficiency of the negative electrode is a big problem. Regarding the charge and discharge efficiency of the positive electrode, there is a phenomenon that the utilization rate decreases at the beginning of the cycle, but eventually the charge and discharge efficiency reaches a value close to 100%.

On the other hand, with respect to the negative electrode, the charge and discharge efficiency is 97% at maximum for metallic lithium and 99% at maximum even when a lithium alloy is used. This means that if the positive and negative electrodes have the same capacity, the negative electrode capacity will decrease by 2 to 3% per cycle, and if the charge and discharge at a deep depth is repeated, the cycle life will be only tens of cycles. ..

The main cause of this is Japanese Patent Laid-Open No. 1-286263.
As described in Japanese Patent Publication, it is thought that this is because the lithium deposited during charging is very active and reduces the solvent, and as a result, lithium changes into an electrochemically inactive compound. There is.

Although the detailed mechanism is not clear, the properties (physical properties, ionic conductivity,
It is believed that the electron conductivity and the like) are closely related to the mechanism of the reaction between the solvent and lithium to be reduced, and the influence of the solvent on the charge and discharge efficiency of lithium.

By the way, various solvents have been studied as solvents for non-aqueous electrolyte batteries, and among them, γ-butyrolactone (abbreviation: γ-BL, the same applies hereinafter), ethylene carbonate (EC), propylene carbonate (P
C), sulfolane (SL), 1,3-dioxolane (D
O), 1,2-dimethoxyethane (DME), 2-methyltetrahydrofuran (2-MeTHF), diethyl carbonate (DEC) and the like have been used as a particularly useful solvent, either alone or as a mixture thereof.

Of these, PC is most often used as a solvent for a non-aqueous electrolyte secondary battery both as a single solvent and as a mixed solvent. However, by repeatedly charging and discharging, PC reacts with negative electrode lithium to give a reduction product. Occurs, which accumulates on the surface of the negative electrode and causes a decrease in charge / discharge efficiency.

The above-mentioned various solvents, especially PC, are also used in the lithium primary battery. In a primary battery, it is not necessary to consider the problem of charging, but there is a problem that the solvent is reduced due to the presence of active lithium at the time of discharging and the performance of the battery is deteriorated. Particularly, when a weak discharge is performed at a high temperature for a long time, the reaction between active lithium and a solvent is performed for a long time, and this tendency becomes remarkable, which may lead to a significant deterioration in battery performance. ..

Therefore, the above-mentioned Japanese Patent Laid-Open No. 1-286263
In the publication, as a practical solution for making it difficult to react with lithium, carbonic acid as an additive is added to a known cyclic carbonic acid ester such as PC and BC, or a solvent containing a mixed solvent thereof and other ester or ether. The one to which lithium is added is used.

This is because the solvent containing cyclic carbonate such as PC reacts with lithium to produce lithium carbonate, but Li ₂ CO ₃ cannot discharge Li, so that lithium as a negative electrode active material is consumed and charged and discharged. Since the cycle becomes short, in order to prevent this, the Li ₂ CO
_The addition of ₃ is intended to prevent an increase in lithium carbonate due to the reaction.

[0015]

However, even if such an additive is added, it is still not a sufficient countermeasure against deterioration of characteristics as a solvent for a lithium secondary battery, and it is considered that the reduction of the solvent is the cause. The deterioration of the cycle characteristics is recognized. This means that even if additives are added,
It is suggested that the easiness of reduction of these cyclic carbonic acid ester itself cannot be sufficiently modified.

By the way, the origin of the idea of the present invention is 1,
3-dioxan-2-one has the following structural formula:

[Chemical 2] In the above, the present inventors have confirmed that all of R _{1 to} R ₆ have a structure occupied by hydrogen and have a high relative dielectric constant. Therefore, it is suitable as an alternative substance that constitutes an electrolytic solution for a non-aqueous battery such as the PC,
Its use is expected.

However, when the reduction resistance of this substance is examined, the oxygen-carbon bond in O ¹ -C ⁶ , O ³ -C ⁴ is likely to be cleaved, and a reduction product which causes deterioration of charge and discharge is generated. The same drawbacks as the PC are noticeable.
Even if only one of R ₁ and R ₆ is substituted with an alkyl group, the oxygen-carbon bond on the non-substituted side is likely to be cleaved for the same reason.

Therefore, although 1,3-dioxan-2-one has the above-mentioned excellent properties, it has not been actually used as an electrolytic solution.

The present inventors have paid attention to the excellent characteristics of 1,3-dioxan-2-one, and have taken note of the C in this basic structure.
^4, C ⁶ both at least one alkyl group of hydrogen carbon bonds or by replacing the alkoxy group, the oxygen of the ^{O 1 -C 6, O 3 -C} 4 by contribution of these substituents, - carbon-carbon cleavage It was assumed that it would be difficult to do, that is, it would be difficult to be reduced.

The present invention has been made by paying attention to the above points, and its purpose is to reduce the structure itself at the negative electrode more than the conventionally used cyclic carbonic acid ester including PC mentioned above. It is an object of the present invention to provide a non-aqueous solvent for an electrolytic solution of a battery, which has a difficult structure and completely satisfies other physicochemical characteristics required as an electrolytic solution solvent of the battery.

[0021]

To achieve the above object, the present invention is represented by the following structural formula:

[Chemical 3] (R ₁ and R ₆ in the formula are represented by the general formula C _n H _{2n + 1} (n = 1 to 4)
Or an alkyl group represented by the general formula OC _n H
Alkoxyl group represented by _{2n + 1} (n = 1 to 4): R in the formula
_{2 to} R ₅ are hydrogen or the general formula C _n H _{2n + 1} (n = 1 to 4
) Or an alkyl group represented by the general formula OC _n H
It is characterized in that a 1,3-dioxan-2-one derivative consisting of an alkoxyl group represented by _{2n + 1} (n = 1 to 4): is mixed with another non-aqueous solvent and used.

The carbon number n of the substituent is preferably about 1 to 4. This is meaningless even if the number of carbons is further increased, and is meaningless, and in addition to other physical characteristics such as an increase in viscosity and a decrease in relative permittivity, battery electrolysis is not performed. This is because problems occur as a liquid solvent. In addition, since the presence or absence of a substituent for C ⁵ does not contribute to the reduction resistance, hydrogen may be used as it is. However, when substituting, the number of carbon atoms is 1 to 4 in consideration of the same problems as described above.

Therefore, when the substituent is an alkyl group, CH ₃ , C ₂ H ₅ , CH (CH ₃ ) ₂ and C (CH ₃ ) ₃
It is desirable to be selected from the following.

When the substituent is an alkoxyl group,
_{OCH3, OC 2 H 5, OC} 3 H 7, OCH (CH 3)
It is desirable to be selected from ₂ , OC (CH ₃ ) ₃ .

The 1,3-dioxan-2-one derivative is generally obtained by the following chemical reaction formula.

[0026]

[Chemical 4] The other non-aqueous solvent mixed with the cyclic carbonic acid ester compound can be selected from the above-mentioned known esters and ethers, but not only has the property of being less likely to be reduced to the negative electrode but also the 1,3-dioxane. It is necessary to select a non-aqueous solvent for a battery that can be adjusted to have generally preferable physicochemical properties by mixing with a 2-one derivative.

The non-aqueous solvent for an electrolytic solution of the present invention uses a metal oxide or a sulfide as a positive electrode active material, and a lithium capable of occluding and releasing metal lithium or a lithium alloy or a lithium ion in a negative electrode. In addition to non-aqueous solvent for electrolyte of non-aqueous electrolyte secondary battery using porous material,
It can be used as a non-aqueous solvent for an electrolytic solution of a lithium primary battery.

[0028]

The non-aqueous solvent comprising the 1,3-dioxan-2-one derivative of the present invention has at least the above structural formula:
R ₁ and R ₆ have an alkyl group or an alkoxyl group, and these groups make it difficult for oxygen-carbon cleavage in O ¹ -C ⁶ , O ³ -C ⁴ to occur, and have a high relative dielectric constant. It becomes a solvent that is less likely to be reduced than PC and BC.

The improvement of the charge / discharge cycle characteristics of the lithium secondary battery using such a non-aqueous solvent is proved to be remarkable as compared with that using PC and BC under the same conditions. Further, in the primary battery, it is possible to prevent deterioration of battery characteristics particularly during long-term discharge under a low load, and increase in discharge capacity demonstrates the usefulness of using the non-aqueous solvent of the present invention.

[0030]

EXAMPLES Next, examples of the present invention will be described. However, the present invention is not limited to the examples described below.

Example 1. In the above structural formula, a methyl group was used as a substituted alkyl group, and as shown in Table 1, 9 types of 2 to 6 substituted compounds were synthesized according to the above chemical reaction formula.

Next, the synthesized derivative and LUM of PC and the molecular orbital of unsubstituted 1,3-dioxan-2-one
When the O (lowest unoccupied orbit) energy (eV) was calculated, the results shown in Table 2 below were obtained. There is a correlation between the reduction potential of the organic compound and the LUMO energy, and the higher the LUMO energy, the lower the reduction potential.
That is, it is difficult to be reduced.

[0033]

[Table 1]

[Table 2] As is clear from the results shown in Table 2 above, Example 1
It is shown that the 1,3-dioxan-2-one derivative obtained in 1. has a higher LUMO energy than conventional PC or unsubstituted 1,3-dioxan-2-one, and thus is difficult to reduce. ing. Further, other properties also show suitable values as the nonaqueous solvent for the electrolytic solution.

Example 2. (Example of Application to Lithium Secondary Battery) Next, Example 1. A non-aqueous electrolyte solution obtained by mixing the solvent obtained in (1) and another non-aqueous solvent and a non-aqueous electrolyte solution obtained by mixing PC, BC and another non-aqueous solvent are used to form coin-type lithium secondary batteries ( 2016 type) was assembled and the cycle characteristics of each were investigated. The composition of the solvent of the non-aqueous electrolyte is
There are eight kinds of combinations of the present invention shown in Table 3 below, the comparative example and the conventional example, and the solute was all LiPF ₆ 1 mol / l.

[0035]

[Table 3] The specifications of the 2016 type coin-type non-aqueous electrolyte secondary battery are as follows.

LiMnO ₂ as a positive electrode was mixed with carbon powder as a conductive material and Teflon powder as a binder at a weight ratio of 100: 10: 4, and the mixture was pressure-molded into pellets and heat-treated to remove water. Used.

A lithium aluminum alloy was used as the negative electrode. The atomic ratio of lithium to aluminum is 1: 1. A polypropylene microporous film (thickness 0.025 mm) was used as the separator. The positive electrode is a circular pellet with a diameter of 15 mm and a height of 0.47 mm,
The negative electrode is a circular pellet having a diameter of 15.4 mm and a height of 0.9 mm. The nominal capacity of this battery is 20 mAh.

Next, when the charge and discharge cycle characteristics of the battery of the above specifications using the nine kinds of electrolytic solutions shown in Table 3 were examined, the results shown in FIG. 1 were obtained.

The test conditions were a constant current charge / discharge at a temperature of 20 ° C. with a charging current of 1 mA and a discharging current of 2 mA. The discharge end voltage was 2.0 V and the charge voltage was 3.4 V.
The figure shows the change in capacity for each cycle due to the difference in the composition of the electrolyte solution when the initial discharge capacity is 100. As is clear from the results shown in FIG. 1, the cycle characteristics are remarkably improved in the battery using the electrolytic solution containing the non-aqueous solvent of the present invention. Further, this suggests that the solvent of the present invention has durability as compared with PC and is less likely to be reduced by the negative electrode.

Example 3. (Evaluation test in test cell) Example 2. Using 9 kinds of non-aqueous electrolytes shown in Table 3 of
The test cell shown in FIG. 2 was assembled.

As the positive electrode 1, LiCoO ₂ , carbon powder as a conductive material, and Teflon powder as a binder were mixed at a weight ratio of 100: 10: 6 and rolled to form a sheet, which was a current collector 2. It was crimped to a titanium net. The negative electrode 3 includes carbonaceous powder obtained by firing pitch-based carbon fiber and EPD as a binder.
M (ethylene propylene diene monomer) 100: 7
Were mixed and rolled into a sheet-like shape and pressed onto a Ni net as the current collector 4. The size of the positive and negative electrodes is a square of 10 × 10 mm, and the thickness of the positive electrode is 0.25 mm.
The thickness of the negative electrode is 0.40 mm. The distance between the electrodes 1 and 3 was set to 2 mm, and the electrodes were arranged in the beaker 5 as shown.

The theoretical filling capacity of the positive electrode is 8.2 mAh,
The negative electrode is 7 mAh. The reason for increasing the theoretical capacity of the positive electrode is that after the first charge, the amount of lithium that can be involved in the next discharge is less than the charge capacity, and this is because the lithium was charged only in the first charge / discharge cycle. This is because a certain amount of lithium is taken into the carbonaceous negative electrode, and it will not be possible to discharge from the next time.

Next, when the charge and discharge cycle characteristics of the test cell of the above specifications using the above 9 kinds of electrolytes were examined, the results of FIG. 3 were obtained. The test conditions were constant current charging / discharging with a charging current of 1 mA and a discharging current of 2 mA. The discharge end voltage is 2.
The upper limit of the charging voltage was 8V and 4.15V. The figure shows the change in capacity for each cycle due to the difference in the composition of the electrolyte solution when the initial discharge capacity is 100. As is clear from the results shown in FIG. 3, in the battery using the electrolytic solution containing the non-aqueous solvent of the present invention, the cycle characteristics were remarkably improved. It was confirmed that the same effect as was obtained.

Example 4. (Example of Application to Lithium Primary Battery) Example 2. No. A non-aqueous electrolyte solution of 1 to 9 was used to assemble a so-called inside-out type lithium primary battery of AA type.

As the positive electrode, LiMnO ₂ , carbon powder as a conductive material, and Teflon powder as a binder were used in a weight ratio of 1;
The mixture was mixed at a ratio of 00: 10: 4, pressure-molded, and then heat-treated to remove water before use. A lithium sheet was used as the negative electrode. As the separator, a polypropylene non-woven fabric having a thickness of 0.2 mm was used. The positive electrode is formed in a hollow cylindrical shape having an outer diameter of 13.7 mm, a length of 40 mm, and an inner diameter of 9.7 mm, and is housed so as to keep the connection to the positive electrode also serving as a container. For the negative electrode, a lithium sheet having a thickness of 1.1 mm, a width of 40 mm, and a length of 24 mm is formed into a cylindrical shape, and the lithium sheet is fitted to face the inside of the positive electrode via a separator. The nominal capacity of this battery is 1.9 Ah.

Next, the discharge characteristics of the primary battery of the above specifications using the above 9 kinds of electrolytic solutions were examined, and the results shown in FIG. 4 were obtained. The test conditions were a temperature of 60 ° C. and a discharge current of 10
μA, and as described above, when a long-term discharge is performed under a low-rate load under such a temperature condition, the active lithium at the time of discharge and the solvent are in contact with each other for a long time, so that the deterioration of the electrolytic solution progresses. However, it is said that the life is shortened.

In this example, as is clear from the results shown in FIG. 4, when the electrolytic solution containing the non-aqueous solvent of the present invention was used, the characteristics were low even with such a low rate discharge. Noticeably improved. This also means that the solvent of the present invention is P
This suggests that it is more durable than C and BC and that it is less likely to deteriorate even if it is in contact with lithium for a long period of time.
Although only CH ₃ was used as the substituent of 1,3-dioxan-2-one in the above-mentioned examples, various selections can be made from an alkyl group or an alkoxyl group having 1 to 4 carbon atoms. For example, the alkyl group is C ₂ H ₅ , CH (CH ₃ ) ₂ ,
C (CH ₃ ) ₃ can be selected, and the alkoxyl group can be OCH 3, OC ₂ H ₅ , OC ₃ H ₇ , OCH.
It can be selected from (CH ₃ ) ₂ and OC (CH ₃ ) ₃ . Further, these substituents may be used alone or in a mixed state, and the combination thereof can be variously selected according to the characteristics suitable as the electrolytic solution.

[0048]

As described in detail in the above examples, by using the cyclic carbonic acid ester according to the present invention as the solvent constituent substance of the electrolytic solution, the charge / discharge cycle characteristics can be remarkably improved in the secondary battery. Therefore, it is useful as a solvent constituent substance of the electrolytic solution.

Further, when applied to a primary battery, there is a feature that deterioration of the characteristics can be prevented especially when discharging for a long period under a low load.

[Brief description of drawings]

FIG. 1 Example 2. 5 is a graph comparing charge / discharge cycle characteristics in FIG.

FIG. 2 Example 3. 3 is a schematic diagram of a test cell in FIG.

FIG. 3 Example 3. 5 is a graph comparing charge / discharge cycle characteristics in FIG.

FIG. 4 is a fourth embodiment. 5 is a graph comparing the discharge characteristics in FIG.

Claims (5)

[Claims] 1. Represented by the structural formula: (R ₁ and R ₆ in the formula are represented by the general formula C _n H _{2n + 1} (n = 1 to 4)
Or an alkyl group represented by the general formula OC _n H
Alkoxyl group represented by _{2n + 1} (n = 1 to 4): R in the formula
_{2 to} R ₅ are hydrogen or the general formula C _n H _{2n + 1} (n = 1 to 4
) Or an alkyl group represented by the general formula OC _n H
_A 1,3-dioxan-2-one derivative consisting of an alkoxyl group represented by _{2n + 1} (n = 1 to 4) :) is mixed with another non-aqueous solvent and used. Non-aqueous solvent. 2. The alkyl group is CH ₃ , C ₂ H ₅ , C
The non-aqueous solvent for a battery electrolyte according to claim 1, wherein the non-aqueous solvent is selected from H (CH ₃ ) ₂ and C (CH ₃ ) ₃ . 3. The alkoxyl group is OCH 3, OC ₂
H ₅ , OC ₃ H ₇ , OCH (CH ₃ ) ₂ , OC (C
The non-aqueous solvent for the electrolytic solution of the battery according to claim 1, which is selected from H ₃ ) ₃ . 4. A non-aqueous electrolyte secondary using a metal oxide, a sulfide or the like as a positive electrode active material and a metallic lithium or lithium alloy or a carbonaceous material capable of absorbing and releasing lithium ions as a negative electrode. It is used as a non-aqueous solvent for an electrolytic solution of a battery, and the non-aqueous solvent for an electrolytic solution of a battery according to any one of claims 1 to 3. 5. The method according to any one of claims 1 to 3, which is used as a non-aqueous solvent for an electrolytic solution of a lithium primary battery.
A nonaqueous solvent for an electrolytic solution of a battery according to any one of 1 to 4 above.