JPH0831452A - Organic electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve a charge/discharge cycle life of a secondary battery provided with organic electrolyte comprising electrolyte dissolved in organic solvent. CONSTITUTION:Metal having lithium storing and discharging ability, that is alloy of aluminum and lithium, for example, is used as active material for a negative electrode 5, and organic electrolyte comprising lithium perfluoromethyl sulfonyl imide [LiN(CF3SO2)2] dissolved in organic solvent comprising three components of propylene carbonate, ethylene carbonate, and diethylene carbonate mixed with each other, for example, is held on a separator 6. A positive electrode 4 is provided, thereby a secondary battery is composed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery used as a main power source for electronic equipment or a memory backup power source.

[0002]

2. Description of the Related Art Conventional organic electrolyte batteries generally have a high energy density, which enables downsizing and weight reduction of equipment used as a power source, and has excellent reliability such as storage characteristics and leakage resistance. Therefore, the demand as a main power source for various electronic devices or a power source for memory backup is increasing year by year.

[0003] In this type of battery, the type of primary battery that cannot be charged is predominant, and as a typical battery system thereof, lithium metal is used as the negative electrode active material and dioxide is used as the positive electrode active material. Those using manganese, fluorocarbon, thionyl chloride, sulfur dioxide, silver chromate, etc. have been proposed.

On the other hand, recently, a rechargeable secondary battery type has been developed, and among them, a lithium secondary battery using a lithium alloy as an active material of a negative electrode has been actively proposed.

In this type of lithium secondary battery, when the same lithium metal as in the case of the conventional lithium primary battery is used as the negative electrode active material, the lithium in the electrolytic solution during charging is the negative electrode active material lithium metal. Dendrites are formed unevenly on the surface to form dendritic deposits, so-called dendrites, which penetrate the separator to cause an internal short circuit, or the discharge reaction becomes non-uniform during discharge and the lithium There is a problem that the battery is dropped and the charge / discharge cycle life of the battery is deteriorated.

In order to solve this problem and improve the charge / discharge cycle life, a lithium secondary battery as described below has been proposed (for example, JP-A-63-269).
53).

As an active material for the negative electrode of a lithium secondary battery, a material using an alloy of lithium and a metal capable of absorbing and releasing this lithium, for example, aluminum, lead, bismuth, indium, tin, etc. is proposed. Thus, in the case of a lithium secondary battery using a lithium alloy for the negative electrode, lithium ions are electrochemically occluded in the alloy during charging, so that dendrite of lithium is deposited on the surface of the negative electrode. Can be prevented.

Further, as an active material for the negative electrode, a material forming an intercalation compound with lithium ions, for example, a material such as a metal oxide such as niobium pentoxide, polyacetylene, polyaniline, polyacene utilizing a doping / undoping reaction of lithium ions. It has been proposed to use a conductive polymer material such as, or a carbon material capable of intercalation / day intercalation reaction with lithium ions. Such a lithium secondary battery is also used for the surface of the negative electrode. It is possible to prevent the deposition of lithium dendrite on the top.

On the other hand, as the active material of the positive electrode, a material that forms an intercalation compound with lithium ions, for example, a metal chalcogen compound such as vanadium pentoxide, manganese dioxide or lithium cobalt oxide, or a sulfide such as titanium disulfide or molybdenum dioxide. Alternatively, a conductive polymer material such as polyaniline, polyacetylene, or polyacene has been proposed.

Further, as the electrolytic solution, an organic electrolytic solution in which salts of an electrolyte are dissolved in a non-aqueous solvent is used, and as the non-aqueous solvent, propylene carbonate, ethylene carbonate,
Tetrahydrofuran, 2-methyltetrahydrofuran, or the like is used, and the electrolyte salt is a combination of anions such as BF ₄ ⁻ and CF ₃ SO ₃ ⁻ and alkali metal cations such as lithium ion, sodium ion, and potassium ion, for example, LiBF 4. ₄ is used.

In a conventional organic electrolyte secondary battery, an alloy of lithium and a metal capable of inserting and extracting lithium, that is, a lithium alloy is used as the negative electrode active material, and the electrolyte is an organic electrolyte. An organic electrolytic solution dissolved in a solvent is used, and the charge / discharge cycle life thereof is generally said to be determined by the charge / discharge cycle life of a lithium alloy used as a negative electrode active material. It is said that the performance of this charge / discharge cycle life depends largely on the performance of the lithium alloy itself, and in order to fully demonstrate the performance of the lithium alloy, it depends very much on the electrolytic solution used. It has been confirmed.

For example, when a lithium aluminum alloy is used as the negative electrode active material, during charging, lithium ions in the electrolytic solution are deposited on the surface of the lithium aluminum alloy as the negative electrode active material and at the same time occluded in the lithium alloy. However, in order to obtain a long-term charge / discharge cycle life, it is necessary to have a characteristic that the reaction of depositing lithium from the electrolytic solution proceeds smoothly. The property that this reaction proceeds smoothly is greatly influenced by the electrolytic solution used.

Further, during charging, the alloy surface of the negative electrode active material is in a very strong reducing atmosphere, but the lithium aluminum alloy has a slower occlusion speed than other lithium alloys, Depending on the electrolyte used, the decomposition reaction (oxidation reaction) proceeds preferentially to deposit electrically insulating decomposition products, which results in the electrically insulating decomposition products coating the surface of the lithium aluminum alloy. Therefore, there is a problem that the ability to insert and extract lithium is affected and the charge / discharge cycle life is shortened.

Originally, the cycle life of the lithium alloy, which is the active material of the negative electrode, depends on the absorption and desorption of lithium,
As a result of repeated expansion and contraction of the alloy surface, the alloy surface becomes finer and loses the ability to store and release lithium, leading to the end of its life.As described above, depending on the electrolyte used, the negative electrode It has a problem that the life of the active material cannot be maximized.

[0015]

The conventional problem to be solved by the present invention is that a negative electrode secondary battery using an alloy of a metal capable of inserting and extracting lithium and lithium as an active material is charged and discharged. It means that the cycle life is short.
Therefore, an object of the present invention is to obtain an organic electrolyte secondary battery having excellent charge / discharge cycle performance by improving the charge / discharge cycle life of this type of secondary battery.

[0016]

In order to achieve the above object, in the organic electrolyte secondary battery of the present invention, an alloy of a metal and lithium having the ability to store and release lithium is used as the negative electrode active material. , A positive electrode, and an organic electrolytic solution in which a lithium salt is dissolved as an electrolyte in an organic solvent, and lithium perfluoromethylsulfonylimide is used as the lithium salt.

Further, it is effective to use aluminum as a metal capable of inserting and extracting lithium into a lithium aluminum alloy, and as an organic solvent,
It is effective to use a mixed solvent of a high viscosity solvent and a low viscosity solvent.

The high-viscosity solvent may be a solvent containing at least one component selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate, and the low-viscosity solvent may be diethylene carbonate, 1,2. -Dimethoxyethane, 1,2-
A solvent containing at least one component selected from the group of diethoxyethane can be used.

Further, as the organic solvent, a solvent containing at least one component selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate, diethylene carbonate, 1,2-dimethoxyethane and 1,2-diethoxyethane. It is preferable to use a mixed solvent with a solvent containing at least one component selected from the group

[0020]

The function of the organic electrolyte solution in the organic electrolyte secondary battery constructed as described above is not clear, but as a result of experiments and investigations, it can be presumed that it works as follows.

First, considering the electrolyte, during charging, lithium ions in the electrolytic solution are occluded in the lithium alloy after being deposited on the surface of the lithium alloy which is the active material of the negative electrode. The precipitation reaction in
It has been confirmed that the electrolyte in the electrolyte is particularly affected, and lithium perfluoromethylsulfonylimide [LiN (CF ₃
SO ₂ ) ₂ ] is considered to be due to the fact that the conductivity of the electrolytic solution is remarkably improved as compared with lithium borofluoride (LiBF ₄ ) used in the conventional organic electrolytic solution secondary battery.

When the conductivity of the electrolytic solution is improved, lithium is efficiently deposited on the surface of the lithium alloy which is the active material of the negative electrode, and further, the lithium is deposited on the surface of the lithium alloy of the negative electrode during charging. Since it is extremely stabilized against the reduction reaction of ions, the charge / discharge cycle life can be improved.

Next, when considering the solvent, it has been confirmed that the action of the above-mentioned electrolyte is considerably influenced by the solvent used, and this is because the reaction with the electrolyte causes the electrolyte itself to be unstable depending on the solvent. It is assumed that the lithium perfluoromethylsulfonyl imide [LiN (C
When F ₃ SO ₂ ) ₂ ] is used, since it is stable to an organic solvent, the electrolyte itself becomes stable and the charge / discharge cycle life is improved.

When an organic solvent obtained by mixing a high-viscosity solvent and a low-viscosity solvent is used, the viscosity of the solvent is adjusted to an appropriate viscosity and the electric conductivity of the electrolytic solution increases, and at the same time, the active material of the separator or the positive electrode, etc. The permeability of the electrolytic solution into the power generation element and the battery constituent element is improved, and the charge / discharge cycle performance is improved.

Furthermore, a solvent containing at least one component selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate is used as the high viscosity solvent, and diethylene carbonate, 1,2-dimethoxyethane, When a solvent containing at least one component selected from the group of 1,2-diethoxyethane is used, the effect of conductivity of lithium perfluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ] which is the electrolyte is maximized. As a result, the charge / discharge performance can be further improved.

[0026]

EXAMPLE An example of the organic electrolyte secondary battery of the present invention will be described first with reference to FIG. 1 showing a sectional view of the structure thereof.

In FIG. 1, reference numeral 1 is a battery case made of stainless steel having excellent corrosion resistance and also serving as a positive electrode terminal, 2 is a sealing plate also serving as a negative electrode terminal made of stainless steel, and 3 is insulating the battery case 1 and the sealing plate 2. A polypropylene gasket 4 is a positive electrode, and its active material is vanadium pentoxide, which is the main ingredient of the active material, carbon black as a conductive agent, and fluororesin powder as a binder.
It is formed into pellets having a diameter of 15 mm and a thickness of 1 mm, and then dried at 200 ° C. for 12 hours. Reference numeral 5 denotes a negative electrode, the active material of which is aluminum and lithium melted and alloyed in an argon atmosphere to form a lithium-aluminum alloy, which is further processed into a sheet having a thickness of 0.2 mm in an argon atmosphere, and then a diameter of 15 mm. It is punched out, and then is closely attached to the back surface of the sealing plate 2. 6 is a separator made of polypropylene non-woven fabric impregnated with an organic electrolytic solution, and 7 is a conductive film that also serves as a positive electrode current collector, and uses carbon as a conductive agent and has a thickness of about 0.05 mm.

Next, the internal resistance value of the organic electrolyte secondary battery,
In order to examine the number of charge and discharge cycle lives, an organic electrolytic solution prepared by dissolving lithium perfluoromethylsulfonylimide as an electrolyte in a mixed organic solvent having a composition shown in Table 1 at a ratio of 1 mol / liter was used. The organic electrolyte secondary battery having the structure shown in FIG.
And In Table 1, the numerical value shows the mixing volume ratio, EC
Is ethylene carbonate, PC is propylene carbonate, BC is butylene carbonate, DEC is diethylene carbonate, DME is 1,2-dimethoxyethane, D
EE represents 1,2-diethoxyethane, respectively.

As a comparative example, a mixed solvent prepared by mixing γ-butyrolactone, which is a high-viscosity solvent, and 1,2-dimethoxyethane (DME), which is a low-viscosity solvent, in a ratio of 2: 1,
A battery I having the same structure as that of FIG. 1 was prepared by using an organic electrolytic solution in which lithium borofluoride was dissolved at a ratio of 1 mol / liter as an electrolyte. Further, an organic electrolytic solution in which lithium perfluoromethylsulfonylimide was dissolved at a ratio of 1 mol / liter as an electrolyte in a mixed solvent having the same composition as the mixed solvent in the case of the battery I was used, and the same constitution as in FIG. 1 was used. Battery J was used.

Each of the batteries A to J was a coin-shaped battery and had a diameter of 20 mm and a thickness of 2.0 mm, and the initial discharge capacity was 20 mAh when discharged from 3V to 2.5V.

[0031]

[Table 1]

The open circuit voltage of each of the batteries A to J immediately after assembly and the internal resistance measured by the AC method of 1 kHz are as shown in Tables 2 and 3, and the initial values from Tables 2 and 3 are as follows. Regarding the battery characteristics, it can be seen that there is almost no difference in any of the batteries. The values in Tables 2 and 3 represent the values of battery voltage and internal resistance,
The average value of 20 batteries is shown.

[0033]

[Table 2]

[0034]

[Table 3]

Next, for each of the batteries A to J, 1
The results of a test in which a charge / discharge cycle in which the discharge capacity per cycle is 20 mAh is repeated are shown in Tables 4 and 5. The numerical values in Tables 4 and 5 are initial discharge capacities (the initial discharge capacity during battery assembly was 20 mA.
h) represents the number of charge / discharge cycles until it deteriorates to 10 mAh (corresponding to 50% of the initial discharge capacity), and is shown as an average value for each of 10 batteries.

[0036]

[Table 4]

[0037]

[Table 5]

As shown in Tables 2 and 3, the batteries A to H and the battery J of the examples and the battery I of the comparative example have almost no difference in the internal resistance and the battery voltage of the initial characteristics. As is clear from Table 4 and Table 5, in the batteries A to H of the example, the effect of the electrolyte appears compared to the battery I of the comparative example, and the charge / discharge cycle life is significantly improved. Also, in the case of the battery J, the effect of the electrolyte appears and the charge / discharge cycle life is improved as compared with the battery I, but the effect of the mixed solvent is inferior to that of the batteries A to H in which the effect of the mixed solvent is synergized. be able to.

Next, the battery A and the battery I that had been subjected to the charge / discharge cycle test were disassembled, and the lithium aluminum alloy in the active material of the negative electrode was investigated.
Most of the lithium aluminum alloy of No. 1 has reached the end of its life due to miniaturization due to charge / discharge cycles, while half of that of Battery I is still in the initial state of battery assembly, and decomposition of the electrolyte solution coated on the surface. It was found that the product hindered charging and discharging and reached the end of its life.

Regarding the organic solvent used for the organic electrolytic solution, the mixed solvent of three or more components is superior to the mixed solvent of two components in the charge / discharge cycle life, which is caused by the interaction of each component. It seems to do.

In the above examples, the case where vanadium pentoxide was used as the material of the positive electrode active material was explained. However, metal oxides such as manganese dioxide, lithium manganese dioxide and lithium cobalt oxide, or nitric oxide are used. It has been confirmed that the same effect can be obtained by using a sulfide such as titanium sulfide or molybdenum disulfide, or a conductive polymer material such as polyaniline, polyacetylene, or polyacene.

[0042]

Since the present invention is constructed as described above, it has the following effects.

Lithium perfluoromethylsulfonyl imide [LiN (CF ₃
SO ₂ ) ₂ ], which is dissolved in an organic solvent to form an organic electrolytic solution. As the organic solvent, a mixed solvent of a high-viscosity solvent and a low-viscosity solvent is used, or a high-viscosity solvent is used. Ethylene carbonate, propylene carbonate,
Using a solvent containing at least one component selected from the group of butylene carbonate, and as a low viscosity solvent, diethylene carbonate, 1,2-dimethoxyethane, 1,
By using a solvent containing at least one component selected from the group of 2-diethoxyethane, the charge / discharge cycle life of the organic electrolyte secondary battery can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an organic electrolyte secondary battery in an example of the present invention.

[Explanation of symbols]

 4 Positive electrode 5 Negative electrode 6 Separator

Claims (6)

[Claims] 1. An organic electrolytic solution in which lithium perfluoromethylsulfonylimide is dissolved as an electrolyte in an organic solvent, using an alloy of lithium and a metal capable of absorbing and releasing lithium as an active material of the negative electrode, and a positive electrode. Organic electrolyte secondary battery. 2. The organic electrolyte secondary battery according to claim 1, wherein aluminum is used as a metal having the ability to insert and extract lithium. 3. The organic electrolyte secondary battery according to claim 1, wherein the organic solvent is a mixed solvent of a high viscosity solvent and a low viscosity solvent. 4. The high-viscosity solvent is ethylene carbonate,
The organic electrolyte secondary battery according to claim 3, comprising at least one component selected from the group consisting of propylene carbonate and butylene carbonate. 5. The organic electrolyte secondary battery according to claim 3, wherein the low-viscosity solvent contains at least one component selected from the group of diethylene carbonate, 1,2-dimethoxyethane and 1,2-diethoxyethane. . 6. An organic solvent containing at least one component selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate, diethylene carbonate, 1,2-dimethoxyethane, 1,2-
The organic electrolyte secondary battery according to any one of claims 1 to 3, which is a mixed solvent with a solvent containing at least one component selected from the group of diethoxyethane.