JP2974739B2 - Organic electrolyte battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an organic electrolyte battery, and more particularly, to an improvement in the organic electrolyte.

[Prior art] Lithium is used as a negative electrode, manganese dioxide mixture is used as a positive electrode, and an organic electrolyte battery represented by a lithium-manganese dioxide battery using an organic electrolyte has a high energy density.
Demand is also increasing due to its light weight and long life.

And recently, to improve battery safety,
The use of CF ₃ SO ₃ Li for electrolytes has come to be used.

[Problems to be solved by the invention]

However, a battery using the above-mentioned CF ₃ SO ₃ Li as an electrolyte has a problem that the open-circuit voltage decreases during storage.

Further, similar to the above CF ₃ SC ₃ Li, the general formula C _n F _{2n + 1} SO ₃ M (n
Is an integer of 2 or more, and M is an alkali metal). Even when a compound represented by the formula (I) is used for the electrolyte, a phenomenon that the open circuit voltage of the battery decreases during storage is observed.

Such a decrease in the open circuit voltage during storage can be suppressed to some extent by pre-discharging after assembling the battery. Nevertheless, the open circuit voltage decreases when stored at a high temperature or for a long time.

[Means for solving the problem]

The present invention (n is an integer of 2 or more, M is an alkali metal a _{is) C n F 2n + 1 SO} 3 M as the electrolyte used, and an organic electrolyte solution (hereinafter simplified as "electrolytic solution") 50-1 in
By containing 000 ppm of water, a decrease in the open circuit voltage of the battery during storage is suppressed, and the above problem is solved.

The progress of completing the present invention will be described in detail as follows.

The present inventors first examined the cause of the decrease in the open-circuit voltage during storage as described above, and found that the decrease in the open-circuit voltage caused the active material of the positive electrode during storage, a current collector, a current collector network, and the like. It was found that this was caused by elution of the metal component from the positive electrode material into the electrolytic solution.

In other words, the metal component eluted from the positive electrode material into the electrolytic solution reacts with the alkali metal of the negative electrode and precipitates as a metal on the surface of the negative electrode, and this is repeated, and the metal grows on the negative electrode and penetrates through the separator, Eventually, the battery reaches the positive electrode, causing an internal short circuit in the battery, lowering the open circuit voltage of the battery and reducing its capacity.

Therefore, it is considered that the above-mentioned decrease in the open circuit voltage during storage can be prevented by preventing the elution of the metal component from the positive electrode material.

The present inventors have made intensive studies along the above _{idea, C n F 2n + 1 SO} 3 M (n as the electrolyte is an integer of 2 or more and
When M is an alkali metal) and the electrolyte contains 50 to 1,000 ppm of water, the metal component is prevented from being eluted from the positive electrode material into the electrolyte, and as a result,
The inventors have found that a decrease in the open circuit voltage during storage is suppressed, and have completed the present invention.

Normally, when an organic electrolyte battery is manufactured with water contained in the electrolyte, the water in the electrolyte reacts with the alkali metal of the negative electrode to generate hydrogen gas, degrade the negative electrode, and generate hydrogen. The gas causes blistering of the battery. However, the above C _n F _{2n + 1} S
O ₃ M (n is an integer of 2 or more, and M is an alkali metal)
When the compound is used, the reaction between water and the alkali metal of the negative electrode is suppressed, and the blister of the battery and the deterioration of the negative electrode can be prevented.

To confirm this, first, LiClO ₄ , LiPF ₆ , LiCF ₃ SO
Typical electrolytes such as ₃ are propylene carbonate and 1,2
-0.6 mol / in a mixed solvent having a volume ratio of 1: 2 with dimethoxyethane.
Dissolve to prepare an electrolytic solution, and add 500 ppm of water to the electrolytic solution.
0.18 mm thick in vials with 10 ml each mixed
Put in a 28mm x 95mm piece of lithium and seal tightly.
After standing for a day, the water content of all of LiClO ₄ , LiPF ₆ and LiCF ₃ SO ₃ was reduced, and hydrogen gas was detected. It was also found that hydroxide was formed on the negative electrode surface.

From the above, it can be seen that when a conventional general electrolyte is used, the moisture in the electrolytic solution reacts with the negative electrode, generating hydrogen gas and deteriorating the negative electrode. Therefore, conventionally, reduction of the water content of the electrolytic solution by various methods has been studied. In general, in an organic electrolytic solution battery, a battery is manufactured in a state where the water content of the electrolytic solution is low.

However, (n is an integer of 2 or more, M is an alkali metal a _{is) C n F 2n + 1 SO} 3 M as the electrolyte when using the reaction between water and the negative electrode is greatly inhibited. For example, C ₄ F ₉ SO ₃ L
When an experiment similar to the above is performed using i, the moisture value hardly changes, as shown in the examples described later. When a battery is manufactured using an electrolytic solution containing 500 ppm of water, a drop in the open circuit voltage during storage is unexpectedly suppressed in this battery.

As described above, the reason why the decrease in the open-circuit voltage during storage can be suppressed by including water in the electrolyte solution is not always clear at present, but protection for suppressing elution of metal components on the surface of the positive electrode is not yet clear. It is considered that the film was formed.

The above C _n F _{2n + 1} SO ₃ M has a greater effect of suppressing the reaction between water and the negative electrode as the molecular weight is larger, and it is necessary that n is 2 or more, and n is preferably 4 or more. . C _n F
_{When n of 2n + 1} SO ₃ M is 4 or more, 500p
Even if about pm is contained, almost no reaction between water and the negative electrode occurs. However, if the molecular weight is too large, the ionic conductivity is reduced, and the discharge characteristics and the like are reduced.
Is preferably 10 or less.

The water content in the electrolytic solution starts to show the effect of suppressing the decrease in the open circuit voltage during storage from about 50 ppm, and in order to obtain a more preferable effect, it is preferable that the water content in the electrolytic solution be 100 ppm or more, particularly If the content is 200 ppm or more, more preferable effects can be obtained. However, if the amount of water in the electrolytic solution becomes too large, the reactivity between the water in the electrolytic solution and the negative electrode starts to increase, even if C _n F _{2n + 1} SO ₃ M is used as the electrolyte. It is necessary to keep the water content of the water below 1,000 ppm.

In preparing the electrolytic solution, for example,
1,2-dimethoxyethane, dimethoxymethane, dimethoxypropane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3
Ethers such as dioxolane, propylene carbonate, ethylene carbonate, butylene carbonate, γ
Esters such as -butyrolactone and γ-valerolactone, and organic solvents such as dimethylformamide, dimethylsulfoxide and acetonitrile are used alone or as a mixture of two or more. In order to obtain a battery with particularly excellent discharge characteristics, ether should be 55% by volume in a solvent, especially
It is preferable to use 60% by volume or more. As the ether, chain ethers such as 1,2-dimethoxyethane, dimethoxymethane, and dimethoxypropane are particularly preferably used because they improve discharge characteristics at low temperatures.

When a metal oxide such as manganese dioxide is used as a positive electrode active material, if an ester such as propylene carbonate is used in a solvent at 10% by volume or more, it is used as a positive electrode active material and an electrolyte solvent during storage. The reaction with the ether which is present can be suppressed, and a decrease in the storage characteristics of the battery can be prevented. If the low-temperature discharge characteristics are particularly important, use a combination of propylene carbonate and 1,2-dimethoxyethane, and adjust the ratio of 1,2-dimethoxyethane to 55 to 80% by volume, particularly 60 to 75% by volume. %
It is preferred that

The concentration of _{C n F 2n + 1 SO 3} M in an electrolytic solution is, 0.05 to 1 mol / are suitable, especially 0.2～0.6Mol / are preferred. This C _n F
_{If 2n + 1} SO ₃ M is contained in the electrolyte at the above concentration, C _n F
_{In addition to 2n + 1} SO ₃ M, for example, a small amount of another electrolyte such as LiClO ₄ , LiBF ₄ , and LiPF ₆ may be contained. That is, C _n F
_It is sufficient that _{2n + 1} SO ₃ M is used as the main electrolyte.

The negative electrode is made of an alkali metal or a compound containing an alkali metal. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include those alkali metals and aluminum, lead, indium, and gallium. And alloys of cadmium, tin, magnesium and the like, and compounds of alkali metals and carbon materials. When the compound of the alkali metal and the carbon material is used for the negative electrode, the reactivity between the water and the negative electrode is further reduced, so that a more preferable result is obtained.

For the positive electrode, a positive electrode active material such as manganese dioxide, vanadium pentoxide, chromium oxide, lithium cobalt oxide, and lithium nickel oxide, or a conductive auxiliary such as carbon black or graphite, or polytetrafluoroethylene A molded product is used together with a current collecting material such as stainless steel using a mixture to which a binder or the like is appropriately added.

Next, the present invention will be described more specifically with reference to examples.

〔Example〕

Example 1 A manganese dioxide mixture made of manganese dioxide, carbon black and polytetrafluoroethylene heat-treated at 450 ° C., having a thickness of 0.4 mm and a width of 3 using a stainless steel mesh as a core material.
The strip-shaped positive electrode formed into a 0 mm sheet shape and attached with a stainless steel current collector was dried at 250 ° C. for 9 hours, and then cooled to room temperature in a dry atmosphere.

Next, this strip-shaped positive electrode was wrapped with a separator made of a microporous polypropylene film having a thickness of 25 μm,
A 0.18 mm, 30 mm wide band-shaped negative electrode made of lithium is stacked, spirally wound into a spiral electrode body, and then filled into a bottomed cylindrical battery case with an outer diameter of 15 mm, and spot welded to the lead body And so on.

Separately, C ₄ F ₉ SO ₃ Li was vacuum-dried at 100 ° C. for 4 hours, and then mixed with a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 2 at a ratio of 0.6 mol /. After dissolving, water was added to the solution to prepare an electrolytic solution containing 200 ppm of water, and the electrolytic solution was poured into the battery case.

Next, the opening of the battery case was sealed according to a conventional method to produce a cylindrical organic electrolyte battery having the structure shown in FIG.

Referring to the battery shown in FIG. 1, (1) is a positive electrode formed with the above-mentioned manganese dioxide mixture, and a stainless steel net is used as a core material in molding.
(2) is a negative electrode made of lithium, and this negative electrode (2)
Is manufactured by crimping on a stainless steel net. However, FIG. 1 does not show a stainless steel net, a current collector, and the like used in manufacturing the positive electrode (1) and the negative electrode (2) in order to avoid complication. (3) is a separator, and (4) is the above-mentioned electrolytic solution.

(5) is a battery case made of stainless steel, and this battery case (5) also serves as a negative electrode terminal. An insulating material (6) made of a polytetrafluoroethylene sheet is disposed on the bottom of the battery case (5), and an insulating material (7) made of a polytetrafluoroethylene sheet is also provided on the inner periphery of the battery case (5). The spirally wound electrode body comprising the positive electrode (1), the negative electrode (2) and the separator (3), the electrolyte (4), and the like are accommodated in the battery case (5).

(8) is a sealing plate made of stainless steel, and a gas ventilation hole (8a) is provided in the center of the sealing plate (8). (9) is a circular packing made of polypropylene, (1)
0) is a flexible thin plate made of titanium, and (11) is an annular polypropylene heat deformable member.
Acts to change the burst pressure of the flexible sheet (10) by being deformed by temperature. (12) is a nickel-plated rolled steel terminal plate. This terminal plate (12) is provided with a cutting blade (12a) and a gas discharge hole (12b) so that gas can flow into the battery. When the internal pressure of the battery is increased and the flexible thin plate (10) is deformed by the increase of the internal pressure, the flexible thin plate (10) is broken by the cutting edge (12a) and the gas inside the battery is destroyed. Is designed to be discharged from the battery through the gas discharge hole (12b). (13) is an insulating packing, (14) is a lead body, and this lead body (14) electrically connects the positive electrode (1) and the sealing plate (8), and the terminal plate (12) is Acts as a positive electrode terminal by contact with the sealing plate (8). (15) is the negative electrode (2)
And a lead body for electrically connecting the battery case and the battery case.

Example 2 0.6 mol / dissolved C ₄ F ₉ SO ₃ Li in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 2,
Water was added to this solution to prepare an electrolytic solution containing 500 ppm of water, and a cylindrical organic electrolytic cell was produced in the same manner as in the example except that this electrolytic solution was used.

Example 3 A cylindrical organic electrolyte battery was produced in the same manner as in Example 1, except that the negative electrode (2) was replaced with a lithium-aluminum alloy (98% lithium content) instead of lithium.

Comparative Example 1 CF ₃ SO ₃ Li was dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 2 at a ratio of 0.6 mol / mol,
Water was added to this solution to prepare an electrolytic solution containing 200 ppm of water, and a cylindrical organic electrolytic cell was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Comparative Example 2 An electrolytic solution was prepared by dissolving C ₄ F ₉ SO ₃ Li in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 2 at a ratio of 0.6 mol / ml. Example 1
In the same manner as in the above, a cylindrical organic electrolyte battery was produced.

Each of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2 was allowed to stand at room temperature for 1 week at room temperature, and those having a battery voltage of 3.4 V or less were regarded as open circuit voltage failures. Rate). The results are shown in Table 1 by [number of open-circuit voltage defective batteries / number of test batteries].

As shown in Table 1, the batteries of Examples 1 to 3 did not have any open circuit voltage defect, but the batteries of Comparative Examples 1 and 2 had the open circuit voltage defect. This result indicates that C ₄
It is shown that the use of F ₉ SO ₃ Li suppresses the reaction between water and the negative electrode, and suppresses the occurrence of open-circuit voltage failure by including water in the electrolyte.

In other words, the batteries of Examples 1 to 3 and the battery of Comparative Example 1 have different electrolytes, but all contain water in the electrolyte. As described above, there was no open circuit voltage failure in the batteries of Examples 1 to 3 in the batteries of Examples 1 to 3 because C ₄ F ₉ SO ₃ Li used as the electrolyte was formed by the moisture in the electrolyte and the negative electrode. Although the reaction was suppressed, the open circuit voltage defect occurred in the battery of Comparative Example 1 because CF ₃ SO ₃ Li used as the electrolyte could not suppress the reaction between the water in the electrolyte and the negative electrode, This is due to the deterioration of.

In addition, the batteries of Examples 1 to 3 and the battery of Comparative Example 2
The electrolyte is the same, but the batteries of Examples 1 to 3 contain water in the electrolyte, and the batteries of Comparative Example 2 do not contain water in the electrolyte. Example 1 as described above
The batteries of Example 3 had no open circuit voltage failure.
This is because the battery contains water in the electrolyte.

Next, the electrolyte used for the batteries of Examples 1 to 3 and the electrolyte used for the battery of Comparative Example 1 were each 10 mL.
Each, 0.18mm thick lithium piece of 28mm x 95mm (However,
In the case of Example 3, the sample was placed in a vial bin together with a lithium-aluminum alloy (lithium content: 98%) piece of the same dimensions], sealed, and allowed to stand at room temperature for 5 days. Table 2 shows the results.

As shown in Table 2, the electrolytic solution used for the batteries of Examples 1 to 3 was smaller than the electrolytic solution used for the battery of Comparative Example 1.
The decrease in water due to standing was small, indicating that the use of C ₄ F ₉ SO ₃ Li suppressed the reaction between water in the electrolyte and lithium.

Next, the following experiment was conducted to confirm that the decrease in the open circuit voltage during storage was due to the elution of the metal component from the positive electrode material.

Electrolyte used for batteries of Examples 1 and 2 and Comparative Example 2
10 ml of the electrolyte solution used for each of the batteries was placed in a vial bin, and the positive electrode used for the batteries of Examples 1 and 2 and the positive electrode used for the battery of Comparative Example 2 were placed in a vial bin, and sealed. Stored at 6 ° C for 6 days. However, the positive electrode used was cut out of the current collector (stainless steel SUS430) except for 1 cm on both sides so that it could be easily put into a vial bin.

As a result, in the electrolyte of Comparative Example 2, corrosion was observed in the stainless steel current collector, and Cr, Fe, and Mn were detected in the electrolyte, and manganese dioxide (MnO ₂ ) as the positive electrode active material and stainless steel were detected. It was confirmed that the metal component was eluted from the steel current collector.

On the other hand, in the case of the electrolyte solutions of Examples 1 and 2, the elution amounts of Cr and Fe are reduced to 1/20 to 1/100 as compared with the case of Comparative Example 2, and the elution amount of Mn is also about half. Had become.

From the above, when no water is contained in the electrolytic solution, the metal component elutes from the positive electrode, and when there is a negative electrode such as lithium (Li), the eluted metal ions react with lithium to form a metal. This is repeated so that the metal grows on the lithium of the negative electrode, penetrates through the separator, and finally reaches the positive electrode, causing internal short-circuiting of the electric storage and lowering the open circuit voltage of the battery. It can be seen that the reduction of the open circuit voltage of the battery is suppressed by suppressing the elution of the metal component from the positive electrode.

〔The invention's effect〕

As described above, in the present invention, C _n F
By using _{2n + 1} SO ₃ M and making the electrolyte contain a certain amount of water, it was possible to suppress a decrease in the open circuit voltage of the battery during storage.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of the organic electrolyte battery according to the present invention. (1)… positive electrode, (2)… negative electrode, (3)… separator, (4)… electrolyte

Claims (2)

(57) [Claims] A positive electrode containing a 1. A metal element, a negative electrode composed of a compound containing an alkali metal or an alkali metal, in the organic electrolyte cell using organic electrolyte and the power generating element, the organic electrolytic solution, C _n as the electrolyte F _{2n + 1} SO ₃ M (n is 2
Wherein M is an alkali metal, and 50 to 1,000 ppm of water. 2. The organic electrolyte battery according to claim 1, wherein the C _n F _{2n + 1} SO ₃ M is C ₄ F ₉ SO ₃ Li.