WO1999067844A1 - Purification of battery electrolytes by means of physical adsorption - Google Patents

Abstract

The present invention relates to the removal of protic impurities from battery electrodes which are suitable for lithium cells by means of physical adsorption.

Description

Purification of battery electrolytes using physical

adsorption

The present invention relates to a method for removing protic impurities from battery electrolytes by means of physical adsorption.

The commonly used lithium batteries (secondary and primary battery cells) generally use electrolytes that consist of conductive salts such as LiPF ₆ , LiBF ₄ , LiCIO ₄ , LiAsF ₆ , Li methide, Li imide or Li triflate and a mixture consist of solvents, mainly organic carbonates, such as propylene carbonate, ethylene carbonate or butylene carbonate, ethers, such as dimethyl ether, and propionates, such as methyl propionate or ethyl propionate.

Despite the high purity of the individual components, these electrolyte solutions normally contain protic impurities such as water, alcohols, peroxides. However, the conductive salts in the electrolyte solutions are extremely sensitive to these impurities and, in the case of LiPF ₆ , decompose, for example, to HF, LiF or POF ₃ and to various oxyfluorophosphoric acids (H _a P _b O _c F _d ). These decomposition products are very harmful to the battery cells because they attack the cell components, i.e. the cathode and anode, and the

Massively influence the formation of cover layers on the electrolytes. This significantly shortens the life of a battery.

Since HF in particular is very aggressive in this regard, it is necessary to significantly reduce the HF content in the electrolyte mixtures, which is normally 50-80 ppm. An HF content of less than 30 ppm is desired for most applications.

The water content of the electrolyte mixture should also be as low as possible so that these decomposition products cannot occur to the extent that existed up to now. The lowest possible water content (for example less than 20 ppm) is therefore desirable. The previously used methods of reducing the water content in a conventional way are not effective enough.

Canadian patent application 2,193,119 describes a method in which the acidic impurities are separated off using hydrogen-free chlorides, bromides or iodides. However, this method is also not optimal, because the reaction products formed HCl, HBr and HI are jointly contain by distillation into the electrolyte mixtures during and even to a small extent after the separation and could therefore trigger _{1 Q} further reactions. Furthermore, the electrolytes are heated during distillation, which can also have negative effects. A further step may be necessary if a solid reaction product still occurs and this should also be separated off.

It is an object of the present invention, a method for _"c separation of protic impurities, in particular, for example, by

Find water, or HF, that is easy, quick, and effective to do, and that can reduce the water content to less than 10 ppm and that of HF to less than 30 ppm.

It has now been found that separation of the protic contaminants from battery solvents is simple and very effective

20 can be carried out by means of physical adsorption.

The invention therefore relates to a process for the purification of electrolyte solutions for lithium cells, characterized by the following steps: a) addition of an adsorbent which contains the protic impurities

25 physically adsorbed, and b) separation of the adsorbent.

The electrolyte solutions according to the invention essentially consist of conductive salts such as LiPF ₆ , LiBF ₄ , LiCIO ₄ , LiAsF ₆ , Li methides, Li imides or Li triflates, preferably in a concentration of 0.7 to 1.8 mol / l, and

30 solvent mixtures selected from the organic solvents organic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, Methyl propyl carbonate, ethyl propyl carbonate and other organic carbonates, and propionates such as methyl propionate or ethyl propionate, formates such as ethyl formate or methyl formate, acetates such as methyl acetate, ethyl acetate, halogenated carbonates such as chlorinated ethylene carbonate, fluorinated ethylene carbonate, fluorinated propylene carbonate or fluorinated

Ethylene carbonate, but also ethers such as dimethoxyethane.

Suitable substances are all substances which can adsorb protic substances in a physical way, such as silica gel, calcium carbonate, calcium oxide or aluminum oxide such as Al ₂ 0 ₃ , 0, but particularly preferably Al ₂ O _{3 is used} as the adsorbent.

The purification according to the invention can be carried out in various ways.

The first option is to mix the electrolyte solution, then add the adsorbent to separate the protic impurities' ⁵ , which is then separated off again.

In the second option, the solvents required for the electrolyte solution are first mixed, then the adsorbent is added.

After the adsorption has ended, the adsorbent is separated off again and only at the end is the conductive salt mixed in. 0

On the one hand, the adsorbent can be introduced into the respective mixture with stirring and then separated off again by filtration.

The reaction time can be chosen as desired, but is preferably kept as short as possible; experience has shown that a short one is sufficient

Stir for up to 10 minutes to complete adsorption.

On the other hand, the adsorbent can be filled into a column. As usual, the solution to be cleaned is passed through the adsorbent column by means of a pump.

3Q The adsorbent to be anhydrous, preferably it is before

Use well dried. The anhydrous Al ₂ O ₃ is preferably dried for a few days or weeks at about 400 ° C. in a stream of nitrogen, cooled and then stored in the absence of moisture or better used immediately.

Preferably, 0.3 to 3% by weight of adsorbent is added to the electrolyte solutions to be cleaned. A content of 0.5 to 1% by weight of adsorbent is particularly preferred.

The adsorbent is separated off by filtration or the like. These conventional methods are known to the person skilled in the art.

In this way, purified electrolyte solutions are obtained that meet the high requirements for low water content and low HF content for electrolytes with fluorinated conductive salts. The battery solvents purified according to the invention have values for the water content of less than 10 ppm and for the HF content of less than 30 ppm.

The electrolyte solutions according to the invention therefore show improved properties, such as higher cycle efficiency and longer service life, when used in lithium-ion and lithium batteries.

The invention thus also relates to electrolyte solutions which are suitable for lithium cells (primary or secondary) and which are characterized in that they are purified by the method described here.

Even without further explanations, it is assumed that a person skilled in the art can use the above description in the broadest scope. The preferred embodiments are therefore only to be understood as a descriptive disclosure, and in no way as a limitation in any way.

The full disclosure of all applications, patents, and publications listed above and below are incorporated by reference into this application.

The following examples are intended to explain the invention in more detail. example 1

Al ₂ O _{3 is} dried anhydrous in a nitrogen stream at 400 ° C. for 4 weeks. After drying, the Al ₂ 0 _{3 is} cooled and stored in the glove box.

The electrolytic solution is prepared as follows:

440 g of ethylene carbonate and 440 g of dimethyl carbonate are mixed and cooled to 10 ° C. Then 120 g of LiPF _{6 are} added and mixed with stirring. The electrolyte contains 60 ppm HF.

Then 10 g of dried Al ₂ 0 _{3 are} added. After stirring for 10 minutes, the Al ₂ O _{3 is} filtered off.

HF content:

Initial mixture: 60 ppm After adsorption: <10 ppm

H ₂ O content after purification: less than 10 ppm

Example 2

Al ₂ 0 ₃ is dried and stored as in Example 1.

The solvents for the electrolyte, 440 g of ethylene carbonate and 440 g of dimethyl carbonate are mixed and the mixture is cooled to 10 ° C. Then 10 g of dried Al ₂ O _{3 are} added, the mixture is stirred for 10 minutes and the adsorbent is filtered off again. Then it is cooled to 10 ° C. and 120 g of LiPF _{s are} added with stirring.

The HF and H ₂ O content is less than 20 ppm after the treatment.

Example 3 Al ₂ 0 ₃ is dried and stored as described in Example 1.

The adsorbent is then filled into a column.

An electrolytic solution is made as follows:

440 g of ethylene carbonate and 440 g of dimethyl carbonate are mixed and the mixture is cooled to 10 ° C. 120 g of LiPF _{6 are added} and the mixture is mixed with stirring. The electrolyte contains 60 ppm HF.

The electrolyte solution is then pumped over the column. Q After purification, the HF and H ₂ O content is less than 10 ppm each.

Example 4

Al ₂ O ₃ is dried and stored as described in Example 1.

500 g of propylene carbonate and 500 g of 1,2-dimethoxyethane are mixed.

^ Then 100 g LiCI0 _{4 are} added with stirring and cooling. The mixture has a water content of 40 ppm.

Then 10 g of dried Al ₂ O _{3 are} added and mixed intensively. After standing for 30 minutes, the aluminum oxide is filtered off.

The electrolyte solution treated in this way has a water content of less

10 ppm. 20th

25

30

Claims

PATENT CLAIMS 1. A process for the purification of electrolyte solutions for lithium cells, characterized by the following steps: a) addition of an adsorbent which physically adsorbs the protic impurities, and b) separation of the adsorbent. 2. The method according to claim 1, characterized in that the adsorbent is added to the mixed electrolyte solution. 0 3. The method according to claim 1, characterized in that the adsorbent is first added to the solvents in order to carry out the adsorption of the impurities, then is separated off and only then the conductive salt is added. 4. The method according to any one of claims 1 to 3, characterized 'characterized that AI ₂ O _{3 is} used as the adsorbent. 5. The method according to any one of claims 1 to 4, characterized in that 0.3 to 3 wt .-%, in particular 0.5 to 1, 0 wt .-%, adsorbent are added. 0 6. electrolytic solution, suitable for lithium cells, characterized in that it is purified by the method described in claim 1. 7. electrolyte solution according to claim 6, which as a solvent organic carbonates and / or propionates and / or formates, 25 and / or acetates and / or and / or halogenated carbonates and / or Contains ether. 8. Electrolyte solution according to claim 6, which as a solvent organic carbonates selected from the group propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, 3 _Q ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and / or propionate, selected from the group methyl propionate and ethyl propionate, and / or formate, selected from the group Ethyl formate and methyl formate, and / or acetates, selected from the group consisting of methyl acetate and ethyl acetate and / or halogenated carbonates, selected from the group consisting of chlorinated ethylene carbonate, fluorinated ethylene carbonate, and fluorinated propylene carbonate, and / or ethers such as dimethoxyethane. Electrolytic solution according to claim 6, which contains LiPF ₆ , LiBF _4l LiCIO ₄ , LiAsF ₆ , Li methide, Li imide or Li triflate as the conductive salt.