DE1671911C3 - Galvanic accumulator with a non-aqueous electrolyte and process for the production of the electrolyte - Google Patents

Description

• The invention relates to a galvanic battery with a negative electrode made of lithium or a corresponding highly reactive metal and a non-aqueous electrolyte, which is an organic Solvent and an inorganic salt dissolved therein, and a process for the preparation of Electrolytes for the accumulator.

An accumulator of the type mentioned is known from DT-AS 11 26 464. The negative electrode made of lithium or alloys of lithium with sodium, zinc, silver, magnesium or mercury immersed in an anhydrous electrolyte, which is made from the solution of an alkali metal or alkaline earth metal perchlorate, -jodides, -rhodanides, -bromides or -chlorates in a saturated aliphatic primary or secondary amine. Elements of the sixth or seventh main group are used as the positive electrode of the periodic table or anions such as rhodanides, nitrates, chlorates or perchlorates as well Oxides. This known accumulator allows the use of the extraordinarily advantageous lithium electrode, but has considerable polarization effects on discharge. This are due to the formation of insoluble lithium salts in the organic solvent.

Furthermore, from GB-PS 9 10930 a battery is known, which is an electrical electrolyte conductive «organic anhydrous solvent with a dielectric constant greater than 12 and has dissolved in this an inorganic Lewis acid. In connection with such an electrolyte is in the known document also the use of a lithium electrode as a negative electrode described, but such an arrangement can at most scientific interest, not but technical. Claim interest. In the electrolyte mentioned, lithium electrodes are pronounced attacked strongly and quickly.

Despite these problems, however, lithium is used as an electrode material for accumulators particularly favorable due to its low specific weight and its very high potential. As before, however, the following are in particular the following for a technically interesting use of lithium electrodes Problems not yet solved satisfactorily: (1) There is still no satisfactory non-corrosive, primarily non-aqueous ionized electrolyte available; (2) the oxidized metal of the negative Electrode must be stored in a form in which it is readily available for the recharge process is available, without polarization when discharging or recharging the battery and (3) for a system that fulfills the stated requirements is not yet sufficient polarization-free material known for the positive electrode.

In view of this prior art, the invention is based on the object of an accumulator of the type mentioned, whose strongly electropositive electrode does not corrode in the electrolyte nor is polarized, neither with repeated nor with long-term use of the battery. The invention is also based on the object of a method for producing the in one to create such a battery usable electrolyte.

To solve this problem, an accumulator of the type mentioned is proposed, which according to the invention characterized in that the electrolyte consists of a liquid, aprotic solution

medium consists in which an ionizable addition complex is dissolved, which consists of an inorganic Lewis acid and an inorganic salt which have an identical anion but whose cations are different are, and that the cation of the salt from which the negative active mass forms in the charged state, reactive metal.

The inventive method for producing the electrolyte for this accumulator is thereby characterized in that one first has an addition complex with the solvent and the inorganic Lewis acid forms, then displaced the solvent from this complex and through the ionizable salt replaced with metallic cation.

The electrode of the accumulator consists in a known manner of a highly reactive, that is, strongly electropositive material. The electrolyte of the accumulator consists of an aprotic liquid solvent in which an ionizable Addition complex is solved. This addition complex consists of an inorganic compound and an inorganic SÜz, both of which have the same anion. The cation of the salt is the oxidized material of the negative electrode.

According to a preferred embodiment of the invention, the addition complex consists partly of an inorganic one Compound which is also able to form an addition complex with the solvent. However, the stability of this solvent complex is lower than that of the addition complex with the inorganic salt.

Fluorine or chlorine are preferably used as the anion of the addition complex. As Katioii der Lewis acid components are preferably boron, phosphorus or aluminum.

The aprotic organic solvents are preferably tetrahydrofuran, tetrahydrofurfuryloxytetrahydrofuran, Diethylene glycol dimethyl ether, N-methyl-2-pyrrolidone, dimethoxyethane or dimethoxymethane used. The solvents used are preferably like those mentioned above Compounds Lewis bases.

The invention is described below on the basis of exemplary embodiments in conjunction with the drawing described in more detail. It shows the

Figure in graphical representation of the specific electrical conductivity of the electrolyte as a function the molar concentration of the ionizable addition complex in tetrahydrofuran.

I. Electrolyte

In order to make the non-aqueous electrolytes conductive, one relied so far always on the knowledge on the properties of the aqueous electrolytes. These are essentially polar while at certain non-aqueous electrolytes, especially the aprotic ones, a non-polar connection structure between Atoms and molecules present. Such a connection is no longer the Acceptance or release of electrons, but rather a merging of electron pairs between two atoms, between two molecules or between atom and molecule, making one more stable Structure is obtained. This is characterized by an octet of electrons, twelve or eighteen Electrons on the outer electron shell.

This explains the failure or the obviously unsatisfactory results that are obtained.

when you want to dissolve a salt in an organic, non-aqueous solvent. One wrongly had assumed that the process is similar to that of decomposition in a polar, aqueous electrolyte would correspond.

To achieve a suitable electrolyte, for. B. proceed as follows:

In the description below, the organic solvent is denoted _{by X, the inorganic compound by S 1} and the inorganic salt by S _2.

The inorganic salt S, has a cation made of highly reactive metal. Above all, it is essential _{to dissolve this salt S 2} in the solvent X. In most cases, however, this cannot be done immediately.

According to the invention, an intermediate stage is first provided in which addition complexes of the X Si type are generated _{between the organic non-aqueous liquid X and the compound S 1.} This procedure makes it possible to dissolve large amounts of the compound S ₁ . The soluble addition _{complex XS 1} generally forms a liquid with little or no conductivity with the non-aqueous, organic liquid X. _{The salt S 2 is} added to this liquid containing the addition complex X Si. It is important that the compound S ₁ and the salt S _{2 have} a common constituent and that both also tend _{to form a more stable addition complex S 1} S ₂ than the original soluble addition complex XS ₁ . The complex S _t S ₂ is thus formed at the expense of the complex XS ₁ . The complex S ₁ S ₂ then becomes ionizable by the lone pair of electrons and the regrouping of the electrons.

The process according to the invention is so advantageous because the salt ₂ cannot be soluble in the non-aqueous, organic liquid X. In this way, large amounts of the salt S _{2 are} dissolved, which forms an ionizable addition complex S ₁ S ₂ with the compound S _1. The whole thing becomes conductive in this way, ie it acts as an electrolyte, since it allows current to flow from one electrode to the other. This electrolyte consisting of complexes allows the use of strongly reactive, negative masses, such as. B. Lithium, the production of electrochemical generators with a very high storage capacity per unit volume or mass.

II. Examples

1. One can start from an organic solvent that can deliver electron pairs and from for this reason is a Lewis base. This is the case with tetrahydrofuran, the following electron formula has:

- C

O:

In addition to oxygen, there are two pairs of electrons; these are those electron pairs, through which the tetrahydrofuran becomes a Lewis base.

If a substance is added to the tetrahydrofuran that is a Lewis acid, ie can accept electrons and, in particular, electron pairs, an addition complex is formed on these free electron pairs.

So a compound like boron fluoride can be used, that by union of a boron atom with three electrons in the outer electron shell with three Fluorine atoms with seven electrons in the outer shell is preserved. This boron fluoride compound has following electron formula:

'5

: Q: B

: F:

In this formula, every fluorine atom on the outer shell has an octet of electrons; the boron is missing but two electrons for an octet of electrons on the outer shell. So the boron fluoride is one Lewis acid, because it could still accept an electron pair. In the presence of Borfluond and tetrahydrofuran forms an addition complex on a lone pair of electrons in tetrahydrofuran. The formula for this complex is

hydrofuran would not be immediately soluble. That is based probably on the fact that the lithium fluoride has a very high lattice energy, which is very similar is attributable to the small diameter of the constituent atoms.

In boron fluoride BF ₃ , all compounds are covalent because this fluoride is the result of a merging of electron pairs. The compound in lithium fluoride, on the other hand, is ionic because the only electron in the outer shell of lithium is transferred to the outer shell of fluorine and forms a compound of the type (F "Li ⁺ ).

Because the boron fluoride-lithium fluoride complex has a full octet around the boron atom, there if it was surrounded by four fluorine atoms, a complete electron octet is formed; the structure

FBF
F.

but receives through the ionic connection with the lithium, which has given up its only electron, a negative charge, so that there is an ionic bond between this structure and the lithium, in which this structure becomes an anion and lithium becomes a cation. This complex has the following Formula:

the boron atom having an octet of electrons on its outer shell.

If tetrahydrofuran and boron fluoride are brought together, an addition complex is formed, and this is so exothermic that the mixture has to be cooled.

The liquid obtained in this way is practically non-conductive. So it must be made conductive.

Since the compound S _{1 is} a fluoride, a different fluoride must be used as SaIzS 2 according to the invention, for example lithium fluoride. The boron fluoride and lithium fluoride form an addition complex that is more stable than the boron-tetrahydrofuran complex; The latter is displaced by the addition of lithium fluoride and forms a new complex in which the boron still has a complete electron octet on the outer shell and which can be expressed by the following formula:

30 It is soluble in tetrahydrofuran because it has a low lattice energy _{due to the large dimensions of the BF 4 group.}

Thus, assuming according to the invention by a tetrahydrofuran-insoluble salt such as lithium fluoride, from, this is due to the formation of an ionized complex, which has a low lattice energy and a

subsequent solvation allowed to be solubilized.

However, the conversions described are still

not completed. The boron fluoride-lithium fluoride complex is ionized as the BF ₄ T anion and Li ⁺ cation; in the process, all of these ions solvate themselves and bind a certain number of molecules of the solvent X. This gives

and

(nX) Li

where η and n ' are integers and η> π' because the solvent is a Lewis base. The lithium cation solvates better because this latter ion is acidic.

In the case of the method according to the invention, a! So the following four stages:

Solution, Ionization, Solvation, Dissociation,

: F: BF:

Li

So it is a soluble complex and the solubility of the lithium fluoride is preserved, which in the tetra- the last two stages taking place practically at the same time and finally a conductive solution receives

During the preparation of the non-aqueous conductive solution according to the invention, the tetrahydrofuran tends _{to polymerize in the presence of the boron fluoride BF 3} under the influence of traces of water. To avoid that, it is advantageous

3

added some pyridine to the liquid. An addition of 1% pyridine has proven to be very effective.

2. Chlorine can also be used instead of fluorine. It is then used instead of boron fluoride e.g. Aluminum chloride used as an inorganic compound. In this case, lithium chloride is used as the salt.

The formula for the aluminum chloride is as follows:

The aluminum atom has three electrons on its outer shell and the chlorine atom seven. Each chlorine in aluminum chloride is surrounded by an octet of electrons while the aluminum atom one electron pair is missing. The aluminum chloride is therefore a Lewis acid. The tetrahydrofuran and the aluminum chloride can form the following addition complex:

CH ₂ -

I.
CH ₂

-CH ₂

CH ₂

/ '■■

: Cl:

Al: Cl

Since the lithium chloride can form a more stable addition complex with the aluminum chloride than the Aluminum chloride - tetrahydrofuran addition complex, it displaces the latter, and the addition complex is obtained

: Cl: Al : C1:
": Cl:

Li

Finally, tetrahydrofuran, the ionizable BF ₄ Li or AlCl ₄ Li-K complex and, depending on the case, an excess of BF ₃ or AlCl ₃ .

4. Other fluorinated compounds can also be used as compound S _{1, such as, for.} B. Phosphorus pentafluoride PF ₅ , the outer shell of which has five electrons. For the interaction of the electron pairs with one phosphorus atom and five fluorine atoms, each fluorine atom is surrounded by an electron octet, but the phosphorus receives ten electrons (five original and five through the interaction with the fluorine atoms). In this case, the stable structure of the outer shell comprises twelve electrons, and this phosphor can consequently still accept one pair of electrons.

The corresponding structure has the following formula:

: F: P: F:

5. N-methyl-2-pyrrolidone is the solvent formula

CH ₂ -CH ₂

CH ₁ C = O

CH ₃
usable.

The available electron pair is on the nitrogen.

The compounds described above, namely BF ₃ , AlCl ₃ and PF _5, can be used as compound S ₁ .

FLi can be used as salt S _{2 if the compound S 1} contains fluorine, and ClLi if it contains chlorine.

the lithium being linked to the AlCl ₄ group by ionic bonding. The anion AlCl ₄ "and the Kaüon Li ⁺ are thus formed, which in turn solvate with a stronger solvation for the cation.
The course according to the invention also takes place here,

namely

Solution,

Ionization, Solvation, Dissociation.

The new solution is consequently conductive, which can be proven experimentally

3. It has been found that the electrolyte of the type according to the invention in the presence of boron fluoride or aluminum chloride in the two preceding examples by using an excess of the inorganic compound can be improved. Thus, the electrolyte comprises

6. Dimethoxyethane or glycol dimethylethane with the following formula are also possible as solvents:

CH ₃ -O-CH ₂ -CH ₂ -O-CH ₃

The electron pairs that can be split off are located

on the two oxygens. The same compounds S] and S ₂ as above can be used.

7. Dimethoxymethane is the solvent

formula

CH ₃ -O-CH ₂ -O-CH ₃

possible: the electron pairs that can be split off sit on the oxygen. As above, S ₁ and S _{2 are} possible.

8. It can also be tetrahydrofurfijryloxitetrahydrofuran of the formula

CH ₂ CH ₂

CH ₂

CH

O CH ₂ -O-CH CH ₂

CH ₂ -CH ₂

to be needed; the electron pairs that can be split off

609637/356

I \ J Il \ J 1 I

sit on the three oxygen atoms. S ₁ and S are the same as in the previous case.

9. It can also be the diglyme or the dimethyl ether of diethylene glycol of the formula

CH ₂ -CH ₂ -O-CH ₂ -CH ₂

CH.,

CH ₃

can be used, whereby the electron pairs that can be split off are located on the three oxygen atoms. S ₁ and S ₂ are the same as above.

The graph shows two curves.

As the abscissa are the amounts of the ionizable complex in moles per liter of tetrahydrofuran and as The values of the conductivity are plotted on the ordinates.

Curve 1 relates to the use of the complex [BF ₄ Li] and curve II of the complex [AlCl ₄ Li].

III. The electrodes

1. In the case of the positive electrode, the active material used must consist of a metallic compound whose anion is identical to that. which the compound S, and the salt S ₂ , which are used to form the ionized complex in the electrolyte, have in common. Thus, in the case of an electrolyte containing fluoride, a metallic fluorine, for example nickel or copper fluoride, is used as the positive active material.

If it is an electrolyte containing chlorides according to the invention, it is considered to be positive Mass a metallic chloride, such as silver chloride, is used.

In the context of the invention, the following active materials can be used.

One way to make a reversible electrode is to make it more soluble in one of its states Shape to use. Since the product of the straight electrochemical reaction is soluble, it has not the effort to polarize the corresponding electrode in the course of this reaction. During the opposite electrochemical reaction puts this product back on the corresponding electrode if the potential of the electrode in question is so high that it does not reach the non-aqueous electrolyte or its connections.

On the other hand, a metallic salt ₂ , even if it is not soluble in the organic liquid X, still _{goes into solution because it can provide an addition complex S 1} S ₂ by extracting the liquid X from the complex XS | repressed.

■ ο Furthermore, according to the invention, there is an electrolyte

of the type X + XSi + S ₁ S ₂ advantageous.

_{If the positive active mass could form the compound S 2} during the discharge with the oxidized lithium, this could be due to its presence

■ 5 of the first addition complex X Si brought into solution will. This is exactly what happens when a metallic fluoride, for example Nickel fluoride, used in an electrolyte with fluorinated complexes. The discharge products are then lithium in the oxidized state and fluorine in the reduced state; both form the lithium fluoride, which enters into a complex with the boron fluoride and thus becomes soluble.

In an analogous manner, silver chloride can be used as the positive active mass in the case of an electrolyte with chlorinated Complexes are used. The discharge products are lithium in the oxidized state and chlorine in the reduced state, which corresponds to the lithium chloride. This can, as described above, form an aluminum chloride-lithium chloride addition complex which is soluble.

Since the lithium is in ionic bond, it can reverse during the charge on the negative Remove the electrode while the fluorine and chlorine anions do the fluorination and chlorination, respectively of the metals forming the metal support of the positive electrodes, namely nickel in the first Case and silver in the second case.

2. The negative electrode must have an active mass which, when charged, consists of a metal which is identical to the cation of the addition complex S, S ₂ .

3. The discharge and charge reactions can be shown schematically; this will be stoichiometric Amounts of the active masses and certain constituents of the electrolyte are used. In the following Description, the abbreviation THF is used to denote tetrahydrofuran.

2Li + ladder

THF
BF ₄ Li

discharge

F, Ni

ladder

2BF ₅
(Structure A)

THF BF ₄ Li Ni + 2F "" + 2Li

ladder

THF BF ₄ Li

(Structure B) 2BF ₄ Li (structure C)

The starting point is structure A in which the electrodes are charged and in which an electrolyte according to the invention is used. During the discharge, the lithium oxidizes to Li ⁺ because it loses its electron in the outer shell, and the fluorine of the nickel fluoride is reduced to F "because it accepts an additional electron, as shown in structure B. To the same extent, As these ions form during the discharge, they form the lithium fluoride compound FLi. This forms a compound with the boron fluoride BF ₃ and forms a soluble addition _{complex BF 4} Li (structure C), with the metallic nickel on the positive side and the negative a suitable conductor, such as ζ. Β the nickel, remain.

The electrolyte mainly contains the ionized addition complex BF ₄ Li; the ionic bond is present between the lithium and the group BF ₄ .

During the charge, this latter, ionized complex releases the lithium ion Li ⁺ on the negative side, which is reduced to metallic lithium by the absorption of an electron. This lithium is deposited on the executive support. A fluorine F "of the anionic group BF *" oxidizes on the positive electrode through the loss of an electron

The fluorine thus formed fluorinates the nickel of the positive electrode. The Borfiuorid BF ₃ gets back into the electrolyte.

Of course, non-stoichiometric amounts of the reacting substances can also be used. The capacity of the electrochemical generator according to the invention is then limited by that reacting substance which is present in the smallest relative amount. The connection BF ₃ has an active role in the process for achieving the capacity. It disappears during discharge and is regenerated during charging.

4. In an analogous manner, the discharge and charge reactions for a silver chloride ClAg existing positive active mass are represented.

According to the invention, the electrolyte then consists of THF, the addition complex AlCl ₄ Li and aluminum chloride Cl ₃ Al. All reacting substances are shown on a stoichiometric scale.

Li f- head

THF

AICl ₄ L '
Cl ₃ Al

ClAg

discharge

ladder

THF

AlCl ₄ Li
Cl ₃ Al

Ag + Li ' + Cl

-pus

THF

AICl ₄ Li

AlCI ₄ Li

! Structure A)

(Structure B)

(Structure C)

During the discharge, the lithium oxidizes to Li ⁺ on the negative side because it loses its electron on the outer shell, while the chlorine supplied by the silver chloride on the positive side is reduced to Cl "because it picks up an electron on the outer shell. The resulting lithium chloride ClLi combines with the aluminum chloride Cl ₃ Al and forms a soluble ionized addition complex AICl ₄ Li; the ionic bond exists between the lithium and the group Cl ₄ Al.

During the charge, the lithium ion Li ⁺ is reduced by accepting an electron, while a chlorine of the anionic group AICl ₄ T is oxidized by releasing an electron. The chlorine thus formed chlorinates the silver support of the positive electrode.

_{The compound Cl 3} Al, which is formed again during charging, is returned to the electrolyte.

The above remarks also apply to the proportions of the reacting substances.

1 sheet of drawings

Claims (8)

i 6 7 1 9 claims: 1. Galvanic accumulator with a negative electrode made of lithium or a corresponding one highly reactive metal and a non-aqueous electrolyte, which is an organic Contains solvent and an inorganic salt dissolved therein, characterized in that that the electrolyte consists of a liquid, aprotic solvent in which an ionizable Addition complex is dissolved, which consists of an inorganic Lewis acid and an inorganic Salt, which have an identical anion, but whose cations are different, and that the cation of the salt from which the negative active mass in the charged state forming, reactive metal. 2. Accumulator according to claim 1, characterized in that the addition complex consists of an inorganic compound which can form an addition complex with the solvent, and that the stability of the complex is lower than that of the addition complex consisting of the inorganic Lewis acid and the inorganic salt. 3. Accumulator according to one of the preceding claims, characterized in that the common Anion for the inorganic Lewis acid and the inorganic salt that form the addition complex form, is chlorine or fluorine. 4. Accumulator according to one of the preceding claims, characterized in that the The cation of the inorganic Lewis acid is boron, phosphorus or aluminum. 5. Accumulator according to one of the preceding claims, characterized in that as aprotic organic solvent tetrahydrofuran, tetrahydrofurfuryloxite tetrahydrofuran. that Diglyme or the dimethyl ether of diethylene glycol, N-methyl-2-pyrrolidone, dimethoxyethane, Dimethoxyrrethane or analog liquids are used whose molecules have electron pairs can deliver and which are therefore Lewis bases. 6. Accumulator according to one of the preceding claims, characterized in that the positive active mass is a salt of a metal, e.g. B. silver, nickel, copper, whose anion with the Anion of the inorganic Lewis acid and the inorganic salt is identical. 7. Accumulator according to one of the preceding claims, characterized in that the inorganic Lewis acid is present in excess in the electrolyte. 8. A method for producing the electrolyte for the accumulator according to any one of the preceding Claims, characterized in that first an addition complex with the solvent and the inorganic Lewis acid then forms the solvent from this complex displaced and replaced by the ionizable salt with a metallic cation.