WO2003001623A2

WO2003001623A2 - Conducting salts comprising niobium or tantalum

Info

Publication number: WO2003001623A2
Application number: PCT/EP2002/005892
Authority: WO
Inventors: Michael Schmidt; Andreas Kühner; Karl. O. Christe
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2001-06-22
Filing date: 2002-05-29
Publication date: 2003-01-03
Anticipated expiration: 2003-12-22
Also published as: WO2003001623A3; AU2002310749A1

Abstract

The present invention relates to salts comprising niobium or tantalum, methods for their preparation, and their use in primary batteries, secondary batteries, condensators, superconductors and/or galvanic cells. Furthermore, the present invention relates to electrolytes, primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells comprising niobium or tantalum salts.

Description

Conducting salts comprising niobium or tantalum

The present invention relates to salts comprising niobium or tantalum, methods for their preparation, and their use in primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells.

Furthermore, the present invention relates to electrolytes, primary batteries, secondary batteries, condensators, superconductors and/or galvanic cells comprising niobium or tantalum salts.

Weakly associated salts are the basis of many electrolytes. They are useful in electrochemical cells such as batteries, electronic parts such as condensators, double layer condensators, super or ultra capacitators as well as for organic synthesis, especially catalysis („ionic liquids"). For non-aquous electrolytes fluorine containg salts are generally used as conducting salts.

For example, commercial lithium-ion cells rely almost exclusively on LiPF₆, whereas super- or ultracaps use N(C₂H₅)₄BF₄. These conducting salts form electrolytes with high ionic conductivity in aprotic solvents such as organic carbonates (in lithium-ion batteries) or acetonitrile (in supercaps).

The temperature and hydrolysis-sensitivity of the instable substances LiPF₆ or N(C₂H₅)₄BF₄ poses a serious disadvantage.

Hydrogenfluoride can result when these salts are brought in contact with water or even with humidity. Next to its toxic properties hydrogen fluoride also has a very negative impact on the cyclic behavior and performance of electrical cells.

These problems can be avoided with alternative lithium salts such as imides, for example bis(trifluoromethylsulfonyl)imide as taught in US 4,505,997) or methanides, for example tris(trifluoromethylsulfonyl)-methanide as taught in US 5,273,840. These salts demonstrate a strong anionic stability and provide solutions of high conductivity in aprotic organic solvents. But aluminum, which is generally used as a cathodic divertant is not rendered passive sufficiently, at least not with imides. On the other side, methanides require an elaborous preparation and purification procedure.

Furthermore, the electrochemical properties such as stability against oxidation and passivation of aluminum depend largely on the purity of the methanide.

Another alternative are lithium spiroborates as taught in EP 0 698 301 B1 or lithium spirophosphates as described in Electrochemical and Solid State Letters, 2(2) 60-62 (1999). Due to the divalent ligands, many of these salts have decomposition temperatures of more than 200 °C. But their oxidation potential of 4,3 V at maximum against Li/Li⁺ does not provide a sufficient electrochemical stability for use in lithium batteries with highly oxidizing electrode materials, such as, for example, LiMn₂0₄ or LiCo ._xNi_x0₂ (0<x<1).

DE 19641138 teaches the use of lithiumfluoroalkylphosphates that preferably comprise perfluorinated ethyl- or isopropyl groups. Their thermal stability as well as their sensitivity towards hydrolysis is much better in comparison to LiPF₆ but their molecular weight is very high. U[F₃P(C₂F₅)₃] has a molecular weight of more than 400 g/mol.

Accordingly, there is a need for the provision of suitable salts for electrolytes in electrochemical cells that provide an excellent conductivity as wells as an electrochemical stability and solubility in aprotic solvents.

A further problem underlying the present invention is the provision of more powerful and more stable primary and secondary batteries, condensators, supercondensators and galvanic cells. This problem is solved according to the present invention by providing new salts comprising niobium or tantalum of the general formula I:

Mⁿ⁺V_n I wherein

Mⁿ⁺ is a mono-, di- or trivalent cation, or a mixture of monovalent cations or a divalent and a monovalent cation, Y^" denotes a TaF₆ ^" or NbF₆ ^"anion, and 1 < n < 3.

In a preferred embodiment the present invention relates to salts that comprise at least one of the following cations:

Li⁺, [NH₄]⁺, [NR¹R²R³R⁴]⁺, [PR¹R²R³R⁴]⁺,

wherein

R¹, R², R³, R⁴ are, in each case independently of one another, C_1-10 alkyl or C_1-10 alkyl and aryl or C_1-10 aryl, wherein C^o alkyl and/or aryl may be further substituted and wherein carbons of C_1-10 alkyl and/or aryl may be substituted by any of the heteroatoms O, N, or S.

Another preferred embodiment relates to salts of the present invention, wherein a cation Mⁿ⁺ is or comprises at least one aromatic heterocyclic cation.

Even more preferred are salts or a mixture of salts comprising at least one aromatic heterocyclic cation, wherein said cation is or comprises at least one of the following cations:

wherein R-i, R_2l R₃, R₄, R₅, R₆ are, in each case independently of one another, a hydrogen or a halogen or a fluoride or a C_{1 t08} alkyl,

wherein one or more of R^ R₂, R₃, R₄, R₅, R₆ may be bonded to each other by single or double bonds,

wherein carbons of C_1-8 alkyl and/or aryl may be substituted by any of the heteroatoms O, N, or S wherein the C-i _{to 8} alkyl may be partially or completely substituted by further functional groups such as

F, Cl, N(C_mF_(2m+1._X)H_x)₂, 0(C_mF_(2m+1._X)H_x), S0₂(C_mF_(2m+1._X)H_x), wherein

1 < m < 6 and 0 < x < 2m+1.

The salts of the present invention provide a number of advantages. They are not sensitive to hydrolysis. Their tendency to decompose is very small. They have a high thermal stability and they are soluble in most standard aprotic solvents. They are useful as salts for electrolytes. Electrolytes comprising said salts are electrochemically stable, temperature and humidity resistent. Also, such electrolytes demonstrate an excellent cyclic behavior and performance in electrical cells.

A further aspect of the present invention relates to a method for the preparation of salts comprising niobium or tantalum of the general formula I:

Mⁿ⁺r_n I wherein M^π+ is a mono-, di- or trivalent cation, or a mixture of monovalent cations or a divalent and a monovalent cation

Y^" denotes a TaF₆ ^" or NbF₆ ^"anion, and 1 < n < 3,

and wherein

TaF₅ or NbF₅ react with a compound Mⁿ⁺F^" _n in the presence of a suitable anhydrous solvent.

Preferably, said reaction is performed in a suitable anhydrous solvent such as hydrogen fluoride or acetonitrile or an organic carbonate, preferably ethylenecarbonate, propylenecarbonate, butylenecarbonate, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate or a mixture of at least two of these solvents.

Anhydrous organic solvents such as ethers, esters, carbamates or amides are also suitable solvents. Preferred esters are methylformiate, ethylformiate, methylacetate, Ethylacetate, methylpropionate, ethylpropionate, methylbutyrate, ethyl buty rate, γ-butyrolactone. Preferred ethers are diethylether, dimethoxyethane, diethoxyethane, tetrahydrofurane, dioxolane and dioxane. Preferred amides are dimethylformamide and dimethylacetamide. Preferred carbamates are methyl- or ethyl-N,N- dimethylcarbamate, methyl- or ethyl-N,N-diethylcarbamate, 2,2,2-trifluoroethyl- N,N-dimethylcarbamate or 2,2,2-trifluoroethyl-N,N-diethylcarbamate.

TaF₅ or NbF₅ are commercially available products.

In preferred embodiment the present invention relates to a method, wherein the cation Mⁿ⁺ is or comprises at least one of the following cations:

Li⁺, [NH₄]⁺, [NR¹R²R³R⁴]⁺, [PR¹R²R³R⁴]⁺,

wherein

R¹, R², R³, R⁴ are, in each case independently of one another, C_1-10 alkyl, Cι_ιo alkyl and aryl or C^oaryl, that may be further substituted and wherein carbons may be substituted by any of the heteroatoms O, N, or S.

In a more preferred embodiment of the method of the present invention the cation Mⁿ⁺ is or comprises at least one aromatic heterocyclic cation.

In a most preferred embodiment the method of the invention the cation Mⁿ⁺ is or comprises at least one of the following aromatic heterocyclic cations:

wherein

of one another, a hydrogen or a halogen or a fluoride or a 0^ _{to 8} alkyl,

wherein carbons of C-ι_-8 alkyl and/or aryl may be substituted by any of the heteroatoms O, N, or S wherein the C-i _t0 β alkyl may be partially or completely substituted by further functional groups such as

F, Cl. N(C_mF_(2m+i._X)H_x)₂₎ 0(C_mF_(2m+1._X)H_x), S0₂(C_mF_(2m+1._X)H_x), wherein 1<m<6 and 0<x<2m+1.

The reaction between TaF₅ or NbF₅ with a compound Mⁿ⁺F^" _n preferably takes place at a temperature of -50 to 50°C, more preferably at a temperature of 15 to 25 °C.

It is also preferred to carry out this reaction in a solvent or solvent mixture that is directly suitable for use in a secondary or primary battery, a condensator, a supercondensator or a galvanic cell.

Preferred solvents that are directly suitable for use in a secondary or primary battery, a condensator or a galvanic cell are organic carbonates, more preferably ethylenecarbonate, propylenecarbonate, butylenecarbonate, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate or a mixture of at least two of these solvents.

The method according to the present invention provides almost pure salts in high yield with little impurities. Often the reaction proceeds to give quantitative yields and only traces of impurities. If necessary, the salts may be further purified according to standard methods, for example, by recrystallisation in a suitable solvent or solvent mixture. A suitable solvent or solvent mixture can easily be selected by preliminary experiments. The method for preparing the salts according to the invention is simply, efficient and without any complicated or dangerous steps.

In a further aspect, the present invention relates to the use of at least one of the salts according to the invention alone or in combination with further salts and/or additives in primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells.

The salts are suitable for preparing electrolytes, preferably electrolytes for primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells.

Such an electrolyte comprises at least one compound of the present invention. The preparation of soluble or solid electrolytes is well known to the average expert in the field of electrochmistry (for example: D. Linden, Handbook of Batteries, Second Edition, McGraw-Hill Inc., New York 1995; J. Barthel and H.- J. Gores, Solution Chemistry: A Cutting Edge in Modern Electrochemical Technology in G. Mamantov and A.I. Popov (publishers) Chemistry of Nonaquous Solutions, Current Progress, VCH Verlagsgemeinschaft, Weinheim 1994). Electrolytes can be prepared as a solution or a solid material. A solid electrolyte may be a polymer electrolyte optionally comprising a cross-linked polymer and at least one conducting salt or a gel electrolyte that comprises at least one solvent in addition to at least one conducting salt and an optional cross-linked polymer.

In a preferred embodiment, these electrolytes have a salt concentration of the elektrolyte of 0,01 - 3 mol/l, preferably of 0,01 - 2 mol/l, most preferably of 0,1 - 1 ,5 mol/l.

Electrolytes according to the present invention provide excellent electrochemical properties for most uses in batteries, conductors and galvanic cells. These electrolytes provide excellent conductivity as well as stability and safety.

In a further aspect of the present invention relates to primary batteries, secondary batteries, condensators, superconductors and/or galvanic cells comprising at least one of the niobium or tantalum salts of the present invention.

Primary batteries, secondary batteries, condensators, superconductors and/or galvanic cells according to the present invention are suitable to be employed under extreme conditions such as high temperatures or high humidity without an effect on the performance or life span of the device.

Examples

The following examples merely serve to illustrate the invention in an exemplary manner. The examples are not meant to limit the general concept of the present invention in any way.

Examples 1 and 2:

Synthesis of N(CH₃)₄MF₆ (M=Ta or Nb) in HF solution

In a typical experiment, TaF₅ (1.310 g, 4.75 mmol) was placed in a drybox into a 3/4 inch Teflon-FEP (FEP=fluoroethylene polymer) ampule that was closed by a stainless steel valve. On a metal vacuum line, about 4 ml of liquid anhydrous HF were added and the mixture was agitated at room temperature.

N(CH₃)₄F (0.442 g, 4.75 mmol) was added to this solution and the mixture was agitated, resulting in a clear colorless solution. The HF solvent was pumped off at room temperature leaving behind N(CH₃)₄TaF₆ (1.752 g, 4.75 mmol) in quantitative yield. The product was identified by its Raman spectrum.

The reaction with NbF₅was carried out in an identical fashion.

Examples 3 and 4:

Synthesis of N(CH₃)₄MF₆ (M = Ta or Nb) in CH₃CN solution In a typical experiment, TaF₅ (1.460 g, 5.29 mmol) and N(CH₃)₄F (0. 493 g, 5.29 mmol) were placed in a drybox into separate baked-out Schlenk ampules that were closed by Teflon-glass valves. On a glass vacuum line, about 6 ml of liquid dry CH₃CN were added to each ampule and the mixtures were agitated at room temperature. The resulting suspensions were combined producing a clear yellow solution. All volatile material was pumped off at room temperature leaving behind yellow N(CH₃)₄TaF₆ (1.953 g, 5.29 mmol) in quantitative yield. The yellow color was removed by washing the product several times with 150 ml of hexane. The product was identified by its Raman spectrum and exhibited only traces of unidentified impurities. The reaction with NbF₅was carried out in an identical fashion.

Examples 5 and 6:

Synthesis of LiTaF₆ and LiNbF₆

In typical preparations, equimolar amounts of LiF and TaF₅ or NbF₅were loaded inside a drybox into Teflon-FEP ampules that were closed by stainless steel valves. On a metal vacuum line, anhydrous HF (about 1 ml liquid per mmol of reactant) was added and the resulting mixtures were agitated at room temperature for several minutes. The solvent was pumped off at room temperature, leaving behind the corresponding LiMF₆ salts (M = Ta or Nb) as white powders in quantitative yield. The Raman spectra of the resulting products showed no detectable impurities.

Example 7:

Synthesis of MTaF₆ and MNbF₆, wherein M is N(C₂H₅)₄ MTaF₆ and MNbF₆, wherein M is N(C₂H₅)₄ were prepared by methathesis in acetonitrile from MTaF₆ and MNbF₆, wherein M is Li by reacting said substances with N(C₂H₅)₄CI. Lithium hexafluorotantalate or Lithium hexafluoroniobate were prepared according to example 1, solved in acetonitrile and then an equimolar amount of N(C₂H₅)₄CI was added to each salt. The reaction mixtures were filtered under vacuum using a glas frit to completely remove LiCI. The solvents were removed by vaccum destination and the resulting MTaF₆ and MNbF₆, wherein M is N(C₂H₅) were dried under vacuum.

Example 8:

Synthesis of 1 -Ethyl, 3-methyl imidazolium hexafluorotantalate

1 -Ethyl, 3-methyl imidazolium hexafluorotantalate was prepared by methathesis in acetonitrile according to the following procedure:

Lithium hexafluorotantalate was prepared according to example 1 , solved in acetonitrile and an equimolar amount of 1 -Ethyl, 3-methyl imidazoliumchloride was added. This reaction mixture was filtered under vacuum using a glas frit to completely remove LiCI. The solvent was removed by vaccum destination and the resulting of 1 -ethyl, 3-methyl imidazolium hexafluorotantalate was dried under vacuum.

Example 9:

Determination of conducticity

Table I: Specific ionic conductivity at 25 °C [conductivity in mS cm -1ι ]

EC stands for ethylenecarbonate, DMC for dimethylcarbonate

Example 10:

Electrochemical stability

Three cyclic voltammograms were recorded consecutively in a measuring cell with a platinum elektrode, a lithium counter electrode and a lithium reference electrode. Starting with the resting potential of the system the potential was increased at a feeding speed of 10 mV/s up to 6,0 V against Li/Li⁺ and then returned to the resting potential.

0,5 molar solutions of LiTaF₆ and LiNbF₆ in EC/DEC (Ethylene carbonate/

Diethylcarbonate 50:50 % by weight) were used as electrolyte. The measured oxidation potentials of the TaF₆- or NbF₆-anions of about 4.8 to

5 V against Li/Li⁺ are in a similar range to the potential of LiPF₆.

Claims

C L A I M S

1. Salts comprising niobium or tantalum of the general formula I:

Mⁿ⁺r_n I wherein

2. Salts according to claim 1 , wherein Mⁿ⁺ is or comprises at least one of the following cations:

Li⁺, [NH₄]⁺, [NR¹R²R³R⁴]⁺, [PR¹R²R³R⁴]\

wherein

R¹, R², R³, R⁴ are, in each case independently of one another, C_1-10 alkyl or C-i.₁0 alkyl and aryl or C- _O aryl, wherein C_1-10 alkyl and/or aryl may be further substituted and wherein carbons of C_1-10 alkyl and/or aryl may be substituted by any of the heteroatoms O, N, or S.

3. Salts according to any one of claims 1 or 2, wherein Mⁿ⁺ is or comprises at least one aromatic heterocyclic cation.

4. Salts according to claim 3, wherein Mⁿ⁺ is or comprises at least one of the following cations:

wherein R_{1 f} R₂, R₃, R₄, R₅, R₆ are, in each case independently of one another, a hydrogen or a halogen or a fluoride or a C-_{\ to 8} alkyl,

wherein one or more of R_{1 (} R₂, R₃, R₄₎ R₅, R₆ may be bonded to each other by single or double bonds,

F, Cl, N(C_mF_(2m+1._X)H_x)₂, 0(C_mF_(2m+1._X)H_x), S0₂(C_mF_(2m+1._X)H_x), wherein 1 < m < 6 and 0 < x < 2m+1.

5. Method for the preparation of salts comprising niobium or tantalum of the general formula I:

Mⁿ⁺Y^" _n I wherein

Mⁿ⁺ is a mono-, di- or trivalent cation, or a mixture of monovalent cations or a divalent and a monovalent cation,

Y^" denotes a TaF₆ ^" or NbF₆ ^"anion, and 1 < n < 3, and wherein

6. Method according to claim 5, wherein the suitable solvent is liquid hydrogen fluoride or acetonitrile or an organic carbonate, preferably ethylenecarbonate, propylenecarbonate, butylenecarbonate, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate or a mixture of at least two of these solvents.

7. Method according to anyone of claims 5 or 6, wherein Mⁿ⁺ is or comprises at least one of the following cations: Li⁺, [NH₄]⁺, [NR¹R²R³R⁴]⁺, [PR¹R²R³R⁴]\ wherein R¹, R², R³, R⁴ are, in each case independently of one another, Cι_ιo alkyl or d.₁₀ alkyl and aryl or C-MO aryl, that may be further substituted and wherein carbons may be substituted by any of the heteroatoms O, N, or S.

8. Method according to claims 5 to 7, wherein Mⁿ⁺ is or comprises at least one aromatic heterocyclic cation.

9. Method according to claim 8, wherein Mⁿ⁺ is or comprises at least one of the following aromatic heterocyclic cations:

wherein R_{1 (} R₂, R₃, R₄, R₅, R₆ are, in each case independently of one another, a hydrogen or a halogen or a fluoride or a Ci t_{o 8} alkyl,

wherein one or more of R_{1 (} R₂, R₃, R₄, R₅, R₆ may be bonded to each other by single or double bonds,

wherein carbons of C_1-8 alkyl and/or aryl may be substituted by any of the heteroatoms O, N, or S

wherein the Ci _t08 alkyl may be partially or completely substituted by further functional groups such as

F, Cl, N(C_mF_(2m+1._x)H_x)₂, 0(C_mF_(2m+1._X)H_x), S0₂(C_mF_(2m+1._X)H_x), wherein 1< m < 6 and 0 < x < 2m+1.

10. Method according to any one of claims 5 to 9, wherein TaF₅ or NbF₅ reacts with a compound Mⁿ⁺F^" _n at a temperature of -50 to 50°C, preferably at a temperature of 15 to 25 °C.

11. Method according to any one of claims 5 to 10, wherein the reaction is carried out in a solvent or solvent mixture that is directly suitable for use in a secondary or primary battery, a condensator, a supercondensator or a galvanic cell.

12. Method according to claim 11 , wherein the solvent is an organic carbonate, preferably an ethylenecarbonate, propylenecarbonate, butylenecarbonate, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, methylpropylcarbonate or a mixture of at least two of these solvents.

13. Use of at least one of the salts according to any one of claims 1 to 4 alone or in combination with further salts and/or additives in primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells.

14. Elektrolyte, preferably for primary batteries, secondary batteries, condensators, supercondensators and/or galvanic cells, comprising at least one compound of the general formula I according to any one of claims 1 to 4.

15. Elektrolyte according to claim 14, wherein the salt concentration of the elektrolyte is 0,01 - 3 mol/l, preferably 0,01 - 2 mol/l, most preferably 0,1

- 1 ,5 mol/l.

16. Primary battery comprising at least one compound of the general formula I according to any one of claims 1 to 4.

17. Secondary battery comprising at least one compound of the general formula I according to any one of claims 1 to 4.

18. Condensator comprising at least one compound of the general formula I according to any one of claims 1 to 4.

19. Supercondensator comprising at least one compound of the general formula I according to any one of claims 1 to 4.

20. Galvanic cell comprising at least one compound of the general formula I according to any one of claims 1 to 4.