CA2371613A1

CA2371613A1 - Process for the purification of methanide electrolytes

Info

Publication number: CA2371613A1
Application number: CA002371613A
Authority: CA
Inventors: Peter Sartori; Nikolai Ignatiev; Peter Barthen
Original assignee: Individual
Current assignee: Merck Patent GmbH
Priority date: 1999-04-28
Filing date: 2000-04-13
Publication date: 2000-11-09
Also published as: BR0010024A; WO2000066547A1; AU4295400A; KR20020020697A; EP1173416A1; CN1350518A; JP2002543178A; DE19919347A1; RU2001130168A

Abstract

The invention relates to a method for preparing organic methanide electrolyt es of the formula (I): M2[R1-SO2-(CF2)n-SO2-R], wherein R means C(SO2RF)2, N(SO2RF), O and R1 means C(SO2RF)2, N(SO2RF) in a quality sufficient for the use in electrochemical cells in batteries. The method comprises the followin g steps: (i) reacting a methanide of the formula (I) with concentrated sulphur ic acid and fractionally rectifying the obtained free acids of said methanide. (ii) Reacting the product of the formula (I), whereby said product is obtain ed in (i), with M=H with phosphorus pentaoxide above the melting point followed by subsequent fractioned rectification. (iii) Receiving the product from (ii ) in an aprotic, organic solvent and reacting with metallic Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba or the chlorides or hydrides thereof to form the corresponding metal methanides of the formula (I) and optionally removing excess reagent, whereby lithium alkyl can be used for M=Li.

Description

Process for the purification of methanide electrolytes (II) The invention relates to a process for the preparation of organic methanide electrolytes in useable quality for use in electrochemical cells.
The tris(perfluoroalkanesulfonyl)methanide ~~lass of compounds was described for the first time by Turowsky et al. in Inorgan. Chem., 1988, 27, 2135-2137 with reference to tris (trifluoromethanesulfonyl.) methane.
This C-H acidic compound reacts with bases to give the corresponding salts. The anion is planar, and the negative charge can be delocalized very well by the strongly electron-withdrawing substituents.
The lithium salt lithium tris(trifluoromethane-sulfonyl)methanide has been investigated for some time with respect to its suitability as conductive salt in secondary batteries owing to its high conductivity and good solubility in aprotic solvents. Further advantages of this salt are its high electrochemical and thermal stability.
There are two processes for the preparation of such compounds. According to Turowsky et al., tris[tri-fluoromethanesulfonyl]methane is prepared by a Grignard reaction with trifluoromethanesulfonyl fluoride.
A two-step process as described by Koshar et al. in J.
Org. Chem., 1973, 38, 3358-3363, and Benrabah et al. in J. Chem. Soc. Faraday Trans., 1993, 89(2), 355-359, likewise gives tris[trifluoromethanesulfonyl]methane.
Both processes give products which require purification for use as conductive salt. Purification methods used hitherto, which are based on reaction of the solvated salt with activated carbon and recrystallization, give products having a purity of, in general, not greater than 99.5 which still contain interfering contamina-tion by water and foreign ions.
However, salts of this quality are not suitable for use in organic electrolytes.
The object of the present invention is therefore to provide an inexpensive, easy-to-perform process by means of which organic methanide electrolytes are obtained in high-purity form, making the products prepared suitable for use in battery electrolytes. For the purposes of the invention, "high-purity" is taken to mean degrees of purity of greater than 99.5~s.
The obj ect according to the invention is achieved by a process for the preparation of high-purity methanides of the formula M2 [Rl-SOz (CF2) n) -S02-R) (I) in which R and R1 are independent of one another, R is C (SOZRF) z, N (SOzRF) or O, Rl is C (SOzRF) z or N (S02RF) , where ~-RF i s ( CXFzX+~ ) .
M is H, Li, Na, K, Cs, Rb, Mgl~z, Cal~z, Srl,~z or Bal~z, n is 1, 2 or 3, and x is 1, 2, 3 or 4, which are suitable as electrolytes, by purification, characterized in that it comprises the following steps:
(i) reaction of a methanide of the formula (I) with concentrated sulfuric acid, and fractional rectifica tion of the resultant free acid of said methanide, (ii) reaction of the product of the formula (I) in which M = H obtained from (i) with phosphorus pentoxide at above the melting point, followed by fractional rectification, (iii) taking-up of the product from (ii) in an aprotic organic solvent, and reaction with metallic Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, or chlorides or hydrides thereof, or with alkyllithium, to give the corresponding metal methanides of the formula (I), and, if necessary, removal of excess reagent.
The process according to the invention gives materials having a purity of greater than 99.5%, preferably from 99.6% to 99.9%, which are thus suitable for use as electrolytes in batteries.
Surprisingly, it has been found that the reaction with concentrated sulfuric acid stabilizes the starting material and thus enables it to be distilled without decomposition. In addition, the addition of equivalent amounts or an -excess of concentrated sulfuric -acid enables the free acid to be obtained directly from its salts M2 [Rl-SOZ (CFz)n) -SOa-R] and purified.
The addition, in accordance with the invention, of highly hygroscopic sulfuric acid already achieves a good drying effect, which can be increased further by addition of sulfur trioxide, corresponding to~ the water content of the crude product.

It has also been found that the fractional rectification of the pure fraction with addition of phosphorus pentoxide gives a pure product having a water content of from 5 to 30 ppm, preferably from 10 to 20 ppm. This highly effective drying can be carried out economically on amounts of any desired size.
The use in accordance with the invention of a solvent which is used exclusively or proportionately in the finished electrolyte is particularly advantageous. This makes isolation of the salt, which is complex, unnecessary.
In the reaction in process step (iii), gaseous hydrogen, hydrogen chloride or alkanes form as easily removable by-products. In this reaction, it was noted that no decomposition phenomena take place at the anion, as has been observed in conventional processes with strong bases.
The reduction of the volume of the electrolyte by distillation in accordance with the invention has the crucial advantage that the large excess of desired oxygen nucleophile present in the solution displaces undesired nucleophiles from the coordination sphere of the lithium. This effect allows impurities to be removed by distillation. A highly concentrated electrolyte is obtained, which enables low storage and transport costs-:-It has been found that the dilution of the highly concentrated electrolytes can be carried out with any desired solvents. It is therefore possible, in a simple manner, to employ the optimum solvent mixture and to provide electrolytes in any desired concentration.
The purification essentially consists of 3 process steps, which can preferably be followed by t.wo further steps.

1st step:
A methanide of the formula (I) having a purity of from 905 to 99.5 is introduced in batches into concentrated sulfuric acid (96 - 98~ sulfuric acid), and the mixture is stirred at temperatures of from 10 to 40°C. The mixture is preferably reacted with freshly distilled sulfuric acid at temperatures of from 20 to 30°C. The sulfuric acid is added in equivalent amounts or in excess. The rectification apparatus with isothermal column is baked out under a protective-gas atmosphere.
The distillation bridge must be heatable by means of heating tapes or the like. This keeps the distillation bridge at a constant temperature above the respective melting point. Fractional rectification is carried out in this apparatus.
2nd step:
The pure fraction from step 1 is mixed with phosphorus pentoxide in a distillation apparatus which has been baked out under a protective-gas atmosphere. The mixture is stirred for from 15 minutes to 5 hours at temperatures at or below the melting point of the acid.
The reaction is preferably carried out for from 30 minutes to 90 minutes. The mixture is subsequently subjected to fractional rectification under reduced pressure.
The fractional rectification of the pure fraction from step 1 with addition of phosphorus pentoxide gives a pure product having a water content of, preferably, from 10 to 30 ppm.
3rd step:
The product from step 2 is dissolved in polar organic solvents under a dry inert-gas atmosphere. Aprotic solvents, such as DMC, DEC, EC, PC, BC, VC, cyclo-pentanone, sulfolane, DMS, 3-methyl-1,3-oxazolidin-2-one, y-butyrolactone, EMC, MPC, BMC, EPC, BEC, DPC, 1,2-diethoxymethane, THF, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, and mixtures thereof, are particularly suitable. The solution is mixed with lithium hydride, with metallic lithium (Li), with lithium chloride, in situ using a lithium positive electrode, or with alkyllithium. In order to prepare the sodium, potassium, rubidium, caesium, magnesium, calcium, strontium or barium compounds, a reaction can be carried out with metallic sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr) or barium (Ba), sodium chloride, potassium chloride, rubidium chloride, caesium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, sodium hydride, potassium hydride, rubidium hydride, caesium hydride, magnesium hydride, calcium hydride, strontium hydride, or barium hydride. The mixture is stirred at temperatures of from 10°C to 200°C for from 10 minutes to 24 hours. The reaction is preferably carried out at temperatures of from 20°C to 100°C for from 25 minutes to 5 hours. The excess alkali metal reagent or alkaline earth metal reagent is subsequently filtered aff.
4th step:
The volume of--_ the solution from step 3 is, . if necessary, reduced to 2/3 to 1/4. The solvent is preferably reduced to 1/3. The distillation is carried out at atmospheric pressure at the boiling point of the corresponding solvent. The distillation can also be carried out under reduced pressure. The boiling points shift correspondingly.

5th step:
The high-viscosity electrolyte can be diluted to any desired extent with any desired solvents and solvent mixtures. Suitable solvents and solvent mixtures are all those employed in electrochemical storage media.
The composition of the electrolyte can thus be matched in accordance with the specific requirements.
The inexpensive process which can be carried out using simple reagents and apparatuses gives products in good yields in a quality which is suitable for use in batteries. No explosive or toxic by-products are formed in this process.
The methanides can also be employed in proportions of from 1 to 99% in combination with other conductive salts which are used in electrochemical cells. Examples of suitable conductive salts are those selected from the group consisting of LiPF6, LiBF4, LiClO~, LiAsF6, LiCF3S03, LiN (CF3S02) 2 and LiC (CF3S02) 3, and mixtures thereof. The electrolytes can also contain organic isocyanates (DE 199 44 603) for reducing the water content. The electrolytes may also contain organic alkali metal salts (DE 199 10 968) as additive.
Suitable alkali metal salts are alkali metal borates of the general formula Li+ B-(OR1)m(ORz)p in which --m and p are 0, 1, 2, 3 or 4, where m + p = 4, and R1 and RZ are identical or different, are optionally bonded directly to one another via a single or double bond, are each, individually or together, an aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid radical, or are each, individually or together, an aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or mono- or tetrasubstituted by A or Hal, or are each, individually or together, a heterocyclic aromatic ring from the group consisting of pyridyl, pyrazyl and bipyridyl, which may be unsubstituted or mono- to trisubstituted by A or Hal, or are each, individually or together, an aromatic hydroxy acid from the group consisting of aromatic hydroxycarboxylic acids and aromatic hydroxysulfonic acids, which may be unsubstituted or mono- to tetrasubstituted by A or Hal, and Hal is F, C1 or Br and A is alkyl having 1 to 6 carbon atoms, which may be mono- to trihalogenated.
Likewise suitable are alkali metal alkoxides of the general formula - Li+ OR- -in which R
is an aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid radical, or is an aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or mono- to tetrasubstituted by A
or Hal, or _ g _ is a heterocyclic aromatic ring from the group consisting of pyridyl, pyrazyl and bipyridyl, which may be unsubstituted or mono- to trisubstituted by A or Hal, or is an aromatic hydroxy acid from the group consisting of aromatic hydroxycarboxylic acids and aromatic hydroxysulfonic acids, which may be unsubstituted or mono- to tetrasubstituted by A or Hal, and Hal is F, C1 or Br and A is alkyl having 1 to 6 carbon atoms, which may be mono- to trihalogenated.
Lithium complex salts of the formula Rs R5 O~ ,O
S~0 Li ~ t ,OR ~

OR

where __ Rl and RZ are identical or different, are optionally bonded directly to one another via a single or double bond, and are each, individually or together, an aromatic ring from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or mono- to hexasubstituted by alkyl (C1 to C6) , alkoxy groups (C1 to C6) or halogen (F, C1 or Br) , or are each, individually or together, an aromatic heterocyclic ring from the group consisting of pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted or mono- to tetrasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6) or halogen (F, C1 or Hr) , or are each, individually or together, an aromatic ring from the group consisting of hydroxybenzocarboxyl, hydroxynaphthalenecarboxyl, hydroxybenzosulfonyl and hydroxynaphthalenesulfonyl, which may be unsubstituted or mono- to tetrasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6) or halogen (F, C1 or Br) , R3 - R6 may each, individually or in pairs and optionally bonded directly to one another via a single or double bond, have the following meanings:
1. alkyl (C1 to C6) , alkoxy (C1 to C6) or halogen (F, C1 or Br) 2. an aromatic ring from the groups consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or mono- to hexasubstituted by alkyl (C1 to C6) , alkoxy groups (C1 to C6) or halogen (F, C1 or Br) .
pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted o-r- mono- to tetrasubstituted by alkyl (C1 to C6) , alkoxy groups (C1 to C6) or halogen (F, C1 or Br) , which are prepared by the following process (DE 199 32 317):
a) chlorosulfonic acid is added to 3-, 4-, 5- or 6-substituted phenol in a suitable solvent, b) the intermediate from a) is reacted with chloro-trimethylsilane, and the reaction mixture is filtered and subjected to fractional distillation, c) the intermediate from b) is reacted with lithium tetramethoxyborate(1-) in a suitable solvent, and the end product is isolated therefrom, may also be present in the electrolyte.
The electrolytes may likewise comprise compounds of the following formula (DE 199 41 566) C ( [R1 (CR2R3) x] lAx) YKt] + ~N (CF3) 2 where Kt = N, P, As, Sb, S or Se, A = N, P, P (O) , O, S, S (O) , 502, As, As (O) , Sb or Sb (O) , Rl , R2 and R3 are identical or different and are H, halogen, substituted and/or unsubstituted alkyl CnH2n+i, substituted and/or unsubstituted alkenyl having 1-18 carbon atoms and one or more double bonds, substituted and/or unsubstituted alkynyl having 1-18 carbon atoms and one or more triple bonds, substituted and/or unsubstituted cycloalkyl CmH2m_1, mono- or polysubstituted and/or unsubstituted phenyl, or substi-tuted and/or unsubstituted heteroaryl, A can be included in R1, R2 and/or R3 :in various positions, Kt can be included in a cyclic or heterocyclic ring, the groups bonded to Kt may be identical or different, where n = 1-18 m = 3-7 k = 0 or 1-6 1 = 1 or 2 in the case where x - 1 and 1 in the case where x = 0 x = 0 or 1 y = 1-4.
The process for the preparation of these compounds is characterized in that an alkali metal salt of the general formula D+ N(CF3)z (II) where D+ is selected from the group consisting of the alkali metals, is reacted, in a polar organic solvent, with a salt of the general formula C ( ~Rl ) CRZR3 ) x] iAX) YKt ] + -E ( I I I ) where Kt , A, R1, Rz , R~ , k, 1, x and y are as def fined above , and ~E is F-, C1-, Br-, I-, BF4-, C104-, AsF6-, SbF6- or PF6-.
However, use can also be made of electrolytes comprising compounds of the general formula (DE 199 53 638) X- ( CYZ ) n,- SOZN ( CRIRzR3 ) 2 where X is H, F, C1, CnFzn+i. CnFzn-~ or (SOz) kN (CR1RZR3) z.
Y is H, F or C1 Z is H, F or C1 R1, Rz and R3 are H and/or alkyl, fluoroalkyl or cyclo-alkyl m is 0-9 and, if X = H, m $ 0 n is 1-9 k is 0 if m = 0 and k = 1 if m = 1-9, prepared by reacting partially or perf:Luorinated alkylsulfonyl fluorides with dimethylamine in organic solvents, and complex salts of the general formula (DE 199 51 804) MX+ ~EZJ Y X/y in which x and y are 1, 2, 3, 4, 5 or 6 M"+ is a metal ion E is a Lewis acid selected from the group consisting of -- -BR1R2R3 , A1R1R2R3 , PR1RZR3R4R5 , AsRIRZR3R4R5 and VR1R2R3R4R5 , R1 to RS are identical or different, are optionally , bonded directly to one another via a single or double bond, and each, individually or together, have the following meanings:
a halogen (F, C1 or Br), an alkyl or alkoxy radical (C1 to C8), which can be partially or fully substituted by F, C1 or Br, an aromatic ring, optionally bonded via oxygen, from S the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or mono-to hexasubstituted by alkyl (C1 to Ce) or F, C1 or Br, an aromatic heterocyclic ring, optionally bonded via oxygen, from the group consisting of pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted or mono- to tetrasubstituted by alkyl (C1 to Ce) or F, C1 ar Br, and Z i s OR6 , NR6R' , CR6R'R8 , OS02R6 , N ( SOzR6 ) ( SOzR' ) , C ( S02R6 ) ( SOZR' ) ( SOzRe ) or OCOR6 , where R6 to R8 are identical or different, are optionally bonded directly to one another via a single or double bond and are each, individually or together, hydrogen or as defined for R1 to R5, prepared by reacting a corresponding boron or phosphorus Lewis acid/solvent adduct with a lithium or tetraalkylammonium imide, methanide or triflate.
They can also be employed in mixtures which comprise the borate salts (DE 199 59 722) of the general formula y_ MX+
Rs R2 X f , in which M is a metal ion or tetraalkylammonium, x and y are 1, 2, 3, 4, 5 or 6, Rl to R'' are identical or different and are alkoxy or carboxyl radicals (C1-Ce), which are optionally bonded directly to one another via a single or double bond.
These electrolytes can be employed in electrochemical cells having negative electrodes made fram common lithium intercalation and insertion compounds, but also with negative-electrode materials consisting of lithium mixed-oxide particles coated with one or more metal oxides or polymers.
Lithium mixed-oxide particles coated with one or more metal oxides are obtained by a process (DE 199 22 522) which is characterized in that the particles are suspended in an organic solvent, a solution of a hydrolysable metal compound and a hydrolysis solution are added to the suspension, and the coated particles are then filtered off, dried and optionally calcined.
Lithium mixed-oxide particles coated with one or more polymers are obtained by a process (DE 199 46 066) which is characterized in that particles are suspended in a solution comprising polymers selected from the group consisting of polyimides, polyanilines, poly-pyrroles, polythiophenes, polyacetylenes, polyacrylo-nitriles, carbonized polyacrylonitriles, poly-p-phenyl-enes, polyphenylenevinylenes, polyquinolines, polyquin-oxalines, polyphthalocyanine-siloxanes, polyvinylidene fluorides, polytetrafluoroethylenes, polyethyl meth acrylates, polymethyl methacrylates, polyamides, co polymers with vinyl ethers, cellulose, polyfluoro ethylenes, polyvinyl alcohols and polyvinylpyridines, and derivatives thereof, and the coated particles are then filtered off, dried, and optionally calcined.
The examples below are intended to illustrate the invention in greater detail, but without representing a limitation.

~

Examples Example 1 Purification of dicaesium hexafluoropropane-1,3-bis-[sulfonylbis(trifluoromethanesulfonyl)methanide]
1st step:
Preparation of dicaesium hexafluoropropane-1,3-bis-[sulfonylbis (trifluoromethanesulfonyl) methanide] as described in P 19733948 (purity 97.5-99.5%). The methanide was introduced in portions into freshly distilled sulfuric acid, and the mixture was stirred at room temperature for fifteen minutes. The round-bottom flask was subsequently connected to a distillation apparatus with isothermal column which had been baked out under an argon atmosphere, and the mixture was subjected to fractional rectification at a pressure of 10 Pa. The distillation bridge was provided with a heating tape from the column head in order to obtain a constant temperature above the respective melting point in the bridge. The ground-glass joints were provided with Teflon sleeves.
Weighed-out amount of Cs2 [ (CF3SO2) 2C-SO2- (CFZ) 3-SO2-C (CF3SO2) 2] 640 g (0. 6 mol) Boiling point of _the acid 170-173°C [10. .Pa]
Yield of the acid 68%
2nd step:
A portion of the pure fraction of H2 [ (CF3S0z) zC-S02- ~
(CF2) 3-S02-C (CF3S02) z] from step 1 was mixed with phosphorus pentoxide, and the flask containing the mixture was connected to the distillation apparatus, which had been baked out under an argon atmosphere. The mixture was melted, stirred for one hour at 180°C under atmospheric pressure and subjected to fractional rectification under reduced pressure.
Weighed-out amount of H2 [ (CF3S02) zC-SOZ- (CFz) a-SOa-C (CF3S02) 2] 174 g Added amount of phosphorus pentoxide 18 g Pressure 10 Pa 3rd step:
124 .6 g (0 . 149 mol) of H2 [ (CF3S02) 2C-SOZ- (CFz) 3-SOz-C (CF3S02) 2] were dissolved in 300 ml of diethyl carbonate under a dry inert-gas atmosphere and reacted with 2.5 g (0.315 mol) of lithium hydride. When the addition was complete, the electrolyte was stirred for 30 minutes, and the excess lithium hydride was subsequently separated off via a filter.
4th step:
The volume of the electrolyte was reduced to 100 ml at room temperature and a pressure of 10-5 Pa.
5th step:
The colourless electrolyte, which was now of high viscosity, was diluted with 200 ml of solvent mixture (ethylene carbonate:dimethyl carbonate 1:1) to give 300 ml of an electrolyte which was 1 molar with respect to Li+ .
Even at the maximum amplification of the 19F-NMR
spectrum, no fluorine-containing impurities were detected (purity > 99.90 .

A water content of 32 ppm was found.

Claims

1. Process for the preparation of high-purity metal methanides of the formula M2 [R1-SO2(CF2)n)-SO2-R](I) in which R and R1 are independent of one another, R is C(SO2R F)2, N(SO2R F) or O, R1 is C(SO2R F)2 or N (SO2R F), where R F is (C X F2X+1), M is H, Li, Na, K, Cs, Rb, Mg1/2, Ca1/2, Sr1/2 or Ba1/2, n is 1, 2 or 3, and x is 1, 2, 3 or 4, which are suitable as electrolytes, by purification, characterized in that it comprises the following steps:
(i) reaction of a methanide of the formula (I) with concentrated sulfuric acid, and fractional rectifica-tion of the resultant free acid of said methanide, (ii) reaction of the product of the formula (I) in which M = H obtained from (i) with phosphorus pentoxide at above the melting point, followed by fractional rectification, (iii) taking-up of the product from (ii) in an aprotic organic solvent, and reaction with metallic Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, or chlorides or hydrides thereof, or, for M - Li, also with alkyllithium, to give the corresponding metal methanides of the formula (I), and, if necessary, removal of excess reagent.

2. Process according to Claim 1, characterized in that from 1/3 to 3/4 of the solvent is removed by distillation after completion of process step (iii) from Claim 1.

3. Process according to Claim 2, characterized in that 2/3 of the solvent is removed by distillation after completion of process step (iii) from Claim 1.

4. Process according to Claim 2 or 3, characterized in that the concentrated solution is diluted with any desired suitable solvents to give a ready-to-use solution.

5. Process according to one of Claims 1 to 4, characterized in that use is made of a solvent which is used exclusively or proportionately in the finished electrolyte.

6. Process according to one of Claims 1 to 5, characterized in that a methanide of the formula (I) which has a purity of from 90% to 99.5% is employed in step (i).

7. Use of metal methanides of the formula (I) prepared by a process according to Claims 1 to 6 in electrochemical cells and primary and secondary batteries.

8. Use of metal methanides of the formula (I) having a purity of greater than 99.5% and a water content of < 60 ppm as electrolyte in electrochemical cells and primary and secondary batteries.