CA2263210C - Process for the preparation of lithium-borate complexes - Google Patents

Abstract

Lithium complex salts have the general formula (I), in which R and R1 are the same or different, are optionally directly interconnected by a simple or double bond, represent alone or together an aromatic ring from the group composed of phenyl, naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or substituted one to four times by A or Hal, or represent alone or together a heterocyclic aromatic ring from the pyridyl group which can be unsubstituted or substituted one to three times by A or Hal; Hal stands for F or Cl; and A stands for alkyl with 1 to 6 C atoms optionally halogenated one to four times. Also disclosed is their use as electrolytes in secondary lithium batteries and a process for preparing these compounds.

Description

Process for the preparation of lithium borate complexes The invention relates to lithium complex salts of the general formula (I) R, O\ ./O--R' ua R O~ \O R , wherein R and R1 are identical or different, are optionally joined together directly by a single or double bond, in each case individually are an aromatic ring from the group phenyl, naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, or in each case together are an aromatic ring from the group naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or monosubstituted to tetrasubstituted by A
or Hal, or in each case individually are a heterocyclic aromatic ring from the group pyridyl, pyrrole, 1,2-diazine, 1,3-diazine or 1,4-diazine, which can be unsubstituted or monosubstituted to trisubstituted by A or Hal, or in each case together are a heterocyclic aromatic ring from the group pyrrole, 1,2-diazine or 1,3-diazine, which can be unsubstituted or monosubstituted to trisubstituted by A or Hal, and Hal is F or C1, and A is alkyl having 1 to 6 C atoms, which can be monohalogenated to tetrahalogenated, to their use as electrolytes in secondary lithium batteries and to a process for the preparation of these compounds.
Because of the low resting potential of lithium, only aprotic compounds are suitable as solvents. Protic compounds, such as alcohols, react with lithium-containing anodes and produce hydrogen, which ultimately leads to explosion of the cell.
Suitable organic solvents in secondary lithium batteries are basically any of the solvents and solvent mixtures known to those skilled in the art for this application. Suitable solvents are, inter alia, both ethers and esters, including cyclic organic carbonates, e.g.
propylene carbonate or ethylene carbonate. However, it is possible to use not only liquids but also polymers as solvents, the prerequisite in this case being that the polymer used dissolves lithium salts and forms ionically conducting mixtures therewith. One of the most commonly used polymers is polyethylene oxide. The conductivity can be increased by using mixtures of a polymer and one or more solvents (Amalgier et al. in: Proceedings of the Symposium on Primary and Secondary Lithium Batteries, Vol. 91-1, 131-141, (1991); K.M. Abraham and M. Salomon (editors), The Electrochemical Society, Pennington N.J.). The use of polymer electrolytes increases the operational safety of the cell because the electrolyte is prevented from escaping and thereby exposing the electrode surfaces if the cell container is mechanically damaged.
The conducting salts used for lithium cells are exclusively salts with large, negatively charged, inorganic or organic counterions. Conducting salts with small counterions, e.g. lithium chloride, are unsuitable because of the low solubility due to the high lattice binding energy.
Lithium salts with fluorinated inorganic anions are among the hitherto most frequently studied conducting salts for secondary lithium cells. Solutions of lithium tetrafluoroborate in various ethers give relatively low cyclization yields on inert substrates. Poor yields have also been achieved with LiBF4/polyethylene carbonate solutions on carbon anodes (Maki Sato et al. in:
Proceedings of the Symposium on Primary and Secondary Lithium Batteries, Vol. 91-3, 407-415, (1991); K.M. Abraham and M. Salomon (editors), The Electrochemical Society, Pennington N.J.). Lithium tetrafluoroborate is therefore not ideally suitable for application in secondary lithium cells. At potentials greater than the equilibrium potential of the reaction of elemental lithium in Li+ + e-, lithium hexafluoroantimonate is reduced inter alia to elemental antimony and consequently cannot be used as a conducting salt.
Lithium hexafluoroarsenate gives very high cyclization yields in most solvents and solvent mixtures on inert substrates. Cyclization yields of over 96o have been found for a solution of LiAsF6 in 2-methyltetrahydrofuran (Goldman et al., J. Electrochem. Soc., Vol. 127, 1461-1467 (1980)). The toxicity and poor environmental compatibility of lithium hexafluoroarsenate and its secondary products are an obstacle to large-scale application (Archuleta, M.M., J. Power Sources 54, 138 (1995)).
LiPF6-containing solutions based on organic carbonates have also been tested in cells with lithium anodes. An essential disadvantage of these systems is the low thermal stability of LiPF6. Partial dissociation into LiF and PFS takes place in solution, which can lead to cationic polymerization of the solvent initiated by the Lewis acid PFS (Koch et al. in: Proceedings of the Symposium [lacuna) Lithium Batteries, Vol. 81-4, 165-171, (1981), The Electrochemical Society, Pennington N.J.; H.V. Venkatasetty (editor) ) .
To avoid the dissociation of inorganic fluorinated counterions, organic lithium salts with perfluorinated organic radicals have also been tested, examples being lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide and lithium tris(trifluoromethanesulfonyl)methide. Because of their high thermal stability, these salts are used principally in sonically conducting polymers. The last two salts mentioned have an appreciably higher conductivity than the first and are substantially stable to oxidation. They have been used successfully in cells with carbon anodes and nickel oxide cathodes (Dahn et al., J. of Electrochem. Soc., Vol. 138, 2207-2211 (1991)). A serious disadvantage, however, is the high price due to the manufacturing process. Because of the high fluorine content of these compounds, there is also a risk of exothermic reactions with lithium.
The use of lithium organoborates has also been studied by Horowitz et al. (in: Proceedings of the Symposium on Lithium Batteries, Vol. 81-4, 131-143, (1981), The Electrochemical Society, Pennington N.J.;
H.V. Venkatasetty (editor)). Because of the low anodic stability, the safety problems associated with the formation of triorganoboranes and their high price, tetraorganoborates are not used in lithium cells.

A synthesis of lithium borate complexes, starting from boric acid in aqueous solution is described in 5 and J. Barthel et al. in J. Electrochem. Soc.
142/8, 2527 (1995). A decisive criterion for electrolytes which can be employed in Li ion batteries is, in addition to the high purity, in particular the absence of water. It is not possible to obtain the products from this synthesis in an absolutely anhydrous manner.
The use of lithium chloroborates has also been studied (Johnson, J.W.; Brody, J.F.; J. Electrochem. Soc., Vol. 129, 2213-2219 (1982)). However, the processes for the preparation and purification of these compounds are very expensive and solutions of these salts tend to undergo phase separation. Their high chlorine content makes them unstable.
One object of the invention was therefore to provide environmentally compatible, stable lithium complex salts with improved properties, which are economic to prepare and, in appropriate solvents, are suitable as electrolytes for the manufacture of secondary lithium batteries: Another object of the invention is to provide a process for the preparation of these lithium complex salts.
It has been found by experiment that the object of the invention can be achieved by means of lithium complex salts of the general formula (I) u' wherein R and R1 are identical or different, are optionally joined together directly by a single or double bond, in each case individually are an aromatic ring from the group phenyl, naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, or in each case together are an aromatic ring from the group naphthyl, anthracenyl or phenanthrenyl, which can be unsubstituted or monosubstituted to tetrasubstituted by A
or Hal, or in each case individually are a heterocyclic aromatic ring from the group pyridyl, pyrrole, 1,2-diazine, ' 1,3-diazine or 1,4-diazine, which can be unsubstituted or monosubstituted to trisubstituted by A or Hal, or in each case together are a heterocyclic aromatic ring from the group pyrrole, 1,2-diazine or 1,3-diazine, which can be unsubstituted or monosubstituted to trisubstituted by A or Hal, and Hal is F or C1, and A is alkyl having 1 to 6 C atoms, which can be monohalogenated to tetrahalogenated, and especially by means of lithium complex salts in which R and R1 are identical or different, are optionally joined together by a single or double bond and are each phenyl or pyridyl. Very particularly suitable lithium complex salts of the general formula (I) are lithium bis[2,2'-biphenyldiolato(2-)-O,O']borate(1-) and lithium bis[2,3-naphthalenediolato(2-)-0,0']borate(1-).

The invention also provides a process for the preparation of the compounds according to the invention and a novel process for the preparation of monofluorinated to tetrafluorinated aromatics hydroxylated on adjacent C atoms, especially tetrafluorocatechol, which are required as intermediates for the preparation of the lithium borate complexes according to the invention.
According to one aspect of the present invention, there is provided lithium bis(2,2'-biphenyldiolato(2-)-0,0']borate(1-).
According to another aspect of the present invention, there is provided lithium bis(2,3-naphthalenediolato(2-)-0,0']borate(1-).
According to still another aspect of the present invention, there is provided a process for preparation of lithium complex salts of the general formula (I) R~ O\ ./O-R, g Lia R O/ \O~R
wherein R and R1 are identical or different, and are optionally joined together directly by a single or double bond:
wherein, when R and R1 are not joined together, each of R and R1 is an aromatic ring selected from phenyl, naphthyl, anthracenyl and phenanthrenyl, which is unsubstituted or monosubstituted to tetrasubstituted by A or Hal; and wherein, when R and R1 are joined together, R and R1 together form an aromatic ring selected from naphthyl, anthracenyl and phenanthrenyl, which is unsubstituted or monosubstituted to tetrasubstituted by A or Hal; or wherein, when R and R1 are not joined together, each of R and R1 is a heterocyclic aromatic ring selected from pyridyl, p~~rrole, 1,2-diazine, 1,3-diazine and 1,4 diazine, which is unsubstituted or monosubstituted to trisubstituted by A or Hal; and wherein, when R and R1 are joined together, R and R1 together form a heterocyclic aromatic ring selected from pyrrole, 1,2-diazine and 1,3-diazine, which is unsubstituted or monosubstituted to trisubstituted by A or Hal;
Hal is F or C1; and A is alkyl having 1 to 6 C atoms, which is unsubstituted or monohalogenated to tetrahalogenated; wherein a) a lithium tetraalcoholatoborate is taken up with an aprotic solvent, b) equimolar amounts of a hydroxyl compound or a 1:1 mixture of two different hydroxyl compounds, dissolved in an aprotic solvent, are added dropwise at a temperature of 10 to 60°C, with stirring, optionally under an inert gas atmosphere, and, optionally, the reaction mixture is subsequently stirred at a temperature of 60 to 90°C, c) optionally, alcohol formed during the reaction is slowly distilled off by application of a slight vacuum at a slightly elevated temperature, d) the product formed is crystallized out, optionally after concentration of the reaction mixture under vacuum at a temperature of 0 to 10°C, and, optionally, is separated off under an inert gas atmosphere, and e) the product which has been separated off is dried by slow heating.
According to yet another aspect of the present invention, there is provided a process as described herein, wherein tetrafluorocatechol is used as the hydroxyl compound for complexation; wherein the tetrafluorocatechol is prepared by: a) reaction of pentafluorophenol with potassium carbonate in aqueous solution to give potassium pentafluorophenate~ b) etherification of the potassium pentafluorophenate prepared in a) with ethylene oxide in DMSO as solvent, under an inert gas atmosphere, to give a cyclic diether, 5,6,7,8-tetrafluoro-(1,4)-benzodioxane, or etherification of the potassium pentafluorophenate prepared in a) with 2-bromoethanol and subsequent cyclization to the cyclic diether in presence of potassium carbonate in DMF as solvent; and c) cleavage of the ether in presence of aluminium chloride with benzene as solvent, under an inert gas atmosphere.
According to a further aspect of the present invention, there is provided a process as described herein, wherein mono-, di- or tricatechol, prepared in the same way as tetrafluorocatechol as described herein, is used as the hydroxyl compound for complexation.
According to yet a further aspect of the present invention, there is provided a process as described herein, wherein the lithium tetraalcoholatoborate used is lithium tetramethanolatoborate, lithium tetraethanolatoborate or lithium tetrapropanolatoborate.
According to still a further aspect of the present invention, there is provided a process as described herein, wherein the aprotic solvent is selected from acetonitrile, acetone, nitromethane, dimethylformamide, dimethylacetamide and dimethyl sulfoxide.
According to another aspect of the present invention, there is provided a process as described herein, wherein equimolar amounts of the hydroxyl compound are added dropwise at room temperature.
According to yet another aspect of the present invention, there is provided a process as described herein, wherein the alcohol formed is distilled off under slight vacuum at a temperature of 50 to 60°C.
According to another aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein as a conducting salt in an electrolyte for an electrochemical cell.
According to still another aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein as a conducting salt in an electrolyte for a battery.
According to yet another aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein as a conducting salt in an electrolyte in a secondary lithium battery.
According to a further aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein in combination with one or more of another lithium salt and a borate complex in an electrolyte of a secondary lithium battery.
According to yet a further aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein in combination with one or more other lithium salts selected from lithium phenate and dilithium 2,2'-biphenyldiolate in an electrolyte of a secondary lithium battery.
According to still a further aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein in a double-layer capacitor or a supercapacitor.
According to another aspect of the present invention, there is provided use of a lithium complex salt of general formula (I) as defined herein in manufacture of a switchable window or display.
Surprisingly, ligands which are not soluble in water, e.g. pyridinediol, dihydroxybiphenyl or other, preferably hydroxylated aromatic compounds, can also be coordinated to the central boron atom by the process according to the invention.
Because of the reaction conditions according to the invention, the presence of water, which in aqueous media can be bound to the central atom as a ligand to form B(OH)4-, both during the complexation reaction and during the isolation of the products prepared, which is carried out inter alia by concentration of the solution, can have an adverse effect due to the formation of by-products with B-0-B
bridges.
The process according to the invention influences the position of the equilibrium of the complexation reaction in such a way that the reaction solution can be evaporated under mild conditions to give product yields of 1000.
One particular advantage of the process according to the invention is the possibility of working under mild conditions without using aggressive reagents like BC13, BF3 or LiBH4, which result in the formation of HC1, HF or H2 during the complexation reaction. Furthermore, the process according to the invention affords the elegant possibility of incorporating a methanolic solution of LiB(OCH3)4 into a polymer matrix, e.g. hydroxylated PEO, and preparing a polymeric electrolyte in which the anion is fixed to the polymer backbone.
The complex salts according to the invention are prepared by placing a lithium tetraalcoholatoborate in an aprotic solvent. This solution is heated slightly, if necessary, to dissolve the borate.
Lithium tetraalcoholatoborates suitable for the reaction are the derivatives of methanol, ethanol and propanol, as well as those of other short-chain alcohols.
However, it is particularly preferable to use the methanol or ethanol derivatives because the low boiling points of these alcohols mean that they can be removed from the reaction mixture at relatively low temperatures after complexation.
For complexation a suitable hydroxyl compound or a 1:1 mixture of different suitable hydroxyl compounds is dissolved in the same aprotic solvent as the lithium tetraalcoholatoborate was previously dissolved in, and slowly added dropwise to the lithium tetraalcoholatoborate solution in an equimolar amount at a temperature of between 10 and 60°C, preferably at room temperature up to about 55°C, if necessary under an inert gas atmosphere. To complete the reaction, the reaction solution is then optionally stirred for some time at a temperature of between 60 and 90°C. The subsequent stirring can be dispensed with in the case of very rapid complexation reactions.

A solvent from the group comprising acetonitrile, acetone, nitromethane, dimethylformamide, dimethylacetamide and dimethyl sulfoxide can be used as the aprotic solvent.
It is preferable to use acetonitrile.
If the alcohol formed during the reaction interferes with the subsequent isolation of the complex salt prepared, it can be separated off by the application of a slight vacuum and, if appropriate, by gentle heating to about 50 to 60°C. Depending on the solubility of the lithium complex salt prepared in the aprotic solvent used, the reaction solution is concentrated or the solbent is completely distilled off and, if the product does not crystallize out spontaneously, the residue is cooled at a temperature of 0 to 10°C for several hours. The crystalline product is separated off in conventional manner and dried by slow heating.
Compounds which are particularly suitable for complexation are aromatics hydroxylated in adjacent positions, such as pyrocatechol, 1,2- or 2,3-dihydroxynaphthalene, and also correspondingly hydroxylated anthracene or phenanthrene. However, aromatics which are joined together by a bond and have hydroxyl groups in the direct vicinity of the bond, e.g. 2,2'-dihydroxybiphenyl, are also suitable. Other compounds suitable for complexation are corresponding heterocycles, e.g. pyridine-2,3-diol and pyridine-3,4-diol, or correspondingly hydroxylated bipyridyl. Other aromatics suitable for complexation are diazines hydroxylated in adjacent positions, e.g. 1,3-diazine-5,6-diol, 1,2-pyrazine-3,4-diol, 1,2-pyrazine-4,5-diol and 1,4-pyrazine-2,3-diol, or the corresponding diols of pyrrole. Corresponding ligands suitable for complexation can be monosubstituted or polysubstituted, both on the heteroatom and on non-hydroxylated carbon atoms of the aromatic ring, by halogen atoms or optionally halogenated alkyl radicals having 1-6 C
atoms. 1-Trifluoromethylpyrrole-2,3-diol is an example of these ligands. However, not only the heterocyclic aromatics but also the other suitable aromatics can be monosubstituted or polysubstituted, i.e. up to tetrasubstituted, by halogen, especially by fluorine or chlorine. Monoalkylated or polyalkylated hydroxylated aromatics, especially hydroxylated phenyl, naphthyl, anthracenyl or phenanthrenyl substituted by methyl, ethyl, n- or i-propyl or n-, sec- or tert-butyl, can also advantageously be used for complexation.
The hydroxyl compounds suitable for complexation also include those which are not commercially available, an example being tetrafluorocatechol. It can only be prepared in low yields by processes known from the literature.
Experiments have now shown that this dihydroxyl compound can be prepared in high yields by reacting pentafluorophenol with potassium carbonate to give potassium pentafluorophenate, then reacting this with 2-bromoethanol in DMSO to give the monoether and then reacting this with potassium carbonate in DMF to give the cyclic diether, from which the desired tetrafluorocatechol is then obtained by cleavage of the ether in benzene [lacuna] presence of aluminium chloride. However, the cyclic diether can also be obtained in one reaction step by reaction with ethylene oxide in DMSO at elevated temperature under an inert gas atmosphere. Depending on how the reaction is conducted, yields of 80 to 95% are obtained by this method. This process can also be used to prepare mono-, di- or tri-fluorinated dihydroxyaromatics.
In cyclization experiments, Li borate complexes of this fluorinated dihydroxyl compound, according to the w invention, have given particularly good results and have proved particularly stable. In combination with other salts, these complexes exhibit a synergistic stabilizing effect towards oxidation. This effect seems to be dependent on the number of fluorine atoms bound per ligand, electrochemical measurements having shown a stabilization of about 0.1 V/fluorine atom/ligand.
This means that these fluorinated borate complex salts according to the invention, as well as the other Li borate complexes according to the invention, are particularly suitable for use in electrochemical cells, not only in primary and secondary batteries but also in double layer or super capacitors, and for the manufacture of displays or electrically switchable windows.
The complex salts according to the invention can be used on their own or in a mixture. However, they can also be used in a mixture with other conducting salts known to those skilled in the art for these applications. The Li salts according to the invention can also be used in a mixture with appropriate ammonium borate complexes or other alkali metal or alkaline earth metal borate complexes.
It has been found by experiment that the complex salts according to the invention, especially lithium bis[2,2'-biphenyldiolato]borate(1-), can be used in conjunction with highly oxidizing cathode materials. These compounds can also be used in a mixture with other lithium compounds in order to guarantee overload protection. When electrolyte mixtures are prepared, it is advantageous to stabilize them by the addition of a lithium alcoholate when lithium bis[perfluoro-1,2-benzenediolato(2)-0,0']borate(1-) is used in a mixture with lithium bis[2,2'-biphenyldiolato]borate(1-) or with other lithium borate complexes according to the invention. Stable mixtures of lithium bis[perfluoro-1,2-benzenediolato(2)-0,0']borate(1-) with other complex salts according to the invention are obtained when complexes are added which have substituents with electron donating properties, i.e. substituents with a +I effect, on the aromatic ring. Examples of substituents with a +I effect are alkyl groups such as methyl, ethyl, propyl, i-propyl, n-butyl, sec-butyl and tert-butyl.
In particular, by electrochemical experiments carried out with a 0.5 molar solution of lithium bis[2,2'-biphenyldiolato]borate(1-) in a solvent mixture consisting of 4:1 propylene carbonate/dimethylethylene glycol (on stainless steel, 0.5 cm2, v = 20 mV/s), have shown that oxidation of the anion only begins at a voltage over 4 V, although only very weak currents flow. After the second discharge cycle, however, oxidation can no longer be measured above 4 V. From the first to the fourth cycle the resistance of the protective coating increases with the deposition of lithium and the yields of the cyclization are approximately constant at 48 m/C to 65 m/C (74%) and are comparable to other salts in PC/DME. If the inversion potential is then raised from 4.5 to 5 V and 6 V, the resistance of the protective coating increases further and the yields of the lithium deposition fall. A particular feature to be emphasized is the high anodic oxidation stability of the protective coating formed. No oxidative current can be observed even at an inversion potential of 8 V, although the solvents are unstable above ca. 5 V (PC) and begin to decompose.
Weak anodic currents were detected in the first cycle in experiments with electrolyte solutions to which lithium phenate had been added as well as lithium bis[2,2'-biphenyldiolato]borate(1-), but no discolouration of the electrolyte occurred, so the oxidation which would otherwise have occurred could be avoided by the addition of lithium phenate. In fact, these experiments were performed by starting from a resting potential of ca. 3000 mV, increasing the potential to 4500 mV at a rate of 20 mV/s, then reducing it to -500 mV and finally bringing it back to the resting potential. The same positive result was obtained in experiments in which the anodic inversion potential was increased to 6000 mV. Electrolyte solutions containing bis[1,2-benzenediolato)borate anions and the solvent dimethylethylene glycol are also protected from oxidation by Li phenate at potentials well above 4000 mV.
Dilithium 2,2'-biphenyldiolate exhibits the same positive properties as Li phenate. Even small amounts added to the electrolyte are sufficient to stabilize it.
Examples Example 1 Lithium bis[2,2'-biphenyldiolato(2-)-O,O']borate(1-) 6.6 g (47 mmol) of lithium tetramethanolatoborate are placed in 80 ml of acetonitrile at 55°C. A solution of 17.5 g (94 mmol) of 2,2'-dihydroxybiphenyl (purity >99~) in 100 ml of acetonitrile is added dropwise. All the lithium tetramethanolatoborate has dissolved when 30 ml of the biphenyl solution have been added. A large amount of colourless product precipitates out rapidly when a further 20 ml have been added. The remaining 50 ml of solution are added without the precipitate dissolving. The methanol formed is removed from the mixture by gentle evacuation at 55°C over 2 hours. The residue is then cooled to room temperature, filtered off under inert gas and washed with acetonitrile. The colourless product which has been filtered off is dried by slow heating to a temperature of 180°C.
Yield: 3.2 g of lithium bis(2,2'-biphenyldiolato(2-)-0,0']borate(1-) (17.70 of theory) 1H NMR (250 MHz, DMSO-d6) [b/ppm]
7.35(dd, 3Jg4/H3 7.5 Hz, 4~JHq/HZ= Hz,H4) = 1.5 7 (td, 3Jg2/H1 7 Hz, 4Jg2/Hq= Hz,H2 . = . 1 ) 25 5 .

6.99(td, 3Jg3/H1 7.4 Hz, 4JH3/H1= Hz,H3) = 0.9 6 (dd, 3JH1/H3 7 Hz, 4tTH1/H3= Hz,H4 . = . 0 ) 91 5 .

11B NMR (128.38 MHz, 0.3 M DMSO-d6, Et20*BF3 ext. ) 8.8 ppm (s) Potentiometric titration:
The titration is performed with dilute HC1.
The theoretical and actual boron contents are 2.800 and 2.7910 respectively.
The purity of the substance is 99.90.
MS (NI-LISIMS; CH3CN):
37 9 . 0 ( 100 0, M-Li+) Solubility:
The substance is soluble in EC/DME and also in PC
up to ca. 0.5 molal, although in pure PC solutions a solvate precipitates out after a short time.

Example 2 Lithium bis[1,2-benzenediolato(2-)-O,0']borate(-1) 6.19 g (43.6 mmol) of lithium tetramethanolatoborate are placed in 100 ml of acetonitrile at 35°C. 9.61 g (887.3 [sic] mmol) of pyrocatechol are added. A yellow solution is formed immediately. It is heated at 80°C for one hour and then concentrated under vacuum to a total volume of 40 ml. The solution turns brown. On cooling, colourless rectangular platelets precipitate out of the solution below 50°C. Crystallization of the product is completed by keeping the solution at a temperature of 5°C for a period of 12 hours.
The supernatant solution is then decanted off and the crystals obtained are dried to constant weight under vacuum at 140°C to give a grey powder.
Yield: 537 g of lithium bis[1,2-benzenediolato(2-)-0,0']borate(-1) (23 mmol, 52.70 of theory) Decomposition point: 270°C
1H NMR (250 MHz, DMSO-d6) [b/ppm]
6.48 ppm (s) 13C NMR ( 62 . 9 MHz, DMSO-d6) 151.6 (s, CI [sic], ppm C2) 117.3 (s, C4, C5) ppm 107.6 (s, C3, C6).
ppm Example 3 Lithium phenate 2.26 g (326 mmol) of lithium are cut in a closed hood equipped with manipulating gloves. 150 ml of tetrahydrofuran are added under an inert gas atmosphere (Ar 6.0). A solution of 27.72 g (294.6 mmol) of phenol p.a.
in 75 ml of tetrahydrofuran is then added dropwise at 40°C
over 3 hours, with magnetic stirring. A colourless precipitate is formed. The mixture is subsequently stirred for 14 hours at room temperature and the precipitate redissolves. Small amounts of unreacted lithium are filtered off in the closed hood. The solvent is evaporated off and the residual product is dried to constant weight under an oil pump vacuum to give a product with a purity of 99.9.
Example 4 Dilithium 2,2'-biphenyldiolate 100 ml of methanol are added dropwise to 1.67 g (0.241 mol) of lithium and the mixture is slowly heated. A
colourless solution forms at a temperature of 50°C. A
solution consisting of 100 ml of methanol and 22.4 g (0.120 mol) of 2,2'-dihydroxybiphenyl is then added dropwise, with stirring. The solvent is distilled from the resulting reaction solution and the colourless product obtained is heated slowly under vacuum to a maximum temperature of 100°C and dried.
Yield: 100 of theory Purity: 99.60 (determined by titration).
Example 5 Lithium bis[tetrafluoro-1,2-phenyldiolato(2-)-0,0']-borate a) Potassium pentafluorophenate A solution of 94.1 g of pentafluorophenol in water is added slowly to 48.4 g of solid potassium carbonate, with stirring, giving rise to a substantial evolution of gas (C02). Crystals separate out which and [sic) only dissolve after a further 200 ml of water have been added and the temperature raised to 95°C. This solution is cooled to 20°C. After 12 hours the crystals formed are separated off and washed three times with 40 ml of water cooled to 0°C.
The crystalline product obtained is dried by raising the temperature slowly to 150°C.
Yield: 93.70 of theory Decomposition point: 240°C.
b) Lithium tetramethanolatoborate 9.92 g of lithium are placed in a PyrexTM flask under an argon atmosphere in a closed hood equipped with manipulating gloves. 250 ml of methanol are added slowly to the lithium, with stirring and while cooling with an ice/methanol mixture. A strongly exothermic reaction takes place. A further 320 ml of methanol are then added gradually.
The reaction mixture is heated to a temperature of 60°C and 148.6 g of trimethyl borate are slowly added dropwise to the homogeneous solution formed. A white crystalline product is formed. After standing for 24 hours at room temperature, the product is filtered off and dried under reduced pressure.
Yield: 93.7 of theory Decomposition temperature: 50°C.
c) 5,6,7,8-Tetrafluoro-(1,4)-benzodioxane 40.2 g of potassium pentafluorophenate are dissolved in 150 ml of dried DMSO which has previously been treated with highly purified argon. 100 ml of dried and argon-treated DMSO are heated to a temperature of 175°C and 75 ml of the potassium pentafluorophenate solution are added dropwise over 30 minutes. 3.1 g of gaseous ethylene oxide are simultaneously introduced. After 45 minutes at 175°C, the solution turns brown and KF salt crystallizes out.
Further phenate solution (25 ml) is added slowly over 20 minutes and 3.1 g of gaseous ethylene oxide are introduced. Over the next 45 minutes the remaining 50 ml of phenate solution are added dropwise and a further 3.9 g of gaseous ethylene oxide are introduced. More ethylene oxide (1.9 g) is finally introduced over 60 minutes. The solution is then stirred for a further 2 hours at a temperature of 175°C. A colourless precipitate forms. The crude product is sublimed under reduced pressure (1 to 2 Torr) at a temperature of between 60 and 70°C.
Yield: 950 of theory Melting point: 78°C.
d) 3,4,5,6-Tetrafluorocatechol The ether is cleaved by placing 41.6 g of ground and dried aluminium chloride and 10.7 g of 5,6,?,8-tetrafluoro-(1,4)-benzodioxane in a glass flask equipped with a reflux condenser, under an argon atmosphere, and dissolving them in 350 ml of toluene. The solution is heated at a temperature of 80 to 110°C for two hours, with stirring, and then heated at a reflux temperature of 110 to 118°C for six hours, during which time the reaction solution turns black. After cooling, the reaction solution is poured onto 400 g of ice. The aqueous phase is retained for extraction. Toluene is distilled from the organic phase and the residual crystals are extracted with hot water. Both the aqueous phases, from the treatment with ice and the extraction with water, are combined and extracted three times with 150 ml of diethyl ether. The ether is distilled off to leave a green oily residue. At 50°C this gives a colourless liquid which vaporizes at 60 to 80°C under reduced pressure (14 - 16 Torr). The purified tetrafluorocatechol is obtained by sublimation at this temperature.
Yield: 63.5% of theory M.p.. 68°C.
e) Lithium bis[tetrafluoro-1,2-benzenediolato(2-)-0,0']borate 5.24 g of lithium tetramethanolatoborate and 13.5 g of tetrafluorocatechol are dissolved in 11 g of acetonitrile under an argon atmosphere. The solution is heated to 50°C and 10 g of acetonitrile are distilled off to leave a lilac-coloured viscous solution. Colourless crystals have formed after three days at 5°C. The yield can be increased by slowly heating the solution to 95°C under reduced pressure. This leaves 15.6 g of a solid brown crude product, which is recrystallized from a mixture consisting of 20 ml of benzene and 5 ml of acetonitrile. Colourless crystals are obtained which are filtered off and washed with benzene.
Yield: 30.8% of theory Decomposition point: 270°C.
Example 6 Lithium bis[2,3-naphthalenediolato(2-)-0,0']borate(1-) 90.0 g of 2,3-dihydroxynaphthalene, 17.4 g of boric acid, 11.8 g of lithium hydroxide monohydrate and 100 ml of water are placed in a glass flask. The mixture is heated to 55°C under an argon atmosphere. The addition of 300 ml of acetone gives a clear solution. Cooling to 5°C gives the product in the form of colourless crystals. The crystals are separated off and dried by slow heating from 10°C to 170°C
under reduced pressure. The product is purified by recrystallization twice from 200 and 160 ml of acetone. The product is then heated slowly to 170°C and kept at this temperature.
Yield: 28.60 of theory Decomposition point: 280°C.

Claims (14)

CLAIMS:

1. A process for preparation of lithium complex salts of the general formula (I) wherein R and R1 are identical or different, and are optionally joined together directly by a single or double bond:
wherein, when R and R1 are not joined together, each of R and R1 is an aromatic ring selected from phenyl, naphthyl, anthracenyl and phenanthrenyl, which is unsubstituted or monosubstituted to tetrasubstituted by A or Hal; and wherein, when R and R1 are joined together, R and R1 together form an aromatic ring selected from naphthyl, anthracenyl and phenanthrenyl, which is unsubstituted or monosubstituted to tetrasubstituted by A or Hal; or wherein, when R and R1 are not joined together, each of R and R1 is a heterocyclic aromatic ring selected from pyridyl, pyrrole, 1,2-diazine, 1,3-diazine and 1,4-diazine, which is unsubstituted or monosubstituted to trisubstituted by A or Hal; and wherein, when R and R1 are joined together, R and R1 together form a heterocyclic aromatic ring selected from pyrrole, 1,2-diazine and 1,3-diazine, which is unsubstituted or monosubstituted to trisubstituted by A or Hal;
Hal is F or Cl; and A is alkyl having 1 to 6 C atoms, which is unsubstituted or monohalogenated to tetrahalogenated; wherein a) a lithium tetraalcoholatoborate is taken up with an aprotic solvent, b) equimolar amounts of a hydroxyl compound or a 1:1 mixture of two different hydroxyl compounds, dissolved in an aprotic solvent, are added dropwise at a temperature of 10 to 60°C, with stirring, optionally under an inert gas atmosphere, and, optionally, the reaction mixture is subsequently stirred at a temperature of 60 to 90°C, c) optionally, alcohol formed during the reaction is slowly distilled off by application of a slight vacuum at a slightly elevated temperature, d) the product formed is crystallized out, optionally after concentration of the reaction mixture under vacuum at a temperature of 0 to 10°C, and, optionally, is separated off under an inert gas atmosphere, and e) the product which has been separated off is dried by slow heating.

2. A process according to claim 1, wherein tetrafluorocatechol is used as the hydroxyl compound for complexation; wherein the tetrafluorocatechol is prepared by:
a) reaction of pentafluorophenol with potassium carbonate in aqueous solution to give potassium pentafluorophenate;
b) etherification of the potassium pentafluorophenate prepared in a) with ethylene oxide in DMSO as solvent, under an inert gas atmosphere, to give a cyclic diether, 5,6,7,8-tetrafluoro-(1,4)-benzodioxane, or etherification of the potassium pentafluorophenate prepared in a) with 2-bromoethanol and subsequent cyclization to the cyclic diether in presence of potassium carbonate in DMF as solvent; and c) cleavage of the ether in presence of aluminium chloride with benzene as solvent, under an inert gas atmosphere.

3. A process according to claim 1, wherein mono-, di-or tricatechol, prepared in the same way as tetrafluorocatechol according to claim 2, is used as the hydroxyl compound for complexation.

4. A process according to claim 1, wherein the lithium tetraalcoholatoborate used is lithium tetramethanolatoborate, lithium tetraethanolatoborate or lithium tetrapropanolatoborate.

5. A process according to claim 1, wherein the aprotic solvent is selected from acetonitrile, acetone, nitromethane, dimethylformamide, dimethylacetamide and dimethyl sulfoxide.

6. A process according to claim 1, wherein equimolar amounts of the hydroxyl compound are added dropwise at room temperature.

7. A process according to claim 1, wherein the alcohol formed is distilled off under slight vacuum at a temperature of 50 to 60°C.

8. Use of a lithium complex salt of general formula (I) as defined in claim 1 as a conducting salt in an electrolyte for an electrochemical cell.

9. Use of a lithium complex salt of general formula (I) as defined in claim 1 as a conducting salt in an electrolyte for a battery.

10. Use of a lithium complex salt of general formula (I) as defined in claim 1 as a conducting salt in an electrolyte in a secondary lithium battery.

11. Use of a lithium complex salt of general formula (I) as defined in claim 1 in combination with one or more of another lithium salt and a borate complex in an electrolyte of a secondary lithium battery.

12. Use of a lithium complex salt of general formula (I) as defined in claim 1 in combination with one or more other lithium salts selected from lithium phenate and dilithium 2,2'-biphenyldiolate in an electrolyte of a secondary lithium battery.

13. Use of a lithium complex salt of general formula (I) as defined in claim 1 in a double-layer capacitor or a supercapacitor.

14. Use of a lithium complex salt of general formula (I) as defined in claim 1 in manufacture of a switchable window or display.