WO2014090877A1

WO2014090877A1 - (hetero)aromatic iso(thio)cyanates as redox shuttle additives for electrochemical cells

Info

Publication number: WO2014090877A1
Application number: PCT/EP2013/076234
Authority: WO
Inventors: Ulrich Wietelmann
Original assignee: Rockwood Lithium GmbH
Priority date: 2012-12-12
Filing date: 2013-12-11
Publication date: 2014-06-19
Also published as: DE102013225596A1

Abstract

The invention relates to a nonaqueous electrolyte for an electrochemical cell, comprising a redox-active additive, in which the additive corresponds to a structure of the general formula A or B, with X = O, S or Se; Y = N or C; Z = O, S or NR (R = alkyl having 1-8 carbon atoms): R¹, R², R³ = independently NCS, NCO, alkyl (1 to 8 carbon atoms), perfluoroalkyl (C_nF2_n+1 with n = 1-8), aryl, F or Cl, CN, OR (R = alkyl having 1-8 carbon atoms, may also contain further alkoxy groups), NR₂ (R = alkyl having 1-8 carbon atoms); R⁴ = H, NCS, NCO, alkyl (1 to 8 carbon atoms), perfluoroalkyl (C_nF_2n+1 with n = 1-8), aryl, F or Cl, CN, OR (R = alkyl having 1 to 8 carbon atoms, may also contain further alkoxy groups), NR² (R = alkyl having 1-8 carbon atoms); R⁵ = only when Y = C; H, NCS, NCO, alkyl (1 to 8 carbon atoms), perfluoroalkyl (C_nF2_n+1 with n = 1-8), aryl, F or Cl, CN, OR (R = alkyl having 1 to 8 carbon atoms, may also contain further alkoxy groups), NR₂(R = alkyl having 1-8 carbon atoms), and it has at least one isocyanate or/and isothiocyanate or/and isoselenocyanate group, and to electrochemical cells comprising these redox-active additives.

Description

(Hetero) Aromatic iso (thio) cyanates as redox shuttle additives for galvanic cells

The invention relates to a non-aqueous electrolyte of a galvanic cell containing a redox-active additive and galvanic cells containing these redox-active additives.

The tuning of a lithium-ion battery system, i. The precise balancing of the electrode masses is very complex and has hitherto mostly been purely empirical. In order to ensure a long service life and safety of lithium-ion batteries, overcharging must be reliably avoided. When using lithium transition metal oxides having a layer structure as cathode materials, delignified, very reactive Co (IV) or Ni (IV) compounds which react exothermically with the organic electrolyte are formed when they are overcharged. As a result, the temperature may rise so high that volatile components and formed gaseous decomposition products increase the internal pressure to such an extent that the battery opens and flammable and / or toxic components leak out. Very often, these gases also ignite spontaneously.

According to the state of the art, overcharging is prevented by a complex electronic battery management system (BMS). Among other things, this system measures the charge state of each individual cell and controls the charging process. In particular, for large-sized batteries with a correspondingly high number of individual cells (typical applications both mobile, ie for electric traction or stationary, so for power back-up) such systems are very complex and expensive. Therefore, an inherent "chemical" overcharge protection is sought, for which redox shuttle additives "RSA") are in principle suitable. With the help of these materials, above all, the safety properties, but also indirectly the performance and the service life of battery cells are to be improved. The battery assembly of several single cells can be simplified in case of success, since the electronic single cell monitoring (the so-called battery management) can be largely replaced by an addition in the electrolyte. The redox-active additive thus provides intrinsic protection against uncontrollable charge states. Existing investigations are predominantly limited to battery cells with relatively low terminal voltage, ie cells with charging end potentials <approx. Li / Li ⁺ , for example those with LiFePO ₄ as the cathode material. For this battery type, aromatic and heteroaromatic compounds have been tested for their use as redox shuttle additives (JRDahn et al., J. Electrochem. Soc 153 (2) A445-9 (2006)). Only a few proved to be at least partially reversible, for example 2,5-di-tert-butyl-1,4-dimethoxybenzene, 3-chloro-10-ethylphenothiazine, 10-methylphenothiazine, 4-fluoro-1,2-dimethoxybenzene and to a limited extent anisole (JRDahn, et al., J. Electrochem Soc 153 (10) A1922-8 (2006)). Furthermore, 2,2,6,6-tetramethylpiperidinyloxyl ("TEMPO") (JR Dahn, J. Electrochem, Soc., 153 (2006) A1800) was investigated for use in lithium batteries with LiFePO ₄ cathode Usually an oxidation potential (E _ox ) <4 V on:

For the z.Zt. Conventional cathode materials with layered or spinel structure, the end of charge potentials of about 4.2 - 4.3 V, there are, however, only a very few studies and (successfully tested in the laboratory) compounds. These are, for example, prohibitively expensive perfluorinated polyborate clusters (EP 1768210A1) or perfluorinated arylborates (US 2007 / 0178370A1 and Z. Chen, Y. Qin, K. Amine, Electrochim, Acta 54 (2009) 5605-13). Arylfluoroborane Perfluoroborate Clusters

₂ [tJ ₁₂ i- ₂ . _x Ul _x J

E Ό, Χ 4.4 V 4.3 - 4.7 V

Recent research activities are in the field of dialkoxyphenyl compounds. Quantum-chemical investigations of the position-dependent electron density by density functional theory (DFT) on 1,4-dimethoxybenzenes were carried out by Weishan Li (W. Li, J. Phys. Chem. A 201 1, 1 15, 4988-94). The result is that the introduction of electron-donating or withdrawing substituents allows the oxidation potential to be varied between 3.8 and 5.9 V vs Li / Li ⁺ . In order to increase the cycle stability, the introduction of sterically demanding residues (mostly terf-butyl) is absolutely necessary. For example, 3M has been offering the compound 1 (2,5-di-tert-butyl-1,4-dimethoxybenzene, "DDB") developed by J. Dahn (A. Xiao, 29 ^th Intl. Batt. Sem Exhib. March 12-15, Ft. Lauderdale, FLO, 2012).

2 3 4a (H) 4b (Br)

DBB 1 has an oxidation potential of about 3.9 V and therefore, as mentioned above, is limited to the use of the cathode material lithium iron phosphate (JRDahn, J. E. Electrochem, Soc., 156 (4) A309-12 (2009)). Disadvantage of the compound 1 is furthermore the low solubility in common battery electrolytes. By introducing glycol ether moieties as in 2 (2,5-di-tert-butyl-1,4-ib / s (2-methoxyethoxy) benzene, "DBBB"), solubility increases significantly (to 0.4 M im Compared to <0.008M for 1_). Since the oxidation potential of 2 versus 1 remains unchanged at about 3.9 V, this compound is also only suitable for metal phosphate cathodes (K. Amine, Energy Environs., 2012, 5, 824-7, US201 1 / 0294003A1). For MCMB / LFP button cells, reversibility was demonstrated for 180 cycles with 100% overload at C / 2.

Cyclic 1,3-benzodioxanes are slightly more resistant to oxidation than the noncyclic ones. Thus, for 3 (4,6-di-tert-butyl-1,3-benzodioxane, "DBBD1"), which is not reversible, E _ox = 4.1 V is given (K. Amine, J. Power Sources 196 (201 1) 1530-6; US201 1 / 0294017A1) Better results are obtained for 1,4-benzodioxanes Compounds 4a and 4b are found to be highly reversible in overcharge tests at oxidation potentials of 4.2 and 4.7 V, respectively however, the high expense of introducing the two tert-butyl groups and the presence of a halide function in case 4b, halides can even cause corrosion of the generally used cathodic current collector made of metallic aluminum, even in trace amounts.

A new class of compounds has been proposed by Argonne National Labs: Aromatic organophosphorus compounds such as tetraethyl-2,5-diterf-butyl-1,4-phenylenediphosphate 5 (US201 1 / 0294018A1):

5 ( "DBDPB") shows a very high lying oxidation potential from 4.7 to 5 V. The reversible overcharge protection was for _Lii, _2Nio, i ₅ _Coo, iMno, 55O ₂ / MCMB cells (300% overload, C / 10) demonstrated However, the disadvantage of this compound is the high molar mass (eg 494 g / mol for 5), which corresponds to a molar concentration of about 0.1 M at conventional additive concentrations of up to 5%, owing to this relatively low concentration and molecular size connected slow Diffusion rate, the overload protection is therefore limited to low current densities. According to US201 1 / 0294018A1, the overcharge protection is consequently limited to very low charge / discharge rates of C / 10, ie 10-hour cycles.

The use of organic isocyanates as additives for non-aqueous electrolytes is known. Thus, for example, by adding 0.5-10% by weight of phenyl isocyanate, the increase of water and HF in LiPF ₆ -based electrolytes is avoided, resulting in improved chemical and electrochemical stability. The organic isocyanate is added to a nonaqueous electrolyte for an electrochemical cell comprising at least one fluorine-containing conductive salt in an amount effective to reduce the water content of the electrolyte (DE10042149A1). Non-aqueous electrolyte solutions containing a lithium salt, a cyclic carbonate, a linear carbonate and an isocyanate-based additive of the formula R ¹ -N = C = O, wherein R ^{1 is} a linear or branched alkyl group or an aromatic group of the general formula

wherein R ² and R ^{3 may be the} same or different and may be positioned at any position of the carbons 2, 2 ', 3, 3' on the benzyl ring and may be hydrogen atoms, halogen atoms, isocyanate groups, ether groups, ester groups or alkyl groups are known (US 6,905,762 B1). The positive effects of phenylisocyanate and 4-fluoro-isocyanate to reduce irreversible capacities and solid electrolyte interface ("SEI" formation) could be demonstrated in lithium / graphite half-cells (SS Zhang, J. Power Sources 163 (2006) 567 The effects of a number of other aromatic monoisocyanates on the morphology of SEI formation of MCMB electrodes have been extensively studied (Korepp, C. et al., J. Power Sources 174 (2007) 387-93). that the isocyanates in the SEI formation electrochemically polymerize, so they are decomposed. The object of the invention has been found to overcome the disadvantages of the prior art.

In particular, it should indicate overcharge tolerant electrolyte formulations containing redox additives with an oxidation potential of at least 3.5 V, preferably> 4.2 V, which

• stable to decomposition, i. are reversibly effective,

The molar masses preferably have <300 g / mol and can be prepared with little expense,

• in aprotic solvents, e.g. Carbonic acid esters in concentrations of> 0.1 M are soluble.

The object is achieved by a non-aqueous electrolyte of a galvanic cell containing a redox-active additive, wherein the additive of a structure of the general formulas A or B

A B with

X = O, S or Se

Y = N or C; Z = O, S or NR (R = alkyl having 1 -8 C atoms)

R ¹ , R ² , R ³ = independently of one another NCS, NCO, alkyl (1 to 8 C atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR ( R = alkyl having 1 to 8 C atoms, may also contain further alkoxy groups), NR ₂ (R = alkyl having 1 -8 C atoms)

R ⁴ = H, NCS, NCO, alkyl (1 to 8 C-atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl with 1 to 8 C atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl with 1 -8 C atoms) R ⁵ = only for Y = C; H, NCS, NCO, alkyl (1 to 8 C atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl having 1 to 8 C atoms) Atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl having 1 -8 carbon atoms) and at least one isocyanate and / or isothiocyanate and / or Isoselenocyanatgruppe has.

In a preferred embodiment of the invention, the aromatic or heteroaromatic redox-active additive contains at least two NCX groups (with X = O or S) and has one of the following structures:

c D

X ¹ , X ² = independently of one another O, S or Se

Y = N or C; Z = O, S or NR (R = alkyl having 1 -8 C atoms)

R ¹ , R ² = independently NCS, NCO, alkyl (1 to 8 C-atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl with 1 to 8 carbon atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl with 1 -8 C atoms)

R ³ = H, NCS, NCO, alkyl (1 to 8 C-atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl with 1 to 8 C atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl with 1 -8 C atoms)

R ⁴ = only for Y = C; H, NCS, NCO, alkyl (1 to 8 C atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl having 1 to 8 C atoms) Atoms, may also contain other alkoxy groups) for Y = C.

In a particularly preferred embodiment, the aromatic redox-active additive contains two NCX groups and all substituents R ¹ to R ⁴ are not H, ie the aromatic or heteroaromatic ring is completely substituted. Very particular preference is given to the structures E and F:

X ¹ , X ² = independently of one another O, S or Se

It has surprisingly been found that the additives according to the invention can be reversibly oxidized and reduced. This is in contrast to the known aromatic iso (thio) cyanate compounds, which are not stable to decomposition, but which decompose irreversibly when an electrochemical potential is applied outside its stability range.

The subject invention is explained with reference to the inventive additive F and G of a comparative compound H not according to the invention.

Show it:

Fig. 1: Cyclic voltammogram of 0.1 mol / LG in 1 M LiPF ₆ / EC-DMC (1: 1 by weight) on a glassy carbon electrode. Potential feed rate: 100 mV / s

Fig. 2: Cyclic voltammogram of 0.1 mol / LH in 1 M LiPF ₆ / EC-DMC (1: 1 by weight) on a glassy carbon electrode, potential feed rate: 10 mV / s

Fig. 3: Galvanostatic overload test of a LiFePO ₄ / Li cell with 0.1 MW in 1 M LiPF ₆ / EC-DMC (1: 1 by weight). Flow rate: C / 5. 100% each

Overload

Fig. 4: Galvanostatic overload test of a LiMn ₂ O ₄ / Li cell with 0.1 MW in 1 M

LiPF ₆ / EC-DMC (1: 1 by weight). Flow rate: C / 5. 100% each

Overload Fig. 5: DSC test (RADEX) of LiPF ₆ 5% F electrolyte solution

Fig. 6: DSC test (RADEX) of LiPF ₆ -electrolyte solution without inventive

additive

Fig. 7: Cyclic voltammogram of 0.01 mol / LF in 1 M LiPF ₆ / EC-DMC (1: 1 by weight) on a glassy carbon electrode, potential feed rate: 100 mV / s.

Thus, while compound G can be reversibly oxidized and reduced with a first oxidation potential of 4.5 V, the non-inventive compound H is irreversibly oxidized at 4.5 V as well.

The redox-active additives according to the invention can be used as overcharge protection in all galvanic cells which use non-aqueous electrolytes. These are in particular all types of lithium batteries, namely lithium-ion batteries, lithium-metal or alloy-anode lithium batteries and lithium batteries with conversion cathode materials.

The electrolyte in a galvanic cell containing a redox-active additive according to the invention can be present in gelatinous or preferably in liquid form. In addition to the redox-active additives of the invention, organic, aprotic solvents (carbonic acid esters (dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, propylene carbonate, ethylene carbonate), cyclic ethers such as tetrahydropyran or tetrahydrofuran, polyethers such as 1, 2-dimethoxyethane or diethylene glycol dimethyl ether, furthermore nitriles such as acetonitrile, adiponitrile , Malononitrile, glutaronitrile and lactones such as γ-butyrolactone), ionic liquids (eg imidazolium salts) and lithium secondary salts (eg LiPF ₆ , lithium fluoroalkyl phosphates, LiBF, imide salts (eg LiN (SO ₂ CF ₃ ) ₂ ), LiOSO ₂ CF ₃ , methide salts (eg LiC (SO ₂ CF ₃ ) ₃ ), LiCIO ₄ , lithium chelatoborates (eg LiBOB), lithium fluorochelato borates (eg LiC ₂ O ₄ BF ₂ ), lithium chelatophosphates (eg LiTOP) and

Lithium fluorochelatophosphates (eg Li (C ₂ O ₄ ) ₂ PF ₂ ), lithium halides (LiCl, LiBr, Lil) and further stabilizing (eg SEI-forming) additives (eg vinylene carbonate) and polar polymers (eg polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride) in any mixture.

Preferred cathode materials include lithiated metal insert cathode materials, preferably layered materials such as UCO 2, LiNiO 2, Li (Ni, Mn, Co) O ₂ , LiNio _, 8oCoo, i5Alo, osO20 spinel structured materials such as LiMn ₂ O ₄ and LiNio _.5 Mni. ₅ O ₄ or those with olivine structure such as LiFePO ₄ and LiMnPO ₄ . It can also nichtlithiierte Metallinsertionsverbindungen as electrolytic manganese dioxide (MnO2) or vanadium oxide (V2O3) or conversion cathode materials such as metal fluorides (for example, NiF _2, CoF _2, FeF _2, FeF ₃₎ or Metalloxyfluoride (for example, BiO _x F _3- 2x, FEOF) are used , For the purposes of the invention it is also possible to use any mixtures of different cathode materials.

The anode material is graphite, Lithiumtitanspinell, (in part) are lithiated transition metal nitrides (eg Li ₂ _{6Coo, 4} N, _{LiCuO, 4} N) of lithium metal, lithium alloys or conversion anode materials such as finely divided magnesium hydride.

The concentration of the redox-active additive according to the invention in the electrolyte is at least 0.01 mol / l, preferably at least 0.05 mol / l and particularly preferably at least 0.1 mol / l.

The actual selection of a redox-active additive according to the invention depends on the electrodes installed in the galvanic element, in particular on the redox potential of the cathode material used. The oxidation potential of the additive according to the invention is generally higher than that of the cathode material. It is at least 0.1 V, preferably at least 0.2 V and at most 0.8 V, preferably at most 0.6 V above that of the cathode material used. Example 1: Preparation of the additive 1, 4-diisocyanato-2,3,5,6-tetramethylbenzene F according to the invention

Compound F can be prepared in a one-pot synthesis from commercially available 2,3,5,6-tetramethyl-1,4-phenylenediamine (e.g., Aldrich Best. No. 523755). It has a molecular weight of only 246 g / mol and can be prepared as follows:

In a dry, argon-rinsed dispensing vessel equipped with a magnetic stir bar and a rubber sealing disc di-tert-butyl-dicarbonate (52.6 g, 241 mmol, 2.2 equivalents) dissolved in 600 ml of dry acetonitrile presented. After adding 4-dimethylaminopyridine (268 mg, 2.2 mmol, 0.02 equiv.) To the reaction mixture, it was stirred at 25 ° C for 5 minutes. Subsequently, 2,3,5,6-tetramethyl-1, 4-phenylenediamine (18.9 g, 1 10 mmol, 1 equivalent) dissolved in 300 ml of dry acetonitrile was added and stirred at 25 ° C for a further 15 minutes. The reaction mixture was extracted 6 times with iso-hexane. The combined isoHexan phases were dried over MgSO ₄ and concentrated by vacuum evaporation. The residue was recrystallized from iso-hexane to give 1,4-diisocyanato-2,3,5,6-tetramethylbenzene as a white solid (12.7 g, 59 mmol, 55% yield).

Melting point: 1 14.8 - 1 15.5 ° C

¹ H NMR (300 MHz, CDCl ₃ ) δ (ppm): 2.27 (s, 12H)

¹³ C NMR (75 MHz, CDCl ₃ ) δ (ppm): 129.7, 128.9, 123.4, 15.8

MS (70 eV, El) m / z (%): 216 (M ⁺ , 100); 201 (27), 188 (15), 174 (14), 161 (14), 145 (11), 77 (10), 53 (12)

IR (ATR) (cm ^"1 ): 3004, 2926, 2870, 2278, 1720, 1510, 1450, 1384, 1356, 1222, 1024, 854, 764

HRMS (El): m / z calculated for C12H12N2O2 (216.0899): 216.0891 (M ⁺ ) Example 2: Determination of electrochemical stability and behavior under charging conditions of 5-chloro-2,4-dimethoxyphenylisocyanate G

The electrochemical stability and the reversibility of the oxidation step were determined by cyclic voltammetry. For this purpose, 0.1 M 5-chloro-2,4-dimethoxyphenyl isocyanate in 1 M LiPF ₆ / EC-DMC (1: 1 by weight) on a glassy carbon electrode (with a surface of 0.196 cm ² ) at a potential feed rate of 100 mV / s examined. The first oxidation step of the substance starts at about 4.2 V vs. Li / Li ⁺ . During the backward scan, a corresponding reductive peak is observed, and the subsequent cycles are nearly congruent, ie the oxidation / reduction is highly reversible.

The behavior under overcharge conditions was determined in LiFePO ₄ / Li and LiMn ₂ O ₄ / Li cells by galvanostatic measurements at a current rate of C / 5. Figure 3 shows the results for the LiFePO ₄ / Li cell. The regular charge of LiFePO ₄ occurs at about 3.45 V vs. Li / Li ⁺ . After less than 5 hours, the cathode material is fully charged and the potential rises steeply during the subsequent overcharge, at around 4.3V vs. Li / Li ⁺ into a new potential plateau, which corresponds to the reversible oxidation of 5-chloro-2,4-dimethoxyphenyl isocyanate. After 10 hours (or 100% overcharge) the cell is discharged. The potential plateau at approx. 3.4 V vs. Li / Li corresponds to the regular discharge of LiFePO ₄ , which can be fully discharged again. The second cycle behaves like the 1. Cycle, suggesting that the cell had not suffered from the overcharge, and consequently 5-chloro-2,4-dimethoxyphenyl isocyanate was active as a reversible overcharge protection.

Similar behavior is observed for the LiMn ₂ O ₄ / Li cell in Figure 4. The two plateaus at about 4.0 and 4.15 V vs. Li / Li ⁺ correspond to the regular charge of LiMn ₂ O ₄ . Under overcharge conditions, 5-chloro-2,4-dimethoxyphenyl isocyanate is found at a potential of approximately 4.3V. Li / Li ⁺ active. After 100% overload, the LiMn ₂ O ₄ can be discharged regularly. Here, too, 5-chloro-2,4-dimethoxyphenylisocyanate acts as a reversible overload protection. Example 3: Stability of a LiPF ₆ -based electrolytic solution containing 5% 1,1,4-diisocyanato-2,3,5,6-tetramethylbenzene F

In an argon-filled glove box, 0.98 g of a 1 1% strength LiPF ₆ solution in ethylene carbonate / ethyl methyl carbonate (weight ratio 1: 1) containing 5% by weight of F were introduced into a steel autoclave of the RADEX system from Systag ( Switzerland) filled and hermetically sealed. This mixture was then heated at a heating rate of 45 K / h to a final temperature of 270 ° C and the thermal events were recorded (Figure 5).

One recognizes the beginning of a weak exotherm at a temperature of about 200 ° C. At 200 ° C, the pressure is about 6 bar.

Example 4 Determination of the electrochemical stability of 1,4-diisocyanato-2,3,5,6-tetramethylbenzene F

The electrochemical stability and the reversibility of the oxidation step were determined by cyclic voltammetry. To this end, 0.01 M of 1,4-diisocyanato-2, 3,5,6-tetramethylbenzene in 1 M LiPF ₆ / EC-DMC (1: 1 by weight) was added to a glassy carbon electrode (having a surface area of 0.196 cm ² ) a potential feed rate of 100 mV / s examined. The first oxidation step of the substance starts at approx. 4.5 V vs. Li / Li ⁺ . During the backward scan, a corresponding reductive peak is observed, ie the oxidation / reduction is reversible (see Fig. 7).

Comparative Example: Stability of a LiPF ₆ -based electrolytic solution containing 0.1 mol / L of 4-methoxyphenylisocyanate H

The electrochemical stability and the reversibility of the oxidation step were determined by cyclic voltammetry. For this, 0.1 mol / L of 4-methoxyphenyl isocyanate in 1 mol / L of LiPF ₆ / EC-DMC (1: 1 by weight) was tested on a glassy carbon electrode (having a surface area of 0.196 cm ² ) at a potential feed rate of 100 mV / s , The first oxidation step of the substance starts at about 4.3 V vs. Li / Li ⁺ . During the backward scan no corresponding reductive peak is observed, ie the oxidation is irreversible (s, Fig. 2). Comparative Example 2: Stability of a LiPF ₆ -based electrolytic solution without inventive additive

In an argon-filled glove box 0.76 g of a 1 1% LiPF ₆ solution in ethylene carbonate / ethyl methyl carbonate (weight ratio 1: 1) in a steel autoclave of the RADEX system of Systag (Switzerland) filled and hermetically sealed. This mixture was then heated at a heating rate of 45 K / h to a final temperature of 270 ° C and the thermal events as well as the pressure were recorded (Figure 6).

One recognizes the beginning of a weak exotherm at a temperature of about 180 ° C. At 200 ° C, the pressure is about 10 bar.

The electrolyte solution according to the invention from Example 3 shows decomposition phenomena only at higher temperatures, i. the additive F stabilizes the electrolyte solution.

Claims

Non-aqueous electrolyte of a galvanic cell containing a redox-active additive, characterized in that the additive of a structure of the general formulas A or B

A B with

X = O, S or Se

Y = N or C; Z = O, S or NR (R = alkyl having 1 -8 C atoms)

R ⁴ = H, NCS, NCO, alkyl (1 to 8 C-atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl with 1 to 8 C atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl with 1 -8 C atoms)

R ⁵ = only for Y = C; H, NCS, NCO, alkyl (1 to 8 C atoms), perfluoroalkyl (C _n F _{2n +} i with n = 1 -8), aryl, F or Cl, CN, OR (R = alkyl having 1 to 8 C atoms) Atoms, may also contain other alkoxy groups), NR ₂ (R = alkyl having 1 -8 carbon atoms) corresponds and it has at least one isocyanate and / or isothiocyanate and / or Isoselenocyanatgruppe.

2. Non-aqueous electrolyte according to claim 1, characterized in that the redox-active additive contains at least two isocyanate and / or isothiocyanate groups and / or isoselenocyanate group.

3. A non-aqueous electrolyte according to claim 1 or 2, characterized in that the redox-active additive contains at least two isocyanate and / or isothiocyanate groups and all substituents present R ¹ to R ^{4 are} not H, ie that the aromatic or heteroaromatic ring is fully substituted.

4. Non-aqueous electrolyte according to claim 1 to 3, characterized in that it contains 1, 4-diisocyanato-2,3,5,6-tetramethylbenzene.

5. Non-aqueous electrolyte according to claim 1 to 4, characterized in that it is in gel or liquid form.

6. Non-aqueous electrolyte according to claim 1 to 5, characterized in that the redox-active additive in a concentration of at least 0.01 mol / l, preferably at least 0.05 mol / l and particularly preferably at least 0.1 mol / l is included.

7. A non-aqueous electrolyte according to claim 1 to 6, characterized in that it contains organic, aprotic solvent selected from the group consisting of: carbonic acid esters, cyclic ethers, polyethers, nitriles, lactones and ionic liquids, lithium salts and the or the redox-active additives.

8. A non-aqueous electrolyte according to claim 7, characterized in that it dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, tetrahydropyran, tetrahydrofuran, 1, 2-dimethoxyethane, diethylene glycol dimethyl ether, acetonitrile, adiponitrile, malononitrile, glutaronitrile, γ-butyrolactone or mixtures thereof imidazolium salts , LiPF ₆ , Lithiumfluoroalkylphosphate, LiBF, Imidsalze, L1OSO2CF3, Methidesalze, LiCIO ₄ , Lithiumchelatoborate, Lithiumfluorochelatoborate, Lithiumchelatophosphate, Lithiumfluorochelatophosphate and / or lithium halides and optionally further stabilizing additives and polar polymers.

9. Galvanic element, characterized in that it contains a nonaqueous electrolyte with a redox-active additive of the general formulas A or B.

10. Galvanic element according to claim 9, characterized in that it contains as the cathode material lithiierte layer or spinellstrukturierte metal insertion cathode materials, those with olivine structure, non-lithiated metal insertion compounds or conversion cathode materials.

1 1. Galvanic element according to claim 10, characterized in that it is a cathode material selected from the group consisting of: UC0O2, LiNiO2, Li (Ni, Mn, Co) O ₂ , LiNio, 8oCo ₀ , i5Alo, o5O ₂ , LiMn ₂ O ₄ , LiNio.5Mn 1.5O4, LiFePO _4, LiMnPO _4, electrolytic manganese dioxide, vanadium oxides, NiF _2, CoF _2, FeF _2, FeF _3, BiO _x F x _3-2, fEOF contains.

12. Galvanic element according to claim 9, characterized in that contains as the anode material graphite, lithium titanium spinel, (partially) lithiated transition metal nitrides lithium metal, lithium alloys or conversion anode materials.

13. Galvanic element according to claim 12, characterized in that it contains an anode material selected from the group consisting of: Li _{2 6} Coo, ₄ N, LiCuo, ₄ N or finely divided magnesium hydride.

14. Galvanic element with non-aqueous electrolyte acc. Claims 8-10 characterized in that the oxidation potential of the additive according to the invention is at least 0.1 V, preferably at least 0.2 V and preferably at most 0.8 V above that of the cathode material used.