ELIMINATING VOLTAGE DELAY AND STABILIZING IMPEDANCE BY ELECTROLYTE ADDITIVES IN ALKALI METAL ELECTROCHEMICAL CELLS

Abstract

The present invention relates to a primary cell, comprising an alkali metal as the active electrode material, in particular as the active anode material, and an electrolyte comprising a boron compound, wherein the boron compound is compound according to formula (1), (2), (3), (4), (7) or (8):

##STR00001##

Claims

1. A primary cell, comprising: an alkali metal as the active electrode material, particularly as the active anode material, and an electrolyte comprising a boron compound, wherein the boron compound is a compound according to formula (1), (2), (3), (4), (7) or (8): ##STR00004## wherein each of R1, R2, R3, R4 and R5 independent from one another is selected from the group consisting of hydrogen, alkyl, alkenyl, cycloalkyl, thioether, heterocyclic compounds, aryl and heteroaryl, wherein R1, R2, R3, R4 or R5 is not thiophene.

2. The primary cell according to claim 1, wherein each of R1, R2, R3, R4 and R5 independent from one another is unsubstituted or is monosubstituted or multiple substituted with at least one substituent selected from the group consisting of: alkyl, fluoroalkyl, alkoxy, carbonyl, carboxyl, thiol, thio alkoxide, aryl, ether, thioether, excluding thiophene, nitro, cyano, amino, azido, amidino, hydrazino, hydrazono, carbamoyl, sulfo, sulfamoyl, sulfonylamino, alkylaminosulfonyl, alkylsulfonylamino and/or halogens, preferably selected from the group consisting of halogen, fluoroalkyl and cyano, wherein R1, R2, R3, R4 or R5 is not thiophene.

3. The primary cell according to claim 1, wherein the boron compound is: a compound according to formula (1), where R1 is an alkyl, particularly a C.sub.1 to C.sub.6 alkyl, particularly methyl, cyclopropyl or cyclohexyl, or an aryl, in particular a phenyl, a benzyl or a naphthyl, which is unsubstituted or substituted with one or more C.sub.1 to C.sub.4 alkyl, —F, —Cl, —Br, —I, —CN, —CF.sub.3 or —OCF.sub.3, and each of R2 to R5 independent from one another is a C.sub.1 C.sub.4 alkyl; a compound according to formula (2), where each of R1 to R5 independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (3), where R1 is an alkyl, an alkenyl, particularly an allyl or an aryl, particularly a benzyl, phenyl, or benzoate, which is unsubstituted, or substituted with a C.sub.1 to C.sub.4 alkyl, —F, —Cl, —Br, —I, —CN, —CF.sub.3 or —OCF.sub.3 or a compound according to formula (3), and each of R2 and R3 independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (4), where each of R1, R2 and R3, independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (7), where each of R1 to R3 independent from one another is an alkyl, particularly a C.sub.1 to C.sub.4 alkyl, particularly methyl, or an aryl, particularly a phenyl, which is unsubstituted or substituted with one or more —F, —Cl, —Br, —I, —CN, —CF R3 —OCF.sub.3; or a compound according to formula (8), where each of R1 to R3 independent from one another is a C.sub.1 to C.sub.4 alkyl.

4. The primary cell according to claim 1, wherein the boron compound is: 4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane; 2-(bromomethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-cyclopropyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-cyclohexyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(naphthalene-1-ylmethyl)-1,3,2-dioxaborolane; 2-benzyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-phenyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(1-naphthyl)-1,3,2-dioxaborolane; 2-(4-chlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(4-fluorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane; 2-(4-bromophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(3,5-dichlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(2-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)benzonitrile; 4,4,5,5-tetramethyl-2-[3-(trifluoromethoxy)phenyl]-1,3,2-dioxaborolane; 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)aniline; 2-[2-(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-[3,5-bis(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-fluoro-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)benzonitrile, 2-ethoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 2-allyl-5,5-dimethyl-1,3,2-dioxaborinane; 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane; 2,2′-(1,4-phenylene)bis[5,5-dimethyl-1,3,2-dioxaborinane]; 2-(2-chlorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 2-(1,3,2-dioxaborinane-2-yl)benzonitrile; 2-(2-fluorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 2-(4-fluorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 4,4′-bis(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)biphenyl; ethyl 2-(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)benzoate; 2-(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)-6-(trifluoromethyl)benzonitrile; 4-(trifluoromethyl)-2-(5,5-dinethyl-1,3,2-dioxaborinane-2-yl)benzonitrile, 2-isopropoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; 2-ethoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; 2-methoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; trimethylboroxine; 2,4,6-triphenylboroxine, 2,4,6-tris(4-fluorophenyl)boroxine; 2,4,6-tris(3,4,5-trifluorophenyl)boroxine; 2,4,6-tris(3.4-fluorophenyl)boroxine; 2,4,6-tris(3,4-dichlorophenyl)boroxine, or 2,4,6-trimethoxyboroxine.

5. The primary cell according to claim 1, wherein the boron compound is present in the electrolyte in a concentration in the range of 0.001 mol*l.sup.−1 to 0.5 mol*l.sup.−1.

6. The primary cell according to a claim 1, wherein the alkali metal is lithium, and the primary cell is a lithium battery.

7. The primary cell according to claim 1, wherein the electrolyte is a non-aqueous electrolyte.

8. The primary cell according to claim 7, wherein the non-aqueous electrolyte, comprises a first solvent, which is selected from the group consisting of an ester, an ether, a dialkyl carbonate and a mixture thereof, in particular tetrahydrofuran, methyl acetate, diglyme, triglyme, tetraglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy, 2-methoxyethane, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or a mixture thereof, and comprises a second solvent, which is selected from the group consisting of a cyclic carbonate, a cyclic ester, a cyclic amide and a mixture thereof, in particular propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, N-methylpyrrolidinone or a mixture thereof, or a polar non-aqueous solvent such as acetonitrile, dimethylsulfoxide, dimethylformamide, dimethylacetamide, or a mixture thereof.

9. The primary cell according to claim 1, wherein the electrolyte comprises an anhydrous alkali salt, in particular an anhydrous lithium salt, preferably LiClO.sub.4, LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6, LiSbF.sub.6, LiClO.sub.4, LiAlCl.sub.4, LiGaCl.sub.4, LiC(SO.sub.2CF.sub.3).sub.3, LiN(SO.sub.2CF.sub.3).sub.2, LiSCN, LiO.sub.3SCF.sub.2CF.sub.3, LiC.sub.6F.sub.5SO.sub.3, LiO.sub.2CF.sub.3, LiSO.sub.3F, LiB(C.sub.6H.sub.5).sub.4, LiCF.sub.3SO.sub.3 or mixtures thereof.

10. The primary cell according to claim 1, furthermore comprising a carbon monofluoride as the active electrode material, particularly as the active cathode material.

11. Use of a boron compound as the electrolyte additive of a primary cell comprising an alkali metal as the active electrode material, wherein the boron compound is a compound according to formula (1), (2), (3), (4), (7) or (8) ##STR00005## wherein each of R1, R2, R3, R4 and R5 independent from one another is selected from the group consisting of hydrogen, alkyl, alkene, cycloalkyl, thioether, heterocyclic compounds, aryl and heteroaryl, wherein R1, R2, R3, R4 or R5 is not thiophene.

12. Use of a boron compound as an electrolyte additive of a primary cell comprising an alkali metal as the active electrode material according to claim 11, wherein each of R1, R2, R3, R4 and R5 independent from one another is unsubstituted or is monosubstituted or multiple substituted with at least one substituent selected from the group consisting of: alkyl, fluoroalkyl, alkoxy, carbonyl, carboxyl, thiol, thio alkoxide, aromatic compound, ether, thioether, nitro, cyano, amino, azido, amidino, hydrazino, hydrazono, carbamoyl, sulfo, sulfamoyl, sulfonylamino, alkylaminosulfonyl, alkylsulfonylamino and/or halogens, wherein R1, R2, R3, R4 or R5 is not thiophene.

13. Use of a boron compound as an electrolyte additive of a primary cell comprising an alkali metal as the active electrode material according to claim 11, wherein the boron compound is: a compound according to formula (1), where R1 is an alkyl, particularly a C.sub.1 to C.sub.6 alkyl, particularly methyl, cyclopropyl or cyclohexyl, or an aryl, particularly a phenyl, a benzyl or a naphthyl, which is unsubstituted or substituted with one or more C.sub.1 to C.sub.4 alkyl, —F, —Cl, —Br, —I, —CN, —CF.sub.3 or —OCF.sub.3, and each of R2 to R5 independent from one another is a C.sub.1 C.sub.4 alkyl; a compound according to formula (2), where each of R1 to R5 independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (3), where R1 is an alkyl, an alkenyl, particularly an allyl or an aryl, particularly a benzyl, phenyl, or benzoate, which is unsubstituted, or substituted with one or more C.sub.1 to C.sub.4 alkyl, —F, —Cl, —Br, —I, —CN, —CF.sub.3 or —OCF, and each of R2 and R3 independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (4), where each of R1, R2 and R3 independent from one another is a C.sub.1 to C.sub.4 alkyl; a compound according to formula (7), where each of R1 to R3 independent from one another is an alkyl, in particular a C.sub.1 to C.sub.4 alkyl, particularly methyl, or an aryl, particularly a phenyl, which is unsubstituted or substituted with one or more —F, —Cl, —Br, —I, —CN, —CF R3 —OCF.sub.3; or a compound according to formula (8), where each of R1 to R3 independent from one another is a C.sub.1 to C.sub.4 alkyl.

14. Use of a boron compound as an electrolyte additive of a primary cell comprising an alkali metal as the active electrode material according to claim 11, wherein the boron compound is: 4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane; 2-(bromomethyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-cyclopropyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-cyclohexyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(naphthalene-1-ylmethyl)-1,3,2-dioxaborolane; 2-benzyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-phenyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(1-naphthyl)-1,3,2-dioxaborolane; 2-(4-chlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(4-fluorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane; 2-(4-bromophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(3,5-dichlorophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-(2-iodophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)benzonitrile; 4,4,5,5-tetramethyl-2-[3-(trifluoromethoxy)phenyl]-1,3,2-dioxaborolane; 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)aniline; 2-[2-(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-[3,5-bis(trifluoromethyl)phenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-fluoro-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)benzonitrile, 2-ethoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane; 2-allyl-5,5-dimethyl-1,3,2-dioxaborinane; 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane; 2,2′-(1,4-phenylene)bis[5,5-dimethyl-1,3,2-dioxaborinane]; 2-(2-chlorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 2-(1,3,2-dioxaborinane-2-yl)benzonitrile; 2-(2-fluorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 2-(4-fluorophenyl)-5,5-dimethyl-1,3,2-dioxaborinane; 4,4′-bis(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)biphenyl; ethyl 2-(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)benzoate; 2-(5,5-dimethyl-1,3,2-dioxaborinane-2-yl)-6-(trifluoromethyl)benzonitrile; 4-(trifluoromethyl)-2-(5,5-dinethyl-1,3,2-dioxaborinane-2-yl)benzonitrile, 2-isopropoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; 2-ethoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; 2-methoxy-4,4,6-trimethyl-1,3,2-dioxaborinane; trimethylboroxine; 2,4,6-triphenylboroxine, 2,4,6-tris(4-fluorophenyl)boroxine; 2,4,6-tris(3,4,5-trifluorophenyl)boroxine; 2,4,6-tris(3.4-fluorophenyl)boroxine; 2,4,6-tris(3,4-dichlorophenyl)boroxine, or 2,4,6-trimethoxyboroxine.

15. Use of a boron compound as an electrolyte additive of a primary cell comprising an alkali metal as the active electrode material according to claim 11, wherein the primary cell is a lithium battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0146] Further features and advantages of the present invention are described hereafter based on the description of the figures of exemplary embodiments. In the drawings:

[0147] FIG. 1 shows the pulse curve of an electrochemical cell without voltage delay;

[0148] FIG. 2 shows the pulse curve of an electrochemical cell with voltage delay;

[0149] FIG. 3 shows the impedance curve of a battery comprising an electrolyte additive known from the prior art (lithium bis(oxalato)borate (LiBOB));

[0150] FIG. 4 shows an impedance curve (a), and a pulse discharge and pulse curve at 180 mAh depth of discharge (B) of a battery comprising an electrolyte additive according to the present invention (4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane (TMTFPDDB); and

[0151] FIG. 5 shows an impedance curve (a), and a pulse discharge and pulse curve at 180 mAh depth of discharge (B) of a battery comprising a further electrolyte additive according to the present invention (trimethylboroxine (TMB)).

DETAILED DESCRIPTION

[0152] Lithium carbon monofluoride cells (Li/CFx) have the highest theoretical specific capacity compared to commercial lithium primary batteries. The overall equation of the discharge is as follows:

CFx+xLi.fwdarw.C+xLiF

[0153] LiF is an anionic and electrical insulator, which, on the one hand, adheres to the surface of the cathode pores and, on the other hand, partially dissolves in the electrolyte. At a depth of discharge between the MOL and EOL states, the fluoride concentration in the electrolyte increases, resulting in a high impedance cover layer of lithium fluoride compounds on the anode surface (Table 1). Under certain pulse discharge conditions, this can result in voltage is delay or in non-monotonic behavior.

TABLE-US-00001 TABLE 1 Fluoride content on lithium anode surface at different depths of discharge. Cell no. DoD [%] Fluoride [μg] Cell 1 50 2.05 Cell 2 50 1.95 Cell 3 50 2.15 Cell 4 80 4.40 Cell 5 80 3.90 Cell 6 80 4.15 Cell 7 90 23.45 Cell 8 90 21.00 Cell 9 90 24.65 Cell 10 95 63.10 Cell 11 95 69.75 Cell 12 95 66.60

[0154] The present invention relates, in general, to an electrochemical alkali metal cell and in particular to a lithium/carbon monofluoride or a lithium/carbon monofluoride metal oxide cell, which are suitable for uses with current pulse discharge and without voltage delay. More precisely, the present invention relates to an electrochemical lithium metal cell comprising a non-aqueous electrolyte, which prevents voltage delay due to an electrolyte additive.

[0155] The present invention relates in particular to dioxaborolane, diboron and boroxine electrolyte additives for alkali metal electrochemical cells comprising carbon monofluoride (CFx) or CFx transition metal oxide hybrid cathodes (such as Li/CFx-MnO2, Li/CFx-SVO, etc.) as the cathode active material. The LiCFx system shows voltage delay under pulse conditions prior to the end-of-life (EOL) state. To suppress the voltage delay and reduce the increase in impedance, according to the present invention in particular dioxaborolane, diboron and boroxine additives are added to the electrolyte.

[0156] The advantage of the present invention is the formation of a solid electrolyte interface (SEI) film on the negative electrode (for example a lithium metal), which protects the electrode surface, that is, the electrolyte additive on the anode surface is reduced, protecting the same against the formation of a high impedance cover layer, which, in turn, improves the stabilization of the internal resistance of the battery, improves the discharge power, and eliminates the voltage delay (Table 2).

TABLE-US-00002 TABLE 2 Boron content on lithium anode surface at EOL state. Cell no. Boron [μg] Cell 13 11.75 Cell 14 10.42

[0157] The present invention preferably relates to the above-described electrochemical alkali metal cell comprising non-aqueous, ionically conductive electrolytes and at least one compound according to general formula (1), (2), (3), (4), (5), (6), (7) and (8).

[0158] The electrochemical cell for the execution and comparison examples were produced from the following components:

TABLE-US-00003 Example 1 Example 2 Example 3 Electrolyte additive LiBOB TMTFPDDB TMB Cathode active material: CFx Conducting additives Graphite (3%) and carbon black (2%) (percentage by weight, %) Cathode binder Polytetrafluoroethylene (3%) (percentage by weight, %) Electrolyte 1M LiClO4 in 1,2-dimethoxyethane, ethylene carbonate and propylene carbonate (4:4:2) Anode Lithium

Example 1 (Comparison Example)

[0159] FIG. 3 shows the impedance curves of the discharge with 12.7 KOhm and daily pulse loading of 10 mA/156 s, wherein the measurement was carried out in each case with a standard electrolyte (without electrolyte additive) and a standard electrolyte containing 0.075 M lithium bis(oxalato)borate (LiBOB) as the additive. As mentioned at the outset, LiBOB is an electrolyte additive known from the prior art. It is clearly apparent that an increase in the internal resistance of the battery occurs with increasing discharge.

Example 2

[0160] FIG. 4 illustrates the discharge data with 12.7 KOhm and daily pulse loading of 10 mA/156 s, wherein the impedance curve of the battery during the discharge is shown in (a) and the pulse curve at 180 mAh is shown in (b). A standard electrolyte and the standard electrolyte containing 0.075 M of an electrolyte additive according to the present invention, which in this case is 4,4,5,5-tetramethyl-2-(3,4,5-trifluorophenyl)-1,3,2-dioxaborolane (TMTFPDDB), were used. It is clearly apparent that the internal resistance of the battery does not increase across wide discharge ranges due to the electrolyte additive according to the present invention.

Example 3

[0161] FIG. 5 illustrates the discharge data with 12.7 KOhm and daily pulse loading of 10 mA/156 s, wherein the impedance curve of the battery during the discharge is shown in (a) and the pulse curve at 180 mAh is shown in (b). A standard electrolyte and the standard electrolyte containing 0.075 M of an electrolyte additive according to the present invention, which in this case is trimethylboroxine (TMB), were used. It is also clearly apparent here that the internal resistance of the battery does not increase across wide discharge ranges due to the electrolyte additive according to the present invention.

[0162] In summary, it was shown that, in particular through the use of dioxaborolane, diboron and boroxine additives, voltage delay can be eliminated, and the battery impedance can be reduced.

[0163] In implantable batteries for cardiac therapies, batteries that showed voltage delays used only a portion of the total capacity (until voltage delay appeared). As a result of the dioxaborolane, diboron and boroxine electrolyte additives, the overall discharge capacity of the implantable batteries can be rendered usable.

[0164] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.