SO.SUB.2.-based electrolyte for a rechargeable battery cell, and rechargeable battery cells

Abstract

This disclosure relates to an SO.sub.2-based electrolyte for a rechargeable battery cell containing at least one conducting salt of the Formula (I) ##STR00001##
wherein M is a metal selected from the group consisting of alkali metals, alkaline earth metals, metals of group 12 of the periodic table of the elements and aluminum; x is an integer from 1 to 3; the substituents R, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from the group consisting of C.sub.1-C.sub.10 alkyl, C.sub.2-C.sub.1 alkenyl, C.sub.2-C.sub.1 alkynyl, C.sub.3-C.sub.10 cycloalkyl, C.sub.6-C.sub.14 aryl, and C.sub.5-C.sub.14 heteroaryl; and Z is aluminum or boron.

Claims

1. An SO.sub.2-based electrolyte for a rechargeable battery cell comprising at least one conducting salt of the Formula (I), ##STR00006## wherein M is a metal selected from the group consisting of alkali metals, alkaline earth metals, metals of group 12 of the periodic table of the elements and aluminum; x is an integer from 1 to 3; the substituents R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from the group consisting of substituted or unsubstituted C.sub.1-C.sub.10 alkyl, C.sub.2-C.sub.10 alkenyl, C.sub.2-C.sub.10 alkynyl, C.sub.3-C.sub.10 cycloalkyl, C.sub.6-C.sub.14 aryl, and C.sub.5-C.sub.14 heteroaryl; and Z is aluminum or boron.

2. The SO.sub.2-based electrolyte according to claim 1, wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from the group consisting of substituted and unsubstituted: C.sub.1-C.sub.6 alkyl; C.sub.2-C.sub.6 alkenyl; C.sub.2-C.sub.6 alkynyl; phenyl; and C.sub.5-C.sub.7 heteroaryl.

3. The SO.sub.2-based electrolyte according to claim 1, wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from the group consisting of substituted and unsubstituted: C.sub.2-C.sub.4 alkyl; C.sub.2-C.sub.4 alkenyl; C.sub.2-C.sub.4 alkynyl; C.sub.3-C.sub.6 cycloalkyl; phenyl; and C.sub.5-C.sub.7 heteroaryl.

4. The SO.sub.2-based electrolyte according to claim 1, wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently selected from the group consisting of substituted and unsubstituted: 2-propyl, methyl and ethyl; ethenyl and propenyl; C.sub.2-C.sub.4 alkynyl; C.sub.3-C.sub.6 cycloalkyl; phenyl; and C.sub.5-C.sub.7 heteroaryl.

5. The SO.sub.2-based electrolyte according to claim 1, wherein one, two, three or all four of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 comprise a substituent independently selected from the group consisting of: at least one fluorine atom; at least one group that comprises at least one fluorine atom; at least one chemical group that is a C.sub.1-C.sub.4 alkyl, C.sub.2-C.sub.4 alkenyl, C.sub.2-C.sub.4 alkynyl, phenyl or benzyl.

6. The SO.sub.2-based electrolyte according to claim 1, wherein one, two, three or all four of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 comprises at least one substituent independently selected from a CF.sub.3 group and an OSO.sub.2CF.sub.3 group.

7. The SO.sub.2-based electrolyte according to claim 1, wherein one, two, three or all four of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 comprises at least two substituents independently selected from a CF.sub.3 group and an OSO.sub.2CF.sub.3 group.

8. The SO.sub.2-based electrolyte according to claim 1, wherein one, two, three or all four of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 comprises at least three substituents independently selected from a CF.sub.3 group and an OSO.sub.2CF.sub.3 group.

9. The SO.sub.2-based electrolyte according to claim 1, wherein the Formula (I) conducting salt comprises a conducting salt selected from the group consisting of ##STR00007## ##STR00008## and combinations thereof.

10. The SO.sub.2-based electrolyte according to claim 1, further comprising at least one conducting salt that does not have a structure of Formula (I).

11. The SO.sub.2-based electrolyte according to claim 10, further comprising at least one conducting salt that comprises an alkali metal compound.

12. The SO.sub.2-based electrolyte according to claim 11, wherein the alkali metal is lithium.

13. The SO.sub.2-based electrolyte according to claim 12, wherein the lithium compound is selected from the group consisting of an aluminate, a halide, an oxalate, a borate, a phosphate, an arsenate and a gallate.

14. The SO.sub.2-based electrolyte according to claim 13, wherein the lithium compound is a lithium tetrahalogenoaluminate, and optionally lithium tetrachloroaluminate.

15. The SO.sub.2-based electrolyte according to claim 1, further comprising at least one additive that is not a conductive salt.

16. The SO.sub.2-based electrolyte according to claim 15, wherein the at least one additive is selected from the group consisting of vinylene carbonate and its derivatives, vinyl ethylene carbonate and its derivatives, methyl ethylene carbonate and its derivatives, lithium (bisoxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithium oxalate, 2-vinylpyridine, 4-vinylpyridine, cyclic exomethylenecarbonates, sultones, cyclic and acyclic sulfonates, acyclic sulfites, cyclic and acyclic sulfinates, organic esters, inorganic acids, acyclic and cyclic alkanes, wherein said acyclic and cyclic alkanes have a boiling point at 1 bar of at least 36° C., aromatic compounds, halogenated cyclic and acyclic sulfonylimides, halogenated cyclic and acyclic phosphate esters, halogenated cyclic and acyclic phosphines, halogenated cyclic and acyclic phosphites, halogenated cyclic and acyclic phosphazenes, halogenated cyclic and acyclic silylamines, halogenated cyclic and acyclic halogenated esters, halogenated cyclic and acyclic amides, halogenated cyclic and acyclic anhydrides, halogenated organic heterocycles, and combinations thereof.

17. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte comprises, based on the total weight of the electrolyte composition: (i) 5 to 99.4% by weight of sulfur dioxide; (ii) 0.6 to 95% by weight of Formula (I) conducting salts; (iii) 0 to 25% by weight of conducting salts having a structure not of Formula (I); and (iv) 0 to 10% by weight of one or more additives that are not conducting salts.

18. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte comprises, based on the total weight of the electrolyte composition: (i) 5 to 99.4% by weight of sulfur dioxide, (ii) 0.6 to 95% by weight of Formula (I) conducting salts, (iii) up to 25% by weight of conducting salts having a structure not of Formula (I); and (iv) up to 10% by weight of one or more additives that are not conducting salts.

19. The SO.sub.2-based electrolyte according to claim 1, wherein the cumulative molar concentration of all Formula (I) conducting salts in the electrolyte, relative to the total volume of the SO.sub.2-based electrolyte, is in a range of 0.05 mol/1 to 10 mol.

20. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount of at least 0.1 mol SO.sub.2 per mol of conducting salt.

21. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount selected from the group consisting of 0.1-2.5 mol SO.sub.2, 2.5-5.0 mol SO.sub.2, 5.0-7.5 mol SO.sub.2, 7.5-10 mol SO.sub.2, 10-15 mol SO.sub.2, 15-20 mol SO.sub.2, 15-25 mol SO.sub.2, 20-25 mol SO.sub.2, 25-50 mol SO.sub.2, 50-75 mol SO.sub.2, 75-100 mol SO.sub.2, 100-500 mol SO.sub.2, 500-1000 mol SO.sub.2, 1000-1500 mol SO.sub.2, 1500-2000 mol SO.sub.2, and 2000-2600 mol SO.sub.2 per mol of conducting salt.

22. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage of up to 4.0 volts.

23. A rechargeable battery cell comprising the SO.sub.2-based electrolyte according to claim 1.

24. The rechargeable battery cell according to claim 23, wherein the rechargeable battery cell comprises an active metal, at least one positive electrode, at least one negative electrode, and a housing.

25. The rechargeable battery cell according to claim 23, wherein the active metal is selected from the group consisting of an alkali metal, an alkaline earth metal, a metal of group 12 of the periodic table of the elements, and aluminum.

26. The rechargeable battery cell according to claim 23, wherein the active metal is selected from the group consisting of lithium, sodium, calcium, zinc, and aluminum.

27. The rechargeable battery cell according to claim 23, wherein the negative electrode is an insertion electrode.

28. The rechargeable battery cell according to claim 27, wherein the negative electrode contains carbon as an active material.

29. The rechargeable battery cell according to claim 28, wherein the carbon is in the form of graphite.

30. The rechargeable battery cell according to claim 23, wherein the positive electrode contains as active material at least one intercalation compound.

31. The rechargeable battery cell according to claim 30, wherein the at least one intercalation compound comprises the composition Li.sub.xM′.sub.yM″.sub.zO.sub.a wherein M′ is at least one metal chosen from the group consisting of the elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn; M″ is at least one element chosen from the group formed by the elements of the groups 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16 of the periodic table of the elements, x and y are greater than 0, z is greater than or equal to 0 and a is greater than O.

32. The rechargeable battery cell according to claim 31, wherein M′ is iron and M″ is phosphorus.

33. The rechargeable battery cell according to claim 32, wherein x, y and z are equal to 1 and a is equal to 4.

34. The rechargeable battery cell according to claim 31, wherein M′ is manganese and M″ is cobalt.

35. The rechargeable battery cell according to claim 34, wherein x, y and z are equal to 1 and a is equal to 4.

36. The rechargeable battery cell according to claim 31, wherein M′ comprises nickel and manganese and M″ is cobalt.

37. The rechargeable battery cell according to claim 23, wherein the positive electrode comprises at least one metal compound selected from the group consisting of a metal oxide, a metal halide and a metal phosphate, and wherein the metal of the metal compound is preferably a transition metal with an atomic number of 22 to 28 of the periodic table of elements.

38. The rechargeable battery cell according to claim 37, wherein the metal of the metal compound is selected from the group consisting of cobalt, nickel, manganese and iron.

39. The rechargeable battery cell according to claim 23, wherein at least one positive electrode, at least one negative electrode, or at least one positive electrode and at least one negative electrode comprise a conducting element that is selected from the group consisting of a planar-shaped metal sheet, a planar-shaped metal foil, and a three-dimensionally-shaped porous metal structure.

40. The rechargeable battery cell according to claim 39, wherein the three-dimensionally-shaped porous metal structure is a metal foam.

41. The rechargeable battery cell according to claim 23, wherein at least one positive electrode, at least one negative electrode, or at least one positive electrode and at least one negative electrode comprise at least one binder.

42. The rechargeable battery cell according to claim 41, wherein the binder is selected from the group consisting of a fluorinated binder, a fluorinated binder comprising polyvinylidene fluoride, a fluorinated binder comprising a terpolymer comprising tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, a binder comprising a polymer comprising monomeric structural units of a conjugated carboxylic acid, a binder comprising a polymer comprising monomeric structural units of an alkali metal, alkaline earth metal or ammonium salt of a conjugated carboxylic acid, a binder comprising a polymer based on monomeric styrene and butadiene structural units, a binder comprising a carboxymethylcelluloses, and combinations of two or more of the foregoing binders.

43. The rechargeable battery cell according to claim 42, wherein the binder is present in a maximum concentration by the total weight of the electrode selected from the group consisting of not greater than 30% by weight, not greater than 20% by weight, not greater than 15% by weight, not greater than 10% by weight, not greater than 7% by weight, not greater than 5% by weight, and not greater than 2% by weight.

44. The rechargeable battery cell according to claim 23, wherein the rechargeable battery cell comprises a plurality of negative electrodes and a plurality of positive electrodes, and wherein the negative and positive electrodes are arranged alternately stacked in the housing.

45. The rechargeable battery cell according to claim 44, wherein the negative and positive electrodes are electrically separated from each other by separators.

46. The SO.sub.2-based electrolyte according to claim 19, wherein the cumulative molar concentration of all Formula (I) conducting salts in the electrolyte, relative to the total volume of the SO.sub.2-based electrolyte, is in a range of 0.1 mol/1 to 6 mol/1.

47. The SO.sub.2-based electrolyte according to claim 19, wherein the cumulative molar concentration of all Formula (I) conducting salts in the electrolyte, relative to the total volume of the SO.sub.2-based electrolyte, is in a range of 0.2 mol/1 to 5 mol/1.

48. The SO.sub.2-based electrolyte according to claim 19, wherein the cumulative molar concentration of all Formula (I) conducting salts in the electrolyte, relative to the total volume of the SO.sub.2-based electrolyte, is in a range of 0.5 mol/1 to 4 mol/1.

49. The SO.sub.2-based electrolyte according to claim 19, wherein the cumulative molar concentration of all Formula (I) conducting salts in the electrolyte, relative to the total volume of the SO.sub.2-based electrolyte, is in a range of 0.2 mol/1 to 3.5 mol/1.

50. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount of at least at least 1 mol SO.sub.2 per mol of conducting salt.

51. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount of at least at least 5 mol SO.sub.2 per mol of conducting salt.

52. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount of at least 10 mol SO.sub.2 per mol of conducting salt.

53. The SO.sub.2-based electrolyte according to claim 1, wherein, relative to the number of moles of conducting salts present in the electrolyte, the SO.sub.2 is present in the electrolyte in an amount of at least 20 mol SO.sub.2 per mol of conducting salt.

54. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage up to 4.2 volts.

55. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage up to 4.4 volts.

56. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage up to 4.6 volts.

57. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage up to 4.8 volts.

58. The SO.sub.2-based electrolyte according to claim 1, wherein the electrolyte is substantially resistant to oxidation at a cell voltage up to 5.0 volts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 illustrates an example of a rechargeable battery cell according to this disclosure, shown in a cross-section.

(3) FIG. 2 shows a detailed electron microscope image of the three-dimensional porous structure of the metal foam electrode shown in FIG. 1.

(4) FIG. 3 illustrates another example of a rechargeable battery cell according to this disclosure, shown in cross-section.

(5) FIG. 4 illustrates a planar metal foil that serves as a conducting element for the positive and negative electrodes the embodiment shown in FIG. 3.

(6) FIG. 5 illustrates, in exploded view, an example of sheathed electrodes that may be employed a rechargeable battery cell according to this disclosure.

(7) FIG. 6 shows the discharge capacity as a function of the number of cycles of full cells containing either the Reference Electrolyte (prepared according to Example 1), or a mixed electrolyte comprising Compound 1 or Compound 3 in the Reference Electrolyte.

(8) FIG. 7 shows charging and discharging potential curves in volts [V] as a function of the percentage charge of full cells filled with Electrolytes 1, 2 and 3 (prepared according to Example 2) or the Reference Electrolyte.

(9) FIG. 8 shows a potential curve in volts [V] as a function of the percentage charge of a full cell filled with Electrolyte 1.

(10) FIG. 9 shows potential curves in volts [V] as a function of the accumulated charge depending on the charge/discharge current of full cells filled with Electrolyte 3.

(11) FIG. 10 shows mean values for the discharge capacities, as a function of the cycle number, of a reference full cell filled with the Reference Electrolyte and a test full cell filled with Electrolyte 1.

(12) FIG. 11 shows the course of the internal resistance of the two full cells in FIG. 10 across the cycle number.

(13) FIG. 12 shows the conductivity depending on the concentration in [mS/cm] of Electrolyte 1.

(14) FIG. 13 shows the potential in [V] of a reference full cell and two test full cells when charging a negative electrode against lithium as a function of capacitance, which is related to the theoretical capacitance of the negative electrode, during topcoat formation on the negative electrode.

DESCRIPTION

(15) The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

(16) Referring now to the figures, FIG. 1 shows a first embodiment example of a rechargeable battery cell 2 according to this disclosure in a cross-sectional diagram. This rechargeable battery cell 2 is designed as a prismatic cell and, among other things, has a housing 1. This housing 1 encloses an electrode array 3, comprising three positive electrodes 4 and four negative electrodes 5. The positive electrodes 4 and the negative electrodes 5 are alternately stacked in the electrode array 3. Housing 1 can, however, also accommodate more positive electrodes 4 and/or negative electrodes 5. In general, it is preferred that the number of negative electrodes 5 is one greater than the number of positive electrodes 4. As a result, the front surfaces of the electrode stack consist of the electrode surfaces of the negative electrodes 5. The electrodes 4, 5 are connected via electrode connections 6, 7 with corresponding contacts 9, 10 of the rechargeable battery cell 2. The rechargeable battery cell 2 is filled with an electrolyte based on SO.sub.2 in such a manner that the electrolyte penetrates as completely as possible into all pores or cavities, particularly within the electrodes 4, 5. The electrolyte is not visible in FIG. 1. In this embodiment, the positive electrodes 4 contain an intercalation compound as active material. This intercalation compound is LiCoMnO.sub.4.

(17) In this embodiment example, electrodes 4, 5 have a flat design, i.e., layers of low thickness in relation to their surface area. They are separated from each other by separators 11. Housing 1 of the depicted rechargeable battery cell 2 is essentially cuboid in shape, the electrodes 4, 5 and the walls of housing 1 shown in cross-sectional diagram extending perpendicularly to the drawing layer and being essentially straight and flat. However, the rechargeable battery cell 2 can also be used as a winding cell in which the electrodes consist of thin layers wound together with a separator material. The separators 11 separate the positive electrode 4 and negative electrode 5 spatially and electrically, but they are also permeable to the ions of the active metal. In this way, large electrochemically effective surfaces are created, which enable a correspondingly high-power yield.

(18) Electrodes 4, 5 also have a discharge element, not depicted in FIG. 1, which allows for the necessary electronically conductive connection of the active material of the respective electrode. This conducting element is in contact with the active material involved in the electrode reaction of the respective electrode 4, 5 (not depicted in FIG. 1). The conducting element consists of porous metal foam 18. This metal foam 18 extends over the entire thickness of the electrodes 4, 5. The active material of the positive electrodes 4 and the negative electrodes 5 is incorporated into the pores of this metal foam 18 so that it fills its pores uniformly over the entire thickness of the metal structure. To improve their mechanical strength, the positive electrodes 4 also contain a binder. This binder is a fluoropolymer. The negative electrodes 5 contain carbon as an active material in a form suitable for the absorption of lithium ions. The structure of the negative electrode 5 is similar to that of the positive electrode 4.

(19) FIG. 2 shows a detailed electron microscope image of the three-dimensional porous structure of the metal foam 18 of the first embodiment example in FIG. 1. The scale shows that the pores P have an average diameter of more than 100 μm, i.e., they are relatively large.

(20) FIG. 3 illustrates another embodiment of a rechargeable battery cell 20 according to this disclosure, shown in a cross-sectional diagram. This rechargeable battery cell 20 is designed as a prismatic cell and, among other things, has a housing 28. The electrodes 22 and 23 are connected via electrode connections 29 and 30 with corresponding contacts 31 and 32 of the rechargeable battery cell 20. The rechargeable battery cell 20 is filled with an electrolyte based on SO.sub.2 in such a manner that the electrolyte penetrates as completely as possible into all pores or cavities, particularly within the electrodes 22 and 23. The electrolyte is not visible in FIG. 3. In this embodiment, the electrode arrangement comprises one positive electrode 23 and two negative electrodes 22. The positive electrode 23 has a conducting element 26 in the form of a planar metal foil to which the active material 24 of the positive electrode 23 is applied on both sides. The negative electrodes 22 also include a conducting element 27 in the form of a planar metal foil to which the active material 25 of the negative electrode 22 is applied on both sides. The electrodes are separated from each other by separators 21.

(21) In an alternative embodiment (not shown), the planar conducting elements of the edge electrodes, i.e., the electrodes that close off the electrode stack, can only be coated with active material on one side. The uncoated side faces the housing wall.

(22) FIG. 4 illustrates one example of a planar metal foil that can serve as a conducting element for the positive and/or negative electrodes in rechargeable battery cells of this disclosure. This metal foil has a perforated or mesh-like structure with a thickness of, e.g., 20 μm.

(23) FIG. 5 illustrates, in exploded view, exemplary electrode configurations 40 within the scope of this disclosure. In this embodiment, the positive electrode 44 is enveloped with a sheath 13. A surface area of the sheath 13 is greater than a surface area of the positive electrode 44, the boundary of which is drawn as dashed line 14. Two layers 15, 16 of the sheath 13, covering the positive electrode 44 on both sides, are connected to each other at the circumferential edge of the positive electrode 44 via an edge connector 17. In this embodiment, the negative electrodes 45 are non-sheathed electrodes. The electrodes 44 and 45 can be connected via the electrode connections 46 and 47.

Example 1: Preparation of a Reference Electrolyte

(24) An electrolyte used as a reference for the examples described below was prepared according to the procedure described in patent specification EP 2 954 588 B1 (hereinafter the “Reference Electrolyte”). Lithium chloride (LiCl) was first dried under vacuum at 120° C. for three days. Aluminum particles (Al) were dried under vacuum at 450° C. for two days. LiCl, aluminum chloride (AlCl.sub.3) and Al were mixed at a molar ratio of AlCl.sub.3:LiC:Al of 1:1.06:0.35 in a glass bottle with an opening allowing gas to escape. This mixture was then heat-treated in stages to produce a molten salt. After cooling, the molten salt formed was filtered, then cooled to room temperature. Finally, SO.sub.2 was added until the desired molar ratio of SO.sub.2 to LiAlCl.sub.4 was formed. The Reference Electrolyte thus formed had the composition LiAlCl.sub.4*xSO.sub.2, where x depends on the amount of SO.sub.2 added.

Example 2: Preparation of Exemplary Electrolytes According to this Disclosure

(25) For the experiments described below, three exemplary electrolytes according to this disclosure were prepared (hereinafter referred to as Electrolytes 1, 2 and 3). For this purpose, first three different conducting salts were prepared according to Formula (I) of a manufacturing process described in the following documents: I. Krossing, Chem. Eur. J. 2001, 7, 490; S. M. Ivanova et al., Chem. Eur. J. 2001, 7, 503; Tsujioka et al., J. Electrochem. Soc., 2004, 151, A1418

(26) These three different conducting salts according to Formula (I) are hereinafter referred to as Compounds 1, 2 and 3. They stem from the family of polyfluoroalkoxyaluminates and were prepared in hexane according to the following reaction equation starting with LiAlH.sub.4 and the corresponding alcohol R—OH with R.sup.1═R.sup.2═R.sup.3═R.sup.4.

(27) ##STR00004##

(28) Compounds 1, 2 and 3 with the following sum and structural formulas were formed:

(29) ##STR00005##

(30) For purification, Compounds 1, 2 and 3 were first recrystallized. This removed residues of the educt LiAlH.sub.4 from the conducting salts, since this educt could possibly lead to spark formation with any traces of water in SO.sub.2.

(31) Subsequently, Compounds 1, 2 and 3 were dissolved in SO.sub.2. It was found that Compounds 1, 2 and 3 dissolve well in SO.sub.2.

(32) The preparation of Electrolytes 1, 2 and 3 was carried out at low temperature or under pressure according to process steps 1 to 4 listed below: 1) Presentation of the respective Compound 1, 2 and 3 in a pressure piston with riser pipe, 2) Evacuation of the pressure pistons, 3) Inflow of liquid SO.sub.2 and 4) Repetition of steps 2+3 until the target amount of SO.sub.2 was added.

(33) The respective concentration of Compounds 1, 2 and 3 in Electrolytes 1, 2 and 3 was 1 mol/l (substance concentration related to 1 liter of the electrolyte), unless stated otherwise in the experiment description. The experiments described below were carried out with Electrolytes 1, 2 and 3 and the Reference Electrolyte.

Example 3: Production of Full Cells

(34) The full cells used in the experiments described below are rechargeable battery cells with two negative electrodes and one positive electrode, each separated by a separator. The positive electrodes contained LiFePO.sub.4 as an active material, a conductivity mediator and a binder. The negative electrodes contained graphite as active material and a binder. The full cells were each filled with the electrolyte required for the experiments, i.e., either with the Reference Electrolyte or Electrolytes 1, 2 or 3.

(35) Several, i.e., two to four identical full cells were produced for each experiment. The results presented in the experiments are mean values of the measurement values obtained for the identical full cells.

Experiment 1: Investigation of Possible Negative Effects of the Presence of Compounds 1 and 3 on the Cycling Behavior of Full Cells

(36) In order to test whether the presence of a Formula (I) conducting salt according to this disclosure had a negative effect on the cycling behavior of full cells, mixed electrolytes were first prepared which contained 5 wt % of either Compound 1 or Compound 3 in the Reference Electrolyte.

(37) Mixed electrolytes consisting of 95 weight percent (wt %) Reference Electrolyte and 5 wt % Compound 1 or 5 wt % Compound 3 were prepared for this purpose. The two mixed electrolytes were compared with a pure Reference Electrolyte (100 wt %). For this purpose, experiments were carried out in full cells as described in Example 3. Full cells were filled with different electrolytes. The full cells were charged with 50 mA up to a potential of 3.6 V. The potential of 3.6 volts was maintained until the current dropped to 40 mA. The discharge was performed with a current of 50 mA to a potential of 2.5 V. 500 charge/discharge cycles were performed. FIG. 6 shows three discharge curves, i.e., the discharge capacities as a function of the number of cycles. All electrolytes showed nearly the same discharge capacity.

(38) It can be concluded from this that the addition of 5 wt % of either Compound 1 or 3 in the Reference Electrolyte has no serious negative effects on cycling behavior of full cells containing the Reference Electrolyte.

Experiment 2: Function of Disclosed Electrolytes in a Battery Cell

(39) Experiments were carried out in full cells according to the above description in Example 3 using the Reference Electrolyte and Electrolytes 1, 2 or 3. The Reference Electrolyte and the Electrolytes 1, 2 and 3 each had a concentration of 0.6 mol/l of conducting salt. Four full cells were filled with the electrolytes. The full cells were charged with 50 mA up to a potential of 3.6 V. The potential of 3.6 volts was maintained until the current dropped to 40 mA.

(40) The discharge was performed with a current of 50 mA to a potential of 2.5 V. In the upper part, FIG. 7 shows the charging curves with reference to the scale of the left y-axis. In the lower part, it shows the discharging curves with reference to the scale of the right y-axis. With Electrolytes 1, 2 and 3 the full cells could be charged and discharged again.

Experiment 3: Verification of High Voltage Capability of Electrolytes 1, 2 and 3

(41) To demonstrate the high voltage capability of Electrolytes 1, 2 and 3, an experiment was carried out in full cells according to Example 3. The full cell was filled with Electrolyte 1 as described in Example 2, which contained Compound 1 as the Formula (I) conducting salt in a concentration of 1 mol/l, based on 1 liter of the electrolyte.

(42) FIG. 8 shows the potential curve of the previously described full cell in volts [V] above the percentage charge in relation to the maximum charge of the full cell. The full cell was charged with an amperage of 50 mA up to a potential of 5 V. The potential was maintained until the charging current dropped to 40 mA. Afterwards the discharge took place with an amperage of 50 mA to a discharge potential of 2.5 V. FIG. 8 shows the charge/discharge curve of the full cell obtained in this experiment 3. Cycling efficiency was greater than 99.5%. This means that no capacity was used for secondary or overcharging reactions of the electrolyte. Electrolyte 1 is stable in this potential range. From this it can be concluded that the electrolyte which contains the Compound 1 conducting salt can also be used for high-energy cells in which high cell voltages occur, without the Compound 1 conducting salt decomposing.

Experiment 4: Cycling Efficiency

(43) The charge/discharge Experiment 3 was repeated, with the difference that the upper potential limit for charging was increased from 3.6 volts to 5.0 volts in 0.2-volt steps. This means that eight cycles were performed. Table 2 shows the cycling efficiencies achieved in each case.

(44) TABLE-US-00002 TABLE 2 Cycling Efficiency as a Function of Charge Potential Charging Potential Cycling Efficiency 3.60 99.7% 3.80 99.6% 4.00 99.7% 4.20 99.7% 4.40 99.7% 4.60 99.7% 4.80 99.7% 5.00 99.7%

(45) The achieved cycling efficiencies are identical for each charging potential and show a stable behavior of Electrolyte 1 in the entire potential range up to 5.0 volts.

Experiment 5: Comparison of Electrolyte 3 to a Reference Electrolyte in a Cycling Experiment

(46) Electrolyte 3 was compared with the Reference Electrolyte in a cycling experiment. Three full cells, as described in Example 3, were used for this purpose; one full cell was filled with the Reference Electrolyte and two full cells with Electrolyte 3. The full cell was charged up to a potential of 3.6 volts and discharged to a potential 2.5 volts. The full cell with the Reference Electrolyte was operated with a current of 100 mA, the two full cells with Electrolyte 3, adapted to the lower conductivity, were charged or discharged once with 10 mA and once with 5 mA respectively. FIG. 9 shows the charge/discharge curves obtained. All full cells show a stable charge and a stable discharge. At lower currents, the attainable capacity for Electrolyte 3 increases.

Experiment 6: Comparison of Discharge Capacities and Internal Resistance of Full Cells with the Reference Electrolyte or Electrolyte 1

(47) In this experiment, the use of the Electrolyte 1 as an alternative to the Reference Electrolyte was investigated.

(48) This experiment was also carried out with the full cells described in Example 3. The full cells were filled either with Reference Electrolyte (hereinafter referred to as the reference full cell) or with Electrolyte 1 (hereinafter referred to as the test full cell). Thus, the reference full cell and the test full cell differed only in the type of electrolyte used.

(49) Several cycling experiments were performed, starting with a formation cycle. Table 3 shows the charging and discharging currents used and the final charging and discharging voltages during charging and discharging of the two full cells. In addition, the limit of the charge current (I.sub.cutoff) at the final charge voltage is 3.6 volts. There was a break of ten minutes between charging and discharging the two full cells.

(50) TABLE-US-00003 TABLE 3 Data of the Cycling Experiments Formation: Charge/ 1 cycle: 15 mA to 125 mAh/ Discharge 15 mA to 2.5 V Cycling: Charge/ 90 cycles: 50 mA to 3.6 V (I.sub.cutoff = 40 mA)/ Discharge 50 mA to 2.5 V 24 h Rest 1 cycle: 50 mA to 3.6 V (I.sub.cutoff = 40 mA)/ 24 h Rest/50 mA to 2.5 V Cycling: Charge/ 410 cycles: 50 mA to 3.6 V (I.sub.cutoff = 40 mA)/ Discharge 50 mA to 2.5 V

(51) FIG. 10 shows mean values for the discharge capacities of the two full cells as a function of the number of cycles. The dashed line shows the average values obtained for discharging capacities of the test full cell. For this purpose, mean values obtained from three identical measurements were used. The solid line shows the discharging capacities of the reference full cell. For this purpose, mean values obtained from two identical measurements were used.

(52) These average discharge capacity values are expressed as a percentage of the nominal capacity. The nominal capacity is obtained by subtracting from the theoretical capacity of the positive electrode the capacity consumed in the first cycle to form a coating on the negative electrode. This top layer is formed on the negative electrode when the full cell is charged for the first time. Lithium ions are irreversibly consumed for this coating formation, so that the respective full cell has less cycling capacity available for the subsequent cycles.

(53) The starting value of the discharge capacity of both full cells is approx. 90% of the nominal capacity. Both full cells show a discharge capacity drop across the number of cycles. The capacity drop for the reference full cell was 19% up to the 500th cycle and the remaining capacity was 71%. The test full cell had a discharge capacity drop of 22% and a remaining capacity of 68% after 500 cycles. Capacity progression in both curves is almost parallel from the 300th cycle onwards and suggests further steady progression. The behavior of the full cells is similar and shows that the electrolyte according to this disclosure can be used as an alternative to the Reference Electrolyte.

(54) During Experiment 6, progression of the internal resistance of the two full cells was also recorded via the cycle number. FIG. 11 shows the results for the reference full cell and for the test full cell. The internal resistance is a loss factor inside the full cell due to its design. The internal resistance of the reference full cell is slightly above 0.2 Ohm. The test full cell shows a higher internal resistance of initially approx. 0.95 Ohm, which is stable at a value of 0.8 Ohm from approx. cycle 200 onwards.

(55) These results are in line with expected values because, as discussed above, the lithium ionic conductivity in an electrolyte with the large anions of the Formula (I) conducting salts is somewhat more difficult.

Experiment 7: Determining Conductivities

(56) The conductivity was determined by preparing the Electrolyte 1 with different concentrations of Compound 1. For each concentration of Compound 1, the conductivity of Electrolyte 1 was determined using a conductive measurement method. After temperature control, a two-electrode sensor was held in contact with the solution and measurement was carried out in a range of 0-50 mS/cm. Table 4 shows the different concentrations, the corresponding SO.sub.2 contents and the conductivity values determined.

(57) TABLE-US-00004 TABLE 4 Conductivity as a Function of the Concentration of Compound 1 in the Electrolyte 1 c of Compound 1 in mol/L wt % SO.sub.2 Conductivity in mS/cm 1.00 34% 13.6 0.60 60% 24.7 0.40 75% 20.8 0.20 87% 11.7

(58) FIG. 12 shows the conductivity of Electrolyte 1 as a function of the concentration of Compound 1. A maximum conductivity of 24.7 mS/cm is depicted at a concentration of Compound 1 of 0.6 mol/L. In comparison, state-of-the-art organic electrolytes such as LP30 (1 M LiPF6/EC-DMC (1:1 weight)) have a conductivity of only approx. 10 mS/cm.

Experiment 8: Determination of a Capacitance Consumed for the Formation of a Surface Layer on the Negative Electrode

(59) In this experiment, the capacitance consumed in the first cycle for the formation of a surface layer on the negative electrode was investigated. This surface layer or cover layer is formed on the negative electrode when the full cell is charged for the first time. Lithium ions are irreversibly consumed for this coating formation, so that the full cell has less cycling capacity available for the subsequent cycles.

(60) For this experiment, the Reference Electrolyte, Electrolytes 1 and Electrolyte 3 were each examined in a full cell having the design described in Example 3. The composition of the Reference Electrolyte used in the full cell was LiAlCl.sub.4*xSO.sub.2 with x>1.5.

(61) FIG. 13 shows the potential in volts of the full cells when charging the negative electrode against lithium as a function of capacity, which is related to the theoretical capacity of the negative electrode. The dotted line shows the results for the Reference Electrolyte and the dotted or solid line shows the results for the Electrolytes 1 and 3. The three curves show averaged results of several experiments with the full cells described above. First the full cells were charged with a current of 15 mA until a capacitance of 125 mAh (Q.sub.cha) was reached. The full cells were then discharged at 15 mA until a potential of 2.5 volts was reached. This is when the discharging capacity (Q.sub.dis) was determined.

(62) The capacitance in % of the theory used to form the cover layer on the negative electrode is calculated according to the following formula:
Cover layer capacity=(Q.sub.cha(125 mAh)−Q.sub.dis(x mAh))/Q.sub.NEL

(63) Q.sub.NEL is the theoretical capacitance of the negative electrode used. In the case of graphite, the theoretical capacitance calculated is 372 mAh/g. The absolute capacity losses are 7.58% and 11.51% respectively for Electrolytes 1 and 3 and 6.85% for the Reference Electrolyte. The capacity for the formation of the surface layer is slightly higher for both Electrolytes 1 and 3 than for the Reference Electrolyte. Values in the range of 7.5%-11.5% for absolute capacity losses are good results in combination with the possibility of using high-voltage cathodes of up to 5 volts.

Experiment 9: Low-Temperature Behavior of the Reference Electrolyte and Electrolyte 1

(64) In order to determine the low-temperature behavior of an electrolyte according to this disclosure in comparison to the Reference Electrolyte, two full cells, as described in experiment 1, were filled with Reference Electrolyte on the one hand and Electrolyte 1 on the other hand.

(65) Both full cells were charged at 20° C. and discharged again. The discharge capacity achieved was rated 100%. In temperature steps of 10° C., the temperature of the full cells was lowered, and a charge/discharge cycle was carried out again. The discharge capacity obtained was described in % of the discharge capacity at 20° C. Table 5 shows the results.

(66) TABLE-US-00005 TABLE 5 Discharge Capacities as a Function of Temperature Discharge Capacity of Discharge Capacity of Temperature Electrolyte 1 Reference Electrolyte  20° C. 100%  100%   10° C. 87% 99%  0° C. 72% 46% −10° C. 61% 21% −20° C. 31% n/a −30° C.  3% n/a −40° C.  0% n/a

(67) The full cell with Electrolyte 1 shows an excellent low-temperature behavior. At −10° C., 61% of the capacity is reached. At −20° C. the capacity reached is still 31%. Even at −30° C., a small amount can still be discharged. In contrast, the full cell with the Reference Electrolyte shows a discharge capacity of only 21% at −10° C., and no capacity is available at −20° C.

(68) While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.