RECHARGEABLE BATTERY CELL

Abstract

This disclosure relates to a rechargeable battery cell comprising an active metal, at least one positive electrode, at least one negative electrode, a housing and an electrolyte, the positive electrode comprising at least one polyanionic compound as an active material and the electrolyte being based on SO.sub.2 and comprising at least one first conducting salt which has the formula (I),

##STR00001##

M being a metal selected from the group formed by alkali metals, alkaline earth metals, metals of group 12 of the periodic table of the elements, and aluminum; x being an integer from 1 to 3; the substituents R.sup.1, R.sup.2, R.sup.3 and R.sup.4 being selected independently of one another from the group formed by 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 being aluminum or boron.

Claims

1. A rechargeable battery cell, comprising: an active metal; at least one positive electrode having a polyanionic compound as an active material; at least one negative electrode; a housing; an SO.sub.2 based electrolyte comprising a first conducting salt which has 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; R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are selected independently of one another from the group consisting of 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 rechargeable battery cell according to claim 1, wherein the polyanionic compound has the composition A.sub.xM.sub.y(X.sub.r1O.sub.s1).sub.aF.sub.b, wherein: A is at least one metal selected from the group consisting of the alkali metals, the alkaline earth metals, the metals of group 12 of the periodic table and aluminum; M is at least one metal selected from the group consisting of the elements of 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.sub.r1O.sub.s1).sup.n− is a first polyanion structural unit in which X is at least one element selected from the group consisting of the elements phosphorus (P), silicon (Si), sulfur (S), boron (B), carbon (C), arsenic (As), molybdenum (Mo), tungsten (W) and vanadium (V), and O is the element oxygen (O); F is the element fluorine (F); n is a number greater than 0; x and y independently of one another are numbers greater than 0; r1 and s1 independently of one another are numbers greater than 0; a is a number greater than 0; and b is a number greater than or equal to 0.

3. The rechargeable battery cell according to claim 2, wherein the metal A is selected from the group consisting of the elements lithium, sodium, calcium or zinc.

4. The rechargeable battery cell according to claim 3, wherein the metal A is lithium or sodium.

5. The rechargeable battery cell according to claim 2, wherein the metal M is selected from the group consisting of the elements titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc.

6. The rechargeable battery cell according to claim 2, wherein the first polyanion structural unit has the composition (XO.sub.4).sup.n−, (X.sub.mO.sub.3m+1).sup.n− or (XO.sub.3).sup.n−, wherein m and n are, independently of one another, numbers greater than 0.

7. The rechargeable battery cell according to claim 6, wherein the first polyanion structural unit has the composition (SO.sub.4).sup.2−, (PO.sub.4).sup.3−, (SiO.sub.4).sup.2−, (AsO.sub.4).sup.3−, (MoO.sub.4).sup.2−, (WO.sub.4).sup.2−, (P.sub.2O.sub.7).sup.4−, (CO.sub.3).sup.2− or (BO.sub.3).sup.3−.

8. The rechargeable battery cell according to claim 7, wherein the polyanionic compound has the composition A.sub.XM.sub.y(PO.sub.4).sub.aF.sub.b.

9. The rechargeable battery cell according to claim 8, wherein the polyanionic compound has the composition LiFePO.sub.4, NaFePO.sub.4, LiMnPO.sub.4, LiCoPO.sub.4, LiNiPO.sub.4, LiVPO.sub.4F, Li(Mn.sub.0.7Fe.sub.0.3)PO.sub.4 or Li(Mn.sub.0.6Fe.sub.0.4)PO.sub.4.

10. The rechargeable battery cell according to claim 7, wherein the polyanionic compound has the composition A.sub.xM.sub.y(SiO.sub.4).sub.aF.sub.b.

11. The rechargeable battery cell according to claim 10, wherein the polyanionic compound has the composition Li.sub.2FeSiO.sub.4, Li.sub.2MnSiO.sub.4, Li.sub.2CoSiO.sub.4, Li.sub.2Mn.sub.0.2Fe.sub.0.8SiO.sub.4 or Li.sub.2Mn.sub.0.5Fe.sub.0.5SiO.sub.4.

12. The rechargeable battery cell according to claim 7, wherein the polyanionic compound has the composition A.sub.xM.sub.y(SO.sub.4).sub.aF.sub.b.

13. The rechargeable battery cell according to claim 12, wherein the polyanionic compound has the composition LiFeSO.sub.4F, LiCoSO.sub.4F, LiNiSO.sub.4F or LiMnSO.sub.4F.

14. The rechargeable battery cell according to claim 1, wherein the polyanionic compound has at least two different polyanion structural units (X.sub.r1O.sub.s1).sup.n− and (G.sub.r2O.sub.s2).sup.k−, wherein n, k, r1, r2, s1 and s2 are, independently of one another, numbers greater than 0.

15. The rechargeable battery cell according to claim 14, wherein the polyanionic compound has the composition A.sub.XM.sub.y(X.sub.r1O.sub.s1).sub.a(G.sub.r2O.sub.s2)F.sub.b, wherein: (X.sub.r1O.sub.s1).sup.n− is at least one first polyanion structural unit wherein X is at least one element selected from the group consisting of the elements phosphorus (P), silicon (Si), sulfur (S), boron (B), carbon (C), arsenic (As), molybdenum (Mo), tungsten (W) and vanadium (V), and O is the element oxygen (O), (G.sub.r2O.sub.s2).sup.k− is at least one second polyanion structural unit in which G is at least one element selected from the group consisting of the elements phosphorus (P), silicon (Si), sulfur (S), boron (B), carbon (C), arsenic (As), molybdenum (Mo), tungsten (W) and vanadium (V), and O is the element oxygen (O), A is at least one metal selected from the group consisting of the alkali metals, the alkaline earth metals, the metals of group 12 of the periodic table or aluminum, M is at least one metal selected from the group consisting of the elements of groups 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16 of the periodic table of the elements, F is the element fluorine (F), x and y independently of one another are numbers greater than 0; a is a number greater than 0, and b is a number greater than or equal to 0.

16. The rechargeable battery cell according to claim 15, wherein the polyanionic compound has the composition A.sub.xM.sub.y(XO.sub.4).sub.a(XO.sub.3)F.sub.b.

17. The rechargeable battery cell according to claim 16, wherein the polyanionic compound has the composition Li.sub.3Fe.sub.0.2Mn.sub.0.8CO.sub.3PO.sub.4 or Na.sub.3Fe.sub.0.2Mn.sub.0.8CO.sub.3PO.sub.4.

18. The rechargeable battery cell according to claim 1, wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 of the first conducting salt are selected independently of one another from the group consisting of: C.sub.1-C.sub.6 alkyl; C.sub.2-C.sub.6 alkenyl; C.sub.2-C.sub.6 alkynyl; C.sub.3-C.sub.6 cycloalkyl; phenyl; and C.sub.5-C.sub.7 heteroaryl.

19. The rechargeable battery cell according to claim 18, wherein: the C.sub.1-C.sub.6 alkyl comprises a C.sub.2-C.sub.4 alkyl; the C.sub.2-C.sub.6 alkenyl comprises a C.sub.2-C.sub.4 alkenyl; and the C.sub.2-C.sub.6 alkynyl comprises a C.sub.2-C.sub.4 alkynyl.

20. The rechargeable battery cell according to claim 19, wherein: the C.sub.2-C.sub.4 alkyl is selected from the group consisting of 2-propyl, methyl and ethyl; and the C.sub.2-C.sub.4 alkenyl is selected from the alkenyl groups consisting of ethenyl and propenyl.

21. The rechargeable battery cell according to claim 1, wherein at least one of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 of the first conducting salt is substituted by at least one fluorine atom and/or by at least one chemical group selected from the group consisting of C.sub.1-C.sub.4 alkyl, C.sub.2-C.sub.4 alkenyl, C.sub.2-C.sub.4 alkynyl, phenyl and benzyl.

22. The rechargeable battery cell according to claim 1, wherein at least one of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 of the first conducting salt is a CF.sub.3 group or an OSO.sub.2CF.sub.3 group.

23. The rechargeable battery cell according to claim 1, wherein the first conducting salt is selected from the group consisting of. ##STR00007##

24. The rechargeable battery cell according to claim 1, wherein the electrolyte comprises at least one second conducting salt different from the first conducting salt.

25. The rechargeable battery cell according to claim 24, wherein the second conducting salt of the electrolyte is an alkali metal compound selected from the group consisting of an aluminate, a halide, an oxalate, a borate, a phosphate, an arsenate and a gallate.

26. The rechargeable battery cell according to claim 25, wherein the second conducting salt comprises a lithium compound.

27. The rechargeable battery cell according to claim 26, wherein the second conducting salt of the electrolyte is a lithium tetrahaloaluminate.

28. The rechargeable battery cell according to claim 27, wherein the second conducting salt comprises lithium tetrachloroaluminate.

29. The rechargeable battery cell according to claim 1, wherein the electrolyte comprises at least one additive.

30. The rechargeable battery cell according to claim 29, wherein the additive of the electrolyte is selected from the group consisting of vinylene carbonate and its derivatives, vinylethylene carbonate and its derivatives, methylethylene carbonate and its derivatives, lithium (bisoxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoro(oxalato)phosphate, lithium oxalate, 2-vinylpyridine, 4-vinylpyridine, cyclic exomethylene carbonates, sultones, cyclic and acyclic sulfonates, acyclic sulfites, cyclic and acyclic sulfinates, organic esters, inorganic acids, acyclic and cyclic alkanes, which acyclic and cyclic alkanes have a boiling point of at least 36° C. at 1 bar, 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, and halogenated organic heterocycles.

31. The rechargeable battery cell according to claim 1, wherein the electrolyte comprises: (i) 5 to 99.4% by weight sulfur dioxide; (ii) 0.6 to 95% by weight of the first conducting salt; (iii) 0 to 25% by weight of the second conducting salt; and (iv) 0 to 10% by weight of the additive; based on the total weight of the electrolyte composition.

32. The rechargeable battery cell according to claim 1, wherein the molar concentration of the first conducting salt is in the range selected from the group consisting of from 0.01 mol/L to 10 mol/L, from 0.05 mol/L to 10 mol/L, from 0.1 mol/L to 6 mol/L, and from 0.2 mol/L to 3.5 mol/L based on the total volume of the electrolyte.

33. The rechargeable battery cell according to claim 1, wherein the electrolyte comprises SO.sub.2 in an amount selected from the group consisting of at least 0.1 mol SO.sub.2, at least 1 mol SO.sub.2, at least 5 mol SO.sub.2, at least 10 mol SO.sub.2, and at least 20 mol SO.sub.2 per mole of conducting salt.

34. The rechargeable battery cell according to claim 1, wherein the active metal comprises: an alkali metal; an alkaline earth metal; a metal from group 12 of the periodic table; or aluminum.

35. The rechargeable battery cell according to claim 34, wherein the active metal comprises: lithium or sodium as the alkali metal; calcium as the alkaline earth metal; zinc as the metal from group 12 of the periodic table; or aluminum.

36. The rechargeable battery cell according to claim 1, wherein the negative electrode is an insertion electrode.

37. The rechargeable battery cell according to claim 36, wherein the active material comprises carbon.

38. The rechargeable battery cell according to claim 37, wherein the carbon is the allotrope graphite.

39. The rechargeable battery cell according to claim 1, wherein the positive electrode and/or the negative electrode have a discharge element.

40. The rechargeable battery cell according to claim 39, wherein the discharge element is formed (i) planar in the form of a metal sheet or a metal foil, or (ii) three-dimensional in the form of a porous metal structure.

41. The rechargeable battery cell according to claim 40, wherein the porous metal structure comprises a metal foam.

42. The rechargeable battery cell according to claim 1, wherein the positive electrode and/or the negative electrode comprises at least one binder, the binder comprising: a polyvinylidene fluoride and/or a terpolymer made of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, or a binder consisting of a polymer which is built up from monomeric structural units of a conjugated carboxylic acid or from the alkali, alkaline earth or ammonium salt of said conjugated carboxylic acid or from a combination thereof, or a binder consisting of a polymer based on monomeric styrene and butadiene structural units, or a binder from the group of carboxymethyl celluloses, wherein the binder is present in a concentration selected from the group consisting of at most 20% by weight, at most 15% by weight, at most 10% by weight, at most 7% by weight, at most 5% by weight and at most 2% by weight based on the total positive electrode weight.

43. The rechargeable battery cell according to claim 1, wherein the negative electrode comprises a plurality of negative electrodes and the positive electrode comprises a plurality of positive electrodes, the negative and positive electrodes being stacked alternately in the housing.

44. The rechargeable battery cell according to claim 43, wherein the positive electrodes and the negative electrodes are each electrically separated from one another by separators.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0145] 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:

[0146] FIG. 1 shows a first embodiment of a rechargeable battery cell according to this disclosure in a cross-sectional illustration;

[0147] FIG. 2 shows an electron microscope image of the three-dimensional porous structure of the metal foam of the first embodiment from FIG. 1 as a detailed illustration;

[0148] FIG. 3 shows a second embodiment of a rechargeable battery cell according to this disclosure in a cross-sectional illustration;

[0149] FIG. 4 shows a detail of the second embodiment from FIG. 3;

[0150] FIG. 5 shows a third embodiment of the rechargeable battery cell according to this disclosure in an exploded illustration;

[0151] FIG. 6 shows a potential profile in volts [V] as a function of the percentage charge of a test full cell having lithium iron phosphate LiFePO.sub.4 (LEP) as the active material of the positive electrode, wherein the end-of-charge voltage is 5 volts;

[0152] FIG. 7 shows the discharge capacity as a function of the number of cycles of test full cells which comprise lithium iron phosphate LiFePO.sub.4 (LEP) as the active material of the positive electrode, wherein the upper potential is increased in steps from 4.5 V to 5.0 V;

[0153] FIG. 8 shows the discharge capacity as a function of the number of cycles of a test full cell having lithium iron phosphate LiFePO.sub.4 as the active material of the positive electrode, wherein the end-of-charge voltage is 3.6 volts;

[0154] FIG. 9 shows the discharge capacity as a function of the number of cycles of a test full cell having lithium iron manganese phosphate Li(Fe.sub.0.3Mn.sub.0.7)PO.sub.4 as the active material of the positive electrode, wherein the end-of-charge voltage is 4.5 volts;

[0155] FIG. 10 shows a potential profile in volts [V] as a function of the percentage charge of a test full cell having lithium iron cobalt phosphate LiFeCoPO.sub.4 as the active material of the positive electrode, wherein the end-of-charge voltage is 5 volts;

[0156] FIG. 11 shows the potential in [V] of a reference test full cell and two test full cells when charging a negative electrode as a function of the capacity, which is related to the theoretical capacity of the negative electrode, during formation of a coating layer on the negative electrode;

[0157] FIG. 12 shows the potential profile during discharge in volts [V] as a function of the percentage charge of three test full cells that have lithium iron phosphate LiFePO.sub.4 (LEP) as the active material of the positive electrode and were filled with three electrolytes 1, 3 and 4;

[0158] FIG. 13 shows the conductivity in [mS/cm] of a first electrolyte 1 as a function of the concentration of compound 1;

[0159] FIG. 14 shows the conductivity in [mS/cm] of the third electrolyte 3 as a function of the concentration of compound 3; and

[0160] FIG. 15 shows the conductivity in [mS/cm] of the fourth electrolyte 4 as a function of the concentration of compound 4.

DESCRIPTION

[0161] 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.

[0162] FIG. 1 shows a first embodiment of a rechargeable battery cell 2 according to this disclosure in a cross-sectional illustration. Said rechargeable battery cell 2 is designed as a prismatic cell and has a housing 1, among other things. Said housing 1 encloses an electrode array 3 which comprises three positive electrodes 4 and four negative electrodes 5. The positive electrodes 4 and the negative electrodes 5 are stacked alternately in the electrode array 3. The housing 1 can, however, also accommodate more positive electrodes 4 and/or negative electrodes 5. In general, it is preferred when the number of negative electrodes 5 is one greater than the number of positive electrodes 4. This has the consequence of the outer end faces of the electrode stack being formed by the electrode surfaces of the negative electrodes 5. The electrodes 4, 5 are connected to corresponding contacts 9, 10 of the rechargeable battery cell 2 via electrode connections 6, 7. The rechargeable battery cell 2 is filled with an SO.sub.2-based electrolyte such that the electrolyte penetrates as completely as possible into all pores or cavities, in particular within the electrodes 4, 5. The electrolyte is not visible in FIG. 1. In the present embodiment, the positive electrodes 4 comprise an intercalation compound as an active material. This intercalation compound is LiFePO.sub.4.

[0163] The electrodes 4, 5 are designed flat in the present embodiment, that is, as layers having a thickness that is smaller in relation to their surface area. They are each separated from one another by separators 11. The housing 1 of the rechargeable battery cell 2 is essentially designed as a rectangular parallelepiped, wherein the electrodes 4, 5 and the walls of the housing 1 shown in a sectional illustration extend perpendicular to the plane of the drawing and are essentially straight and flat. The rechargeable battery cell 2 can, however, also be designed as a winding cell in which the electrodes consist of thin layers that are wound up together with a separator material. The separators 11, on the one hand, separate the positive electrode 4 and the negative electrode 5 spatially and electrically and, on the other hand, are permeable to the ions of the active metal, among other things. In this way, large electrochemically effective surfaces are created, which enable a correspondingly high current yield.

[0164] The electrodes 4, 5 also have a discharge element which serves to enable the required electronically conductive connection of the active material of the respective electrode. Said discharge 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 discharge element is designed in the form of a porous metal foam 18. The metal foam 18 extends over the thickness dimension of the electrodes 4, 5. The active material of the positive electrodes 4 and the negative electrodes 5 is incorporated into the pores of said metal foam 18, such that it fills the pores of the metal foam evenly over the entire thickness of the metal structure. The positive electrodes 4 comprise a binder to improve the mechanical strength. This binder is a fluoropolymer. The negative electrodes 5 comprise carbon as an active material in a form suitable as an insertion material for the absorption of lithium ions. The structure of the negative electrode 5 is similar to that of the positive electrode 4.

[0165] FIG. 2 shows an electron microscope image of the three-dimensional porous structure of the metal foam 18 of the first embodiment from FIG. 1. On the basis of the specified scale, it can be seen that the pores P have an average diameter of more than 100 μm, that is, are relatively large. This metal foam is a metal foam made of nickel.

[0166] FIG. 3 shows a second embodiment of a rechargeable battery cell 20 according to this disclosure in a cross-sectional illustration. Said second embodiment differs from the first embodiment shown in FIG. 1 in that the electrode array comprises a positive electrode 23 and two negative electrodes 22. They are each separated from one another by separators 21 and surrounded by a housing 28. The positive electrode 23 has a discharge 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 comprise a discharge 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. Alternatively, the planar discharge elements of the edge electrodes, that is, of the electrodes that close off the electrode stack, can only be coated with active material on one side. The non-coated side faces the wall of the housing 28. The electrodes 22, 23 are connected to corresponding contacts 31, 32 of the rechargeable battery cell 20 via electrode connections 29, 30.

[0167] FIG. 4 shows the planar metal foil which serves as a discharge element 26, 27 for the positive electrodes 23 and the negative electrodes 22 in the second embodiment from FIG. 3. This metal foil has a perforated or mesh-like structure having a thickness of m.

[0168] FIG. 5 shows a third embodiment of a rechargeable battery cell 40 according to this disclosure in an exploded illustration. This third embodiment differs from the two embodiments explained above in that the positive electrode 44 is enveloped by a sheath 13. In this case, a surface area of the sheath 13 is greater than a surface area of the positive electrode 44, the boundary 14 of which is shown in FIG. 5 as a dashed line. Two layers 15, 16 of the sheath 13 that cover the positive electrode 44 on both sides are connected to one another at the circumferential edge of the positive electrode 44 by an edge connection 17. The two negative electrodes 45 are not enveloped. The electrodes 44 and 45 can be contacted via the electrode connections 46 and 47.

Example 1: Preparation of a Reference Electrolyte

[0169] A reference electrolyte used for the examples described below was produced according to the method described in patent specification EP 2 954 588 B1 (hereinafter referred to as [V4]). First, lithium chloride (LiCl) was dried under vacuum at 120° C. for three days. Aluminum particles (Al) were dried under vacuum for two days at 450° C. LiCl, aluminum chloride (AlCl.sub.3) and Al were mixed together in an AlCl.sub.3:LiCl:Al molar ratio of 1:1.06:0.35 in a glass bottle having an opening to allow gas to escape. This blend was thereafter heat-treated in stages to produce a molten salt. After cooling, the salt melt formed was filtered, then cooled to room temperature and 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*x SO.sub.2, wherein x is dependent on the amount of SO.sub.2 supplied.

Example 2: Preparation of Four Embodiments 1, 2, 3 and 4 of an SO.SUB.2.—Based Electrolyte for a Battery Cell

[0170] Four embodiments 1, 2, 3 and 4 of the SO.sub.2-based electrolyte were prepared for the experiments described below (hereinafter referred to as electrolytes 1, 2, 3 and 4). For this purpose, four different first conducting salts according to formula (I) were initially prepared using a manufacturing process described in the following documents [V5], [V6] and [V7]: [0171] [V5] “I. Krossing, Chem. Eur. J. 2001, 7, 490; [0172] [V6] S. M. Ivanova et al., Chem. Eur. J. 2001, 7, 503; [0173] [V7] Tsujioka et al., J. Electrochem. Soc., 2004, 151, A1418”

[0174] These four different, first conducting salts according to formula (I) are referred to below as compounds 1, 2, 3 and 4. They come from the family of polyfluoroalkoxyaluminates and were prepared in hexane according to the following reaction equation, starting from LiAlH.sub.4 and the corresponding alcohol R—OH with R.sup.1═R.sup.2═R.sup.3═R.sup.4.

##STR00004##

[0175] As a result, compounds 1, 2, 3 and 4 shown below were formed using the sum and structural formulas:

##STR00005##

[0176] Compounds 1, 2, 3 and 4 were first recrystallized for purification. As a result, residues of the educt LiAlH.sub.4 were removed from the first conducting salt, since said educt could possibly lead to the formation of sparks with possibly existing traces of water in SO.sub.2.

[0177] Compounds 1, 2, 3 and 4 were then dissolved in SO.sub.2. It was found that compounds 1, 2, 3 and 4 dissolve well in SO.sub.2.

[0178] The preparation of electrolytes 1, 2, 3 and 4 was performed at low temperature or under pressure according to process steps 1 to 4 listed below: [0179] 1) receiving of the respective compound 1, 2, 3 and 4 in a pressure piston each with a riser pipe, [0180] 2) evacuation of the pressure pistons, [0181] 3) inflow of liquid SO.sub.2 and [0182] 4) repetition of steps 2+3 until the target amount of SO.sub.2 was added.

[0183] The respective concentration of compounds 1, 2, 3 and 4 in electrolytes 1, 2, 3 and 4 was 0.6 mol/L (molar concentration based on 1 liter of the electrolyte), unless otherwise described in the description of the experiment. The experiments described below were performed using electrolytes 1, 2, 3 and 4 and the reference electrolyte.

Example 3: Production of Test Full Cells

[0184] The test full cells used in the experiments described below are rechargeable battery cells having two negative electrodes and one positive electrode, each separated by a separator. The positive electrodes included an active material, a conductivity mediator and a binder. The negative electrodes comprised graphite as the active material and also a binder. As mentioned in the experiment, the negative electrodes can also comprise a conductivity additive. The active material of the positive electrode is named in the respective experiment. The discharge element of the positive and negative electrodes was made of nickel. Among other things, the aim of the investigations is to confirm the use of various active materials for the positive electrode in a battery cell according to this disclosure in combination with the electrolyte according to this disclosure. Table 2 shows which polyanionic compounds were investigated as active materials of the positive electrode and which upper potentials were used.

TABLE-US-00002 TABLE 2 Polyanionic Compounds Investigated Upper Experiment Active Material Potential 1 Lithium iron phosphate LiFePO.sub.4 (LEP) 4.5-5.0 V 2 Lithium iron phosphate LiFePO.sub.4 (LEP) 3.6 V 3 Lithium iron manganese phosphate 4.5 V Li(Fe.sub.0.3Mn.sub.0.7)PO.sub.4 4 Lithium iron cobalt phosphate LiFeCoPO.sub.4 5.0 V

[0185] The test full cells were each filled with the electrolyte required for the experiments, that is, either with the reference electrolyte or electrolytes 1, 2, 3 or 4.

[0186] Several, that is, two to four, identical test whole cells were produced for each experiment. The results presented in the experiments are each mean values from the measured values obtained for the identical test full cells.

Example 4: Measurement in Test Full Cells

[0187] For measurements in test full cells, for example, the discharge capacity is determined from the number of cycles.

[0188] For this purpose, the test full cells are charged with a certain charge current intensity up to a certain upper potential. The corresponding upper potential is held until the charge current has dropped to a certain value. The discharge then takes place with a certain discharge current intensity up to a certain discharge potential. This charging method is a so-called I/U charging. This process is repeated depending on the desired number of cycles.

[0189] The upper potentials or the discharge potential and the respective charge or discharge current intensities are given in the experiments. The value to which the charge current must have dropped is also described in the experiments.

[0190] The term “upper potential” is used as a synonym for the terms “charge potential,” “charge voltage,” “end-of-charge voltage” and “upper potential limit.” The terms denote the voltage/potential up to which a cell or battery is charged with the aid of a battery charger.

[0191] The battery is preferably charged at a current rate of C/2 and at a temperature of 22° C. With a charge or discharge rate of 1C, by definition, the nominal capacity of a cell is charged or discharged in one hour. A charge rate of C/2 means a charge time of 2 hours.

[0192] The term “discharge potential” is used synonymously with the term “lower cell voltage.” This describes the voltage/potential up to which a cell or battery is discharged with the aid of a battery charger.

[0193] The test full cell is preferably discharged at a current rate of C/2 and at a temperature of 22° C.

[0194] The discharge capacity is obtained from the discharge current and the time until the criteria for ending the discharge are fulfilled. These mean values of the discharge capacities are expressed as a percentage of the nominal capacity, often standardized to the maximum capacity that was achieved in the respective test. These mean values of the discharge capacities are expressed as a percentage of the nominal capacity. The nominal capacity is obtained by subtracting from the theoretical capacity of the positive electrode that capacity that is consumed in the first cycle for the formation of a coating layer on the negative electrode. This coating layer is formed on the negative electrode when the test full cell is charged for the first time. Lithium ions are irreversibly consumed for this formation of a coating layer, so that the respective test full cell has less cyclic capacity available for the subsequent cycles.

Experiment 1: Test Full Cells Having Lithium Iron Phosphate LiFePO.SUB.4 .(LEP) as the Active Electrode Material—High Upper Potential

[0195] A test full cell according to Example 3 was produced using lithium iron phosphate LiFePO.sub.4 (LEP) as the active electrode material of the positive electrode. The test full cell was filled with electrolyte 1 described in Example 2.

[0196] FIG. 6 shows the potential profile in volts [V] as a function of the percentage charge, which is related to the maximum charge of the test full cell. The test full cell was charged at a current of 50 mA up to an upper potential of 5 V. The potential was held until the charge current had dropped to 40 mA. The discharge then took place with a current intensity of 50 mA up to a discharge potential of 2.5 volts.

[0197] The charge/discharge experiment was repeated again, with the difference that the upper potential limit when charging was increased from 4.5 volts to 5.0 volts in 0.1 volt steps. 5 cycles were performed with each potential. FIG. 7 shows the discharge capacity and the associated charge potential (upper potential).

[0198] The achieved discharge capacities are almost identical for each charge potential and are 99%. This means that the discharge capacities obtained are independent of the charge potential. A higher charge potential does not cause any undesired reactions, such as decomposition of the electrolyte or irreversible destruction of the active material LEP.

Experiment 2: Test Full Cells Having Lithium Iron Phosphate LiFePO.SUB.4 .(LEP) as the Active Electrode Material

[0199] A test full cell according to Example 3 was produced using lithium iron phosphate LiFePO.sub.4 (LEP) as the active electrode material of the positive electrode. The test full cell was filled with electrolyte 1 described in Example 2. The test full cell was cycled as described in Experiment 1 to determine the discharge capacities (see Example 4). The upper potential of test full cell was 3.6 volts. FIG. 8 shows the discharge capacities of the test full cell as a function of the number of cycles. These mean values of the discharge capacities are expressed as a percentage of the nominal capacity. The test full cell shows exceptionally stable behavior of the discharge capacity over more than 1880 cycles. A capacity of 78% is still obtained even after this very high number of cycles. The combination of a positive electrode with a polyanionic compound, such as lithium iron phosphate, in connection with the electrolyte 1 leads to an extremely long-lasting test full cell having good stability.

Experiment 3: Test Full Cells Having Lithium Iron Manganese Phosphate Li(Fe.SUB.0.3.Mn.SUB.0.7.)PO.SUB.4 .as the Active Electrode Material

[0200] In order to test further lithium metal phosphates as the active electrode material, a test full cell according to Example 3 was produced in a further experiment. The active material of the positive electrodes (cathodes) consisted of lithium iron manganese phosphate Li(Fe.sub.0.3Mn.sub.0.7)PO.sub.4.

[0201] The test full cell was filled with electrolyte 1 described in Example 2. The test full cell was cycled as described in Experiment 1 to determine the discharge capacities (see Example 4). The upper potential of the cells according to this disclosure is 4.5 volts.

[0202] FIG. 9 shows mean values for the discharge capacities of the test full cell as a function of the number of cycles. These mean values of the discharge capacities are expressed as a percentage of the nominal capacity. The cell shows very stable behavior of the discharge capacity. A capacity of 97% is still obtained at cycle 200.

Experiment 4: Test Full Cells Having Lithium Iron Cobalt Phosphate LiFeCoPO.SUB.4 .as the Active Electrode Material

[0203] In order to test further lithium metal phosphates as the active electrode material, a test full cell according to Example 3 was produced in a further experiment. The active material of the positive electrodes (cathodes) consisted of lithium iron cobalt phosphate (LiFeCoPO.sub.4). The test full cell was filled with electrolyte 1 described in Example 2.

[0204] FIG. 10 shows the potential profile of the first cycle in volts [V] as a function of the percentage charge, which is related to the maximum charge of the test full cell [% of the max. charge]. A coating layer forms on the negative electrode in the first cycle of the full test cell. Lithium ions are irreversibly consumed for said formation of a coating layer, such that the discharge capacity of the test full cell is less than the charge capacity. The test full cell was charged at a charge rate of C/10 up to an upper potential of 5.0 V. The discharge then took place at a discharge rate also of C/10 up to a discharge potential of 4.0 volts.

[0205] The test full cell can be charged up to a high upper potential of 5 volts and then discharged again. No electrolyte decomposition can be seen even at high potentials.

Experiment 5: Test Full Cells Having Lithium Iron Phosphate LiFePO.SUB.4 .(LEP) as the Active Electrode Material in Combination with Electrolyte 1 and Electrolyte 3 and the Reference Electrolyte

[0206] Various experiments were performed to investigate electrolytes 1 and 3 in combination with lithium iron phosphate as the active material. On the one hand, the coating layer capacities of electrolytes 1 and 3 were determined. This coating layer is formed on the negative electrode when the test full cell is charged for the first time. Lithium ions are irreversibly consumed for this formation of a coating layer, so that the test full cell has less cyclic capacity available for the subsequent cycles. On the other hand, the discharge capacities in electrolytes 1 and 3 were determined. Both experiments were also performed in the reference electrolyte for comparison.

[0207] The reference electrolyte, electrolyte 1 and electrolyte 3 were each investigated in a test full cell for this experiment. The structure corresponded to the structure described in Example 3. The reference electrolyte used in a first experiment had the composition LiAlCl.sub.4*x SO.sub.2 with x>1.5. Electrolytes 1 and 3 were investigated in a second and third experiment.

[0208] FIG. 11 shows the potential in volts of the test full cells when charging the negative electrode as a function of capacity, which is related to the theoretical capacity of the negative electrode. Here, the dotted line shows the results for the reference electrolyte and the dashed and solid lines show the results for electrolytes 1 and 3 according to this disclosure. The three curves depicted show averaged results of several experiments with the test whole cells described above. First, the test full cells were charged with a current of 15 mA until a capacity of 125 mAh (Q.sub.lad) was reached. The test full cells were then discharged at 15 mA until a potential of 2.5 volts was reached. The discharge capacity (Q.sub.ent) was determined.

[0209] The capacity in % of the theory that was used to form the coating layer on the negative electrode is calculated according to the following formula:

Coating layer capacity=(Q.sub.lad(125mAh)−Q.sub.ent(x mAh))/Q.sub.NEL

[0210] Q.sub.NEL is the theoretical capacity of the negative electrode used. The theoretical capacity is calculated, in the case of graphite, to a value of 372 mAh/g. The absolute capacity losses are 7.58% and 11.51% for electrolytes 1 and 3, respectively, and 6.85% for the reference electrolyte. The capacity for the formation of the coating layer is somewhat higher in both electrolytes according to this disclosure than in the reference electrolyte. Values in the range of 7.5%-11.5% for the absolute capacity losses are good results in combination with the possibility of using positive cathodes up to 5 volts.

[0211] For the discharge experiments, three test full cells according to Example 3 were filled with electrolytes 1 and 3 described in Example 2 and the reference electrolyte. The test full cells had lithium iron phosphate as the active material of the positive electrode. To determine the discharge capacities (see Example 4), the test full cells were charged with a current intensity of 15 mA up to a capacity of 125 mAh. The discharge then took place with a current intensity of 15 mA up to a discharge potential of 2.5 volts.

[0212] FIG. 12 shows the potential profile during the discharge over the discharged amount of charge in % [% of the maximum charge]. All test full cells show a flat discharge curve, which is necessary for good operation of a battery cell.

Experiment 6: Determination of the Conductivities of Electrolytes 1, 3 and 4

[0213] To determine the conductivity, electrolytes 1, 3 and 4 were prepared using different concentrations of compounds 1, 3 and 4. The conductivities of the electrolytes were determined using a conductive measurement method for each concentration of the various compounds. After temperature control, a two-electrode sensor was held touching in the solution and measured in a measuring range of 0-50 mS/cm. During the measurements, it was noted that the sensor can react with the SO.sub.2-containing electrolyte solution.

[0214] FIG. 13 shows the conductivity of electrolyte 1 as a function of the concentration of compound 1. A maximum of the conductivity can be seen at a concentration of compound 1 of 0.6 mol/L-0.7 mol/L having a value of approx. 37.9 mS/cm. In comparison, the organic electrolytes known from the prior art, such as LP30 (1 M LiPF.sub.6/EC-DMC (1:1 weight)) have a conductivity of only approx. 10 mS/cm.

[0215] FIGS. 14 (electrolyte 3) and 15 (electrolyte 4) show the conductivity values for electrolytes 3 and 4 determined for the different concentrations.

[0216] With electrolyte 4, a maximum of 18 mS/cm is achieved at a conducting salt concentration of 1 mol/L. Electrolyte 3 shows its highest conductivity of 0.5 mS/cm at a conducting salt concentration of 0.6 mol/L. Although electrolyte 3 shows a lower conductivity, as in experiment 4, charging or discharging of a test full cell is quite possible.

Experiment 7: Low Temperature Behavior

[0217] Two test full cells according to example 3 were produced in order to determine the low-temperature behavior of electrolyte 1 in comparison to the reference electrolyte. One test full cell was filled with reference electrolyte of the composition LiAlCl.sub.4*6SO.sub.2 and the other test full cell with electrolyte 1. The test full cell having the reference electrolyte comprised lithium iron phosphate (LEP) as the active material, the test full cell having electrolyte 1 comprised lithium nickel manganese cobalt oxide (NMC) as the active material of the positive electrode. The test full cells were charged to 3.6 volts (LEP) or 4.4 volts (NMC) at 20° C. and discharged again to 2.5 volts at the respective temperature to be investigated. The discharge capacity reached at 20° C. was rated as 100%. The temperature for the discharge was lowered in temperature steps of 10° K. The discharge capacity obtained was described in % of the discharge capacity at 20° C. Since the low-temperature discharges are almost independent of the active materials used for the positive and negative electrodes, the results can be transferred to all combinations of active materials. Table 3 shows the results.

TABLE-US-00003 TABLE 3 Discharge Capacities as a Function of the Temperature Discharge Capacity of Discharge Capacity of the Temperature Electrolyte 1 Reference Electrolyte 20° C. 100%  100%  10° C. 99% 99% 0° C. 95% 46% −10° C. 89% 21% −20° C. 82% n/a −30° C. 73% n/a −35° C. 68% n/a −40° C. 61% n/a

[0218] The test full cell having electrolyte 1 shows very good low-temperature behavior. At −20° C., 82% of the capacity is reached, at −30° C., 73%. Even at a temperature of −40° C., 61% of the capacity can still be discharged. In contrast, the test full cell having the reference electrolyte only shows a discharge capacity down to −10° C. A capacity of 21% is achieved here. The test full cell having the reference electrolyte can no longer be discharged at lower temperatures.

[0219] 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.