High capacity primary lithium cells and methods of making thereof

Abstract

A high capacity primary electrochemical lithium cell includes an anode comprising metallic lithium, a hybrid cathode comprising a liquid SO.sub.2 cathode and a solid cathode including a cathode material characterized by having a first electromotive force (EMF) when coupled to a metallic lithium anode. The first EMF is greater than a second EMF of a cell having a metallic lithium anode and a liquid SO.sub.2 cathode. A separator may separate the anode from the solid cathode. The cell includes an electrolyte solution including at least one ionizable salt dissolved in at least one organic solvent. The solid cathode material may include carbon monofluoride (CF.sub.X), a transition metal oxide, a mixture of two or more transition metal oxides or any combinations of such cathode materials. The solid cathode may also include a binder and a carbon based conductive material.

Claims

1. A primary electrochemical lithium cell, comprising: an anode comprising metallic lithium therein; a cathode comprising a current collector and both a liquid SO.sub.2 cathode and a solid cathode which comprises a cathode material characterized by having a first electromotive force (EMF) when coupled to a metallic lithium anode, the first EMF is greater than a second EMF of a cell having a metallic lithium anode and a single liquid SO.sub.2 cathode; an electrolyte solution comprising at least one ionizable salt dissolved in at least one organic solvent; and a separator disposed between the anode and the solid cathode of the cell.

2. The primary cell according to claim 1, wherein the second EMF is in the range of 2.9-3.1 Volt.

3. The primary cell according to claim 1, wherein the cathode material of the solid cathode is selected from, carbon monofluoride (CF.sub.X), a transition metal oxide, a mixture of two or more transition metal oxides and any combinations thereof.

4. The primary cell according to claim 3, wherein the transition metal oxide is selected from the list consisting of MnO.sub.2, CoO.sub.2, NiO.sub.2, V.sub.2O.sub.5.

5. The primary cell according to claim 3, wherein the solid cathode comprises a mixture of CF.sub.X with one or more transition metal oxides, and wherein the weight of the CF.sub.X is in the range of 10%-45% of the total weight of the cathode material of the solid cathode.

6. The primary cell according to claim 3, wherein the solid cathode material comprises CF.sub.X and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

7. The primary cell according to claim 3, wherein the solid cathode material comprises a mixture of CF.sub.X and MnO.sub.2 and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

8. The primary cell according to claim 3, wherein the solid cathode material comprises MnO.sub.2 and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

9. The primary cell according to claim 1, wherein the at least one ionizable salt is selected from LiBr, LiClO.sub.4 and any combination thereof.

10. The primary cell according to claim 1, wherein the at least one organic solvent is Acetonitrile (AN).

11. The primary cell according to claim 1, wherein the cell is selected from a Jelly Roll type cell, a wafer type cell, a bobbin type cell and a prismatic type cell.

12. The primary cell according to claim 1, wherein the first EMF is in the range of 3.0-4.5 Volt.

13. A method for constructing a primary electrochemical cell, the method comprising the steps of: providing an anode including a current collector and metallic lithium; providing a cathode including a current collector and both a liquid SO.sub.2 cathode and a cathode material which comprises a solid material characterized by having a first electromotive force (EMF) when coupled to a metallic lithium anode, the first EMF is greater than a second EMF of a cell having a metallic lithium anode and a single liquid SO.sub.2 cathode; inserting the anode and the cathode with a separator interposed therebetween into a canister; injecting into the canister under vacuum a mixture of liquid SO.sub.2, and an electrolyte solution comprising at least one ionizable salt and at least one organic solvent; and hermetically sealing the cell after the step of injecting.

14. The method according to claim 13, wherein the second EMF is in the range of 2.9-3.1 Volt.

15. The method according to claim 14, wherein the cathode material of the solid cathode is selected from, carbon monofluoride (CF.sub.X), a transition metal oxide, a mixture of two or more transition metal oxides and any combinations thereof.

16. The method according to claim 15, wherein the transition metal oxide is selected from the list consisting of MnO.sub.2, CoO.sub.2, NiO.sub.2, V.sub.2O.sub.5.

17. The method according to claim 15, wherein the solid cathode material comprises CF.sub.X and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

18. The method according to claim 15, wherein the solid cathode material comprises a mixture of CF.sub.X and MnO.sub.2 and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

19. The method according to claim 15, wherein the solid cathode material comprises MnO.sub.2 and wherein the energy density of the primary cell exceeds 215 Wh/Kg and/or exceeds 395 Wh/liter.

20. The method according to claim 13, wherein the first EMF is in the range of 3.0-4.5 Volt.

Description

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

Abbreviations

(1) The following abbreviations are used throughout the present application:

(2) TABLE-US-00001 Abbreviation Meaning m micrometer AN Acetonitrile cm centimeter cm.sup.2 Square centimeter DMC Dimethyl carbonate EMF Electromotive force g gram Kg Kilogram L Liter Li Metallic Lithium Li+ Lithium Ion mA milliampere mm millimeter OCV Open Cell Voltage PC Propylene carbonate PTFE Polytetrafluoroethylene PVDF Polyvinylidenefluoride SO2 Sulfur dioxide THF Tetrahydrofuran V Volt Wh Watt hour

(3) The present application discloses a new type of primary lithium/SO.sub.2/X electrochemical cell having a markedly increased capacity and energy density as compared to prior art primary liquid cathode Li/SO.sub.2 cells.

(4) The new type of cells disclosed herein have a lithium anode and a hybrid cathode including a liquid SO.sub.2 cathode and a solid cathode material X having an EMF (of the corresponding Li/X anode/cathode couple) higher than the EMF of the Li/SO.sub.2 anode/cathode couple).

(5) Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. It is expected that during the life of a patent maturing from this application many relevant electrochemically suitable solid cathodes will be developed and the scope of the terms solid cathode and solid cathode material are intended to include all such new technologies a priori. As used herein the term about refers to 10%. The word exemplary is used herein to mean serving as an example, instance or illustration. Any embodiment described as exemplary is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

(6) The word optionally is used herein to mean is provided in some embodiments and not provided in other embodiments. Any particular embodiment of the invention may include a plurality of optional features unless such features conflict.

(7) The terms comprises, comprising, includes, including, having and their conjugates mean including but not limited to.

(8) The term consisting of means including and limited to.

(9) The term consisting essentially of means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

(10) As used herein, the singular form a, an and the include plural references unless the context clearly dictates otherwise. For example, the term a compound or at least one compound may include a plurality of compounds, including mixtures thereof.

(11) The term hybrid cell is used throughout the specification and the claims hereinafter to mean an electrochemical cell having a metallic lithium anode and a combination of a liquid SO.sub.2 cathode and a solid cathode including a solid cathode active material. The cell includes an electrolyte solution including a suitable ionizable salt dissolved in one or more organic solvents (which also includes the SO.sub.2 dissolved in the solvent). Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

(12) Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases ranging/ranges between a first indicate number and a second indicate number and ranging/ranges from a first indicate number to a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

(13) It was serendipitously discovered by the inventors of the present application that it is possible to substantially increase the capacity of liquid cathode Li/SO.sub.2 system cells by incorporation of a solid cathode material in the liquid cathode cells. The liquid and the solid cathodic materials can be reduced simultaneously during the discharge provided that a proper ratio between the EMF of the liquid cathode and the EMF of the solid cathode is kept.

(14) Generally speaking, from thermodynamic considerations, when a liquid cathode and a solid cathode are present in the same cell having a metallic lithium anode, the cathode material with a higher EMF value will react preferentially to the cathode material of the lower EMF value, unless the first reaction is kinetically hindered. When the difference in the EMF value between the two different cathode materials is too high, separate discharge steps are expected. The discharge curve has two plateaus. A first plateau is expected for the high EMF anode/cathode couple and a second plateau is expected for the lower EMF anode/cathode couple. When the EMF of the two anode/cathode couples is too close, one single curve is expected with a gradual voltage change over the discharge time.

(15) Therefore, incorporation of a MnO.sub.2 solid cathode (having an EMF of 3.2V) into a Li/SOCl.sub.2 cell (having an EMS of 3.7V) will not give any capacity gain in the cell in comparison to a cell having SOCl.sub.2 as the sole cathode. Since the EMF of the Li/SOCl.sub.2 anode/cathode couple is substantially higher than Li/MnO.sub.2 anode cathode couple and in addition the SOCl.sub.2 is a sole solvent that serves dual role as cathode material and as a solvent to transport the ions, it is preferable in this case to use the sole cathode only with the higher EMF. The same rational holds for the Li/CF.sub.X anode/cathode couple and the Li/FeS.sub.2 couple. The difference in the voltages is so high that it is better to use just CF.sub.X. The same rational holds for liquid cathode SOCl.sub.2 and solid cathode FeS.sub.2.

(16) Similarly, a cell with a combination liquid SO.sub.2 cathode and a solid FeS.sub.2 cathode will show two voltage plateaus during cell discharging. During the first voltage plateau Li and SO.sub.2 are the active couple but after consumption of the SO.sub.2, the undesirable reactions of the metallic lithium with the AN solvent is expected. So this combination cannot yield a practical cell.

(17) Thus, a combination of a liquid SO.sub.2 cathode with MnO.sub.2 solid cathode material in a cell or a combination of a liquid SO.sub.2 cathode with CF.sub.X solid cathode material is expected to give a significantly higher capacity than the capacity of a prior art Li/SO.sub.2 cell.

(18) It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

(19) The solvents described in the examples below were lithium battery grade materials obtained from BASF SE, Germany, the MnO.sub.2 was obtained from Tronox Ltd., USA, the CF.sub.X is commercially available from Advanced Research Chemicals (ACR), USA.

(20) Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

EXAMPLES

(21) Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

Example 1: A Prior Art Li/SO.SUB.2 .Cell

(22) A standard D size Li/SO.sub.2 cell was fabricated. The anode of the cell consists of lithium metal foil having a thickness of 170 m a length of 650 mm and a width of 39 mm. The current collector was a copper strip having a thickness of 75 m and a width of 3 mm. The total weight of lithium in the anode was 2.2 g. The geometrical surface area of anode was about 510 cm.sup.2.

(23) The cell's cathode was made from a mixture of 95% percent (by weight) of acetylene black carbon and 5% (by weight) PTFE binder on a sheet of aluminum expanded metal as current collector. The geometrical dimensions of the cathode were 700 mm length, 41 mm width and 750 m thickness. The porosity of the cathode was about 80%. Prior to cell assembly, the cathode was dried for eighteen (18) hours under vacuum at 130 C. in a dry room. An aluminum tab was welded to the aluminum expanded metal sheet as an electrical contact.

(24) A micro-porous polypropylene separator separated between anode and cathode. The electrodes together with the separator were spirally wound in the jelly-roll configuration and inserted into a D size nickel plated cold rolled steel canister serving as the negative pole. The cell's cover was made from nickel plated cold rolled steel and a molybdenum positive pole. Glass to metal seal (GTMS) separated between the positive pole and the negative pole of the cell. The anode tab was welded to the negative pole and the cathode aluminum tab was welded to the positive pole of the cell. The can and cover are mechanically closed and welded together using a cirrocumulus welding laser. The electrolyte solution of the cell included 1 molar of lithium bromide (LiBr) dissolved in a mixture of liquid SO.sub.2 and acetonitrile (AN) in a ratio of 4:1 by weight, respectively. The electrolyte solution was injected into the cell in vacuum through the molybdenum pole tube and the cell was hermetically sealed. The cell open circuit voltage (OCV) reached 3.16V after about 24 hours. The OCV stabilized at 3.10V after 10 days of storage at room temperature. The cell was discharged under a constant current of 250 mA to a 2.0V cutoff. The cell's capacity was 7.4 Ah delivered after about 30 hours of continuous discharge.

Example 2: Prior Art Li/MnO.SUB.2 .Cell

(25) The constructed cell was a standard D size cell and the cell's canister and cover were identical to the can and cover disclosed in EXAMPLE 1 above. The anode had the same construction and the same length and width as described in EXAMPLE 1 except that the thickness of the anode was 270 m and the weight of the lithium in the anode was 3.7 g.

(26) The cathode material included a mixture of 87% (by weight) of electrochemical manganese dioxide (EMD) (MnO.sub.2), 10% (by weight) of conductive carbon and 3% polyvinylidene fluoride PVDF. The current collector was identical to the expanded aluminum metal current collector used in EXAMPLE 1. The length and the width of the cathode were identical to those in EXAMPLE 1. The thickness of the cathode was 680 m. The total weight of MnO.sub.2 was 54 g and the porosity of the cathode was about 40%. The cathode was dried in a vacuum at 250 C. prior to cell assembly. The electrolyte solution was a 1 molar lithium perchlorate (LiClO.sub.4) dissolved in a solvent containing a mixture of PC:THF (1:1 by volume, respectively).

(27) The porous polypropylene separator used was similar to the separator used in EXAMPLE 1. The cell assembly was performed as disclosed for the cell of EXAMPLE 1. The cell was filled with the electrolyte solution in a vacuum after the laser welding as disclosed for the cell of EXAMPLE 1. After the electrolyte insertion, the cell was hermetically sealed by welding. The OCV of the cell started at 3.38V and stabilized at 3.25V about 10 days after electrolyte filling. The cell was discharge at a constant current of 250 mA to a 2.0V cut off. The cell delivered a capacity of 11.7 Ah.

Example 3: Hybrid Cell with Solid MnO.SUB.2 .Cathode and SO.SUB.2 .Liquid Cathode

(28) A standard D size cell was constructed with a canister and a cover identical to those of EXAMPLE 1. The cell's anode was a metallic lithium cathode having the same construction and materials as disclosed for EXAMPLE 1 and EXAMPLE 2 hereinabove, except that the weight of the lithium use in the anode construction was 4.4 gram and the thickness of the lithium foil was 330 m. The cell's cathode had a similar construction as in EXAMPLE 2, except that the thickness of the cathode and the cathode's porosity were lower than those of the cathode of EXAMPLE 2 to cope with the increase in the thickness of the anode and the expected cell capacity. The thickness of the cathode was 610 m. The cell was filled with 16.8 g of an electrolyte solution including 1 molar LiBr in a mixture of 4:1 by weight of SO.sub.2:AN, respectively. The OCV of the hybrid cell was 3.35V after 24 hours and stabilized at 3.28V after 10 days of storage at room temperature. The cell was discharged at a constant current of 250 mA to a 2.0V cut off. The hybrid cell delivered a capacity of 15.2 Ah.

(29) It is clear that in EXAMPLE 3 the liquid SO.sub.2 cathode together with the solid MnO.sub.2 cathode contribute to the discharge capacity of the cell. It can be shown that 9.8 Ah was delivered by the solid cathode and 5.4 Ah was delivered by the liquid SO.sub.2 cathode. The increase in the capacity of example results from the capacities of the SO.sub.2 material and the solid cathode MnO.sub.2.

Example 4: Hybrid Cell with Solid CF.SUB.X .Cathode and Liquid SO.SUB.2 .Cathode

(30) A standard D size cell was fabricated as in EXAMPLE 2 except that the solid MnO.sub.2 cathode was replaced by a CF.sub.X solid cathode and the quantity of lithium metal in the anode was increased to balance the total capacity of the cathode that is the sum of the solid cathode capacity and the liquid SO.sub.2 cathode capacity. The length of the anode was 650 mm, the width of the anode was 39 mm and the thickness of the anode was 390 m. The total weight of lithium metal in the anode was about 5.2 g.

(31) The cathode consisted of a mixture of 87% by weight of carbon monofluoride CF.sub.X, 10% by weight conductive carbon and 3% by weight PVDF.

(32) The length of the cathode was 700 mm, the width of the cathode was 41 mm and the thickness of the cathode was 560 m. The porosity of cathode material was calculated to be 42% and the CF.sub.X weight was 22 g. The electrolyte solution had the same composition as the electrolyte solution of EXAMPLE 1. (1 molar LiBr dissolved in SO.sub.2:AN mixture of 4:1 by weight). The total weight of electrolyte solution was 13 g. The porous polypropylene separator was identical to the separator of EXAMPLE 1. The cell was assembled in a similar manner as described for EXAMPLE 1 and filled with cell electrolyte in a vacuum after the s of the laser welding. After the electrolyte insertion the cell was hermetically sealed by welding. The OCV of the cell started at 3.43V and stabilized at 3.32V at about 14 days of storage at room temperature after electrolyte solution filling. The cell was discharged at a 250 mA constant current to a 2.0V cut off. The cell delivered a capacity of 18.3 Ah. it was calculated that about 14.5 Ah of the cell's capacity came from the solid CF.sub.X and about 3.8 Ah from the liquid SO.sub.2.

Example 5: Hybrid Cell with a Mixture of Two Solid Cathode Materials and a Liquid SO.SUB.2 .Cathode

(33) As CF.sub.X material is much more expensive than EMD MnO.sub.2, a mixture of MnO.sub.2 and CF.sub.X was used in this example. A standard D size cell was constructed. The canister and cell cover were identical to those used in EXAMPLE 1 above. The cell construction method was similar to that of EXAMPLE 4 above, except that the solid cathode material was a mixture of MnO.sub.2 and CF.sub.X in a ratio of 5:1 (by weight). The anode length and width were similar to example 4 but the thickness of the lithium foil was just 340 m and the total weight of lithium metal in the anode was 4.8 g. The cathode length was 700 mm and it thickness was 590 m. The net weight of CF.sub.X in the cathode was 7.7 g and the net weight of MnO.sub.2 was 34.5 g.

(34) The electrolyte solution was the same composition as in EXAMPLE 1. (1 molar LiBr in a mixture of 4:1 by weight of SO.sub.2:AN). The total weight of the electrolyte solution in the cell was 13 g. The porous polypropylene separator was similar to that used in EXAMPLE 1. The cell was assembled in a similar manner as described for EXAMPLE 1. The cell was filled with the electrolyte solution under vacuum after the laser welding of the cover to the canister as disclosed hereinabove. After the electrolyte insertion the cell was hermetically sealed by welding.

(35) The OCV of the cell started at 3.40V and stabilized at 3.30V at 14 days after electrolyte filling. The cell was discharge at a constant current of 250 mA to a 2.0V cut off. The cell delivered a capacity of 16.8 Ah. It was calculated that out of this total cell capacity, 7.7 Ah were delivered by the MnO.sub.2 cathode material, 5.3 Ah were delivered by the CF.sub.X cathode material and about 3.8 Ah were delivered by the liquid SO.sub.2 liquid cathode.

(36) It was found that as long as an unreduced solid cathode is present in the cell, the SO.sub.2 will not be totally consumed. In other words as long as a non-reduced cathode material is present in the cell, SO.sub.2 will remain in the solution and no reaction of metallic lithium with the acetonitrile solvent will occur. This finding enables to increase the capacity of the SO.sub.2 cell by incorporation of one or more solid cathode materials in addition to the liquid SO.sub.2 cathode. The MnO.sub.2 cathode (when coupled to a metallic Lithium anode) and the CF.sub.X cathode (when coupled to a metallic lithium anode) are found to have higher EMF than the EMF of a cell having a liquid SO.sub.2 cathode only (when coupled to a metallic lithium anode) and therefore the above two cathode materials are adequate to increase the capacity of the liquid SO.sub.2 cathode cell.

(37) On the other hand, a Li/FeS.sub.2 solid cathode cell (having a metallic lithium anode) has an EMF lower than the EMF of a cell having a liquid SO.sub.2 cathode only (when coupled to a metallic lithium anode) and therefore cannot be used for this application because during the discharge of such a hypothetical cell, after consumption of all SO.sub.2, the acetonitrile solvent may react with the lithium metal remaining in the anode leading to the undesirable formation of LiCN and HCN that may result in cell rapture.

(38) As demonstrated in EXAMPLE 3 the incorporation of MnO.sub.2 cathode material into a cell having an SO.sub.2 cathode in liquid the resulting cell's capacity is increased to beyond 15 Ah in comparison to just 7.5 Ah capacity of a standard liquid SO.sub.2 cathode in D size cells.

(39) Moreover, the hybrid cell (having MnO.sub.2+SO.sub.2 cathodes) capacity and the energy density of SO.sub.2 were increased significantly beyond 7.5 Ah by incorporation of CF.sub.X into the solid cathode of the cell. As the equivalent weight of CF.sub.X is lower than the equivalent weight of MnO.sub.2 (for x=1 the equivalent weight of CF.sub.X is 31 as compared to an equivalent weight of 72 for MnO.sub.2) the energy density per unit cell weight for a hybrid cell including a liquid SO.sub.2 cathode and a solid CF.sub.X cathode material is higher than the energy density of a hybrid cell including a liquid SO.sub.2 cathode and a solid cathode material including a mixture of CF.sub.X and MnO.sub.2.

(40) TABLE 1 below summarizes some electrochemical properties of prior art Li/SO.sub.2 and Li/MnO.sub.2 primary cells including some examples of primary lithium batteries commercial available from different manufacturers.

(41) TABLE-US-00002 TABLE 1 (prior art cells) Nominal D size cell OCV Energy Density capacity Cell type (V) Wh/Kg Wh/L (Ah) REMARKS Li/SO.sub.2 2.9 255 405 7.5 Example 1 Li/SO.sub.2 2.9 215 395 7.7 LO26SX Saft Li/MnO.sub.2 3.1 308 640 12.6 M-20 Saft Li/MnO.sub.2 3.1 295 620 11.7 Example 2 Li/CF.sub.x 3.0 472 838 16.0 LCF-129 Eagle Pitcher

(42) TABLE 2 below summarizes some electrochemical properties of the novel hybrid cells of the present invention.

(43) TABLE-US-00003 TABLE 2 Nominal D size cell OCV Energy Density capacity Cell type (V) Wh/Kg Wh/L (Ah) REMARKS Li/(SO.sub.2 + MnO.sub.2) 3.28 395 770 15.2 Example 3 Li/(SO.sub.2 + CF.sub.x) 3.32 590 870 18.3 Example 4 Li/(SO.sub.2 + CF.sub.x + 3.30 450 825 16.8 Example 5 MnO.sub.2)

(44) It may be seen from TABLE 1 and TABLE 2 above that the incorporation of a solid cathodic material into a Li/SO.sub.2 liquid cathode cell substantially increases the cells capacity and the energy density of the cell as compared to the standard prior art, as well as compared to a primary lithium cell having only the solid cathode material that was incorporated into the hybrid cathode cell.

(45) Furthermore, while CF.sub.X cathode material is relatively expensive, it is possible to significantly increase the hybrid cell's capacity by including a relatively small amount of CF.sub.X (such as, for example 16.7% CF.sub.X by weight) to a mixed solid cathode material composed of MnO.sub.2+CF.sub.X that is incorporated in a Li/SO.sub.2 liquid cathode cell. While the Energy density of such a cell is lower than that of a standard Li/CF.sub.X cell (by about 5%) or that of a hybrid cell Li/(CF.sub.X+SO.sub.2) (by about 23%), it enables to advantageously substantially increase the capacity of the cell at a relatively low cost of manufacturing and makes the Li/(SO.sub.2+MnO.sub.2+CF.sub.X) of EXAMPLE 4 hereinabove quite attractive for applications where the total cell's weight is not an important consideration but cell capacity and cost are important.

(46) It will be appreciated that the hybrid cells disclosed herein are not limited to using the specific solid cathode compositions disclosed in the examples 3-5 above. Rather, many other types of transition metal oxide cathodic materials, different than those given in the examples above, may be successfully used in the hybrid cells of the present invention.

(47) Some examples of such cells may include but are not limited to the following systems: Li/(SO.sub.2+CoO.sub.2), Li/(SO.sub.2+NiO.sub.2), Li/(SO.sub.2+V.sub.2O.sub.5), Li/(SO.sub.2+CoO.sub.2/MoO.sub.2), Li/(SO.sub.2+MnO.sub.2/CF.sub.X), Li/(SO.sub.2+CoO.sub.2/CF.sub.X), Li/(SO.sub.2+NiO.sub.2/CF.sub.X), Li/(SO.sub.2+V.sub.2O.sub.5/CF.sub.X).

(48) Furthermore, any solid cathode having a mixture of any type of suitable mixture of transition metal oxides (which in a cell with a metallic lithium anode exhibits an EMF larger than the EMF of the prior art Li/SO.sub.2 cell) may be used together with SO.sub.2 in the hybrid cathode cells of the present invention. Moreover, such multi metal oxide cathodes may include an amount of CF.sub.X cathode material (typically about 10%-45% by weight) of the cathode material mixture.

(49) Furthermore, it is noted that the type of electrolyte solutions described in the examples hereinabove are not to be regarded as obligatory to practicing the cells of the present invention. It may be possible to use different ionizable salts and/or different types of organic solvents (or solvent mixtures) as long as they are compatible with the SO.sub.2 liquid cathode and with the solid cathode being used in the cell.

(50) Furthermore, it is noted that although the experimental cells described in Examples 3-5 above were constructed as a Jelly Roll type cell, this is not obligatory to practicing the invention and any other suitable type of cell structure may be used. For example, button type, wafer type, prismatic type and bobbin type hybrid cells may all be constructed and are included within the scope of the hybrid cells of the present invention. Any other type of cell construction and/or any size of such cells may be used as long as it is compatible with the cell's ingredients.

(51) Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

(52) All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.