Europäisches Patentamt *EP001179870A1* (19) European Patent Office Office européen des brevets (11) EP 1 179 870 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.7: H01M 6/14, H01M 4/36 13.02.2002 Bulletin 2002/07 (21) Application number: 01306671.7 (22) Date of filing: 03.08.2001 (84) Designated Contracting States: (71) Applicant: WILSON GREATBATCH LTD. AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU Clarence New York 14031 (US) MC NL PT SE TR Designated Extension States: (72) Inventor: Krehl, Paul W. AL LT LV MK RO SI Williamsville, New York 14221 (US) (30) Priority: 07.08.2000 US 633467 (74) Representative: Bradley, Josephine Mary et al Mathys & Squire 100 Gray’s Inn Road London WC1X 8AL (GB) (54) High voltage electrochemical cell capable of operating at extremely low temperatures (57) An alkali metal/oxyhalide cell which provides greatly enhanced low temperature performance and increased safety during operation, is described. The preferred cell includes a novel combination of halogens and/or interhalogens incorporated into the lithium/SOCl2 system. EP 1 179 870 A1 Printed by Jouve, 75001 PARIS (FR) 1 EP 1 179 870 A1 2 Description codepolarizer with SOCl2 in a 1:6 mole ratio, respective- ly. These cells exhibit an open circuit voltage (OCV) of BACKGROUND OF THE INVENTION about 3.90 volts at room temperature, and their opera- tional temperature range is from -40°C to 85°C. 1. Field of the Invention 5 [0005] Fig. 1 is a graph constructed from the dis- charge of two prior art Li/BCX cells having a 1:6 mole [0001] The present invention generally relates to the ratio of BrCl in SOCl2 and discharged at room temper- art of electrochemical cells, and more particularly to a ature under a 56 ohm load. The discharge curves are new and an improved electrochemical cell comprising labeled 10 and 12, respectively. It is believed that the an alkali metal anode and a catholyte including a mixed 10 high voltage plateau in the first 15% of discharge (curve soluble depolarizer having a halogen and/or interhalo- portions 10A and 12A) is related to the partial discharge gen. Still more particularly, the present invention relates of the BrCl codepolarizer. According to the present in- to a high voltage, lithium/oxyhalide cell that is operable vention, it is believed that the high voltage plateau in at extremely low temperatures through a unique bal- alkali metal/oxyhalide cells, such as a Li/BCX cell, is ac- ance of halogens and/or interhalogens with inorganic 15 centuated during low temperature discharge by increas- chemical systems. The present chemistry also has en- ing the ratio of the halogens and/or interhalogens to the hanced safety characteristics over conventional oxyhal- inorganic depolarizer system to improve both the safety ide systems. and low temperature discharge performance of such chemistries. 2. Prior Art 20 SUMMARY OF THE INVENTION [0002] In general, lithium inorganic electrochemical systems have a high energy density and operate over [0006] The present invention, therefore, provides an a wide temperature range. For example, lithium/SOCl2 electrochemical cell of high energy density including an D-size cells have an energy density of approximately 25 alkali metal anode, a cathode current collector of elec- 350 to 400 Wh/kg at 20°C. The nominal cell voltage at trically conductive and/or electroactive material, and an room temperature is 3.3 to 3.5 volts. Depending on cell ionically conductive catholyte solution operatively asso- design, such cells can operate over a temperature range ciated with the anode and the cathode current collector. of -40°C to >85°C. However, low temperature discharge The catholyte consists essentially of a first depolarizer tests show that the specific energy density and load volt- 30 component selected from the group consisting of free age of Li/SOCl2 cells are significantly reduced when dis- halogens, interhalogens and mixtures thereof dissolved charged at the lower end of that operating range. At - in a second depolarizer component in the form of a non- 40°C, the discharge efficiency of such cells drops to ap- aqueous solvent or a mixture of nonaqueous solvents. proximately 45% of their room temperature perform- A metal salt can be dissolved in the catholyte solution ance, reducing the energy density to about 180 Wh/kg. 35 to enhance the ionic conductivity thereof. The preferred In addition, the cell's load voltage is reduced to about active material for the anode is lithium or an alloy there- 2.7 volts. of, and the electrically conductive material of the cath- [0003] Furthermore, tests on Li/SOCl2 cells indicate ode comprises a carbonaceous material. that when this chemistry is discharged and/or forced into [0007] The foregoing and additional advantages and voltage reversal at low temperatures, those cells may 40 characterizing features of the present invention will be- vent or explode when warmed to room temperature. It come clearly apparent upon a reading of the ensuing has been reported in the literature [Proc. Power Sources detailed description taken in conjunction with the ac- Symp. 31 (1984) 400] that this unsafe condition may be companying drawings. the result of a build-up of unstable intermediates (OClS) formed during low temperature discharge. The unstable 45 BRIEF DESCRIPTION OF THE DRAWING FIGURES intermediates then react at room temperature to cause the cell to either vent or explode. [0008] Fig. 1 is a graph of the discharge of Li/BCX [0004] In an attempt to develop an improved alkali cells constructed according to the prior art. metal/oxyhalide cell which offers enhanced low temper- [0009] Fig. 2 is a graph including plots of discharge ature performance and increased safety during dis- 50 characteristics for a test cell and a cell according to an- charge, halogen and/or interhalogen codepolarizers other embodiment of the present invention. such as BrCl in SOCl2 were developed. In particular, the [0010] Fig. 3 is a graph including a plot of the dis- Li/BrCl in SOCl2 (Li/BCX) system has been shown to charge characteristic of a cell according to another em- have significantly improved performance in both safety bodiment of the present invention. and low temperature discharge in comparison to the Li/ 55 [0011] Fig. 4 is a graph including plots of discharge SOCl2 system. Specifically, Li/BCX cells commercially characteristics for a test cell and a prototype cell accord- available from Wilson Greatbatch Ltd., Clarence, New ing to an embodiment of the present invention. York under model nos. 3B70 and 3B75 utilize BrCl as a 2 3 EP 1 179 870 A1 4 DETAILED DESCRIPTION OF THE PREFERRED black, carbon black and/or graphite. Metals such as EMBODIMENTS nickel, aluminum, titanium and stainless steel in powder form are also useful as conductive diluents when mixed [0012] The electrochemical cell of the present inven- with the above listed active materials. Fluoro-resin pow- tion includes an anode selected from Groups IA, IIA or 5 ders such as powdered polytetrafluoroethylene (PTFE) IIIB of the Periodic Table of Elements, including lithium, or powdered polyvinylidene fluoride (PVDF) are pre- sodium, potassium, etc., and their alloys and interme- ferred for the binder of the cathode current collector. tallic compounds. The preferred anode comprises lithi- This mixture is rolled onto a conductive substrate such um, and the more preferred anode comprises a lithium as nickel, stainless steel, or copper foil or screen. alloy, for example Li-Si, Li-B and Li-Si-B alloys and in- 10 [0017] The electrochemical cell of the present inven- termetallic compounds. The preferred lithium alloy is a tion further comprises a nonaqueous, ionically conduc- lithium-aluminum alloy. The greater the amount of alu- tive catholyte operatively associated with the anode and minum present by weight in the alloy, however, the lower the cathode current collector. The catholyte serves as a the energy density of the cell. medium for migration of ions between the anode and [0013] The form of the anode may vary, but preferably 15 cathode current collector during the cell electrochemical the anode is a thin metal sheet or foil of the anode metal, reactions and nonaqueous solvent depolarizers suitable pressed or rolled on a metallic anode current collector, for the present invention are chosen so as to exhibit i.e., preferably comprising nickel, to form an anode com- those physical properties necessary for ionic transport ponent. In the exemplary cell of the present invention, (low viscosity, low surface tension and wettability). Suit- the anode component has an extended tab or lead of 20 able nonaqueous depolarizers are comprised of an in- the same material as the anode current collector, i.e., organic salt dissolved in a nonaqueous codepolarizer preferably nickel, integrally formed therewith such as by system and, more preferably, an alkali metal salt dis- welding and contacted by a weld to a cell case of con- solved in a catholyte solution comprising a halogen and/ ductive metal in a case-negative electrical configuration. or interhalogen dissolved in a nonaqueous solvent, the Alternatively, the anode may be formed in some other 25 halogen and/or interhalogen serving as a soluble depo- geometry, such as a bobbin shape, cylinder or pellet to larizer in the high energy density cell of the present in- allow an alternate low surface cell design. vention. The halogen and/or interhalogen also can [0014] The electrochemical cell of the present inven- serve as a cosolvent in the electrochemical cell. The hal- tion further comprises a cathode current collector of ogen is selected from the group of iodine, bromine, chlo- electrically conductive material which serves as the oth- 30 rine or fluorine while the interhalogen is selected from er electrode of the cell.