CA2348175C - Control of cell swelling by the proper choice of carbon monofluoride (cfx) cathode material for high rate defibrillator cells - Google Patents
Control of cell swelling by the proper choice of carbon monofluoride (cfx) cathode material for high rate defibrillator cells Download PDFInfo
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/5835—Comprising fluorine or fluoride salts
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/54—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of silver
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Abstract
The minimization or elimination of swelling in lithium cells containing CF x as part of the cathode electrode and discharged under high rate applications is described. When C:F x materials are synthesized from fibrous carbonaceous materials, in comparison to petroleum coke, cell swelling is greatly reduced, and in some cases eliminated. Preferred precursors are carbon fibers and MCMB.
Description
CONTROL OF CELL STnlELLING
BY THE PROPER CHOICE OF CARBON MONOFLUORIDE (CFx) CATHODE MATERIALS IN HIGH RATE DEFIBRILLATOR CELLS
i;:
BACKGROUND OF THE INVENTION i I. Field of Invention The present invention generally relates to the ~:'' conversion of chemical energy to electrical energy.
More particularly, the present invention is directed to the use of carbon monofluoride (CFX) in high pulse power cells containing a transition metal oxide such as silver '' vanadium oxide (SVO).
It has been discovered that when CFx material is prepared from highly structured carbon precursors, cell swelling during high current pulse discharge conditions is markedly reduced, and in some cases eliminated.
ti.l ~~ :T!O_c? prity'VL:'_rr_.i, t~~ ~r'~SC'_"_r i_p~j~r~-1C;~ CeSCY'1_heS
a lithium electrochemical cell designed for high rate discharge applications in which the cathode electrode preferably has a sandwich design of the configuration:
SVO/current collector/CFX/current collector/SVO. Cells with this cathode electrode design are particularly applicable for powering implantable medical devices, such as cardiac defibrillators, requiring a relatively low electrical current for device monitoring functions interrupted from time to time by a high cur~er_t pulse discharge for device activation.
BY THE PROPER CHOICE OF CARBON MONOFLUORIDE (CFx) CATHODE MATERIALS IN HIGH RATE DEFIBRILLATOR CELLS
i;:
BACKGROUND OF THE INVENTION i I. Field of Invention The present invention generally relates to the ~:'' conversion of chemical energy to electrical energy.
More particularly, the present invention is directed to the use of carbon monofluoride (CFX) in high pulse power cells containing a transition metal oxide such as silver '' vanadium oxide (SVO).
It has been discovered that when CFx material is prepared from highly structured carbon precursors, cell swelling during high current pulse discharge conditions is markedly reduced, and in some cases eliminated.
ti.l ~~ :T!O_c? prity'VL:'_rr_.i, t~~ ~r'~SC'_"_r i_p~j~r~-1C;~ CeSCY'1_heS
a lithium electrochemical cell designed for high rate discharge applications in which the cathode electrode preferably has a sandwich design of the configuration:
SVO/current collector/CFX/current collector/SVO. Cells with this cathode electrode design are particularly applicable for powering implantable medical devices, such as cardiac defibrillators, requiring a relatively low electrical current for device monitoring functions interrupted from time to time by a high cur~er_t pulse discharge for device activation.
- 2 -2. Prior Art United States Patent No. 6,551,747 filed April 27, 2000; which is assigned to the assignee of the present invention describes a sandwiched cathode design for use in a high rate electrochemical cell. The sandwich cathode is composed of a first cathode active material of a relatively high energy density but of a relatively low rate capability, such as Cfy, Ag202 and even SVO, sandwiched between two layers of current collector.
This assembly is, in turn, sandwiched between two layers of a second cathode active material of a relatively high rate capability but of a relatively low energy density, such as SVO, copper silver vanadium oxide (CSVO) and Mn02. Significantly higher capacities are obtained from lithium cells having sandwich cathode designs of - SVO/CF;~/SVO relative to those of lithium cells using only SVO active material in a conventional cathode design. A
conventional cathode design has the SVO active material contacted to both sides of an intermediate cathode current collection. in addition, the higher capacity of the present invention cell is achieved without sacrificing the cell's power capability. Therefore, i :ithium cel l s constructed with ~ sandwich cathode electrode design are very good candidates as power sources for cardiac defibrillators and other implantable medical devices requiring a high power cell.
Other than cell capacity, an important consideration for an implantable medical device application is cell swelling during discharge. In order to prevent damage to device circuitry, enough void space must be left inside the powered device to accommodate this volume change. The more cell swelling, the more
This assembly is, in turn, sandwiched between two layers of a second cathode active material of a relatively high rate capability but of a relatively low energy density, such as SVO, copper silver vanadium oxide (CSVO) and Mn02. Significantly higher capacities are obtained from lithium cells having sandwich cathode designs of - SVO/CF;~/SVO relative to those of lithium cells using only SVO active material in a conventional cathode design. A
conventional cathode design has the SVO active material contacted to both sides of an intermediate cathode current collection. in addition, the higher capacity of the present invention cell is achieved without sacrificing the cell's power capability. Therefore, i :ithium cel l s constructed with ~ sandwich cathode electrode design are very good candidates as power sources for cardiac defibrillators and other implantable medical devices requiring a high power cell.
Other than cell capacity, an important consideration for an implantable medical device application is cell swelling during discharge. In order to prevent damage to device circuitry, enough void space must be left inside the powered device to accommodate this volume change. The more cell swelling, the more
- 3 -void space that must be reserved. Cell swelling, therefore, impacts the device total volume. In the field o:f implant<~b~le biomedical devices, a smaller total device volume is desired. Thus, in order to provide a more compact device design, it is desirable to minimize or eliminate cel:L swelling. Excessive cell swelling is also dei~rimental to the proper functioning of the implantable medical device and, consequently, to its safe use.
Carbon monofluoride, CFx is a cathode active material that has found wide spread use for low-weight lithium cells. 7:n fact, Li/CFX cells are particularly useful f:or discharge applications requiring relatively low currents of about 1 microamperes to about 100 milliamperes. At: these discharge rates, cell swelling is generally not observed. However, when Li/CFX cells c.having the cathode active material synthesized from petroleum coke are discharged under relatively high current applications, i.e., from about 15.0 mA/cm2 to about 35.0 mA/cm2, significant cell swelling is observed.
Cells powering implantable cardiac defibrillators are periodically pulse discharged under very high current densities of 15.0 mA/cm2 and higher. Therefore, when CF;~.is included in a sandwich cathode design as part of an electrode as;~embly powering an implantable medical device, such as a cardiac defibrillator, and the active material is synthe~;ized from certain carbonaceous precursors such as petroleum coke, a potential cell swelling problem e~:ists.
Accordingly, w?-iat is needed is a fluorinated carbon active material w~~zich is capable of being subjected to relative:Ly high rate discharge conditions without appreciably swell:in.g. Such a material would be very
Carbon monofluoride, CFx is a cathode active material that has found wide spread use for low-weight lithium cells. 7:n fact, Li/CFX cells are particularly useful f:or discharge applications requiring relatively low currents of about 1 microamperes to about 100 milliamperes. At: these discharge rates, cell swelling is generally not observed. However, when Li/CFX cells c.having the cathode active material synthesized from petroleum coke are discharged under relatively high current applications, i.e., from about 15.0 mA/cm2 to about 35.0 mA/cm2, significant cell swelling is observed.
Cells powering implantable cardiac defibrillators are periodically pulse discharged under very high current densities of 15.0 mA/cm2 and higher. Therefore, when CF;~.is included in a sandwich cathode design as part of an electrode as;~embly powering an implantable medical device, such as a cardiac defibrillator, and the active material is synthe~;ized from certain carbonaceous precursors such as petroleum coke, a potential cell swelling problem e~:ists.
Accordingly, w?-iat is needed is a fluorinated carbon active material w~~zich is capable of being subjected to relative:Ly high rate discharge conditions without appreciably swell:in.g. Such a material would be very
- 4 -desirable for inclusion into a high rate cell powering an implantable medical device.
SUMMARY OF THE INVENTION
According to the present invention, the swelling of cells containing ~~andwich cathodes, such as of a SVO/CFx/SVO configuration, is significantly minimized by using a CFX material synthesized from carbon fibers, and mesopha;se carbon microbeads (MCMB). These carbonaceous materials are identified as those which result in the least amount of swelling in cells containing CFx as part of the cathode material relative to those synthesized from graphite or petroleum coke. This is especially important when the cell is being pulse discharged.
These and other aspects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and the appended drawing.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic view of carbon fibers having an annual ring layered structure according to the present invention.
Fig. 2 is a cross-sectional view along line 2-2 of Fig. 1.
Fig. 3 is a schematic view of carbon fibers having a radial layered S1=~rilCtur_e acccrding to the present invention.
Fig. 4 is a cross-seCtianal view along line 4-4 of Fig. 3.
Fig. 5 is a scahematic view of mesophase carbon microbeads with a radial-like structure according to the present invention.
SUMMARY OF THE INVENTION
According to the present invention, the swelling of cells containing ~~andwich cathodes, such as of a SVO/CFx/SVO configuration, is significantly minimized by using a CFX material synthesized from carbon fibers, and mesopha;se carbon microbeads (MCMB). These carbonaceous materials are identified as those which result in the least amount of swelling in cells containing CFx as part of the cathode material relative to those synthesized from graphite or petroleum coke. This is especially important when the cell is being pulse discharged.
These and other aspects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and the appended drawing.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic view of carbon fibers having an annual ring layered structure according to the present invention.
Fig. 2 is a cross-sectional view along line 2-2 of Fig. 1.
Fig. 3 is a schematic view of carbon fibers having a radial layered S1=~rilCtur_e acccrding to the present invention.
Fig. 4 is a cross-seCtianal view along line 4-4 of Fig. 3.
Fig. 5 is a scahematic view of mesophase carbon microbeads with a radial-like structure according to the present invention.
- 5 -Fig. 6 is a cross-sectional view along line 6-6 of Fig. 5.
Fig. 7 is a ~>canning electron microscope photograph of standard CFx synthesized from petroleum coke having a plate like morphology.
Fig. 8 is a scanning electron microscope photograph of CFx synthesized from a fibrous carbon material according to the present invention.
Fig. 9 is a graph of cell thickness versus depth of discharge for a prior art cell having CFx synthesized from petroleum coke in comparison to a present invention cell having CFX synthesized from carbon fiber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
ThE~ present invention relates to minimization and even elimination of swelling in lithium cells containing ~,CFx as part of the cathode electrode and discharged under high rage applications. This improvement in cell functionality results from CFX materials being synthesized from carbonaceous precursors having special structural characaeristics. Preferred precursors are carbon fibers and. I~ICMB. During discharge, and especially during high rate discharge, these CFx materials retain the layered structure of the carbonaceous precursor.
Upon being discharged in lithium cells, lithium ions intercalate l.Tltc the layered carbonaceous structure to react with fluorine, which is attached to the carbon backbone either covalently or sonically. This forms lithium .fluoride and the reaction is shown below:
C:FK + xLs. --- C + xLiF
Fig. 7 is a ~>canning electron microscope photograph of standard CFx synthesized from petroleum coke having a plate like morphology.
Fig. 8 is a scanning electron microscope photograph of CFx synthesized from a fibrous carbon material according to the present invention.
Fig. 9 is a graph of cell thickness versus depth of discharge for a prior art cell having CFx synthesized from petroleum coke in comparison to a present invention cell having CFX synthesized from carbon fiber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
ThE~ present invention relates to minimization and even elimination of swelling in lithium cells containing ~,CFx as part of the cathode electrode and discharged under high rage applications. This improvement in cell functionality results from CFX materials being synthesized from carbonaceous precursors having special structural characaeristics. Preferred precursors are carbon fibers and. I~ICMB. During discharge, and especially during high rate discharge, these CFx materials retain the layered structure of the carbonaceous precursor.
Upon being discharged in lithium cells, lithium ions intercalate l.Tltc the layered carbonaceous structure to react with fluorine, which is attached to the carbon backbone either covalently or sonically. This forms lithium .fluoride and the reaction is shown below:
C:FK + xLs. --- C + xLiF
6 -It i.s well known that lithium ions exist in the electrolyte mostly as solvent solvated ions. When lithium ions intercalate into-the carbon layers of CFX
during discharge, solvent co-intercalation is also thought to occur. It is hypothesized that the co-intercalated solvent molecules form a solvated reaction intermediate. This intermediate causes destruction of the carbon structure and results in expansion of the discharged CF;~ active material. During high rate discharge conditions, a greater amount of solvent molecules co-intercalate into the layered carbonaceous structure within a shorter period of time. Such rapid co-intercalation creates a relatively high concentration of solvent molecules locally which, in turn, causes destruction or expansion of the layered structure at the local region. Therefore, in order to minimize or eliminate cell swelling, destruction or expansion of the layered carbonaceous structure due to solvent co-intercalation needs to be minimized.
Minimization of carbonaceous structure destruction due to co-intercalation is achieved by carefully selecting the microstructure of the carbonaceous precursor rr,aterials. In that respect, various carbon Tiber materials Ore suitable for svnthesizina C~'.. active materials. fcr e.~ample, Figs. 1 and 2 show a schematic:
of carbon fibers 10 having annual ring layers 12 where graphite crystallite edges are exposed only on the cross section. Figs. 3 and 4 show a schematic of carbon fibers 20 with radial layers 22 where the entire fiber 30, surface has the graphite crystallite edges exposed.
Figs. 5 and 6 show a schematic of a MCMB 30 with a radial-like texture where the entire surface of the microbead has exposed graphite crystallite edges 32.
_ 7 _ CFX material synthesized from carbon fibers exhibit a markE~dly different morphology than standard CFX
material synthesized from petr-oleum coke. When imaged using a scanning electron microscope at 1000x, the standard material displays a plate like morphology (Fig.
during discharge, solvent co-intercalation is also thought to occur. It is hypothesized that the co-intercalated solvent molecules form a solvated reaction intermediate. This intermediate causes destruction of the carbon structure and results in expansion of the discharged CF;~ active material. During high rate discharge conditions, a greater amount of solvent molecules co-intercalate into the layered carbonaceous structure within a shorter period of time. Such rapid co-intercalation creates a relatively high concentration of solvent molecules locally which, in turn, causes destruction or expansion of the layered structure at the local region. Therefore, in order to minimize or eliminate cell swelling, destruction or expansion of the layered carbonaceous structure due to solvent co-intercalation needs to be minimized.
Minimization of carbonaceous structure destruction due to co-intercalation is achieved by carefully selecting the microstructure of the carbonaceous precursor rr,aterials. In that respect, various carbon Tiber materials Ore suitable for svnthesizina C~'.. active materials. fcr e.~ample, Figs. 1 and 2 show a schematic:
of carbon fibers 10 having annual ring layers 12 where graphite crystallite edges are exposed only on the cross section. Figs. 3 and 4 show a schematic of carbon fibers 20 with radial layers 22 where the entire fiber 30, surface has the graphite crystallite edges exposed.
Figs. 5 and 6 show a schematic of a MCMB 30 with a radial-like texture where the entire surface of the microbead has exposed graphite crystallite edges 32.
_ 7 _ CFX material synthesized from carbon fibers exhibit a markE~dly different morphology than standard CFX
material synthesized from petr-oleum coke. When imaged using a scanning electron microscope at 1000x, the standard material displays a plate like morphology (Fig.
7), whereas the present invention material displays a fiber like morpholagy (Fig. 8). The difference between the materials is also reflected in the five point BET
surface' area. The surface area of CFX synthesized from petroleum coke is about 155 mz/g, whereas the surface area of CFX synthesized from fibrous materials according to the present invention ranges from about 295 m2/g to about 346 mz/g. The prior art CFX material has a mean particle size, by volume %, of about 16.47 um, whereas the particle size for the fiber material ranges, by volume %, from about 4.37 um to about 6.92 ~Zm. A
thermogravimetric/differential thermal analysis (TGA/DTA) was simultaneously conducted on both materials under a flowing argon atmosphere at a rate of 20°C from room temperature t:o 750°C, and the results are set forth below in Table 1.
Table 1 Parameter standard CFX fiber CFX
BET surface area (m2/g) 155 295-346 particle size volume % (um) 16.5 4.37-6.92 particle size surface area ~ 3.97 1.71-2.12 particle size number % 0.716 0.642-0.686 DTA exotherm (C) 667 652-656 min TGA % weight loss to 79.5 75.7 max TGA % weight ~_oss to 83.7 83.7 The benefit of diminished solvent co-intercalation swelling by using these carbonaceous precursor materials for CFx synthesis is based on their structure. Since the layered structure of carbon is expected to be maintained after f.luorination, the effect of carbon structure on solvent co-intercalation and, consequently, on the swelling of the ~za.rbonaceous particles upon discharge is significant. For carbon fibers with an annual ring structure, swelling most likely occurs in the dimension perpendicular to the ring central axis due to the d spacing increase between the graphite ring layers.
However, increase of the d spacing between the graphite layers is limited because the strength of the carbon-carbon r~onds within the graphite layer prevents further expansion of the graphite rings.
In the case of carbon fibers and MCMB with radial ,:like structures, solvent co-intercalation expansion of the carbonaceous materials is expected to be small due to the physical restraint of the carbon layered structure.
When solvent molecules intercalate into the carbon layers of these materials, the increased d spacing between the graphite layers generates expansion tension parallel to the carbon surface. Thus, unless the three dimensional structure of the MCM~ carbon fibers breaks apart, the carbon particles are unlikely to swell. As a result, the cell swelling phenomenon is minimized.
In general, any carbonaceous material with a structure which re:>tricts an increase in the d spacing between graphite layers is considered a good precursor for CFX synthesis according to the present invention.
Accordingly, the usce of CFX synthesized from these carbon materials is beneficial to minimize or eliminate cell swelling..
As used herein, the term "pulse" means a short burst of electrical current of a significantly greater amplitude than that of a pre-pulse current immediately prior to the pulse. A pulse train consists of at least two pulaes of electrical current delivered in relatively short succession with or without open circuit rest between the pulses. A typical current pulse is of about 15. 0 mA/ cm2 to about 35. 0 mA/cm2.
An electrochemical cell that possesses sufficient energy density and discharge capacity required to meet the vigorous requirements of implantable medical devices comprises an anode of a metal selected from Groups IA, IIA and IIIB of t.hf=_ Periodic Table of the Elements. Such anode acaive materials include lithium, sodium, potassium, etc., and their alloys and intermetallic compounds including, for example, Li-Si, Li-A1, Li-B and ~Li-Si-B alloys and intermetallic compounds. The preferred anode connprises lithium. An alternate anode comprises a lithium alloy such as a lithium-aluminum alloy. The greater the amount of aluminum present by weight in the alloy, however, the lower the energy density of the cell.
The form of the anode may vary, but preferably the anode is a thin metal sheet or foil of the anode metal, pressed or rc;lled are a metallic anode current collector, i.e., preferabl.y ~~omprising titanium, titanium alloy or nickel, to farm an anode component. Copper, tungsten and tantalum are also suitable materials for the anode current collector. In an exemplary cell according to the present invention,, the anode component has an extended tab or lead of thE~ same material as the anode current collector, i.e., preferably nickel or titanium, integral:_y formed therewith such as by welding and ' , J -contacted by a weld to a cell case of conductive metal in a case-negative electrical configuration. Alternatively, the anode may be formed in some. other geometry, such as a bobbin shape, cylinder or pellet to allow an alternate low surface cell design..
The electrochemical cell of the present invention further comprises a cathode of at least a first electrically conductive material which serves as the other electrode of the cell. The cathode is preferably of solid materials and in one embodiment has a sandwich design as described in the previously referenced U.S.
Patent No, 6,551,747. The sandwich cathode design comprises a first active material of a fluorinated carbon compound prepared from the carbonaceous materials described above. Fluorinated carbon is represented by the formula (CFx)" wherein x varies between about 0.1 to 1.9 and preferably between about 0. 5 and 1. 2, and (C2F) ~, wherein the r. refers to the number of monomer units which can vary widely.
The sandwich cathode design further includes a seccnd active material of a relatively low energy density and a relatively high rate capability in comparison to the rust fluorinated carbon ca-thode active material.
~?:c~' pre~erred SeCCTld aCtiVe material 1S a L-ail.5i tiCn metal oxide having the general formula SIMyV.,O~ where Si~I is a metal selected from Groups IB to VIIB and VIII of the Periodic Table of Elements, wherein x is about 0.30 to 2.0 and y is about 4.5 to 6.0 in the general formula. By way of illustration, and in no way intended to be 30, limiting, one exemplary cathode active material comprises silver vanadium oxide having the general formula AgxV20Y
in any one of its many phases, i.e., Q-phase silver vanadium oxide having in the general formula x = 0.35 arid 1 ' -y1 y = 5.8, y-phase silver vanadium oxide having in the general formula x = 0.80 and y = 5.40 and s-phase silver vanadium oxide having in the general formula x = 1.0 and y = 5.5, and combination and mixtures of phases thereof.
For a more detailed description of such cathode active materials reference is made to U.S. Patent No..4,310,609 to Ziang et al., which is assigned to the assignee of the present invention, Another preferred composite transition metal oxide cathode material includes V20z wherein z <_ 5 is combined with Ag20 with silver in either the silver(II), silver(I) or silver(0) oxidation state and Cu0 with copper in either the copper(II), copper(I) or copper(0) oxidation state to provide the mixed metal oxide having the general formula Cu,tAgyV20Z, (CSVO) . Thus, the composite cathode active material may be described as a metal oxide-metal oxide-metal oxide, a metal-metal oxide-metal oxide, or a .
metal-metal-metal oxide and the range of material composition found for CuxAgYV20Z is preferably about 0.01 s z s 6.5. Typical forms of CSVO are Cu~_l~Ago_67VLOZ with z being about 5.5 and Cuo.SAg~.SV~Oz with z being about 5.75.
The oxygen content is designated by z since the exact stoichiometric proportion of oxygen in CSVO can care depending on whe~her the catode material is prepared ~n an oxidizing atmosphere such as air or oxygen, or in an inert atmosphere such as argon, nitrogen and helium. For a more detailed description of this cathode active material reference is made to U.S. Patent Nos-. 5,472,810 s to Takeuchi et al. and 5,516,340 to Takeuchi et al., both of which are assigned to the assignee of the present invention, One exemplary sandwich cathode electrode has the following configuration:
SVO/current c;ollector/CFX/current collector/SVO
Another exemplary sandwich cathode electrode configuration is :
SVO/cu:rrent col:Lector/SVO/CFx/SVO/current collector/SVO
Still another configuration for an electrochemical cell with a sandwich electrode has a lithium anode and a cathode configuration of:
SVO/current collector/CFX, with the SVO facing the lithium anode.
In a broader aense, i.t is contemplated by the scope of the present invention that the second active material ..of the sandwich cai:hode design is any material which has a relatively lower energy density but a relatively higher rate capability than the first active material. In that respect, other than silver vanadium oxide and copper silver vanadium oxide, V205, Mn02, LiCo02, LiNi02, LiMn209, TiS2, Cu2S, FeS, fe;a;>, Cu02, copper vanadium oxide (CVO) , and mixtures thereof are useful as the second active material.
Before fabrication into a sandwich electrode for incorpor<~tion into an electrochemical cell according to the present inven-,.ion, the first and second cathode active materials prepared as described above are preferab_y mixed with a binder material such as a 20 powdered fluoro-polymer, more preferably powdered polytetrafluoroethylene or powdered polyvinylidene fluoride present at about 1 to about 5 weight percent of the cathode mixture. Further, up to about 10 weight percent of a conductive diluent is preferably added to the cathode mixtui°e to improve conductivity. Suitable materials for thi:~ purpose include acetylene black, carbon black and/or graphite or a metallic powder such as powdered nickel, aluminum, titanium and stainless steel.
The preferred cathode active mixture thus includes a powdered fluoro-polymer binder present at about 3 weight percent, a conductive diluent present at about 3 weight percent and abou~~ 94 weight percent of the cathode active material.
A second embodiment of a present invention cell is constructed according to U.S. Patent No. 5,639,577 to Takeuchi et al. This patent describes a cathode active blend of. fluorinated carbon and a transition metal oxide.
By blending is meant that the already prepared active materials of CFX and CSVO are comingled together in a ,relatively homogeneous mixture. Again, the fluorinated carbon i.s prepared from the carbonaceous precursors described above. According to this patent, the preferred transition metal o:~ide is CSVO. However, other active materials including SVO as described above with respect to the second cathode active material of the sandwich electrode design are also useful when blended with CFx.
This cell is descr~_bed as being particularly useful for high current pulse discharge applications, for example at about 15.0 mA/cmz and above.
Cathode components for incorporation into an electrochemical cel'~ according to the present invention may be prepared by rolling, spreading or pressing the first an~i second ,oa.thode active materials onto a suitable current collector selected from the group consisting of stainless steel, titanium, tantalum, platinum, gold, aluminum,, cobalt nickel alloys, nickel-containing alloys, highly alloyed ferritic stainless steel containing molybdenum.and chromium, and nickel-, chromium- and molybdenum-containing alloys. The preferred current collector material is titanium, and most preferably the titanium cathode current collector has a thin layer of graphite/carbon material, iridium, iridium oxide or platinum applied thereto. Cathodes prepared as described above may be in the form of one or mare plates operatively associated with at least one or more plates of anode material, or in the form of a strip wound with a corresponding strip of anode material in a structure similar to a "jellyroll".
In order to prevent internal short circuit conditions, the cathode is separated from the Group IA, IIA or IIIB anode by a suitable separator material. The separator is of electrically insulative material, and the separator material also is chemically unreactive with the anode and cathode active materials and both chemically unreactive with and insoluble in the electrolyte. In addition, the separator material has a degree of porosity sufficient to allow flow there through of the electrolyte during the electrochemical reaction of the cell.
Illustrative separator materials include fabrics woven ?=rom ilucrcpolymer~c ziners includ~r~g pcly~inyl'dine flucride, pclyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene used either alone or laminated with a fluoropolymeric microporous film, non-woven glass, polypropylene, polyethylene, glass fiber materials, ceramics, polytetrafluoroethylene membrane co~ercially available from Chemplast Inc. under the trade-mark ZITEX, polypropylene membrane commercially available from Celanese Plastic Company, Inc. under the trade-mark CELGARD and a membrane commercially available from C.H. Dexter, a Division of Dexter Corp.
under the trade-mark DEXIGLAS
The electrochemical cells. of the present invention further include a nonaqueous, sonically conductive electrolyte which serves as a medium for migration of ions between the anode and the cathode electrodes during the electrochemical reactions of the cells. The electrochemical reaction at the electrodes involves conversion of ions in atomic or molecular forms which migrate from the anode to the cathode. Thus, nonaqueous electrolytes suitable for the present invention are substantially inert to the anode and cathode materials, and they exhibit those physical properties necessary for ionic transport, namely, low viscosity, low surface tension and wettability.
A suitable electrolyte has an inorganic, sonically conductive salt dissolved in a nonaqueous solvent, and more preferably, the electrolyte includes an ionizable alkali metal salt dissolved in a mixture of aprotic organic solvents comprising a low viscosity solvent and a high permittivity solvent. The inorganic, sonically conductive salt serves as the vehicle for migration of the anode ions to intercalate or .react with the cathode aCCL'I~~ Mld~crlcl. i~rCL~iGDly, ~.Ilc ~On lOrm_.ng dllK~l1 metal salt is similar to the alkali metal comprising the anode.
In the case of an anode comprising lithium, the alkali metal salt of the electrolyte is a lithium based salt. Known lithium salts that are useful as a vehicle for transport of alkali metal ions from the anode to the cathode include LiPFo, LiBF4, LiAsF6, LiSbF6, LiC104, LiOz, LiA1C14, LiGaCl4, LiC (SOZCF~) 3, LiN (SO2CF3) 2, LiSCN, -Li03SCF3, LiC6F5S03, LiOZCCF3, LiS06F, LiB (C6H5) 4,. LiCF3S03, and mixtures thereof.
Law viscosity solvents useful with the present invention include esters, linear and cyclic ethers and 5 dialkyl carbonates such as tetrahydrofuran (THF), methyl acetate (M_A), diglyme, trigylme, tetragylme, dimethyl carbonate (DMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), I-ethoxy,2-methoxyethane (EME), ethyl methyl carbonate, methyl propyl carbonate, ethyl 10 propyl carbonate, diethyl carbonate, dipropyl carbonate, and mixtures thereof, and high permittivity solvents include cyclic carbonates, cyclic esters and cyclic amides such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, y-valerolactone, y-butyrolactone (GBL), N-methyl-pyrrolidinone (NMP), and mixtures thereof.
A preferred chemistry for a sandwich cathode electrode according to the present invention has a lithium metal anode and a cathode electrode comprising (SVO) and fluorinated carbon (CF;~). In the sandwich structure, CF.t material is sandwiched between two cathoc'~e current collectors. This assembly is, in turn, sal'1CWICrIE.'C'~., ~~'tWee:1 t.LJG laVerS OL S~J~~ :llaterlal. l:ie electrolyte activating the cells is 0.8M to 1.5NI LiAsr6 or LiPF6 in a 1:1, by volume, mixture of propylene carbonate and 1,2-dimethoxyethane. Preferably, the electrolyte also contains 0.05M dibenzyl carbonate (DBC), as described in U.S. Patent Nos. 5,753,389 and 6,221,534, both to Gar. et al. and both assigned to the assignee of ', the present invention, _ 1~ _ The following examples describe the manner and process of an elecarochemical cell according to the present invention, and they se.t forth the best mode contemplated by the inventors of carrying out the invention, but they are not to be construed as limiting.
EXAMPLE I
Si:x test cells were constructed having lithium anode material pressed on a nickel current collector screen.
The cathodes used two layers of titanium current collector screen and had the sandwich configuration of:
SVO/current collector/CFX/current collector/SVO. A
prismat_~c cell stack assembly comprising two layers of microporous membrane polypropylene separator disposed between the anode and cathode was prepared. The electrode assembly was then hermetically sealed in a ~,stainle~;s steel c:a;sing in a case negative configuration and activated with an electrolyte of 1.OM LiAsF6 in a 50:50 mixture, by volume of PC and DME with 0.05M DBC
dissolved therein. The theoretical capacity of the cells was 2.645 Ah.
Two of the test cells were constructed having CFX
synthesized from petroleum coke (group 1) while four of the cells were con:~tructed with CFX synthesized from carbon fiber (group '.?). A representative cell from each of groups 1 and 2 was accelerated p~~lse discharged. This discharge regime cc~nsisted of pulse trains of four 10 second 2 Amp currah.t pulses with a 15 second rest between each pulse. The pulse trains were applied every 30 minutes. The capacities delivered to three voltages cut-offs are summarized in Table 2.
Table 2 Group Capacity Efficiency at at Cut Cut Off Off (%) 2.V 1.7V 1.5V 2.OV 1.7V 1.5V
1 1816 2069 2274 68.7 78.2 86.0 2 1967 2205 2320 74.4 83.4 87.7 The data in Table 2 demonstrate that the representative group 2 cell having a sandwich cathode design with CFX synthesized from carbon fiber delivered more discharge capacity at a higher efficiency than the representative group.l cell having CFX in a sandwich cathode design synthesized from petroleum coke to all three voltages cut offs.
EXAMPLE II
To demonstrate the swelling characteristics of the groups 1. and 2 cells, one cell from group 1 and three cells from group 2 were discharged in a similar manner as the cells in Example I except only 50% of the theoretical capacity was removed. Cell thickness was measured before and after this discharge test. Cell thickness was also measured before and after discharge of the cell of Example I. 'The th:i~~kness data from these tests is summarized in Fig. 9 where tre group 1 cell, curve 40, swelled significant=ly. In fact, the larger the DOD, the greater the cel.i swelling. In contrast, the group 2 cells, curve 42, exhibited fairly insignificant swelling throughout discha.rc~e.
It .is appreciated that various modifications to the inventive concepts described herein may be apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined by the hereinafter appended claims.
surface' area. The surface area of CFX synthesized from petroleum coke is about 155 mz/g, whereas the surface area of CFX synthesized from fibrous materials according to the present invention ranges from about 295 m2/g to about 346 mz/g. The prior art CFX material has a mean particle size, by volume %, of about 16.47 um, whereas the particle size for the fiber material ranges, by volume %, from about 4.37 um to about 6.92 ~Zm. A
thermogravimetric/differential thermal analysis (TGA/DTA) was simultaneously conducted on both materials under a flowing argon atmosphere at a rate of 20°C from room temperature t:o 750°C, and the results are set forth below in Table 1.
Table 1 Parameter standard CFX fiber CFX
BET surface area (m2/g) 155 295-346 particle size volume % (um) 16.5 4.37-6.92 particle size surface area ~ 3.97 1.71-2.12 particle size number % 0.716 0.642-0.686 DTA exotherm (C) 667 652-656 min TGA % weight loss to 79.5 75.7 max TGA % weight ~_oss to 83.7 83.7 The benefit of diminished solvent co-intercalation swelling by using these carbonaceous precursor materials for CFx synthesis is based on their structure. Since the layered structure of carbon is expected to be maintained after f.luorination, the effect of carbon structure on solvent co-intercalation and, consequently, on the swelling of the ~za.rbonaceous particles upon discharge is significant. For carbon fibers with an annual ring structure, swelling most likely occurs in the dimension perpendicular to the ring central axis due to the d spacing increase between the graphite ring layers.
However, increase of the d spacing between the graphite layers is limited because the strength of the carbon-carbon r~onds within the graphite layer prevents further expansion of the graphite rings.
In the case of carbon fibers and MCMB with radial ,:like structures, solvent co-intercalation expansion of the carbonaceous materials is expected to be small due to the physical restraint of the carbon layered structure.
When solvent molecules intercalate into the carbon layers of these materials, the increased d spacing between the graphite layers generates expansion tension parallel to the carbon surface. Thus, unless the three dimensional structure of the MCM~ carbon fibers breaks apart, the carbon particles are unlikely to swell. As a result, the cell swelling phenomenon is minimized.
In general, any carbonaceous material with a structure which re:>tricts an increase in the d spacing between graphite layers is considered a good precursor for CFX synthesis according to the present invention.
Accordingly, the usce of CFX synthesized from these carbon materials is beneficial to minimize or eliminate cell swelling..
As used herein, the term "pulse" means a short burst of electrical current of a significantly greater amplitude than that of a pre-pulse current immediately prior to the pulse. A pulse train consists of at least two pulaes of electrical current delivered in relatively short succession with or without open circuit rest between the pulses. A typical current pulse is of about 15. 0 mA/ cm2 to about 35. 0 mA/cm2.
An electrochemical cell that possesses sufficient energy density and discharge capacity required to meet the vigorous requirements of implantable medical devices comprises an anode of a metal selected from Groups IA, IIA and IIIB of t.hf=_ Periodic Table of the Elements. Such anode acaive materials include lithium, sodium, potassium, etc., and their alloys and intermetallic compounds including, for example, Li-Si, Li-A1, Li-B and ~Li-Si-B alloys and intermetallic compounds. The preferred anode connprises lithium. An alternate anode comprises a lithium alloy such as a lithium-aluminum alloy. The greater the amount of aluminum present by weight in the alloy, however, the lower the energy density of the cell.
The form of the anode may vary, but preferably the anode is a thin metal sheet or foil of the anode metal, pressed or rc;lled are a metallic anode current collector, i.e., preferabl.y ~~omprising titanium, titanium alloy or nickel, to farm an anode component. Copper, tungsten and tantalum are also suitable materials for the anode current collector. In an exemplary cell according to the present invention,, the anode component has an extended tab or lead of thE~ same material as the anode current collector, i.e., preferably nickel or titanium, integral:_y formed therewith such as by welding and ' , J -contacted by a weld to a cell case of conductive metal in a case-negative electrical configuration. Alternatively, the anode may be formed in some. other geometry, such as a bobbin shape, cylinder or pellet to allow an alternate low surface cell design..
The electrochemical cell of the present invention further comprises a cathode of at least a first electrically conductive material which serves as the other electrode of the cell. The cathode is preferably of solid materials and in one embodiment has a sandwich design as described in the previously referenced U.S.
Patent No, 6,551,747. The sandwich cathode design comprises a first active material of a fluorinated carbon compound prepared from the carbonaceous materials described above. Fluorinated carbon is represented by the formula (CFx)" wherein x varies between about 0.1 to 1.9 and preferably between about 0. 5 and 1. 2, and (C2F) ~, wherein the r. refers to the number of monomer units which can vary widely.
The sandwich cathode design further includes a seccnd active material of a relatively low energy density and a relatively high rate capability in comparison to the rust fluorinated carbon ca-thode active material.
~?:c~' pre~erred SeCCTld aCtiVe material 1S a L-ail.5i tiCn metal oxide having the general formula SIMyV.,O~ where Si~I is a metal selected from Groups IB to VIIB and VIII of the Periodic Table of Elements, wherein x is about 0.30 to 2.0 and y is about 4.5 to 6.0 in the general formula. By way of illustration, and in no way intended to be 30, limiting, one exemplary cathode active material comprises silver vanadium oxide having the general formula AgxV20Y
in any one of its many phases, i.e., Q-phase silver vanadium oxide having in the general formula x = 0.35 arid 1 ' -y1 y = 5.8, y-phase silver vanadium oxide having in the general formula x = 0.80 and y = 5.40 and s-phase silver vanadium oxide having in the general formula x = 1.0 and y = 5.5, and combination and mixtures of phases thereof.
For a more detailed description of such cathode active materials reference is made to U.S. Patent No..4,310,609 to Ziang et al., which is assigned to the assignee of the present invention, Another preferred composite transition metal oxide cathode material includes V20z wherein z <_ 5 is combined with Ag20 with silver in either the silver(II), silver(I) or silver(0) oxidation state and Cu0 with copper in either the copper(II), copper(I) or copper(0) oxidation state to provide the mixed metal oxide having the general formula Cu,tAgyV20Z, (CSVO) . Thus, the composite cathode active material may be described as a metal oxide-metal oxide-metal oxide, a metal-metal oxide-metal oxide, or a .
metal-metal-metal oxide and the range of material composition found for CuxAgYV20Z is preferably about 0.01 s z s 6.5. Typical forms of CSVO are Cu~_l~Ago_67VLOZ with z being about 5.5 and Cuo.SAg~.SV~Oz with z being about 5.75.
The oxygen content is designated by z since the exact stoichiometric proportion of oxygen in CSVO can care depending on whe~her the catode material is prepared ~n an oxidizing atmosphere such as air or oxygen, or in an inert atmosphere such as argon, nitrogen and helium. For a more detailed description of this cathode active material reference is made to U.S. Patent Nos-. 5,472,810 s to Takeuchi et al. and 5,516,340 to Takeuchi et al., both of which are assigned to the assignee of the present invention, One exemplary sandwich cathode electrode has the following configuration:
SVO/current c;ollector/CFX/current collector/SVO
Another exemplary sandwich cathode electrode configuration is :
SVO/cu:rrent col:Lector/SVO/CFx/SVO/current collector/SVO
Still another configuration for an electrochemical cell with a sandwich electrode has a lithium anode and a cathode configuration of:
SVO/current collector/CFX, with the SVO facing the lithium anode.
In a broader aense, i.t is contemplated by the scope of the present invention that the second active material ..of the sandwich cai:hode design is any material which has a relatively lower energy density but a relatively higher rate capability than the first active material. In that respect, other than silver vanadium oxide and copper silver vanadium oxide, V205, Mn02, LiCo02, LiNi02, LiMn209, TiS2, Cu2S, FeS, fe;a;>, Cu02, copper vanadium oxide (CVO) , and mixtures thereof are useful as the second active material.
Before fabrication into a sandwich electrode for incorpor<~tion into an electrochemical cell according to the present inven-,.ion, the first and second cathode active materials prepared as described above are preferab_y mixed with a binder material such as a 20 powdered fluoro-polymer, more preferably powdered polytetrafluoroethylene or powdered polyvinylidene fluoride present at about 1 to about 5 weight percent of the cathode mixture. Further, up to about 10 weight percent of a conductive diluent is preferably added to the cathode mixtui°e to improve conductivity. Suitable materials for thi:~ purpose include acetylene black, carbon black and/or graphite or a metallic powder such as powdered nickel, aluminum, titanium and stainless steel.
The preferred cathode active mixture thus includes a powdered fluoro-polymer binder present at about 3 weight percent, a conductive diluent present at about 3 weight percent and abou~~ 94 weight percent of the cathode active material.
A second embodiment of a present invention cell is constructed according to U.S. Patent No. 5,639,577 to Takeuchi et al. This patent describes a cathode active blend of. fluorinated carbon and a transition metal oxide.
By blending is meant that the already prepared active materials of CFX and CSVO are comingled together in a ,relatively homogeneous mixture. Again, the fluorinated carbon i.s prepared from the carbonaceous precursors described above. According to this patent, the preferred transition metal o:~ide is CSVO. However, other active materials including SVO as described above with respect to the second cathode active material of the sandwich electrode design are also useful when blended with CFx.
This cell is descr~_bed as being particularly useful for high current pulse discharge applications, for example at about 15.0 mA/cmz and above.
Cathode components for incorporation into an electrochemical cel'~ according to the present invention may be prepared by rolling, spreading or pressing the first an~i second ,oa.thode active materials onto a suitable current collector selected from the group consisting of stainless steel, titanium, tantalum, platinum, gold, aluminum,, cobalt nickel alloys, nickel-containing alloys, highly alloyed ferritic stainless steel containing molybdenum.and chromium, and nickel-, chromium- and molybdenum-containing alloys. The preferred current collector material is titanium, and most preferably the titanium cathode current collector has a thin layer of graphite/carbon material, iridium, iridium oxide or platinum applied thereto. Cathodes prepared as described above may be in the form of one or mare plates operatively associated with at least one or more plates of anode material, or in the form of a strip wound with a corresponding strip of anode material in a structure similar to a "jellyroll".
In order to prevent internal short circuit conditions, the cathode is separated from the Group IA, IIA or IIIB anode by a suitable separator material. The separator is of electrically insulative material, and the separator material also is chemically unreactive with the anode and cathode active materials and both chemically unreactive with and insoluble in the electrolyte. In addition, the separator material has a degree of porosity sufficient to allow flow there through of the electrolyte during the electrochemical reaction of the cell.
Illustrative separator materials include fabrics woven ?=rom ilucrcpolymer~c ziners includ~r~g pcly~inyl'dine flucride, pclyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene used either alone or laminated with a fluoropolymeric microporous film, non-woven glass, polypropylene, polyethylene, glass fiber materials, ceramics, polytetrafluoroethylene membrane co~ercially available from Chemplast Inc. under the trade-mark ZITEX, polypropylene membrane commercially available from Celanese Plastic Company, Inc. under the trade-mark CELGARD and a membrane commercially available from C.H. Dexter, a Division of Dexter Corp.
under the trade-mark DEXIGLAS
The electrochemical cells. of the present invention further include a nonaqueous, sonically conductive electrolyte which serves as a medium for migration of ions between the anode and the cathode electrodes during the electrochemical reactions of the cells. The electrochemical reaction at the electrodes involves conversion of ions in atomic or molecular forms which migrate from the anode to the cathode. Thus, nonaqueous electrolytes suitable for the present invention are substantially inert to the anode and cathode materials, and they exhibit those physical properties necessary for ionic transport, namely, low viscosity, low surface tension and wettability.
A suitable electrolyte has an inorganic, sonically conductive salt dissolved in a nonaqueous solvent, and more preferably, the electrolyte includes an ionizable alkali metal salt dissolved in a mixture of aprotic organic solvents comprising a low viscosity solvent and a high permittivity solvent. The inorganic, sonically conductive salt serves as the vehicle for migration of the anode ions to intercalate or .react with the cathode aCCL'I~~ Mld~crlcl. i~rCL~iGDly, ~.Ilc ~On lOrm_.ng dllK~l1 metal salt is similar to the alkali metal comprising the anode.
In the case of an anode comprising lithium, the alkali metal salt of the electrolyte is a lithium based salt. Known lithium salts that are useful as a vehicle for transport of alkali metal ions from the anode to the cathode include LiPFo, LiBF4, LiAsF6, LiSbF6, LiC104, LiOz, LiA1C14, LiGaCl4, LiC (SOZCF~) 3, LiN (SO2CF3) 2, LiSCN, -Li03SCF3, LiC6F5S03, LiOZCCF3, LiS06F, LiB (C6H5) 4,. LiCF3S03, and mixtures thereof.
Law viscosity solvents useful with the present invention include esters, linear and cyclic ethers and 5 dialkyl carbonates such as tetrahydrofuran (THF), methyl acetate (M_A), diglyme, trigylme, tetragylme, dimethyl carbonate (DMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), I-ethoxy,2-methoxyethane (EME), ethyl methyl carbonate, methyl propyl carbonate, ethyl 10 propyl carbonate, diethyl carbonate, dipropyl carbonate, and mixtures thereof, and high permittivity solvents include cyclic carbonates, cyclic esters and cyclic amides such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, y-valerolactone, y-butyrolactone (GBL), N-methyl-pyrrolidinone (NMP), and mixtures thereof.
A preferred chemistry for a sandwich cathode electrode according to the present invention has a lithium metal anode and a cathode electrode comprising (SVO) and fluorinated carbon (CF;~). In the sandwich structure, CF.t material is sandwiched between two cathoc'~e current collectors. This assembly is, in turn, sal'1CWICrIE.'C'~., ~~'tWee:1 t.LJG laVerS OL S~J~~ :llaterlal. l:ie electrolyte activating the cells is 0.8M to 1.5NI LiAsr6 or LiPF6 in a 1:1, by volume, mixture of propylene carbonate and 1,2-dimethoxyethane. Preferably, the electrolyte also contains 0.05M dibenzyl carbonate (DBC), as described in U.S. Patent Nos. 5,753,389 and 6,221,534, both to Gar. et al. and both assigned to the assignee of ', the present invention, _ 1~ _ The following examples describe the manner and process of an elecarochemical cell according to the present invention, and they se.t forth the best mode contemplated by the inventors of carrying out the invention, but they are not to be construed as limiting.
EXAMPLE I
Si:x test cells were constructed having lithium anode material pressed on a nickel current collector screen.
The cathodes used two layers of titanium current collector screen and had the sandwich configuration of:
SVO/current collector/CFX/current collector/SVO. A
prismat_~c cell stack assembly comprising two layers of microporous membrane polypropylene separator disposed between the anode and cathode was prepared. The electrode assembly was then hermetically sealed in a ~,stainle~;s steel c:a;sing in a case negative configuration and activated with an electrolyte of 1.OM LiAsF6 in a 50:50 mixture, by volume of PC and DME with 0.05M DBC
dissolved therein. The theoretical capacity of the cells was 2.645 Ah.
Two of the test cells were constructed having CFX
synthesized from petroleum coke (group 1) while four of the cells were con:~tructed with CFX synthesized from carbon fiber (group '.?). A representative cell from each of groups 1 and 2 was accelerated p~~lse discharged. This discharge regime cc~nsisted of pulse trains of four 10 second 2 Amp currah.t pulses with a 15 second rest between each pulse. The pulse trains were applied every 30 minutes. The capacities delivered to three voltages cut-offs are summarized in Table 2.
Table 2 Group Capacity Efficiency at at Cut Cut Off Off (%) 2.V 1.7V 1.5V 2.OV 1.7V 1.5V
1 1816 2069 2274 68.7 78.2 86.0 2 1967 2205 2320 74.4 83.4 87.7 The data in Table 2 demonstrate that the representative group 2 cell having a sandwich cathode design with CFX synthesized from carbon fiber delivered more discharge capacity at a higher efficiency than the representative group.l cell having CFX in a sandwich cathode design synthesized from petroleum coke to all three voltages cut offs.
EXAMPLE II
To demonstrate the swelling characteristics of the groups 1. and 2 cells, one cell from group 1 and three cells from group 2 were discharged in a similar manner as the cells in Example I except only 50% of the theoretical capacity was removed. Cell thickness was measured before and after this discharge test. Cell thickness was also measured before and after discharge of the cell of Example I. 'The th:i~~kness data from these tests is summarized in Fig. 9 where tre group 1 cell, curve 40, swelled significant=ly. In fact, the larger the DOD, the greater the cel.i swelling. In contrast, the group 2 cells, curve 42, exhibited fairly insignificant swelling throughout discha.rc~e.
It .is appreciated that various modifications to the inventive concepts described herein may be apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined by the hereinafter appended claims.
Claims (32)
1. An electrochemical cell, which comprises:
a) an anode;
b) a cathode of a first fluorinated carbon of a first energy density and a first rate capability and a second cathode active material of a second energy density and a second rate capability, wherein the first energy density of the first fluorinated carbon is greater than the second energy density while the first rate capability is less than the second rate capability of the second cathode active material;
c) a cathode current collector comprising spaced apart major sides with the first fluorinated carbon positioned proximate one of the major sides and the second cathode active material contacting the other major side of the cathode current collector; and d) an electrolyte comprising at least one solvent for activating the anode and the cathode, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation.
a) an anode;
b) a cathode of a first fluorinated carbon of a first energy density and a first rate capability and a second cathode active material of a second energy density and a second rate capability, wherein the first energy density of the first fluorinated carbon is greater than the second energy density while the first rate capability is less than the second rate capability of the second cathode active material;
c) a cathode current collector comprising spaced apart major sides with the first fluorinated carbon positioned proximate one of the major sides and the second cathode active material contacting the other major side of the cathode current collector; and d) an electrolyte comprising at least one solvent for activating the anode and the cathode, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation.
2. The electrochemical cell of claim 1 wherein the cell is dischargeable at a current pulse of at least about 15.0 mA/ cm2
3. The electrochemical cell of claim 1 wherein the fluorinated carbon synthesized from the fibrous carbonaceous material has a BET surface area of greater than about 250 m2/g.
4. The electrochemical cell of claim 1 wherein the fluorinated carbon synthesized from the fibrous carbonaceous material has a particle size, by volume %, of less than about 15 µm.
5. The electrochemical cell of claim 1 wherein the fluorinated carbon synthesized from the fibrous carbonaceous material has a particle size surface, by area %, of less than about 3.5.
6. The electrochemical cell of claim 1 wherein the fluorinated carbon synthesized from the fibrous carbonaceous material has a DTA exotherm of about 652°C to about 656°C.
7. The electrochemical cell of claim 1 wherein the carbonaceous material is selected from the group consisting of carbon fibers with an annual ring layered structure having graphite crystallite edges exposed only on the cross-section, carbon fibers with a radial layered structure having the entire fiber surface with exposed graphite crystallite edges, and mesophase carbon microbeads with a radial-like texture having the entire surface of the microbead with exposed graphite crystallite edges.
8. The electrochemical cell of claim 1 wherein the second.
cathode active material is selected from the group consisting of silver vanadium oxide, copper silver vanadium oxide, V2O5, MnO2, LiCoO2, LiNiO2, LiMnO2, CuO2, TiS, CuS, FeS, FeS2, copper vanadium oxide, and mixtures thereof.
cathode active material is selected from the group consisting of silver vanadium oxide, copper silver vanadium oxide, V2O5, MnO2, LiCoO2, LiNiO2, LiMnO2, CuO2, TiS, CuS, FeS, FeS2, copper vanadium oxide, and mixtures thereof.
9. The electrochemical cell of claim 1 wherein the cathode has the configuration: SVO/current collector/CF x/current collector/SVO.
10. The electrochemical cell of claim 1 wherein the cathode has the configuration: SVO/current collector/SVO/CF x/SVO/current collector/SVO.
12. The electrochemical cell of claim 1 wherein the anode is lithium and the cathode has the configuration:
SVO/current collector/CF x, with the SVO facing the lithium anode.
SVO/current collector/CF x, with the SVO facing the lithium anode.
12. The electrochemical cell of claim 1 wherein the first fluorinated carbon is sandwiched between a first and second current collectors with the second cathode active material contacting the first and second current collectors opposite the fluorinated carbon.
13. The electrochemical cell of claim 12 wherein the first and second current collectors are titanium having a coating selected from the group consisting of graphite/carbon material, iridium, iridium oxide and platinum provided thereon.
24. The electrochemical cell of claim 1 wherein the anode is lithium, the second cathode active: material is SvO
and the cathode current collector is titanium or aluminum.
and the cathode current collector is titanium or aluminum.
15. The electrochemical cell of claim 14 wherein the cathode current collector is titanium.
26. The electrochemical cell of claim 1 wherein the electrolyte has a first solvent selected from an ester, a linear ether, a cyclic ether, a dialkyl carbonate, and mixtures thereof, and a second solvent selected from a cyclic carbonate, a cyclic ester, a cyclic amide, and mixtures thereof.
17. The electrochemical cell of claim 16 wherein the first solvent is selected from the group consisting of tetrahydrofuran, methyl acetate, diglyme, trigylme, tetragylme, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy,2-methoxyethane, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate, dipropyl carbonate, and mixtures thereof, and the second solvent is selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, .gamma.-valerolactone, .gamma.-butyrolactone, N-methyl-pyrrolidinone, and mixtures thereof.
18. The electrochemical cell of claim 1 including a lithium salt selected from the group consisting of LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, LiO2, LiAlCl4, LiGaCl4, LiC(SO2CF3)3 , LiN(SO2CF3)2 , LiSCN, LiO3SCF3 , LiC6F5SO3, LiO2CCF3, LiSO6F, LiB(C6H5)4, LiCF3SO3 , and mixtures thereof.
19. The electrochemical cell of claim 1 wherein the electrolyte is 0.8M to 1.5M LiAsF6 or LiPF6 dissolved in a 50:50 mixture, by volume, of propylene carbonate and 1,2-dimethoxyethane.
20. An electrochemical cell, which comprises:
a) a lithium anode;
b) a cathode of a first cathode active material of CF x sandwiched between a first and second current collectors with a second cathode active material selected from the group consisting of SVO, CSVO, V2O5, MnO2, LiCoO2, LiNiO2, LiMnO2, CuO2, TiS, Cu2S, FeS, FeS2, CVO, and mixtures thereof, contacting at least one of the first and second current collectors apposite the first cathode active material; and c) an electrolyte comprising at least one solvent for activating the anode and the cathode, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation.
a) a lithium anode;
b) a cathode of a first cathode active material of CF x sandwiched between a first and second current collectors with a second cathode active material selected from the group consisting of SVO, CSVO, V2O5, MnO2, LiCoO2, LiNiO2, LiMnO2, CuO2, TiS, Cu2S, FeS, FeS2, CVO, and mixtures thereof, contacting at least one of the first and second current collectors apposite the first cathode active material; and c) an electrolyte comprising at least one solvent for activating the anode and the cathode, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation.
21. The electrochemical cell of claim 20 wherein the current collectors are of titanium.
22. A method for powering an implantable medical device, comprising the steps of:
a) providing the medical device;
b) providing an electrochemical cell comprising the steps of:
i) providing an anode of an alkali metal;
ii) providing CF x as a first cathode active material of a first energy density and a first rate capability and providing a second cathode active material of a second energy density and a second rate capability, wherein the first energy density of the CF x is greater than the second energy density while the first rate capability is less than the second rate capability of the second cathode active material;
iii) providing a cathode current collector comprising spaced apart major sides;
iv) positioning the CF x proximate one of the major sides of the cathode current collector;
v) contacting the second cathode active material to the other major side of the cathode current collector; and vi) activating the anode and cathode with an electrolyte comprising at least one solvent, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation; and c) electrically connecting the electrochemical cell to the medical device.
a) providing the medical device;
b) providing an electrochemical cell comprising the steps of:
i) providing an anode of an alkali metal;
ii) providing CF x as a first cathode active material of a first energy density and a first rate capability and providing a second cathode active material of a second energy density and a second rate capability, wherein the first energy density of the CF x is greater than the second energy density while the first rate capability is less than the second rate capability of the second cathode active material;
iii) providing a cathode current collector comprising spaced apart major sides;
iv) positioning the CF x proximate one of the major sides of the cathode current collector;
v) contacting the second cathode active material to the other major side of the cathode current collector; and vi) activating the anode and cathode with an electrolyte comprising at least one solvent, wherein the fluorinated carbon is characterized as having been synthesized from a fibrous carbonaceous material having sufficient spacing between graphite layers to substantially restrict expansion due to solvent co-intercalation; and c) electrically connecting the electrochemical cell to the medical device.
23. The method of claim 22 including discharging the cell to provide a current pulse of at least about 15.0 mA/cm2.
24. The method of claim 22 including providing the fluorinated carbon synthesized from the fibrous carbonaceous material having a BET surface area of greater than about 250 m2/g.
25. The method of claim 22 including providing the fluorinated carbon synthesized from the fibrous carbonaceous material having a particle size, by volume %, of less than about 15 µm.
26. The method of claim 22 including providing the fluorinated carbon synthesized from the fibrous carbonaceous material having a particle size surface, by area %, of less than about 3.5.
27. The method of claim 22 including providing the fluorinated carbon synthesized from the fibrous carbonaceous material having a DTA exotherm of about 652°C
to about 656°C.
to about 656°C.
28. The method of claim 22 including selecting the second cathode active material from the group consisting of silver vanadium oxide, copper silver vanadium oxide, V2O5, MnO2, LiCoO2, LiNiO2, LiMnO2, CuO2, TiS, CuS, FeS, FeS2, copper vanadium oxide, and mixtures thereof.
29. The method of claim 22 wherein the anode is lithium, the first cathode active material is CF X and the second cathode active material is SVO.
30. The method of claim 22 including providing the cathode having the configuration: SVO/current collector/CF x/current collector/SVO.
31. The method of claim 22 including providing the cathode having the configuration: SVO/current collector/SVO/CF x/SVO/current collector/SVO.
32. The method of claim 22 including providing the anode of lithium and the cathode having the configuration:
SVO/current collector/CF x, with the SVO facing the lithium anode.
SVO/current collector/CF x, with the SVO facing the lithium anode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20536100P | 2000-05-18 | 2000-05-18 | |
| US60/205,361 | 2000-05-18 |
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| CA2348175A1 CA2348175A1 (en) | 2001-11-18 |
| CA2348175C true CA2348175C (en) | 2006-01-31 |
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| EP (1) | EP1156541B1 (en) |
| JP (1) | JP2002100361A (en) |
| CA (1) | CA2348175C (en) |
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- 2001-05-17 US US09/859,558 patent/US6783888B2/en not_active Expired - Lifetime
- 2001-05-18 CA CA002348175A patent/CA2348175C/en not_active Expired - Fee Related
- 2001-05-18 EP EP01112257A patent/EP1156541B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JP2002100361A (en) | 2002-04-05 |
| CA2348175A1 (en) | 2001-11-18 |
| EP1156541B1 (en) | 2013-01-30 |
| US6783888B2 (en) | 2004-08-31 |
| EP1156541A2 (en) | 2001-11-21 |
| US20020012844A1 (en) | 2002-01-31 |
| EP1156541A3 (en) | 2003-03-26 |
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