CA2060712C - High voltage lithium rechargeable electrochemical cell - Google Patents
High voltage lithium rechargeable electrochemical cellInfo
- Publication number
- CA2060712C CA2060712C CA002060712A CA2060712A CA2060712C CA 2060712 C CA2060712 C CA 2060712C CA 002060712 A CA002060712 A CA 002060712A CA 2060712 A CA2060712 A CA 2060712A CA 2060712 C CA2060712 C CA 2060712C
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- CA
- Canada
- Prior art keywords
- cell
- electrolyte
- electrochemical cell
- cathode
- polymer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M6/00—Primary cells; Manufacture thereof
- H01M6/14—Cells with non-aqueous electrolyte
- H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
- H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
A high voltage, rechargeable lithium electrochemical cell is provided that exhibits high cycling efficiency over many cycles. The cell comprises metallic lithium as the anode, poly 3-methylthiophene (PMT) polymer as the cathode, and LiAsF salt dissolved in dimethylcarbonate (DMC) as the electrolyte.
Description
Z~7~ ~
FIELD OF INVENTION
This invention relates in general to a high voltage lithium rechargeable electrochemical cell and in particular to such a cell with a thin conducting polymer cathode and electrolyte ccntaining an alkyl-carbonate solvent.
BACKGROUND OF THE INVENTION
Rechargeable lithium batteries, especially those contain-ing organic liquid based solvents, have generally suffered from poor cycling efficiencies of lithium, solvent oxidation (degrada-lo tion) on charge, diminishing cathode capacity with increased cycling and hazardous situations resulting from cell abuse con-ditions aR for example short circuit and overdischarge. Some sol-vents allow,good lithium cycling efficiencies but are unstable to the high anode potentials required during charging. Similarly, 2r~
electrolytes that are stable to oxidation often allow poor lithiurn cycling efficiency. Cell short circuiting that results from dendrite formations or from overdischarge may cause explosions.
Overcharge may degrade the electrolyte or irreversibly diminish performance of certain cathodes.
SUMMARY OF THE INVENTION
The general object of this inventlon is to provide a high voltage lithium rechargeable electroc~lcal ~ell in which the aforementioned difficultie~ are overcome. A more particular object of the invention is to provide such a cell that is highly efficient on discharge and charge. A more particular object of the invention is to provide such a cell that is stable to oxida-tion of the electrolyte on charge and also stable to modest over-charge of the cathode. A still further object of the invention is to provide such a cell that allows much more cathode area to be packaged per unit volume than is possible for state-of-the-art porous carbon cathodes. Another object of the invention is to provide such a cell in which the ~afety hazards normally associ-ated with lithium cells that are overdischarged or short circuited are diminished because the cathode becomes electrically insulating on discharge. A particular ob~ect of the invention is to provide such a cell that is efficient during discharge and charge over hundreds of cycles.
It has now been found that a high voltage, rechargeable, lithium electrochemical cell can be provided that exhibits high 2~
cycling efficiency over many cycles, the cell includin~ a metallic lithium anode, poly 3-methylthiophene (PMT) polymer cathode, and electrolyte including lithium hexafluoroar~enate LiAsF salt dissolved in dimethyl carbonate (DMC).
Cell features include a high voltage cell employing a lithium anode which is able to be recharged. Also included is an electrically conductive polymer film as the cathode that is also rechargeable with excellent cycling efficiency. The electrolyte is composed of LiAs~ in DMC, providing an electrolyte that is neither oxidized nor reduced during cell operation. On discharge, no harmful products or adverse chemical reactions occur other than the release of Li cations and AsF anions into the electrolyte.
There is a built-in safety feature to render extreme conditions such as short-circuit or overdischarge less hazardous; because the polymer becomes electrically more insulating during undoping (which occurs during cell discharge), as the polymer becomes less conduc-tive and cell resistance increases, the polymer will act as an internal fuse to terminate cell operation. On charge, Li is replated at the lithium anode and AsF migrates to the oxidized (positively charged) P~T cathode to electrically neutralize its charge. Another attractive feature of the cell is the ability to overcharge the cathode over many cycles without deleterious effects. The cell reactions are:
DISCHARGE
o +
Anode: Li -~ xLi + x electrons o Cathode: [PMT AsF ] + x electrons ~ xPMT + xAsF
il~l~V
2~
CHARGE
Anode: xLi + x electrons _ ~ Li o -- +
Cathode: xPMT + xAsF > [PMT AsF ] + x electrons 6 6 x Since no deleterious reactions occur, hundreds or thousands of cycles may be expected with negligible loss in discharge capacity or charge ef~iciency.
The metallic lithium anode is desired to create a high cell potential (> 3 v) when coupled with the cathode. To ~i~imi ze the quantity of lithium for increased safety, one can also use a lithium intercalating compound, such as graphite or one of the metal oxide compounds. Intercalating compounds would be useful to reduce the hazards associated with metallic lithium such as cell shorting resulting from such conditions as dendrite formation with cycling, abuse during discharge/charge and disposal.
The cathode is comprised of electrochemically formed, electrically conducting poly 3-methylthiophene polymer film.
Depending on the level of doping, electrical conductivity of the polymer can be in the range of 1~ to 2 x 10 S cm . Because it i5 formed electrochemically, a very thin film can be produced on a suitable substrate which can then serve as the current collector in the cell. PMT films on the order of one micrometer thick can be formed, allowing more electrode area to be packaged per unit volume (compared to carbon electrodes common to lithium cells). Although there are many methods that one skilled in the art might use to prepare the polymer, a suitable procedure used for polymerizing PMT on a substrate is as follows:
2 ~ 6 ~ 7 9 ~
Preparation of PMT is in a 125 ml Europeall flask (Ace Glass) using a 1 cm platinum flag counter electrode, a satur-ated sodi~n calomel reference electrode, ~nd a platinum rod work-ing electrode. The platin~n rod is polished to a mirror finish with 0.1 micron alumina/water paste and sheathed in heat shrink-able Teflon so as to expose only the 0.071 cm cross sectional area at the polished end of tlle rod. The cell is also fitted with a glass tube for bubbling gas and a gas outlet. The cell is flooded with electrolyte contailling hig~ purity 3-methylthiopllene monomer and litlliwn hexafluoroarsenate at 0.1 molar concentratiol~s in redistilled acetonitrile as the solvent. Ultra higll purity dry argon is bubbled througl~ the electrolyte to remove oxygen.
PMT polymerizes when the potential (working vs reference) is 1.5 V and above. ~n adherent film 1.4 microns thick is pro-duced by pulse depositioJI. This is carried out at a constant cur-rent of 10 r~A cm by passing ~.25 coulombs per Clll 011 five successive cycles with five minute rest periods (at open circuit between cycles to restore equilibrium conditiolls. Films of poor quality formed if the rest periods were omitted. The PM'r-coa~ed 2~ platinum sur~ace is ~hell rinsed in acetonitrile and dried under vacuum at 50 C. In the oxidized (~sF -doped, electrically conductive) state PMT is blue in color, while reduced (undoped, electrically insulating) PMT is red. During cell cycling, t~le polymer becomes oxidized and reduced, being electrically neutra-lized by the insertion and loss of AsF anions. Once the polymer becomes doped to its maximum level, an overcharge * Trade Mark XC~7~ ~
condition will exist where no more anion~ will be in~erted, and additional charge will ~e wasted. If mode~tly overcharged, no harmful cell reactions will occur.
A conductive electrolyte that i8 ~table during cell charg-ing has been a concern in lithium systems because of the high oxi-dation potential~ required. It is difficult to find ~olvents that are ~table (will not become oxidized) during cell charging and will permit good lithium cycling efficiencieR. One suitable sol-vent is dimethyl carbonate. DMC is stable to oxidation potentials up to 4.4 V. ~ stable, conductive electrolyte is formed with the addition of dry, high purity LiAsF salt in redistilled DMC. In a 1.5 M LiAsF -DMC electrolyte, conductivity i~ approximately 0.01 S cm Constant current recharge of the system described herein is most efficient up to a cutoff potential of 3.8 V. Charging to a potential of 4.0 V provides additional capacity on discharge but exhibits a loss in efficiency on charge. These potentials are well within the limits of electrolyte stability.
DESCRIPTION OF THE P~EFERRED EM~ODIMENT
A cell is constructed with a lithium metal anode, a 1.4 micrometer thick poly 3-methylthiophene polymer cathode doped with AsF and supported on a platinum substrate, and a lithium reference electrode. The cell is flooded with 10 ml of electrolyte composed of 1.46 ~ LiAsF in dimethyl carbonate.
The cell is di~charged at o.1 mA cm constant current until cell voltage falls to 2.7 V. After a one minute rest period at open circuit, the cell i8 charged at 0.05 mA cm con~tant current until cell potential reaches 3.8 V, allowing a one minute rest period prior to the next discharge. Under these conditions, cell discharge is reproducible over many cycles; likewise, cell recharge is reproducible over many cycles, replacing exactly the same number of coulombs as are rem~ved on discharge.
DESCRIPTION OF THE D~AWING
Figure 1 shows a Li/1.46 M LiAsF -DMC~1.4~4m thick PMT
cell di~charge at 0.1 mA cm constant current to a 2.7 V
cutoff. Discharge curves are shown for di~charge numbers 20, 30, 40, S0 and 63. Recharge is by constant current at 0.~5 mA cm to a 3.8 V cutoff.
Figure 2 shows a Li/1.46 M LiAsF -DMC/1.4 ~m thick PMT cell cycled after recharge at 0.05 mA cm to 3.8 V follow-ing short-circuiting of the cell and allowing it to sit for two days. Curves for 0.1 mA cm constant current discharge to a 2.7 V are ~hown for cycle numbers 63, 90 and 116.
Figure 3 shows a Li/1.46 M LiAsF -DMC/1.4 ~m thick PMT
cell discharge at 0.1 mA cm constant current to a 2.7 V cutoff.
Recharge is by constant current at 0.05 mA cm to a 4.0 V cut-off over fourteen cycles. Cycle numbers 117, 125 and 130 are shown.
;~r~
Figure 1 illustrates some of the cell discharges during the first 63 cyclefi. Cell capacity is extremely reproducible.
Each recharge cycle replaces exactly 1~0~ of the charge previou~ly remo~ed. Cell operating po~ential exceeds 3 V for nearly the entire di~charge.
After cycle 63, the cell is intentionally ~hort-circuited and remains sitting for two days. The cell is again recharged (to the 3.8 V cutoff) and cycling continues. Approximately 12% of cell discharge capacity i8 irreversibly lost, but no further loss is observed over the next 53 cycles to cycle 116 (Figure 2).
The next 14 cycles (Figure 3, cycles 117 through 130) as performed are with a recharge voltage cutoff o~ 4.0 v. Capacity increases over the first couple of cycles and then stabilizes for the remaining cycles. The increase in discharge capacity is presumed a result of doping the polymer to a higher level with AsF ani~ns . Recharge of the cell to 4.0 V results in an overcharge condition. Approximately 108~ of the coulombs removed on discharge are passed during charging. After the initial increase in discharge capacity, overcharge remains at about 108%, 2~ and discharge capacity remains constant. This i8 important because it shows that in addition to the electrolyte being stable at a potential as high as 4.~ V, the polymer cathode i8 also stable to this potential. Further, the polymer cathode is stable to overcharge conditions, capable of continuing to provide a - reproducible discharge.
~ ~ 27~ ~ :
There i~ ~ome charging voltage cutoff, not yet deter-mined, that better balances cell cycling; precluding current being wasted on cell overcharging while allowing maximum discharge capacity.
In the invention, in lieu o~ l~thium as the anode, one might u~e lithium intercalating materials such as gr~phite, or any of ~everal metal oxide6 or metal sulfides. The anode material might also be a metal such a~ calcium, sodium, magnesium, barium, potassium, titanium or strontium. The anode could also be com-prised of alloy~ of lithium, sodium, aluminum, magnesium, calcium, barium, pota~sium, titanium or 6trontium. Then too, the anode might be metallic cation intercalating materials such as graphite or any of several metal oxides or metal sulfides.
As for the cathode, one might use poly 3-methylthiophene prepared by other methods to alter physical, chemical or electro-; nic characteristic~ of the polymer. Al~o, one might prepare PMT
on other ~ubstrates such as nickel or aluminum foil. One might also use other electrically conductive polymers with electro-chemical characteristics ~imilar to PMT.
A~ for the electrolyte, one might use a mixed solvent including DMC with methylformate, methylacetate, or some other solvent that provide~ higher electrolyte conductivity and lithium cycling ef~iciency. One might also use diethylcarbonate which is resistant to oxidation or diethylcarbonate mixed with methylfor-nate, methylactate or some other solvent. One might also use other stable ~alt~ and/or ~olvents, organic or inorganic. One _g _ ~~7~ ?
might also use mixtures of these salts or solvents or mixtures of both salts and solvents.
The electrochemical cell of the invention can be use for high voltage electrical power in the form of a rechargeable battery. The cell can also be used as a power source where there is a requirement for a high degree of 6afety and a,large number of cycles. The cell might also find use as a high pulse power device when configured in a bipolar arrangement, since one is able to stack many cells in a small volume due to the very thin cathode.
Then too, the cell might find use as a backup power in circuit board applications or as a reserve cell, especially in cases where it is desired to maintain constant trickle charge to ensure battery readiness.
We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.
FIELD OF INVENTION
This invention relates in general to a high voltage lithium rechargeable electrochemical cell and in particular to such a cell with a thin conducting polymer cathode and electrolyte ccntaining an alkyl-carbonate solvent.
BACKGROUND OF THE INVENTION
Rechargeable lithium batteries, especially those contain-ing organic liquid based solvents, have generally suffered from poor cycling efficiencies of lithium, solvent oxidation (degrada-lo tion) on charge, diminishing cathode capacity with increased cycling and hazardous situations resulting from cell abuse con-ditions aR for example short circuit and overdischarge. Some sol-vents allow,good lithium cycling efficiencies but are unstable to the high anode potentials required during charging. Similarly, 2r~
electrolytes that are stable to oxidation often allow poor lithiurn cycling efficiency. Cell short circuiting that results from dendrite formations or from overdischarge may cause explosions.
Overcharge may degrade the electrolyte or irreversibly diminish performance of certain cathodes.
SUMMARY OF THE INVENTION
The general object of this inventlon is to provide a high voltage lithium rechargeable electroc~lcal ~ell in which the aforementioned difficultie~ are overcome. A more particular object of the invention is to provide such a cell that is highly efficient on discharge and charge. A more particular object of the invention is to provide such a cell that is stable to oxida-tion of the electrolyte on charge and also stable to modest over-charge of the cathode. A still further object of the invention is to provide such a cell that allows much more cathode area to be packaged per unit volume than is possible for state-of-the-art porous carbon cathodes. Another object of the invention is to provide such a cell in which the ~afety hazards normally associ-ated with lithium cells that are overdischarged or short circuited are diminished because the cathode becomes electrically insulating on discharge. A particular ob~ect of the invention is to provide such a cell that is efficient during discharge and charge over hundreds of cycles.
It has now been found that a high voltage, rechargeable, lithium electrochemical cell can be provided that exhibits high 2~
cycling efficiency over many cycles, the cell includin~ a metallic lithium anode, poly 3-methylthiophene (PMT) polymer cathode, and electrolyte including lithium hexafluoroar~enate LiAsF salt dissolved in dimethyl carbonate (DMC).
Cell features include a high voltage cell employing a lithium anode which is able to be recharged. Also included is an electrically conductive polymer film as the cathode that is also rechargeable with excellent cycling efficiency. The electrolyte is composed of LiAs~ in DMC, providing an electrolyte that is neither oxidized nor reduced during cell operation. On discharge, no harmful products or adverse chemical reactions occur other than the release of Li cations and AsF anions into the electrolyte.
There is a built-in safety feature to render extreme conditions such as short-circuit or overdischarge less hazardous; because the polymer becomes electrically more insulating during undoping (which occurs during cell discharge), as the polymer becomes less conduc-tive and cell resistance increases, the polymer will act as an internal fuse to terminate cell operation. On charge, Li is replated at the lithium anode and AsF migrates to the oxidized (positively charged) P~T cathode to electrically neutralize its charge. Another attractive feature of the cell is the ability to overcharge the cathode over many cycles without deleterious effects. The cell reactions are:
DISCHARGE
o +
Anode: Li -~ xLi + x electrons o Cathode: [PMT AsF ] + x electrons ~ xPMT + xAsF
il~l~V
2~
CHARGE
Anode: xLi + x electrons _ ~ Li o -- +
Cathode: xPMT + xAsF > [PMT AsF ] + x electrons 6 6 x Since no deleterious reactions occur, hundreds or thousands of cycles may be expected with negligible loss in discharge capacity or charge ef~iciency.
The metallic lithium anode is desired to create a high cell potential (> 3 v) when coupled with the cathode. To ~i~imi ze the quantity of lithium for increased safety, one can also use a lithium intercalating compound, such as graphite or one of the metal oxide compounds. Intercalating compounds would be useful to reduce the hazards associated with metallic lithium such as cell shorting resulting from such conditions as dendrite formation with cycling, abuse during discharge/charge and disposal.
The cathode is comprised of electrochemically formed, electrically conducting poly 3-methylthiophene polymer film.
Depending on the level of doping, electrical conductivity of the polymer can be in the range of 1~ to 2 x 10 S cm . Because it i5 formed electrochemically, a very thin film can be produced on a suitable substrate which can then serve as the current collector in the cell. PMT films on the order of one micrometer thick can be formed, allowing more electrode area to be packaged per unit volume (compared to carbon electrodes common to lithium cells). Although there are many methods that one skilled in the art might use to prepare the polymer, a suitable procedure used for polymerizing PMT on a substrate is as follows:
2 ~ 6 ~ 7 9 ~
Preparation of PMT is in a 125 ml Europeall flask (Ace Glass) using a 1 cm platinum flag counter electrode, a satur-ated sodi~n calomel reference electrode, ~nd a platinum rod work-ing electrode. The platin~n rod is polished to a mirror finish with 0.1 micron alumina/water paste and sheathed in heat shrink-able Teflon so as to expose only the 0.071 cm cross sectional area at the polished end of tlle rod. The cell is also fitted with a glass tube for bubbling gas and a gas outlet. The cell is flooded with electrolyte contailling hig~ purity 3-methylthiopllene monomer and litlliwn hexafluoroarsenate at 0.1 molar concentratiol~s in redistilled acetonitrile as the solvent. Ultra higll purity dry argon is bubbled througl~ the electrolyte to remove oxygen.
PMT polymerizes when the potential (working vs reference) is 1.5 V and above. ~n adherent film 1.4 microns thick is pro-duced by pulse depositioJI. This is carried out at a constant cur-rent of 10 r~A cm by passing ~.25 coulombs per Clll 011 five successive cycles with five minute rest periods (at open circuit between cycles to restore equilibrium conditiolls. Films of poor quality formed if the rest periods were omitted. The PM'r-coa~ed 2~ platinum sur~ace is ~hell rinsed in acetonitrile and dried under vacuum at 50 C. In the oxidized (~sF -doped, electrically conductive) state PMT is blue in color, while reduced (undoped, electrically insulating) PMT is red. During cell cycling, t~le polymer becomes oxidized and reduced, being electrically neutra-lized by the insertion and loss of AsF anions. Once the polymer becomes doped to its maximum level, an overcharge * Trade Mark XC~7~ ~
condition will exist where no more anion~ will be in~erted, and additional charge will ~e wasted. If mode~tly overcharged, no harmful cell reactions will occur.
A conductive electrolyte that i8 ~table during cell charg-ing has been a concern in lithium systems because of the high oxi-dation potential~ required. It is difficult to find ~olvents that are ~table (will not become oxidized) during cell charging and will permit good lithium cycling efficiencieR. One suitable sol-vent is dimethyl carbonate. DMC is stable to oxidation potentials up to 4.4 V. ~ stable, conductive electrolyte is formed with the addition of dry, high purity LiAsF salt in redistilled DMC. In a 1.5 M LiAsF -DMC electrolyte, conductivity i~ approximately 0.01 S cm Constant current recharge of the system described herein is most efficient up to a cutoff potential of 3.8 V. Charging to a potential of 4.0 V provides additional capacity on discharge but exhibits a loss in efficiency on charge. These potentials are well within the limits of electrolyte stability.
DESCRIPTION OF THE P~EFERRED EM~ODIMENT
A cell is constructed with a lithium metal anode, a 1.4 micrometer thick poly 3-methylthiophene polymer cathode doped with AsF and supported on a platinum substrate, and a lithium reference electrode. The cell is flooded with 10 ml of electrolyte composed of 1.46 ~ LiAsF in dimethyl carbonate.
The cell is di~charged at o.1 mA cm constant current until cell voltage falls to 2.7 V. After a one minute rest period at open circuit, the cell i8 charged at 0.05 mA cm con~tant current until cell potential reaches 3.8 V, allowing a one minute rest period prior to the next discharge. Under these conditions, cell discharge is reproducible over many cycles; likewise, cell recharge is reproducible over many cycles, replacing exactly the same number of coulombs as are rem~ved on discharge.
DESCRIPTION OF THE D~AWING
Figure 1 shows a Li/1.46 M LiAsF -DMC~1.4~4m thick PMT
cell di~charge at 0.1 mA cm constant current to a 2.7 V
cutoff. Discharge curves are shown for di~charge numbers 20, 30, 40, S0 and 63. Recharge is by constant current at 0.~5 mA cm to a 3.8 V cutoff.
Figure 2 shows a Li/1.46 M LiAsF -DMC/1.4 ~m thick PMT cell cycled after recharge at 0.05 mA cm to 3.8 V follow-ing short-circuiting of the cell and allowing it to sit for two days. Curves for 0.1 mA cm constant current discharge to a 2.7 V are ~hown for cycle numbers 63, 90 and 116.
Figure 3 shows a Li/1.46 M LiAsF -DMC/1.4 ~m thick PMT
cell discharge at 0.1 mA cm constant current to a 2.7 V cutoff.
Recharge is by constant current at 0.05 mA cm to a 4.0 V cut-off over fourteen cycles. Cycle numbers 117, 125 and 130 are shown.
;~r~
Figure 1 illustrates some of the cell discharges during the first 63 cyclefi. Cell capacity is extremely reproducible.
Each recharge cycle replaces exactly 1~0~ of the charge previou~ly remo~ed. Cell operating po~ential exceeds 3 V for nearly the entire di~charge.
After cycle 63, the cell is intentionally ~hort-circuited and remains sitting for two days. The cell is again recharged (to the 3.8 V cutoff) and cycling continues. Approximately 12% of cell discharge capacity i8 irreversibly lost, but no further loss is observed over the next 53 cycles to cycle 116 (Figure 2).
The next 14 cycles (Figure 3, cycles 117 through 130) as performed are with a recharge voltage cutoff o~ 4.0 v. Capacity increases over the first couple of cycles and then stabilizes for the remaining cycles. The increase in discharge capacity is presumed a result of doping the polymer to a higher level with AsF ani~ns . Recharge of the cell to 4.0 V results in an overcharge condition. Approximately 108~ of the coulombs removed on discharge are passed during charging. After the initial increase in discharge capacity, overcharge remains at about 108%, 2~ and discharge capacity remains constant. This i8 important because it shows that in addition to the electrolyte being stable at a potential as high as 4.~ V, the polymer cathode i8 also stable to this potential. Further, the polymer cathode is stable to overcharge conditions, capable of continuing to provide a - reproducible discharge.
~ ~ 27~ ~ :
There i~ ~ome charging voltage cutoff, not yet deter-mined, that better balances cell cycling; precluding current being wasted on cell overcharging while allowing maximum discharge capacity.
In the invention, in lieu o~ l~thium as the anode, one might u~e lithium intercalating materials such as gr~phite, or any of ~everal metal oxide6 or metal sulfides. The anode material might also be a metal such a~ calcium, sodium, magnesium, barium, potassium, titanium or strontium. The anode could also be com-prised of alloy~ of lithium, sodium, aluminum, magnesium, calcium, barium, pota~sium, titanium or 6trontium. Then too, the anode might be metallic cation intercalating materials such as graphite or any of several metal oxides or metal sulfides.
As for the cathode, one might use poly 3-methylthiophene prepared by other methods to alter physical, chemical or electro-; nic characteristic~ of the polymer. Al~o, one might prepare PMT
on other ~ubstrates such as nickel or aluminum foil. One might also use other electrically conductive polymers with electro-chemical characteristics ~imilar to PMT.
A~ for the electrolyte, one might use a mixed solvent including DMC with methylformate, methylacetate, or some other solvent that provide~ higher electrolyte conductivity and lithium cycling ef~iciency. One might also use diethylcarbonate which is resistant to oxidation or diethylcarbonate mixed with methylfor-nate, methylactate or some other solvent. One might also use other stable ~alt~ and/or ~olvents, organic or inorganic. One _g _ ~~7~ ?
might also use mixtures of these salts or solvents or mixtures of both salts and solvents.
The electrochemical cell of the invention can be use for high voltage electrical power in the form of a rechargeable battery. The cell can also be used as a power source where there is a requirement for a high degree of 6afety and a,large number of cycles. The cell might also find use as a high pulse power device when configured in a bipolar arrangement, since one is able to stack many cells in a small volume due to the very thin cathode.
Then too, the cell might find use as a backup power in circuit board applications or as a reserve cell, especially in cases where it is desired to maintain constant trickle charge to ensure battery readiness.
We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.
Claims (6)
1. A rechargeable lithium electrochemical cell that operates over a plurality of cycles, said cell comprising metallic lithium as the anode, poly 3-methylthiophene polymer as the cathode, and LiAsF6 salt dissolved in dimethyl carbonate as the electrolyte.
2. An electrochemical cell according to claim 1 wherein the electrolyte is 1.46M
LiAsF6 - dimethyl carbonate.
LiAsF6 - dimethyl carbonate.
3 . An electrochemical cell according to claim 1 wherein the cathode is a 1.4 1 µm thick poly 3-methylthiophene polymer.
4. An electrochemical cell according to claim 1 wherein the electrolyte is 1.46M LiAsF6-dimethyl carbonate and wherein the cathode is a 1.4 ,µm thick poly 3-methylthiophene polymer.
5. An electrochemical cell according to claim 1, further comprising the electrolyte having a dry, high purity LiAsF6 salt.
6. An electrochemical cell according to claim 1, further comprising the electrolyte having redistilled dimethyl carbonate.
1. An electrochemical cell according to claim 1, further comprising constructing the electrolyte by adding a dry, high purity LiAsF6 salt to redistilled dimethyl carbonate in order to provide the electrolyte with oxygen stable and conductive properties.
1. An electrochemical cell according to claim 1, further comprising constructing the electrolyte by adding a dry, high purity LiAsF6 salt to redistilled dimethyl carbonate in order to provide the electrolyte with oxygen stable and conductive properties.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/703,319 USH1422H (en) | 1991-05-20 | 1991-05-20 | High voltage lithium rechargeable electrochemical cell |
| US07/703,319 | 1991-05-20 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2060712A1 CA2060712A1 (en) | 1992-11-21 |
| CA2060712C true CA2060712C (en) | 1998-12-01 |
Family
ID=24824924
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002060712A Expired - Fee Related CA2060712C (en) | 1991-05-20 | 1992-02-05 | High voltage lithium rechargeable electrochemical cell |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | USH1422H (en) |
| CA (1) | CA2060712C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7767335B2 (en) * | 2003-05-16 | 2010-08-03 | The United States Of America As Represented By The Secretary Of The Navy | High-voltage battery switch |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4728589A (en) * | 1980-03-11 | 1988-03-01 | University Patents, Inc. | Reversible electrochemical doping of conjugated polymers and secondary batteries based thereon |
| DE3843412A1 (en) * | 1988-04-22 | 1990-06-28 | Bayer Ag | NEW POLYTHIOPHENES, METHOD FOR THEIR PRODUCTION AND THEIR USE |
-
1991
- 1991-05-20 US US07/703,319 patent/USH1422H/en not_active Abandoned
-
1992
- 1992-02-05 CA CA002060712A patent/CA2060712C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| USH1422H (en) | 1995-03-07 |
| CA2060712A1 (en) | 1992-11-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |