WO2002011218A1 - Electrochemical cell comprising tungsten (iv) oxide/liwmxmnyoz electrode structure - Google Patents

Electrochemical cell comprising tungsten (iv) oxide/liwmxmnyoz electrode structure Download PDF

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Publication number
WO2002011218A1
WO2002011218A1 PCT/US2001/041480 US0141480W WO0211218A1 WO 2002011218 A1 WO2002011218 A1 WO 2002011218A1 US 0141480 W US0141480 W US 0141480W WO 0211218 A1 WO0211218 A1 WO 0211218A1
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Prior art keywords
electrochemical cell
cell according
cathode
anode
active material
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PCT/US2001/041480
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French (fr)
Inventor
Narayan Doddapaneni
Zhendong Hu
Shigenobu Denzumi
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Imra America, Inc.
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Priority to AU2001283517A priority Critical patent/AU2001283517A1/en
Publication of WO2002011218A1 publication Critical patent/WO2002011218A1/en

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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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/46—Alloys based on magnesium or aluminium
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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

Definitions

  • the invention relates to an electrochemical cell.
  • the invention has particular applicability to the manufacture of primary and rechargeable power sources, and has use in, for example, mobile telephones, electrically powered vehicles, medical devices and security systems.
  • FIG. 1 is a graph of energy density versus power density for conventional electrochemical batteries and capacitors
  • the capacitors can be charged and discharged at very high rates but possesses low energy densities and are capable of several thousand charge/discharge cycles, while the batteries provide high energy densities and low self discharge rates and low charge/discharge cycles.
  • the electrochemical cell For many high rate applications such as mobile telephones, electrically powered vehicles, medical devices and security systems, it would be desirable for the electrochemical cell to provide high energy densities and to be capable of charging and discharging at high rates, as shown by the area enclosed by the dashed line.
  • lithium ion cells employ carbon as the anode active material. Recently, it has been shown that lithium ion cells with carbon anodes and metal oxide cathodes outperform most of the existing rechargeable cells.
  • the metal oxides used in the lithium ion cells are special materials which accept guest atoms/ions into their structures. Commonly used cathode metal oxides include, for example, lithiated cobalt oxide (LiCoO 2 ), lithiated nickel oxide (LiNiO 2 ) and lithiated manganese oxide (LiMn 2 O 4 ).
  • lithium ion cells which employ carbon anodes perform very well.
  • the performance characteristics of such cells deteriorates when charged or discharged at high rates and/or when operated or stored at elevated temperatures.
  • carbon is capable of accepting lithium atoms into its crystal lattice and of performing well at ambient temperatures
  • the anode performance degrades at higher temperatures (e.g., greater than 45 °C) due to possible exfoliation caused by mechanical stress after repeated lithium intercalation and de-intercalation.
  • lithium metal tends to deposit on the surface of the carbon electrode.
  • Such metal deposition on the carbon surface creates safety concerns due to dendrite formation as well as causing premature cell failure.
  • litliium ion cells are extremely unsafe under abuse conditions such as overcharge, overdischarge, nail penetration and crush.
  • an object of the present invention to provide an electrochemical cell employing tungsten (IV) oxide and Li w M x Mn y O z as the active materials in the anode and cathode, respectively.
  • the electrochemical cell can be charged and discharged at high rates like an electrochemical capacitor, while also providing a high energy density and low self-discharge rates like a battery.
  • the electrochemical cell is much safer than known lithium ion cells under abuse conditions such as overcharge, overdischarge, nail penetration and crush.
  • the electrochemical cell has particular applicability in mobile telephones, electrically powered vehicles, medical devices and security systems.
  • a novel electrochemical cell comprises an anode comprising a tungsten (IV) oxide active material, a cathode comprising a metal oxide active material of the following general formula (I):
  • M can be, for example, a metal selected from the group consisting of Al, Ni and Co.
  • the active material of the cathode can be of the following general formula (V):
  • LiAlo.i 4 Mnj. 8 gO 4 LiAlo.i 4 Mnj. 8 gO 4 .
  • the electrolyte can be non-aqueous, for example, an electrolyte comprising LiPF 6 in ethylene carbonate and diethylcarbonate or LiPF 6 in methyl acetate and propylene carbonate.
  • a mobile telephone, an electrically powered vehicle, for example, a hybrid electric vehicle, a medical device, and a security system comprising the electrochemical cell can be provided.
  • an electrochemical cell comprises an anode comprising a tungsten (IV) oxide active material, a cathode comprising a metal oxide active material of the following general formula (I): Li w M x Mn y O z (I) wherein M is a metal, and w, x, y and z are non-zero numbers, and an electrolyte providing a conducting medium between said anode and said cathode.
  • the cell is capable of delivering greater than 4 W-h/kg at a discharge power density of 0.5 W-h/kg when charged only for 20 seconds, and 20 W-h/kg at a discharge power density of 0.5 W-h/kg when charged for 60 minutes.
  • FIG. 1 is a graph of energy density versus power density for various electrochemical capacitors and batteries, and for electrochemical cells in accordance with the invention
  • FIG. 2 is an illustration of an exemplary electrochemical cell in accordance with the invention
  • FIG. 3 is a graph of energy density versus power density for various charge rates, for a plastic encased electrochemical cell in accordance with the invention
  • FIG. 4 is a graph of energy density versus power density for various temperatures, for a plastic encased electrochemical cell in accordance with the invention
  • FIG. 5 is a graph of discharge energy versus number of cycles for density versus power density for various temperatures, for a plastic encased electrochemical cell in accordance with the invention
  • FIG. 6 is a graph of current and cell voltage versus time for a plastic encased electrochemical cell in accordance with the invention.
  • FIG. 7 is a graph of discharge energy density versus number of cycles for two plastic encased electrochemical cells in accordance with the invention.
  • FIG. 8 is a graph of discharge energy versus charge time for a plastic encased electrochemical cell in accordance with the invention.
  • FIG. 9 is a graph of discharge energy versus number of cycles for a plastic encased electrochemical cell in accordance with the invention.
  • an exemplary electrochemical cell 200 in accordance with the invention will now be described.
  • One or more anodes 202 and an equal number of cathodes 204 typically of the same thickness are formed on anode and cathode current collectors 206, 208.
  • the anodes and cathodes are typically formed on opposite surfaces of the anode current collectors 206 and cathode current collectors 208, respectively.
  • a separator 210 is placed for each of the anode-cathode pairs to prevent contact between the anodes 202 and cathodes 204 in the final structure.
  • the anodes 202 and cathodes 204 are alternately stacked in an array as shown.
  • the electrochemical cell 200 is placed into a container 212, such as a plastic bag, and the anode and cathode current collectors 206, 208 are each connected to a respective terminal or electrical feedthrough 214, 216 in the container. Electrolyte 218 is then added to the cell, and the cell is sealed.
  • a container 212 such as a plastic bag
  • the electrolyte can be filled after pulling a vacuum on the interior of container 212.
  • the anodes 202 are formed from a tungsten (IV) oxide active material, and can be formed by known methods.
  • an electrode paste or slurry can be formed by mixing together a binder, a conductive material such as a conductive carbon material, a solvent and tungsten (IV) oxide powder.
  • Typical binders include, for example, polyvinylidene fluoride (PVDF) and TEFLON powder.
  • Suitable solvents include, for example, l-methyl-2-pyrrolidinone (NMP), dimethyl sulfoxide (DMSO), acetonitrile (AN), or dimethyl formate (DMF).
  • the conductive carbon material can be, for example, acetylene black conductive carbon, graphite or other known materials.
  • the paste or slurry can then be coated on a smooth, solid or mesh metal current collector surface.
  • a desired thickness e.g., from about 0.001 to 0.01 inch
  • the material is then dried, preferably under vacuum, at a temperature typically from about 130 to 170°C, preferably about 150°C, for a period of from about 6 to 15 hours.
  • the cathodes 204 are formed from a metal oxide active material of the following general formula (I):
  • metals M include, for example, Al, Ni and Co.
  • the active material in the cathode is of the following general formula (I'): LiM x Mn 2 . x O 4 (T) wherein 0 ⁇ x ⁇ 2.
  • a particularly preferred active material in the cathode is
  • Additional exemplary active cathode materials include, for example, LiNiO 2 , LiCoO 2 , etc.
  • the cathodes in accordance with the invention can be formed by known methods, for example, by the methods described in U.S. Patent No. 5,567,401, to Doddapaneni et al, the entire contents of which are incorporated herein by reference.
  • the anode and cathode current collectors 206, on which the anodes and cathodes are formed, are constructed of, for example, aluminum, copper or nickel. Of these, aluminum is preferred due to light weight and cost
  • the material of construction of the separators 210 can be, for example, polypropylene, polyethylene, and the like, with Celgard® 3501, commercially available from Hoechst Celanese, being an exemplary material.
  • Particularly preferred electrolytes include, for example, LiPF 6 in ethylene carbonate (EC) and diethylcarbonate (DEC) or LiPF 6 in methyl acetate (MA) and propylene carbonate (PC).
  • EC ethylene carbonate
  • DEC diethylcarbonate
  • MA methyl acetate
  • PC propylene carbonate
  • Other known, non-aqueous electrolytes that are suitable for lithium cells can alternatively be employed.
  • a binder solution was formed by dissolving 7g PVDF into lOOg of NMP solvent at 90 °C. 8g of the Super P Carbon material was added to the binder solution, and the mixture was blended thoroughly for at least 10 minutes in an ultrasonic mixer for 60 minutes. 85g of the WO 2 was added to the mixture and was blended thoroughly for at least 10 minutes in the mixer.
  • Aluminum foils were cut to areas of 10 by 20 cm to form anode current collectors.
  • the aluminum foils were smoothed out on a glass surface using isopropanol and a straight edge.
  • a strip of aluminum foil was placed on one or both of the long edges of the aluminum foil to define the shape of the electrode.
  • the anode slurry was placed on each aluminum foil such that it covered the designated area. Using a fixed blade, the anode slurry was pulled across the aluminum foil to produce a smooth surface. When completed, the structure was removed from the glass and placed on a tray to be baked.
  • the structures were placed in a fume hood to slowly remove some of the
  • Cathodes having 80 wt% LiAlo.j 4 Mnj. 86 O 4 , 10 wt% XC-72R Carbon and 10 wt% PVDF binder were fabricated as follows. A binder solution was formed by dissolving lOg PVDF into 90g NMP solvent at 90°C. lOg of the carbon material was added to the binder solution, and the mixture was blended thoroughly for at least 10 minutes in an ultrasonic mixer for 60 minutes. 80g of the LiAl 0 . 14 Mn ⁇ 86 O 4 was added to the mixture and was blended thoroughly for at least 10 minutes in the mixer.
  • Aluminum foils were cut to areas of 10 by 20 cm to form cathode current collectors.
  • the aluminum foils were smoothed out on a glass surface using isopropanol and a straight edge.
  • a strip of aluminum foil was placed on one or both of the long edges of the aluminum foil to define the shape of the electrode.
  • the anode slurry was placed on each aluminum foil such that it covered the designated area. Using a fixed blade, the cathode slurry was pulled across the aluminum foil to produce a smooth surface. When completed, the structure was removed from the glass and placed on a tray to be baked.
  • the structures were placed in a fume hood to slowly remove some of the NMP solvent. Trays of electrodes were next placed in a vacuum oven, which was pumped down to remove the remaining NMP solvent. The electrodes were baked at 150 °C under vacuum overnight. The oven was allowed to cool down, and the electrodes were transferred to a dry room.
  • Multi-plate cells having an electrode area of 12.5 cm 2 , 25 cm 2 and 150 cm 2 were fabricated. For example, a cell having 12 anodes and 12 cathodes of 2.5 by 5 cm electrodes and an active geometric area of 150 cm 2 was fabricated.
  • the multi-plate cells were then sealed in thermo-plastic bags (shield pack® Inc., of West Monroe, LA). From 0.5 to 1.5 ml of electrolyte containing 1.0 M LiPF 6 in EC/DEC in a 1:2 volume basic ratio was then added to the bags which were then sealed.
  • the cells as prepared above were subjected to (a) constant current (cc), (b) constant voltage (cv), and (c) constant current followed by constant voltage (cccv) charging methods, and various performance characteristics of the cell were measured to understand the effects on discharge performance and cycle life performance using a Maccor battery tester.
  • FIG. 3 is a Ragone plot of energy density versus power density for the different charge/discharge rates. As can be seen, energy density is strongly influenced by the charge rate, particularly below discharge power densities of 1.0 kW/kg.
  • Electrochemical cells having a 12.5 cm 2 electrode area as prepared above were charged at 3 mA/cm 2 (0.35 kW/kg) to 3.35 V and then discharged at various rates to 1.65 V at 25 °C. These results are shown in FIG. 1.
  • Test 2 Temperature Effects The following tests were performed to understand the influence of temperature on performance characteristics of the electrochemical cells. Four electrochemical cells having a 12.5 cm 2 electrode area as prepared above were charged at 2 mA/cm 2 to 3.45 V, and then discharged at various rates to 2.00 V at respective temperatures of -40, -30, -20 and 25 °C. The results from this test are shown in FIG. 4, which is a Ragone plot of energy density versus power density for the different charge/discharge temperatures. The poor performance at low temperatures is believed to be due to an increase in the resistance of the electrolyte.
  • FIG. 5 is a graph of discharge energy versus number of cycles. As can be seen, the cell performed well with a fade rate of about 0.2% per one thousand cycles after initial loss. The fade appears to be due to the increased internal cell resistance. The initial drop in performance is most likely due to the corrosion of current collectors and the slight dissolution of the binder.
  • Cell-A and Cell-B Two cells having a 25 cm 2 electrode area as prepared above were repeatedly charged at a constant voltage of 3.45 V for 40 seconds, and then discharged at a rate of 40 mA/cm 2 to 2.00 V, at ambient temperature.
  • the cycle life performance of the cells is shown in FIG. 7.
  • the difference in energy density between the two cells is believed to be due to the variation in active material loading in the electrodes.
  • Each of the cells exhibited small cyclical variations in discharge energy density which correspond to the time of day and ambient temperature at such time. The data indicates that the cells can be charged at very high rates with little adverse effect on the cycle life performance.
  • Test 6 Energy Density as a Function of Time This test was conducted to study the effects of charge time on discharge energy.
  • a cell having a 150 cm 2 electrode area as prepared above was charged at room temperature at a rate of 4 mA/cm 2 to 3.40 V, with the charge being maintained at a constant voltage of 3.40 V for various time periods before being discharged at 10 mA/cm 2 to 2.00 V.
  • the results of this test are shown in FIG. 8, which is a graph of discharge energy versus charge time. As shown in FIG. 8, the cell was charged approximately to 95% of its capacity within 45 minutes. In certain applications, very high charge currents generated under a constant voltage charge may not be desirable. In this test, therefore, the cells were charged under constant current to a fixed cell voltage followed by a constant voltage.
  • Test 7 Cycle Life Performance A cell having a 150 cm 2 electrode area as prepared above was charged at a rate of 30 mA/cm 2 to 3.45 V, followed by holding the voltage constant at 3.45 V for 15 seconds, and then a constant current discharge to 2.00 V at a rate of 30 mA/cm 2 . This cycle was repeatedly performed at 15 °C.
  • FIG. 9 is a graph of discharge energy versus number of cycles. As shown, the discharge energy increased slightly from one to about 150 cycles, but remained essentially constant at about 5.7 Wh/kg thereafter. This initial increase in energy is believed to be due to the heat generation under high rate charge and discharge conditions.
  • the electrochemical cells in accordance with the invention can be charged and discharged at very high rates like electrochemical capacitors.
  • the charge mode appears to have little effect on the cycle life.
  • the cells provide high energy densities and low self- discharge, as obtained with batteries. For example, these cells can deliver 4 Wh/kg at a discharge power density of 0.5 kW/kg when charged only for 20 seconds, and 20 Wh/kg at a discharge power density of 0.5 kW/kg when charged for 60 minutes.
  • electrochemical cells in accordance with the invention particularly suitable for example, as a battery in cellular or other forms of mobile telephones; in electrically powered vehicles such as a pure electric vehicle, a hybrid electric vehicle or a power assisted electric vehicle (e.g., automobiles, trucks, mopeds, motorcycles powered by an engine and a battery or by a fuel cell and a battery); in medical devices; in power tools; and in security systems such a personal computer or building security systems; in security cards or credit cards which use an internal power supply; and in backup power supplies and SLI (starting lighting ignition) batteries.
  • the invention is applicable to any type of device where a capacitor or battery are used.

Abstract

Provided is a novel electrochemical cell. The electrochemical cell features an anode which includes a tungsten (IV) oxide active material, a cathode which includes a metal oxide active material of the following general formula (I):Liw MxMnyOz (I) wherein M is a metal, and w, x, y and z are non-zero numbers, and an electrolyte which provides a conducting medium between the anode and the cathode. The electrochemical cell can be charged and discharged at high rates, while also providing a high energy density and low discharge. The electrochemical cell has particular applicability to mobile telephones, electrically powered vehicles, medical devices and security systems.

Description

ELECTROCHEMICAL CELL COMPRISING TUNGSTEN (IV) OXIDE/LivvMxMnyOz ELECTRODE STRUCTURE
BACKGROUND OF THE INVENTION
1. Field of the Invention The invention relates to an electrochemical cell. The invention has particular applicability to the manufacture of primary and rechargeable power sources, and has use in, for example, mobile telephones, electrically powered vehicles, medical devices and security systems.
2. Description of the Related Art Metal oxides have been extensively used as electrode active materials in electrochemical systems, for example, in batteries and capacitors. As can be seen from FIG. 1, which is a graph of energy density versus power density for conventional electrochemical batteries and capacitors, the capacitors can be charged and discharged at very high rates but possesses low energy densities and are capable of several thousand charge/discharge cycles, while the batteries provide high energy densities and low self discharge rates and low charge/discharge cycles. For many high rate applications such as mobile telephones, electrically powered vehicles, medical devices and security systems, it would be desirable for the electrochemical cell to provide high energy densities and to be capable of charging and discharging at high rates, as shown by the area enclosed by the dashed line.
Most of the commercially available lithium ion cells employ carbon as the anode active material. Recently, it has been shown that lithium ion cells with carbon anodes and metal oxide cathodes outperform most of the existing rechargeable cells. The metal oxides used in the lithium ion cells are special materials which accept guest atoms/ions into their structures. Commonly used cathode metal oxides include, for example, lithiated cobalt oxide (LiCoO2), lithiated nickel oxide (LiNiO2) and lithiated manganese oxide (LiMn2O4).
At ambient temperatures and at low charge/discharge rates, these lithium ion cells which employ carbon anodes perform very well. However, the performance characteristics of such cells deteriorates when charged or discharged at high rates and/or when operated or stored at elevated temperatures. For example, while carbon is capable of accepting lithium atoms into its crystal lattice and of performing well at ambient temperatures, the anode performance degrades at higher temperatures (e.g., greater than 45 °C) due to possible exfoliation caused by mechanical stress after repeated lithium intercalation and de-intercalation. In addition, at high charge rates during intercalation, lithium metal tends to deposit on the surface of the carbon electrode. Such metal deposition on the carbon surface creates safety concerns due to dendrite formation as well as causing premature cell failure. Furthermore, such litliium ion cells are extremely unsafe under abuse conditions such as overcharge, overdischarge, nail penetration and crush.
To overcome or conspicuously ameliorate the disadvantages of the related art, it is an object of the present invention to provide an electrochemical cell employing tungsten (IV) oxide and LiwMxMnyOz as the active materials in the anode and cathode, respectively. The electrochemical cell can be charged and discharged at high rates like an electrochemical capacitor, while also providing a high energy density and low self-discharge rates like a battery. In addition, the electrochemical cell is much safer than known lithium ion cells under abuse conditions such as overcharge, overdischarge, nail penetration and crush. The electrochemical cell has particular applicability in mobile telephones, electrically powered vehicles, medical devices and security systems. Other objects, advantages and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.
SUMMARY OF THE INVENTION According to a first aspect of the invention, a novel electrochemical cell is provided. The electrochemical cell comprises an anode comprising a tungsten (IV) oxide active material, a cathode comprising a metal oxide active material of the following general formula (I):
LiwMxMnyOz (I) wherein M is a metal, and w, x, y and z are non-zero numbers, and an electrolyte providing a conducting medium between said anode and said cathode. In formula (I), M can be, for example, a metal selected from the group consisting of Al, Ni and Co.
The active material of the cathode can be of the following general formula (V):
LiMxMn2.xO4 (T) wherein 0 < x < 2, and preferably, of the following formula:
LiAlo.i4Mnj.8gO4.
The electrolyte can be non-aqueous, for example, an electrolyte comprising LiPF6 in ethylene carbonate and diethylcarbonate or LiPF6 in methyl acetate and propylene carbonate.
In accordance with further aspects of the invention, a mobile telephone, an electrically powered vehicle, for example, a hybrid electric vehicle, a medical device, and a security system comprising the electrochemical cell can be provided. In accordance with yet a further aspect of the invention, provided is an electrochemical cell. The electrochemical cell comprises an anode comprising a tungsten (IV) oxide active material, a cathode comprising a metal oxide active material of the following general formula (I): LiwMxMnyOz (I) wherein M is a metal, and w, x, y and z are non-zero numbers, and an electrolyte providing a conducting medium between said anode and said cathode. The cell is capable of delivering greater than 4 W-h/kg at a discharge power density of 0.5 W-h/kg when charged only for 20 seconds, and 20 W-h/kg at a discharge power density of 0.5 W-h/kg when charged for 60 minutes.
BRIEF DESCRIPTION OF THE DRAWINGS The objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiments thereof in connection with the accompanying drawings, in which like numerals designate like elements, and in which:
FIG. 1 is a graph of energy density versus power density for various electrochemical capacitors and batteries, and for electrochemical cells in accordance with the invention;
FIG. 2 is an illustration of an exemplary electrochemical cell in accordance with the invention;
FIG. 3 is a graph of energy density versus power density for various charge rates, for a plastic encased electrochemical cell in accordance with the invention; FIG. 4 is a graph of energy density versus power density for various temperatures, for a plastic encased electrochemical cell in accordance with the invention;
FIG. 5 is a graph of discharge energy versus number of cycles for density versus power density for various temperatures, for a plastic encased electrochemical cell in accordance with the invention;
FIG. 6 is a graph of current and cell voltage versus time for a plastic encased electrochemical cell in accordance with the invention;
FIG. 7 is a graph of discharge energy density versus number of cycles for two plastic encased electrochemical cells in accordance with the invention;
FIG. 8 is a graph of discharge energy versus charge time for a plastic encased electrochemical cell in accordance with the invention; and
FIG. 9 is a graph of discharge energy versus number of cycles for a plastic encased electrochemical cell in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS OF THE INVENTION
With reference to FIG. 2, an exemplary electrochemical cell 200 in accordance with the invention will now be described. One or more anodes 202 and an equal number of cathodes 204 typically of the same thickness are formed on anode and cathode current collectors 206, 208. The anodes and cathodes are typically formed on opposite surfaces of the anode current collectors 206 and cathode current collectors 208, respectively. As shown, a separator 210 is placed for each of the anode-cathode pairs to prevent contact between the anodes 202 and cathodes 204 in the final structure. The anodes 202 and cathodes 204 are alternately stacked in an array as shown. The electrochemical cell 200 is placed into a container 212, such as a plastic bag, and the anode and cathode current collectors 206, 208 are each connected to a respective terminal or electrical feedthrough 214, 216 in the container. Electrolyte 218 is then added to the cell, and the cell is sealed.
Optionally, the electrolyte can be filled after pulling a vacuum on the interior of container 212.
The anodes 202 are formed from a tungsten (IV) oxide active material, and can be formed by known methods. For example, an electrode paste or slurry can be formed by mixing together a binder, a conductive material such as a conductive carbon material, a solvent and tungsten (IV) oxide powder. Typical binders include, for example, polyvinylidene fluoride (PVDF) and TEFLON powder. Suitable solvents include, for example, l-methyl-2-pyrrolidinone (NMP), dimethyl sulfoxide (DMSO), acetonitrile (AN), or dimethyl formate (DMF). The conductive carbon material can be, for example, acetylene black conductive carbon, graphite or other known materials. The paste or slurry can then be coated on a smooth, solid or mesh metal current collector surface. A desired thickness (e.g., from about 0.001 to 0.01 inch) is obtained by use of a suitable tool such as a doctor blade. The material is then dried, preferably under vacuum, at a temperature typically from about 130 to 170°C, preferably about 150°C, for a period of from about 6 to 15 hours.
The cathodes 204 are formed from a metal oxide active material of the following general formula (I):
LiwMxMnyO2 (I) wherein M is a metal, and w, x, y and z are non-zero numbers. Particularly suitable metals M include, for example, Al, Ni and Co. Preferably, the active material in the cathode is of the following general formula (I'): LiMxMn2.xO4 (T) wherein 0 < x < 2. A particularly preferred active material in the cathode is
LiAl0.14Mn1.86O4. Additional exemplary active cathode materials include, for example, LiNiO2, LiCoO2, etc.
The cathodes in accordance with the invention can be formed by known methods, for example, by the methods described in U.S. Patent No. 5,567,401, to Doddapaneni et al, the entire contents of which are incorporated herein by reference.
The anode and cathode current collectors 206, on which the anodes and cathodes are formed, are constructed of, for example, aluminum, copper or nickel. Of these, aluminum is preferred due to light weight and cost
The material of construction of the separators 210 can be, for example, polypropylene, polyethylene, and the like, with Celgard® 3501, commercially available from Hoechst Celanese, being an exemplary material.
Particularly preferred electrolytes include, for example, LiPF6 in ethylene carbonate (EC) and diethylcarbonate (DEC) or LiPF6 in methyl acetate (MA) and propylene carbonate (PC). Other known, non-aqueous electrolytes that are suitable for lithium cells can alternatively be employed.
In order to further illustrate the present invention and the advantages thereof, the following specific examples are given, it being understood that same are intended only as illustrative and in nowise limitative. The following examples demonstrate the significantly improved results which can be achieved through use of the electrochemical cells in accordance with the invention.
EXAMPLES
1. Preparation of WO2 Anodes Anodes having 85 wt% WO2, 8 wt% SUPER P Carbon conductive additive
(OBTAINED FROM sa. MMM nv of Brussels, Belgium) and 7 wt% PVDF binder were fabricated as follows. A binder solution was formed by dissolving 7g PVDF into lOOg of NMP solvent at 90 °C. 8g of the Super P Carbon material was added to the binder solution, and the mixture was blended thoroughly for at least 10 minutes in an ultrasonic mixer for 60 minutes. 85g of the WO2 was added to the mixture and was blended thoroughly for at least 10 minutes in the mixer.
Aluminum foils were cut to areas of 10 by 20 cm to form anode current collectors. The aluminum foils were smoothed out on a glass surface using isopropanol and a straight edge. A strip of aluminum foil was placed on one or both of the long edges of the aluminum foil to define the shape of the electrode. The anode slurry was placed on each aluminum foil such that it covered the designated area. Using a fixed blade, the anode slurry was pulled across the aluminum foil to produce a smooth surface. When completed, the structure was removed from the glass and placed on a tray to be baked.
The structures were placed in a fume hood to slowly remove some of the
NMP solvent. Trays of electrodes were next placed in a vacuum oven, which was pumped down to remove the remaining NMP solvent. The electrodes were baked at 150°C under vacuum overnight. The oven was allowed to cool down, and the electrodes were transferred to a dry room. 2. Preparation of LiAl0 ^Mnj z60^ Cathode
Cathodes having 80 wt% LiAlo.j4Mnj.86O4, 10 wt% XC-72R Carbon and 10 wt% PVDF binder were fabricated as follows. A binder solution was formed by dissolving lOg PVDF into 90g NMP solvent at 90°C. lOg of the carbon material was added to the binder solution, and the mixture was blended thoroughly for at least 10 minutes in an ultrasonic mixer for 60 minutes. 80g of the LiAl0.14Mnι 86O4 was added to the mixture and was blended thoroughly for at least 10 minutes in the mixer.
Aluminum foils were cut to areas of 10 by 20 cm to form cathode current collectors. The aluminum foils were smoothed out on a glass surface using isopropanol and a straight edge. A strip of aluminum foil was placed on one or both of the long edges of the aluminum foil to define the shape of the electrode. The anode slurry was placed on each aluminum foil such that it covered the designated area. Using a fixed blade, the cathode slurry was pulled across the aluminum foil to produce a smooth surface. When completed, the structure was removed from the glass and placed on a tray to be baked.
The structures were placed in a fume hood to slowly remove some of the NMP solvent. Trays of electrodes were next placed in a vacuum oven, which was pumped down to remove the remaining NMP solvent. The electrodes were baked at 150 °C under vacuum overnight. The oven was allowed to cool down, and the electrodes were transferred to a dry room.
3. Preparation of Electrochemical Cell
2.5 by 5 cm electrodes (12.5 cm2 geometric area) were cut and assembled with a single layer of CELGARD 3501 separator. Multi-plate cells having an electrode area of 12.5 cm2, 25 cm2 and 150 cm2 were fabricated. For example, a cell having 12 anodes and 12 cathodes of 2.5 by 5 cm electrodes and an active geometric area of 150 cm2 was fabricated. The multi-plate cells were then sealed in thermo-plastic bags (shield pack® Inc., of West Monroe, LA). From 0.5 to 1.5 ml of electrolyte containing 1.0 M LiPF6 in EC/DEC in a 1:2 volume basic ratio was then added to the bags which were then sealed.
4. Analysis of Cell Characteristics
The cells as prepared above were subjected to (a) constant current (cc), (b) constant voltage (cv), and (c) constant current followed by constant voltage (cccv) charging methods, and various performance characteristics of the cell were measured to understand the effects on discharge performance and cycle life performance using a Maccor battery tester.
(a) Constant Current Charge
Tests 1(a) and (b): Charge/Discharge Rate Effects The following tests were performed to understand the influence of charge/discharge rate on performance characteristics of the electrochemical cells.
Four electrochemical cells having a 12.5 cm2 electrode area as prepared above were charged at respective constant current rates of 1, 2, 5 and 10 mA/cm2 to 3.35 V, and then discharged at various rates to 1.65 V at 25 °C. The results from this test are shown in FIG. 3, which is a Ragone plot of energy density versus power density for the different charge/discharge rates. As can be seen, energy density is strongly influenced by the charge rate, particularly below discharge power densities of 1.0 kW/kg.
Electrochemical cells having a 12.5 cm2 electrode area as prepared above were charged at 3 mA/cm2 (0.35 kW/kg) to 3.35 V and then discharged at various rates to 1.65 V at 25 °C. These results are shown in FIG. 1. Test 2: Temperature Effects The following tests were performed to understand the influence of temperature on performance characteristics of the electrochemical cells. Four electrochemical cells having a 12.5 cm2 electrode area as prepared above were charged at 2 mA/cm2 to 3.45 V, and then discharged at various rates to 2.00 V at respective temperatures of -40, -30, -20 and 25 °C. The results from this test are shown in FIG. 4, which is a Ragone plot of energy density versus power density for the different charge/discharge temperatures. The poor performance at low temperatures is believed to be due to an increase in the resistance of the electrolyte.
Test 3 : Cycle Life Performance
To study the cycle life performance of the electrochemical cells, a cell having a 12.5 cm2 electrode area as prepared above was charged at 10 mA/cm2 to 3.35 V, and then discharged at 20 mA/cm2 to 1.65 V. The results of this test are shown in FIG. 5, which is a graph of discharge energy versus number of cycles. As can be seen, the cell performed well with a fade rate of about 0.2% per one thousand cycles after initial loss. The fade appears to be due to the increased internal cell resistance. The initial drop in performance is most likely due to the corrosion of current collectors and the slight dissolution of the binder.
(b) Constant Voltage Charge Test 4: Charge Acceptability
The current and voltage behavior of a cell under constant voltage charge and constant current discharge was tested to understand the charge acceptability of the anode. A cell having a 25 cm2 electrode area as prepared above was charged with a constant voltage at 3.45 V for 15 seconds, and then discharged at a rate of 40 mA/cm2 to 2.00 V. The results of this test are shown in FIG. 6, which is a graph of charge/discharge current and cell voltage versus time. Test 5: Cycle Life Performance The following test was conducted to further understand the cycle life of the electrochemical cells. Two cells (Cell-A and Cell-B) having a 25 cm2 electrode area as prepared above were repeatedly charged at a constant voltage of 3.45 V for 40 seconds, and then discharged at a rate of 40 mA/cm2 to 2.00 V, at ambient temperature. The cycle life performance of the cells is shown in FIG. 7. The difference in energy density between the two cells is believed to be due to the variation in active material loading in the electrodes. Each of the cells exhibited small cyclical variations in discharge energy density which correspond to the time of day and ambient temperature at such time. The data indicates that the cells can be charged at very high rates with little adverse effect on the cycle life performance.
(c) Constant Current and Constant Voltage Charge
Test 6: Energy Density as a Function of Time This test was conducted to study the effects of charge time on discharge energy. A cell having a 150 cm2 electrode area as prepared above was charged at room temperature at a rate of 4 mA/cm2 to 3.40 V, with the charge being maintained at a constant voltage of 3.40 V for various time periods before being discharged at 10 mA/cm2 to 2.00 V. The results of this test are shown in FIG. 8, which is a graph of discharge energy versus charge time. As shown in FIG. 8, the cell was charged approximately to 95% of its capacity within 45 minutes. In certain applications, very high charge currents generated under a constant voltage charge may not be desirable. In this test, therefore, the cells were charged under constant current to a fixed cell voltage followed by a constant voltage. Test 7: Cycle Life Performance A cell having a 150 cm2 electrode area as prepared above was charged at a rate of 30 mA/cm2 to 3.45 V, followed by holding the voltage constant at 3.45 V for 15 seconds, and then a constant current discharge to 2.00 V at a rate of 30 mA/cm2. This cycle was repeatedly performed at 15 °C. The results are illustrated in FIG. 9, which is a graph of discharge energy versus number of cycles. As shown, the discharge energy increased slightly from one to about 150 cycles, but remained essentially constant at about 5.7 Wh/kg thereafter. This initial increase in energy is believed to be due to the heat generation under high rate charge and discharge conditions.
Based on the results for the constant current, constant voltage and constant current followed by constant voltage charging methods, the electrochemical cells in accordance with the invention can be charged and discharged at very high rates like electrochemical capacitors. The charge mode appears to have little effect on the cycle life. At the same time, the cells provide high energy densities and low self- discharge, as obtained with batteries. For example, these cells can deliver 4 Wh/kg at a discharge power density of 0.5 kW/kg when charged only for 20 seconds, and 20 Wh/kg at a discharge power density of 0.5 kW/kg when charged for 60 minutes.
These characteristics make the electrochemical cells in accordance with the invention particularly suitable for example, as a battery in cellular or other forms of mobile telephones; in electrically powered vehicles such as a pure electric vehicle, a hybrid electric vehicle or a power assisted electric vehicle (e.g., automobiles, trucks, mopeds, motorcycles powered by an engine and a battery or by a fuel cell and a battery); in medical devices; in power tools; and in security systems such a personal computer or building security systems; in security cards or credit cards which use an internal power supply; and in backup power supplies and SLI (starting lighting ignition) batteries. In general, the invention is applicable to any type of device where a capacitor or battery are used.
These inventive cells can meet or exceed the desired targets established for hybrid electric vehicles with fast response engine set by the United States Advanced Battery Consortiums (US ABC) under Partnership for New Generation of Vehicles
(PNGV) program.
While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made, and equivalents employed, without departing from the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:
1. An electrochemical cell, comprising: an anode comprising a tungsten (IV) oxide active material; a cathode comprising a metal oxide active material of the following general formula (I):
LiwMxMnyOz (I) wherein M is a metal, and w, x, y and z are non-zero numbers; and an electrolyte providing a conducting medium between the anode and the cathode.
2. The electrochemical cell according to claim 1, wherein M is a metal selected from the group consisting of Al, Ni and Co.
3. The electrochemical cell according to claim 1, wherein the active material of the cathode is of the following general formula (I1):
LiMxMn2.xO4 (T) wherein 0 < x < 2.
4. The electrochemical cell according to claim 3, wherein M is a metal selected from the group consisting of Al, Ni and Co.
5. The electrochemical cell according to claim 3, wherein the active material of the cathode is of the following formula: LiAlo.i4Mnj.86O4.
6. The electrochemical cell according to claim 1, wherein the anode and the cathode further comprise a polymeric binder material.
7. The electrochemical cell according to claim 6, wherein the polymeric binder material is polyvinylidene fluoride or TEFLON powder.
8. The electrochemical cell according to claim 1, wherein the electrode composition further comprises a conductive additive material.
9. The electrochemical cell according to claim 1, wherein the cell comprises a plurality of the anodes and a plurality of the cathodes.
10. The electrochemical cell according to claim 1, further comprising a separator interposed between the anode and cathode.
11. The electrochemical cell according to claim 10, wherein the separator is formed from polypropylene or polyethylene.
12. The electrochemical cell according to claim 1, wherein the electrolyte is non-aqueous.
13. The electrochemical cell according to claim 12, wherein the electrolyte comprises LiPF6 in ethylene carbonate and diethylcarbonate or LiPF6 in methyl acetate and propylene carbonate.
14. A mobile telephone comprising the electrochemical cell according to claim 1.
15. An electrically powered vehicle comprising the electrochemical cell according to claim 1.
16. The electrically powered vehicle according to claim 15, wherein the electrically powered vehicle is a hybrid electric vehicle.
17. A medical device comprising the electrochemical cell according to claim 1.
18. A security system comprising the electrochemical cell according to claim 1.
19. An electrochemical cell, comprising: an anode comprising a tungsten (IV) oxide active material; a cathode comprising a metal oxide active material of the following general formula (I):
LiwMxMnyOz (I) wherein M is a metal, and w, x, y and z are non-zero numbers; and an electrolyte providing a conducting medium between the anode and the cathode, wherein the cell is capable of delivering greater than 4 W-h/kg at a discharge power density of 0.5 W-h/kg when charged for 20 seconds, and 20 W-h/kg at a discharge power density of 0.5 W-h/kg when charged for 60 minutes.
20. The electrochemical cell according to claim 19, wherein the active material of the cathode is of the following general formula (T): LiMxMn2.xO4 (T) wherein 0 < x < 2.
PCT/US2001/041480 2000-07-31 2001-07-31 Electrochemical cell comprising tungsten (iv) oxide/liwmxmnyoz electrode structure WO2002011218A1 (en)

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