WO2003088374A2

WO2003088374A2 - Asymmetric supercapacitor device with extended capability

Info

Publication number: WO2003088374A2
Application number: PCT/CA2003/000508
Authority: WO
Inventors: Jeffrey Philips; Donald Hewson
Original assignee: Powergenix Systems, Inc.
Priority date: 2002-04-08
Filing date: 2003-04-04
Publication date: 2003-10-23
Also published as: CA2380954A1; AU2003227150A1; WO2003088374A3; AU2003227150A8

Abstract

An energy storage device has a nickel-based positive electrode, a carbon-based negative electrode, a separator, and an aqueous electrolyte. The positive electrode comprises from 3% to 95% by weight of nickel hydroxide, with the balance being chosen from the group consisting of: nickel powder, cobalt powder, carbon powder, and mixtures thereof. The negative electrode comprises from 10% to 95% by weight of carbon, with the balance being at least one redox couple. The electrolyte is an aqueous alkaline solution, and the separator is chosen from the group consisting of: non-woven nylon separator material, microporous polypropylene, microporous polyethylene, and combinations and mixtures thereof. Typically, the redox couple is chosen from the group of active redox couples which include, as their active material, bismuth oxide, indium oxide, cobalt oxide, iron oxide, iron hydroxide, hydrides of metals from the Groups IIIA, IIIB, IVA, IVB, VB, VIB, VIIB, and VIII, of the Periodic Table, hydrides of mischmetals, oxides of mischmetals, and combinations thereof.

Description

SUPERCAPACITOR DEVICE WITH EXTENDED CAPABILITY

FIELD OF THE INVENTION:

[0001] This invention relates to energy storage devices, and particularly the present invention relates to such energy storage devices that provide high power with high voltage compliance, low impedance, small size, and enhanced discharge capability. Such energy storage devices are typically configured as a supercapacitor; and as such, supercapacitors provide peak power requirements of variable pulse loads, particularly when functioning otherwise in association with - typically in parallel with ~ a battery for an electronic device.

BACKGROUND OF THE INVENTION:

[0002] There is an ever increasing requirement for batteries and other energy storage devices to be used in conjunction with electrical devices of all sorts. Some such electrical devices may operate in such a manner that they have varying energy requirements for electrical energy to be delivered to them from time to time. Particularly, many electrical devices such as cellular telephones, personal digital assistants, laptop and portable computers, and the like, will function as a pulsed load on the battery which is providing energy to such electrical device, thus creating a demand for electrical energy storage devices that will satisfy the pulse load requirements of such electrical devices.

[0003] There is, therefore, a requirement for low impedance power sources that will not suffer undue voltage losses particularly during millisecond current pulses of the electrical device. For example, it is not unusual for the voltage response of a battery in a present day cellular telephone to cause the telephone to prematurely shut down during a "talk" pulse energy requirement, even though the battery still retains quite sufficient electrical energy otherwise to provide power to the cellular telephone. [0004] An approach that has been taken to provide a longer battery life under variable pulse loads is to separate the power component and the energy component of the power source, by the parallel addition of a low impedance supercapacitor. The additional supercapacitor will support the pulse load during high current pulses, and will be recharged during the "off or low current periods of operation of the electrical device.

[0005] Unfortunately, however, prior art supercapacitors are expensive, and they do not have a suitable charge storage capacity. Moreover, such prior art supercapacitors generally employ a non-aqueous electrolyte, resulting in low conductivity within the supercapacitor. This, in turn, necessitates employment of high surface area electrode components, thereby resulting in expensive construction. [0006] Still further, in stand-alone applications, a prior art supercapacitor may have insufficient charge content to provide adequate runtime for the electrical device with which the supercapacitor is associated. For example, if a supercapacitor were providing auxiliary power to a portable or laptop computer, it would be convenient to the user of the computer if the supercapacitor were to provide full operational capability for tlie computer while the main batteries for the computer were being exchanged. This, however, would require an excessively large 12 Volt supercapacitor, one having capacitance values in excess of 50 Farads.

[0007] Moreover, pulse load situations exist which would not benefit from the addition of the supercapacitor. Those situations include pulse loads which do not allow sufficient time for recharge of the supercapacitor, and thereby which continuously deplete the energy storage of the supercapacitor. This renders the use of a supercapacitor to be superfluous for high current management in many circumstances. [0008] Still further, mismatched impedances may result in a load sharing circumstance which would render use of the supercapacitor to be ineffective. [0009] Where pure carbon-carbon supercapacitors are employed, yet another particular problem arises, one which is associated with such pure carbon-carbon supercapacitors. That is, there is a requirement for strict and close maintenance of a voltage window for discharge circumstances for the supercapacitor, otherwise electrolyte decomposition may ensue. A normal precaution which ensures long operating lifetimes for such supercapacitors is to operate them with a reduced voltage range. Leakage currents will generally then be lower, with correspondingly less gas generation, but this is also underutilization of expensive supercapacitors. [0010] The purpose of the present invention is to provide for the construction and implementation of a small, low cost, high current carrying device which combines the features, characteristics, and advantages, of both rechargeable batteries and supercapacitors. As will be noted hereafter, energy storage devices in keeping with present invention will provide for voltage compliance which will be greater than 1 Volt. Moreover, the present invention provides for low impedance devices which can therefore be used in a number of applications that place high current requirements on the energy storage devices which provide electrical energy for the respective electrode devices.

[0011] Energy storage devices in keeping with present invention can be customized as to their design so as to maximize their lifetime and yet, at the same time, minimize their size.

[0012] The present inventors have quite unexpectedly discovered that these goals can be achieved in an energy storage device which employs a nickel-based positive electrode, a carbon-based negative electrode, and an aqueous electrolyte; where redox couples are associated with the negative electrode. DESCRIPTION OF THE PRIOR ART:

[0013] Stepanov et al United States patents 5,986,876 issued November 16,

1999 and 6,181 ,546 issued Jan. 31 , 2001 each teach double layer capacitors. The' 876 patents teaches a double layer capacitor where one of the electrodes is a fibrous carbonic material, and the other electrode is a nickel hydroxide positive electrode, together with an aqueous alkali-metal carbonate electrolyte. The fibrous carbonic material may be metallized by nickel or copper, in the range of 9% to 60% by weight of the electrode.

[0014] The' 546 patents teaches a double layer capacitor where one of the electrodes is polarizable, and the other of the electrodes is non-polarizable.

SUMMARY OF THE INVENTION:

[0015] In accordance with one aspect of the present invention, there is provided a energy storage device having a nickel-based positive electrode, a carbon-based negative electrode, a separator, and an aqueous electrolyte.

[0016] The positive electrode comprises from 3% to 95% by weight of nickel hydroxide, with the balance being chosen from the group consisting of: nickel powder, cobalt powder, carbon powder, and mixtures thereof.

[0017] The negative electrode comprises from 10% to 95% by weight of carbon, with the balance being at least one redox couple.

[0018] An electrolyte is employed which is an aqueous alkaline solution.

[0019] Typically, the separator is chosen from the group consisting of: non- woven nylon separator material, microporous polypropylene, microporous polyethylene, and combinations and mixtures thereof.

[0020] Also, typically, an energy storage device in accordance with the present invention will be configured as a supercapacitor. [0021] In keeping with the provisions of the present invention, the positive electrode is a thin film electrode chosen from the group consisting of: a vacuum deposited layer of positive electrode formulation material on a conductive substrate, a pasted positive electrode formulation in a conductive nickel foam substrate, an electro- precipitated or chemically precipitated positive electrode formulation in a thin substrate of a conductive sintered nickel matrix, and combinations thereof. [0022] Also, the negative electrode is a thin film electrode comprising a conductive substrate chosen from the group consisting of: porous nickel foam, porous copper foam, porous silver foam, and mixtures and combinations thereof, together with said negative electrode formulation being loaded thereinto.

[0023] In general, the negative electrode formulation comprises powdered carbon in the range of 10% to 95% by weight, together with at least one metal-based redox couple.

[0024] Typically, the at least one redox couple is chosen from the group of active redox couples which include, as their active material, bismuth oxide, indium oxide, cobalt oxide, iron oxide, iron hydroxide, hydrides of metals from the Groups IIIA, IIIB, IV A, IVB, VB, VIB, VIIB, and VIII, of the Periodic Table, hydrides of mischmetals, oxides of mischmetals, and combinations thereof. [0025] The present invention provides that an energy storage device in keeping with present invention may have a group of redox couples that is chosen so as to have overlapping oxidation voltages, and thereby so as to extend the range of discharge voltage of the energy storage device during a discharge operation. [0026] In the formulation and construction of a negative electrode in keeping with the present invention, the basis weight of the conductive substrate is in the range of200 g/m² to 500 g/m². [0027] Either electrode in keeping with the present invention may have a thiclcness of the thin film electrode which is in the range of 0.0762mm to 0.3048mm( 0.003 inch to 0.012 inch).

[0028] Still further, the formulation of the positive electrode may further comprise at least one of silver (I) oxide, silver (II) oxide, and mixtures thereof. [0029] Also, the charge and discharge voltage ranges of the positive electrode may be extended by the addition of selected amounts of cobalt oxide to various portions of the positive electrode formulation.

[0030] Another aspect of the present invention is the provision of hybrid batteries which will comprise an energy storage device in keeping with the present invention, in parallel with a high energy capacity battery, which may be a nickel zinc battery or a lithium ion battery.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0031] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example. It is expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. Embodiments of this invention will now be described by way of example in association with the accompanying drawings in which: [0032] Figure 1 shows the charge behavior of a fully discharged energy storage device manufactured in keeping with present invention;

[0033] Figure 2 illustrates the manner in which an energy storage device in keeping with present invention extends the run time of a high energy battery by damping the voltage response thereof to a cut off voltage; and [0034] Figure 3 demonstrates the extended pulse capability of an energy storage device in keeping with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0035] The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.

[0036] As noted above, the purpose of the present invention is to provide a carbon-based energy storage device that permits for high current delivery, which allows wider voltage compliance and other aqueous based supercapacitors, and which provides for extended discharge times of the device and any high energy battery with which the energy storage device of the present invention is connected in parallel. All of this is achieved, as will be discussed hereafter, by the employment of electrochemical redox couples at the negative electrode.

[0037] Accordingly, energy storage devices in keeping with present invention may function alone, or in conjunction with high energy batteries — particularly, such high energy batteries which are incapable of supporting high current drains either as a consequence of safety concerns or as a consequence of their own high impedance. The present invention contemplates that energy storage devices in keeping herewith may be used directly in parallel with a high energy battery, more often they will be used in a circuit with a high energy battery together with a DC/DC converter and a switch arrangement which will ensure more controlled and complete charging of the energy storage device in keeping with present invention from the high energy battery and/or from an external power source.

[0038] A preferred configuration for an energy storage device in keeping with present invention, so as to provide for low impedance and high current capability, is achieved by the provision of highly conductive positive and negative electrodes which are also designed to have maximum electrolyte accessibility. A typical electrolyte which may be employed with energy storage devices in keeping with present invention, and which will promote a good electrolyte conductivity, is 30% potassium hydroxide solution.

[0039] Each of the positive and negative electrodes is a thin film electrode, and each is designed to provide for a high cycle life with high energy density and high conductivity.

[0040] Typically, a positive electrode for an energy storage device in keeping with present invention is nickel-based, comprising nickel hydroxide as the active component. Various forms for positive electrodes in keeping with present invention are contemplated, including a thin film of positive electrode formulation which may be vacuum deposited onto a suitable conductive metal substrate, a thin pasted layer within a three-dimensional nickel foam, or an electro-precipitated or chemically precipitated positive electrode formulation in a thin sintered nickel matrix.

[0041] Indeed, the formulation of the positive electrode in keeping with the present invention may comprise from 3% up to 95% of nickel hydroxide, with the balance of the active material of the positive electrode formulation being nickel powder, cobalt powder, carbon powder, and mixtures thereof. Typically, the addition of carbon powder, nickel powder, and cobalt powder, to the positive electrode formulation is in excess of 10% by weight of the positive electrode, so as to provide additional conductivity and capacitive charge for the positive electrode.

[0042] Likewise, a typical negative electrode in keeping with present invention is a thin layer of highly conductive carbon which is embedded in a nickel foam, or silver foam substrate. The metallic foam substrate, of course, provides particularly for electron conductivity within the negative electrode. [0043] However, in keeping with present invention, the formulation for the negative electrode may comprise from 10% up to 95% of carbon, with the balance being at least one redox couple.

[0044] The employment of redox couples in the negative electrode will extend the discharge capability thereof beyond that which is normally associated with the capacitance and the pseudo-capacitance which is associated with carbon per se. A typical redox couple which may be employed in keeping with the present invention may include bismuth/bismuth oxide, iron (II) hydroxide/iron (III) hydroxide, indium oxide, cobalt oxide, metal hydrides, other metal/metal oxide materials, and oxides and hydroxides of mischmetals.

[0045] It is been discovered that the following are particularly useful for the at least one redox couple when it is chosen from the group of active redox couples which include, as their active material, bismuth oxide, indium oxide, cobalt oxide, iron oxide, iron hydroxide, hydrides of metals from the Groups IIIA, IIIB, IVA, IVB, VB, VIB, VIIB, and VIII, of the Periodic Table, hydrides of mischmetals, oxides of mischmetals, and combinations thereof.

[0046] The ratio of the carbon to redox couple can be varied, and will typically be in the range of 95: 5 to 10: 90, as to the carbon:redox couple ratio. The chosen ratio will be dependent on the size requirement for the energy storage device, as well as the required duty cycle lifetime for the energy storage device.

[0047] Moreover, the chemical energy component of the negative electrode may support the current requirements placed on the negative electrode in a number of different ways. For example, the chemical energy component may independently support the load current; or for an intermittent or pulsed load, it may provide both load support and recharge of the double layer capacity of the negative electrode. However, because the stored chemical energy component is energy dense, a much smaller device than prior art supercapacitors is achieved. [0048] It should be noted that typical separator materials that may be employed in the construction of energy storage devices in keeping with present invention, to electrically isolate the negative and positive electrodes, may include microporous polypropylene and microporous polyethylene. However, typically conventional non- woven nylon separator materials are preferred, so as to enhance any oxygen recombination which may occur within the energy storage device. [0049] Several examples now follow which illustrate various embodiments and utilizations of energy storage devices in keeping with the present invention. Each of the examples is described below, and each has resulted in specific test results that are illustrated in the accompanying Figures.

Example 1 :

[0050] A 4 Volt test unit was assembled using four cells which were connected in series. Each cell contained a high porosity nickel foam, which was such as to have a basis weight of less then 500 gm/m². This conductive substrate was employed for both the positive and negative electrodes. The foam was pre-compressed to a thiclcness of 0.015 inch, and was loaded with active material for each of the respective positive and negative electrodes before being compressed to a final thickness of 0.011 inch. Each cell comprised one positive electrode and two negative electrodes; and the size of the electrodes was approximately 3.048cm by 2.286cm (1.2 inches by 0.9 inches). [0051] Each of the negative electrodes of each of the cells was loaded with 0.32 g of a mixture of carbon (58%), bismuth oxide (40%), and PTFE binder (2%). [0052] Each of the positive electrodes of each of the cells was loaded with a mixture of nickel hydroxide (82%), cobalt oxide (3%), zinc oxide (3%), and a mixture of nickel and cobalt powders (10%). The remaining 2% of the formulation comprised PTFE emulsion binder. [0053] Each of the individual cells was given a forming charge over 14 hours at 6 mA, the 4 Volt unit was assembled, and was then tested. The testing comprised fully discharging the 4 Volt unit, and then charging it at 312 mA for approximately six minutes before allowing for a rest period, followed by a 312 mA discharge. The result of the test is shown in Figure 1 at curve 12.

[0054] It was noted that initially the voltage rose quickly, which is attributed to the double layer capacity of the unit. According to the following equation, that double layer capacity is calculated as 27 Farads.

Q = CV (Equation 1)

Where Q is the coulombs passed; Where C is the capacitance in Farads; and Where V is the voltage in Volts

[0055] After the initial sharp rise in voltage, is noted that the voltage profile flattens out as the bismuth oxide is transformed to bismuth. During the discharge period, both the bismuth and the double layer capacitance are discharged.

Example 2:

[0056] Then, the device as described above was placed in parallel with a 1 Ah lithium ion battery. The lithium ion battery, and the combination of the lithium ion battery, were each subjected to a 1.2 mS discharge pulse of 750 mA every 5.2 mS. [0057] Two curves are shown in Figure 2, the first being identified by the numeral 20, and the second being identified by the numeral 30. The first curve 20 shows the terminal voltage of the lithium ion battery itself, to a cut off voltage of 3.6 Volts. It will be seen that the cut off voltage was reached at about 4:20 hours. The second curve 30 shows the terminal voltage of the parallel combination of the 4 Volt unit of the present invention together with the lithium ion battery; and it will be seen that the cut off voltage was reached at about 5:55 hours. Approximately 95 minutes was added to the discharge life of the combination 4 Volt unit/lithium ion battery over the discharge life of the lithium ion batteiy per se. In other words, the discharge life was extended by 95/355 min., or approximately 26.7%.

Example 3 :

[0058] In order to achieve uniform current density in the negative electrode, it is advantageous to use a highly conductive powdered carbon having a high surface area.

Two commercially available products which satisfied that criterion are Black Pearls

2000™ and Conductex 975™.

[0059] Moreover, metallic oxide additions to the carbon are favored as redox couples because of their conversion to conductive metal during formation of the negative electrode. However, as noted above, the proportion of carbon to redox couple may be dictated in keeping with the specific application to which the energy storage device of the present invention is to be applied.

[0060] In the present example, a small prismatic cell was constructed, and then assembled into a 6 Volt battery which had dimensions of 12.3698cm by 5.08cm by

5.715cm( 4.87 inches by 2.0 inches by 2.25 inches). The 6 Volt battery weighed 800 g; and had a capacitance of 20 Farads. This capacitance was primarily associated with the surface area of the carbon (250 m²/gm).

[0061] A bismuth oxide/bismuth (Bi₂O₃)/Bi redox couple added more than 1

Ampere hour of stored energy to the battery. The device was then subjected to a series of 50 Ampere current pulses, each of which lasted for 0.1 seconds. Figure 3 illustrates the results of that test; and it will be noted that there was minimal fade in the terminal voltage.

[0062] However, it should be noted that the theoretical calculation of the capacitance of the carbon in the battery suggests that it should not have been able to support more than four pulses before reaching a cut off voltage of 4.6 Volts [0063] In many cases, it may be beneficial simply to add a single redox couple to the negative electrode, so as to provide voltage stability above a specific cut off voltage. However, there are some occasions when multiple redox couples will provide certain advantages. For example, if the energy storage device of the present invention is to be charged by the continuously fading voltage of a directly connected parallel high energy battery, it may be advantageous to provide several redox couples in order that the energy storage device of the present invention may be charged over a wider range. It will be understood that, typically, such a configuration is that of a supercapacitor being connected in parallel with a high energy battery.

[0064] Moreover, it should also be noted that various portions of the nickel hydroxide active material of the positive electrode may be doped with varying amounts of cobalt oxide so as to vary the charge/discharge voltages over a range of values. Similarly, silver (I) oxide or silver (II) oxide may be employed by being admixed to the active material of the positive electrode. Such techniques as are discussed immediately above will obviate the necessity for DC/DC conversion which is otherwise aimed at boosting the charging voltages sufficiently high so as to provide for effective charging. [0065] Finally, it should be noted that energy storage devices in keeping with the present invention, particularly when configured as supercapacitors, may function not only as a high current partner to lithium ion batteries, but also as a voltage limiting device which is capable of shunting overcharge current around the lithium ion battery. In such a configuration, the nickel electrode is appropriately sized to approach the full charge before the redox couple in the negative electrode.

[0066] Thus, with the appropriate choice of a negative redox couple, and then appropriate selection of the number of unit cells in the energy storage device, the oxygen recombination cycle for the negative redox couple can be used as a voltage limiter for the system. [0067] There has been described an energy storage device which advantageously may be configured as a high power battery, or more particularly as a supercapacitor. The effectiveness of the energy storage device in keeping with the present invention arises as a consequence particularly of the employment of oxide redox couples, particularly metal-based oxide redox couples, on the negative electrode. The methods of construction of energy storage devices in keeping with the present invention are simple and economic; the other components of the energy storage devices, particularly the alkaline electrolyte and the separator are well Icnown to those skilled in the art. Thus, energy storage devices in keeping with the present invention may be provided in an economic manner and in large quantities of varying configurations, sizes, capacities, and current capabilities.

Claims

WHAT IS CLAIMED IS:

1. An energy storage device having a nickel-based positive electrode, a carbon-based negative electrode, a separator, and an aqueous electrolyte; said energy storage device by c h a r a c t e r i z e d in that said positive electrode comprises from 3% to 95% by weight of nickel hydroxide, with the balance being chosen from the group consisting of: nickel powder, cobalt powder, carbon powder, and mixtures thereof; wherein said negative electrode comprises from 10% to 95% by weight of carbon, with the balance being at least one redox couple; wherein said electrolyte is an aqueous alkaline solution; and wherein said separator is chosen from the group consisting of: non- woven nylon separator material, microporous polypropylene, microporous polyethylene, and combinations and mixtures thereof.

2 The energy storage device of claim 1 , configured as a supercapacitor.

3 The energy storage device of claim 2, wherein said positive electrode is a thin film electrode chosen from the group consisting of: a vacuum deposited layer of positive electrode formulation material on a conductive substrate, a pasted positive electrode formulation in a conductive nickel foam substrate, an electro-precipitated positive electrode formulation in a thin substrate of a conductive sintered nickel matrix, a chemically precipitated positive electrode formulation in a thin substrate of a conductive sintered nickel matrix and combinations thereof.

4 The energy storage device of claim 2, wherein said negative electrode is a thin film electrode comprising a conductive substrate chosen from the group consisting of: porous nickel foam, porous copper foam, porous silver foam, and mixtures and combinations thereof, together with said negative electrode formulation being loaded thereinto.

5 The energy storage device of claim 4, wherein said negative electrode formulation comprises powdered carbon in the range of 10% to 95% by weight together with at least one metal-based redox couple.

6 The energy storage device of claim 5, wherein said at least one redox couple is chosen from the group of active redox couples which include, as their active material, bismuth oxide, indium oxide, cobalt oxide, iron oxide, iron hydroxide, hydrides of metals from the Groups IIIA, IIIB, IV A, IVB, VB, VIB, VIIB, and VIII, of the Periodic Table, hydrides of mischmetals, oxides of mischmetals, and combinations thereof.

7 The energy storage device of claim 6, where a group of redox couples is chosen having overlapping oxidation voltages so as to extend the range of discharge voltage of said energy storage device during a discharge operation.

8 The energy storage device of claim 4, wherein the basis weight of said conductive substrate is in the range of 200 g/m² to 500 g/m².

9 The energy storage device of claim 3, where the thickness of said thin film electrode is in the range of 0.003 inch to 0.012 inch.

10 The energy storage device of claim 4, where the thiclcness of said thin film electrode is in the range of 0.003 inch to 0.012 inch. 11 The energy storage device of claim 3 , wherein the formulation of said positive electrode further comprises at least one of silver (I) oxide, silver (II) oxide, and mixtures thereof.

12 The energy storage device of claim 3 , wherein the charge and discharge voltage ranges of said positive electrode are extended by the addition of selected amounts of cobalt oxide to various portions of said positive electrode formulation.

13 A hybrid of the battery comprising an energy storage device of claim 1 in parallel with a high energy capacity nickel zinc battery.

14 A hybrid of the battery comprising an energy storage device of claim 1 in parallel with a high energy capacity lithium ion battery