WO2003088381A2

WO2003088381A2 - High rate, thin film, bipolar, nickel zinc battery having oxygen recombination facility

Info

Publication number: WO2003088381A2
Application number: PCT/CA2003/000514
Authority: WO
Inventors: Jeffrey Phillips
Original assignee: Powergenix Systems, Inc.
Priority date: 2002-04-08
Filing date: 2003-04-04
Publication date: 2003-10-23
Also published as: AU2003218568A8; CA2380952A1; WO2003088381A3; AU2003218568A1

Abstract

A high rate, alkaline nickel zinc cell (12) is structured as a bipolar cell having a current collector (22), with a positive nickel hydroxide electrode (14) on one side and a zinc negative electrode (46) on the other side. The current collector comprises a sheet copper substrate in contact with the negative electrode. A sheet nickel substrate (24) is laminated to the copper current collector, and is in contact with the positive electrode. The nickel hydroxide positive electrode is applied in a thin film to the respective face of the sheet nickel substrate. The zinc negative electrode comprises copper foam which is secured to the copper current collector at its edges, and is pasted. The copper foam is pressed so as to form a plurality of pockets (50) which face the copper current collector when assembled. Thus, access is provided to the negative electrode for oxygen generated at the positive electrode during overcharge conditions.

Description

HIGH RATE, THIN FILM, BIPOLAR, NICKEL ZINC BATTERY HAVING OXYGEN RECOMBINATION FACILITY

FIELD OF THE INVENTION:

[0001] This invention relates to high rate batteries, and particularly relates to high rate, thin film, bipolar, nickel zinc batteries, and the cells from which such a battery is constituted.

BACKGROUND OF THE INVENTION:

[0002] The present inventor is also the inventor in several commonly assigned

PCT applications relating to rechargeable zinc electrodes and cells containing the same, which cells may contain among them nickel zinc cells. For example, the following applications are referenced;

PCT Application CA01/01715 (Priority Canadian Application No. 2,325,791 filed 10 November 2000 (10-11-00) entitled Negative Electrode Formulation for a Low Toxicity Zinc Electrode Having Additives with Redox Potentials Positive to Zinc Potential; PCT Application CA01/01581 (Priority Canadian Application No. 2,325,308 filed 10 November 2000 (10-11-00) entitled Negative Electrode Formulation for a Low Toxicity Zinc Electrode Having Additives with Redox Potentials Negative to Zinc Potential; PCT Application CA01/01717 (Priority Canadian Application No. 2,325,640 filed 10 November 2000 (10-11-00) entitled Positive and Negative Interactive Formulation for a Zinc-containing Cell Having an Alkaline Electrolyte; and PCT Application CA01/01719 (Priority Canadian Application No. 2,325,637 filed 10 November 2000 (10-11-00) entitled Formulation of Zinc Negative Electrode for Rechargeable Cells Having an Alkaline Electrolyte

[0003] Also, the present inventor is the inventor in a commonly owned patent application entitled Hybrid Battery Configuration, filed of even date herewith, Serial Number 2,380,900.

[0004] Cells, and particularly batteries, in keeping with the present invention are typically employed as high rate, high power batteries in hybrid batteiy configurations such as those referred to in the above noted co-pending application. As stated therein, the purpose for the provision of high rate, high power batteries for use in hybrid battery configurations is to augment high energy batteries, which may have slow power delivery rates, and thereby to provide high current pulses when needed. Other purposes, such as when the hybrid battery is being used in a traction device such as a motor vehicle, include ensuring that adequate acceleration and hill climbing capability are provided for the vehicle, where short duration but high power demands may be placed on the hybrid battery.

[0005] The present invention provides a stable and high rate configuration for a nickel zinc battery that serves the purposes of a high rate battery as described above. In order to meet that goal, it is necessary for a high rate battery to have the characteristic of extremely low impedance. Such low impedance may be achieved in several ways; however, the present invention is particularly directed to low impedance, high rate batteries that have a bipolar configuration and which use extremely thin films of nickel hydroxide as the positive active material.

[0006] Of course, it must be noted that nickel hydroxide has very poor electrical conduction characteristics; and in keeping with a provision of the present invention, a nickel positive substrate is provided. Those details are discussed in greater detail hereafter.

[0007] Moreover, in order to provide a stable system using nickel zinc chemistry with an alkaline electrolyte, it is important that the electrolyte be highly conductive, and that it will be such as to confer stability upon the zinc electrode. [0008] By providing a thin film, bipolar structure, the present invention combines the current carrying capability of a double layer capacitor with the additional capacity of a thin film nickle electrode. Indeed, thin film nickel zinc batteries in keeping with the present invention are capable of energy densities which are greater than 60 Watt Hours per kilogram, and have a power density greater than 1,000 Watts per kilogram.

[0009] Thus, by providing such a low impedance device, effectively a high rate battery or, in some respects, a low impedance capacitor, in parallel with a high energy battery, it is possible to maximize the energy density of the battery independently of the power output.

[0010] High rate, thin film, bipolar nickel zinc batteries in keeping with the present invention also have another major application, which relates to power conditioning. A small size, high energy unit can provide on-site backup in the event of short duration AC power interruption. Since the most expensive component of such a system is the battery, the provision of a thin film configuration battery permits optimisation of power delivery for minimal cost.

SUMMARY OF THE INVENTION:

[0011] In accordance with one aspect of the present invention, there is provided a high rate nickel zinc cell, which has a nickel hydroxide positive electrode, a nickel zinc negative electrode, an alkaline electrolyte, and a microporous separator. [0012] The cell is structured as a bipolar cell having a current collector with the positive electrode at one side thereof and the negative electrode at the other side thereof. The electrolyte contacts at least one of the positive electrode and the negative electrode, and is contained by the separator.

[0013] The current collector comprises a sheet copper substrate which is in contact with the zinc negative electrode.

[0014] Also, a sheet nickel substrate is laminated to the copper current collector, and is in contact with the nickel hydroxide positive electrode.

[0015] In this invention, the zinc negative electrode comprises copper foam which is secured to the copper current collector at the edges thereof, and which is pasted with a paste mixture consisting primarily of zinc oxide.

[0016] The copper foam is pressed so as to form a pluarlity of pockets which face the copper current collector when assembled thereto.

[0017] Thus, access to the negative electrode for oxygen which is generated at the positive electrode during overcharge conditions, is provided.

[0018] Typically, after the copper foam has been pasted with the paste mixture, and the paste mixture has dried, the negative electrode is than sprayed with an emulsion of polytetrafluoroethylene.

[0019] Typically, the alkaline electrolyte is such that it will restrict the solubility of the zinc of the zinc negative electrode.

[0020] In order to provide a higher surface area, typically the side of the nickel substrate which is in contact with the nickel hydroxide positive electrode material has been treated accordingly.

[0021] That treatment may be such as etching, and embossing, scoring, grinding, particle blasting, rolling, coining, pebbling, and combinations thereof.

[0022] In keeping with the particular provision of the present invention, the thin film of nickel hydroxide positive electrode material may be applied to the respective surface of the nickel substrate by a method which is chosen from the group consisting of chemical vapour deposition, plasma deposition, ion implantation, electrostatic powder spray application techniques, and combinations thereof.

[0023] The present invention provides that the ampere hour capacity of the zinc negative electrode is at least twice the ampere hour capacity of the nickel hydroxide positive electrode.

[0024] Indeed, typically the ampere hour capacity of the zinc negative electrode is three to five times higher than that of the nickel hydroxide positive electrode.

[0025] Another particular aspect of the present invention is to provide a high rate nickel zinc battery which comprises an assembly of at least two high rate nickel zinc cells which are otherwise in keeping with the present invention.

[0026] That assembly comprises a series arranged assembly of at least two cells, with a microporous separator being placed between each cell configuration thereof.

[0027] Each of the respective cells is contained in a housing, and the respective housings for each of the cells are assembled together so as to provide a leak proof containment for the electrolyte on each side of the microporous separator.

[0028] The present invention provides that batteries in keeping herewith may be assembled in a fully charged state.

[0029] Alternatively, batteries in keeping with the present invention may be assembled in a discharged state.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0030] 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: [0031 ] Figure 1 is a plan view of a high rate nickel zinc battery comprising two high rate nickel zinc cells, in keeping with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0032] 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.

[0033] It will first be noted that a bipolar, thin film configuration of a cell - or a battery, being an assembly of a plurality of cells - achieves high power output by using, in this case, a highly conducting copper substrate as the current collector in the zinc electrode. Of course, the use of thin film technology in the nickel electrode is also employed.

[0034] As will be noted hereafter, a bipolar cell is one which is constructed on a centrally located current collector, and a bipolar battery is a series assembly of a plurality of similar cells.

[0035] Here, the copper current collector in the zinc negative electrode is laminated to a nickel positive substrate, which is a planar nickel sheet. The nickel hydroxide active material is applied to the nickel sheet in a thin film, as described hereafter.

[0036] It should be noted that, in order for the cell or battery in keeping with the present invention to obtain an extended life time, it is important that an electrolyte be employed which restricts the solubility of the zinc electrode. A typical electrolyte, although not the only such electrolyte, is the alkaline electrolyte which is taught in Eisenberg United States Patent 5,215,836, issued June 1, 1993. That electrolyte comprises a solution of a salt formed by the reaction of boric acid, phosphoric acid, or arsenic acid, with an alkaline or earth alkaline hydroxide which is present in a sufficient amount so as to produce a stoichiometric excess of hydroxide to acid in the range of 2.5 to 11.0 equivalents per litre. Also, a soluble alkaline or earth alkaline fluoride is provided, in an amount corresponding to a concentration range of 0.01 to 1.0 equivalents per litre of total solution.

[0037] In any event, an assembly of a bipolar battery in keeping with the present invention provides for the series assembly of a plurality of similar cells, the number of cells being dependent upon the voltage for the battery which is required. Such an assembly employs the use of a containment cage as a separator; and the assembly is also such that any solution leakage paths are precluded so as to not to create electrical short circuits.

[0038] In order for the cell or battery of the present invention to provide a high cycle life at high discharge rates, there is an excess of zinc ampere hour capacity in the negative electrode, with respect to the ampere hour capacity of the nickel hydroxide positive electrode material. Typically, such excess in zinc electrode capacity is in the range of three times that of the nickel hydroxide ampere hour capacity. [0039] Turning now to Figure 1, a typical battery 10 is shown, comprised of two identical bipolar cells 12. Each of those cells comprises a nickel hydroxide positive electrode 14 and a zinc negative electrode 46. Voids 18 are shown, where an alkaline electrolyte, will be located. Also, a microporous separator 20 will be employed; in the event of a single cell, the microporous separator may wrap the cell so as also to occupy locations as indicated at 21.

[0040] As seen in Figure 1 , each cell 12 is structured as a bipolar cell, and has a current collector with the positive electrode 14 at one side thereof, and the negative electrode 46 at the other side thereof. [0041 ] In this case, the current collector comprises a sheet copper substrate 22, which is in contact with the zinc negative electrode 46.

[0042] Also, there is laminated to the copper current collector 22 a sheet nickel substrate 24. Thus, the copper current collector forms part of the negative electrode, and the sheet nickel substrate 24 forms part of the positive electrode of the cell.

[0043] The nickel hydroxide positive electrode material 14 is applied to the face of the sheet nickel substrate 24, which is remote from the copper current collector 22, in a thin film.

[0044] Typically, the face of the nickel substrate 24 which is in contact with the nickel hydroxide active material has been surface treated so as to provide a high surface area.

[0045] The surface treatment to which the surface of the nickel substrate has been exposed may be such as etching or embossing, it could have been scored or ground, particle blasted such as by sand blasting, or it may have been rolled, coined, or pebbled, or any combination of the above.

[0046] Also, it should be noted that the application of the thin film of nickel hydroxide positive electrode material to the respective surface to the nickel substrate

24 may be such as by any of the methods from the group which consist of chemical vapour deposition, plasma deposition, ion implantation, electrostatic powder spray application techniques, and combinations thereof.

[0047] As previously stated, in order for the cell or battery in keeping with the present invention to provide high cycle life at high discharge rates, there must be an excess of zinc capacity at the negative electrode, compared to the ampere hour capacity of the thin film of nickel hydroxide active material on the positive electrode. Typically, that excess is at least twice the ampere hour capacity of the nickel hydroxide positive electrode material, and more usually the excess capacity is in the range of three to five times the ampere hour capacity of nickel hydroxide positive electrode material. [0048] As seen in Figure 1 , a battery may be assembled from at least two, and usually a plurality, of cells 12. Of course, each cell is contained in a housing having header and footer assemblies 30, 32. Those assemblies are typically formed of a suitable polymer material, as is well known in the art.

[0049] The series assembly of a plurality of cells into a battery is such that a leak proof containment for the electrolyte on each side of the microporous separator 20 is provided. Thus, O-rings may be placed in grooves 36 and 38 for that purpose. By such assembly, the risk of solution leakage paths that would create electrical short circuits between adjacent cells, is precluded.

[0050] As noted, the assembly is such that the microporous separator 20 is interposed between contiguous pairs of cells.

[0051 ] In keeping with a particular provision of the present invention, batteries may be assembled in a fully charged state; or they may be assembled in a fully discharged state.

[0052] The provision of high rate, thin film, bipolar nickel zinc cells in keeping with the present invention, and assemblies of batteries comprising a plurality of such cells, provides a compact, relatively low mass, high power density, high rate battery which is very suitable for the purposes intended. As noted, such batteries may have energy densities in the range of 60 watts hours per kilogram, or more; and they may have power densities in the range of 1,000 watts per kilogram, or more.

[0053] It is sometimes desirable, particularly in high rate cells and batteries, and particularly in such high rate cells and batteries that may be subject to overcharge conditions, to provide an oxygen recombination facility on the negative electrode.

[0054] Accordingly, the present invention provides a negative substrate that allows backside recombination of oxygen - that is, at the side of the negative electrode which is adjacent to the copper current collector. [0055] Thus, the negative zinc electrode 46 is comprised of a copper foam material. That material is typically compressed at its edges to form a solid sheet, as shown at 48 ; and that area is spot welded or seam welded to the copper current collector 22 so as to form a good electrical contact.

[0056] It will also be noted that there are a plurality of pockets or channels 50

- a channel being an elongated pocket, for purposes of the present discussion - which are formed vertically in the foam copper substrate material for the zinc electrode. Those pockets 50 will provide access for oxygen which is generated at the positive electrode 14, during overcharge conditions.

[0057] The manufacture of the zinc negative electrode 46 comprises pasting the copper foam with a zinc oxide mix which is primarily zinc oxide. Additional materials such as those disclosed in the above identified PCT application PCT/C A01/01719, may also be employed.

[0058] Typically, after the pasted foam from the zinc oxide mixture has dried, the rear side of the copper foam substrate for the zinc negative electrode is scraped with such as a wire brush, to reveal the channels or pockets 50. Then, the electrode 46 is sprayed with an emulsion of polytetrafluoroethylene which creates a three phase boundary, while leaving some pockets or channels area open for gaseous oxygen to accumulate in. The use of the PTFE emulsion is effective in promoting oxygen recombination at the zinc negative electrode.

[0059] Moreover, the fact that the channels or pockets 50 have been coated with

PTFE effectively precludes wetting by the aqueous electrolyte, and thereby precludes any substantial collection of electrolyte drops, or collection of electrolyte into the channels or pockets 50.

Claims

WHAT IS CLAIMED IS:

1. A high rate, nickel zinc cell (12) having a nickel hydroxide positive electrode (14), a zinc negative electrode (46), an alkaline electrolyte, and a microporous separator (20); wherein said cell is structured as a bipolar cell having a current collector (22), with said positive electrode at one side thereof and said negative electrode at the other side thereof, and where said electrolyte contacts at least one of said positive electrode and said negative electrode and is contained by said separator; said cell being c h a r a c t e r i z e d in that said current collector comprises a sheet copper substrate in contact with said zinc negative electrode; wherein a sheet nickel substrate (24) is laminated to said copper current collector, in contact with said nickel hydroxide positive electrode; wherein said nickel hydroxide positive electrode is applied in a thin film to the face of said sheet nickel substrate remote from said copper current collector; wherein said zinc negative electrode comprises copper foam which is secured to said copper current collector at the edges thereof, and which is pasted with a paste mixture consisting primarily of zinc oxide; and wherein said copper foam is pressed so as to form a plurality of pockets (50) which face said copper current collector when assembled thereto; whereby access to said negative electrode for oxygen generated at said positive electrode during overcharge conditions is provided.

2. The high rate nickel zinc cell of claim 1 , wherein after said copper foam has been pasted with said paste mixture, and said paste mixture has dried, said negative electrode is sprayed with an emulsion of polytetrafluoroethylene.

3. The high rate nickel zinc cell of claim 1, wherein said alkaline electrolyte is such as to restrict the solubility of the zinc of said zinc negative electrode.

4. The high rate nickel zinc cell of claim 1 , wherein the side of said nickel substrate in contact with said nickel hydroxide positive electrode has been treated so as to provide a higher surface area.

5. The high rate nickel zinc cell of claim 4, wherein said treated surface of said nickel substrate has been treated by a method chosen from the group consisting of etching, embossing, scoring, grinding, particle blasting, rolling, coining, pebbling, and combinations thereof.

6. The high rate nickel zinc cell of claim 1 , wherein said thin film nickel hydroxide positive electrode material is applied to the respective surface of said nickel substrate by a method chosen from the group consisting of chemical vapour deposition, plasma deposition, ion implantation, electrostatic powder spray application, and combinations thereof.

7. The high rate nickel zinc cell of claim 1, wherein the ampere hour capacity of said zinc negative electrode is at least twice the ampere hour capacity of said nickel hydroxide positive electrode.

8. The high rate nickel zinc cell of claim 1, wherein the ampere hour capacity of said zinc negative electrode is three to five times higher than the ampere hour capacity of said nickel hydroxide positive electrode.

9. A high rate nickel zinc battery (10) comprising an assembly of at least two high rate nickel zinc cells according to claim 1 ; wherein said batteiy comprises a series arranged assembly of said at least two cells with a microporous separator (20) being placed between each contiguous pair of cells; and wherein each respective cell is contained in a housing (30, 32), and the respective housings for each of said cells are assembled together so as to provide a leak proof containment for said electrolyte on each side of said microporous separator.

10. The battery of claim 9, when assembled in a fully charged state.

11. The battery of claim 9, when assembled in a fully discharged state.