WO2015089205A1 - Beveled cell design for an alkaline battery to remove gas - Google Patents
Beveled cell design for an alkaline battery to remove gas Download PDFInfo
- Publication number
- WO2015089205A1 WO2015089205A1 PCT/US2014/069583 US2014069583W WO2015089205A1 WO 2015089205 A1 WO2015089205 A1 WO 2015089205A1 US 2014069583 W US2014069583 W US 2014069583W WO 2015089205 A1 WO2015089205 A1 WO 2015089205A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- battery
- electrode
- iron
- electrodes
- cell
- Prior art date
Links
- 125000006850 spacer group Chemical group 0.000 claims abstract description 21
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 68
- 229910052742 iron Inorganic materials 0.000 claims description 31
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 30
- 239000003792 electrolyte Substances 0.000 claims description 25
- 239000000758 substrate Substances 0.000 claims description 21
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 19
- 239000011149 active material Substances 0.000 claims description 19
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 16
- 239000011230 binding agent Substances 0.000 claims description 16
- 238000000576 coating method Methods 0.000 claims description 16
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 14
- 239000011248 coating agent Substances 0.000 claims description 12
- 229910052717 sulfur Inorganic materials 0.000 claims description 12
- 239000011593 sulfur Substances 0.000 claims description 12
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 10
- 239000000654 additive Substances 0.000 claims description 10
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 10
- 229910052759 nickel Inorganic materials 0.000 claims description 8
- 230000000996 additive effect Effects 0.000 claims description 7
- 229920000098 polyolefin Polymers 0.000 claims description 6
- 239000002356 single layer Substances 0.000 claims description 6
- 239000011148 porous material Substances 0.000 claims description 5
- 229910052977 alkali metal sulfide Inorganic materials 0.000 claims description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims 1
- 229910052748 manganese Inorganic materials 0.000 claims 1
- 239000011572 manganese Substances 0.000 claims 1
- 239000011701 zinc Substances 0.000 claims 1
- 229910052725 zinc Inorganic materials 0.000 claims 1
- 210000004027 cell Anatomy 0.000 description 70
- 239000007789 gas Substances 0.000 description 27
- 239000000463 material Substances 0.000 description 15
- 229910003271 Ni-Fe Inorganic materials 0.000 description 11
- 239000000203 mixture Substances 0.000 description 10
- 229910052751 metal Inorganic materials 0.000 description 9
- 239000002184 metal Substances 0.000 description 9
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 6
- 238000010276 construction Methods 0.000 description 6
- 238000000034 method Methods 0.000 description 6
- 239000006260 foam Substances 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- BFDHFSHZJLFAMC-UHFFFAOYSA-L nickel(ii) hydroxide Chemical compound [OH-].[OH-].[Ni+2] BFDHFSHZJLFAMC-UHFFFAOYSA-L 0.000 description 5
- 238000003487 electrochemical reaction Methods 0.000 description 4
- 229910052979 sodium sulfide Inorganic materials 0.000 description 4
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 230000002411 adverse Effects 0.000 description 3
- 238000009472 formulation Methods 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- 238000011282 treatment Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 210000002421 cell wall Anatomy 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000010924 continuous production Methods 0.000 description 2
- 230000001351 cycling effect Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000004744 fabric Substances 0.000 description 2
- 229910021506 iron(II) hydroxide Inorganic materials 0.000 description 2
- 239000006262 metallic foam Substances 0.000 description 2
- 229910000480 nickel oxide Inorganic materials 0.000 description 2
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 2
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910002640 NiOOH Inorganic materials 0.000 description 1
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- OSOVKCSKTAIGGF-UHFFFAOYSA-N [Ni].OOO Chemical compound [Ni].OOO OSOVKCSKTAIGGF-UHFFFAOYSA-N 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 238000010923 batch production Methods 0.000 description 1
- PLLZRTNVEXYBNA-UHFFFAOYSA-L cadmium hydroxide Chemical compound [OH-].[OH-].[Cd+2] PLLZRTNVEXYBNA-UHFFFAOYSA-L 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- ASKVAEGIVYSGNY-UHFFFAOYSA-L cobalt(ii) hydroxide Chemical compound [OH-].[OH-].[Co+2] ASKVAEGIVYSGNY-UHFFFAOYSA-L 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000006056 electrooxidation reaction Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000000835 fiber Chemical group 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- UGKDIUIOSMUOAW-UHFFFAOYSA-N iron nickel Chemical compound [Fe].[Ni] UGKDIUIOSMUOAW-UHFFFAOYSA-N 0.000 description 1
- 239000004816 latex Substances 0.000 description 1
- 229920000126 latex Polymers 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910052987 metal hydride Inorganic materials 0.000 description 1
- 150000004681 metal hydrides Chemical class 0.000 description 1
- 229910000000 metal hydroxide Inorganic materials 0.000 description 1
- 150000004692 metal hydroxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910000483 nickel oxide hydroxide Inorganic materials 0.000 description 1
- 229910021508 nickel(II) hydroxide Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920003023 plastic Chemical group 0.000 description 1
- 239000004033 plastic Chemical group 0.000 description 1
- 239000005060 rubber Substances 0.000 description 1
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000011669 selenium Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 229910052714 tellurium Inorganic materials 0.000 description 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- DEXZEPDUSNRVTN-UHFFFAOYSA-K yttrium(3+);trihydroxide Chemical compound [OH-].[OH-].[OH-].[Y+3] DEXZEPDUSNRVTN-UHFFFAOYSA-K 0.000 description 1
- UGZADUVQMDAIAO-UHFFFAOYSA-L zinc hydroxide Chemical compound [OH-].[OH-].[Zn+2] UGZADUVQMDAIAO-UHFFFAOYSA-L 0.000 description 1
- 229910021511 zinc hydroxide Inorganic materials 0.000 description 1
- 229940007718 zinc hydroxide Drugs 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/24—Alkaline accumulators
- H01M10/28—Construction or manufacture
- H01M10/288—Processes for forming or storing electrodes in the battery container
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
-
- 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
- H01M10/04—Construction or manufacture in general
- H01M10/0468—Compression means for stacks of electrodes and separators
-
- 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
- H01M10/24—Alkaline accumulators
-
- 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
-
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
- H01M50/103—Primary casings; Jackets or wrappings characterised by their shape or physical structure prismatic or rectangular
-
- 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 present invention is in the technical field of energy storage devices. More particularly, the present invention is in the technical field of rechargeable batteries using an alkaline electrolyte, and having a particular cell design.
- Batteries with an alkaline electrolyte have been known for over a hundred years. Most of these batteries are based on the use of a nickel oxide active material as the cathode paired with a various metals or metal-hydrides as the anode. A number of types of cell construction are possible for each of these batteries. These variations in cell construction lie mostly in the nature of electrode support utilized. For the positive electrode three principal types are recognized - pocket plate, sintered plate and foam-based plates. An electrode support is necessary because the active material (nickel hydroxide) is a solid and held in pockets in the pocket- plate-design, held in the pores of the sintered plate design, or mixed with gel or paste and placed in foam-based plate electrodes. Also, cobalt, cobalt hydroxide, zinc hydroxide, cadmium hydroxide, yttrium hydroxide, and/or other metal hydroxides need to be added to improve the conductivity of nickel hydroxide.
- nickel hydroxide nickel hydroxide
- Negative electrode designs make use of an even broader range of materials including pocket plates, sintered nickel powder, fiber, foam and plastic bonded supports. It is the physical stability of the active material in the negative electrode that permits such a wide variety of support materials. Nickel hydroxide in the positive electrode, however, swells appreciably during charge and discharge, straining the support and restricting the choice of support type at the positive electrode.
- Nickel-iron (Ni-Fe) batteries have been known for over a hundred years. These batteries are based on the use of a nickel oxide active material as the cathode paired with an iron electrode as the anode with an alkaline electrolyte. These batteries are known for their long cycle and calendar life, tolerance to electrical abuse such as overcharge and overdischarge, and overall physical ruggedness. These batteries however, do have disadvantages such as poor charge retention, poor low temperature performance, and low power density.
- Ni-Fe cells currently contain a thick spacer or meshlike material between each electrode. The large distance between electrodes which is enforced by the thick spacer has a negative impact on the power performance in the cell as the internal resistance of the cell increases with electrode spacing. A larger electrode spacing also lowers the energy density of the cell.
- a separator is placed between the two electrodes to prevent short circuits.
- separator materials and separator designs that may be used in these batteries.
- the function of the separator is to prevent electrical contact between the anode (negative electrode) and cathode (positive electrode) while providing minimal electrolyte (ionic) resistance.
- the design of the separator may be a non-woven sheet or felt, cloth, microporous fabric, a gridlike mesh inlay, or take the form of a spacer with an open area between the cathode and anode.
- the separators used in the cell construction depends upon the types of electrodes used.
- the anode and cathode are kept electrically isolated using a spacer or a grid-like mesh inlay and are typically held in a rigid frame.
- the open space between the electrodes allows for hydrogen and oxygen gas to diffuse away from the electrode and out of the electrolyte where it will not interfere with ionic transport and the electrochemical reactions at the electrode-electrolyte interface.
- the construction of these cells is more expensive as the electrode design is not amenable to lower-cost manufacturing methods.
- the large interelectrode spacing of these batteries imposed by the rigid support limits high rate performance as it increases electrolyte (ionic) resistance.
- Cells with thin separators such as nonwoven polyolefin separators would allow for improved performance and higher energy density for Ni-Fe batteries compared to batteries with thicker spacers.
- thin separators there is intimate contact between the separator and the electrodes as the electrode stack is fairly tight. This lowers the internal resistance of the cell and allows higher charge and discharge rates to be realized.
- the overall fit of the electrode stack inside the cell case is fairly tight and the pressure applied to the electrode stack is uniform.
- the relatively small pore structure and tortuous nature of these separators can trap gas generated at the electrode surface. Such trapped gas can interfere with ionic transport and electrochemical reactions at the electrode surface and adversely affect battery performance.
- Gas can be generated on the surface of both the iron and nickel electrodes via electrolysis of water.
- the generation of gas is especially significant in some alkaline batteries such as Ni-Fe batteries where the electrochemical potential for the reduction of water is actually more positive (ie. more favored thermodynamically) than the reduction of Fe(OH) 2 to iron metal which recharges the anode as shown in Equation 2.
- the electrochemical potential for the oxidation of water, Equation 3 is also more positive than the reaction at the cathode during charge, Equation 4. Both electrodes are thermodynamically unstable in their charged state. Ultimately, this leads to significant gas generation during charging and during self-discharge.
- Gas generation in these cells which occurs from the electrochemical oxidation and reduction of the electrolyte, is generally not regarded as a problem with regard to its effect on battery performance in cells with large electrode spacing, as in the case with cells of the pocket plate design that use spacers or grid-like inlays to enforce separation of the anode and cathode. This is because the large space between electrodes allow gas to flow out of the cell.
- gas generation is a disadvantage in Ni-Fe batteries with small electrode spacing as in cells with polyolefin separators. In this situation, the gas generated in the cell has a difficult time escaping and is trapped between the electrodes. Such trapped gas can interfere with ionic transport and electrochemical reactions at electrode surfaces and adversely affect battery performance.
- an object of this invention is to provide such a cell design that allows gas to more easily escape from an alkaline cell to achieve improved charge and discharge performance as well as higher energy density Summary of the Invention
- an alkaline battery comprising at least one positive electrode and at least one negative electrode with a separator disposed therebetween, which are contained in a cell casing that applies greater pressure to the electrodes towards the bottom of the electrode stack and less pressure towards the top of the electrode stack.
- the alkaline battery comprises an electrode stack having at least one positive electrode and at least one negative electrode with a separator disposed therebetween and a spacer between the tabs of similarly polarized electrodes of the electrode stack, which is contained in a cell casing that applies greater pressure to the electrode towards the bottom of the electrode stack and less pressure towards the top of the electrode stack.
- the alkaline battery is a Ni-Fe battery comprising at least one positive nickel electrode and at least one negative iron electrode with a separator disposed therebetween and a spacer between the tabs of similarly polarized electrodes of the electrode stack.
- the battery comprises a NaOH electrolyte also containing LiOH and an alkali metal sulfide.
- the spacers between the tabs of similarly polarized electrodes are the teeth of a comb structure.
- Figure 1 is a drawing of a cell case that has two interior cell walls that are angled such that the distance between them is slightly larger at the top of the case than at the bottom. The face of these walls are facing the face of the electrodes.
- Figure 2 is a drawing of a comb structure with teeth spacers that can be placed between the tabs of electrodes of similar polarity.
- Figure 3 is a drawing of an electrode stack with a comb structure with teeth spacers that are used in separating the tabs of electrodes of similar polarity.
- Figure 4 is a perspective view of a coated iron electrode.
- Figure 5 is a side view and cross-section view of an iron electrode coated on both sides of the substrate.
- Figure 6 is a plot of cell capacity versus cycle number for Ni-Fe cells with and without a beveled case design.
- the solid lines represent the cells of the present invention with a beveled case.
- the dashed lines represent cells without a beveled design where the pressure is applied evenly across the electrode stack.
- the present invention provides a cell design that allows gas to more easily escape from between the electrodes in an alkaline battery, e.g., a Ni-Fe or Zn-Mn battery, that uses separators, e.g., microporous separators.
- the invention provides a structure by which the advantages of higher charge and discharge rates and higher energy density may be achieved for alkaline batteries while reducing or avoiding trapped gases that interfere with electrochemical reactions at the electrode surface, which reactions degrade cell performance.
- the cell design of the present invention creates a pressure gradient on the electrode stack that directs the gas out of the electrode stack.
- the pressure gradient is enforced on the electrode stack by the cell case design where some regions of the electrode stack are under greater pressure than other areas. Gas that forms between the electrodes flows from areas of high pressure to areas of lower pressure.
- the cell is designed so that the gradient directs the gas to the outside of the electrode stack where it no longer interferes with electrochemical processes and is able to bubble out of the electrolyte and leave the cell.
- the cell comprises a case that applies greater pressure to the electrodes towards the bottom of the electrode stack and less pressure towards the top of the electrode stack.
- Figure 1 shows a side view of the cell case 1.
- the angle 2 formed between the cell wall 3 that faces the face of the electrode stack 4 and the bottom of the cell case 5 is greater than 90°. This creates a larger gap 6 between the electrode stack towards the top of cell case than at the bottom. Because the electrode stack is tight fitting in the cell case, the larger gap at the top than at the bottom creates a pressure gradient along the electrode stack with greater pressure at the bottom. This greater pressure will force gas that is generated to migrate towards the top of the cell and out of the electrode stack. Once gas escapes from the top of the electrode stack it no longer interferes with electrochemical processes and the gas is able to leave the cell.
- the cell case may have a cover which is not shown in Figure 1 .
- Figure 2 shows a comb structure 20 with teeth 21 that fit in the gaps 22 between the tabs 23 of similarly polarized electrodes.
- the teeth or other separator material help prevent the top of the electrodes from being pinched together which could lead to gas being trapped between the electrodes rather than escaping from the electrode stack.
- Figure 3 shows the teeth 31 of the comb 30 between the tabs 33 of electrodes of similar polarity within an electrode stack. It is preferable, although not strictly necessary, that the spacer material between the tabs not be electrically conducting since contact between this and the electrodes of opposite polarity would cause a short.
- the spacer is comprised of polyolefin. It is also preferable that the spacer material of the comb structure separating the tabs be resistant to alkali since it could come into contact with the electrolyte.
- the battery may be prepared by conventional processing and construction.
- the electrodes can be sintered or a coated single substrate electrode.
- the electrodes of the present invention are generally single layer substrates, e.g., sintered or a coated single substrate electrode.
- a nickel oxyhydroxide positive electrode, an alkaline electrolyte, and an iron electrode are employed.
- the nickel electrode may be of a sintered type well known in the art or may be of a pasted type employing a foam or felt matrix.
- the iron electrode may be of a sintered type well known in the art or may be of a pasted type employing a foam or comprised of a single layer of conductive substrate coated with iron active material on one or both sides.
- a preferred negative electrode is a pasted iron electrode.
- a single layer of substrate is used. This single layer acts as a carrier with coated material bonded to at least one side. In one embodiment, both sides of the substrate are coated.
- This substrate may be a thin conductive material such as a metal foil or sheet, metal foam, metal mesh, woven metal, or expanded metal. For example, 0.004 inch thick perforated nickel plated steel has been used, or a metal foam.
- the invention comprises a battery with an iron anode.
- the battery can be any battery with an iron electrode, such as a Ni-Fe or Mn-Fe battery.
- the battery is a Ni-Fe battery.
- the battery in one embodiment comprises an iron electrode comprised of a single, coated conductive substrate, prepared by a simple coating process, which can be continuous. The substrate can be coated on one side, or on both sides.
- the coating mix for the iron electrode is a combination of binder and active materials in aqueous or organic solution.
- the mix can also contain other additives such as pore formers. Pore formers are often used to insure sufficient H 2 movement in the electrode. Without sufficient H 2 diffusion, the capacity of the battery will be adversely affected.
- the binder materials have properties that provide adhesion and bonding between the active material particles, both to themselves and to the substrate current carrier.
- the binder is generally resistant to degradation due to aging, temperature, and caustic environment.
- the binder can comprise polymers, alcohols, rubbers, and other materials, such as an advanced latex formulation that has been proven effective.
- a polyvinyl alcohol (PVA) binder is used in one embodiment.
- the PVA binder is present in an amount ranging from 2.5 to 4 wt.% of the iron anode coating mix.
- Use of a binder to mechanically adhere the active material to the supporting single substrate eliminates the need for expensive sintering or electrochemical post-treatment.
- Aqueous based solutions have the advantage of lower toxicity and removal of water during the drying process is environmentally friendly and does not require further treatment or capture of the solvent.
- the active material for the mix formulation can be selected from iron species that can be reversibly oxidized and reduced. Such materials include metal Fe and iron oxide materials. The iron oxide material will convert to iron metal when a charge is applied. Suitable iron oxide materials include Fe 3 0 4 and Fe 2 0 3 . In addition, any other additives may be added to the mix formulation. These additives include but are not limited to sulfur, antimony, selenium, and tellurium.
- the mix and therefore the iron electrode comprises a polyvinyl alcohol binder and a sulfur additive.
- the sulfur additive can be elemental sulfur.
- Sulfur as an additive has been found to be useful in concentrations ranging from 0.25 to 1 .5%, and higher concentrations may improve performance even more.
- the combination of the sulfur additive with a polyvinyl alcohol binder has been found to provide particular advantages in an iron electrode.
- Nickel has been used as a conductivity improver and concentrations ranging from 8 to 20% have been found to improve performance, and higher concentrations may improve performance even more.
- the coating method for producing the iron electrode can be a continuous process that applies the active material mixture to the substrate, such as spraying, dip and wipe, extrusion, low pressure coating die, or surface transfer.
- a batch process may also be used, but a continuous process is advantageous regarding cost and processing.
- the coating method must maintain a high consistency for weight, thickness, and coating uniformity. This insures that finished electrodes will have similar loadings of active material to provide uniform capacity in the finished battery product.
- the coating method of the iron electrode employed is conducive to layering of various materials and providing layers of different properties, such as porosities, densities, and thicknesses.
- the substrate can be coated with three layers; the first layer being of high density, second layer of medium density, and final layer of a lower density to create a density gradient. This gradient improves the flow of gases from the active material to the electrolyte and provides better electrolyte contact and ionic diffusion with the active material throughout the structure of the electrode.
- the iron electrode employed in the invention may include continuous in-line surface treatments.
- the treatments can apply sulfur, polymer, metal spray, surface laminate, etc.
- a polymer post-coat is applied.
- Figure 4 is a prospective view of a coated iron electrode.
- the substrate 41 is coated on each side with the coating 42 comprising the iron active material and binder. This is further shown in Figure 5.
- the substrate 50 is coated on each side with the coating 51 of the iron active material and binder.
- the substrate may be coated continuously across the surface of the substrate, or preferably, as shown in Figures 4 and 5, cleared lanes of substrate may be uncoated to simplify subsequent operations such as welding of current collector tabs.
- the battery electrolyte may be comprised of a KOH solution or alternatively a NaOH based electrolyte.
- a preferred electrolyte comprises of NaOH, LiOH, and a sulfide additive such as Na 2 S.
- the electrolyte comprises 6M NaOH, 1 M LiOH and 1 wt.% Na 2 S.
- the batteries particularly including the continuous coated iron electrode, can be used, for example, in a cellphone, thereby requiring an electrode with only a single side coated. However, both sides are preferably coated, allowing the battery to be used in many applications as known in the art.
- Two cells were constructed that had shims inserted into the cell case so that the pressure was less at the top of the electrode stack than at the bottom.
- the shims were each 3" long and had a thickness of 0.27" at one end and 0.41 " at the other.
- Two shims were inserted into the cell case so that the bottom inside the cell case was 0.28" thinner than the top (eg. a was 0.28" smaller than b in Figure 1 ).
- the cell was constructed using three negative and two positive electrodes, each of which were 2.75 x 1 .75 x 0.025 in.
- the electrode stack alternated the positive and negative electrodes with two negative electrodes being placed on the outside.
- the positive electrodes were sintered nickel with nickel hydroxide active material.
- the negative electrode consisted of 16% nickel powder #255, 3.5% PVA, 80.1 % iron (325 mesh), and 0.4% sulfur adhered to a perforated metal strip.
- the negative electrodes were wrapped with a polyolefin separator.
- the cells were filled with an electrolyte comprised of 6 M NaOH, 1 M LiOH, and 1 wt% Na 2 S.
- the cells had a nominal capacity of 1 .6 Ah.
- Cells were constructed that had no shims inside the cell so that the space at top of the cell was the same as the bottom (eg. a was equal to b in Figure 1 ).
- the cell was constructed using three negative and two positive electrodes, each of which were 2.75 x 1 .75 x 0.025 in.
- the electrode stack alternated the positive and negative electrodes with two negative electrodes being placed on the outside.
- the positive electrodes were sintered nickel with nickel hydroxide active material.
- the negative electrode consisted of 16% nickel powder #255, 3.5% PVA, 80.1 % iron (325 mesh), and 0.4% sulfur adhered to a perforated metal strip.
- the negative electrodes were wrapped with a polyolefin separator.
- the cells were filled with an electrolyte consisting of 6 M NaOH, 1 M LiOH, and 1 wt% Na 2 S.
- the cells had a nominal capacity of 1 .6 Ah.
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Abstract
Provided is an alkaline battery comprising an electrode stack having at least one positive electrode and at least one negative electrode with a separator disposed therebetween, which battery is contained in a cell casing that applies greater pressure to the electrode towards the bottom of the electrode stack and less pressure towards the top of the electrode stack. In one embodiment, spacers are between the tabs of similarly polarized electrodes of the electrode stack. In one embodiment, the spacers between the tabs of similarly polarized electrodes are the teeth of a comb structure.
Description
BEVELED CELL DESIGN FOR AN ALKALINE BATTERY TO REMOVE GAS
Field of Invention
[0001] The present invention is in the technical field of energy storage devices. More particularly, the present invention is in the technical field of rechargeable batteries using an alkaline electrolyte, and having a particular cell design.
State of the Art
[0002] Batteries with an alkaline electrolyte have been known for over a hundred years. Most of these batteries are based on the use of a nickel oxide active material as the cathode paired with a various metals or metal-hydrides as the anode. A number of types of cell construction are possible for each of these batteries. These variations in cell construction lie mostly in the nature of electrode support utilized. For the positive electrode three principal types are recognized - pocket plate, sintered plate and foam-based plates. An electrode support is necessary because the active material (nickel hydroxide) is a solid and held in pockets in the pocket- plate-design, held in the pores of the sintered plate design, or mixed with gel or paste and placed in foam-based plate electrodes. Also, cobalt, cobalt hydroxide, zinc hydroxide, cadmium hydroxide, yttrium hydroxide, and/or other metal hydroxides need to be added to improve the conductivity of nickel hydroxide.
[0003] Negative electrode designs make use of an even broader range of materials including pocket plates, sintered nickel powder, fiber, foam and plastic bonded supports. It is the physical stability of the active material in the negative electrode that permits such a wide variety of support materials. Nickel hydroxide in the positive electrode, however, swells appreciably during charge and discharge, straining the support and restricting the choice of support type at the positive electrode.
[0004] Nickel-iron (Ni-Fe) batteries have been known for over a hundred years. These batteries are based on the use of a nickel oxide active material as the cathode paired with an iron electrode as the anode with an alkaline electrolyte. These batteries are known for their long cycle and calendar life, tolerance to electrical abuse such as overcharge and overdischarge, and overall physical ruggedness. These batteries however, do have disadvantages such as poor charge retention, poor low temperature performance, and low power density.
[0005] Commercially available Ni-Fe cells currently contain a thick spacer or meshlike material between each electrode. The large distance between electrodes which is enforced by the thick spacer has a negative impact on the power performance in the cell as the internal resistance of the cell increases with electrode spacing. A larger electrode spacing also lowers the energy density of the cell.
[0006] In all cell construction types, a separator is placed between the two electrodes to prevent short circuits. There is a variety of separator materials and separator designs that may be used in these batteries. The function of the separator is to prevent electrical contact between the anode (negative electrode) and cathode (positive electrode) while providing minimal electrolyte (ionic) resistance. The design of the separator may be a non-woven sheet or felt, cloth, microporous fabric, a gridlike mesh inlay, or take the form of a spacer with an open area between the cathode and anode.
[0007] The separators used in the cell construction depends upon the types of electrodes used. In cells with a pocket plate electrodes, the anode and cathode are kept electrically isolated using a spacer or a grid-like mesh inlay and are typically held in a rigid frame. The open space between the electrodes allows for hydrogen and oxygen gas to diffuse away from the electrode and out of the electrolyte where it will not interfere with ionic transport and the electrochemical reactions at the electrode-electrolyte interface. However, the construction of these cells is more expensive as the electrode design is not amenable to lower-cost manufacturing methods. Furthermore, the large interelectrode spacing of these batteries imposed by the rigid support limits high rate performance as it increases electrolyte (ionic) resistance.
[0008] Cells with thin separators such as nonwoven polyolefin separators would allow for improved performance and higher energy density for Ni-Fe batteries compared to batteries with thicker spacers. With thin separators, there is intimate contact between the separator and the electrodes as the electrode stack is fairly tight. This lowers the internal resistance of the cell and allows higher charge and discharge rates to be realized. The overall fit of the electrode stack inside the cell case is fairly tight and the pressure applied to the electrode stack is uniform.
However, in providing intimate contact between the separator and the electrode surface, the relatively small pore structure and tortuous nature of these separators can trap gas generated at the electrode surface. Such trapped gas can interfere with
ionic transport and electrochemical reactions at the electrode surface and adversely affect battery performance.
[0009] Gas can be generated on the surface of both the iron and nickel electrodes via electrolysis of water. The generation of gas is especially significant in some alkaline batteries such as Ni-Fe batteries where the electrochemical potential for the reduction of water is actually more positive (ie. more favored thermodynamically) than the reduction of Fe(OH)2 to iron metal which recharges the anode as shown in Equation 2. The electrochemical potential for the oxidation of water, Equation 3, is also more positive than the reaction at the cathode during charge, Equation 4. Both electrodes are thermodynamically unstable in their charged state. Ultimately, this leads to significant gas generation during charging and during self-discharge.
2 H20 + 2 e"→ H2 + 2 OH" E° = -0.828 V 1
Fe(OH)2 + 2 e"→ Fe + 2 OH" E° = -0.877 V 2
40H" (aq)→ 02(g) + 2H20(I) + 4e" E° = -0.40 V 3
Ni(OH)2 + OH"→ NiOOH + H20 + e" E° = -0.52 V 4
[0010] Gas generation in these cells, which occurs from the electrochemical oxidation and reduction of the electrolyte, is generally not regarded as a problem with regard to its effect on battery performance in cells with large electrode spacing, as in the case with cells of the pocket plate design that use spacers or grid-like inlays to enforce separation of the anode and cathode. This is because the large space between electrodes allow gas to flow out of the cell. However, gas generation is a disadvantage in Ni-Fe batteries with small electrode spacing as in cells with polyolefin separators. In this situation, the gas generated in the cell has a difficult time escaping and is trapped between the electrodes. Such trapped gas can interfere with ionic transport and electrochemical reactions at electrode surfaces and adversely affect battery performance.
[0011 ] It is therefore desirable to have a cell design that utilizes separators, but allows improved rate performance and energy densities by allowing gas to escape from between the electrodes. Such a design would be welcome to the industry, particularly for Ni-Fe cells. Therefore, an object of this invention is to provide such a cell design that allows gas to more easily escape from an alkaline cell to achieve improved charge and discharge performance as well as higher energy density
Summary of the Invention
[0012] Provided is an alkaline battery comprising at least one positive electrode and at least one negative electrode with a separator disposed therebetween, which are contained in a cell casing that applies greater pressure to the electrodes towards the bottom of the electrode stack and less pressure towards the top of the electrode stack. In one embodiment, the alkaline battery comprises an electrode stack having at least one positive electrode and at least one negative electrode with a separator disposed therebetween and a spacer between the tabs of similarly polarized electrodes of the electrode stack, which is contained in a cell casing that applies greater pressure to the electrode towards the bottom of the electrode stack and less pressure towards the top of the electrode stack. In one embodiment, the alkaline battery is a Ni-Fe battery comprising at least one positive nickel electrode and at least one negative iron electrode with a separator disposed therebetween and a spacer between the tabs of similarly polarized electrodes of the electrode stack. In one embodiment, the battery comprises a NaOH electrolyte also containing LiOH and an alkali metal sulfide. In one embodiment, the spacers between the tabs of similarly polarized electrodes are the teeth of a comb structure.
[0013] Among other factors, it has been discovered that when an alkaline battery is used in which the cell casing is beveled, i.e., the walls of the cell diverge outwardly so that the top of the cell is wider than the bottom of the cell, improved capacity is achieved. Higher capacity is particularly achieved at higher discharge currents. The design of the cell results in greater pressure being applied to the electrode stack at the bottom of the cell, and less pressure at the top of the electrode stack. The spacers between the tabs of the electrodes, when present, also prevents the tops of the electrodes from being pinched together, thereby enhancing the escape of gas. This combination allows the gas to bubble out of the electrolyte and leave the electrode stack, and the cell. The gas no longer interferes with the electrochemical processes of the cell.
Brief Description of the Drawings
[0014] Figure 1 is a drawing of a cell case that has two interior cell walls that are angled such that the distance between them is slightly larger at the top of the case than at the bottom. The face of these walls are facing the face of the electrodes.
[0015] Figure 2 is a drawing of a comb structure with teeth spacers that can be placed between the tabs of electrodes of similar polarity.
[0016] Figure 3 is a drawing of an electrode stack with a comb structure with teeth spacers that are used in separating the tabs of electrodes of similar polarity.
[0017] Figure 4 is a perspective view of a coated iron electrode.
[0018] Figure 5 is a side view and cross-section view of an iron electrode coated on both sides of the substrate.
[0019] Figure 6 is a plot of cell capacity versus cycle number for Ni-Fe cells with and without a beveled case design. The solid lines represent the cells of the present invention with a beveled case. The dashed lines represent cells without a beveled design where the pressure is applied evenly across the electrode stack.
Detailed Description of the Preferred Embodiment of the Invention
[0020] The present invention provides a cell design that allows gas to more easily escape from between the electrodes in an alkaline battery, e.g., a Ni-Fe or Zn-Mn battery, that uses separators, e.g., microporous separators. The invention provides a structure by which the advantages of higher charge and discharge rates and higher energy density may be achieved for alkaline batteries while reducing or avoiding trapped gases that interfere with electrochemical reactions at the electrode surface, which reactions degrade cell performance.
[0021] The cell design of the present invention creates a pressure gradient on the electrode stack that directs the gas out of the electrode stack. The pressure gradient is enforced on the electrode stack by the cell case design where some regions of the electrode stack are under greater pressure than other areas. Gas that forms between the electrodes flows from areas of high pressure to areas of lower pressure. The cell is designed so that the gradient directs the gas to the outside of the electrode stack where it no longer interferes with electrochemical processes and is able to bubble out of the electrolyte and leave the cell. The cell comprises a case that applies greater pressure to the electrodes towards the bottom of the electrode stack and less pressure towards the top of the electrode stack. In one embodiment, there are also spacers between the tabs of the similarly polarized electrodes so that the tops of the electrodes are not pinched together when the tabs are connected
which could trap gas. This can better be seen in reference to Figures 1 -3 of the drawing.
[0022] Figure 1 shows a side view of the cell case 1. The angle 2 formed between the cell wall 3 that faces the face of the electrode stack 4 and the bottom of the cell case 5 is greater than 90°. This creates a larger gap 6 between the electrode stack towards the top of cell case than at the bottom. Because the electrode stack is tight fitting in the cell case, the larger gap at the top than at the bottom creates a pressure gradient along the electrode stack with greater pressure at the bottom. This greater pressure will force gas that is generated to migrate towards the top of the cell and out of the electrode stack. Once gas escapes from the top of the electrode stack it no longer interferes with electrochemical processes and the gas is able to leave the cell. The cell case may have a cover which is not shown in Figure 1 .
[0023] Figure 2 shows a comb structure 20 with teeth 21 that fit in the gaps 22 between the tabs 23 of similarly polarized electrodes. The teeth or other separator material help prevent the top of the electrodes from being pinched together which could lead to gas being trapped between the electrodes rather than escaping from the electrode stack. Figure 3 shows the teeth 31 of the comb 30 between the tabs 33 of electrodes of similar polarity within an electrode stack. It is preferable, although not strictly necessary, that the spacer material between the tabs not be electrically conducting since contact between this and the electrodes of opposite polarity would cause a short. In one embodiment, the spacer is comprised of polyolefin. It is also preferable that the spacer material of the comb structure separating the tabs be resistant to alkali since it could come into contact with the electrolyte.
[0024] The battery may be prepared by conventional processing and construction. The electrodes can be sintered or a coated single substrate electrode. The electrodes of the present invention are generally single layer substrates, e.g., sintered or a coated single substrate electrode.
[0025] In one embodiment, a nickel oxyhydroxide positive electrode, an alkaline electrolyte, and an iron electrode are employed. The nickel electrode may be of a sintered type well known in the art or may be of a pasted type employing a foam or felt matrix. The iron electrode may be of a sintered type well known in the art or may be of a pasted type employing a foam or comprised of a single layer of conductive substrate coated with iron active material on one or both sides.
[0026] A preferred negative electrode is a pasted iron electrode. In the electrode, a single layer of substrate is used. This single layer acts as a carrier with coated material bonded to at least one side. In one embodiment, both sides of the substrate are coated. This substrate may be a thin conductive material such as a metal foil or sheet, metal foam, metal mesh, woven metal, or expanded metal. For example, 0.004 inch thick perforated nickel plated steel has been used, or a metal foam.
[0027] In one embodiment, the invention comprises a battery with an iron anode. The battery can be any battery with an iron electrode, such as a Ni-Fe or Mn-Fe battery. In one embodiment, the battery is a Ni-Fe battery. The battery, in one embodiment comprises an iron electrode comprised of a single, coated conductive substrate, prepared by a simple coating process, which can be continuous. The substrate can be coated on one side, or on both sides.
[0028] The coating mix for the iron electrode is a combination of binder and active materials in aqueous or organic solution. The mix can also contain other additives such as pore formers. Pore formers are often used to insure sufficient H2 movement in the electrode. Without sufficient H2 diffusion, the capacity of the battery will be adversely affected. The binder materials have properties that provide adhesion and bonding between the active material particles, both to themselves and to the substrate current carrier. The binder is generally resistant to degradation due to aging, temperature, and caustic environment. The binder can comprise polymers, alcohols, rubbers, and other materials, such as an advanced latex formulation that has been proven effective. A polyvinyl alcohol (PVA) binder is used in one embodiment. Advantageously, in one embodiment, the PVA binder is present in an amount ranging from 2.5 to 4 wt.% of the iron anode coating mix. Use of a binder to mechanically adhere the active material to the supporting single substrate eliminates the need for expensive sintering or electrochemical post-treatment. Aqueous based solutions have the advantage of lower toxicity and removal of water during the drying process is environmentally friendly and does not require further treatment or capture of the solvent.
[0029] The active material for the mix formulation can be selected from iron species that can be reversibly oxidized and reduced. Such materials include metal Fe and iron oxide materials. The iron oxide material will convert to iron metal when a charge is applied. Suitable iron oxide materials include Fe304 and Fe203. In addition, any other additives may be added to the mix formulation. These additives include but are
not limited to sulfur, antimony, selenium, and tellurium. In one embodiment, the mix and therefore the iron electrode comprises a polyvinyl alcohol binder and a sulfur additive. The sulfur additive can be elemental sulfur.
[0030] Sulfur as an additive has been found to be useful in concentrations ranging from 0.25 to 1 .5%, and higher concentrations may improve performance even more. The combination of the sulfur additive with a polyvinyl alcohol binder has been found to provide particular advantages in an iron electrode. Nickel has been used as a conductivity improver and concentrations ranging from 8 to 20% have been found to improve performance, and higher concentrations may improve performance even more.
[0031 ] The coating method for producing the iron electrode can be a continuous process that applies the active material mixture to the substrate, such as spraying, dip and wipe, extrusion, low pressure coating die, or surface transfer. A batch process may also be used, but a continuous process is advantageous regarding cost and processing. The coating method must maintain a high consistency for weight, thickness, and coating uniformity. This insures that finished electrodes will have similar loadings of active material to provide uniform capacity in the finished battery product.
[0032] The coating method of the iron electrode employed is conducive to layering of various materials and providing layers of different properties, such as porosities, densities, and thicknesses. For example, the substrate can be coated with three layers; the first layer being of high density, second layer of medium density, and final layer of a lower density to create a density gradient. This gradient improves the flow of gases from the active material to the electrolyte and provides better electrolyte contact and ionic diffusion with the active material throughout the structure of the electrode.
[0033] The iron electrode employed in the invention may include continuous in-line surface treatments. The treatments can apply sulfur, polymer, metal spray, surface laminate, etc. In one embodiment, a polymer post-coat is applied.
[0034] Figure 4 is a prospective view of a coated iron electrode. The substrate 41 is coated on each side with the coating 42 comprising the iron active material and binder. This is further shown in Figure 5. The substrate 50 is coated on each side with the coating 51 of the iron active material and binder. The substrate may be coated continuously across the surface of the substrate, or preferably, as shown in
Figures 4 and 5, cleared lanes of substrate may be uncoated to simplify subsequent operations such as welding of current collector tabs.
[0035] The battery electrolyte may be comprised of a KOH solution or alternatively a NaOH based electrolyte. A preferred electrolyte comprises of NaOH, LiOH, and a sulfide additive such as Na2S. In one embodiment, the electrolyte comprises 6M NaOH, 1 M LiOH and 1 wt.% Na2S.
[0036] The batteries, particularly including the continuous coated iron electrode, can be used, for example, in a cellphone, thereby requiring an electrode with only a single side coated. However, both sides are preferably coated, allowing the battery to be used in many applications as known in the art.
[0037] The following examples are provided to further illustrate the present invention. They are solely meant to be illustrative, and not limiting.
Example
[0038] Two cells were constructed that had shims inserted into the cell case so that the pressure was less at the top of the electrode stack than at the bottom. The shims were each 3" long and had a thickness of 0.27" at one end and 0.41 " at the other. Two shims were inserted into the cell case so that the bottom inside the cell case was 0.28" thinner than the top (eg. a was 0.28" smaller than b in Figure 1 ). The cell was constructed using three negative and two positive electrodes, each of which were 2.75 x 1 .75 x 0.025 in. The electrode stack alternated the positive and negative electrodes with two negative electrodes being placed on the outside. The positive electrodes were sintered nickel with nickel hydroxide active material. The negative electrode consisted of 16% nickel powder #255, 3.5% PVA, 80.1 % iron (325 mesh), and 0.4% sulfur adhered to a perforated metal strip. The negative electrodes were wrapped with a polyolefin separator. The cells were filled with an electrolyte comprised of 6 M NaOH, 1 M LiOH, and 1 wt% Na2S. The cells had a nominal capacity of 1 .6 Ah.
Comparative example
[0039] Cells were constructed that had no shims inside the cell so that the space at top of the cell was the same as the bottom (eg. a was equal to b in Figure 1 ). The cell was constructed using three negative and two positive electrodes, each of which were 2.75 x 1 .75 x 0.025 in. The electrode stack alternated the positive and negative
electrodes with two negative electrodes being placed on the outside. The positive electrodes were sintered nickel with nickel hydroxide active material. The negative electrode consisted of 16% nickel powder #255, 3.5% PVA, 80.1 % iron (325 mesh), and 0.4% sulfur adhered to a perforated metal strip. The negative electrodes were wrapped with a polyolefin separator. The cells were filled with an electrolyte consisting of 6 M NaOH, 1 M LiOH, and 1 wt% Na2S. The cells had a nominal capacity of 1 .6 Ah.
Cell Cycling
[0040] Following formation cycling all cells were charged at 0.8 A for three hours for all cycles. The voltage cut-off during discharge was 1 .0 V for all cycles. The discharge rate was varied and the discharge currents following formation is shown in Table 1 . The capacity versus cycle number is plotted in Figure 6. The data clearly shows that cells with the beveled design clearly have improved capacity especially at high discharge currents.
Table 1
[0041 ] While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.
Claims
1 . An alkaline battery comprising at least one positive electrode and at least one negative electrode with a separator disposed therebetween, which are contained in a cell casing that applies greater pressure to the electrodes towards the bottom of the electrode stack and less pressure towards the top of the electrode stack.
2. The battery of claim 1 comprising an electrode stack having at least one positive electrode and at least one negative electrode with a separator disposed therebetween and spacers between the tabs of similarly polarized electrodes of the electrode stack.
3. The battery of claim 1 , wherein the battery comprises a NaOH electrolyte.
4. The battery of claim 3, wherein the NaOH electrolyte further comprises LiOH and an alkali metal sulfide.
5. The battery of claim 1 , wherein the separator is comprised of a polyolefin.
6. The battery of claim 1 , wherein the positive electrode is comprised of nickel or manganese.
7. The battery of claim 1 , wherein the negative electrode is comprised of iron or zinc.
8. The battery of claim 2, wherein the spacers between the tabs of similarly polarized electrodes are the teeth of a comb structure.
9. The battery of claim 1 , wherein the battery comprises an iron electrode which comprises a single layer of a conductive substrate coated on at least one side with a coating comprising an iron active material and a binder.
10. The battery of claim 9, wherein the binder comprises polyvinyl alcohol.
1 1 . The battery of claim 9, wherein the coating comprises a pore former.
12. The battery of claim 10, where the coating further comprises a sulfur additive.
13. The battery of claim 12, wherein the sulfur additive comprises elemental sulfur.
14. The battery of claim 9, wherein the porosity of the electrode is in the range of about 30-50 %.
15. The battery of claim 9, wherein the binder comprises polyvinyl alcohol, the coating on at least one side comprises sulfur, and the battery comprises a NaOH electrolyte containing LiOH and an alkali metal sulfide.
16. The battery of claim 2, wherein the spacers between the tabs of similarly polarized electrodes are the teeth of a comb structure.
17. The battery of claim 2, wherein the negative electrode is an iron electrode which comprises a single layer of a conductive substrate coated on at least one side with a coating comprising an iron active material and a binder.
18. The battery of claim 17, wherein the binder comprises polyvinyl alcohol, the coating on at least one side comprise sulfur, and the battery comprises a NaOH electrolyte containing LiOH and an alkali metal sulfide.
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US201361914108P | 2013-12-10 | 2013-12-10 | |
US61/914,108 | 2013-12-10 | ||
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US4008099A (en) * | 1975-03-14 | 1977-02-15 | Olle Birger Lindstrom | Chemoelectric battery |
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US20040131923A1 (en) * | 2003-01-03 | 2004-07-08 | David Anglin | Alkaline cell with flat housing |
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