Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/42—Alloys based on zinc
• • 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
  • H01M4/06—Electrodes for primary cells
  • H01M4/08—Processes of manufacture
  • H01M4/12—Processes of manufacture of consumable metal or alloy electrodes

Definitions

• This invention relates to the use of uniformly shaped non-mercury- added zinc particles as the anode's active material in an electrochemical cell.
• This invention also relates to the use of uniformly shaped and uniformly sized non-mercury-added zinc particles as the anode's active material in an electrochemical cell.
• Aqueous alkaline manganese dioxide zinc batteries consume zinc metal particles during electrochemical discharge.
• Zinc particle electrodes have the advantage of high active surface area per gram of zinc which allows high average current densities without excessive polarization. The particles are made to contact a current collector.
• An aqueous electrolyte solution provides ionic conduction between the anode and the cathode.
• the aqueous electrolyte may also function as a reactant or provide reactants.
• the electrolyte solution is typically an aqueous alkaline electrolyte containing potassium hydroxide, sodium hydroxide, or a mixture thereof.
• the zinc particles produce electricity and a reaction product consisting of zinc hydroxides, zincate ions, or zinc oxides.
• conventional zinc particles have had irregular shapes.
• the elimination of mercury in the zinc anode of an electrochemical cell has resulted in poor electrical contact between the zinc particles and has led to an increase in corrosion.
• One method used to overcome poor electrical contact has been to use higher concentration of zinc in the anode. However, this reduces the space available for reaction products.
• Another method used to overcome poor electrical contact has involved concentrating the zinc by creating connected agglomerates of zinc.
• Patents and applications that describe the use of agglomerates include European Patent Application EP 414,990 Al; U.S. Patent No. 4,963,447 to Nishimura et. al.; and U.S. Patent No. 3,884,722 to Tucholski.
• using the gelling agents described in these patents can impair the cell's discharge characteristics by inhibiting the reaction efficiency of the zinc.
• anode comprising zinc particles having uniform morphology and/or size. It would also be desirable to have zinc particles having the same porosity, chemical composition, reactivity, morphological, topological, and physical properties.
• Battery systems in which zinc particles of this invention may be used include alkaline manganese dioxide-zinc cells, zinc-air button cells, and the like, including primary and secondary batteries.
• This invention is an electrochemical cell comprising a cathode, an aqueous alkaline electrolyte, and a non-mercury-added anode comprising uniformly shaped zinc particles.
• this invention is an electrochemical cell comprising a cathode, an aqueous alkaline electrolyte, and a non-mercury-added anode comprising uniformly shaped zinc particles having uniform size.
• the electrochemical cell of the present invention includes the uniformly shaped zinc particles having a tap density less than 2.5 g/cc, preferably having a tap density less than 2.0 g/cc, very preferably having a tap density less than 1.5 g/cc, and most preferably having a tap density less than 1.3 g/cc.
• the uniformly shaped zinc particles comprise fifty percent or less of the zinc in the anode, preferably the uniformly shaped zinc particles comprise twenty percent or less of the zinc in the anode, very preferably the uniformly shaped zinc particles comprise fifteen percent or less of the zinc in the anode, and most preferably the uniformly shaped zinc particles comprise ten percent or less of the zinc in the anode.
• the zinc weight concentration of the anode is less than 70 percent, preferably the zinc weight concentration of the anode is less than 68 percent, very preferably the zinc weight concentration of the anode is less than 66 percent, most preferably the zinc weight concentration of the anode is less than 64 percent or below 62 percent.
• the uniformly shaped particles have the length, width and thickness dimensions in the range of 0.06, 0.06 and 0.0025 to 0.01 , 0.01 and 0.0004 inches, most preferably the length, width and thickness dimensions are in the range of 0.04, 0.025 and 0.0008 inches to 0.02, 0.025, and 0.0008 inches.
• the zinc weight concentration of the anode is less than 67 percent
• the uniformly shaped zinc particles comprise twenty percent or less of the zinc in the anode
• the uniformly shaped zinc particles having a tap density less than 2.5 g/cc.
• the present invention is an electrochemical cell comprising the novel use of a non-mercury-added anode comprising uniformly shaped zinc particles.
• the use of zinc particles having a uniform morphology increases the performance of the zinc anode in an electrochemical cell.
• the use of uniformly shaped zinc particles can have one or more of the following advantages.
• Seventh, processability, flowability, and dispensability of the anode is improved.
• Eighth, the use of large particle gelling agents can be eliminated.
• Ninth, the quantity of gelling agent used in the anode can be reduced.
• Twelfth the distribution of zinc in the gelled electrolyte is improved.
• uniform shape or "uniformly shaped” is intended to mean individual particles having substantially consistent morphology. This definition is contrasted against the prior art zinc powders with consistently irregularly shapes, few of which are similar to each other. To have a uniform shape as described and claimed, each of the particles shape factor must be substantially similar to all other particles. Therefore for example, if the uniform shape is flakes, then all of the particles must be flakes. In order to produce uniformly shaped particles, control of the forming or classification process should be used to ensure this required consistent particle shape.
• the shapes of zinc particles can be determined by examining the particles with a scanning electron microscope.
• the zinc particles of this invention will also have substantially consistent surface finishes and porosity characteristics.
• the shape of zinc particles is critical to electrochemical activity and anode processing.
• the size can also be critical to electrochemical activity and anode processing. When the particles are irregularly shaped or too large, processability of the anode is difficult.
• the zinc particles of this invention will have a uniform morphology and a uniform size.
• the use of uniformly shaped zinc particles with uniform size has the advantages of providing uniform bulk density and consistent particle-to-particle contact.
• the shape and size of the zinc particle can be optimized depending on the application.
• For uniformly shaped spherical zinc particles provide enhanced processability of the anode.
• Zinc particles having a "dog-bone" morphology provide an advantage when used in continuous drain applications.
• flowability of the anode may decrease.
• the large particles provide relatively larger areas of contact, the smaller particles are preferred due to enhanced zinc-to-zinc contact and improved flowability.
• the zinc particles of this invention can also have substantially similar porosity characteristics.
• porosity is meant a particle having intraparticle void volume greater than zero.
• a porous zinc particle can also comprise interconnected pores.
• the total porosity of the zinc is preferably greater than 25 percent porosity and, more preferably, greater than 50 percent porosity as determined by bulk or tap density analyses.
• An advantage to having a highly porous zinc electrode is the ability to store electrolyte in the pores of the electrode and then use this electrolyte to replenish the water and hydroxyl ions which are consumed during discharge of the cell.
• Porous zinc particles provide a high surface area-to-volume ratio which is important in high drain rate applications.
• Particle morphologies having intraparticle void volume can be shaped as a sponge, honeycomb, foam, tube, and the like.
• the zinc particles of this invention can also be solid zinc particles with no internal void volume.
• Particle morphologies having no intraparticle void volume can be shaped as a flake, snake, filament, donut, sphere, dogbone, biscuit, or dendrite. These particles may be corrugated. Suitable morphologies include tentacle-like, helix, or faceted. Flakes can have the shapes of discs, ribbons, clamshells, triangles, squares, troughs, rhomboids, rectangles, boomerangs, and the like. "Snake” morphology can have the shapes of rods, cylinders, carrots, needles, worms, or bananas.
• "snake" morphology would include those shapes having an approximately round cross-section, not necessarily uniform along its length, ,where the ratio of length to average diameter is greater than 1 and wherein the axis is defined as a line connecting a locus of points through the centers of all cross-sections. This axis of round cross-section is not necessarily straight.
• Filament morphology resembles wire, hair, thread, spaghetti, fibrils, fiber, ribbon, or turnings.
• the zinc particles can also have "donut" or torus morphology.
• the zinc particles can also have spheroid morphology, such as spheres, tadpoles, teardrops, pears, or squash-like shapes.
• Zinc particles having "dog bone” morphology can best be described as those particles having an approximately round cross-section, not necessarily uniform along its length, where the ratio of length to average diameter is greater than 1 , the axis is not necessarily straight, and the diameters of both ends are greater than the average diameter along the axis.
• a biscuit mo ⁇ hology is described as a briquette, flattened sphere, or cookie-like morphology.
• a dendrite mo ⁇ hology resembles feathers or snowflakes.
• a corrugated mo ⁇ hology resembles waffles, or mesh screens.
• a tentacle mo ⁇ hology resembles plant roots, octopus, or squid.
• a helix mo ⁇ hology resembles springs, scrolls, or turnings.
• a faceted mo ⁇ hology resembles pyramid or multifaceted objects.
• Surface finishes that are suitable for use with particles of this invention include: smooth, mossy, porous, grooved, dendritic and waffle-like.
• the uniformly shaped zinc particles of this invention can be formed in a variety of ways.
• U.S. Patent No. 4,154,284 describes a process of producing flake particles having a small length-to-width or small length-to-thickness ratio by extraction from a molten pool or unconfmed drop.
• the process utilizes a rotatable heat-extracting member having a serrated circular peripheral edge with each serration having a leading surface angularly shaped to contact the surface of the molten material. This process is capable of controlling the shape, size, and thickness of the final flake product.
• the flakes will be "substantially uniformly shaped.”
• the precise shape and dimensions of the individual flake particles can be controlled by changing one or more of the following process parameters: the angle at which the serrated edge contacts the molten material; the height of the serration, the length of the serration, the diameter of the rotating member; the rate at which the molten flake is cooled; the atmosphere (air vs. vacuum); etc.
• a process for manufacturing "uniform particulate" is disclosed in U. S. Patent No. 4,385,013.
• This process produces particulate directly from a supply of molten material by the use of a rotating member having discrete serrations in the periphery thereof.
• the leading surfaces of the serration contact the molten material and propel a portion into a cavity formed by the surfaces of the serration while under the effect of a surface of a dam means, in proximity to which the serrations pass.
• the dam means is immersed in the supply of molten material adjacent to the periphery of the rotating member. Provided that each of the serrations on the rotating member is identical, the particulate produced will be uniform in shape and size.
• the shape of the particulate can be altered to any one of a wide variety of shapes.
• three of the shapes disclosed include: quadrahedron, a five-sided triangular particle, and a six-sided particle.
• the zinc particles of this invention can be purchased from known zinc manufacturers such as Transmet Co ⁇ oration of Columbus, Ohio, U.S.A. or Eckart-PM-Laboratory of Vetroz, Switzerland.
• Two different zinc shapes were added to a conventional zinc powder composition in different amount using a total zinc weight percent of the anode in the range of 62-64%.
• a control was used with 100 wt. % conventional zinc powder and a total zinc weight percent of the anode in the range of 69-71%.
• Each of the experimental cells were manufactured so that the cathode theoretical Ampere hour value and anode theoretical Ampere hour value were kept constant regardless of the total zinc content. This was accomplished by using a larger cathode ID for the 62-64 weight percent total content anodes.
• Performance testing - 1A continuous, 1A Photofiash, and 3R9 Continuous.
• Impedance testing the impedance of the anodes were measured on an Autolab PGSTAT20 using FRA software from EchChemie.
• the tap density of all zinc samples were first measured according to the following procedure:
• Zinc is put in a pre-weighed 25ml measuring cylinder.
• the zinc is then tapped on a rubber bung whereby the level of the zinc falls.
• the weight of zinc which occupies 25ml can then be calculated.
• the Tap density is the weight of zinc which occupies 25ml / 25ml
• the SCA (Flash Amps) of the cell is measured 1 week after manufacture.
• the cell is allowed to fall down a vertical shaft.
• the length of the shaft is lm.
• the SCA (Flash Amps) of the cell is measured immediately after being rolled down the vertical shaft.
• Table 2 shows the results of the drop test for various anode concentrations.
• concentrations should be inte ⁇ reted as (% of zinc powder/ % of zinc flake/ anode zinc weight percent).
• Amperage maintenance is amperage after drop divided by amperage before drop.
• the tap density of the zincs used in this study are given above in Table 1.
• the flake has a very low tap density. And it is believed that this is the key to why the flakes work with 62-64% total zinc content gel but the needles do not.
• the low density flakes make a matrix through the anode gel which gives resistance to shock. Also very high rate 1 A performance is boosted.
• the needles are too high a density to make the required matrix, so shock resistance & 1 A performance suffer.
• Adding low tap density zinc allows low total zinc content to be used in alkaline manganese.
• the total zinc content of the anode paste has been raised.
• the total zinc content of AA anode paste was as low as 64.75%).
• the typical total zinc content is 70%.
• Attempts of local densification have been made by adding nuggets.
• the use of low tap density zinc allows total zinc contents of 62-64% to be used with 0% Hg. The extra electrolyte bound in such a gel leads to improved efficiency. This in turn leads to improved performance.
• Figure 1 is a scanning electron micrograph of zinc particles having a uniform biscuit shape of the present invention.
• Figure 2 is a scanning electron micrograph of zinc particles having a uniform needle shape of the present invention.
• Figure 3 is a scanning electron micrograph of zinc particles having a uniform, ribbon shape of the present invention.
• Figure 4 is a representative drawing of a scanning electron micrograph of zinc particles having a uniform, flake shape of the present invention.
• Figure 5 is a representative drawing of ascanning electron micrograph of zinc particles having a non-uniform shape. This type of zinc particle is typical of the prior art and is normally referred to as zinc powder.
• Figure 6 is a cross-sectional view of an electrochemical cell of the present invention.
• Figure 7 is a graph showing the results of a drop test described in the examples specifically in relation with Table 2.
• Figure 8 is a graph showing the results of cell testing as described in the examples. DETAILED DESCRIPTION OF THE DRAWINGS
• the cell 30 contains both a cathode 32 and an anode 34.
• the anode contains a mixture of uniformly shaped particles and electrolyte.
• the electrolyte is preferably potassium hydroxide, however other alkaline or nonalkaline electrolyte are suitable alternatives.
• the anode can also contain a gelling substance, several of which are well known in the art.
• the anode can also contain a zinc powder comprising non-uniform shaped, which can be mixed with the uniformly shaped particles of the present invention.
• the cell 30 also includes a separator 36 which electrically insulates the anode from the cathode, while allowing for ionic diffusion there through.
• the cell 30 also contains a current collector 38 which acts to collect the electrons from the anode 344 and transport them to a external apparatus so that work can be performed.

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• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Battery Electrode And Active Subsutance (AREA)
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Citations (4)

• 1998
  • 1998-05-01 JP JP54823798A patent/JP2001524254A/ja not_active Ceased
  • 1998-05-01 EP EP98918897A patent/EP0979533A1/de not_active Withdrawn
  • 1998-05-01 WO PCT/US1998/008824 patent/WO1998050969A1/en not_active Application Discontinuation
  • 1998-05-01 AU AU71728/98A patent/AU7172898A/en not_active Abandoned
  • 1998-05-01 CA CA002288776A patent/CA2288776A1/en not_active Abandoned

Patent Citations (4)

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