WO1997041607A1 - Alkaline battery and separator - Google Patents

Alkaline battery and separator Download PDF

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Publication number
WO1997041607A1
WO1997041607A1 PCT/US1997/006580 US9706580W WO9741607A1 WO 1997041607 A1 WO1997041607 A1 WO 1997041607A1 US 9706580 W US9706580 W US 9706580W WO 9741607 A1 WO9741607 A1 WO 9741607A1
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WIPO (PCT)
Prior art keywords
separator
accordance
porous
battery
ceramic
Prior art date
Application number
PCT/US1997/006580
Other languages
French (fr)
Inventor
Thomas N. Gardner
Gregory K. Maclean
John L. Stempin
Dale R. Wexell
Original Assignee
Corning Incorporated
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Filing date
Publication date
Application filed by Corning Incorporated filed Critical Corning Incorporated
Priority to AU26779/97A priority Critical patent/AU2677997A/en
Publication of WO1997041607A1 publication Critical patent/WO1997041607A1/en

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409Separators, membranes or diaphragms characterised by the material
    • H01M50/431Inorganic material
    • H01M50/434Ceramics
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491Porosity
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00Electrolytes
    • H01M2300/0002Aqueous electrolytes
    • H01M2300/0014Alkaline electrolytes
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Definitions

  • the field is alkaline battery construction and a ceramic separator for use therein.
  • alkaline electrolyte batteries are known in the art. These are commonly categorized on the basis ofthe characteristic electrodes employed.
  • the different types known include, but are not limited to: nickel-zinc (Ni/Zn) aluminum-air (Al/O 2 ) silver-zinc (Ag/Zn) nickel-metal hydride (Ni/MH) silver-cadmium (Ag/Cd) nickel-cadmium (Ni/Cd) zinc-manganese dioxide (Zn/MnO 2 ) nickel-iron (Ni/Fe) zinc-air (Zn/O 2 )
  • alkaline refers to the electrolyte being alkaline in nature. This is in contrast to the well-known lead acid battery.
  • the usual alkaline electrolyte is an aqueous solution of KOH which may range from 10% to 45% in strength.
  • the present invention is generally applicable to all alkaline electrolyte-type batteries.
  • the nickel-zinc (Ni/Zn) battery resulted from an effort to combine the virtues ofthe nickel electrode in a nickel-cadmium battery with those ofthe zinc electrode in a silver-zinc battery. The aim was to achieve the long cycle life time ofthe nickel-cadmium battery in conjunction with the advantageous high capacity feature of the silver-zinc battery.
  • the Ni/Zn battery concept dates back to work by Drumm et al. in the l930's.
  • the Ni/Zn battery has yet to achieve commercial significance, primarily due to the limited cycle life ofthe zinc electrode. This limits battery life to no more than about 300 cycles of charge/discharge. On repetitive cycling, the zinc electrode partially dissolves in the electrolyte. It redeposits during the cycle, but not necessarily in the same location, or with the same mo ⁇ hology. Consequently, there is a loss of usable active material, capacity decay, and shortened life.
  • the redeposited zinc can grow into needle-like dendrites under certain circumstances. These dendrites have a tendency to grow toward the counter electrode and penetrate the separator. This causes short- circuiting ofthe cells. Efforts have been made to alleviate this problem by additives to the electrolyte, by use of polymeric membrane-type separator materials, and by controlled-charging techniques. However, the problem still persists.
  • a specific need is for a material having a system of pores that inhibit dendrite growth through the separator.
  • the separator material must also function to hold the electrolyte while having a high resistance to chemical attack by that electrolyte.
  • Battery assembly would be facilitated by having available a rigid separator. Such separator could be easily positioned, and would not be subject to movement, or being torn, during assembly or in service.
  • a particular purpose is to provide a novel separator for such battery that will remain in place, and thus lessen electrode disintegration and relocation of active material.
  • Another purpose is to provide a separator that will inhibit dendrite growth through the separator.
  • a battery comprising an alkaline electrolyte and electrodes separated by a porous, ceramic separator, the separator exhibiting good durability when immersed in a KOH solution, and having a porous system of sufficient pore size to hold the alkaline electrolyte.
  • the single FIGURE in the accompanying drawing is a side view of a single cell in a Ni/Zn battery.
  • the Ni/Zn battery system uses zinc as the negative active material and nickel oxide as the positive active material.
  • the electrolyte is an alkaline KOH solution, normally in the 10% to 45% by weight concentration range.
  • the charge and discharge reactions are as follows: Charge:
  • FIGURE in the drawing is a side view illustrating a single cell 10 of a Ni/Zn battery.
  • Cell 10 is of traditional design consisting of parallel plate, prismatic construction.
  • Electrode 12 is a strip of active material composed of a mixture of zinc oxide, additives and binder. It is applied to an electrically conductive substrate 16.
  • the strip may be formed by such known means as electrochemically or chemically precipitating, extruding, or pasting the active material mixture onto conductive substrate 16.
  • Electrode 14 may also be in the form of a strip of active material.
  • the strip is composed of a mixture of nickel hydroxide hydrate, additives and binder on an electrically conductive substrate 18. This strip may be formed by such means as electrochemically or chemically precipitating, pasting, or extruding the active material onto the conductive substrate 18.
  • the conductive substrates serve as current collectors for the electrodes.
  • the nickel strip conductive substrate 18 may be connected to a common positive te ⁇ ninal in single cells.
  • the zinc strip conductive substrate 16 may be connected to a common negative terminal in single cells. Electrode construction for other alkaline electrolyte battery systems will, likewise, be carried out in accordance with known practice. No novel features with respect to the electrode materials are introduced by the present invention. Accordingly, reference is made to published art for electrode construction details for such other battery types. Electrodes 12 and 14 are separated by a porous, ceramic separator 20.
  • Separator 20 has the multiple function of providing an electrolyte reservoir for the respective electrodes, retarding zinc, or silver dendrite short-circuiting, and retarding zinc relocation. This is usually accomplished, albeit imperfectly, in existing batteries by using multiple layers of absorbent material, and microporous, or membrane-type, material on the surface ofthe positive and negative electrodes to retard zinc dendrite penetration.
  • Typical, commercially-available separator materials for Ni/Zn cells are microporous, polymer membranes composed of such materials as nylon, polypropylene, polyethylene and cellophane.
  • separator 20 is a thin plate of porous, ceramic material. It is a primary purpose ofthe separator to hold the electrolyte. To this end, there must be sufficient porosity for the purpose, but the pores must not be so large that the electrolyte flows out. Also, the ceramic selected must resist attack by the alkaline electrolyte. In those batteries employing zinc, or silver electrodes, the pore size ofthe material must be sufficiently small, and the nature ofthe pores must be highly tortuous, so that dendrite growth through the separator is substantially hindered.
  • the material selected is preferably free of uncombined sihca which is readily dissolved by an alkaline electroh/te. However, up to one % free silica can be tolerated without undue interference with pore size and stability. The material must, of course, be resistant to appreciable attack by the alkaline electrolyte.
  • the test piece is weighed before and after immersion and must show a weight change less than 2% to be accepted.
  • These materials may be extruded, pressed, or cast as thin strips, flat plates, tubes, honeycombs, or channeled structures.
  • the materials, after sintering, have a porosity of about 20-40%. This permits holding adequate alkaline electrolyte, such as KOH solution, to provide the necessary ionic transfer for the charge-discharge cycle.
  • the pore size of these materials is sufficiently small and the pores thus provided are sufficiently tortuous in nature, to substantially prevent growth of zinc dendrites into and through the separator during operation of a battery with zinc electrodes. This prolongs battery life by inhibiting the loss of active material from the zinc electrode, and by avoiding short-circuiting.
  • Pore volume represents the percent ofthe total volume of a body that is constituted by pores.
  • a pore volume of at least 20-25% is necessary to accommodate the electrolyte in a Ni/Zn battery, and to permit electrical transfer during cycling.
  • Extruded ceramic materials may provide up to about 40% inherent porosity when fired. Where greater porosity is desired, a combustible additive, such as powdered carbon, or other carbonaceous material, may be included in the batch. When this batch is fired and sintered, the combustible additive is partially or completely removed to leave openings or pores in the ceramic body. While porosities as high as 80% may thus be obtained, we prefer a range of 40-70%.
  • a combustible additive such as powdered carbon, or other carbonaceous material
  • Pore size has an impact on pore volume. More important, however, is the control that it exercises on material transfer and dendrite growth during cycling.
  • the separator for a battery with a zinc, or silver electrode should have a pore size less than
  • the nickel-metal hydride, nickel-iron and nickel-cadmium batteries do not have as severe a dendrite growth problem as batteries with zinc or silver electrodes.
  • a rigid, ceramic separator such as improved electrode compression and reduced shedding of active materials.
  • a larger pore size in the separator is preferred to provide a greater capacity for electrolyte accommodation and lower resistance to ion flow.
  • the pore size may be greater than 0.1 micron and range up to 20 microns in diameter.
  • Pore size may be controlled primarily by controlling particle size of batch materials, that is, the ceramic and additives in the extruded or rolled batch.
  • larger particle size batch materials contribute to larger pore size and greater porosity.
  • the mechanical strength ofthe body tends to be lower so that the body is more fragile.
  • fine, presintered batch materials that pack closely may be used.
  • Pore size in the finished ceramic separator can also be controlled, or reduced, by applying a wash coat to the pores in the original ceramic body.
  • the wash coat applied may be a slurry of either similar, or different, material. Its application is followed by a further firing ofthe body. This wash coating-firing sequence may be repeated, if necessary, until a desired pore size is obtained.
  • the tape cast process was used to fabricate thin battery separators ⁇ 0.25 mm (0.010") in thickness for alkaline battery systems.
  • the tape casting process incorporates a mixture of inorganic materials with binders, solvents, and plasticizers to produce thin, flexible, plastic-like sheets. These thin sheets can easily be cut, punched, or drilled to produce thin, consolidated materials with or without intricate patterns.
  • a typical batch of powdered materials consists of, in parts by weight: Platelet clay 16.66
  • the batch was originally formulated for another product where it was necessary to control expansion effects by crystal orientation. Accordingly, a combination of clays was used; a practice that may be unnecessary for present purposes.
  • the tape cast materials were mixed thoroughly after each addition and then roll mixed for 16 hours. After mixing, the samples were cast on a standard tape casting table, using a doctor blade, and allowed to air dry. The thin flexible samples were then cut to size and slowly fired at 1400-1550°C. Porosity and pore size were controlled by the particle size ofthe batch materials and the firing temperature ofthe ceramics. Thus, a batch comminuted to an average particle size of 1-10 microns provided a pore size of 0.3-0.4 microns. Thickness ofthe ceramics ranged from 0.075-0.25 mm (0.003- 0.010"). It was controlled by the thickness ofthe doctor blade and the shrinkage ofthe ceramics.
  • extruded ceramic separators The same powdered batch materials, with the addition of a binder system including methyl cellulose, a dispersant and water, were used to prepare extruded ceramic separators.
  • the extruded samples were also fired from 1400-1550°C.
  • Porosity and pore size ofthe extruded ceramics were also controlled by the particle size ofthe batch materials and the firing temperature ofthe ceramics. Thickness ofthe fired ceramics ranged from 0.150-0.550 mm (0.006-0.022").
  • the initial ceramics used for nickel-metal hydride batteries ranged from 40-60% in porosity. They exhibited a pore size range of 1-2 microns.
  • a nickel-metal hydride button cell battery made with an alumina separator having 50% porosity was successfully cycled 140 times. The performance ofthe battery remained constant throughout. By comparison, a control battery made with a non- woven, nylon separator exhibited a small loss in capacity during the same cycle testing. A third battery was made with a 60% porosity alumina separator. This battery demonstrated excellent performance throughout cycling which was stopped after 60 cycles.
  • a reduction in the distribution of soluble zinc throughout a cell is significant in reducing the potential for zinc dendrite formation and penetration through a separator. This, in turn, reduces the potential for creating an internal short circuit. Therefore, an experiment was designed to compare the zinc diffusion rates, or flux, through various types of separator materials. This comparison had the potential for indicating how well a separator may prevent the formation of zinc dendrites. Thus, the higher the zinc diffusion rate, the greater the probability of dendritic shorting occurring.
  • the TABLE below shows the average diffusion rate of zinc through each separator material. Several tests were run with each material, and the average for each material is shown in the TABLE.
  • the comparative rates show the superiority of a ceramic separator, in this case alumina, in reducing the diffusion of zinc through a separator, and hence throughout the electrochemical cell.

Abstract

A battery (10) having an alkaline electrolyte and a porous, ceramic separator (20), the separator resisting attack by the alkaline electrolyte and having a porous system of sufficient pore size to hold the alkaline electrolyte.

Description

ALKALINE BATTERY AND SEPARATOR
This application claims the benefit of U.S. Provisional Application No. 60/016,478 filed April 29, 1996, entitled ALKALINE BATTERY AND SEPARATOR, by Thomas N. Gardner, Gregory K. MacLean, John L. Stempin and
Dale R. Wexell.
FIELD OF THE INVENTION
The field is alkaline battery construction and a ceramic separator for use therein.
BACKGROUND OF THE INVENTION
Several types of alkaline electrolyte batteries are known in the art. These are commonly categorized on the basis ofthe characteristic electrodes employed. The different types known include, but are not limited to: nickel-zinc (Ni/Zn) aluminum-air (Al/O2) silver-zinc (Ag/Zn) nickel-metal hydride (Ni/MH) silver-cadmium (Ag/Cd) nickel-cadmium (Ni/Cd) zinc-manganese dioxide (Zn/MnO2) nickel-iron (Ni/Fe) zinc-air (Zn/O2)
The term "alkaline" refers to the electrolyte being alkaline in nature. This is in contrast to the well-known lead acid battery. The usual alkaline electrolyte is an aqueous solution of KOH which may range from 10% to 45% in strength. The present invention is generally applicable to all alkaline electrolyte-type batteries. However, development work initially involved the nickel-metal hydride battery. That work led to the nickel-zinc battery. Therefore, the invention is largely described with respect to the latter type of alkaline electrolyte battery. Historically, the nickel-zinc (Ni/Zn) battery resulted from an effort to combine the virtues ofthe nickel electrode in a nickel-cadmium battery with those ofthe zinc electrode in a silver-zinc battery. The aim was to achieve the long cycle life time ofthe nickel-cadmium battery in conjunction with the advantageous high capacity feature of the silver-zinc battery. The Ni/Zn battery concept dates back to work by Drumm et al. in the l930's.
The Ni/Zn battery has yet to achieve commercial significance, primarily due to the limited cycle life ofthe zinc electrode. This limits battery life to no more than about 300 cycles of charge/discharge. On repetitive cycling, the zinc electrode partially dissolves in the electrolyte. It redeposits during the cycle, but not necessarily in the same location, or with the same moφhology. Consequently, there is a loss of usable active material, capacity decay, and shortened life.
In addition to the material redistribution problem, the redeposited zinc can grow into needle-like dendrites under certain circumstances. These dendrites have a tendency to grow toward the counter electrode and penetrate the separator. This causes short- circuiting ofthe cells. Efforts have been made to alleviate this problem by additives to the electrolyte, by use of polymeric membrane-type separator materials, and by controlled-charging techniques. However, the problem still persists.
There is a need for an improved porous separator for alkaline electrolyte batteries. A specific need is for a material having a system of pores that inhibit dendrite growth through the separator. The separator material must also function to hold the electrolyte while having a high resistance to chemical attack by that electrolyte. Battery assembly would be facilitated by having available a rigid separator. Such separator could be easily positioned, and would not be subject to movement, or being torn, during assembly or in service. It is a basic purpose ofthe present invention to provide an improved alkaline electrolyte battery in which these needs are better met. A particular purpose is to provide a novel separator for such battery that will remain in place, and thus lessen electrode disintegration and relocation of active material. Another purpose is to provide a separator that will inhibit dendrite growth through the separator.
SUMMARY OF THE INVENTION
A battery comprising an alkaline electrolyte and electrodes separated by a porous, ceramic separator, the separator exhibiting good durability when immersed in a KOH solution, and having a porous system of sufficient pore size to hold the alkaline electrolyte.
BRIEF DESCRIPTION OF THE DRAWING
The single FIGURE in the accompanying drawing is a side view of a single cell in a Ni/Zn battery.
PRIOR ART
Prior literature known to applicants and deemed of possible relevance is listed in a separate document.
DESCRIPTION OF THE INVENπON
The Ni/Zn battery system uses zinc as the negative active material and nickel oxide as the positive active material. The electrolyte is an alkaline KOH solution, normally in the 10% to 45% by weight concentration range. The charge and discharge reactions, in simplified form, are as follows: Charge:
Zn(OH)2 + 2Ni(OH)2 > 2NiOOH + Zn + 2H2O Discharge:
2NiOOH + Zn + 2H2O > 2Ni(OH)2 + Zn(OH)2
The single FIGURE in the drawing is a side view illustrating a single cell 10 of a Ni/Zn battery. Cell 10 is of traditional design consisting of parallel plate, prismatic construction.
Cell 10 embodies a zinc electrode 12. Electrode 12 is a strip of active material composed of a mixture of zinc oxide, additives and binder. It is applied to an electrically conductive substrate 16. The strip may be formed by such known means as electrochemically or chemically precipitating, extruding, or pasting the active material mixture onto conductive substrate 16.
Cell 10 further includes a nickel electrode 14. Electrode 14 may also be in the form of a strip of active material. The strip is composed of a mixture of nickel hydroxide hydrate, additives and binder on an electrically conductive substrate 18. This strip may be formed by such means as electrochemically or chemically precipitating, pasting, or extruding the active material onto the conductive substrate 18.
The conductive substrates serve as current collectors for the electrodes. The nickel strip conductive substrate 18 may be connected to a common positive teπninal in single cells. The zinc strip conductive substrate 16 may be connected to a common negative terminal in single cells. Electrode construction for other alkaline electrolyte battery systems will, likewise, be carried out in accordance with known practice. No novel features with respect to the electrode materials are introduced by the present invention. Accordingly, reference is made to published art for electrode construction details for such other battery types. Electrodes 12 and 14 are separated by a porous, ceramic separator 20.
Separator 20 has the multiple function of providing an electrolyte reservoir for the respective electrodes, retarding zinc, or silver dendrite short-circuiting, and retarding zinc relocation. This is usually accomplished, albeit imperfectly, in existing batteries by using multiple layers of absorbent material, and microporous, or membrane-type, material on the surface ofthe positive and negative electrodes to retard zinc dendrite penetration. Typical, commercially-available separator materials for Ni/Zn cells are microporous, polymer membranes composed of such materials as nylon, polypropylene, polyethylene and cellophane.
It is a feature ofthe present invention that separator 20 is a thin plate of porous, ceramic material. It is a primary purpose ofthe separator to hold the electrolyte. To this end, there must be sufficient porosity for the purpose, but the pores must not be so large that the electrolyte flows out. Also, the ceramic selected must resist attack by the alkaline electrolyte. In those batteries employing zinc, or silver electrodes, the pore size ofthe material must be sufficiently small, and the nature ofthe pores must be highly tortuous, so that dendrite growth through the separator is substantially hindered. We have found that extruded, pressed, or tape cast strips of alumina, mullite, and mixtures thereof, after sintering, meet the several requirements of a ceramic separator for an alkaline electrolyte battery. The material selected is preferably free of uncombined sihca which is readily dissolved by an alkaline electroh/te. However, up to one % free silica can be tolerated without undue interference with pore size and stability. The material must, of course, be resistant to appreciable attack by the alkaline electrolyte. We employ a rather severe accelerated test in screening materials. In this test, a piece ofthe material is immersed for 48 hours in a 30% KOH solution held at 70°C. The test piece is weighed before and after immersion and must show a weight change less than 2% to be accepted. These materials may be extruded, pressed, or cast as thin strips, flat plates, tubes, honeycombs, or channeled structures. The materials, after sintering, have a porosity of about 20-40%. This permits holding adequate alkaline electrolyte, such as KOH solution, to provide the necessary ionic transfer for the charge-discharge cycle. The pore size of these materials is sufficiently small and the pores thus provided are sufficiently tortuous in nature, to substantially prevent growth of zinc dendrites into and through the separator during operation of a battery with zinc electrodes. This prolongs battery life by inhibiting the loss of active material from the zinc electrode, and by avoiding short-circuiting.
The porosity of a material involves pore volume and pore size. Pore volume represents the percent ofthe total volume of a body that is constituted by pores. A pore volume of at least 20-25% is necessary to accommodate the electrolyte in a Ni/Zn battery, and to permit electrical transfer during cycling.
Extruded ceramic materials may provide up to about 40% inherent porosity when fired. Where greater porosity is desired, a combustible additive, such as powdered carbon, or other carbonaceous material, may be included in the batch. When this batch is fired and sintered, the combustible additive is partially or completely removed to leave openings or pores in the ceramic body. While porosities as high as 80% may thus be obtained, we prefer a range of 40-70%.
Pore size has an impact on pore volume. More important, however, is the control that it exercises on material transfer and dendrite growth during cycling. The separator for a battery with a zinc, or silver electrode should have a pore size less than
0.1 micron in diameter, preferably less than 0.05 micron. However, it should be greater than about 0.005 micron in order to provide adequate electrolyte containment and ion mobility in the body. The nickel-metal hydride, nickel-iron and nickel-cadmium batteries do not have as severe a dendrite growth problem as batteries with zinc or silver electrodes.
However, they may benefit from other features of a rigid, ceramic separator, such as improved electrode compression and reduced shedding of active materials. For these batteries, a larger pore size in the separator is preferred to provide a greater capacity for electrolyte accommodation and lower resistance to ion flow. The pore size may be greater than 0.1 micron and range up to 20 microns in diameter.
Pore size may be controlled primarily by controlling particle size of batch materials, that is, the ceramic and additives in the extruded or rolled batch. In general, larger particle size batch materials contribute to larger pore size and greater porosity. The mechanical strength ofthe body, however, tends to be lower so that the body is more fragile. For smaller pore size, fine, presintered batch materials that pack closely may be used.
Pore size in the finished ceramic separator can also be controlled, or reduced, by applying a wash coat to the pores in the original ceramic body. The wash coat applied may be a slurry of either similar, or different, material. Its application is followed by a further firing ofthe body. This wash coating-firing sequence may be repeated, if necessary, until a desired pore size is obtained.
The tape cast process was used to fabricate thin battery separators < 0.25 mm (0.010") in thickness for alkaline battery systems. The tape casting process incorporates a mixture of inorganic materials with binders, solvents, and plasticizers to produce thin, flexible, plastic-like sheets. These thin sheets can easily be cut, punched, or drilled to produce thin, consolidated materials with or without intricate patterns.
Alumina and mulUte-alumina ceramic materials, having no free silica, were processed. A typical batch of powdered materials consists of, in parts by weight: Platelet clay 16.66
Stacked clay 5.54
Calcined clay 27.6
Alumina 50.7
The batch was originally formulated for another product where it was necessary to control expansion effects by crystal orientation. Accordingly, a combination of clays was used; a practice that may be unnecessary for present purposes.
Tape casting batches were made in small amounts by mixing the following materials in 500 ml plastic bottles,
81 g small ceramic tøllmill balls 12 g ethanol
4 g polyvinylbutyral 16.1 g methylisobutylketone 0.91 g Tergitol® 1.7 g dibutylpthalate 50 g powdered batch
The tape cast materials were mixed thoroughly after each addition and then roll mixed for 16 hours. After mixing, the samples were cast on a standard tape casting table, using a doctor blade, and allowed to air dry. The thin flexible samples were then cut to size and slowly fired at 1400-1550°C. Porosity and pore size were controlled by the particle size ofthe batch materials and the firing temperature ofthe ceramics. Thus, a batch comminuted to an average particle size of 1-10 microns provided a pore size of 0.3-0.4 microns. Thickness ofthe ceramics ranged from 0.075-0.25 mm (0.003- 0.010"). It was controlled by the thickness ofthe doctor blade and the shrinkage ofthe ceramics.
The same powdered batch materials, with the addition of a binder system including methyl cellulose, a dispersant and water, were used to prepare extruded ceramic separators. The extruded samples were also fired from 1400-1550°C. Porosity and pore size ofthe extruded ceramics were also controlled by the particle size ofthe batch materials and the firing temperature ofthe ceramics. Thickness ofthe fired ceramics ranged from 0.150-0.550 mm (0.006-0.022"). The initial ceramics used for nickel-metal hydride batteries ranged from 40-60% in porosity. They exhibited a pore size range of 1-2 microns.
The invention is further illustrated with reference to the foUowing specific embodiments:
Examples 1-3
A nickel-metal hydride button cell battery made with an alumina separator having 50% porosity was successfully cycled 140 times. The performance ofthe battery remained constant throughout. By comparison, a control battery made with a non- woven, nylon separator exhibited a small loss in capacity during the same cycle testing. A third battery was made with a 60% porosity alumina separator. This battery demonstrated excellent performance throughout cycling which was stopped after 60 cycles.
Examples 4-6
A reduction in the distribution of soluble zinc throughout a cell is significant in reducing the potential for zinc dendrite formation and penetration through a separator. This, in turn, reduces the potential for creating an internal short circuit. Therefore, an experiment was designed to compare the zinc diffusion rates, or flux, through various types of separator materials. This comparison had the potential for indicating how well a separator may prevent the formation of zinc dendrites. Thus, the higher the zinc diffusion rate, the greater the probability of dendritic shorting occurring.
For test purposes, two solutions of 45% by weight of KOH were prepared. One ofthe solutions was made 1 molar in ZnO, while the other solution remained free of ZnO. Equal volumes of each solution were placed in a container partitioned by a separator to prevent direct mtermingling ofthe solutions. Three different separators were tested as partitioning members. Diffusion of zinc through each material in a given period of time was measured.
The TABLE below shows the average diffusion rate of zinc through each separator material. Several tests were run with each material, and the average for each material is shown in the TABLE.
Average Zinc Diffusion Rate
MalerjaJ fmoles/cmVminute^
CELGARD 3400® 1.73 x 10"6 Cellophane 0.47 x W6
Al2O3 sheet (58% porosity) 0.17 x 10-6
The comparative rates show the superiority of a ceramic separator, in this case alumina, in reducing the diffusion of zinc through a separator, and hence throughout the electrochemical cell.

Claims

WE CLAIM:
1. A battery comprised of an alkaline electrolyte and electrodes separated by a porous, ceramic separator, the separator exhibiting good durability when immersed in a KOH solution, and having a porous system of sufficient pore size to hold the alkaline electrolyte.
2. A battery in accordance with claim 1 wherein the separator is composed of a ceramic selected from the group consisting of alumina, muUite and mixtures thereof, and containing no more than about one % free silica.
3. A battery in accordance with claim 2 wherein the selected material is alumina.
4. A battery in accordance with claim 2 wherein the selected material is mullite.
5. A battery in accordance with claim 1 wherein the separator has a porosity between 20% and 80%.
6. A battery in accordance with claim 5 wherein the porosity is 40-70%.
7. A battery in accordance with claim 1 wherein the electrolyte is a solution of KOH.
8. A battery in accordance with claim 1 wherein the separator form is selected from a group composed of thin strips, flat plates, tubes, honeycombs and channelled structures.
9. A battery in accordance with claim 1 wherein the porosity ofthe separator is enhanced by removal of a carbonaceous material added to the batch from which the separator is produced.
10. A battery in accordance with claim 9 wherein the carbonaceous material is a carbon powder.
11. A battery in accordance with claim 1 having non-zinc, or non-silver electrodes and a ceramic separator having a porous system in which the pores have an average pore size of 0.1-20 microns diameter.
12. A battery in accordance with claim 1 having a zinc, or silver electrode and a ceramic separator having a porous system with pores of sufficiently small size and sufficiently tortuous nature to inhibit zinc, or silver dendrite growth through the separator.
13. A battery in accordance with claim 12 wherein the pores in the separator are less than 0.1 micron in diameter.
14. A battery in accordance with claim 13 wherein the pores in the separator have a size in the range of 0.005-0.05 microa
15. A porous, ceramic separator for an alkaline electrolyte battery exhibiting a good durability when immersed in a KOH solution, and having a porous system of sufficient pore size to hold the alkaline electrolyte.
16. A porous, ceramic separator in accordance with claim 15 wherein the separator is composed of a ceramic selected from the group consisting of alumina, mullite and mixtures thereof, and containing no more than about one % free silica.
17. A porous, ceramic separator in accordance with claim 15 that exhibits a weight change of less than 2% when immersed in a 30% KOH solution for 48 hours at 70°C.
18. A porous, ceramic separator in accordance with claim 16 wherein the selected material is alumina.
19. A porous, ceramic separator in accordance with claim 16 wherein the selected material is mullite.
20. A porous, ceramic separator in accordance with claim 15 wherein the separator has a porosity between 20% and 80%.
21. A porous, ceramic separator in accordance with claim 20 wherein the porosity is 40-70%.
22. A porous ceramic separator in accordance with claim 15 having a porous system in which the pores have an average pore size of 0.1-20 microns diameter.
23. A porous ceramic separator in accordance with claim 15 having a porous system with pores of sufficiently small size and sufficiently tortuous nature to inhibit zinc, or silver dendrite growth through the separator.
24. A porous, ceramic separator in accordance with claim 23 wherein the pores in the separator are less than 0.1 micron in diameter.
25. A porous, ceramic separator in accordance with claim 24 wherein the pores in the separator have a size in the range of 0.005-0.05 micron.
26. A porous, ceramic separator in accordance with claim 15 wherein the separator form is selected from a group composed of thin strips, flat plates, tubes, honeycombs and channelled structures.
27. A porous, ceramic separator in accordance with claim 15 wherein the porosity is enhanced by complete or partial removal of a carbonaceous material added to the batch from which the separator is produced.
28. A porous, ceramic separator in accordance with claim 27, wherein the carbonaceous material is a carbon powder.
PCT/US1997/006580 1996-04-29 1997-04-21 Alkaline battery and separator WO1997041607A1 (en)

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US60/016,478 1996-04-29

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6849702B2 (en) 1999-02-26 2005-02-01 Robert W. Callahan Polymer matrix material

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3861963A (en) * 1968-02-23 1975-01-21 Mc Donnell Douglas Corp Battery separator construction
US5342709A (en) * 1991-06-18 1994-08-30 Wisconsin Alumni Research Foundation Battery utilizing ceramic membranes

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3861963A (en) * 1968-02-23 1975-01-21 Mc Donnell Douglas Corp Battery separator construction
US5342709A (en) * 1991-06-18 1994-08-30 Wisconsin Alumni Research Foundation Battery utilizing ceramic membranes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6849702B2 (en) 1999-02-26 2005-02-01 Robert W. Callahan Polymer matrix material

Also Published As

Publication number Publication date
AU2677997A (en) 1997-11-19

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