IL131842A

IL131842A - Chargeable electrochemical cell

Info

Publication number: IL131842A
Application number: IL131842A
Authority: IL
Original assignee: Unibat Ltd
Priority date: 1999-09-09
Filing date: 1999-09-09
Publication date: 2007-03-08
Also published as: KR20020059392A; WO2001018890A1; RU2264004C2; CN100449821C; AU6862300A; JP2003509818A; CN1373909A; EP1238437A1; KR100861098B1; EP1238437A4; IL131842A0

Description

CHARGEABLE ELECTROCHEMICAL CELL Eitan, Pearl, Latzer & Cohen-Zedek Chargeable Electrochemical Cell FIELD OF THE INVENTION This invention relates to a flexible design for accumulators, fuel cells and electrolyzers based on super light and super strong conductive and insulative materials in the form of special woven fabrics. This design may withstand very heavy overloads (property weight) at high accelerations of up to 50,000 g. As a result, there is an increase in kinetic uses of such accumulators. The same is true for insulation and cell materials which can be provided in a monolithic design. This kind of design can withstand accelerations of up to 55,000 g i.e., known products including artillery shells. The drastic decrease by 10-50 times in distance between electrodes in lead acid accumulators with the resulting decrease in internal resistance of the accumulator (principal part of internal accumulator resistance) creates an element with high electrical efficiency. The used active material permits to realize deep cycle charge - twice that of accumulators with semi-rigid electrodes- discharge and realized capacity of accumulator at multicycle work. A specific electrode material layout permits using pairs of electrode materials with dendrite problems for multicycle battery. The invention is suitable for lead-acid or silver-zinc accumulators, fuel cells, and electrolyzers, where weight and cost are important parameters.

P-2684-IL BACKGROUND OF THE INVENTION The problem of the high specific weight of accumulators, fuel cells and electrolyzers arises from the use of heavy metal electrodes, such as lead, silver, zinc, platinum, etc. These metals have very high densities and low mechanical strengths. Discharge depth is limited by electrode strength since active materials also have a structural function in electrodes.

These metals also have high active surface areas. A specific surface area of special electrodes such as porous electrodes or slurry or powder electrodes, is advantageous and may be used with or without a catalytic plate.

Some electrode pairs, such as zinc - silver, also have dendrite problems. As a result, dendrite induced short circuits limit the number of cycles during the life of a rechargeable battery.

An object of this invention is to decrease the weight and increase the strength of accumulator, fuel cell and electrolyzer electrodes. A design using carbon paper is described in U.S. Patent 4,894,355. This patent proposes to decrease the active surface area by cutting the ends of the fibers which consist of a carbon paper/polytetraflouroethylene composition. In this case, the main load of design takes carbon carrier material - paper, and conductivity parameters, determines thickness and span of electrode. 2 P-2684-IL SUMMARY OF THE INVENTION One object of this invention is to combine the conductivity or insulation parameters with a high strength/low weight ratio in one unit. Active and/or catalytic materials may be used in plate form (catalytic fuel cell or electrolyser) or in friable form (accumulator). This latter form permits a better use of the chemically active material without weakening the electrode's structure. The efficiency of the electrodes is increased as a result of enhanced intergranular contact induced by a spring element and/or by the battery's outer casing. The invention unifies these parameters and as a result there is a decrease in weight per discharged energy.

According to the invention, the battery cell comprises a flexible envelope in which a flat electrically conductive flexible wire or fabric grid is embedded in a matrix of granular or powder particles of an active material. Another envelope is also present containing an electrically conducting wire or fabric grid on which grains or particles of a complementary active metal or compound are positioned. The envelopes are separated by an insulating membrane which is permeable to the ions of a suitable electrolyte. There are conductive leads from each of the battery's cells. There is also a flexible spring element that supplies the required pressure to counteract the electrode's volume changes resulting from the chemical reaction in the cell.

The active material can be placed in a membrane bag or between sheets. The grains of active material can be fixed in position as distinct units by welding the cover. 3 P-2684-IL The present invention provides a means for applying pressure to the external surface of the assembled cell, ensuring close contact during charging and discharging between the granular or powder particles and between the particles and the electrode. This contact is maintained despite significant volume changes of the active material during the reaction.

Various pairs of metals or compounds can be used, such as Ni/Cd, Ag/Zn, Pb/PbO, etc.

The electrodes can be fabricated in the form of lengthy ribbons which can then be rolled into a spiral configuration. In such a design, it is advantageous to provide a spring to apply pressure to the external surface of the cells and to fabricate the cells in cylindrical form.

The spring element may be an entirely separate element included in the battery. Alternatively, the flexibility of the battery cell's walls can function as the spring element. A separate spring element is best suited for flat batteries where cell wall height is limited. The side walls of the cell are best suited to serve as the spring element when the cell has a cubic, or at least rectangular, shape. Flexible outer cylindrical containers can function as the spring element for cells with helical electrodes.

The powder or grains of the active material are preferably in the 5 to 10 micron range, although other sizes can be used.

The sheet grids may be made from expanded metals, such as gold. These are manufactured from expanded metal foil relevant to the active material of the cathode or anode. Conductive fabric thickness is generally about 10 μ to 500 μ with the preferable thickness being about 100 μ. The fabric can be woven from carbon fibers. Conductive materials may be coated 4 P-2684-IL with suitable metals, the exact metal depending on the nature of the electrochemical couple in the cell and the environment in which the cell operates.

For multicell versions, the conductive fabric may also be used in combination with non-conductive fibers. In such conductive fabrics, a plurality of parallel carbon fibers interwoven with fibers of Kevlar, nylon, polyester, etc. can be used. The configuration may be such that each carbon fiber constitutes an electrode. It is clear that the carbon fibers must be connected and a conductor lead provided for the current output.

A modification of the invention based on the same concept comprises fuel cells in which each membrane bag contains catalyst particles preferably attached to a suitable support. The catalyst may be in the form of ceramic particles coated with an active material, such as Ni, Pt or Cd. A suitable acid can serve as a catalyst in the fuel cell with oxygen and hydrogen reacting to form water and produce electric current. Suitable electrode connections are provided for current uptake. In the case of fuel cells, no external pressure on the cell is required. A catalyst may be directly plated on the carbon fibers increasing the active surface area.

Due to the thin elements of the novel electrochemical cells, the weight to power output is improved. Since the main elements of the cells are a conductive fabric, granular active material, suitable membranes and an electrolyte, the cells can withstand extreme accelerations and decelerations without detrimental effect on cell performance.

A high energy, high speed chargeable battery cell can be produced when provided in a helical configuration.

P-2684-IL According to this invention, electrodes, connection elements and cell walls are made from high-strength, conductive or insulative fibers/fabrics, catalyst, and active material in plate or friable form or the like. Carbon fibers may be used as the conductive part of electrodes while for the insulative parts, nylon, polyester, Kevlar or glass fibers can be used. The exact choice of insulative material depends on the electrolyte chosen.

Different designs can be used depending on the electrochemical principles. Parts should be designed to obtain stable electrical contact, resulting in conductivity in friable forms of the active material. Similarly, there should be adequate contact between the active material and the current input-output elements.

Suitable designs can include: 1. Electrodes, insulation elements, spring and outer cell casing made from separate parts and assembled into a single unit. 2. Electrodes and insulation elements in one unit. One piece of fabric woven in accordance with the need for the combination of conductivity and insulation or conductivity, insulation and active materials.

Different electrolytic principles of accumulator design may be realized in the first group of design.

Determination of some of the parameters suggests the following design specifications: a fiber thickness of 10 μ, a fabric thickness of 0.05, a specific area for the electrode of 31 .5cm2 per 1 cm2 of electrode geometry area. This is without special surface treatment to increase the microsurface.

The active area per unit weight in this case is 1875 cm2/g. i.e. 1 100 times greater than a solid surface. 6 P-2684-IL Additional specifications include conductivity cross-section per span distance, 0.0157 cm2/cm, electrical resistance, 0.4 -0.5 ohm*mm2 , and a permissible stress of 50 kg/mm2 given a fabric density of 168 g/m2 i.e. a maximum destroying length of 30 km. In comparison, lead has a value of is 0.122 km, zinc 0.63 km and copper 2.263 km. Therefore, a coated graphite fiber electrode can withstand acceleration 15 times greater than a copper electrode and 300 times greater than a lead electrode for electrodes of equal lengths. 7 P-2684-IL BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a sectional view of the configuration of an accumulator of the Zn -Air or Zn- Ag type with anodes of the Zn - ZnO or Zn - AgO or Ag -ZnO slurry type Figure 2 is a sectional view of the design of a Zn-Air accumulator cell or one with Zn - Ag pairs with anodes of the Zn - ZnO or Zn - AgO or Ag -ZnO slurry type Fig. 2a is a sectional view.

Figure 3 is a sectional view of a spiral design for the electrode couple. Figure 4 illustrates a parallel or serial connection between cells.

Figure 5 illustrates a multicell "one piece design" of a special fabric.

Figure 6 illustrates multi-electrodes and multicells made from one piece of special fabric. 8 P-2684-IL DETAILED DESCRIPTION OF THE PRESENT INVENTION Reference is now made to FIG. 1. Figure 1 is a sectional view of an example of a unit cell of fabric with central coaxially displaced fabric conductivity elements.

Electrode conductive element 1 (cathode or anode) is a woven carbon fiber fabric. In this case, the fibers do not need a special treatment to increase their microsurface.

Electrode housing 3 has a flat piece of conductive fabric 2 inserted into the electrical insulation bag 5 filled with a zinc, lead or silver oxide slurry 2 on both sides of the conductive element 1.

The electrode bag 6 and both layers 2 are pressed together by a spring and intake are in separate insulation chamber 5 executed from electrolyte permeability insulation fabrics which represents an accumulator element.

Figure 2 is a sectional view of a design of a unit cell of fabric. Electrode conductor 1 (cathode or anode) is woven from carbon fibers. Again, the fibers do not require special treatment to increase their surface area.

Electrode conductor 1 is made from a zinc, lead or silver oxide slurry 2. Electrode bag 1 can be provided with lattice or diagonal seams 7 to avert agglomeration of the slurry powder into a single piece. This helps to ensure an adequate powder distribution on the electrode surface. The electrode bag and both intakes are in separate insulation chambers 3 made of electrolyte permeable insulation fabrics.

The insulation chambers may be changed and divided into pieces of fabrics, which may be sewn to form an electrode bag from the sides of a pair of electrodes. The sewing threads may be made of insulating material. 9 P-2684-IL A couple of these insulated electrodes (cathode and anode) have one difference: the consistency of slurry 2. In an accumulator design the electrode pair or set of electrode pairs may be held under pressure by spring elements 8 of a different form. This saves the pressure needed for electrical contact between slurry and conductive fabric and between separate slurry nucleus (about 0.5 kg/cm2). However, this pressure supply needs structural integrity.

The electrode couple is located in a common shell 4 and constitutes a single cell. Shell 4 may be produced from flexible or rigid plastic materials like polyethylene, polypropylene, polyurethane or PVC. This material may be reinforced with glass, polyester, Kevlar, etc. fibers. The connection of all elements into a single unit may be done by heat welding at 5. The free electrode ends 6 may be used for the electrical connection of the cell.

The shape of the electrode and its position in a battery cell may vary. Among the various alternatives which can be used in a plate electrode with trim placing or a circular electrode in a coaxial structure. Electrolyte may be stored permanently in shell 4 or supplied periodically by special welding tubes.

Figure 3 is a sectional view of a spiral design for electrodes. A pair of flexible electrodes 1 and 2 of the form shown Figure 1 or Figure 2 are rolled into a spiral and inserted into an elastic sleeve 3, the latter serving as a spring element to ensure adequate contact pressure (0.5 kg/cm2). The rolled spiral with spring elements is inserted into outer housing 4. In principle, the outer housing may also serve as the spring elements in some embodiments.

Figure 4 illustrates a connection between cells which can be connected, serially or in parallel. Some electrode bags which are meant to be P-2684-IL connected can be made from a single piece of conductive fabric. In this case, all conventional connection parts are excluded decreasing accumulator weight and complexity and increasing reliability.

Figure 5 illustrates a one piece multi-electrode design which consists of a special fiber combination with a trim conductivity and insulation fiber or group of fibers, for use as electrode insulation or connecting elements. This trim may be different for weft and warp, for different accumulator designs, or because of weave problems.

The one-piece multi-electrode design includes a conductive part of electrode 1 made from conductive fibers and an insulative part 2 made of insulative fibers. Conductive parts of fabrics may also be used in conjunction with cross conductive thread stripes, which can connect electrode parts.

For a better connection between electrode parts and the connection strip, the connection may be preliminarily plated and welded, The trim of conductive parts does not determine what kind of electrode (cathode or anode) may be connected and what type of connection, parallel or series, should be used.

These parameters may be chosen as in common battery designs, where a one piece multi-electrode fabric is a common element that permits different designs and electrical configurations of accumulators, fuel cells, or electrolyzers.

The fabric may have a one-sided coating of PVC, polyethylene, polypropylene or polyurethane, for welding with other layers of the design, and outer shell formation. In this case, conductive fibers must be first treated to permit adhesion to the coating material. 1 1 P-2684-IL Figure 6 illustrates a design that can be realized with a multi-electrode one piece fabric. This design is an example of a slurry electrode accumulator with serial connection of separate cells. The design consists of two one-piece multi-electrode units 1 , separated by an electrolyte permeable fabric 2 that can be sewn or welded separately from the electrode design piece.

The welding seams position is in a form that provides insulation of separate cells formation with intake and outlet channels if a flow electrolyte system is used and permeability of outer space.

EXAMPLES Example #1 Battery layout Flat Battery active material Silver - Zinc Number of cells in battery 2 Battery voltage 3 volt Battery capacity 5AH Battery housing thickness 5.4 mm Battery housing area 18.5 cm2 Electrode particle diameter 0.005-0.01 mm2 Silver electrode thickness 0.8 mm Zinc electrode thickness 0.92 mm Silver weight 19.45g Zinc weight 1 1.78g Weight of total active material 31.23g Weight of conductive material 1.90g I2 P-2684-IL Weight of insulation material 1.64g Weight of electrolyte, KOH 21.4g Weight of accessories 37.1g Total weight of battery 88.77 Example #2 Battery layout Flat Active material Silver - Zinc Number of cells per battery 16 Battery voltage 24 volt Battery capacity 100AH Battery housing thickness 200mm Battery housing area 200 cm2 Electrode particle diameter 0.005-0.01 mm2 Silver electrode thickness 0.8 mm Zinc electrode thickness 0.92 mm Silver weight 3169g Zinc oxide weight 2023g Weight of total active material 5 92g Weight of conductive material 93.5g Weight of insulation material 215g Weight of electrolyte, KOH 2545 g Weight of accessories 765g Total weight of battery 8810 g Battery layout Flat Battery active material Lead Number of cells in battery 6 Battery voltage 12 volt Battery capacity 60 AH Battery housing thickness 150 mm Battery housing area 120cm2 Electrode particle diameter 0.005-0.01 mm2 Anode thickness 0.8 mm Cathode thickness 0.92 mm Lead weight 6,300g Lead oxide weight 7,100g Weight of total active material 13,400g Weight of conductive material 421g Weight of insulation material 85g Weight of electrolyte, acid 1 1 0g Weight of accessories 521g Total weight of battery 15,452g Example #4 Battery layout Spiral Battery active material design Silver - Zinc Number of cells in battery 1 Battery voltage 1.5-1.8 volt Battery capacity 15 AH Battery spiral diameter 30mm Battery spiral height 27mm Electrode particle diameter 0.01 mm2 Silver electrode thickness 0.8 mm Zinc electrode thickness 0.92 mm Silver weight 45.32g Zinc weight 11.78g Weight of total active material 57.1 g Weight of conductive material 1.90g Weight of insulation material 1.64g Weight of electrolyte, KOH 28.9g Weight of accessories 19.5g Total weight of battery 109.04g P-2684-IL ABSTRACT The invention refers to flexible rechargeable electrochemical cells, which utilize super light and supers tong conducting and insulating materials.

Technical result of the invention is reducing of weight and increase of strength of the electrodes of the electrochemical cell.

According to the invention the electrochemical cell comprises one or more pair of electrodes. The first electrode is comprised of a flexible electrically insulating and ion-conducting envelope, which contains a flexible conducting substrate.

The flexible conductor can be made of as conductive material in the form of fabric or grid, inserted into an active material in granular or powdered form. The second electrode is also a flexible electrically insulating envelope containing an electrical conductor inserted into a layer of an electrochemically complementary active material. The cell also contains a means for applying pressure to the assembly of electrodes, the membrane separator, and the counter electrodes so as to maintain constant pressure contact between every single particle of electrode active materials, separator and the conductor (substrate). One or both of electrodes may be sintered, pressed, glued or in the form of slurry. 19

Claims

131842/3 Claims: T. A rechargeable electrochemical battery cell comprising: a housing; at least one pair of flat electrodes encased in said housing and immersed within an electrolyte, at least one of said electrodes including an electrically conductive substrate and compressed particles of an electrode material on said substrate; a flexible separator permeable to ions of the electrolyte, said separator enveloping said substrate and said compressed particles of an active material; means for applying pressure on said electrodes.

2. An electrochemical cell according to claim 1 , characterized in that said substrate is made of a fabric woven from fibers of a material selected from the group consisting of carbon, synthetic material, nylon and polyester.

3. An electrochemical cell according to claim 2, characterized in that the thickness of the fabric is between about 10 and 100 microns.

4. An electrochemical cell according to claim 1 , characterized in that the electrodes are selected from the group consisting of : Ni/Cd, Ag/Zn, Pb/PbO.

5. An electrochemical cell according to claim 1 , characterized in that the thickness of each electr4ode is between 1 and 10 mm.

6. A battery according to claim 1 , characterized in that the particles have a particle size between about 1 and 10 microns.

7. An electrochemical cell according to claim 1 , characterized in that said means for applying pressure comprises a spring.

8. An electrochemical cell according to claim 1 , characterized in that the electrodes are helically wound. 16 131842/3

9. An electrochemical cell according to claim 1 , characterized in that the separator is made of a woven fabric having high mechanical strength.

10. An electrochemical cell according to claim 1 , characterized in that the substrate is made of a flexible metal grid.

11. An electrochemical cell according to claim 1 r characterized in that . said substrate is made of fabric woven from graphite fibers, said graphite fibers being coated with a gas-impermeable coating.

12. An electrochemical cell according to claim 1 , characterized in that said metal coating has thickness of about 5 to 15 microns.

13. An electrochemical cell according to claim 1 , characterized in that the cell is a Silver-Zinc rechargeable cell, and wherein the cathode coating is made of Nickel or Silver and the anode coating is made of Tin, Indium, Cadmium, Lead or Zinc.

14. An electrochemical cell according to claim 1 , characterized in that said housing is elastic and wherein said means for applying pressure comprises said elastic housing.

15. An electrochemical cell battery according to claim 1 , characterized in that the separator is made of a material, which is capable to swallow within the electrolyte, wherein said means for applying pressure comprises said separator.

16. An electrochemical cell according to claim 1 , characterized in that the separator is made of a material, which ensures separation of ions.

17. An electrochemical cell according to claim 16, characterized in that said separator comprises polyethylene-polypropylene film.

18. An electrochemical cell according to claim 16, characterized in that said separator is made of a porous material, which is capable to impede the growth of dendrites.

19. An electrochemical cell according to claim 1 , characterized in that said active materials are Carbon and Silver. 17 131842/3 For the Applicant: Patent Attorney 18