MXPA00007877A - Prismatic electrochemical cell - Google Patents

Abstract

A sealed prismatic electrochemical cell (14) has an electrode plate (38 or 44) comprising a porous structure with a maximum linear dimension of the porous structure in the principle direction of ion flow of at least 20 percent of the maximum linear dimension of the housing cavity in the principle direction of ion flow. The cell can produce good current density while having a high capacity. The electrode construction can result in a low diffusion polarization despite the thickness of the electrode. The overall cell can be economically manufactured, and has a low percentageof its internal volume occupied by inactive materials. Electrode plaque construct ions and active material compounds are also disclosed.

Description

ELECTROCHEMICAL CELL PRISM TICA BACKGROUND OF THE INVENTION The present invention is concerned with sealed prismatic electrochemical cells. The cylindrical electrochemical cells have a cylindrical box. Some cylindrical cells contain a roll of thin flexible electrodes coiled together with a separating layer therebetween. This cell construction is sometimes called a "gelatinous roll" due to the coiled configuration of the electrode and separator components. The electrodes of such cells can be made by impregnating porous, metallic substrates synthesized with an active material or by activating a paste containing active material on a metal substrate. Some other cylindrical cells contain powder pellets (or agglomerates) of compressed active material arranged in concentric cylinders inside the box, with a separator tube between the opposing electrodes. Cylindrical cells can be relatively inexpensive to manufacture and the cylindrical shape of the can withstands stress and strain concentrations due to internal pressure changes. Standard size AA and nickel cadmium (NiCd) and nickel metal hydride (NiMH) batteries are examples of cylindrical winding type cells. The REF: 122019 alkaline batteries standard AA, C and D are examples of cylindrical cells type coil (pellet or agglomerate). Prismatic cells, cells with boxes that have polygonal side walls (such as parallelepiped or rectangular boxes) are found in many applications that require high energy densities, since their shape can provide a high efficiency of volumetric stacking in packages of battery, such as for cell phones for example. A typical prismatic nickel metal hydride F6 cell has three positive nickel hydroxide electrode plates sandwiched between four negative metal hydride alloy electrode plates, with separating bags isolating each plate layer from the next. This electrode stack is inserted into a rectangular metal can with all the negative electrode plates connected to a terminal by means of a series of metal tab strips and all the positive electrode plates connected by means of a series of reed strips to the other terminal. Each of the metal tab strips is insulated sufficiently to prevent short internal circuits between the components of the electrode. In general, the can itself consists of one of the two terminals. Prismatic cells are generally more complex and expensive than comparable cylindrical cells due to the greater number of internal components and concurrent assembly operations. Two important performance characteristics for a battery are its previous global capacity (expressed in Amperes-hour) and its discharge efficiency at a given discharge speed. The nominal capacity is a measure of the total amount of usable energy stored in the cell and is relative to the number of hours the cell can energize a given load. The capacity is primarily a function of the amount of active material that can react within the cell, in particular the amount of any active material that is consumed first. Commonly, the capacity of the cell is measured at a discharge velocity of C / 5 as described in standard C18.2M-1991 of the ANSI, published by the American National Standards Institute. The . The theoretical volumetric capacity of a single electrode is the total energy density of the active material contained within a given volume of the electrode and can be expressed in ampere-hours per liter. The discharge velocity efficiency is affected by the amount of interfacial surface area between the electrodes and the subsequent degree of polarization which tends to reduce the output voltage as the discharge velocity increases. The greater the interfacial surface area, the greater is the maintainable discharge velocity above a given voltage, since the discharge velocity can be seen as a maximum current per unit interfacial surface area (current density). A standard nickel metal hydride cell F6, for example, can have a total of 32 or more square centimeters of interfacial area between the stacked electrodes. Polarization, which refers in general to the difference in open-circuit load voltage and closed circuit of the cell, is a function of current density and consists of three separate terms: activation polarization, ohmic polarization, polarization concentration. The activation polarization reduces the charging voltage to a given load and is an inherent function of the properties of the active materials chosen for the cell. The ohmic polarization also reduces the charging voltage at a given speed due to the collective resistance contributions of the individual cell components, connections and interfaces and can be reduced by reducing the resistivity of the individual cell components and the interfaces. Concentration polarization reduces the charging voltage due to the diffusion speed limitations of the charged ions in and out of the electrode plates at the electrolyte interface and the electrode surface and can be reduced by improving the efficiency of the electrode. electrode reaction which in turn improves the diffusion rate of charged ions within the electrode. If the capacity of the cell is determined by the amount of active material in the positive electrode, the cell is said to be of a type of positive limited electrode. The cells that are designed to produce the negative active material first are called negative limited electrodes. The nickel-metal hydride cells, for example, are of limited positive electrode due to the reduced probability of overpressurization if the cell is overloaded. As the cell is charged, oxygen is generated on the surface of the positive electrode of nickel hydroxide and subsequently reduced by the negative electrode of metal hydride. If the positive electrode is not charged before the negative electrode, hydrogen gas can form on the negative electrode, resulting in internal pressure. A typical ratio of negative to positive capacity is more than 1.6. In other words, a 650 mA-hour cell will normally contain enough negative material (eg, metal hydride alloy) to store 1,040 mA-hour of energy. Some of this excess negative capacity is lost due to the corrosion of the metal hydride alloy in the cell environment with respect to the life of the cell.

BRIEF DESCRIPTION OF THE INVENTION The invention features a sealed prismatic electrochemical cell with electrodes having porous structures filled with active material. According to one aspect of the invention, the sealed electrochemical cell includes a prismatic box defining an internal cavity, a negative electrode plate disposed within the box cavity and in dielectric communication with the box and a negative electrode plate having a porous structure disposed within the cavity of the box. The porous structure is electrically insulated from the case and the negative electrode plate and defines a principal ion flow direction. The maximum linear dimension of the porous structure in the main direction of the ionic flow is at least 20% (preferably at most 30%, more preferably 40% and more preferably between about 52 and 56%) of the linear dimension maximum of the cavity of the box in the main direction of the ion flow. In some embodiments, the overall external dimension of the box, measured in the main direction of the ion flow, is between about 2 and 8 mm (preferably between about 4 and 6 mm and more preferably about 5.6 mm). The porosity of the porous structure of the positive electrode plate is preferably between about 30 and 40% (more preferably between about 34 and 36%). In some embodiments, the positive electrode plate includes an active metal hydroxide compound containing nickel and from 0 to about 4% (in some cases, about 2% and in some other cases about 0.5%) by weight of cobalt. The cobalt may be in the form of cobalt oxide, the weight of the cobalt oxide is about 0.03 and 0.10 times the weight of the active metal hydrogen compound. The active metal hydrogen compound preferably also contains from 0 to about 8% (more preferably between about 4 and 6%, more preferably about 5%) by weight of zinc. The active metal hydroxide compound also contains in some embodiments, at least about 50% (preferably at least 55%, more preferably between about 56 and 58%) by weight of nickel. In some embodiments, the cell also contains a separator between the negative and positive electrodes, the separator has a thickness between about 0.12 and 0.20 mm. Preferred spacer materials include non-woven fabrics containing polyolefin. The separator has in some cases, an average pore size of between about 6 and 30 microns. In some embodiments, the empty volume of the separator is less than about 30% (preferably less than about 20%) of the sum of the empty volumes of the electrodes and the separator. The active metal hydroxide compound, in some embodiments, has an aggregate surface area of between about 10 and 30 square meters per gram (preferably about square meters per gram).

In a preferred configuration, the active metal hydroxide compound is spheroidal, has a derivative density (as defined by ASTM: D527-93) of between about 1.8 and 2.2 grams per cubic centimeter and has a spacing. of crystal plane D101 of less than about 100 angstroms. In some embodiments, the negative electrode plate is U-shaped having a central portion and two arms extending from the portion on opposite sides of the positive electrode plate. The central portion of the negative U-shaped electrode plate can be welded to the box. In some embodiments, the proportions of the total capacities of the positive and negative electrode plates, at a discharge rate of C / 5, to the volume of the cavity of the box may exceed approximately 100 amperes-hours per liter. Preferably, these proportions exceed approximately 150 amperes-hours per liter (more preferably approximately 250 amperes-hours per liter). According to another aspect of the invention, the sealed electrochemical cell includes a prismatic box defining an internal cavity, a negative electrode plate disposed within the cavity of the box and in electrical communication with the box and only a positive electrode plate having a single unitary porous structure disposed within the cavity of the box. The porous structure is electrically isolated from the box and the negative electrode plate defines a main ion flow direction. The maximum linear dimension of the porous structure in the main direction of the ion flow is at least 15% of the maximum linear dimension of the cavity of the box in the principal direction of the ion flow. In accordance with another aspect of the invention, a miniature electrochemical cell is provided for use in portable electronic equipment. The cell has a prismatic box defining an internal cavity with a volume of approximately 20 cubic centimeters, an external electrode disposed within the cavity of the box and an internal electrode adjacent to the external electrode. The internal and external electrodes jointly define a main direction of ionic flow, the "internal electrode has a thickness of at least 1.0 mm in the main direction of the ionic flow." Some modalities of the cell are constructed to produce a sustained electric current of at least about 80 mA (preferably, at least about 100 mA, more preferably at least about 120 mA) per square centimeter cross-sectional area of the inner electrode perpendicular to the main direction of the ion flow, at a higher voltage about 1.0 volts In some configurations, the ratio of the total capacity of each of the anode and cathode to the volume of the cavity of the box exceeds about 275 amperes-hour per liter.According to another aspect of the invention, the sealed electrochemical cell has a prismatic box with an internal cavity volume of less than approxdam With 20 cubic centimeters, the maximum linear dimension of the porous structure in the main ion flow direction is at least 20% of the maximum linear dimension of the cavity of the box in the main ion flow direction. According to yet another aspect, a nickel electrode plate is provided for use in a nickel metal hydride electrochemical cell. The plate contains a porous metal substrate and a metal hydroxide compound disposed within the cavities of the substrate. The compound is of spherical powder form and has at least 50% nickel in the form of nickel hydroxide. The plate has a thickness of approximately 0.5 and 3 mm and a total volumetric capacity of at least 560 amperes-hour per liter. According to yet another aspect, a metal hydride electrode plate is provided for use in a nickel metal hydride electrochemical cell. The plate contains a porous metal substrate and a nickel metal hydride compound disposed within the cavities of the substrate. The plate has a thickness between approximately 0.5 and 3 mm and a total theoretical volumetric capacity of at least 1000 amperes per hour per liter. Several aspects of the construction of the electrode and the cell together allow high internal current densities (and resulting discharge velocities) while obtaining a very high capacity. Several implementations of the invention can provide an electrochemical cell with a very low percentage of internal volume absorbed by the inactive materials, such as interconnecting tabs and multiple spacer layers, leaving a high percentage of internal volume for the active material. The simple construction of the cell can also provide efficient and inexpensive manufacturing and assembly that can result in minimal waste and low cost. The invention can provide high energy densities, in particular for rechargeable applications that do not require extremely high discharge speeds. In addition, the maximum internally limited discharge velocity can help protect the battery against overheating if it is externally short-circuited. Other advantages and modalities will be apparent from the following description of the drawings and the claims.BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a prismatic electrochemical cell. Fig. 2 is a sectional view of the cell of Fig. 1 showing an electrode configuration. Figure 2A is an enlarged view of area 2A in Figure 2. Figure 3 is a view of a spherical metal hydroxide alloy powder expanded to 4000 X. Figure 3A is a view of the powder of Figure 3 enlarged to 10,000 X.

Fig. 3B is a view of the powder of Fig. 3 enlarged 10,000 X. Figs. 4A-4F sequentially illustrate the production of a positive electrode plate. Figures 5A-5D sequentially illustrate the production of a negative electrode plate. Figures 6A-6C illustrate other electrode configurations.

DESCRIPTION OF THE MODALITIES With reference to Figure 1, a rechargeable cell 10 of miniature prismatic metal nickel hydride has a rectangular tin or box 12 of cold rolled steel, nickel coated, stamped or stretched as is known in the art. Cell 10 is of size F6 used in some portable communications equipment, having an overall length L of between about 48 to 50 mm, a width W of between 15 and 16 mm and an overall thickness T of about 5.6 millimeters. Due to its thickness, an array of such cells can be packed into devices such as thin portable phones and computer equipment. The thickness of the cell 10 is preferably about 2 to 8 mm, more preferably between about 4 and 6 mm. Referring also to Figure 2, one end of the box 10 is solid, while the other is capped with a cover assembly 14 that includes a cover plate 16 and to which a contact button 18 is attached. The lid plate 16 is laser welded to the lid 12 along the seam joint 20, such that the entire battery is sealed. The cavity inside the can 12 has an overall cavity thickness tc of about 4.6 mm. The main ionic flow direction (ie, the normal direction to the interelectrode interface between opposing electrode surfaces) is indicated by the arrow P. Also with reference to FIG. 2A, the contact button 18 is welded to a rivet 24 which is sealed to and electrically isolated from the lid plate 16 by a nylon seal 22. The seal 22 sits within a recess in the plate 16 and is held in place by the rivet 24, which also retains a tongue. metal 26. The rivet 24 and the tongue 16 are electrically isolated from the lid plate 16 by the seal 22 and an inner insulator 27. The contact button 18 is in electrical contact with the positive electrode 28 of the cell by means of the tongue 26; the negative electrode 30 is in electrical contact with the walls of the can 12. When an external electric charge is applied between the button 12 and the can 20, there is an internal flow of charged ions between the positive and negative electrodes and an electric current external is produced through the load. The positive electrode 28 is electrically isolated from the negative electrode 30 by a thin separator 32 in the form of a pocket enclosing the positive electrode. The separator 32 is made of a non-woven polyolefin material and can be produced either by dry laying or wet laying methods known in the non-woven fabric art. The separator 32 is preferably treated on its surface to improve its weather resistance in aqueous electrolytes. The material of the separator is either wrapped around the positive electrode or formed in a sealed bag, sealed to avoid electrical conduction between the positive electrode 28 and the negative electrode 30 and the can 12. The positive electrode 28 consists of a three-dimensional porous metal substrate such as a foam or metal felt, which has been filled with an active material containing a metal hydroxide compound in the form of a spherical powder. The active compound contains at least about 50% by weight of nickel (preferably more than about 55% and more preferably between 56 and 58%) in the form of nickel hydroxide, to which cobalt and zinc have been coprecipitated to form part of the crosslinked metal hydroxide. The maximum linear dimension of the porous structure of the cathode is illustrated by the dimension tp +.

With reference to Figures 3, 3A and 3B, the active material is formulated specifically to provide a high rate of diffusion of hydrogen protons in and out of the spherical metal hydroxide powder. The metal hydroxide is in the form of small crystallites 34 which together form substantially spherical particles 36 with an average particle diameter of about 10 to 15 microns and an aggregate surface area of about 14 square meters per gram. To reduce the required proton diffusion depth to the crystallites, the crystalline plane spacing of 101 is maintained at less than about 100 angstroms. In addition, the metal hydroxide crosslinked contains from 0 to about 4% by weight of cobalt and from 0 to 8% by weight of zinc. By increasing the cobalt in the hydroxide lattice beyond about 4%, the discharge potential of the cell can be reduced and the overall capacity can be reduced by displacing the nickel in the lattice. The addition of zinc helps control the swelling or expansion of nickel hydroxide during cycles by preventing the formation of low density gamma-phase nickel oxyhydroxide and the subsequent hydration of hydroxide, which can consume water from the electrolyte and reduce the capacity with the passage of time. Suitable spherical metal hydroxide powders include TANAKA Chemical Type ZD, available from Sumitomo Corporation of America in Atlanta, Georgia. In addition to the cobalt in the active metal hydroxide compound, the positive electrode contains cobalt in the form of cobalt oxide. Preferably, the weight of cobalt oxide in the positive electrode plate is between about 0.03 and 0.10 times the weight of the active metal hydroxide compound and is evenly distributed among the hydroxide particles to minimize the contact resistance during the cycles. The average particle size of the cobalt oxide is between about 0.5 and 2.5 microns. The cobalt oxide is preferably mixed with the metal hydroxide, a crosslinking agent such as 0.3 to 0.7% by weight of tetrafluoroethylene or a hydrocarbon binder and 0.3 to 0.4% by weight of the thickening agent, such as carboxymethylcellulose (CMC) or Sodium polyacrylate (SPA) before filling the electrode. Figures 4A to 4F illustrate the production of the positive electrode 28 shown in Figure 2. Prior to filling, the nickel foam substrate 38 of the electrode is preferably more than 90% porous, more preferably more than 99% porous, has a basis weight of between 500 and 600 grams per square meter and is approximately 2.3 mm in thickness (Figure 4A). The pore density of the metal foam is 80 to 110 pores per inch. In order to ensure proper packing efficiency of the dry powder, the bypass density of the metal hydroxide powder is between 1.8 and 2.2 grams per cubic centimeter. The powder is applied to the foam as an aqueous suspension, as is known in the art. Once the metal foam is full and the water separated by drying, the active material is removed from a narrow region 40 through the center of the plate (Figure 4B), such as by ultrasonic vibration with a gas flow to separate the loosened powder, leaving the region 40 essentially free of particulate material. Then the region 40 is reinforced with a strip of 1.5 to 2.0 mm thick foam or light felt, which is placed on the region 40 before calendering. Then the plate is calendered to a thickness of about 1.28 to 1.32 millimeters, cut to width and scorched along the center of the cleared region 40 (Figure 4C). Calendering densifies the plate by removing excess space and improves electrical contact between the particles and between the active material and the substrate. In addition, the calendering process coats the central region 40, improving the contact between the substrate and the reinforcing strip and producing a metal region of dense substrate. As it is calendered, the plate has a total theoretical volumetric capacity, based on the amount of active material contained therein, of approximately 600 amperes-hour per liter. The calendered plate is folded along the slagging line, such that the reinforcing strip is inside the fold and the rinsed metal area is compressed to produce a highly dense edge 42 of clean nickel with a wc width of about 0.2 mm (figure 4D). After folding, the plate is cut to form several individual electrode plates of approximately 4 to 4.3 millimeters in length, approximately 1.45 millimeters in width (Figure 4E) and an overall thickness tp + of approximately 2.60 to 2.66 millimeters (Figure 2). To ensure that there is no blockage of the vent hole in the assembled cell, a central notch 44 is cut into the rinsed edge of the final plate (Figure 4F). Figures 5A to 5D illustrate the formation of negative electrode 30 (Figure 2). A substrate 44 of porous nickel felt or foam about 2 millimeters thick and a basis weight of about 400 to 550 grams / cm 2 (FIG. 5A) is filled with an active nickel metal hydride alloy powder and a charcoal. high surface area, preferably as an aqueous suspension. The carbon improves the conductivity of the electrode and helps in the recombination of the oxygen during the overload. As described above with reference to the positive electrode, a PTFE binder and CMC or SPA thickeners are added to improve processability. After drying of the filled plate, the aggregate materials are separated from a central portion 46 of 3 to 5 millimeters in width of the plate (Figure 5B). The clearance of the central portion 46 helps prevent the cracking of the negative electrode as it is bent around the positive electrode. Such cracking can result in electrical discontinuity. Optionally, a separate strip of empty nickel foam can be added to the central portion 46 to improve its strength and conductivity. Then the full plate is densified by calendering to a thickness of approximately 0.9 to 0.95 millimeters and cut into several individual negative electrode plates sized to fit inside the battery case (figure 5C). As they are calendered, the plates have a total theoretical volumetric capacity, based on the amount of active material contained therein of approximately 1190 amperes-hour per liter. Each final negative electrode plate has a width Wp_ of about 1.5 millimeters and a total length Lp_ of about 8.2 to 8.7 millimeters. The finished negative electrode can be either wrapped around the positive electrode before it is inserted into the can or can be bent and press fit into the can 12 itself. During the cycles, the thickness of the electrode stack increases slightly due to swelling, thus reducing the contact resistance with the can. Optionally, the central portion of the negative electrode can be welded, such as by resistance or laser welding, to the bottom of the can (Figure 5D) to increase the conductivity. Referring again to Figure 2, with the negative electrode 30 mounted to the can 12, the positive electrode 28 is welded to the tongue 26 of the lid assembly 14 (before joining the contact button 18), surrounded by the bag 32 of the separator and inserted in the can 12 between the opposite sides of the positive electrode 30. Then the lid assembly 14 is welded to the can 12 around the seam 20 (Figure 1). After welding the assembly or lid assembly of the can, approximately 1.2 to 1.3 cubic centimeters of electrolyte are added to the cell, by a vacuum filling process, by means of a hole through the rivet 24 of the lid assembly . The electrolyte is mainly an alkaline salt of potassium hydroxide dissolved in distilled deionized water. Optionally, small amounts of lithium hydroxide and / or sodium hydroxide may also be added. Just before the electrolyte is added to fill the remaining gaps in the electrode plates and the separate one and to compensate for the hydration of the cobalt in the positive electrode (that is, the "exhausted" type cell). A recyclable rubber pressure vent 48 is placed inside the contact button 18, which is then welded on the base of the rivet 24 to complete the sealing of the cell. A remarkable feature of the cell 10 of the construction described above and the arrangement of the electrodes 28 and 30, which allows a very high proportion of the internal volume of the cell to be used by the active materials. The thickness of each electrode plate is of a high percentage of the thickness tc of the total cavity of the cell, thereby reducing the need for inactive materials such as spacers and tabs. For example, the ratio of the thickness of the central electrode to the thickness of the cavity is approximately 0.55 and the ratio of the thickness of the external electrode to the thickness of the cavity is approximately 0.2. In addition, the capacity ratio of negative to positive is only between 1.35 to 1.45 (preferably about 1.4). This lower capacity ratio allows an increase in total capacity and energy density in that it provides sufficient excess metal hydride to avoid excessive pressure during overload. The resulting cell is I especially suitable for use in applications in which the capacity is determined to be a more significant motivation than the cycle life in excess of 200 full discharge cycles at room temperature. The construction of the electrode plates helps to reduce the effects of polarization by diffusion that would be expected with such thick electrode design. For example, the final porosity of both electrode plates, after filling and calendering, is between about 35 and 40%. This, combined with the thickness of the separator 32, means that a significant portion of the electrolyte is contained within the electrode plates, improving diffusion of the proton on the surface of the particles of the active material. Only about 18% of the electrolyte is contained within the separator, the other 82% are contained within the electrodes, as calculated by the proportion of their empty volumes. In addition, the crystalline structure of the active material, discussed above with reference to Figure 3, helps to improve the diffusion of the proton. The resulting high diffusivity allows higher current densities with thick electrode plates and no unacceptable voltage surges, thus allowing higher net currents to be produced from a cell with a relatively small amount of interfacial surface area. For example, the cell mode discussed above has an energy density (ie, minimum ratio of electrode capacity to cavity volume) of about 330 Watts-hours per liter of internal cell volume and is capable of generating a density of current of more than about 50 milliamps per square centimeter of interfacial area at a voltage greater than 1 volt, with a central electrode thickness of approximately 2.6 millimeters. In terms of gravimetric energy density, the cell is able to produce approximately 62 Watts-hour per kilogram of cell mass. Cell 10 of Figure 2 has a one-piece positive electrode 28 and a one-piece negative electrode 30. Some other configurations are illustrated in Figures 6A and 6B. For example, the positive electrode of cell 70 in Figure 6A consists of two separately formed plates 72a and 72b which are each welded to a common tab 74. This configuration can be useful to prevent separation and folding of the central electrode. In Figure 6B, cell 76 has two separate negative electrode plates 78a and 78b, each in electrical contact with can 80. In another embodiment (not shown), the two-piece positive electrode configuration of Figure 6A is combined with the two-piece negative electrode configuration of Figure 6B. In still other modalities, the negative electrode (metal hydride) is placed in the center of the cell and the positive electrode (nickel) is positioned near the walls of the can, although the negative electrode / can interface of the cell Figure 2 provides additional area for gas recombination during overload. A positive electrode configured to be the external electrode would be about half the thickness of the same electrode configured to be the internal electrode. With the addition of a layer of electrically insulating material between the can and the external electrode, the electrode in the center of the cell can be in electrical communication with the can. Figure 6C illustrates another embodiment of a cell 82 with a coarse one-piece internal electrode 84 and a one-piece coarse external electrode 86, folded to overlap each other to increase the interfacial area between the electrodes. In cell 82, the inner electrode 84 is U-shaped and the outer electrode 86 is W-shaped, with the two arms of the inner electrode 84 extending to the two enclosures or cavities formed by the external electrode 86. Each The inner electrode arm is contained within a separator bag 88 for electrically isolating one electrode from the other. Alternatively, a single separating sheet, wider than the inner electrode can be folded around the inner electrode to isolate it from the external electrode and the can. Compared to the configurations of Fig. 6A and 6B, this electrode configuration allows a higher discharge velocity capacity insofar as it has minimal impact on the overall capacity of the cell. The main direction of the ion flow between the electrodes is indicated by the arrow P in figures 2 and 6A-6C. This direction is normal to the inter-electrode interface between the opposing electrode surfaces. In all the illustrated modes, the main direction of the ion flow is normal to the wider faces of the can. The maximum linear dimension of the porous structure of the cathode, in each case, is illustrated by the dimension tp_. Other embodiments and features are also within the scope of the following claims. It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention is the conventional one for the manufacture of the objects to which it refers.

Claims (43)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A sealed electrochemical cell, characterized in that it comprises: a prismatic box defining a cavity thereof; a negative electrode plate disposed within the cavity of the box and in electrical communication with the box; a positive electrode plate comprising a porous structure disposed within the cavity of the box, the porous structure being electrically isolated from the box and the negative electrode plate and defining a main ion flow direction; The maximum linear dimension of the porous structure and the main direction of the ion flow is at least 20% of the maximum linear dimension of the cavity of the box in the principal direction of the ion flow.
2. 2. The cell in accordance with the claim 1, characterized in that the maximum linear dimension of the porous structure in the main ion flow direction is at least 30% of the maximum linear dimension of the cavity of the box in the main ion flow direction.
3. The cell according to claim 1, characterized in that the maximum linear dimension of the porous structure in the main ion flow direction is at least 40% of the maximum linear dimension of the cavity of the box in the main direction of the ionic flow.
4. The cell according to claim 1, characterized in that the maximum linear dimension of the porous structure in the main direction of the ion flow is between 52 and 56% of the maximum linear dimension of the cavity of the box in the main direction of the ionic flow.
5. The cell according to claim 1, characterized in that the box has an overall external dimension, measured in the main direction of ionic flux, of between about 2 and 8 millimeters.
6. 6. The cell in accordance with the claim 5, characterized in that the overall external dimension is between approximately 4 and 6 millimeters.
7. 7. The cell in accordance with the claim 6, characterized in that the overall external dimension is approximately 5.6 millimeters.
8. The cell according to claim 1, characterized in that the porosity of the porous structure of the positive electrode plate is between about 30 and 40%.
9. The cell according to claim 8, characterized in that the porosity of the porous structure of the positive electrode plate is between about 34 and 36%.
10. 10. The cell in accordance with the claim I, characterized in that the positive electrode plate comprises an active metal hydrogen compound comprising nickel and from 0 to about 4% by weight of cobalt.
11. The cell according to claim 10, characterized in that the active metal hydroxide compound comprises approximately 2% by weight of cobalt.
12. 12. The cell in accordance with the claim II, characterized in that the active metal hydroxide compound comprises approximately 0.5% by weight of cobalt.
13. 13. The cell according to claim 10, characterized in that the cobalt is in the form of cobalt oxide, the weight of the cobalt oxide is between about 0.03 and 0.10 times the weight of the active metal hydroxide compound.
14. The cell according to claim 10, characterized in that the active metal hydroxide compound further comprises from 0 to about 8% by weight of zinc.
15. 15. The cell in accordance with the claim 14, characterized in that the active metal hydroxide compound comprises between about 4 and 6% by weight of zinc.
16. 16. The cell in accordance with the claim 15, characterized in that the active metal hydroxide compound comprises about 5% by weight of zinc.
17. 17. The cell according to claim 10, characterized in that the active metal hydroxide compound comprises at least about 50% by weight of nickel.
18. 18. The cell in accordance with the claim 17, characterized in that the active metal hydroxide compound comprises at least about 55% by weight of nickel.
19. 19. The cell in accordance with the claim 18, characterized in that the active metal hydroxide compound comprises between about 56 and 58% by weight of nickel.
20. 20. The cell according to claim 1, characterized in that it further comprises a separator disposed between the negative and positive electrodes, the separator has a thickness between approximately 0.12 and 0.20 millimeters.
21. 21. The cell according to claim 20, characterized in that the separator comprises a nonwoven fabric containing polyolefin.
22. 22. The cell according to claim 20, characterized in that the separator has an average pore size between about 6 and 30 microns.
23. 23. The cell according to claim 10, characterized in that the positive electrode, the negative electrode and the separator each have a corresponding void volume, the empty volume of the separator is less than about 30% of the sum of the empty volumes of both electrodes and the separator.
24. 24. The cell according to claim 23, characterized in that the empty volume of the separator is less than about 20% of the. sum of the empty volumes of both electrodes and the separator.
25. 25. The cell according to claim 10, characterized in that the active metal hydroxide compound has an aggregate surface area of between about 10 and 30 square meters per gram.
26. 26. The cell according to claim 25, characterized in that the active metal hydroxide compound has an aggregate surface area of about 15 square meters per gram.
27. 27. The cell according to claim 25, characterized in that the active metal hydroxide compound is spheroidal.
28. 28. The cell according to claim 25, characterized in that the active metal hydroxide compound has a derivatization density of between about 1.8 and 2.2 grams per cubic centimeter.
29. 29. The cell according to claim 25, characterized in that the active metal hydroxide compound has a crystallite plane spacing D101 of less than about 100 angstroms.
30. 30. The cell according to claim 1, characterized in that the negative electrode plate is U-shaped, has a central portion and two arms extending from the central portion on opposite sides of the positive electrode plate.
31. 31. The cell according to claim 30, characterized in that the central portion of the negative electrode plate is welded to the box.
32. 32. The cell according to claim 1, characterized in that the proportions of the total capacities of both positive and negative electrode plates, at a discharge speed of C / 5 to the volume of the cavity of the box, exceed each of approximately 100 amperes-hour per liter.
33. 33. The cell according to claim 32, characterized in that said proportions exceed about 150 amp-hours per liter.
34. 34. The cell in accordance with the claim 33, characterized in that such proportions exceed about 250 amperes-hour per liter.
35. 35. A sealed electrochemical cell, characterized in that it comprises: a prismatic box defining a cavity therein; a negative electrode plate disposed within the cavity of the box and in electrical communication with the box and only a positive electrode plate comprising only a unitary porous structure disposed within the cavity of the box, the porous structure being electrically isolated from the box and the negative electrode plate define a principal direction of ion flow; The maximum linear dimension of the porous structure in the main ion flow direction is at least 15% of the maximum linear dimension of the cavity of the box in the main ion flow direction.
36. 36. A miniature electrochemical cell for use in portable electronic equipment, the cell is characterized in that it comprises: a prismatic box that defines an internal cavity with a volume of approximately 20 cubic centimeters; an external electrode disposed within the cavity of the box and an internal electrode adjacent to the external electrode, the internal and external electrodes jointly define a main direction of ionic flow; the internal electrode has a thickness of at least 1.0 millimeters in the main direction of ionic flow.
37. 37. The electrochemical cell according to claim 36, characterized in that the internal electrode has a cross-sectional area perpendicular to the main direction of ionic flow, the cell is constructed to produce a sustained electric current of at least about 80 milliamperes per centimeter square of the cross-sectional area of the internal electrode at a voltage greater than about 1.0 volts.
38. 38. The electrochemical cell according to claim 37, characterized in that it is constructed to produce a sustained electric current of at least about 100 milliamperes per square centimeter cross-sectional area of the internal electrode at a voltage greater than about 1.0 volts.
39. 39. The electrochemical cell according to claim 38, characterized in that it is constructed to produce a sustained electric current of at least about 120 milliamperes per square centimeter of the cross-sectional area of the internal electrode at a voltage greater than about 1.0 volts.
40. 40. The cell in accordance with the claim 36, characterized in that the proportion of the total capacity of each of the anode and cathode to the volume of the cavity of the box exceeds approximately 275 amperes-hour per liter.
41. 41. A sealed electrochemical cell, characterized in that it comprises: a prismatic box defining a cavity therein, the cavity has a volume of less than about 20 cubic centimeters; a negative electrode plate disposed within the cavity of the box and in electrical communication with the box and a positive electrode plate comprising a porous structure disposed within the cavity of the box, the porous structure being electrically isolated from the box and the negative electrode plate and defines a principal direction of ionic flow; The maximum linear dimension of the porous structure in the main direction of the ion flow is at least 20% of the maximum linear dimension of the cavity of the box and the main direction of the ion flow.
42. 42. A nickel electrode plate for use in a nickel metal hydride electrochemical cell, the plate is characterized in that it comprises: a porous metal substrate defining cavities therein and a composite metal hydroxide compound within the cavities of the nickel metal hydride. substrate, the compound is of spherical powder form and comprises at least 50% nickel in the form of nickel hydroxide; The plate has a thickness between approximately 0.5 and 3 millimeters and a total volumetric capacity of at least 560 amperes per hour.
43. 43. A metal hydride electrode plate for use in an electrochemical cell, nickel metal hydride, the plate is characterized in that it comprises: a porous metal substrate defining cavities therein and a nickel metal hydride compound composed within the cavities of the substrate; the plate has a thickness of between

    0. 5 and 3 millimeters and a total theoretical volumetric capacity of at least 1000 amp-hours per liter.