Abstract:
A winding assembly including positive and negative electrodes and a separator sheet wound in an overlying relationship such that the separator sheet is positioned between the positive and negative electrodes, and such that an exposed edge of the positive electrode is spaced longitudinally from an unexposed edge of the negative electrode at one end, and such that an exposed edge region of the negative electrode is spaced longitudinally from an unexposed edge of the positive electrode at an opposite end, and wherein a portion of the positive electrode proximate to the exposed edge of the positive electrode comprises a first plurality of apertures and a portion of the negative electrode proximate to the exposed edge of the negative electrode comprises a second plurality apertures.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to co-pending to U.S. provisional application No. 61/499,828, filed 22 Jun. 2011, entitled “WINDING ASSEMBLY FOR ELECTROCHEMICAL CELLS, METHODS OF MAKING THE WINDING ASSEMBLY, AND THE ELECTROCHEMICAL CELL”, which is entirely incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates general to winding assemblies for electrochemical cells, methods of making the winding assembly and electrochemical cells, and more particularly to winding assemblies for high performance lead-acid electrochemical cells and batteries. 
       BACKGROUND OF THE INVENTION 
       [0003]    The need for improvements in lead-acid storage batteries is widely recognized. One example of a use in which a better battery is needed is in Hybrid Electric Vehicles (HEVs). A hybrid car may obtain up to 50 miles per gallon using the combination of gasoline and electric motors. The battery packs used in current commercially available hybrid cars such Prius sold by Toyota Motors Corporation are based on nickel-metal hydride chemistries and are expensive. 
         [0004]    Accordingly, a continual need exists for improved electrochemical cells for high performance battery applications. 
       SUMMARY OF THE INVENTION 
       [0005]    Disclosed herein are winding assemblies for electrochemical cells, methods of making the winding assembly and electrochemical cells. In embodiments, the winding assemblies can be used in high performance lead-acid electrochemical cells and batteries. 
         [0006]    In one embodiment, a winding assembly for an electrochemical cell, comprises a positive electrode; a negative electrode; a separator sheet, wherein the positive and negative electrodes and the separator sheet are wound in overlying relationship such that the separator sheet is positioned between the positive and negative electrodes, and such that an exposed edge of the positive electrode is spaced longitudinally from an unexposed edge of the negative electrode at one end, and such that an exposed edge region of the negative electrode is spaced longitudinally from an unexposed edge of the positive electrode at an opposite end, and wherein a portion of the positive electrode proximate to the exposed edge of the positive electrode comprises a first plurality of apertures and a portion of the negative electrode proximate to the exposed edge of the negative electrode comprises a second plurality apertures; a first current collector connected to the exposed edge of the positive electrode; and a second current collector connected to the exposed edge of the negative electrode. 
         [0007]    In one embodiment, an electrochemical cell, comprises a generally cylindrical container; a liquid acid electrolyte disposed in the generally cylindrical container; a winding assembly disposed in the generally cylindrical container, wherein the winding assembly comprises a positive electrode comprising a lead and a positive electrode active material disposed in a first plurality of grid openings; a negative electrode comprising lead and a negative electrode active material disposed in a second plurality of grid openings; a separator sheet, wherein the positive and negative electrodes and the separator sheet are wound in overlying relationship such that the separator sheet is positioned between the positive and negative electrodes, and such that an exposed edge of the positive electrode is spaced longitudinally from an unexposed edge of the negative electrode at one end, and such that an exposed edge region of the negative electrode is spaced longitudinally from an unexposed edge of the positive electrode at an opposite end, and wherein a portion of the positive electrode proximate to the exposed edge of the positive electrode comprises a first plurality apertures and a portion of the negative electrode proximate to the exposed edge of the negative electrode comprises a second plurality apertures; a first current collector connected to the exposed edge of the positive electrode, wherein the first current collector is void of apertures; and a second current collector connected to the exposed edge of the negative electrode, wherein a the second current collector is void of apertures. 
         [0008]    In one embodiment, a method of making a winding assembly for an electrochemical cell, comprises winding a positive and negative electrodes with a separator sheet in overlying relationship such that the separator sheet is positioned between the positive and negative electrode, and such that an exposed edge of the positive electrode is spaced longitudinally from an unexposed edge of the negative electrode at one end, and such that an exposed edge region of the negative electrode is spaced longitudinally from an unexposed edge of the positive electrode at an opposite end, and wherein a portion of the positive electrode proximate to the exposed edge of the positive electrode comprises a first plurality of apertures and a portion of the negative electrode proximate to the exposed edge of the negative electrode comprises a second plurality of apertures; casting a first current collector onto the exposed edge of the positive electrode; and casting a second current collector onto the exposed edge of the negative electrode. 
         [0009]    The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawing, and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Referring now to the figures, which are exemplary embodiments, and wherein like elements are numbered alike: 
           [0011]      FIG. 1  is front perspective view of an embodiment of an electrochemical cell; 
           [0012]      FIG. 2  is a cross sectional view of the electrochemical cell of  FIG. 1 ; 
           [0013]      FIG. 3  is a partial exploded view of the electrochemical cell of  FIG. 1 ; and 
           [0014]      FIG. 4  is detailed partial prospective of the winding assembly of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIGS. 1-3  illustrate one embodiment of an electrochemical cell  10 . The electrochemical cell  10  includes a container  12  having a first cover  14  and a second cover  16 . The container  12  is illustrated as having a generally cylindrical shape, but other shapes are envisioned (e.g., oval, elliptical). The first cover  14  and the second cover  16  can be affixed to the container by any suitable means. In one embodiment, the first cover  14  and the second cover  16  are ultrasonically welded or adhesively bonded to the container  12 . The container  12 , the first cover  14  and the second cover  16  comprise a material that is electrically insulative material. Examples of electrically insulative materials included, but are not limited to a polymeric material (e.g., polycarbonate, acrylonitrile-butadiene-styrene, and blends and copolymers of the foregoing) and polymer lined metals. 
         [0016]    In one embodiment, as illustrated, the electrochemical cell  10  is a valve-regulated lead-acid (VRLA) design comprising a valve  18  (e.g., a Bunsen valve). The valve  18  can be disposed in an opening formed in the container  12 , the first cover  14  and/or the second cover  16 . For ease in manufacturing, there may be advantages of disposing the valve  18  in one of the first cover  14  or the second cover  16 . The valve  18  comprises an electrically insulative material such as a polymeric material (e.g., ethylene propylene diene Monomer (EPDM) or neoprene rubber). 
         [0017]    Metal inserts  20  and  22  with male or female threads are respectively disposed through an opening the first cover  14  and the second cover  16 . The placement of the respective metal inserts  20  and  22  within the first cover  14  and the second cover  16  can vary depending on the desired application. The respective metal inserts  20  and  22  can be placed in the same or different relative location within the first cover  14  and the second cover  16 . The respective metal inserts  20  and  22  are in electrical communication with respective first current collector  24  and second current collector  26 . In one embodiment, the metal inserts  20  and  22  are non-lead to prevent the metal inserts from easily being bent or otherwise being damaged. The metal inserts  20  and  22  facilitate the connection of multiple cells to form a battery (not shown). Suitable materials for the metal inserts  20  and  22  include, but are not limited to, copper, brass and copper containing alloys. 
         [0018]    In one embodiment, a winding assembly (sometimes referred to in the art as a “jelly roll”), generally designated  50 , is disposed within the container  12 . The winding assembly  50  has a size and shape generally corresponding to the size and shape of the container  12 . A positive electrode  30  and a negative electrode  32  are disposed in a disposed in a circumferentially wound configuration about an axis in which they are separated from direct contact with one another by separators  36  and  38 . As used herein, the term “circumferentially wound” in reference to one or more layers means that the layer defines a path about a central axis in which, for a given angle relative to an imaginary baseline that extends normal to the axis, subsequent layers increase in distance from the axis. The term is intended to include non-circular spiral paths, such as those in which the path formed by a layer is generally elliptical, oblong or oval in shape, as well as spiral paths in which a circumferentially wound circular, elliptical or oval shape is flattened somewhat, such as by the application of pressure from opposite sides. 
         [0019]    The positive electrode  30  and the negative electrode  32  each comprise a plurality of apertures adapted to receive an active material paste. The choice of the active material can vary depending on the application. Suitable active materials include sulfated lead oxides pasted used in both the positive electrode  30  and the negative electrode  32 . 
         [0020]    The thickness of the positive electrode  30  and negative electrode  32  can vary depending on the power density of the battery. For example, for high power density applications, it is desirous to make the positive electrode  30  and the negative electrode  32  as thin as manufacturing capabilities will allow. In one specific embodiment, the positive electrode  30  and the negative electrode  32  are made using ultra-thin grids. The term “ultra-thin” used in reference to the girds refers to a grid having a nominal thickness of less than 0.60 millimeters (mm), specifically, 0.3 mm to 0.6 mm. 
         [0021]    The materials for the positive electrode  30  and negative electrode  32  are selected such that they have the capacity to exhibit the desired electrochemical relationship for the generation of electric power. Similarly, the materials for the separators  36 ,  38  are selected to enhance this electrochemical relationship. The materials for positive electrode  30  and negative electrode  32  and the separators  36 ,  38  are selected to have a sufficient flexibility and toughness to be successfully circumferentially wound and further processed into the desired shape. Exemplary materials for the positive electrode  30  grid materials include lead-containing materials, such as lead alloys. As used herein, “lead-containing material” means that the material contains at least 50 percent lead by weight; preferred lead-containing materials include at least 70 percent lead by weight. Exemplary materials for the negative electrode  32  grid materials include lead-containing materials such as lead alloys. Exemplary materials for the separators  36 ,  38  include glass microfibers and organic particularly polymeric materials. 
         [0022]    As illustrated in  FIG. 4 , the positive electrode  30  and negative electrode  32  are circumferentially wound such that a top edge of the positive electrode is longitudinally spaced from the top edge of the negative electrode  32 . Similarly, the bottom edge of the negative electrode  32  is longitudinally spaced from the bottom edge of the positive electrode  30 . In this configuration, the top edge of the positive electrode  30  is available for electrical communication with first current collector  24  without the negative electrode  32  being in electrical communication therewith. Similarly, the negative electrode  32  can be in electrical communication with second current collector  26  without the second current collector  26  being in electrical communication with the positive electrode  30 . 
         [0023]    In one embodiment, the positive electrode  30  and the negative electrode  32  each includes a region exposed from the covering of the separators  36 ,  38  having a respective plurality of apertures  28  adapted to allow electrolyte to flow there-through during a filling operation. The apertures  28  can comprise any number of shapes and sizing including round, square, rectangle, triangle, U-shaped, V-shaped, and X-shaped. The apertures  28  advantageously allow the first current collector and second current collector to be cast-on ends of the winding assembly  50 , which can allow for speed in manufacturing production. 
         [0024]    In one embodiment, the first current collector  24  and the second current collector  26  are each void of apertures. Without wanting to be bound by theory, it is believed that by having a greater surface of the respective current collector in physical and electrical communication with the edge of a given electrode, higher charging and discharging can be achieved compared to designs with apertures. Furthermore, manufacturing advantages can be obtained by not having to weld the current collector onto the edge of the electrode. 
         [0025]    Embodiments disclosed herein advantageously can be used to produce high power density electrochemical cells and batteries. Further, location of apertures in an exposed region of the electrode advantageously allows for ease in manufacturing of the electrochemical cell, which helps in filing the long felt need for lower cost batteries for Hybrid Electric Vehicles (HEVs) applications, for example. 
         [0026]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.