Abstract:
A battery plate for a lead acid battery includes a grid having a plurality of interconnected wires, an electro-chemically active material paste applied to the grid, at least one reinforcing member disposed in the paste, and the paste is cured. Preferably the reinforcing member is embedded in the active material, provides structural support for the active material and reduces the likelihood that in use the active material paste will shed from the grid.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuing application of copending application, Ser. No. 10/626,961, filed on Jul. 25, 2003, the benefit of which is claimed under 35 U.S.C. 120 and the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates generally to lead acid batteries, and more particularly to plates for these batteries. 
       BACKGROUND OF THE INVENTION 
       [0003]    Lead acid batteries include battery plates composed of a grid and active material applied to the grid. Typical lead acid battery grids are formed by casting, stamping or punching and have a reticulated framework including a plurality of spaced apart longitudinally extending wires that are interconnected by a plurality of wires extending transversely thereto. The wires define a grid having open spaces between adjacent portions of the wires. The grid is usually “over pasted” so that the wires are completely embedded in and surrounded by the paste, and the paste fills the open spaces between the wires. 
         [0004]    Common failure modes of lead acid batteries include corrosion of the positive grid, shedding of the paste from the surface of the positive plate, and shrinkage of the paste from the negative grid wires. One form of paste shedding from the positive plate is the paste shedding off the surface of the positive plate during cycling of the battery. While both the paste and the grid may still be useable after such shedding, during cycling when the positive grid grows or expands, the paste may shed off the surface of the plate and this causes a reduction in performance of the battery which will in time cause the battery to fail to meet performance ratings in laboratory tests, and will also cause early failure in service. One form of paste shrinkage in the negative plate is the paste shrinking away from the negative grid wires which causes the paste to lose contact with the negative wires, and the battery will fail to make performance ratings and can also cause early failure in service. 
       SUMMARY OF THE INVENTION 
       [0005]    A battery plate for a lead acid battery includes a grid having a plurality of interconnected wires, an electro-chemically active material paste applied to the grid, and at least one reinforcing member disposed in the paste. In the presently preferred embodiment, the reinforcing member is embedded in the paste, provides structural support for the paste and reduces the likelihood that paste will shed or shrink from the grid. 
         [0006]    In one form, the reinforcing member is a thin sheet of material that includes glass fibers. This sheet of material can be incorporated into the battery plate before or after the paste has been applied to the grid. If the sheet of material is applied to the plate after the paste has been applied to the grid, rollers may be used to press the sheet of material into the paste. Preferably, the sheet of material is fully embedded in the paste, and is permeable so that the paste may flow through the sheet of material. 
         [0007]    Some of the objects, features and advantages of the invention include providing a battery plate for a lead acid battery that reduces shedding and shrinkage of paste from battery grids, improves the performance of battery grids, improves the durability, reliability and average useful life of batteries incorporating the plates, can be manufactured with limited additional cost compared to conventional batteries, can be manufactured with existing tooling and machinery, and is of relatively simple design and economical manufacture and assembly. Of course, battery plates embodying the present invention may achieve some, all, different or none of these advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments, appended claims and accompanying drawings in which: 
           [0009]      FIG. 1  is a perspective view partially in section of a lead acid battery; 
           [0010]      FIG. 2  is a plan view of a grid for a battery plate of the lead acid battery; 
           [0011]      FIG. 3  is a fragmentary cross-sectional view of the battery grid of  FIG. 2  including a reinforcing member disposed adjacent to one face of the battery grid and paste covering the grid and reinforcing member; 
           [0012]      FIG. 4  is a fragmentary cross-sectional view like  FIG. 3  which also includes an additional reinforcing member disposed adjacent to the other face of the battery grid; 
           [0013]      FIG. 5  is a fragmentary cross-sectional view like  FIG. 4  illustrating the battery grids and reinforcing members being passed through compression rollers; and 
           [0014]      FIG. 6  is a fragmentary cross-sectional view illustrating a battery plate formed according to one presently preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    Referring in more detail to the drawings,  FIG. 1  illustrates a lead acid battery  10  with a housing  12  having a case  14  and a top cover  16  both constructed from a plastic material such as polypropylene. The case  14  has a plurality of integrally molded battery cell dividers  18  providing a plurality of battery cell wells  20  within the housing  12 . A battery cell  22  is disposed within each of the wells  20  between the dividers  18  and has a set or book of interleaved positive plates  24  and negative plates  26 , and a separator  28  disposed between each plate of different polarity to prevent them from touching and producing a short circuit within the cell  22 . A positive plate strap  30  and a negative plate strap  32  electrically connect together the associated positive and negative plates  24 ,  26  of each cell  22  across the top of plates. To connect the individual cells  22  together in series, an intercell connector  34  made of lead is disposed between and welded to the positive plate strap  30  and adjoining negative plate strap  32  of adjoining cells  22  in series. A positive terminal post  36  is connected to the positive plate strap  30  of the first cell and a negative terminal post  38  of lead is connected to the negative plate strap  32  of the last cell. Each post  36 ,  38  projects through the cover  16  and is sealed to the cover and welded to its associated strap  30 ,  32  of the same polarity. In use, dilute sulfuric acid solution fills the majority of the remaining space within each well  20  and is the electrolyte necessary to produce the chemical reactions which take place within each battery cell  22 . As will be apparent to skilled persons, other materials may be used for the housing, the battery plates, and the electrolyte, as desired. 
         [0016]    As noted above, each book of battery plates preferably includes a plurality of positive plates  24  and a plurality of negative plates  26 . Each of the positive and negative plates  24 ,  26  includes a battery grid  40  covered and preferably embedded in an active material that is usually applied to the grid in the form of a paste  42  and cured. As shown in  FIG. 2 , each grid  40  includes a reticulated framework of wires  44  with at least some of the wires  44  intersecting each other and defining open spaces  46  between adjacent wires  44 . Each grid preferably also has a tab  48  extending from some of the wires. To facilitate connecting together plates of the same polarity, the tab  48  on each positive plate grid is offset from the location of the tab  48  on each negative plate grid so the positive plate strap  30  engages only positive plates  24  and the negative plate strap  32  engages only negative plates  26 . 
         [0017]    As shown in  FIG. 3 , a reinforcing member  50  may be disposed adjacent to one face  52  of the grid  40  and some electrochemically active paste  42  may be disposed onto the grid  40  and down onto and into the reinforcing member  50 . The reinforcing member  50  may be a generally flat sheet of material that may include glass fibers, other reinforcing fibers, or other reinforcement. The fibers may be elongated and overlapped in any desired manner. The reinforcing member  50  is preferably permeable to the paste and permits the paste  42  to saturate and, more preferably, flow through it so that the reinforcing member  50  becomes embedded in the paste  42  during manufacture of the battery plate  24  or  26 . The reinforcing member  50  may be porous, have openings formed therein or may be formed of a material otherwise permeable to the paste without significant openings. This reinforcing member is not like conventional cellulose pasting paper or glass microfiber pasting paper used to support wet battery paste when applying it to a grid and to prevent stacked wet pasted battery grids from sticking to each other or to processing equipment during manufacture of lead acid battery plates. The wet battery paste cannot permeate or flow through conventional cellulose pasting paper and/or glass microfiber pasting paper. 
         [0018]    A suitable reinforcing member of a fiberglass sheet may have an air permeability or air flow rate at 100 Pa of at least 4,000 liters per square meter per second (L/m 2 s), desirably in the range of about 4,000 to 8,000 L/m 2 s, and preferably in the range of about 5,000 to 6,000 L/m 2 s. This fiberglass sheet may have a thickness of at least about 0.12 millimeters (mm), desirably in the range of about 0.14 to 0.30 mm, and preferably in the range of about 0.14 to 0.20 mm; a weight of at least 18 grams per square meter of area (g/m 2 ), desirably about 20 to 40 g/m 2  and preferably about 22 to 28 g/m 2 ; a longitudinal tensile strength of at least about 45 Newtons per 50 millimeters (N/50 mm), desirably in the range of about 50 to 90 N/50 mm, and preferably about 60 to 80 N/50 mm; and a transverse tensile strength of at least 25 N/50 mm, desirably in the range of about 30 to 50 N/50 mm and preferably in the range of about 35 to 45 N/50 mm. A suitable glass fiber reinforcing member is commercially available from Owen Corning, P. O. Box 30, Liversedge, West Yorkshire, England WF15 88A as glass fiber vail product BL25A. 
         [0019]    In the presently preferred embodiment, as shown in  FIG. 4 , after paste  42  is applied to the grid  40  and to the reinforcing member  50  on one face  52  of the grid  40 , a second reinforcing member  50  is disposed on the opposite face  54  of the grid  40 . The reinforcing member  50  on the opposite face  54  is preferably pressed into the paste  42  and presently is made of same material as or a similar material to the first reinforcing member  50  so that it is permeable to the paste  42  and preferably becomes embedded in the paste  42 . 
         [0020]    As shown in  FIG. 5 , after the reinforcing members  50  and paste  42  have been applied to the grid  40 , the entire unit may be passed between a pair of rollers  56 ,  58  to compress the reinforcing members  50 , grid  40  and paste  42  together. Preferably, the reinforcing members  50  are firmly embedded in the paste  42  and become part of the paste layer and provide structural integrity to the paste  42  when cured and increase resistance to bending of the entire plate or assembly. Preferably, as shown in  FIG. 6 , the reinforcing members  50  are embedded in and “over pasted” so that a layer of paste  42  overlies the reinforcing members  50  with the grid  40  disposed between the reinforcing members  50 . 
         [0021]    The reinforcing members  50  may have a thickness that is the same as, greater than or less than the thickness of the grid  40 . Reinforcing members  50  may be generally planar and lie generally parallel to the plane of the grid  40 . The reinforcing members  50  may overlie a portion of or the entire grid  40 . The reinforcing members  50  may extend at least partially between the faces  52 ,  54  of the grid  40 , within the open spaces  46  defined between adjacent wires  44  of the grid  40 . While the presently preferred embodiment has been disclosed as having a pair of reinforcing members  50 , one on each of the opposed faces  52 ,  54  of the grid  40 , only one reinforcing member  50  may be used, and it may overlie part or all of one face or both faces  52 ,  54  of the grid  40 . 
         [0022]    While not wishing to be held to any particular theory, it is currently believed and theorized that the reinforcing members  50  disposed in the paste  42  provide structural rigidity to the paste  42  when cured and in use reduce shedding and shrinkage of the cured paste  42  from the grid  40 , thereby increasing the durability, reliability and effective useful life of the battery plate  24 ,  26 . Further, by reducing shedding and shrinkage of the active material, the performance of the plate  24 ,  26  is improved during its effective useful life. 
         [0023]    Those skilled in the art will recognize that the description of the presently preferred embodiments has been provided in terms of description and not limitation. Various modifications and amendments to the lead acid batteries and battery plates can be made without departing from the spirit and scope of the invention as defined by the appended claims. For example, while the reinforcing member has been disclosed as comprising a sheet or mat of material, the reinforcing member could comprise a plurality of individual members, or even individual fibers or groups of fibers or smaller pieces of material disposed in the paste and on the grid. Further, while certain objects, features and advantages have been set forth with respect to the presently preferred embodiments of the invention, a battery plate and/or lead acid battery falling within the spirit and scope of the appended claims may perform all, some or none of the listed advantages, or achieve objects and advantages different from those set forth herein.