Abstract:
A method of manufacturing a battery includes providing a cell for a battery having alternating positive and negative electrode plates, each of the electrode plates being separated by an electrically insulative separator layer. Each of the positive and negative electrode plates includes a projecting tab extending from an adjacent upper portion thereof, the projecting tabs of the positive plates being generally aligned, and the projecting tabs of the negative plates being generally aligned. The method comprises attaching a conductive connecting strap to the projecting tabs The method comprises applying a cap material onto the connecting positive strap and allowing the cap material to spread and drip to the exposed portions of the projecting tabs and the adjacent upper portions of the negative and positive plates and separator material. The cap material hardens to provide a cap.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to batteries, and more particularly to lead-acid batteries. 
     BACKGROUND OF THE INVENTION 
     A typical battery includes one or more electrochemical cells which are electrically connected within the battery and provide the source of electrical power for the battery. These cells generally comprise four basic components: a positive electrode (anode on charge and cathode on discharge) that receives electrons from an external circuit as the cell is discharged; a negative electrode (cathode on charge and anode on discharge) that donates electrons to the external circuit as the cell is discharged; an electrolyte (often in a solution or paste) which provides a mechanism for electrical charge to flow between the positive and negative electrodes; and one or more separators which electrically isolate the positive and negative electrodes. This configuration enables the cell to generate electric power because of the electrochemical relationship of these components. Once the current is generated, it is typically carried from the positive electrode plates through a current carrier to a terminal, from which it is conveyed to the external circuit and back into the battery through a terminal connected with the negative electrode plates (typically through another current carrier). 
     Lead-acid batteries are popular when rechargeability is desired. These batteries are particularly desirable for rechargeable use due to their high tolerance for abuse and relatively low manufacturing cost, particularly when battery weight is not a great concern. As a result, lead-acid batteries are often employed to power automobiles and other vehicles, as these environments can be quite harsh and present varied forms of maltreatment. Lead acid batteries are also often used in backup systems that provide power when an electrical power grid fails. 
     Most lead-acid batteries generally rely on the same fundamental electrochemical reaction to produce power and typically employ the same active materials. The electrochemical reaction is shown below: 
                                 CATHODE       PbO 2  + SO 4   −2  + 4H +  + 2e −  → PbSO 4  + 2H 2 O       ANODE       Pb + SO 4   −2  → PbSO 4  + 2e −                      
At the anode, metallic lead reacts with sulfate ion (SO 4   2− ) and is converted to lead sulfate (PbSO 4 ). At the cathode, lead dioxide (PbO 2 ) reacts with sulfate ion (SO 4   2− ) and is also converted to lead sulfate. Electrons are donated by the anode and travel through the external circuit to be received by the cathode.
 
     In practice, a typical lead-acid battery includes multiple overlying anode and cathode layers. Most often, these are arranged in one of two configurations: stacked plates or spirally wound elongate strips. In either instance, the anode and cathode layers are separated from each other by separator layers formed of an electrically-insulative material (typically a glass fiber mat or the like). A dilute sulfuric acid solution is typically used as the electrolyte to provide the sulfate ion. 
     The stacked plate variety of lead-acid battery ordinarily includes multiple anode and cathode plates alternately sequenced in a stack separated by separator layers. In other words, the typical arrangement comprises a cathode plate, a separator layer, an anode plate, another separator layer, a second cathode plate, and so on. Some lead-acid battery cells include as many as 29 cathode and anode plates stacked in this fashion. 
     To harness the energy created by the electrochemical reactions occurring with the plates, the cathode plates are connected to each other in parallel, and the anode plates are separately connected to each other in parallel. One common technique for connecting the plates is to include a projecting tab from one edge of each plate. The tabs are located in the same position on each cathode plate so that they align when the plates are stacked. The tabs are attached to a conductive connecting strap that is, in turn, connected to the battery terminal. Similar aligned tabs project from the anode plates and are connected by a connecting strap, but the tabs are located in a different position on the anode plates so as to avoid interfering with the cathode strap. One example of this configuration is described in U.S. Pat. No. 4,383,011 to McClelland et al. 
     One difficulty that can be experienced by lead-acid batteries having this design regards the vibration resistance and durability of the batteries. As discussed above, because lead-acid batteries are typically hardy, they are often used in harsh environments. As such, they are subjected to rigorous testing, particularly for shock, bump, impact and vibration resistance (for an exemplary test, see VG96924-2, BS6290 part 4, IEC). In some instances, fractures occur at the joints between the tabs of the positive electrode plates and the connecting strap. This area of the positive electrode plate can become brittle due to oxidation (i.e. the formation of PbO 2 ) that takes place on the surface of the tabs to protect the underlying bulk metallic lead (Pb). The PbO 2  layer is relatively brittle, and can crack under the shearing loads imparted during vibration tests. These cracks then expose the bulk metallic lead underneath, which then oxidizes. This pattern of oxidation followed by cracking repeats until the tabs fracture completely from the plate. 
     SUMMARY OF THE INVENTION 
     The invention is directed to cells and batteries and methods of their manufacture that can assist fracture resistance at the joint between the positive electrode plate tabs and the connecting strap during vibration and other rigorous mechanical tests. As a first aspect of the invention, a method of manufacturing a battery comprises as an initial step providing a cell for a battery having alternating positive and negative electrode plates, wherein each of the electrode plates is separated by an electrically insulative separator layer, and the positive and negative electrode plates are in overlying relationship. Each of the positive electrode plates includes a projecting tab extending from an adjacent upper portion thereof, the projecting tabs of the positive plates being generally aligned. Each of the negative electrode plates includes a projecting tab, the projecting tabs of the negative plates being generally aligned. Next, the method comprises attaching a conductive connecting strap to the projecting tabs of the positive plates. The method then comprises applying a cap material to portions of the projecting tabs and the adjacent upper portions of the positive plates (such as through pouring an adhesive material onto the positive connecting strap and allowing it to spread and drip to the tabs and upper portions of the positive and typically, negative electrode plates as well as the separators), and allowing the cap material to harden to provide a cap attached to the projecting tabs and the adjacent upper portions of the positive and negative plates. This method can produce a cell in which the joints between the positive electrode plate tabs and the connecting strap are rigidified and/or protected from oxidation, each of which can improve performance in mechanical testing. 
     As a second aspect, the invention is directed to a battery comprising: a housing; a plurality of alternating positive and negative electrode plates; two conductive connecting straps; and a cap. Each of the positive and negative electrode plates is separated by an electrically insulative separator layer, with the positive and negative electrode plates being in overlying relationship and positioned in the housing. Each of the positive electrode plates includes a projecting tab extending from an adjacent upper portion thereof, the projecting tabs of the positive plates being generally aligned, and each of the negative electrode plates includes a projecting tab, the projecting tabs of the negative plates being generally aligned. One conductive connecting strap is attached to the projecting tabs of the positive plates, and the other conductive connecting strap is attached to the projecting tabs of the negative plates. The cap (by way of example, formed of an adhesive material) covers portions of the projecting tabs and the adjacent upper portions of the positive (and, typically, negative electrode plates as well as the separators) 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a perspective view of a stack of positive and negative plates and separators of a battery cell of the invention. 
         FIG. 1B  is an exploded perspective view of the battery cell of  FIG. 1A . 
         FIG. 2A  is a schematic perspective view of the cell of  FIG. 1A  being dipped into molten material for the formation of connecting straps according to embodiments of the invention. 
         FIG. 2B  is a section view of the cell of  FIG. 2A  taken along line  2 B- 2 B thereof. 
         FIG. 3  is a schematic side view showing the insertion of a cell of  FIGS. 2A and 2B  into a battery housing according to embodiments of the invention. 
         FIG. 4  is a schematic side view showing a battery of the invention containing multiple cells of  FIGS. 2A and 2B . 
         FIG. 5  is a schematic perspective view of a battery of  FIG. 4  with each of its cells receiving a cap according to embodiments of the invention. 
         FIG. 6  is a perspective view of the battery of  FIG. 5  with completed cap layers. 
         FIG. 7  is a schematic side view of a battery of  FIG. 6  illustrating the cap layers. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawings, the thickness of lines, layers and regions may be exaggerated for clarity. It will be understood that when an element such as a layer, region, substrate, or panel is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. It will be understood that when an element is referred to as being “connected” or “attached” to another element, it can be directly connected or attached to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly connected” or “directly attached” to another element, there are no intervening elements present. The directional terms “upwardly”, “downwardly”, “vertical”, “horizontal” and the like are used herein for the purpose of explanation only. 
     Referring now to the drawings, a battery cell, designated broadly at  10 , is illustrated in  FIGS. 1A and 1B . The cell  10  includes a plurality of substantially planar positive electrode plates  12  and a plurality of substantially planar negative electrode plates  14  arranged in alternating, stacked, overlying fashion, with each adjacent pair of positive and negative electrode plates being separated by a separator  16 . The positive and negative electrode plates  12 ,  14  and the separators  16  can be any material known by those skilled in this art to be suitable for use in a cell or battery. In lead-acid cells, the positive and negative electrode plates  12 ,  14  are formed of lead-based materials (as used herein, “lead-based” materials comprise at least 99% percent lead). The separators  16  are typically formed of glass microfibre or synthetic loaded glass microfibre. Sizes and thicknesses of the positive and negative electrode plates  12 ,  14  and separators  16  are known to those skilled in this art and need not be described in detail herein. 
     Referring still to  FIG. 1 , each of the positive electrode plates  12  includes a projecting tab  12   a  that extends upwardly from the upper edge of the positive electrode plate  12 . The tab  12   a  extends from substantially the same location on each positive electrode plate  12  to enable the tabs  12   a  to be generally aligned when the positive electrode plates  12  are stacked. The tab  12   a  facilitates electrical connection of all of the positive electrode plates  12  in parallel. Similarly, each of the negative electrode plates  14  includes a projecting tab  14   a  that extends upwardly from the upper edge of the negative electrode plate  14  and tht due to the tabs  14   a  being positioned at substantially the same location on each plate  14  and generally aligned, facilitates electrical connection of the negative electrode plates  14  in parallel. The precise configuration of the tabs  12   a ,  14   a  can vary, but the selected configuration should extend sufficiently from the edge of the respective electrode plate to enable electrical connection thereof. 
     Interconnection of the positive electrode plates  12  and the negative electrode plates  14  is illustratively and typically accomplished through the application of a positive connecting strap  18  to the tabs  12   a  and a negative connecting strap  22  to the tabs  14   a  (see  FIGS. 3-6 ). The straps  18 ,  22  can be applied, for example, by inverting the cell  10  and dipping the tabs  12   a ,  14   a  into wells  28 ,  30  of a mold  26  as the wells  28 ,  30  contain a molten material  29 ,  32  such as lead (see  FIGS. 2A and 2B ). The tabs  12   a ,  14   a  remain in the wells  28 ,  30  until the molten material  29 ,  32  freezes. The cell  10  with the attached straps  18 ,  22  is then lifted from the mold  26 . Those skilled in this art will recognize that other techniques for attaching connecting straps  18 ,  22  to the tabs  12   a ,  14   a , respectively, such as hand burning or any other mechanical jointing method, may also be employed with the invention. 
     After the straps  18 ,  22  have been applied to the cell  10 , the cell  10  can then be positioned with additional cells  10  in a multi-cell battery  50  (see  FIGS. 3 and 4 ). The battery  50  includes a plurality of cells  10  (typically these are similarly sized cells) and a compartmentalized housing  52 , with each compartment  54  of the housing containing one cell  10  inserted therein. The cells  10  are positioned with the positive terminal  20  of one cell  10  being adjacent to the negative terminal  24  of another cell  10 . 
     Referring now to  FIG. 5 , after the cells  10  have been inserted into the housing  52 , a cap material  42  (typically an adhesive) is applied to the positive connecting strap  18  of each cell  10  (the negative electrode plates  14  do not ordinarily oxidize, so the aforementioned embrittlement and cracking does not tend to occur there). The cap material  42  can be applied, for example, with a dispenser  40  that deposits the cap material  42  on an upper surface  18   a  of the positive connecting strap  18 . The cap material  42  spreads over the upper surface  18   a  and drips down the sides  18   b  of the positive connecting strap  18  to cover exposed portions of the tabs  12   a  and the adjacent upper portions  12   e ,  14   e ,  16   e  of the positive and negative electrode plates  12 ,  14  and the separators  16  (see  FIG. 7 ). The cap material  42  typically oozes into the spaces between the positive and negative electrode plates  12 ,  14  and the separators  16  a distance of 0.5 cm to 1.0 cm (dimensions can vary depending on battery type/size) from the upper portions  12   e ,  14   e ,  16   e  of the positive and negative electrode plates  12 ,  14  and the separators  16 , but the cap material  42  may be permitted to ooze over more or less of these components as desired. The cap material  42  then hardens to form a cap  44 . 
     In some embodiments, the cap  44  can unify the positive connecting strap  18  with the top edges of the positive and negative electrode plates  12 ,  14  and the separators  16 , thereby providing a rigidifying structure that can improve the structural integrity and vibration resistance of the cell  10 . In some other embodiments, the cap  44  can coat, inter alia, the tabs  12   a  of the positive electrode plates  12  and provide a protective layer against oxidation of the tabs. In still further embodiments, the cap  44  can provide structural integrity, vibration resistance and protection against oxidation. 
     The cap  44  may be formed of any material that can provide the aforementioned rigidifying and/or protective functions. Exemplary cap materials include adhesives, such as epoxies, reactive acrylics or jointing compounds. In some embodiments, the cap  44  may be formed of a material that has a viscosity (typically about 19 centipoise at 25 degrees C.) that enables it, as illustrated, to be deposited on the positive connecting strap  18  and spread therefrom to the upper portions  12   e ,  14   e  of the positive and negative electrode plates  12 ,  14  and portions of the tabs  12   a ,  14   a . The cap material may also be resistant to acid (particularly sulfuric acid, as it is typically employed in the electrolyte solution of lead-acid batteries) and to temperatures up to 80° C. to withstand the internal environment of a battery. Further, the cap material may not significantly “out-gas” in order to avoid the generation of internal pressure within the battery, and should adhere to at least the positive electrode plates  12 . An exemplary cap material is S-2470-E epoxy, available from Structural Adhesives Ltd, Bushby Brooks Works, 16 Spence Street, Leicester. LE5 3NW, United Kingdom. 
     Those skilled in this art will recognize that other techniques of applying the cap  44  to the positive connecting strap  18  and the upper portions  12   e  of the positive electrode plates  12  may be employed. For example, the cap  44  may be applied by spraying or directly injecting the material onto the upper portions  12   e  of the positive electrode plates  12  and tabs  12   a . As another example, the cap  44  may be applied as a mold is positioned around the positive connecting strap  18  so that the cap material  42  flows to fill the mold and take a predetermined shape. 
     After the application of the cap layer  44 , the positive and negative terminals  20 ,  24  of adjacent cells  10  are electrically connected. The battery  50  is then covered and filled with electrolyte solution. The filled battery is vented and capped prior to use. 
     Those skilled in this art will recognize that, although the cap illustrated and discussed herein is employed with a multi-cell battery, the cap may also be employed with a single cell battery. Further, although a “parallel plate” battery is illustrated and described herein, a cap may also be employed advantageously with a “spirally wound” battery, in which the positive and negative electrode plates are spirally wound in overlying fashion. Moreover, a cap may also be included on the negative connecting strap and adjacent top edges of electrode plates and separators, but need not be. 
     The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.