AU2012238223A1 - An Improved Electrode Assembly for a Lead-Acid Battery - Google Patents

Abstract

Abstract The invention relates, in one aspect, to a lead-acid battery including a house, a positive terminal block, a negative terminal block and at least one cell disposed 5 within the housing. The at least one cell includes at least one positive electrode assembly and at least one negative electrode assembly. An electrolyte is disposed between the positive and negative electrode assemblies. In accordance with one embodiment of the invention, the positive electrode assembly includes a plurality of positive plates that are connected together by a 10 plurality of positive distributor bars. Each positive distributor bar is connected to at least one positive plate connector that is in turn connected to the positive terminal block. The negative electrode assembly includes a plurality of negative plates that are connected to the negative terminal block. The positive distributor bars and the positive plate connectors are configured so that electrical 15 resistance from the positive terminal block to the negative terminal block during use of the lead-acid battery encourages a desired utilisation of active material on each of the positive plates. The invention also relates to an improved form of positive plate for a lead-acid 20 battery. In 0 c-c

Description

P/00/01 1 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: An Improved Electrode Assembly for a Lead Acid Battery Applicant: Subtrade of SB Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: 1 2 An Improved Electrode Assembly for a Lead-Acid Battery Field of the Invention The present invention relates generally to the field of lead-acid batteries, and 5 more particularly to an electrode assembly for a lead-acid battery. An electrode assembly in accordance with an embodiment of the present invention has particular, but not exclusive application, in a lead-acid battery for deep cycle or partial state of charge applications. 10 Backqround of the Invention Conventional lead-acid batteries incorporate electrode assemblies (including positive and negative electrodes) having a current collector, in the form of an electrically conductive body. The electrically conductive body typically includes one or more conducting elements in the form of current collecting elements. 15 These elements typically include a plate or an arrangement of plural spines, and an active material in electrical contact with the current collecting element(s). The electrode assembly also includes a lug that is connected to the electrically conductive body to provide a current path between the electrically conductive body and a battery terminal. 20 The effective life of a lead-acid battery in some applications depends on the positive electrode. This dependency arises because the positive electrode typically fails before the negative electrode of a lead-acid battery. Failure usually occurs as a result of corrosion of the current collecting elements which 25 leads to a reduction in current carrying capacity. In this respect, significant capacity reduction may be observed when the current collecting element(s) of the positive electrode are substantially entirely corroded. One effect which contributes to corrosion of the current collecting element(s) is 30 uneven utilisation of the active material on the current collector(s). In addition, uneven utilisation of the active material may cause a considerable amount of unreacted active material to remain in the electrically conductive body even after the battery has discharged.

3 The ratio of reacted active material to the amount of active material originally present is referred to as the utilisation efficiency of the active material. It is not uncommon for the remaining unreacted material to exceed the reacted material 5 at the end of a discharge cycle. Thus, in some conventional lead-acid batteries utilisation efficiencies of less than 50% are not uncommon. One factor which contributes to the uneven utilisation of the active material, and thus to a poor utilisation efficiency, is the variation in values of electrical 10 resistance across the electrically conductive body relative to the lug. Such differences in the values of electrical resistance affect the utilisation of the active material throughout the positive (and negative) electrode, and thus the distribution of utilisation of the active material within a conventional positive electrode varies according to the distribution of the electrical resistance across 15 the positive electrode. For example, the variation in values of electrical resistance in the negative plate can be reduced significantly through the use of copper as the electrical conductive body. This method is, however, usually only used on the negative 20 plate as the electrical potential of the cell protects the copper from corrosion. Use of copper as a conductive element for the positive plate is also possible if suitably protectively coated to avoid rapid corrosion. Also, an uneven distribution of values of electrical resistance may be caused by 25 the position of the lug relative to the electrically conductive body. In a conventional positive electrode, for example, the electrical resistance between the lug and the electrically conductive body increases with distance from the lug. By way of example, Figure 1 depicts a conventional positive electrode assembly 100 including an electrically conductive body 102 in the form of a 30 single plate 103 and a lug 104 connected to the plate 103 to provide a current path between the plate 103 and the lug 104. CP1 represents a first current collection point of the plate 103 and CP2 represents a second current collection point of the plate 103. In this example, the distance between the lug 104 and 4 CP2 is greater than the distance between the lug 104 and CP1 and thus, with reference to Figure 2, the electrical resistance R2 of the current path between CP2 and the lug 104 will be higher than the electrical resistance R1 of the current path between CP1 and the lug 104. Since the utilisation of the active 5 material is more efficient at regions of lower electrical resistance, the utilisation of the active material at CP1 will be higher than the utilisation of the active material at CP2, and thus result in uneven utilisation of the active material. As shown in Figure 1, the electrical resistance will be greatest at current collection points located furthest from the lug 104. Hence, utilisation of the active material 10 will generally be less efficient towards the lower sections of the plate 103. In view of the above, utilisation of the active material is higher at locations closer to the lug than elsewhere in the electrically conductive body. Consequently, the uneven utilisation of the active material may be exacerbated 15 as distance from the lug increases, such as would be the case in conventional lead-acid batteries having a large positive electrode. Uneven utilisation of the active material is further exacerbated in tall cells (in other words, cells which are more than about 500mm high). In "tall" plates the 20 electrolyte may tend to stratify, particularly during charging such that the specific gravity of the electrolyte varies up the height of the plate. 'This effect also contributes to unequal use of the plates as the "driving" reaction of producing high concentration acid tends to be more vigorous at the top of the cell. In addition, the unequal use of the plates increases as the charge 25 continues. Hence, a typical solution is to avoid cells over about 500mm as being impractical or to fit an acid circulating system. It would be desirable to provide a positive electrode that has an improved distribution of utilisation of active material. Indeed it would be particularly 30 desirable to provide a cell in which utilisation of the active material across the positive and negative plates was more even across the entire width and height of the plates to allow optimal use of active material and improved corrosion life.

5 The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of this application. 5 Summary of the Invention In accordance with a first aspect of the invention there is provided an electrode assembly for a lead-acid battery, the electrode assembly including: a plurality of positive plates loaded with an active material, the positive 10 plates connected together by a plurality of positive distributor bars positioned along a height direction of the positive plates, each of the positive distributor bars connected to at least one positive plate connector to establish current paths from the positive plates to a positive terminal block, a plurality of negative plates loaded with an active material, the negative 15 plates connected to a negative terminal block to establish current paths from the negative plates to the negative terminal block, wherein the positive plate connectors and/or distributor bars have values of electrical resistance adapted to encourage a desired utilisation of the active material across the positive plates when the electrode assembly is in use. 20 The desired utilisation of the active material will be selected to achieve the desired operational requirements of the lead-acid battery. For example, the desired utilisation of the active material may be chosen to be as equal as possible between the positive and negative plates, or, for example, to 25 encourage as low as possible power losses. Further, for example, where battery weight is a driving factor, restriction on the number of distributor bars or dimension of those bars may facilitate determination of the required electrical resistance of the connectors and/or the distributor bars. 30 In accordance with one embodiment of this first aspect of the invention, the negative plates are connected together by a plurality of negative distributor bars respectively positioned along a height direction of the negative plates, each of 6 the negative distributor bars connected to respective negative plate connectors which are in turn connected to the negative terminal block, In accordance with a second aspect of the invention there is provided a lead 5 acid battery including: a housing; a positive terminal block; a negative terminal block; at least one cell disposed within the housing, the at least one cell 10 including at least one positive electrode assembly and at least one negative electrode assembly; an electrolyte disposed between the positive and negative electrode assemblies; said positive electrode assembly including a plurality of positive plates, 15 the positive plates connected together by a plurality of positive distributor bars, each positive distributor bar connected to a positive plate connector that is in turn connected to the positive terminal block, said negative electrode assembly including a plurality of negative plates, the negative plates connected to the negative terminal block, 20 and wherein the positive distributor bars and/or the positive plate connectors are configured so that electrical resistance from the positive terminal block to the negative terminal block during use of the lead-acid battery encourages a desired utilisation of active material on each of the positive plates. 25 In accordance with an embodiment of the second aspect of the invention, the positive distributor bars of the positive electrode assembly are positioned substantially horizontally and are spaced along a height direction of the cell. Each of the positive distributor bars is connected to one longitudinal edge of each of the positive plates. 30 In accordance with another embodiment of the second aspect of the invention, the plurality of negative plates are connected together by a plurality of negative distributor bars, each negative distributor bar connected to a negative plate 7 connector that is connected to the negative terminal block. The negative distributor bars of the negative electrode assembly are preferably positioned substantially horizontally and along the height direction of the cell, and each of the negative distributor bars is preferably connected to one longitudinal edge of 5 the negative plates. The positive and the negative distributor bars may align horizontally with one another as they extend down the height direction of the cell. However, in accordance with another embodiment, the positive and the negative distributor 10 bars are offset vertically with one another as they extend down the height direction of the cell. In accordance with such an arrangement, the positive electrode assembly will include N positive distributor bars and the negative electrode assembly may include (N + 1) negative distributor bars. It will be appreciated by those persons skilled in the art, however, that other 15 configurations are possible. In an example, the offset configuration of the distributor bars is such that each negative bar is positioned between (approximately halfway) between each positive bar to create more even voltage differentials across and up the plate, leading to more equal utilisation of the active material. This arrangement also reduces end effects by positioning a 20 current collector at the edges of the negative plates. In an embodiment of the second aspect of the invention, the positive and negative terminal blocks are located within the battery to encourage more equal utilisation of the active material across the positive and negative plates. This is 25 to help ensure that areas of active material closest to the collectors are not over utilised. The plate connectors of the positive plates preferably extend substantially vertically along the height direction of the positive plates. The plate connectors 30 of the negative plates also preferably extend substantially vertically along the height direction of the negative plates.

8 Preferably, the resistance of the positive plate connectors and/or distributor bars is selected or "tuned" to encourage the desired utilisation of active material on each of the positive plates. Even utilisation of the active material across each of the positive plates may be a desired utilisation. This can be achieved, for 5 example, by increasing or decreasing the cross-sectional dimension of the various plate connectors and/or distributor bars, or otherwise varying the resistance of the various plate connectors and/or distributor bars. According to a third aspect of the present invention there is provided a positive 10 plate for a lead-acid battery, said positive plate having a width direction and a height direction and including a plurality of lead spines extending in the width direction and forming a generally rectangular shaped plate. In use, the positive plate is orientated so that the width direction is located 15 substantially horizontally and thus the spines are arranged to extend in a width or horizontal direction of the lead-acid battery. Each spine is preferably received within a porous tubular member or gauntlet which is packed with active material to form cylindrical active elements. The 20 free ends of the spines preferably connect to a border element that bounds the generally rectangular shaped plate. The border element includes a first vertical or height edge that may be electrically conductive or non-electrically conductive. Description of the Drawings 25 Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates schematically a conventional positive electrode assembly; 30 Figure 2 is a circuit diagram for a current collector points CP1 and CP2 identified in Figure 1; 9 Figure 3 is a first isometric view of a cell in accordance with a first embodiment of the invention; Figure 4 is a second isometric view of the cell shown in Figure 3; 5 Figure 5 illustrates one of the positive plates used in the cell of Figures 2 and 3; Figure 6 illustrates one of the negative plates used in the cell of Figures 2 and 3; 10 Figure 7 is a graph showing current distribution in the positive plate for differing numbers of plate collectors in accordance with a first embodiment of the invention. 15 Figure 8 is a first isometric view of a cell in accordance with a second embodiment of the invention; Figure 9 is a second isometric view of the cell shown in Figure 8; 20 Figure 10 is an end view of the cell shown in Figure 8; Figure 1 1A is a front view of the cell shown in Figure 8; Figure 11 B is a rear view of the cell shown in Figure 8; 25 Figure 12 is a top view of the cell shown in Figure 8; Figure 12A is an expanded view of portion G of Figure 12; 30 Figure 13 is a vertical cross-sectional view of the cell shown in Figure 8; Figures 14A, 14B and 14C depict current output contours respectively for a positive plate with conventional pick up points to the positive terminal block, a 10 positive plate with four distributor bars and connectors according to an embodiment of the invention and a positive plate with eight distributor bars and connectors according to an embodiment of the invention; and 5 Figure 15 depicts current output contours respectively for a positive plate with eight connector arms and a positive plate with eight tuned connector arms. Detailed Description of the Preferred Embodiments Figures 3 and 4 illustrate a cell 10 in accordance with a first embodiment of the 10 invention. The cell 10 is arranged to be disposed within a battery housing (not illustrated). More than one cell 10 may be included within the battery housing. The cell 10 includes a top positive electrode assembly 20 and a top negative electrode assembly 40, as well as a bottom positive electrode assembly 20-1 15 and a bottom negative electrode assembly 40-1. The top and bottom positive electrode assemblies 20, 20-1 are identical. Similarly, the top and bottom negative assemblies 40, 40-1 are identical. As depicted, each of the top and bottom positive electrode assembly 20 20 includes twenty-four positive plates 22 and the top and bottom negative electrode each include twenty-five negative plates 42. Separators (riot shown) are located between the interleaved positive and negative plates 22, 42. In this manner it will be understood that a positive plate 22 is always located between two negative plates 42. It is to be appreciated by those persons skilled in the art 25 that the same, or similar, construction and assembly arrangements to those shown in the Figures can be used with more or fewer plates. It will also be appreciated that the vertical height of the plates 22, 42 may vary, however, it is envisaged that embodiments of the present invention will include 30 plates 22, 42 over approximately 600mm in vertical height. Figure 5 depicts a single positive plate 22 and Figure 6 depicts a single negative plate 42. Each positive plate 22 includes plural lead spines 25 that 11 extend in the width direction (i.e. horizontally) to form a generally rectangular shaped positive plate 22. Each spine 25 is received within a porous tubular member or gauntlet which is packed with active material to form cylindrical active elements. The free ends of the spines 25 connect to a side bar 24a that 5 extends down the height or vertical sides of the generally rectangular shaped positive plate 22 formed by the spines 25. The side bar 24a is non-electrically conductive and serves to stop the active material from falling out of the gauntlet. The opposing ends of the spines 25 are connected to a conductive side bar 24b. Conductive side bar 24b is arranged to be connected to the distributor 10 bars 26 as will be described later. In one arrangement, for example, the top of the plate 22 is fitted with a top bar that is electrically conductive (e.g. made of lead) while the bottom of the plate 22 is fitted with a bottom bar that is not electrically conductive. Also, the spines 15 25 are fitted, in one arrangement, with a plastic bottom bar including the active material of the spines 25. In the illustrated embodiment, the positive plates 22 allow for a reduction in the length of the spines 25 as they extend across the width of the plate 22 (i.e. 20 horizontally) rather than along the length or height of the plate 22. This also allows for a greater number of spines 25 to be arranged in parallel, which reduces the resistance of the plate 22 significantly. For example, if a standard tubular plate has 28 spines x 490mm long, an alternative arrangement will be the same size but will have 51 spines at 280mm length; this leads to a reduction 25 in resistance of up to 70% (at end of discharge) when compared to a similarly designed positive plate with vertically extending spines 25 (i.e. spines extending in the height direction). The described construction of the positive plate 22 allows for more even active 30 material packing density during manufacture, use of lead alloys with lower creep strength and therefore lower corrosion rates, leading to longer life, shorter spines 25 and reduced shedding (i.e. the reduction in the active material falling out of the bottom of the gauntlet) due to the reduced load on the side bar 24a.

12 Each negative plate 42 of Figure 6 includes a highly conductive grid formed of at least a lead alloy, copper foam, a punched or expanded copper metal grid, or a grid from some other suitably conductive metal or non-metal material. It will 5 be appreciated by those persons skilled in the art that, while copper is generally used for its high conductivity, the plate 42 could be implemented without copper negative plates. The foam or grid is also packed with active material. Each negative plate 42 is bounded by a border 44 that includes a first vertical edge 44a that is electrically conductive and, in some cases, all edges are electrically 10 conductive. A thin coating of lead is also provided to any exposed copper of the negative grid. As shown in Figure 3, eight horizontally extending distributor bars 26 are spaced vertically along the height direction of the positive plates 22 and are 15 connected to the conductive side bar 24b of each of the positive plates 22. The distributor bars 26 are made from copper and are coated with a suitably applied layer of lead or other material to prevent electrolyte permeation and exposure of copper conductor to the electrolyte. Lead coating may be achieved by standard methods such as casting or by wrapping a sheet of lead around the copper and 20 sealing. The lead coating is typically in the order of 1-3mm in thickness. The side bars 24b of the positive plates 20 include appropriately positioned lugs (not shown in Figure 3) that seat the distributor bars 26. It will be appreciated by those persons skilled in the art that the distributor bars 26 may be connected to 25 the lugs of the positive plates 20 by a lead weld or some other type of weld. At least one positive connector 28 is, in turn, connected to each of the distributor bars 26. Each positive connector 28 is made from copper and like the positive distributor bars 26 is covered with a thick coating of lead to prevent 30 corrosion. The positive connectors 28 extend down the "height side" of the interleaved positive and negative electrode assemblies 20, 40. The "height side" being that side of the interleaved assemblies including the side bar 24b of 13 the positive plates 22. The upper end of each of the positive connectors 28 is connected to a positive terminal block 30. The distributor bars 26 and positive connectors 28 are shown as having a 5 rectangular cross-section but this may not necessarily be the case. Other configurations are envisaged. As shown in Figure 4, and in accordance with this embodiment, nine horizontally extending distributor bars 46 are spaced vertically along the 10 negative plates 42 and are connected to the side edges 44a of the negative plates 42. The first edges 44a include appropriately positioned lugs 45 that seat the negative distributor bars 46. The negative distributor bars 46 may be connected to the lugs 45 of the negative plates 40 by a copper braze or a lead weld. 15 At least one negative connector 48 is in turn connected to each of the distributor bars 46. The negative connectors 48 extend down the "width side" of the interleaved positive and negative electrode assemblies 20, 40 (the "width side" being perpendicular to the "length side" and the "height side" as indicated by the 20 arrows shown in Figure 4). The upper end of each of the negative connectors 48 is connected to a negative terminal block 50. The connectors 28, 48 are insulated from one another by either sufficient spacing or an insulated coating so as to ensure that no current paths exist 25 between any of the connectors. In an embodiment, the cell 10 includes N positive distributor bars 26 (e.g. 8 positive distributor bars 26 as shown in Figure 3) and N + 1 negative distributor bars 46 (e.g. 9 negative distributor bars 46 as shown in Figure 4). Accordingly, 30 the positive distributor bars 26 are vertically offset from the negative distributor bars 46. By offsetting the distributor bars 26, 46 the current is, in the depicted embodiment, more equalised between the alternate positive and negative distributor bars 26, 46 particularly at the edges of the plates.

14 The positive and negative terminal blocks 30, 50 are located at opposite longitudinal edges of the positive and negative plates 22, 42 to encourage more equal utilisation of the active material across the plates 22, 42. This is to 5 ensure that areas of active material closest to the positive and negative connectors 28, 48 are not over utilised. During the manufacturing process, the positive and negative distributor bars 26, 46 are seated in a jig and then the individual positive and negative plates 22, 42 10 are positioned in the jig. The plates 22, 42 are then attached to the -respective distributor bars 26, 46 and separators are interleaved between the positive and negative plates 22, 42. The connectors 28, 48 of the positive and negative assemblies 20, 40 may 15 adopt many different configurations. However, in accordance with the embodiment, the connectors 28, 48 should be configured so that the electrical resistance from the positive terminal block 30 to the negative terminal block 50 is substantially equal for any current flow path so as to encourage more equal utilisation of the active material on the plates 22, 42 and more particularly the 20 active material on the positive plate 20. It should be appreciated that the total value of the electrical resistance of any current path in the cell is dependent on many different factors. Simplistically, the total value of electrical resistance of any current path in the cell can be 25 considered as being equivalent to: Rtotal = Rpositive connector + Rnegative connector + Rother where Rother is a combination of different factors that cannot be easily controlled 30 and may change throughout cycling of the batttery.

15 These factors include, for example, the electrical resistance attributable to the spine, the active material, the electrolyte, the gauntlet and the boundary between the active material and the spline. 5 Assuming that Rother cannot be readily controlled, then an embodiment of the present invention seeks to equate the electrical resistance of the various possible current paths between the positive and negative terminal blocks 30, 50 by controlling the electrical resistance through the positive and negative connectors 28, 48. As is shown in Figures 3 and 4, this is achieved by 10 changing the configuration (e.g. the cross-section dimension) of the different positive and negative connectors 28, 48 so that more equal resistance can be achieved for the different current flow paths. Looking more closely at Figure 3, positive connector 28-1 which connects to an 15 uppermost distributor bar 26-1 to the positive terminal block 30 is the shortest positive connector 28 and thus will have the smallest cross-sectional dimension. Connector 28-7 connects to the 2 nd lowest distributor bar 26-7, has the second longest length of all of the positive connectors 28 and thus has an increased 20 cross-sectional dimension in comparison to the connectors 28 connected to the uppermost six distributor bars 26. Connected to the lowermost positive distributor bar 26-8 are two positive connectors 28-8. The two positive connectors 28-8 replace a single very large 25 cross-sectional dimensioned connector and thus the combined cross sectional dimensions of the two positive connectors 28-8 is greater than the cross sectional dimension of any of the other positive connectors 28. It will be appreciated that by varying the cross-sectional dimensions of the 30 connectors 28, the resistance along any given connector path can be equated irrespective of the length of that path. This will encourage more even utilisation of the active material on the positive plates 22.

16 At certain connector 28 lengths, which may be determined by future testing, it may be advisable to include multiple connectors 28 to the distributor bar 26, as per connectors 28-8, rather than just a single connector 28. The use of multiple connectors 28 is expected to even out the usage of active material 5 across the positive plates 22. However, it is appreciated that there are restrictions as to the number and size of positive connectors 28 particularly due to the added weight of such connectors because of the need to heavily coat them in lead. 10 Now looking at Figure 4, it will be noted that the negative connector 48-1 which connects to the uppermost negative distributor bar 46-1 to the negative terminal block 50 is the shortest negative connector 48 and thus has the smallest cross sectional dimension. 15 Connector 48-9 connects to the lowest distributor bar 46-9, has the longest length of all of the negative connectors 48 and thus has an increased cross sectional dimension in comparison to the connectors 48 connected to the uppermost seven distributor bars 46. 20 The connectors 48 connected to the intervening negative distributor bars 46 have varying cross-sectional dimensions depending on their length. By varying the cross-sectional dimension of each of the positive and negative connectors 28, 48 based on their length, it is possible to reduce or to perhaps 25 even eliminate differences in electrical resistance between the points at which a particular positive or negative plate 22, 42 contacts the associated distributor bars 26, 24 and the associated positive or negative terminal block 30, 50. This should result in more even utilisation of active material across the plates 22, 42. 30 It should be appreciated that, for example, the electrical resistance of the positive connector 28-1 does not need to necessarily equal the electrical resistance of the negative connector 48-1. However, the resistance from the positive terminal block 30 to the negative terminal block 50 via a current flow 17 path through the positive connector 28-1 and negative connector 48-1 is preferably equal or substantially equal to the resistance from the positive terminal block 30 to the negative terminal block 50 via a current flow path through any other of the sets of positive and negative connectors (e.g. 28-1 and 5 48-1). It should however be appreciated that the exact configuration of the lead-acid battery and selection of the resistance of the positive and negative connectors 28, 48 will depend upon the operational requirements of the battery. For 10 example, in a battery which requires high discharge rates, plates with areas of higher current density may be required. Hence, the design would not need to be as 'equal', as equalisation requires increased ohmic losses in, for example, the plate connectors. This is because in order to make the current paths even, the connectors connected to the upper distributor bars are made smaller, in 15 order to thereby increase the resistance to those related areas of the plates as compared to resistance values at the bottom or lower areas of the plates. In a cycling/low discharge rate battery, increased ohmic losses are acceptable as the current is much lower (Losses = 1 2 R). Therefore, the connectors to the 20 various areas of the plates can be substantially equal in resistance. This will result in a more even distribution of the current density across the battery plates. In a low weight battery, we may need to forsake 'evenness' for weight in order 25 to reach the required capacities. Therefore the number of distributor bars would be reduced, but still optimised based on the methodologies discussed above. It is appreciated that as the number of pick up points from the plates 22, 42 increases the more equal the electrical draw from the cell 10. However, 30 increasing the number of pick up points means increasing the number of distributor bars 26, 46 and connectors 28, 48 which thereby increases the weight, size and overall design complexity of the cell 10. The graph shown in 18 Figure 7 best illustrates the effect on current distribution of the positive plate 22 as the number of pick up points (distributor bars 26) is increased. It should also be appreciated that any copper components on the positive side 5 of the cell 10 must be heavily coated in lead to protect against corrosion. This lead covering increases the size of the cell and its weight and in most use applications there are strict limitations on allowable size and weight. Although not depicted, the positive and negative terminal blocks 30, 50 extend 10 out of the battery housing (not shown) to enable connection of the cell to another cell (not shown) in the circuit (not shown). As described, the location and configuration of the positive and negative connectors 28, 48 and their connection to the associated positive and negative 15 distributor bars 26, 48 may vary. Different locations are envisaged depending on the size and shape constraints of the cell 10. Additionally, compression of the positive and negative plates 22, 42 of the cell 10 can be achieved by locating the positive and negative connectors 28, 48 at the "width side" of the cell 10. 20 Figures 8 to 12 illustrate a cell 100 in accordance with a second embodiment of the invention. As shown in these Figures, the cell 100 includes twenty-five positive plates 122 interleaved between twenty-six negative plates 124. Separators 125 are located between the interleaved positive and negative 25 plates 122, 124. Unlike the arrangement shown in Figure 3, cell 100 does not include top and bottom electrode assemblies. Rather, full length positive and negative plates 122, 124 are used. Figure 13 depicts the cell 100 within a container 200 that is lined with a rubber 30 liner 210. The cell 100 is mounted on rubber supports 220. A cell cover 230 is fitted to the upper end of the container 200.

19 Each positive plate 122 includes plural horizontally extending lead spines 126 that together form a generally rectangular shaped plate. Each spine 126 is received within a porous tubular member or gauntlet which is packed with active material to form cylindrical active elements. The free ends of the spines 126 5 connect to a border that bounds the generally rectangular shaped plate 122. The border includes a first side bar or vertical edge 122a that may be electrically conductive or non-electrically conductive. Each negative plate 124 includes a highly conductive grid formed of at least a 10 lead alloy, copper foam, a punched or expanded copper metal grid, or a grid from some other suitably conductive metal or non-metal material. The foam or grid is also packed with active material. Each negative plate 124 includes a single lug 127 at its upper end. Negative plate 124 need not adopt the form of negative plate 42 described with reference to the embodiment shown in Figures 15 3 to 7. As best shown in Figure 11, eight horizontally extending distributor bars 128 are spaced vertically along the height direction of the positive plates 122 and are connected to the side bar or first edge 122a of each of the positive plates 122. 20 The distributor bars 128 are made from copper and are coated with a suitably applied layer of lead or other material to prevent electrolyte permeation and exposure of copper conductor to the electrolyte. The first edges 122a of the positive plates 122 include appropriately positioned lugs 122b (Figure 13) that seat the distributor bars 128. 25 At least one positive connector 130 is, in turn, connected to each of the distributor bars 128. The positive connectors 130 extend down the "height side" of the interleaved positive and negative plates 122, 124. As explained previously, the "height side" is that side of the positive and negative plates 122, 30 124 including the first edges 122a of the positive plates 122. The upper end of each of the positive connectors 130 is connected to a positive terminal block 140.

20 In contrast to the cell 10 described previously, the negative plates 12.4 adopt a conventional arrangement in that each negative plate 124 connects via its associated lug 130 to a negative terminal block 150. 5 In accordance with the second embodiment of the invention, it is possible to configure the components of the cell 100 to provide required battery design features. For example, by increasing the number of distributor bars 128 and related connectors 130 more even resistance across the positive plate 122 can be achieved. This is illustrated by comparing Figures 14A, 14B and 14C. 10 Figure 14A illustrates current production per mm 2 for a positive plate with nine conventional pick up points along the edge of the positive plate. Figure 14B illustrates current production per mm 2 for the same positive plate but with four distributor bars 128 and four connectors 130 of equal resistance. Figure 14C illustrates current production per mm 2 for the same positive plate but with eight 15 distributor bars 128 and eight connectors 130 of equal resistance. As shown by a comparison of these Figures, the use of distributor bars 128 and related connectors 130 creates more even current production across the plate 122 and that areas of very small current production can be reduced further by increasing the number of distributor bars 128 and related connectors 130 per plate 122. 20 It should also be noted that it is possible to "tune" the positive connectors 130 of a cell 100. For example, for a battery requiring high rate capacity, the positive connectors 130 can be configured or "tuned" to reduce the "evenness" of the utilisation across the positive plate 122. This can be achieved, for example, by 25 "tuning" the resistance of the connectors 130 connected to the upper distributor bars 128 of the positive plate 122 (i.e. by increasing or decreasing the cross sectional dimension of those connectors 130). For example, by reducing the resistance in those upper connectors 130, there is an increase in the areas of high current capacity across the positive plate 122. Such a design will still allow 30 improved utilisation at low rates, but will have lower losses allowing higher performance. Accordingly it will be appreciated that the resistance of each of the positive connectors of a particular cell may differ.

21 It will also be appreciated that the resistances of the connectors 130 of the positive plate 122 can be "tuned" depending on the conductivity of the negative plate 124 and/or other factors impacting the internal resistance of the cell. This may be done for example by varying the position of the negative lug 127. This 5 results in improved utilisation across both the positive and negative plates 122, 124. Figure 15 compares the current production per mm 2 for a positive plate 122 fitted with eight distribution bars 128 and eight "untuned" or equal connectors 10 130 with the same positive plate 122 fitted with eight distribution bars 128 and eight "tuned" or weighted connectors 130 and for the same negative plate 124. As shown in Figure 15, the plate 124 with "tuned" connectors 130 has smaller areas of low current density and a more even distribution of higher current density. 15 It is envisaged that embodiments of the present invention will permit current paths between the positive and negative terminals of the cell of the same or very similar value of electrical resistance in order to improve the equalisation of the utilisation of the plates by altering Rconductor. Such an approach may provide 20 improvements in deep discharge capacity, performance at high rates of discharge, longer life, reduced capacity loss and reduced gas charging. Indeed, it is believed that embodiments of the present invention may reduce the capacity loss of the cell by equalising the distribution of electrical resistance. A further advantage may be provided during charging, since the whole plate may 25 be charged more equally, leading to less need for gas charging. By reducing the amount of equalisation or gas charging that the cell has to do, corrosion of the lead splines may be minimised. It is envisaged that these improvements can be achieved without overly impacting on the weight or finished size of the cell. 30 The embodiments have been described by way of example only and modifications within the spirit and scope of the invention are envisaged.

Claims (26)

1. An electrode assembly for a lead-acid battery, the electrode assembly including: a plurality of positive plates loaded with an active material, the positive 5 plates connected together by a plurality of positive distributor bars positioned along a height direction of the positive plates, each of the positive distributor bars connected to at least one positive plate connector to establish current paths from the positive plates to a positive terminal block, a plurality of negative plates loaded with an active material, the negative 10 plates connected to a negative terminal block to establish current paths from the negative plates to the negative terminal block, wherein the connectors and/or the distributor bars have values of electrical resistance adapted to encourage a desired utilisation of the active material across the positive plates when the electrode assembly is in use. 15

2. An electrode assembly according to claim 1 wherein the negative plates are connected together by a plurality of negative distributor bars respectively positioned along a height direction of the negative plates, each of the negative distributor bars being connected to respective negative plate connectors which 20 are in turn connected to the negative terminal block.

3. An electrode assembly according to claim 1 or claim 2 wherein each positive plate includes plural spines extending in a width direction with reference to a height direction of the cell. 25

4. A lead-acid battery including: a housing; a positive terminal block; a negative terminal block; 30 at least one cell disposed within the housing, the at least one cell including at least one positive electrode assembly and at least one negative electrode assembly; 23 an electrolyte disposed between the positive and negative electrode assemblies; said positive electrode assembly including a plurality of positive plates, the positive plates connected together by a plurality of positive distributor bars, 5 each positive distributor bar connected to at least one positive plate connector that is in turn connected to the positive terminal block, said negative electrode assembly including a plurality of negative plates, the negative plates connected to the negative terminal block, and wherein the positive distributor bars and/or the positive plate 10 connectors are configured so that electrical resistance from the positive terminal block to the negative terminal block during use of the lead-acid battery encourages a desired utilisation of active material on each of the positive plates.

5. A lead-acid battery according to claim 4 wherein the positive distributor 15 bars of the positive electrode assembly are positioned substantially horizontally and are spaced along a height direction of the cell.

6. A lead-acid battery according to claim 5 wherein each of the positive distributor bars is connected to one longitudinal edge of each of the positive 20 plates.

7. A lead-acid battery according to any one of claims 4 to 6 wherein the positive and negative terminal blocks are located within the housing battery. 25

8. A lead-acid battery according to any one of claims 4 to 7 wherein the plurality of negative plates are connected together by a plurality of negative distributor bars, each negative distributor bar connected to a negative plate connector that is connected to the negative terminal block. 30

9. A lead-acid battery according to claim 8 wherein the negative distributor bars of the negative electrode assembly are preferably positioned substantially horizontally and along the height direction of the cell. 24

10. A lead-acid battery according to claim 9 wherein each of the negative distributor bars is connected to one longitudinal edge of each of the negative plates. 5

11 A lead-acid battery according to claim 9 or claim 10 wherein the positive and the negative distributor bars align horizontally with one another as they extend down the height direction of the cell.

12. A lead-acid battery according to claim 9 or claim 10 wherein the positive 10 and the negative distributor bars adopt a vertically offset configuration as they extend down the height direction of the cell.

13. A lead-acid battery according to claim 12 wherein the offset configuration is such that each negative distributor bar is positioned approximately halfway 15 between each positive distributor bar.

14. A lead-acid battery according to any one of claims 4 to 13 wherein the plate connectors of the positive plates extend substantially vertically along the height direction of the cell. 20

15. A lead-acid battery according to any one of claims 8 to 14 wherein the plate connectors of the negative plates extend substantially vertically along the height direction of the cell. 25

16. A lead-acid battery according to any one of claims 5 to 15 wherein each positive plate includes plural spines that extend in a width direction with reference to the height direction of the cell.

17. A lead-acid battery according to claim 16 wherein an end of each of the 30 plural spines of each positive plate is connected to a side bar and each distributor bar is connected to the side bar of each positive plate. 25

18. A lead-acid battery according to any one of claims 4 to 17 wherein the resistance of the positive plate connectors differs.

19. A lead-acid battery according to any one of claims 4 to 18 wherein more 5 than one positive plate connector is connected to at least one of the positive distributor bars.

20. A positive plate for a lead-acid battery, said positive plate having a width direction and a height direction, said positive plate including a plurality of spines 10 extending in the width direction and forming a generally rectangular shaped plate.

21. A positive plate according to claim 20 wherein each spine is received in a porous tubular gauntlet packed with an active material. 15

22. A positive plate according to claim 21 wherein the spines have free ends connected to respective side bars that extend down the height direction of the plate. 20

23. A positive plate according to claim 22 further including a bottom bar arranged for connection to the plate.

24. A positive plate according to claim 22 or claim 23 further including a top bar arranged for connection to the plate.

25

26. An electrode assembly and/or a lead-acid battery and/or a plate assembly substantially as hereinbefore described with reference to Figures 3 to 15. 30