AU2012200583A1 - An improved current collector arrangement - Google Patents

Abstract

-15 Abstract The invention relates to a current collector arrangement for a plate of an electrochemical cell. The current collector arrangement provides more even resistance along the length of the plate when compared to the other collector 5 arrangements. The invention has particular application in long plates, for example, plates greater than 500mm in length. 16' -12

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: AN IMPROVED CURRENT COLLECTOR ARRANGEMENT 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 CURRENT COLLECTOR ARRANGEMENT Cross Reference This application is related to Australian Provisional Patent Application No. 5 2011900320 filed on 2 February 2011, the contents of which are to be taken as incorporated herein by this reference. Field of Invention The present invention relates to an improved current collector arrangement for 10 an electrochemical cell. The current collector arrangement has particular, but not exclusive application, in lead acid batteries. Background of the Invention Lead acid batteries include at least one positive current collector, at least one 15 negative current collector and an electrolytic solution including, for example, sulphuric acid diluted with distilled water. Typically, both the positive current collector and the negative current collector are made from a grid manufactured from lead or copper and are covered in an active material in the form of a porous paste. Once covered in this paste, the grid provides 20 structural support for the active material. Once coated in active material the positive and negative current collectors are referred to respectively as positive and negative plates. The plates transfer electric current to and from the battery terminals during the charging and 25 discharging processes. The storage and release of electrical energy in lead acid batteries is enabled by chemical reactions that occur in the paste deposited on the current collectors. The paste allows the acid to react with the lead of the plates and 30 thus increases the active surface area. It is desirable to maximise the active surface area and thus it is important to maintain good contact between the paste and each of the current collectors. These chemical reactions also cause corrosion of the positive collector and sulfation on the negative plate.

-3 Corrosion of the positive collector results in volume expansion of the positive plate as the lead dioxide corrosion product has a greater volume than the lead of the positive collector that is consumed to create the lead dioxide. The volume expansion induces mechanical stresses on the positive current 5 collector that cause deformation and stretching. Eventually, the amount of corrosion of the positive plate will reach a point where there is no longer an easy path for the electrons to flow and thus there is a drop in battery capacity and ultimately an end to the battery's service life. 10 Sulfation is the process by which lead sulphate formed in the discharge reaction forms a more stable crystalline form coating the negative plate. Crystalline lead sulphate does not conduct electricity and cannot be converted back into lead and lead oxide under normal charging conditions. The crystalline lead sulphate blocks the conductive path needed for recharging 15 and thus affects the charging cycle, resulting in longer charging times, less efficient and incomplete charging and excessive heat generation. Various attempts have been made to address the problems of corrosion and sulfation in lead acid batteries. The present invention seeks to create a more 20 uniform distribution of resistance along the plates and thus provide a more uniform distribution of active material utilisation. The invention has particular application in long plates, for example, those greater than about 500mm in length. 25 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. 30 Summary of the Invention According to the present invention there is provided a current collector arrangement for a plate of an electrochemical cell, said current collector arrangement including a grid structure, at least one lug and a conductive frame, said conductive frame arranged for electrical connection to a lower part -4 of the grid structure that is distal from the at least one lug and not to an upper part of the grid structure, whereby the conductive frame reduces the difference in resistance along the length of the plate by providing an additional electrical conductive path for the lower part of the grid structure to the at least 5 one lug. The conductive frame may be formed as an assembly and may extend about all sides of the grid structure or only along one side of the grid structure. It is envisaged that when the frame assembly only extends along one side of the 10 grid structure the remaining sides of the grid structure would be coated with a non-conductive plastic material. It is envisaged that the present invention would have particular application in long plate designs where the length of the plate is greater than twice the width 15 of the plate. The conductive frame may be formed as a channel or may include opposed strips of material arranged to sandwich the edges of the grid structure therebetween. 20 The frame may include a conductor member arranged to provide the additional electrical conductive path for the lower part of the grid structure to the at least one lug. 25 In accordance with one embodiment of the invention, the current collector arrangement includes an upper grid structure and a lower grid structure and a conductive frame supporting the upper and lower grid structures, said upper grid structure including opposed first and second side edges and opposed top and bottom edges, said lower grid structure including opposed first and 30 second side edges and opposed top and bottom edges, said frame arranged to extend around the periphery of the upper and lower grid structures and further arranged so that the first and second side edges and the top edge of the upper grid structure are not directly electrically connected to the frame, whilst the bottom edge of the upper grid structure, the first and second side -5 edges and bottom edge of the lower grid structure are directly electrically connected to the frame. Preferably the upper edge of the lower grid structure is directly connected to 5 the frame. Each of the upper and lower grid structures may include one or more electrically conductive sheets of material. 10 The conductive frame may also include a conductor member arranged for electrical connection to the bottom edge of the upper grid structure. The conductor member is preferably further arranged for electrical connection to the upper edge of the lower grid structure. The bottom edge of the upper grid structure and the upper edge of the lower grid structure are preferably also 15 mechanically supported by the conductor member. The conductor member may be integrally formed with the frame. One or more insulating members may be provided to electrically insulate the 20 first and second side edges and the top edge of the upper grid structure from the conductive frame. Similarly, the edge of the grid structure may be coated with a non-conductive material, to which the conductor member could then adhere to, giving mechanical support whilst insulating the conductor member from the required edges of the grid structure. 25 Brief Description of the Accompanyinq Drawings The following description refers in more detail to the various features and steps of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the 30 invention is illustrated by way of preferred embodiment(s). It is to be understood however that the invention is not limited to the embodiment(s) illustrated in the drawings. In the drawings: -6 Figure 1A is an exploded view of two sheets of material that when combined together form a grid structure suitable for use in a current collector arrangement according to an embodiment of the invention; 5 Figure 1 B is a front view of the structure shown in Fig. 1A; Figure 2 illustrates a current collector arrangement according to a first embodiment of the invention; 10 Figure 3 illustrates a current collector arrangement according to a second embodiment of the invention; Figure 4 is a graph showing the resistance down the length of a plate for 15 various current collector arrangements; Figure 5 illustrates a current collector arrangement according to a third embodiment of the invention; 20 Figure 6 is a graph showing resistance down the length of a plate for various current collector arrangements; Figure 7 is a table summarising the variations in resistance of various collector arrangements; and 25 Figure 8 is a graph showing resistance down the length of a plate for various current collector arrangements. Detailed Description of the Preferred Embodiments 30 Figures 1A and 1B illustrate a grid structure 10 suitable for forming a current collector for a negative collector plate or electrode of an electrochemical cell, such as a lead-acid battery. The structure 10 includes a pair of adjoined layers 12, 14 of electrically conductive sheets. The layers 12, 14 are formed from metal sheet, such as lead, aluminium or copper.

-7 The layers 12, 14 may be manufactured by cutting, stamping, expansion, or other processing from a thin sheet of metal, although in alternative embodiments the layers 12, 14 may be formed as a woven mesh sheet of 5 metal strands or wires. The processing may create a layer as a generally rectangular layer having a generally planar form with a notional primary plane. Although the above described grid structure 10 includes two adjoined layers 12, 14, it is possible that only one or more than two adjoined layers may be 10 used to form the grid structure. Figure 2 illustrates a current collector arrangement 900 for an electrode plate in accordance with an embodiment of the invention. The current collector arrangement 900 includes an upper structure 10 and a lower structure 10'. 15 The upper structure 10 and lower structure 10' are supported in a frame assembly 902 comprising current collector edging 904. The current collector edging 904 is arranged so that the frame assembly 902 provides an electrical conductor which extends entirely around the periphery of the current collector arrangement 900. 20 In the illustrated embodiment, side edges 906, 908 (shown dashed) and upper edge 910 (shown dashed) of the upper structure 10 are not electrically connected to the current collector edging 904, whereas the side edges 920, 922 (shown dashed) and lower edge 924 (shown dashed) of the lower 25 structure 10' are electrically connected to the current collector edging 904. Although not electrically connected to current collector edging 904, the side edges 906, 908 and upper edge 910 of the upper structure 10 are mechanically supported within the current collector edging 904 in a manner 30 which secures the edges 906, 908, 910 therein, but which electrically insulates the side edges 906, 908 and upper edge 910 of the upper structure 10 from the current collector edging 904.

-8 Electrically insulating the edges 906, 908, 910 of the upper structure 10 may involve, for example, locating an insulator, such as a resin, between the side edges 906, 908 and upper edge 910 of the upper structure 10 and the respective channel of the current collector edging 904 receiving those edges. 5 Suitable insulators would be well known to a skilled addressee. The bottom or lower edge 912 of the upper structure 10 is electrically and mechanically connected to a central conductor member 916 which bridges across the current collector arrangement 900. The conductor member 916 10 may include a I-section channel or other suitable channel adapted to receive the lower edge 912 of the upper structure 10, and the upper edge 918 of the lower structure 10' to form an electrical and mechanical connection therebetween across the width of each structure 10, 10'. In the present example, opposite ends of the central conductor member 916 are terminated 15 to the current collector edging 904 to form electrical connection therewith. However, it will be appreciated that it is possible the central conductor member 916 may be integrally formed with the frame assembly 902. Similarly, the whole grid structure may be made from a single piece and the central conductor 91may be connected to a flattened section of the structure. 20 The upper edge 918 of the lower structure 10' is also electrically and mechanically connected to the central conductor member 916. Side edges 920, 922, and a lower edge 924 of the lower structure 10' are similarly electrically and mechanically connected to corresponding locations of the 25 current collector edging 904 using a suitable bonding or joining process. In the illustrated arrangement, because the side edges 906, 908 and upper edge 910 of the upper structure 10 are not directly electrically connected to the current collector edging 904, the only current conduction path available 30 between the upper structure 10 and the lug 926 disposed on the upper edge 928 of the current collector edging 904 is via the central conductor member 916. Consequently, and as is represented by the arrows generally indicating the current conduction path, the length of the current conduction path from areas within the upper grid structure 10 disposed towards the upper edge 928 -9 is effectively increased compared to the length of the current conduction path which would be available if the side edges 906, 908 and upper edge 910 of the upper structure 10 were directly electrically connected to the current collector edging 904. An advantage of this arrangement is that it creates a 5 more uniform distribution of resistance along the length of the electrode and thus provides a more uniform distribution of active material utilisation of the electrode plates. Figure 3 illustrates a second embodiment of the invention. The current 10 collector arrangement 1000 includes a structure 1010, 1010' having edges supported in a current collector edging 1904. The upper half of the structure 1010 is not connected to the current collector edging 1904 and this is depicted by the broken form of the lines showing the current collector edging 1904. The upper edge of the upper half of the structure 1010 is connected to the lug 15 1926. The lower half of the structure 1010' is connected to the current collector edging 1904 and to a central conductor member 1916 and this is depicted by the solid form of the lines showing the current collector edging 1904 and the central conductor member 1916. The upper and lower halves of the structure 1010, 1010' are integrally formed. 20 In accordance with the second embodiment of the invention, the pickup point for the upper half of the structure 1010 is the central conductor member 1916. The current collector edging 1904 is made from, for example, by two 25 1.6mmx5mm copper strips. Figure 4 shows a graph of resistance down the length of three collector arrangements having different configurations. Line 1 represents the resistance in a long collector plate with side current collector edging as 30 depicted in Figure 3 but connected at all points to the grid, Line 2 represents the resistance in a long plate without side current collector edging and Line 3 represents the resistance in a long plate as shown and described in relation to Figure 3.

-10 As shown in the graph of Figure 4, the plate formed in accordance with the second embodiment of the invention provides more even resistance along the length of the plate when compared to the other collector arrangements tested. 5 Figure 5 illustrates a third embodiment of the invention. The current collector arrangement 1500 includes a single expanded mesh structure 1510 formed with diamond shaped openings. As depicted in Figure 5 the diamond shaped openings run vertically and includes 22 diamonds across the width and 39.5 diamonds along the length. 10 The mesh structure 1510 is located within a non-conductive frame assembly 1512. The frame assembly 1512 is mechanically but not electrically connected to the upper half of the mesh structure 1510. The frame assembly 1512 includes a current collector edge 1520 that runs down the length of one side 15 of the structure 1510 and provides electrical connection between the lug 1526 located along the upper edge of the structure 1510 and the bottom half of the structure 1510. The other edges of the frame assembly 1512 are made from a plastic material and merely provide support to the mesh structure 1510. 20 The current collector edge 1520 is formed from two 1.6mm x 5mm wide strips that site either side of the edge of the structure 1510. The mesh structure 1510 is between 258-262 mm wide and is between 1034-1038 mm in length. Figure 6 shows a graph of resistance down the length of three current 25 collector arrangements having different configurations. The three current collector arrangements include the current collector arrangement 1500 as shown in Figure 5, a current collector arrangement similar to that shown in Figure 5 but with the diamond shaped openings of the expanded mesh running horizontally and a current collector arrangement with a conventional 30 vertical grid and without a side current collector edge. As shown in Figure 6, the current collector arrangement 1500 (as per Figure 5) provides more even resistance along the length of the plate when compared to the other collector arrangements tested.

-11 A current collector arrangement according to a further embodiment of the invention is similar to that shown in Figure 5 but has a current collector edge 1520 formed from two 1.6mm x 10mm wide strips. The resistance down the 5 length of the plate for this current collector arrangement was tested and compared with other current collector arrangements. As shown in Figure 7 and in the table of Figure 8, the variation in resistance along the length of the plate for the current collector arrangement 1500 was 290pOhm, whilst the variation for the similar current collector arrangement with 10mm wide current 10 collector edge was 294pOhm. The increased size of the current collector edging resulted in a reduction in the maximum resistance as shone in the table, however the variation in resistance is slightly greater. This suggests that in changing the conductivity of the current collector the optimum connection point between the grid and the current collector has also changed. 15 For this reason, the optimum point for the connection of the current collector to grid is dependent upon the size, density and conductivity of the grid, and the current collector structure. It should also be noted, that the final arrangement of the negative current 20 collector structure may be altered to adjust the overall resistance of the battery, that is, when including the resistance of the positive plate and other components (i.e. the negative plate current collector is connected such that the overall resistance of the cell is as equal as possible). This may mean that the negative plate current collector structure is not connected such that the 25 negative plate resistance when considered separately is optimised, but that when the sum of the resistances within the battery are considered together, the resistance is kept as even as possible. It will be appreciated by persons skilled in the art that numerous variations 30 and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 35

Claims (16)

1. A current collector arrangement for a plate of an electrochemical cell, said current collector arrangement including a grid structure, at least one lug and a conductive frame, said conductive frame arranged for electrical 5 connection to a lower part of the grid structure that is distal from the at least one lug and not to an upper part of the grid structure, whereby the conductive frame reduces the difference in resistance along the length of the plate by providing an additional electrical conductive path for the lower part of the grid structure to the at least one lug. 10

2. A current collector arrangement according to claim 1 wherein the conductive frame extends along at least one side of the grid structure.

3. A current collector arrangement according to claim 2 wherein the 15 conductive frame extends about all sides of the grid structure.

4. A current collector arrangement according to any one of the preceding claims wherein the frame further includes a conductor member arranged for electrical connection to the lower part of the grid structure. 20

5. A current collector arrangement for a plate of an electrochemical cell including an upper grid structure and a lower grid structure and a frame supporting the upper and lower grid structures, said upper grid structure including opposed first and second side edges and opposed top and bottom 25 edges, said lower grid structure including opposed first and second side edges and opposed top and bottom edges, said frame arranged to provide an electrical conductor that extends around the periphery of the upper and lower grid structures and further arranged so that the first and second side edges and the top edge of the upper grid structure are not directly electrically 30 connected to the frame, whilst the bottom edge of the upper grid structure, the first and second side edges and bottom edge of the lower grid structure are directly electrically connected to the frame. -13

6. A current collector according to claim 5 wherein the conductive frame includes an edging that extends about the first side edge, top edge and second side edge of the upper grid structure and the second side edge, bottom edge and the first side edge of the lower grid structure. 5

7. A current collector according to claim 5 wherein the upper edge of the lower grid structure is directly connected to the frame.

8. A current collector arrangement according to any one claims 5 to 7 10 wherein each of the upper and lower grid structures includes one or more electrically conductive sheets of material.

9. A current collector arrangement according to any one claims 5 to 8 claims wherein the frame further includes a conductor member arranged for 15 electrical connection to the bottom edge of the upper grid structure.

10. A current collector arrangement according to claim 9 wherein the conductor member is further arranged for electrical connection to the upper edge of the lower grid structure. 20

11. A current collector arrangement according to any one of claims 5 10 wherein the upper grid structure and lower grid structure are integrally formed.

12. A current collector arrangement according to any one of the preceding 25 claims wherein the frame is formed as a channel or includes opposed strips of material arranged to sandwich the edges of the grid structure therebetween.

13. A current collector arrangement according to any one of the preceding claims wherein the plate has a length of greater than about 500mm. 30

14. A current collector arrangement according to any one of the preceding claims wherein the plate has a length greater than about twice its width. - 14

15. A current collector arrangement substantially as hereinbefore described with reference to any of the accompanying drawings.

16. A battery including a current collector arrangement according to any 5 one of claims 1 to 15.