Battery packs provide power for various technologies ranging from portable electronics to renewable power systems and environmentally friendly vehicles. For example, hybrid electric vehicles use a battery pack and an electric motor in conjunction with a combustion engine to increase fuel efficiency. Battery packs may be formed of a plurality of battery modules, where each battery module includes several electrochemical cells. Within the battery module, the cells are electrically connected in series or in parallel. Likewise, the battery modules are electrically connected in series or in parallel within the battery pack.
Different cell types have emerged in order to deal with the space requirements of a very wide variety of applications and installation situations, and the most common types used in vehicles are cylindrical cells, prismatic cells, and pouch cells. Regardless of cell type, each cell includes an electrode assembly that is sealed within a cell housing along with an electrolyte to form a power generation and storage unit. The electrode assembly may include an alternating arrangement of positive and negative electrode elements separated by intermediate separator plates, and can be provided in various configurations. The electrode assembly of a cylindrical cell is typically formed by winding an elongated electrode pair into a jelly-roll configuration.
Due to their curved shape, cylindrical cells do not pack efficiently in a battery module. In addition, it is advantageous to provide spacing between adjacent cells within the battery module in order to minimize the propagation of heat from cell to cell, and to permit a cooling fluid to be passed between the cells to remove heat from the cells. Although it is known to provide cell support structures within a battery module, some conventional support structures are complex in structure and have sufficient bulk to further reduce the battery module packing efficiency. A device is needed that is simple to use and manufacture, can provide a stable, ordered arrangement of cylindrical cells within the battery module, and can maintain a spacing between adjacent cells of a cell array while occupying a minimal volume of the space within the battery module.
In some aspects, a cap assembly is provided for an electrochemical cell. The electrochemical cell has a cell first end, a cell second end that is opposed to the cell first end, and a cell outer surface. The cap assembly includes a first cap configured to receive the cell first end; and a second cap configured to receive the cell second end. Each of the first cap and the second cap include a tubular body. The body includes an inner surface that has a shape and dimensions that correspond to the shape and dimensions of the cell outer surface; and a lip that protrudes inward from the inner surface. The lip is disposed at a first end of the body, and a terminal end of the lip defines an opening in the first end of the body.
In some embodiments, the body has a second end that is opposed to the first end, and the second end of the body is free of a lip.
In some embodiments, the opening has a dimension that is at least 50 percent of a corresponding dimension of the inner surface.
In some embodiments, an outer surface of the body includes surface features that enhance fixation of an adhesive to the outer surface.
In some embodiments, the surface features comprise grooves that alternate with ridges along a circumference of the body. The grooves and the ridges each extend between the first end of the body and a second end of the body, and the second end of the body is opposed to the first end of the body.
In some embodiments, the surface features comprise a helical thread.
In some embodiments, the surface features comprise a knurl.
In some embodiments, the body has a circular cross-sectional shape, and the opening has a circular cross-sectional shape.
In some embodiments, the opening is centered on the first end of the body.
In some aspects, a battery module includes an array of electrochemical cells. Each electrochemical cell includes a cell first end; a cell second end that is opposed to the cell first end; a cell outer surface; and a cap assembly. The cap assembly includes a first cap disposed on the cell first end; and a second cap disposed on the cell second end. Each of the first cap and the second cap include a tubular body. The body has an inner surface that has a shape and dimensions that correspond to the shape and dimensions of the cell outer surface. In addition, the body has a lip that protrudes inward from the inner surface. The lip is disposed at a first end of the body, and a terminal end of the lip defining an opening in the first end of the body.
In some embodiments, the body includes a second end that is opposed to the first end, each of the first cap and the second cap have a cap length that corresponds to a distance between the first end of the body and the second end of the body, each cell has a cell length that corresponds to a distance between the cell first end and the cell second end, and a ratio of the cap length to the cell length is in a range of 0.05 to 0.30.
In some embodiments, the body has a second end that is opposed to the first end, and the second end of the body is free of a lip.
In, some embodiments, the opening has, a dimension that is at least 50 percent of a corresponding dimension of the inner surface.
In some embodiments, an outer surface of the body includes surface features that enhance fixation of an adhesive to the outer surface.
In some embodiments, a first terminal protrudes from the cell first end of each cell, and the opening in the first cap surrounds the first terminal.
In some embodiments, the cell housing of each cell of the cell array is cylindrical, and all the cells of the cell array have the same diameter.
In some embodiments, at least one cell of the cell array is the surrounded by other cells of the cell array in such a way that the first cap of the at least one cell is in direct contact with the first cap of six other cells of the cell array, and the second cap of the at least one cell is in direct contact with the second cap of six other cells of the cell array.
In some embodiments, the outer surface of the at least one cell is spaced apart from the outer surfaces of the six other cells, and the distance between the outer surface of the at least one cell and the outer surfaces of the six other cells corresponds to twice the thickness of the body, where the thickness of the body is the distance between the inner surface of the body and an outer surface of the body.
Since the typical battery pack and/or module has a polygonal (rectangular or other) prismatic shape, cylindrical cells provide a relatively low volumetric efficiency within a polygonal battery pack or module when compared to, for example, prismatic cells. This volumetric inefficiency can be minimized by employing a close-packed arranaement of cells with in the battery pack or module. By providing spacer caps on the ends of each cell to ensure a space exists between adjacent cells, and by providing the cell-and-cap assembly in a close-packed arrangement within a battery module or pack, volumetric efficiency is maximized while providing a stable, ordered and arrangement of cylindrical cells. In addition, a spacing is maintained between adjacent cells of a cell array that allows for passage of a cooling fluid, whereby temperature of the cells can be controlled.
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An electrode assembly 26 is sealed within the cell housing 12 along with an electrolyte to form a power generation and storage unit. The electrode assembly 26 includes a stacked arrangement of a positive electrode 28, a first separator 30, a negative electrode 32 and a second separator 34, in which the stacked arranged has been rolled to provide a “jelly roll”. One of the electrodes, for example the positive electrode 28, is electrically connected to the lid 14, which serves as a positive terminal 36 of the cell 10. In addition, the other electrode, for example the negative electrode 32, is electrically connected to the container portion 16, which serves as a negative terminal 38 of the cell 10.
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The body 46 includes a lip 58 that protrudes inward from the inner surface 48. The lip 58 is disposed at the first end 52 of the body 46. A terminal end 60 of the lip 58 (e.g., a surface of the lip 58 that faces a centerline of the body 46) defines an opening 62 in the first end 52 of the body 46. The opening 62 is circular, and is centered on the body first end 42. The opening 62 is large relative to the size of the body first end 52. For example, the opening 62 has a dimension that is at least 50 percent of a corresponding dimension of the body first end 52. In the illustrated embodiment, the opening 62 has a diameter d1 that is about 85 percent of the diameter d2 of the body first end 52.
The second end 54 of the body 46 is free of a lip, and thus provides an unobstructed opening that receives an end (for example, the first end 14) of the cell housing 12 therein.
The outer surface 50 of the body 46 includes surface features that enhance engagement with the outer surfaces of adjacent caps 42. For example, the surface features may include elongated, linear grooves 84 that alternate with elongated, linear ridges 82 along a circumference of the body 46. The grooves 84 and the ridges 82 each extend between the first and second ends 52, 54 of the body 46.
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In other embodiments, the grooves 84 and ridges 82 of the cell cap 42(1), 44(1) of one cell 10(1) form an interlocking engagement with the corresponding grooves 84 and ridges 82 of the cell cap 42(2), 44(2) of an adjacent cell 10(2). The interlocking engagement may be employed alone, or in combination with an adhesive, to retain the cells in the desired array configuration.
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The first cap 42 may be formed of an electrically insulating material such as plastic.
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As previously discussed, each cell 10 of the cell array 8 is supported within the battery module housing 2, and relative to other cells 10 of the cell array 8, via the cap assemblies 40 disposed on each cell 10. That is, each cell 10 of the cell array includes a first cap 42 disposed on the first end 14 of the cell housing 12, and a second cap 44 disposed on the second end 20 of the cell housing 12. When the first cap 42 is disposed on the cell housing first end 14, the cell housing first end 14 abuts the body inner surface 48 at the lip 58, and the positive terminal 36 is accessible via the opening 62. In the illustrated embodiment, the lid 14, which serves as the positive terminal 36, includes a protrusion 35 that is surrounded by and extends into the opening 62. The protrusion 35 may serve as a welding location that is connected to a bus bar (not shown) via welding. Similarly, when the second cap 44 is disposed on the cell housing second end 20, the cell housing second end 20 abuts the body inner surface 48 at the lip 58, and a portion of the negative terminal 38 (e.g., the portion associated with the second end 20) is accessible via the opening 62. In this configuration, the body second ends 54 of the first and second caps 42, 44 are disposed between the body first ends 52 of the first and second caps 42, 44.
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In cell arrays having several rows R and columns C of cells 10, each cell 10 of the array is adjacent to multiple other cells 10 of the array. For example, in the array 8 illustrated in
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The cell arrays 8, 108 shown in
Although the cell 10 is described herein as being a lithium-ion cell, the cell 10 is not limited to having a lithium-ion chemistry. For example, the cell 10 may have other chemistries, including aluminum-ion, alkaline, nickel-cadmium, nickel metal hydride, or other appropriate chemistry.
Moreover, although the cell 10 is described as having a cylindrical shape, the cell 10 may be formed in an alternative shape, such as a prismatic or a pouch shape. For cells having an alternative shape, the body 46 of the first and second caps 42, 44 has a corresponding shape.
Although the positive electrode 28 is described here as being electrically connected to the lid 14, and the negative electrode 32 is described here as being electrically connected to the container portion 16, it is understood that the cell 10 may alternatively be configured so that the positive electrode 28 is electrically connected to the container portion 16, and the negative electrode 32 is electrically connected to the lid 14.
Selective illustrative embodiments of the battery module including electrochemical cells supported in an array by spacer caps are described above in some detail. It should be understood that only structures considered necessary for clarifying these devices have been described herein. Other conventional structures, and those of ancillary and auxiliary components of the battery module, electrochemical cells and/or the spacer caps, are assumed to be known and understood by those skilled in the art. Moreover, while working examples the battery module, electrochemical cells and/or the spacer caps been described above, the the battery module, electrochemical cells and/or the spacer caps are not limited to the working examples described above, but various design alterations may be carried out without departing from the devices as set forth in the claims.