Patent Application
20050079411
This invention relates in general to a battery can, and deals more particularly with a battery can having a plurality of longitudinal lands and grooves formed on the inside thereof for promoting increased battery performance.
Electrochemical cells are commonly employed to provide voltage for electrically operated devices, and are particularly well suited for portable electrically operated devices. One type of commonly known electrochemical cells are conventional alkaline cells which are of a generally cylindrical shape and are commercially available in sizes ranging from D, C, AA, AAA and AAAA, amongst other sizes and configurations.
Of great importance to manufacturers of electrochemical cells is the available energy density of the cells themselves. As utilized hereinafter, the term ‘energy density’ is defined as the energy obtainable per unit weight (gravimetric energy density) or per unit volume (volumetric energy density). Energy density is typically measured by determining the capacity and noting the average potential during discharge. Gravimetric (or ‘weight’) energy density is expressed in Wh/kg (watt-hours/kilogram), while volumetric energy density Wh/m3.
While there are many methods of increasing the overall energy density of electrochemical cells, including advancements being made in the nature of the electrochemical materials utilized therein, it has also been known to augment the manufacture of the battery can, i.e., the metal outer cylindrical shell, or can, of the electrochemical cell, itself.
In particular, attempts at making the outer longitudinal wall of the battery can as thin as possible, so as to increase the inner volume of the battery can, have resulted in increases in overall energy density. Still other configurations have relied upon a limited number of inwardly formed ribs to boost the energy density of electrochemical cells.
It has also been known to manufacture battery cans utilizing a Drawing and Ironing technique (DI). The known DI technique is also utilized to improve the volumetric energy density of the battery and employs a deep-drawing step using a press, followed by an ironing step using an ironing machine. While the DI technique is known for producing incidental, minor indentations on the inner surface of the battery can, on the order of approximately 1 micron, these indentations are neither uniform in size or shape, nor are they evenly distributed about the inner surface of the battery can.
With the foregoing problems and concerns in mind, it is the general object of the present invention to provide a battery can having increased performance characteristics.
It is another object of the present invention to provide a battery can having a thinner outer wall.
It is another object of the present invention to provide a battery can having an outer wall that varies in cross-sectional thickness.
It is another object of the present invention to provide a battery can having a plurality of longitudinal lands and grooves formed on the inside thereof.
It is another object of the present invention to provide a battery can having a plurality of substantially uniform longitudinal lands and grooves formed on the inner surface thereof.
The present invention is generally a battery can having a plurality of longitudinal lands and grooves formed on the inner surface thereof, whereby the lands and grooves define a continuous and substantially repeating pattern across the entire inner surface area of the outer wall of the battery can.
Further, a preferred embodiment of the present invention includes a battery can having a plurality of lands and grooves extending longitudinally and for substantially an entire axial length of the battery can, whereby the longitudinally extending lands and grooves have a substantially uniform and continuously repeating sinusoidal pattern, as seen in cross-section.
These and other objectives of the present invention, and their preferred embodiments, shall become clear by consideration of the specification, claims and drawings taken as a whole.
It is therefore an important aspect of the present invention that the presence of the pattern 14 of the lands and grooves significantly increases the total internal surface area of the battery can 10, thus correspondingly increasing the capacity of the inner surface of the battery can 10 to contact the electrochemical materials housed therein. In this manner, the energy density of the battery can 10 is similarly increased.
Moreover, it will be readily appreciated that by forming the lands 18 and the grooves 16, as best seen in
In a preferred embodiment of the present invention, approximately 100 to approximately 150 grooves 16, and a separate but substantially equal number of lands 18, may be formed about the inner surface of the battery can 10, assuming a standard AA-sized battery. More preferably, approximately 120 grooves 16 and 120 lands 18 are formed on the inner surface of the battery can 10 for a standard AA-sized battery. It will be readily appreciated that a correspondingly greater, or lesser, number of lands 18 and grooves 16 may be formed in batteries of differing sizes from that of a standard AA-type battery, in dependence upon the actual dimensions of the lands 18 and grooves 16, as will be discussed in more detail later.
In addition to increasing the internal surface area of the battery can 10, the present invention also increases the total internal volume of the battery can 10 by reducing the total average thickness of the shell 12.
It is therefore another important aspect of the present invention that the architecture of the battery cell 10, as perhaps best seen in cross-section in
Moreover, it has been determined that the minimum value for the depth, D, of the grooves 16 is in the range of approximately 0.0005 inches to approximately 0.001 inches, as any lesser depth would have only a negligible effect on the total internal surface area and internal volume of the battery can 10. Conversely, the maximum value for the depth, D, of the grooves 16 is dependent upon the concern that no cross-sectional portion of the shell 12 ever falls below approximately 0.004 inches, thereby ensuring the structural stability and durability of the battery can 10.
It will also be noted by a review of
Turning to the radii, R, of the raised-area lands 18 shown in
It is therefore another important aspect of the present invention that a sinusoidal cross-sectional geometry is utilized not only to ensure the greatest possible increase in internal surface area while still maintaining the structural integrity of the shell 12, but also because differing cross-sectional patterns, such as rectangular, trapezoidal or V-shaped patterns, have been shown to weaken the punch that forms the lands and grooves 14 if employed at a scale commensurate with lands 18 of 0.005 inches of radii, R, utilized in conjunction with the sinusoidal pattern of
That is, in the formation of very fine and numerous lands 18 and grooves 16, on the order of approximately 120-150 for a standard AA-type battery, the sinusoidal cross-sectional geometry is preferred as maximizing the number of lands 18 and grooves 16 to the greatest practical extent, given the practical constraints of the punch tooling utilized in their formation. However, it should be noted that should the ratio of the number of the lands 18 and grooves 16 to the inner surface area, or circumference, of the battery can 10 decrease, differing cross-sectional configurations, such as rectangular, trapezoidal or V-shaped cross-sectional patterns, may be utilized without harming the punch tooling or departing from the broader aspects of the present invention.
As compared to the conventionally formed battery can A, the internal volume of battery can B has increased from 0.3736 cubic inches to 0.3773 cubic inches, or by approximately 1.0%. Similarly, the internal surface area of battery can B has increased from 3.0393 square inches to 3.2129 square inches, an increase of approximately 5.4%, while the cross-sectional wall area of battery can B has decreased from 0.0135 square inches to 0.0118 square inches, a decrease of approximately 12.6%.
As will be appreciated, the increases in both the internal volume and the internal wall surface area of the battery can 10, as well as the decrease in the cross-sectional wall area, result in a electrochemical cell which is capable of housing a greater volume of electrochemical materials, while providing for more contact between the shell 12 and these electrochemical materials—all without increasing the outer dimensional characteristics of the battery can 10. The net effect of such an architecture is to create a battery can 10 capable of exhibiting greater energy density, without sacrificing either structural stability or standard dimensional requirements.
The process by which the battery can 10 is formed will now be described. A Drawn and Ironed (DI) process is utilized for formation of the battery can 10 and generally involves utilizing a transfer press having a plurality of grooves formed thereon so as to provide the longitudinally extending lands and grooves 14 to the inner surface of the battery can 10.
As shown in step 20 of
In the process disclosed in
While the grooved battery can 10 has been described in conjunction with an AA-sized battery, the present invention is not so limited in this regard as the formation of uniform and continuous longitudinally formed grooves may be alternatively employed in batteries of any size or shape.
While the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various obvious changes may be made, and equivalents may be substituted for elements thereof, without departing from the essential scope of the present invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention includes all embodiments falling within the scope of the appended claims.
