CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/062,356, filed Oct. 15, 1997.

BACKGROUND OF THE INVENTION

The present invention generally relates to an electrochemical cell and battery and, more particularly, to an electrochemical cell and an assembly of multiple cells in a rectangularly housed battery.

Conventional alkaline batteries commonly employ cylindrical cells, each generally having a cylindrically shaped steel can provided with a positive cover at one end and a negative cover at the opposite end. The cylindrical cell often includes a cathode preferably formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionized water, and a TEFLON® solution, formed about the interior side surface of the cylindrical steel can. A cup-shaped separator is usually disposed about the interior surface of the cathode. An anode, typically formed of zinc powder, a gelling agent, and other additives, is dispensed with electrolyte solution within the separator.

Standard alkaline cells are commercially available for providing an open circuit voltage of about 1.5 volts. When a higher voltage is required, it is common practice to combine multiple cells to form a battery having the required voltage. In so doing, a plurality of cells are commonly housed in a container and connected in series, with external terminals attached to the container and making contact with the series connected cells. In particular, the standard rectangular-housed, 9-volt battery, which is commonly used in smoke detectors and portable electronic devices, includes six, 1.5-volt cells connected in series. One example of a rectangular battery employs two stacks of three cylindrical cells disposed parallel to each other as is disclosed in U.S. Pat. No. 4,959,280 entitled “Battery Assembly,” which is hereby incorporated by reference. It is also known to employ six, 1.5-volt cylindrical cells arranged in parallel with each other in a 2×3 array. However, the use of multiple, parallel disposed cylindrical cells housed together within a rectangular container results in unused space between adjacent cells, as well as between each cell and the inside walls of the battery container.

A primary goal in designing alkaline batteries is to increase the service performance of the cell. The service performance is the length of time for the cell to discharge under a given load to a specific voltage at which the cell is no longer useful for its intended purpose. Commercially available alkaline cells and batteries commonly have an external size that is defined by industry standards, thereby limiting the ability to increase the amount of active materials within a given cell and confining the volume available in a multiple cell battery. However, conventional batteries often do not optimize volume consumption within the housing of the battery. Accordingly, the need to find new ways to increase service performance remains the primary goal of the cell and battery designers.

SUMMARY OF THE INVENTION

The present invention improves the performance of a cell and a rectangularly housed, multiple cell battery by providing the cell with a prismatic can, preferably of a rectangular configuration, having a round open end to accommodate a round cover. To achieve this and other advantages, and in accordance with the purpose of the invention as embodied and described herein, the present invention provides an electrochemical cell which includes a prismatic can configured to have a prismatic section, such as a rectangular section, and a round open end that is covered with a round cover. The rectangular prismatic section has a substantially prismatic radial cross section and houses the active materials of the cell including a cathode and an anode, as well as a separator. The anode is preferably provided in an inner cylindrical volume of the cell, and the cathode consumes the volume between the anode and the interior walls of the can. The cell may be assembled with a round cover and seal assembly provided on the round open end.

According to a further aspect of the present invention, a plurality of prismatic cells, such as rectangular cells, are assembled in a housing, such as a rectangular housing of a multiple cell battery. The cells are each configured with a prismatic section, such as a rectangular section, to allow multiple cells to be assembled close together and thereby optimize volume consumption within the battery housing.

These and other features, objects, and benefits of the invention will be recognized by those who practice the invention and by those skilled in the art, from reading the following specification and claims, together with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1

is a partial perspective view of a rectangular battery having six rectangular electrochemical cells with round covers and assembled according to the present invention;

FIG. 2

is a top plan view of the battery of

FIG. 1

showing the cells assembled in the battery housing;

FIG. 3

is a partial exploded view of the battery of

FIG. 1

;

FIG. 4

is an elevational view of one rectangular electrochemical cell with a round top end and adjoining round cover according to the present invention;

FIG. 5

is a top view of the electrochemical cell shown in

FIG. 4

;

FIG. 6

is a cross-sectional view of the electrochemical cell taken through lines VI—VI in

FIG. 5

;

FIG. 7

is a cross-sectional view of the electrochemical cell taken through lines VII—VII in

FIG. 4

; and

FIG. 8

is a cross-sectional view of the electrochemical cell taken through lines VII—VIII of FIG.

5

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to

FIG. 1

, a multiple cell battery

10

is shown having a rectangular housing

12

, preferably including a metal jacket, with a non-conductive coating, defining four sidewalls and top and bottom terminal boards

14

and

16

defining the respective top and bottom surfaces. The battery

10

has positive and negative contact terminals

18

and

20

assembled to the top terminal board

16

via rivets (not shown). According to the embodiment shown and described herein, the size and shape of the housing

12

, as well the location of the positive and negative contact terminals

18

and

20

, is provided in accordance with the standard commercially available 9-volt rectangular battery according to current industry standards. Nine-volt rectangularly housed batteries of this size and shape are widely available, particularly for use with smoke detectors and portable electronic devices.

While a rectangular configured cell and a rectangular battery housing multiple rectangular cells are shown and described herein according to the preferred embodiment, it should be appreciated that the teachings of the present invention are not limited to the specific embodiments shown. The teachings of the invention may be applicable to various multiple cell battery housings and various electrochemical cell configurations having a generally prismatic shape. Additionally, the present invention is not limited to the alkaline cell having manganese dioxide/zinc, as various other cells may be used, such as carbon/zinc, nickel metal/hydride, nickel/cadmium, nickel/zinc, cells containing lithium, as well as other electrochemical cells. The cell of the present invention may be constructed as a bobbin type cell, a jelly roll type cell, or may incorporate flat plate construction, all of which types of cells are known in the art.

According to the preferred embodiment, the battery

10

houses a plurality of rectangular cells

30

each having a prismatic section and a round end, according to the present invention. The rectangular cells

30

are advantageously assembled parallel to each other in a compact relationship such that adjacent cell walls are close together and preferably abut each other and the remaining cell walls closely abut the interior sides of the housing so as to fit compactly within battery housing

12

. This configuration maximizes volume consumption of housing

12

which allows for realization of increased performance achievable for a given size battery housing. Accordingly, the series connected cells

30

substantially consume the internal volume of housing

12

so as to substantially fully utilize the space available in a standard size battery housing.

Referring particularly to

FIG. 2

, the assembly of cells

30

within housing

12

are seen from a top view with the top terminal board

16

and top cover assembly removed. The six cells

30

are assembled side-by-side in a 3×2 array and substantially consume the available volume within rectangular housing

12

of battery

10

. The six cells

30

are arranged within housing

12

in an alternating fashion such that the positive and negative terminal ends of cells

30

are flip-flopped relative to adjacent cells. The cells

30

are electrically interconnected in series such that battery

12

provides a battery supply voltage across terminals

18

and

20

equal to the total aggregate voltage supply of the cells

30

. According to one example, each of the six cells

30

supplies an approximate 1.5 volts, thereby providing an approximate 9-volt battery voltage supply.

With particular reference to

FIG. 3

, the multiple-cell battery

10

and assembly thereof is shown in an exploded view with the metal jacket walls of housing

12

removed. Cells

30

are disposed in contact with bottom conductive contact strips

40

on the bottom side and top conductive contact strips

38

on the top side, which provide a series interconnection of the cells

30

. Contact strips

40

are assembled on a thin insulating paper

26

which, in turn, is disposed on the top surface of a resilient pad

28

. Resilient pad

28

lies on top of the bottom terminal board

14

of battery

10

. Resilient pad

28

preferably includes a rubber material which provides a spring-like surface. When compressed, resilient pad

28

forcibly urges contact strips

40

against the corresponding terminals on the cells

30

on the bottom side, while also forcibly urging the upper terminals of cells

30

against contact strips

38

on the top side. This pressure contact ensures a continuous series electrical interconnection of the multiple cells

30

. Although the conductive contact strips provide pressured contact against the cells, it should be appreciated that one or more of the contact strips could be soldered or welded to the cells using conventional methods.

Contact strips

38

similarly are assembled to contact the corresponding terminals on the top side of cells

30

. Contact strips

38

are disposed below a support pad

36

, which may include cardboard. Disposed about opposite corners of support pad

36

are metal contact pads

32

and

42

, which wrap around the top and bottom sides of support pad

36

. Contact pads

32

and

42

are assembled on top of thin layers of insulating paper

34

and

44

, respectively. Metal contact pad

32

directly contacts both the positive terminal of one cell

30

and the positive contact terminal

20

of battery

10

. Metal conductive pad

42

directly contacts both the negative terminal of another cell

30

and the negative contact terminal

18

of battery

10

. The two cells

30

in contact with contact pads

32

and

42

are at opposite ends of the series electrical interconnection. Accordingly, positive and negative contact terminals

20

and

18

, respectively, provide a voltage potential across the series electrical interconnection of cells

30

.

Referring to

FIG. 4

, one of the electrochemical cells

30

is shown configured with a rectangular steel can

60

having an open round top end for receiving a round cover according to the present invention. Steel can

60

has a rectangular section

50

extending along a vast majority of the length of the cell and transitions to a round end

52

provided at the top end. The rectangular section

50

of cell

30

has four substantially planar rectangular side walls and a substantially rectangular radial cross section with rounded corners. Rectangular section

50

transitions to the round top end

52

via a bottleneck section

54

. The round top end

52

of can

60

extends from the rectangular section

50

with a taper neck and allows a round cover and seal assembly

56

to be easily welded, attached by adhesive or otherwise assembled to the round top end. In addition, the bottleneck section

54

of steel can

60

may also include a substantially cylindrical section that transitions from the tapered bottleneck section

54

at one end and provides the round opening at the other end. The cylindrical section is preferably short in length and allows the round cover

56

to matingly engage and seal closed the open round end.

The cell

30

has a bottom end

58

defined by the bottom side of the rectangular section

50

. The bottom end

58

serves as a positive cover to provide a positive cell terminal. At the top end of the cylindrical section

52

is cover and seal assembly

56

with a substantially rounded shape which includes a negative cell cover or terminal

62

. The top end of cell

30

is further shown in FIG.

5

. According to the configuration shown, cell

30

realizes increased volume in the rectangular section

50

in contrast to the conventional cylindrical cell used in a rectangular battery, while having a round top end

52

that easily accommodates the standard round negative cover and seal assembly

56

. This allows for an increase in active cell materials over that of the conventional cylindrical cell of a size having a diameter equal to the width of the side walls of the rectangular section

50

.

Referring to

FIGS. 6 and 8

, the electrochemical cell

30

is further illustrated in cross-sectional views taken along the longitudinal axis of the cell

30

and at an angular displacement of forty-five degrees relative to the two views. The cell

30

includes steel can

60

having a rectangular shape with a closed bottom end

58

forming a positive terminal and having a seal assembly

56

with outer negative cover

62

assembled on the top end of the cell

30

. A thin layer of shrink tube insulation

72

covers the sides of steel can

60

to electrically insulate the metal casing of the cell from adjacent cells and also from the housing

12

of battery

10

. A positive electrode, referred to herein as cathode

64

, preferably formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionized water, and other additives is formed about and abuts the interior side surface of steel can

60

. A cup-shaped separator

66

, which is preferably formed of a non-woven fabric that prevents migration of any solid particles in the battery, is disposed about the interior surface of cathode

64

. A negative electrode, referred to herein as anode

68

, such as a gelled anode, is injected into or otherwise disposed within the interior of the cup-shaped separator

66

. Disposed within anode

68

is a current collector

70

in contact with zinc concentration in anode

68

. The current collector

70

provides a negative contact to the negative cell terminal

62

. The active materials of cell

30

, including the anode

68

and cathode

64

, are substantially disposed within the rectangular section

50

.

The cover and seal assembly

56

provides a closure to the assembly of cell

30

and includes a seal body

76

and compression member

74

. The seal body

76

is generally shaped like a disk and made from electrically non-conductive material. The compression member

74

is a tubularly-shaped metallic component that compresses the seal body

76

around the current collector

70

. The seal assembly

56

also includes the outer negative cover

62

welded to the exposed end of the current collector

70

to form the cell's negative terminal. The rim of steel can

60

is crimped inwardly toward the cell body to form a seal. The seal assembly

56

with cover

62

may include a conventional round assembly, such as that disclosed in U.S. Pat. No. 5,422,201, which is hereby incorporated by reference.

According to one embodiment, the rectangular section

50

of cell

30

has a substantially square radial cross section with rounded corners and equal width W side walls, as shown in FIG.

7

. It should be appreciated that the negative electrode, referred to as the anode

68

, is preferably disposed in the inner cylindrical volume of the rectangular section

58

of steel can

60

, while the positive electrode, referred to as the cathode

64

, fills the volume between separator

66

and the interior walls of steel can

60

, including the four corners of can

60

. By providing a rectangular configuration, the volume within the rectangular section

50

of cell

30

is larger than that of a conventional cylindrical cell having dimensions that would fit within the rectangular walls of cell

30

. This allows for an increase in the volume of the cathode

64

as well as the anode

68

. In addition, the cup-shaped separator

66

may be further disposed radially outward from the longitudinal axis of cell

30

so as to provide a greater anode-to-cathode interface surface area separating the anode

68

and cathode

64

from each other. It should be appreciated that the additional active materials, including those disposed within the corners of the cathode

64

, discharge to increase the capacity of cell

30

.

According to one example, a cell

30

having a square cross section can experience a gain in service performance by as much as approximately twenty-five percent (25%) over the performance experienced with a cylindrical cell having a diameter equal to the width W of the side walls of the rectangular section. The rectangular configuration of cell

30

according to the present invention allows for approximately twenty-one to twenty-five percent (21%-25%) more active cell materials to be used and allows for an approximate twelve percent (12%) increase in anode-to-cathode interface surface area. Cathode-to-can contact resistance is a significant factor in high current discharge of conventional cylindrical cells. With the square cross section of cell

30

of the present invention, the cell

30

may achieve up to a twenty-seven percent (27%) lower contact resistance because the can-to-cathode contact area is increased up to twenty-seven percent (27%).

The cell

30

can be assembled by starting with a cylindrical steel can having a closed bottom end and an open top end. According to this embodiment, the cylindrical steel can is reshaped in a rectangular configured mold to form the rectangular section

50

. According to one assembly approach, the materials of cathode

64

are dispensed within the cylindrical can and the can is thereafter disposed within the rectangular configured mold. A ramrod, which sealingly engages the can with a stripper ring, can be forcibly injected into the can with sufficient force to form a cylindrical passage for the separator and anode, while at the same time forcing a portion of the cylindrical can to be reshaped into a rectangular section as defined by the surrounding rectangular mold. Once this is achieved, the ramrod can be removed and the separator

66

and anode

68

disposed in the cylindrical opening. Thereafter, the collector

70

is inserted into place and the cover and seal assembly

56

with outer negative cover

62

is assembled to the can. Alternatively, the assembly of cell

30

could include starting with a rectangular steel can having a rectangular closed bottom end and a rectangular open top end, and reshaping the open rectangular top end of the rectangular can to form a round top end. It should also be appreciated that the steel can

60

of cell

30

could otherwise be manufactured in a mold to include both the rectangular section

50

and round open end.

It should be appreciated that the cell

30

of the present invention can be suitably manufactured in accordance with an impact mold manufacturing process. According to one impact mold manufacturing process, the cathode mix is dispensed within the can and a ramrod is forcibly injected into the cathode mix and removed to form a cylindrical passage extending centrally through the cathode, thereby molding under impact a cylindrical-shaped anode cavity. The separator

66

and anode

68

are then disposed within the volume of the cavity. It should be further appreciated that the impact molding assembly process can further be utilized to reshape a cylindrical steel can into the rectangular section

50

, as described above.

While cell

30

is shown and described in connection with one embodiment having a rectangular section with a square radial cross section, it should be appreciated that a rectangular radial cross section with unequal sides or other non-round prismatic section may be employed without departing from the teachings of the present invention. In addition, it should be appreciated that an electrochemical cell with a prismatic housing having a tapered bottleneck section leading to a round end can be used as a component of a single cell battery or a multiple cell battery, without departing from the spirit and scope of the present invention.

The electrochemical cell

30

of the present invention preferably includes a non-cylindrical section having one or more substantially flat sidewalls extending parallel to the longitudinal axis of the cell

30

. It is further preferred that the non-cylindrical section of cell

30

have multiple, substantially planar sidewalls which provide a non-round radial cross section having substantially straight sides, and may or may not include rounded corners. The substantially planar sidewalls are particularly advantageous in allowing for multiple cells to be arranged to conform compactly together within a given housing such that cell walls of adjacent cells may be arranged juxtaposed. According to an embodiment shown herein, the non-cylindrical section has four planar sidewalls configured as a rectangular radial cross section. However, the non-cylindrical section may include various prismatic configurations. Prismatic, as used herein, is intended to include a number of possible geometric configurations having at least one substantially planar surface, and preferably having three or more substantially planar surfaces.

According to another embodiment, cell

30

has a prismatic radial cross section configured as a pentagon having five, substantially planar and equal sides. Yet, according to other embodiments of cell

30

, the prismatic radial cross section may include a six-sided hexagon, a seven-sided neptagon, or an eight-sided octagon. According to the aforementioned configurations of a pentagon, hexagon, neptagon, and octagon, such cells may easily be arranged together in a honeycomb arrangement to form a multiple cell battery such that adjacent cell walls of adjacent cells abut one another to maximize use of the available volume within a multiple cell battery housing. It should further be appreciated that a varying number of sidewalls may be employed in accordance with various polygon configurations to provide prismatic radial cross section configurations of the cell

30

according to the present invention.

The electrochemical cell

30

of the present invention employs a prismatic radial cross section which has an effective maximum radial cross-sectional area that is greater than the cross-sectional area available with a conventional cylindrical cell having a cylindrical radial cross section with an effective diameter D

eff

equal to the width W of the prismatic radial cross section of cell

30

. For example, the conventional cylindrical cell has a radial cross-sectional area defined by

π

⁢

⁢

D

eff

2

4

.

In contrast, cell

30

of the present invention with the prismatic radial cross section has a radial cross-sectional area defined by the distance W between opposing sidewalls. For the square cross-sectional embodiment, the radial cross-sectional area is substantially defined by the width W of one wall multiplied by the width W of the adjoining wall. Using this width dimension W, a cylindrical cell having the effective diameter D

eff

provides a lesser radial cross-sectional area and therefore a lesser volume which limits the amount of materials to be disposed within the cell and thereby limits the service performance of the conventional cylindrical cell. By providing multiple, substantially planar surfaces as defined herein, the present invention realizes a cell that may fit within a standard battery housing, such as that provided with a battery-operated electrical device, while providing enhanced service performance to the device.

It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.