US20200168869A1

US20200168869A1 - Battery pack with reduced magnetic field emission

Info

Publication number: US20200168869A1
Application number: US16/693,996
Authority: US
Inventors: David S. Giessel; Bruce Hildesheim
Original assignee: 9013733 Canada Inc
Current assignee: 9013733 Canada Inc
Priority date: 2017-01-24
Filing date: 2019-11-25
Publication date: 2020-05-28
Also published as: US10516147B2; US20180212217A1

Abstract

Implementations of a battery pack with reduced magnetic field emission are provided. The battery pack is configured to reduce or eliminate the magnetic field normally generated while electrical current is being drawn from cylindrical-steel electrochemical cells (e.g., AA batteries) by a connected electrical device. In some implementations, a battery pack with reduced magnetic field emission comprises two or more electrochemical cells positioned in a coaxial configuration. In this coaxial configuration, the supply path is through the center of each electrochemical cell, and the return path is through a conductive sleeve positioned about each electrochemical cell of the battery pack. In this way, the supply path and the return path are as close as is physically possible, thereby minimizing any magnetic field generated between the conductors (i.e., between the electrochemical cells and their conductive sleeves). An insulating layer of material separates each cylindrical-steel electrochemical cell from the conductive sleeve positioned thereabout.

Description

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application claiming the benefit of U.S. patent application Ser. No. 15/676,986, filed on Aug. 14, 2017, which claims the benefit of U.S. Provisional Application Ser. No. 62/449,727, which was filed on Jan. 24, 2017, both applications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to implementations of a battery pack with reduced magnetic field emission.

BACKGROUND

In general, a magnetic field is generated when electrical current (or current) flows through a wire. Similarly, a magnetic field is generated when current is drawn from a battery by a connected device. If a wire having current flowing therethrough, or a battery having current drawn therefrom, is too close to a device that is sensitive to magnetic fields (e.g., an electronic compass—magnetometer), it will interfere with the proper function (e.g., orientation) of the device.
As an example, the magnetic fields generated by the flow of electrical current are a problem in the field of remotely piloted vehicles and unmanned aerial systems/drones (UAS). These devices rely heavily on an electronic compass (e.g., a magnetometer) that measures the magnetic field of the earth to determine flight direction. As such, reliable autonomous flight is not possible if the electronic compass is unable to work properly due to magnetic interference.
Since a strong magnetic field is generated by the battery and wiring of an unmanned aerial system during operation, their dependence on an electronic compass is a major safety issue. When the electronic compass experiences magnetic field interference, the UAS can experience what is known as a “fly away”. In this condition, due to the electronic compass being unable to provide accurate direction references, the flight controller attempts to achieve a position in space as instructed by the operator, or other system, but the sensors of the UAS cause it to “fly away” in a random direction. For example, the flight control system may instruct a UAS to fly north. Instead, due to magnetic field interference, the UAS flies south. The “fly away” condition is dangerous because the operator is no longer in control of the UAS and is therefor unable to keep it within the confines of a designated safe operating area. Also, magnetic field interference is a leading cause of UAS crashes.
Lithium chemistry batteries come in two form factors: pouch cells and cylindrical cells. Pouch cells may comprise an anode, a cathode, and an electrolyte packaged in a polyethylene lined aluminum pouch. Cylindrical electrochemical cells may comprise an anode, a cathode, and an electrolyte sealed inside a steel cylinder.
New battery chemistries are most readily available in cylindrical cells (e.g., the 18650 format which is 18 mm in diameter and 65 mm in length) that are standardized and widely available. In general, there are no standardized pouch cells. Thus, obtaining pouch cells with new chemistry typically requires a high volume purchase, the cost of which makes using pouch cells impractical for many applications.
Cylindrical-steel electrochemical cells, as compared to pouch cells, are physically robust and offer better protection from environmental and operational damage. Cylindrical-steel electrochemical cells have low structural failure rates and are able to withstand the impact of a crash. This reduces the likelihood of a battery fire following the crash of a UAS. Unlike pouch cells, cylindrical electrochemical cells do not require special packaging techniques to extract maximum performance and battery life therefrom.
The primary challenge with utilizing cylindrical-steel electrochemical cells in UAS applications is the presence of iron in the steel cylinder. The iron is ferromagnetic and acts as a magnetic core within the current loop (i.e., the supply path and the return path for the electrical current), amplifying the magnetic field strength of the current loop thousands of times over an equivalent current loop having only non-ferrous material therein (e.g., an aluminum/polyethylene pouch cell).
As such, batteries built using cylindrical-steel cells generate large magnetic fields when current is flowing through them. This magnetic field can cause an electronic compass (e.g., a magnetometer) to malfunction if it is positioned near the power source (i.e., one or more cylindrical steel electrochemical cells) of an UAS, making the use of cylindrical-steel electrochemical cells impractical on small/compact UAS.

SUMMARY OF THE INVENTION

Implementations of a battery pack with reduced magnetic field emission are provided. In some implementations, the battery pack may be configured to reduce and/or eliminate the magnetic field normally generated while electrical current is being drawn from one or more cylindrical-steel electrochemical cells (e.g., AA batteries) by a connected electrical device. In some implementations, the magnetic field generated by the battery pack may be reduced by minimizing or eliminating the loop area of the electrical conductors (e.g., wires or other conductive elements) used to complete the supply path and the return path thereof. In some implementations, the supply path and the return path of a battery pack may be placed into a coaxial arrangement in which only a thin layer of insulating material is positioned therebetween. In this way, the loop area of the electrical conductors is minimized.
In some implementations, a battery pack with reduced magnetic field emission comprises two or more electrochemical cells positioned in a coaxial configuration. In this coaxial configuration, the supply path is through the center of each electrochemical cell, and the return path is through the conductive sleeve positioned about each electrochemical cell to the negative terminal of the bottom electrochemical cell. In this way, the supply path and the return path are as close as is physically possible, thereby minimizing any magnetic field generated between the conductors (i.e., between the electrochemical cells and their conductive sleeves).
In some implementations, a battery pack with reduced magnetic field emission comprises: a first cylindrical-steel electrochemical cell and a conductive sleeve, the conductive sleeve is separated from the first cylindrical-steel electrochemical cell by an insulating layer of material; a second cylindrical-steel electrochemical cell and a conductive sleeve, the conductive sleeve is separated from the second cylindrical-steel electrochemical cell by an insulating layer of material; wherein the first cylindrical-steel electrochemical cell and the second cylindrical-steel electrochemical cell are positioned in a coaxial configuration, thereby positioning a positive terminal of the first cylindrical-steel electrochemical cell against a negative terminal of the second cylindrical-steel electrochemical cell; and wherein the conductive sleeve of the first cylindrical-steel electrochemical cell is conductively connected on one end thereof to the conductive sleeve of the second cylindrical-steel electrochemical cell, together the conductive sleeves form a return path for electrical current being drawn from the cylindrical-steel electrochemical cells by a connected device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a top, front perspective view of an example battery pack with reduced magnetic field emission according to the principles of the present disclosure.

FIG. 1B illustrates a bottom, back perspective view of the battery pack with reduced magnetic field emission shown in FIG. 1A.

FIG. 1C illustrates a top perspective view of the battery pack with reduced magnetic field emission shown in FIG. 1A.

FIG. 2 illustrates an isometric view of a cylindrical-steel electrochemical cell having a conductive sleeve thereon that is separated therefrom by an insulating layer of material according to the principles of the present disclosure.

FIG. 3 illustrates a top, front perspective view of another example battery pack with reduced magnetic field emission according to the principles of the present disclosure.

FIG. 4 illustrates a cut-away view of yet another example battery pack with reduced magnetic field emission according to the principles of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-1C illustrate an example battery pack with reduced magnetic field emission 100 according to the principles of the present disclosure. In some implementations, the battery pack 100 may be configured to reduce and/or eliminate the magnetic field normally generated while electrical current is being drawn from one or more cylindrical-steel electrochemical cells (e.g., AA batteries) by a connected electrical device. In some implementations, the magnetic field generated by the battery pack 100 may be reduced by minimizing or eliminating the loop area of the electrical conductors (e.g., wires or other conductive elements) used to complete the supply path and the return path thereof. In some implementations, the supply path and the return path of a battery pack 100 may be placed into a coaxial arrangement in which only a thin layer of insulating material is positioned therebetween. In this way, the loop area of the electrical conductors is minimized.
As shown in FIGS. 1A-1C, in some implementations, a battery pack 100 may be comprised of six cylindrical-steel electrochemical cells 110 (or batteries) conductively connected together. In some implementation, each electrochemical cell 110 of a battery pack 100 may include a conductive sleeve 120 comprised of four conductive strips 122 that are separated from the electrochemical cell 110 by a thin insulating layer of material 130. In some implementations, the conductive sleeve 120 on each electrochemical cell 110 may be configured to provide a return path for electrical current that minimizes the loop area between the electrochemical cell 110 and the electrical conductor(s) (i.e., the conductive sleeve 120) used to complete the return path of each electrochemical cell 110 used as part of a battery pack 100. In some implementations, a battery pack 100 may comprise more than six cylindrical-steel electrochemical cells 110 or less than six cylindrical-steel electrochemical cells 110 conductively connected together.
As shown in FIGS. 1A-1C, in some implementations, the six electrochemical cells 110 of a battery pack 100 may be conductively connected in series by parallel pairs of electrochemical cells 110 (i.e., a 3S2P configuration). In some implementations, the six electrochemical cells 110 of a battery pack 100 may be conductively connected in series (i.e., a 6S configuration). In some implementations, the six electrochemical cells 110 of a battery pack 100 may be conductively connected in series by parallel triplets (i.e., a 2S3P configuration). In some implementations, the electrochemical cells 110 of a battery pack 100 may be conductively connected to form any series and/or parallel arrangement suitable to the number of electrochemical cells 110 being used as part of the battery pack 100 and/or the needs of the device being powered thereby.
As shown in FIG. 2, in some implementations, the four conductive strips 122 a, 122 b, 122 c, 122 d (collectively 122) of a conductive sleeve 120 may be equally spaced 90 degrees apart and/or positioned longitudinally on a cylindrical-steel electrochemical cell 110, separated therefrom by the insulating layer of material. This is the most effective way to minimize any magnetic field generated by an electrochemical cell 110 and/or the battery pack 100 as a whole. In some implementations, the four conductive strips 122 of the conductive sleeve 120 may not be equally spaced apart (not shown).
As shown in FIG. 2, in some implementations, each conductive strip 122 may be longer than an electrochemical cell 110. In some implementations, each conductive strip 122 (e.g., element 122 a) may be positioned on an electrochemical cell 110 so that a first end 124 a and a second end 124 b thereof overhang the positive terminal 112 and the negative terminal 114, respectively (see, e.g., FIG. 2). In this way, the first end 124 a and the second end 124 b of each conductive strip (e.g., 122 a, 122 b, 122 c, 122 d) may be folded over to make conductive contact with the first end 124 a and the second end 124 b, respectively, of the other conductive strips 122 positioned on a single electrochemical cell 110 (see, e.g., FIG. 1A). In some implementations, the conductive strips 122 may be flat (see, e.g., FIG. 2). In some implementations, the conductive strips 122 may be round (not shown).
In some implementations, each conductive strip 122 may be made of copper. In some implementations, each conductive strip 122 may be a length of copper foil tape. In some implementations, each of the conductive strips 122 may be made of any conductive material suitable for managing the discharge current requirements associated with the device to be powered by the battery pack 100. In some implementations, each of the conductive strips 122 may be made of any conductive material suitable for use as part of a battery pack with reduced magnetic field emission 100.
As shown in FIG. 2, in some implementations, the insulting layer of material 130 may be positioned between the conductive sleeve 120 and the exterior of each cylindrical-steel electrochemical cell 110 to prevent short circuits. In some implementations, an insulating layer of material 130 may be shaped to match the profile (e.g., width and length) of each conductive strip 122 a, 122 b, 122 c, 122 d and be positioned thereunder. In some implementations, an insulating layer of material 130 is no thicker than is required to prevent a short circuit between the conductive sleeve 120 and the cylindrical-steel electrochemical cell 110 on which it is positioned. In some implementations, each insulating layer of material 130 may be fabricated from polyimide tape. In some implementations, any insulating material suitable for use with a battery pack with reduced magnetic field emission 100 may be positioned between the conductive strips 122 and the exterior of each cylindrical-steel electrochemical cell 110.
As shown in FIGS. 1A-1C and 2, in some implementations, due to the arrangement of the conductive strips 122 a, 122 b, 122 c, 122 d on each electrochemical cell 110, two or more electrochemical cells 110 may be positioned side-by-side so that the conductive strips 122 positioned on each electrochemical cell 110 reside in the gap(s) naturally formed between two cylindrical objects positioned side-by-side. In this way, two or more electrochemical cells 110 may be positioned side-by-side without conductive contact occurring between their respective conductive sleeves 120.
As shown in FIGS. 1A-1C, in some implementations, the battery pack 100 may be configured to provide a supply path and a return path for the flow of current being used to operate a connected electrical device. In some implementations, the supply path and the return path may be placed into a coaxial arrangement in which only a thin layer of insulating material is positioned therebetween.
In some implementations, the following steps may be used to assemble a battery pack 100 constructed in accordance with the present disclosure.
Initially, to complete the supply path for current flow through the battery pack 100, in some implementations, the positive terminals 112 of the first and second electrochemical cells 110 a, 110 b may be connected to the negative terminals 114 of the third and fourth electrochemical cells 110 c, 110 d by a conductive strip of material 103 a (see, e.g., FIG. 1C). In some implementations, a first portion of insulating material 108 a may be positioned to cover the conductive strip of material 103 a conductively connecting the positive terminals 112 of the first and second electrochemical cells 110 a, 110 b to the negative terminals 114 of the third and fourth electrochemical cells 110 c, 110 d (see, e.g., FIG. 1B).
Then, in some implementations, the positive terminals 112 of the third and fourth electrochemical cells 110 c, 110 d may be conductively connected to the negative terminals 114 of the fifth and sixth electrochemical cells 110 e, 110 f by a conductive strip of material. In some implementations, a second portion of insulating material 108 b may be positioned to cover the conductive strip of material conductively connecting the positive terminals 112 of the third and fourth electrochemical cells 110 c, 110 d to the negative terminals 114 of the fifth and sixth electrochemical cells 110 e, 110 f (see, e.g., FIG. 1A).
Next, in some implementations, a supply path wire 102 or other conductive element may be conductively connected to the positive terminals 112 of the fifth and sixth electrochemical cells 110 e, 110 f (see, e.g., FIG. 1B). In some implementations, the first portion of insulating material 108 a may extend to cover the junction between the positive terminals 112 of the fifth and sixth electrochemical cells 110 e, 110 f and the supply path wire 102 (see, e.g., FIG. 1B).
Then, to complete the coaxial return path for current flow through the battery pack 100, in some implementations, the second end 124 b of each conductive strip 122 positioned on the first electrochemical cell 110 a may be conductively joined together and/or to the negative terminal 114 thereof (see, e.g., FIG. 1A). In some implementations, the second end 124 b of each conductive strip 122 positioned on the second electrochemical cell 110 b may be conductively joined together and/or to the negative terminal 114 thereof (see, e.g., FIG. 1A). In some implementations, a wire 107 may be used to conductively connect the negative terminals 114 of the first and second electrochemical cells 110 a, 110 b (see, e.g., FIG. 1A).
Next, in some implementations, the first end 124 a of the conductive sleeve 120 positioned about the first and second electrochemical cells 110 a, 110 b may be conductively connected to the second end 124 b of the conducive sleeve 120 positioned about the third and fourth electrochemical cells 110 c, 110 d by a conductive strip of material 106 a (see, e.g., FIG. 1B).
Then, in some implementations, the first end 124 a of the conductive sleeve 120 positioned about the third and fourth electrochemical cells 110 c, 110 d may be conductively connected to the second end 124 b of the conducive sleeve 120 positioned about the fifth and sixth electrochemical cells 110 e, 110 f by a conductive strip of material 106 b (see, e.g., FIG. 1A).
Next, in some implementations, the first end 124 a of the conductive sleeve 120 positioned about the fifth and sixth electrochemical cells 110 e, 110 f may be conductively connected together and/or to a return path wire 104 (see, e.g., FIG. 1B).
In this way, a battery pack with reduced magnetic field emission 100 may be assembled.
In some implementations, the magnetic field generated by the battery pack 100 is reduced because the loop area between the electrical conductors (e.g., the wires, the electrochemical cells, and/or the conductive sleeves) used to complete the supply path and the return path has been minimized.
In some implementations, as those of ordinary skill in the art would understand, a battery pack 100 comprised of more than six or less than six electrochemical cells 110 may be assembled using the same or similar techniques.
As shown in FIGS. 1A-1C, in some implementations, it is important that the return paths on parallel electrochemical cells 110 (e.g., cells 110 a and 110 b, cells 110 c and 110 d, and/or cells 110 e and 110 f) be geometrically and electrically identical, otherwise the return current will flow along the path of least resistance creating an imbalance in return path current flow. This imbalance may generate stray magnetic fields because the coupling between the supply path and the return path is no longer optimized, resulting in an increase in effective loop area.
In some implementations, the supply path and the return path of a battery pack 100 are electrically insulated from each other by insulating material positioned therebetween. In this way, a short circuit between the supply path and the return path is prevented.
In some implementations, each portion of insulating material 130, 108 a, 108 b used to insulate the return path from the supply path may be polyimide tape. In some implementations, each portion of insulating material 130, 108 a, 108 b used to insulate the return path from the supply path may be any material suitable for preventing a short circuit between the supply path and the return path of a battery pack 100.
FIG. 3 illustrates another example implementation of a battery pack with reduced magnetic field emission 300 in accordance with the present disclosure. In some implementations, the battery pack with reduced magnetic field emission 300 is similar to the battery pack with reduced magnetic field emission 100 discussed above but includes a first circuit board 303 a and a second circuit board 303 b that are configured to conductively connect one or more cylindrical-steel electrochemical cells 310. As a result of the geometric precision afforded by the PCB manufacturing process, the loop area between the supply path and the return path may be minimized and the magnetic field generated by the battery pack 300 reduced thereby.
In some implementations, the circuit boards 303 a, 303 b may be designed to have the same, or similar, conductor and/or insulator geometries as those shown and described in connection with the battery pack 100 discussed above.
As shown in FIG. 3, in some implementations, the first end 324 a and the second end 324 b of each conductive sleeve 320 positioned about an electrochemical cell 310 may be conductively connected to either the first circuit board 303 a or the second circuit board 303 b. In some implementations, when the battery pack 300 is assembled, the positive terminal and the negative terminal of each electrochemical cell 310 may be in conductive contact with either the first circuit board 303 a or the second circuit board 303 b (see, e.g., FIG. 3).
In some implementations, each circuit board 303 a, 303 b may be comprised of at least two (2) layers of copper (or other conductive material) separated by a fiberglass substrate (or other dielectric substrate). In some implementations, the two layers of copper may be configured so that the supply path and the return path are positioned directly on top of each other, only separated by a thin layer of insulation (e.g., a coplanar arrangement). In this way, the battery pack 300 may be configured to minimize any magnetic field generated thereby during use. Stated another way, in some implementations, the circuit boards 303 may be configured to reduce magnetic field emission through the use of trace geometry that minimizes the gap, and maximizes the coupling, between the supply path and the return path. In this way, the loop area is minimized and the magnetic field generated by the battery pack 300 is reduced or eliminated. In some implementations, stripline geometry (e.g., a four (4) layer circuit board in conjunction with via fences) could be used to create a coaxial conductor coupling, further increasing coupling, and thereby minimize any magnetic field generated by a battery pack 300.
FIG. 4 illustrates yet another example implementation of a battery pack with reduced magnetic field emission 400 in accordance with the present disclosure. In some implementations, the battery pack with reduced magnetic field emission 400 is similar to the battery packs with reduced magnetic field emission 100, 300 discussed above but the electrochemical cells 410 a, 410 b, 410 c are positioned in a coaxial configuration. In this coaxial configuration, the supply path is through the center of each electrochemical cell 410 and the return path is through the conductive sleeve 420 positioned about each electrochemical cell 410 to the negative terminal 414 of the first electrochemical cell 410 a. In this way, the supply path and the return path are as close as is physically possible thereby minimizing any magnetic field generated between the conductors (i.e., between the electrochemical cells and their conductive sleeves 420).
As shown in FIG. 4, in some implementations, a thin insulating layer of material 430 may be positioned between the exterior of each electrochemical cell 410 and the conductive sleeve 420 positioned thereabout. In this way, short circuits between the conductive sleeves 420 (return path) and the stacked electrochemical cells 410 may be prevented.
As shown in FIG. 4, in some implementations, the conductive sleeve 420 may comprise a hollow cylinder configured to fit about the exterior of a first cylindrical-steel electrochemical cell 410 a and be conductively connected on at least one end to another conductive sleeve 420 positioned about a second cylindrical-steel electrochemical cell 410 b. In some implementations, each conductive sleeve 420 may be constructed the same as, or similar to, the conductive sleeve 120 discussed above.
In some implementations, even in the presence of steel/iron casings used with some electrochemical cells, the coaxial return path of the battery pack 400 may result in very small stray magnetic fields being generated. This allows readily available cylindrical-steel electrochemical cells (e.g., AA batteries, 18650 batteries, etc.) to be used with magnetically sensitive devices (e.g., a magnetometer or compass) in place of more expensive and/or less safe pouch cells.
In some implementations, any permanent magnetic field (a magnetic field that is present when no current is flowing) in the casing of an electrochemical cell 110, 310, 410 may be controlled by positioning mu-metal magnetic shielding between the battery pack 100, 300, 400 and any magnetically sensitive element(s) of the device being powered thereby. In this way, the operation of magnetically sensitive elements (e.g., a magnetometer or other electronic compass) is not disrupted by the battery pack 100, 300, 400. As used herein, a permanent magnetic field refers to any magnetic field resulting from the magnetization of the ferrous casing of an electrochemical cell.
In some implementations, a battery pack with reduced magnetic field emission 100, 300, 400 may be used as a power source for any electrical device that is configured to be powered by cylindrical-steel electrochemical cells. For example, remotely piloted vehicles and unmanned aerial systems/drones, electric cars, etc.
In some implementations, when reducing exposure to magnetic fields(s) is desirable, a battery pack with reduced magnetic field emission 100, 300, 400 may be used to power an electrical device.
Reference throughout this specification to “an embodiment” or “implementation” or words of similar import means that a particular described feature, structure, or characteristic is included in at least one embodiment of the present invention. Thus, the phrase “in some implementations” or a phrase of similar import in various places throughout this specification does not necessarily refer to the same embodiment.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.
The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the above description, numerous specific details are provided for a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that embodiments of the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations may not be shown or described in detail.
While operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown, or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Claims

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13. A battery pack with reduced magnetic field emission comprising:

a first cylindrical-steel electrochemical cell and a conductive sleeve, the conductive sleeve is separated from the first cylindrical-steel electrochemical cell by an insulating layer of material;

a second cylindrical-steel electrochemical cell and a conductive sleeve, the conductive sleeve is separated from the second cylindrical-steel electrochemical cell by an insulating layer of material;

wherein the first cylindrical-steel electrochemical cell and the second cylindrical-steel electrochemical cell are positioned in a coaxial configuration thereby positioning a positive terminal of the first cylindrical-steel electrochemical cell against a negative terminal of the second cylindrical-steel electrochemical cell; and

wherein the conductive sleeve of the first cylindrical-steel electrochemical cell is conductively connected on one end thereof to the conductive sleeve of the second cylindrical-steel electrochemical cell, together the conductive sleeves form a return path for electrical current being drawn from the cylindrical-steel electrochemical cells by a connected device.

14. The battery pack of claim 13, wherein each conductive sleeve is a hollow cylinder configured to fit about at least one of the cylindrical-steel electrochemical cells.

15. The battery pack of claim 13, wherein the layer of insulating material positioned between each cylindrical-steel electrochemical cell and the conductive sleeve thereof is fabricated from polyimide.