Reversible electrical connector and method

A method of reversibly connecting two substrates includes positioning an electrically conductive adhesive connector including a shape memory polymer (SMP) between the substrates, heating the connector to a temperature higher than the SMP transition temperature, applying a load and cooling the connector below the transition temperature to transform the connector to a conforming shape to form an adhesive bond attaching the substrates and providing an electrical connection therebetween. The method may include disconnecting the connector from the substrates by heating the connector above the SMP transition temperature, which may disrupt the electrical connection between the substrates. The connector may be a battery tab connector configured to connect a battery cell to another battery cell or a terminal. The connector may be releasable from the battery tab such that the battery tab is reusable after removal of the connector. The connector may be multi-layer and generally arcuate in a permanent shape.

TECHNICAL FIELD

The present invention relates to a reversible electrical connector for the attachment of electrically conductive substrates including battery tabs of a multicell battery.

BACKGROUND

Battery packs may consist of a plurality of battery cells, where the tabs of the battery cells are conductively joined to one another to form the battery pack. The battery tabs may be joined by resistance or laser welding to form an electrically conductive path between battery cells or between a battery cell and a terminal of the battery. Variability in the welding process may result in variation in the welded connections between the tabs which may cause variation in the electrical conductivity of the battery pack. The battery tab is irreversibly modified by the welding process such that upon separation of one battery tab from another, the welded battery tabs may become damaged or deteriorated such that the tabs and corresponding battery cells are no longer usable.

Multicell battery packs, e.g., battery packs containing multiple battery cells which are electrically connected to one another, may be used in automotive applications including hybrid vehicles. At the end of the useful life for the automotive application, a battery cell in a multicell battery pack may retain a significant percentage of its capacity such that the battery cell may be recycled to or reused in a lighter duty application with lower voltage and/or capacity requirements. Reuse of the battery cell may require disassembly of the battery cell from the battery with the battery tab substantially intact, e.g., in an undamaged or reusable state. Welded battery tabs may be damaged when separating the welded connection to the extent that the tabs are not reusable, such that the battery cell cannot be recycled, e.g., cannot be attached to another battery cell or terminal or reconfigured into another battery pack. Additionally, deterioration and/or damage to the battery tab during separation of the welded joint may limit the ability to recover materials from the damaged battery cell, by affecting the ability to deconstruct the battery cell for materials recycling.

SUMMARY

A thermo-reversible adhesive connector configured to releasably attach the battery tabs of battery cells, and a method for reversibly connecting the tabs of battery cells using the releasable connector is provided herein. The electrically conductive connector described herein allows for recycling of battery packs and battery pack cells by providing a simple, releasable means of connecting the battery cell tabs which when released or reversed provides a recyclable battery cell including a reusable battery tab, and a reusable connector. In one example, the battery packs may be battery packs initially used in a battery of a hybrid vehicle, wherein at the end of useful vehicle service life each battery pack and/or battery cell may retain a significant portion of its capacity such that the battery pack and/or battery cell may be recycled and repurposed to other applications requiring lesser capacity than the initial vehicle battery application. By providing a releasable attachment for battery cell tabs, the battery cell can be detached at the end of the vehicle service life without compromising the integrity of the battery tab.

A releasable battery tab connector is provided. The releasable connector may have a multi-layer construction including at least one layer comprised of a shape memory polymer (SMP) interposed between adhesive layers, which may be dry adhesive layers. As used herein, dry adhesives refer to intrinsically sticky materials that do not rely on melting or solvent to activate their adhesion properties. The SMP and adhesive layers are electrically conductive making the releasable connector electrically conductive. The SMP layer has a generally C-shaped or arcuate permanent shape facilitating detachment of the connector from the battery tab. The connector may be positioned between adjacent battery tabs and a force applied after heating the connector to a temperature above the SMP transition temperature such that the connector transforms into a temporary shape conforming with the battery tab surface, which may be a substantially flat shape, then cooled below the transition temperature while under the applied force to attach the battery tabs and provide an electrically conductive path between the battery tabs.

The connector may be detached from the battery tab by activating the connector above the SMP transition temperature such that the connector recovers its permanent shape, causing the adhesive layer and the connector to peel away from the surface of the battery tab, substantially disconnecting the connector from the battery tab and battery cell. The connection is reversed such that the battery tab when disconnected is substantially unmodified and/or in a condition rendering the attached battery cell suitable for recycling. In one example, the releasable battery tab connector may have a single layer construction including a shape memory polymer, wherein the shape memory polymer is adhesive.

A method of reversibly connecting two electrically conductive substrates includes positioning an electrically conductive adhesive connector including a shape memory polymer (SMP) between the substrates, heating the connector to a temperature higher than the SMP transition temperature, and applying a load and cooling the connector below the transition temperature while under load to transform the connector to a conforming shape, thereby forming an adhesive bond attaching the substrates and providing an electrical connection therebetween. The method may include disconnecting or releasing the connector from the substrates by heating the connector above the SMP transition temperature, wherein disconnecting the connector includes progressively peeling the adhesive portion of the connector from the substrate. Transformation of the connector from the temporary conforming shape to the curved permanent shape may generate a detaching force sufficient to initiate and progress detachment of the adhesive layer and the connector from the substrate.

Disconnecting the connector may disrupt the electrical connection between the substrates, such that the connector may be configured as a limit switch or fuse activated when the connector is heated to a temperature limit corresponding to the SMP transition temperature. The connector may be reattached after disconnecting, to reattach the substrates and reestablish the electrical connection, wherein the connector may act as a circuit breaker. The connector may be a battery tab connector configured to connect a battery cell to another battery cell or a terminal. The connector may be releasable from the battery tab such that the battery tab and/or the connector is reusable after removal of the connector.

The above features and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION

Referring to the drawings wherein like reference numbers represent like components throughout the several figures, the elements shown inFIGS. 1-5Care not necessarily to scale or proportion. Accordingly, the particular dimensions and applications provided in the drawings presented herein are not to be considered limiting.FIG. 1shows a battery10including a battery pack12. The battery10may be referred to herein as a battery assembly. The battery10may include a plurality of battery packs12. A terminal14, which may also be referred to herein as a bus bar or u-channel, may be connected to one or more battery packs12to conduct electric energy provided by the battery pack12in the battery10. The battery10may be configured for use in a hybrid vehicle (not shown), for example, to provide electrical energy to one or more systems of the hybrid vehicle which may include the vehicle powertrain system.

The battery pack12includes a plurality of battery cells20. In one example, the battery cell20may be lithium-polymer or lithium ion type (Li-Ion) cell, and/or may be configured as a pouch cell or prismatic cell. Each battery cell20includes a battery body22including an electrode (not shown) and at least one battery tab24. The battery tab24is connected to the battery body22and/or to the electrode in the battery body22and may be configured as an electrically conductive foil tab. The battery tab24, which may also be referred to herein as a substrate or an electrically conductive substrate, defines at least one interface surface26, which may also be referred to herein as a tab interface, a tab interface surface, a substrate interface, or a substrate surface. The battery tab24, e.g., the conductive substrate, may be made of an electrically conductive material. In one example, the battery tab24may be comprised of a metallic material, which may include, for example, one or more of copper, silver, and iron. A reversible connector30including a shape memory polymer in a permanent shape may be interposed between adjacent tabs24as shown inFIG. 1, and converted to a temporary shape as shown inFIG. 2to electrically connect, e.g., to provide an electrically conductive path between the adjacent tabs24by adhering to the interface surfaces26. The battery pack12may be electrically connected to the battery terminal14, by interposing a reversible connector30in a permanent curved shape between the terminal14and an adjacent battery tab24, as shown inFIG. 1, and converting the connector30to a temporary conforming shape as shown inFIG. 2to provide an electrically conductive path between the tab24and the terminal14, thereby electrically connecting the battery pack12to the terminal14. The terminal14, which may also be referred to herein as a substrate or an electrically conductive substrate, defines at least one interface surface16, which may also be referred to herein as a terminal interface, a terminal interface surface, a substrate interface, or a substrate surface.

The connector30may be referred to herein as a reversible connector, a releasable connector, an adhesive connector, a thermo-reversible connector, a detachable connector or a reversible attachment. The connector30is electrically conductive and adhesive, e.g., the connector30has adhesive properties such that the connector30may adhere to a substrate such as the substrates14,24, thus defining a contact area28between the connector30and the substrate14,24. The contact area28may define an electrically conductive path formed between the connector30and the substrate. The connector30may be converted from the curved permanent shape shown inFIG. 1to the temporary generally flat and/or conforming shape shown inFIG. 2by applying a force18to the battery tabs24and the connectors30interposed therebetween while the connectors30are at a temperature above the transition temperature of the shape memory polymer comprising the connectors30, such that each of the connectors30conforms to and forms an attachment to the interface surfaces16,26adjacent to the connector30to provide an electrically conductive joint or path generally defined by the contact area28between the substrates adjacent to the connector30. The substrates adjacent to the connector30may be, for example, adjacent tabs24, or the terminal14and a tab24adjacent to the terminal14. The connectors30are subsequently cooled below the transition temperature of the shape memory polymer prior to removing the applied force18such that each of the cooled connectors30retains its temporary shape, as shown inFIG. 2, thus electrically connecting the plurality of battery cells20to form the battery pack12, and electrically connecting the battery pack12thus formed to the terminal14.

As shown inFIG. 3, the connections formed as described forFIG. 2may be reversed such that each of the connectors30may be easily detached from the interfaces16,26by elevating the temperature of the connector30above the transition temperature of the shape memory polymer comprising the connector30, such that the connector30reverts to its permanent curved shape and in so doing exerts a detaching force42initiating detachment of the connector30by causing the connector30to progressively pull and/or peel away from the interface16,26thus minimizing or substantially eliminating the contact area28between the connector30and the interface16,26allowing removal of the connector30from the interface16,26without damaging the tab24, e.g., without rendering the tab24unusable. The disconnected battery cell20including the battery tab24in a reusable condition may be recycled or reused in another application, where reuse may include forming an electrical connection including the battery tab24. The removed connector30may be recycled or reused in another application, where reuse may include forming another electrical connection using the removed connector30.

Referring toFIGS. 4A-4C, an example of a reversible connector30is shown. The reversible connector30as shown inFIGS. 4A-4Cmay be configured as a thermo-reversible multi-layer connector. In the example shown, the connector30is configured as a quadruple layer connector30including two layers or portions of a shape memory polymer (SMP)32,34and two layers or portions of adhesive36,38. The adhesive layers, which may be referred to as a first adhesive layer36and a second adhesive layer38, or collectively as the adhesive layers, may be configured as an elastomeric dry adhesive. The SMP layers may be referred to as a first SMP layer32and a second SMP layer34, or collectively as the SMP layers. Each of the SMP layers32,34and the adhesive layers36,38is electrically conductive, due to the electrical conductivity of the respective SMP and adhesive and/or due to electrically conductive filler included in the layer. The SMP may be characterized by a glass transition temperature, which may be referred to herein as a transition temperature or an SMP transition temperature.

Each SMP layer32,34is configured with a generally arcuate or C-shape curvature when the SMP layer is in its permanent shape. The SMP layers32,34are positioned adjacent to each other such that the curvature of the SMP layers32,34are opposing to define an opening or cavity40therebetween, as shown inFIG. 4A, and such that the outermost surface of each of the SMP layers32,34is generally convex. The first adhesive layer36may be positioned adjacent to the first SMP layer32and may be configured to extend across the outermost surface of the SMP layer32to edges46,48. The second adhesive layer38may be positioned adjacent to the second SMP layer34and may be configured to extend across the outermost surface of the SMP layer34to edges46,48.

In one example, the connector30is positioned, as shown inFIG. 4A, between a first electrically conductive substrate, which may be a first battery tab24and a second electrically conductive substrate, which may be a second, or adjacent battery tab24. Small or minimal contact areas28may be defined between the adhesive layers36,38of the connector30and the interface surfaces26of the adjacent tabs24, due to adhesion of the curved adhesive layer to the surface26. The minimal adhesion provided by the contact areas28shown inFIG. 4Amay assist in assembling the connector30and tabs24by maintaining the connector30in position between the adjacent tabs24prior to thermal activation of the connector30and application of the force18.

The connector30is activated by heating the connector30to a temperature above the glass transition temperature of the SMP of the first and second SMP layers32,34, and imposing a force or load18on the connector30as shown inFIG. 4Awhile the connector30is at a temperature above its transition temperature, causing the connector30to deform to a temporary shape shown inFIG. 4Bas the connector30is compressed between the adjacent tabs24. Under pressure and at a temperature above the SMP transition temperature, the connector30deforms and complies to the adjacent tabs by flattening the curvature of each of the SMP layers32,34such that each SMP layer32,34and the connector30assumes a generally flattened shape. As the connector30flattens, each of the adhesive layers36,38flattens and adheres to the adjacent interface surface26, significantly increasing the contact area28between the connector30and the adjacent tabs24, and adhering the connector30to the interface surface26. The connector30is cooled to a temperature below the SMP transition temperature while the load18continues to be applied, thereby transforming each of the SMP layers32,34of the connector30from the permanent curved C-shape shown inFIG. 4Ato the temporary flattened shape shown inFIG. 4B. As used herein, the permanent shape may be referred to as the curved or arcuate shape, and the temporary shape may be referred to as the flattened shape, the generally flat shape, or the conforming shape. In one example, the connector30may be cooled to about 25° C. After the connector30has cooled below the transition temperature, the load18is removed.

Upon cooling under the load, the cavity40may become very small or insignificant, or may disappear altogether such that the innermost surfaces of the SMP layers32,34form the conductive interface44. In one example, the connector30may include a fifth layer, which may be an electrically conductive adhesive layer (not shown) positioned adjacent to the innermost surface of at least one of the SMP layers32,34, which may form the conductive interface44between the SMP layers32,34. The adhesive layer forming the interface44may be sufficiently adhesive to bond or join the inner surfaces of the SMP layers32,34to form the interface44and sufficiently weak to allow separation of the inner surfaces of the SMP layers32,34when the connector30is activated above the SMP transition temperature, e.g., when the connection is reversed to release the connector30.

The adhesive layers36,38and the conforming temporary shape of the SMP layers32,34of the connector30form a strongly adhesive bond between the battery tabs24, as shown inFIGS. 2 and 4B. The connector30in the conforming temporary shape provides an electrical connection between the battery tabs24bonded to the connector30, which includes an electrical path defined by at least the contact areas28and the connector30. The electrical connection provided by the connector30configured as shown inFIGS. 2 and 4Aprovides an electrical path which, in comparison to a welded electrical connection, e.g., an electrical connection formed by welding the tabs24directly to each, may be more consistent in configuration and electrical conductivity, and of a greater cross-sectional area than a welded electrical connection, thus providing a connection less susceptible to detrimental conditions which may be exhibited by a welded electrical connection which may include variability in conductivity, welding discontinuities, and susceptibility to overheating or current overload.

The connected battery tabs24may be separated from one another or from the terminal14by reversing the connection provided by the connector30in the temporary shape, as shown inFIG. 4C. The connection may be reversed by heating the connector30to a temperature above the glass transition temperature of the SMP of the SMP layers32,34without constraining the connector30, e.g., by heating the connector30in the absence of an applied load. Upon heating above the transition temperature, each of the SMP layers32,34begins to deform from the flattened temporary shape and to recover the curved permanent shape. As each of the SMP layers32,34transitions to the curved permanent shape, the changing shape of the connector30exerts a detaching force42against the tabs24connected by the connector30as shown inFIGS. 3 and 4C, which causes the adhesive layers36,38to peel away from the surfaces26of the tabs24beginning from near the outer edges46,48of the connector30. When the detaching force is employed in a peel-off mode, complete detachment is achieved gradually by overcoming small adhesion forces corresponding to very small areas. Thus, the adhesion is easily reversed. As the SMP layers32,34recover their curved permanent shape, the cavity40forms between the SMP layers32,34contributing to the detaching force42, and the adhesive layers36,38continue to progressively peel away, minimizing and/or substantially eliminating the contact areas28to complete the reversal of the connection, e.g., substantially detaching the connector30from the tab24, and/or minimizing the contact areas28such that the connector30may be detached from the interface26without damaging and/or rendering the tab24unusable. The detached battery cell20may be recycled, which may include reusing the cell20and/or electrically reconnecting the detached tab24to another substrate, which may be another battery tab24or terminal14, using a connector such as the connector30, or by other means. The detached connector30may be recycled, which may include reusing the detached connector30to provide an electrical and adhesive connection between two substrates24.

Referring now toFIGS. 5A-5C, shown is another example configuration of the connector30. The reversible connector30as shown inFIGS. 5A-5Cmay be configured as a thermo-reversible multi-layer connector. In the example shown, the connector30is configured as a triple layer connector30including one layer or portion of a shape memory polymer (SMP)32and two layers or portions of adhesive36,38. The adhesive layers36,38may be configured as an elastomeric dry adhesive. The SMP layer32and the adhesive layers36,38are each electrically conductive, due to the electrical conductivity of the respective SMP and adhesive and/or due to electrically conductive filler included in the layer. The SMP is characterized by a glass transition temperature.

The SMP layer32is configured with a generally arcuate or C-shape curvature when in its permanent shape. The SMP layer32is positioned adjacent to the tab24such that the curvature of the SMP layer32defines an opening40therebetween, as shown inFIG. 5A, and such that the surface of the SMP layer32opposite the opening40is generally convex. The first adhesive layer36may be positioned adjacent to one side of the SMP layer32and may be configured to extend across the outermost surface of the SMP layer32to edges46,48. The second adhesive layer38may be positioned adjacent to the opposing side of the SMP layer32and may be configured to extend across the outermost surface of the SMP layer32to edges46,48.

In one example, the connector30is positioned, as shown inFIG. 5A, between a first electrically conductive substrate, which may be a first battery tab24and a second electrically conductive substrate, which may be a second, or adjacent battery tab24. Small or minimal contact areas28may be formed between adhesive layers36,38of the connector30and the interface surface26of the tab24. The minimal adhesion provided by the contact areas28shown inFIG. 5Amay assist in assembling the connector30and tabs24by maintaining the connector30in position between the adjacent tabs24prior to thermal activation of the connector30and application of the force18.

The connector30is activated by heating the connector30to a temperature above the glass transition temperature of the SMP of the SMP layer32, and a load or force18is imposed on the connector30as shown inFIG. 5Aand while the connector30is at a temperature above its transition temperature, causing the connector30to deform to a temporary shape shown inFIG. 5Bas the connector30is compressed between the adjacent tabs24. Under pressure and at a temperature above the SMP transition temperature, the connector30deforms and complies to the adjacent tabs by flattening the curvature of the SMP layer32such that the connector30assumes a generally flattened shape. As the connector30flattens, each of the adhesive layers36,38flattens and adheres to the adjacent interface surface26, significantly increasing the contact area28between the connector30and the adjacent tabs24, and adhering the connector30to the interface surface26. The connector30is cooled to a temperature below the SMP transition temperature while the load18continues to be applied, thereby transforming the SMP layer32of the connector30from the permanent C-shape shown inFIG. 5Ato the temporary flattened shape shown inFIG. 5B. In one example, the connector30may be cooled to about 25° C. After the connector30has cooled below the transition temperature, the load18is removed. Upon cooling under the load18, the opening40may become very small or insignificant, or may disappear altogether as the adhesive layer38conforms to the surface26. The adhesive layers36,38and the conforming temporary shape of the SMP layer32of the connector30form a strongly adhesive bond between the battery tabs24, as shown inFIG. 5B. The connector30in the conforming temporary shape provides an electrical connection between the battery tabs24bonded to the connector30, which includes an electrical path defined by at least the contact areas28and the connector30. The electrical connection provided by the connector30configured as shown inFIG. 5Aprovides an electrical path which may be more consistent in configuration and electrical conductivity, and of a greater cross-sectional area than a welded electrical connection, thus providing a connection less susceptible to detrimental conditions which may be exhibited by a welded electrical connection which may include variability in conductivity and susceptibility to overheating.

The connected battery tabs24may be separated from one another or from the terminal14by reversing the connection provided by the connector30in the temporary shape, as shown inFIG. 5C. The connection may be reversed by heating the connector30to a temperature above the glass transition temperature of the SMP of the SMP layer32without constraining the connector30, e.g., by heating the connector30in the absence of an applied load. Upon heating above the transition temperature, the SMP layer32begins to deform from the flattened temporary shape to the curved permanent shape. As the SMP layer32transitions to the curved permanent shape, the changing shape of the connector30exerts a detaching force42against the tabs24connected by the connector30as shown inFIG. 5C, which causes the adhesive layer38to peel away from the surface26beginning from near the outer edges46,48of the connector30. When the detaching force is employed in a peel-off mode, complete detachment is achieved gradually by overcoming small adhesion forces corresponding to very small areas. Thus, the adhesion is easily reversed. As the SMP layer32recovers its curved permanent shape, the cavity40forms between the SMP layer32contributing to the detaching force42, and the adhesive layer38progressively peels away, minimizing and/or substantially eliminating the contact areas28to complete the reversal of the connection, e.g., substantially detaching the connector30from the tab24, and/or minimizing the contact areas28such that the connector30may be detached from the interface26without damaging and/or rendering the tab24unusable. The detached battery cell20may be recycled, which may include reusing the cell20and/or electrically connecting the detached tab24using a connector such as the connector30, or by other means. The detached connector30may be recycled, which may include reusing the detached connector30to provide an electrical and adhesive connection between two substrates24.

By way of example, the shape memory polymer comprising the SMP layers32,34may be an epoxy. By way of example, the components of the dry adhesive layers36,38and/or the components of the SMP layers32,34may include a rigid epoxy and a flexible epoxy. The range of possible crosslinking chemistries which may be used to achieve a dry adhesive or shape memory polymer may include alpha, omega-diaminoalkanes, organic multi-carboxylic acid, anhydride, or catalytic (as in imidazole type) crosslinking reactions. There are many different ways to achieve the appropriate relationships between the molecular properties. For example, the dry adhesives or shape memory polymers may include a rigid epoxy, an epoxy extender, and a crosslinking agent; or a rigid epoxy, a flexible crosslinking agent, and a flexible epoxy; or a rigid epoxy, a rigid crosslinking agent, and a flexible epoxy; or a rigid epoxy, a flexible epoxy, and a catalytic curing agent; or a rigid epoxy, a crosslinking agent, and a diluent; or a flexible epoxy, a crosslinking agent, and a diluent; or a rigid epoxy and a flexible crosslinking agent; or a flexible epoxy and a catalytic curing agent; or a flexible epoxy and a crosslinking agent; and wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, the epoxy extender has one epoxide group, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride, and the diluent is a monoamine or a mono-carboxylic acid. In various example configurations, the catalytic curing agent (or catalytic cure) promotes epoxy-to-epoxy or epoxy-to-hydroxyl reactions. The catalytic curing agent may include, but is not limited to, tertiary amines, amine salts, boron trifluoride complexes, or amine borates. In one example, the components of the dry adhesive may be present in an amount sufficient to provide, upon curing of the composition, a dry adhesive having a glass transition temperature (Tg) of −90° C. to 200° C. and having a pull-off strength of 1-200 N/cm2from a substrate. In another example, the dry adhesive may have a glass transition temperature of −90° C. to 25° C.

One or more of the SMP layers32,34and/or the adhesive layers36,38may be configured to include a filler such that the SMP layers32,34and the adhesive layers36,38are each electrically conductive. The filler may be, for example, a metallic filler which may contain one of more of iron, copper, silver, or other conductive metals. The filler may be provided in powder form and may have a concentration range of 30% volume or greater to provide electrical conductivity to the SMP layers32,34and/or the adhesive layers36,38. The filler may be thermally conductive, to facilitate conductive and/or inductive heating and/or cooling of the connector30, for example, to heat the connector30during transformation from the permanent shape to the temporary shape, or to thermally activate the connector30to disconnect or detach, by heating the connector30above its transition temperature when the connector is in its temporary shape. The thermal conductive properties of the filler may increase the temperature of the connector30, for example, when the connector30is conducting electricity from battery tabs24to which the connector30is attached, e.g., during operation of the battery pack12, by inductively heating the connector30. Other types and forms of electrically conductive fillers, which may also be thermally conductive, may be used. For example, carbon-based fillers such as carbon black, carbon fibers, and/or carbon nanotubes may be used.

Numerous shape memory polymers may be utilized, and the examples provided herein are not intended to be limiting. In one example, the components of the shape memory polymer composition may be present in an amount sufficient to provide, upon curing of the composition, an epoxy shape memory polymer having a change in storage modulus of 2 to 3 orders of magnitude before and after its glass transition. In one example, the shape memory polymer has a Tgof 25° C. to 200° C. For example, starting with a typical aromatic diepoxy/diamine system with a Tgof about 90° C., the aromatic epoxy component is replaced systematically with an aliphatic diepoxy to yield a series of epoxy shape memory polymers with glass transition temperatures ranging from 3° C. to 90° C. As such, a shape memory polymer may be tailored for use with a dry adhesive as desired for a particular application operated within certain temperature ranges.

In one example, the shape memory polymer comprising each of the SMP layers32,34may be characterized by a transition temperature which is higher than the operating temperature of the battery10. In one example, the normal operating temperature of the battery10may be in the range of 25° C. to 35° C., with a specified or anticipated maximum operating temperature of approximately 45° C. The shape memory polymer and adhesive, in this example, may be configured with a transition temperature above the normal operating temperature, such that the connector30in its connected condition, e.g., in the temporary shape, will not be subjected to temperatures above the transition temperature, to prevent activation of the connector30and transformation to its detached permanent shape during normal battery operation. The SMP and adhesive of the connector30may, by example, be configured with a transition temperature above the maximum operating temperature, to prevent activation and detachment of the connector30under battery operating conditions up to this temperature.

In one example, the connector30may be configured to provide protection of the battery cells20and battery10from an over-amperage, current overload, and/or over-heating condition, by being configured as an electrical switch, a limit switch, a circuit breaker, or a fuse. In this example, the SMP of the connector30may be configured to have a transition temperature which corresponds to a temperature limit established for at least one of the battery cell20, the battery pack12and the battery10, wherein the transition temperature may be equal to or less than the temperature limit. The connector30, when heated to a temperature at or above the temperature limit, is heated above its transition temperature and activated to transform from the connected temporary shape to its permanent shape, detaching the connector30from the battery tabs24, thereby disconnecting the battery cells20including the battery tabs24from each other, and from the battery pack12and battery10, and discontinuing or disrupting the current flow between the battery tabs24. By disconnecting the battery cells20, the cells20may be automatically disassembled (detached) and/or electrically shut off when the temperature limit is exceeded, such that the electrical connection between the cells20is disrupted, which may protect the disconnected cell20from deterioration or damage to maintain the integrity and functionality of the cell20.

The temperature limit may be specified to avoid an overheating condition of at least one of the battery cell20, the battery pack12and the battery10. The temperature limit may correspond to an ambient operating temperature limit of the battery10, such that the connector30may be heated to its transition temperature when the operating temperature of the battery10, the temperature of the surroundings of connector30exceeds the temperature limit. The temperature limit may correspond to a maximum operating temperature of the battery cell20, e.g., a temperature above which the battery cell20in a connected state may experience deterioration or damage or a reduction in cell integrity. The temperature limit may correspond to an electrical condition, such as a current overload, power surge, open circuit, or other condition which may cause an increase in the current conducted through the connector30which may be damaging to at least one of the battery cell20, the pack12or the battery10. The increased current may cause an increase in the temperature of the connector30, for example, through resistive heating of the conductive filler or other materials of the connector30, such that the temperature of the connector30meets or exceeds the temperature limit, activating the connector30to transform to its temporary shape, thereby detaching from the battery tabs24and disconnecting the cells20, such that current flow to and from the cell20ceases or is substantially disrupted or discontinued. The connector30may be configured as a fuse wherein when the connector30is exposed to temperatures at or above the temperature limit, the connector30opens, e.g., is activated to transform to its permanent shape, reopening the cavity40and substantially eliminating the contact areas28. The connector30may function as a circuit breaker, such that after being activated by a temperature above the temperature limit and opening the electrical circuit between the battery tabs24, the connector30may be reheated above the transition temperature, a force18reapplied to deform the connector30into the conforming temporary shape, and cooled below the transition temperature while the force18is applied to reconnect the battery tabs24using the connector30, such that the battery tabs24become reattached and an electrically conductive path is reestablished therebetween.

The examples provided herein are not intended to be limiting. Other configurations of the electrically conductive reversible connector may be used. For example, the SMP may have sufficient adhesive properties such that the connector may be configured as a single SMP layer connector or a double SMP layer connector, wherein the SMP layer is in direct contact with and attached to the substrate in a connected condition. For example, the SMP may be a cross-linked polymer, such as a crosslinked vinyl acetate polymer or an ethylene-vinyl acetate (EVA) polymer exhibiting adhesive properties, such that the SMP layer in this instance may provide the combined functionality of the SMP layer32,34and the adhesive layer36,38. The battery pack12may be a non-automotive battery pack, and/or the battery10may be configured for non-automotive applications. The battery cell20may be of any suitable configuration, and is not limited to the pouch or prismatic battery cell configurations described as examples herein. The substrate24may be an electrically conductive substrate other than a battery tab or battery element, and may be a non-battery element, which may be connected using the reversible connector30to establish an electrically conductive path between the substrate24and the connector30.