Method and apparatus for the external application of a battery pack adhesive

A method and apparatus for simplifying battery pack assembly that allows inspection of the cell-to-housing bonding region is provided. In particular, a battery pack housing member is provided that includes an interior surface that partially defines the interior region of the battery pack and that includes a plurality of cell mounting wells and an exterior surface that includes a plurality of bonding wells. Adhesive introduced into the bonding wells forms a mechanical bond between an exterior surface of a cell introduced into an adjacent cell mounting well and the housing member.

FIELD OF THE INVENTION

The present invention relates generally to battery packs and, more particularly, to a method and apparatus for efficiently bonding a plurality of cells within a battery pack.

BACKGROUND OF THE INVENTION

Battery packs, also referred to as battery modules, have been used for years in a variety of industries and technologies that include everything from portable electric tools and laptop computers to small hand-held electronic devices such as cell phones, MP3 players, and GPS units. In general, a battery pack is comprised of multiple individual batteries, also referred to as cells, contained within a single piece or multi-piece housing. Single piece housings are often comprised of shrink-wrap while multi-piece housings often rely on a pair of complementary housing members that are designed to fit tightly around the cells when the housing members are snapped or otherwise held together. Typically a conventional battery pack will also include means to interconnect the individual cells as well as circuitry to, enable charging and/or to protect against overcharging.

Battery packs offer a number of advantages over the use of individual battery cells. From the end user's perspective, combining multiple cells into a single housing simplifies battery removal, replacement and/or battery recharging, since the user is only required to deal with a single unit. From the manufacturer's perspective, the use of battery packs provides additional marketing flexibility. For example, a manufacturer may offer a variety of interchangeable battery packs at different price points for the same device(s), the different battery packs providing different capacities, cell types (e.g., lithium ion versus nickel-metal-hydrid), or other variations. A manufacturer may also find it advantageous to market multiple devices that all utilize a single, interchangeable battery pack.

Recent advances in the development of hybrid and electric vehicles have lead to the need for a new type of battery pack, one capable of housing hundreds to thousands of individual cells and surviving the inherent thermal and mechanical stresses of a car for a period of years. Additionally, while the housing used to package a multi-cell vehicle battery must be structurally sound enough to allow battery pack inspection and/or replacement, it must do so with minimal weight since hybrids and electric cars are exceptionally sensitive to excess weight. Lastly, the design of a vehicle battery pack should lend itself to efficient, and preferably automated, manufacturing practices. The present invention provides such a battery pack.

SUMMARY OF THE INVENTION

The present invention provides a battery pack housing member that simplifies battery pack assembly and allows inspection of the cell-to-housing bonding region. In at least one embodiment of the invention, the battery pack housing member is comprised of (i) an interior surface that partially defines the interior region of the battery pack and that includes a plurality of cell mounting wells, each of which is adapted to receive a first end portion of a corresponding cell of a plurality of cells, and (ii) an exterior surface that includes a plurality of bonding wells, each of which is defined, in part, by an exterior surface of the first end portion of the corresponding cell. Adhesive, preferably a sag-resistant and/or high viscosity adhesive, introduced into the bonding wells forms a bond between the corresponding cell and the housing member. The sag-resistant and/or high viscosity characteristic of the adhesive minimizes and/or prevents seepage of the adhesive through the radial gap formed between the mounting well of the housing member and the corresponding cell. A feature, such as a bonding well surface protrusion, may be used to reduce the volume within the bonding well which, in turn, reduces the volume of adhesive needed to fill the bonding well. The exterior surface of each of the cell mounting wells may include an interconnect aperture, the interconnect aperture providing access to the first end portion of the corresponding cell.

In at least one embodiment of the invention, a battery pack is provided that is comprised of (i) a first housing member that includes a first plurality of cell mounting wells formed within the interior surface of the housing member and a first plurality of bonding wells formed within the exterior surface of the housing member, where the first plurality of cell mounting wells is adapted to receive a first end portion of a corresponding cell of a plurality of cells; (ii) a second housing member complementary to the first housing member that includes a second plurality of cell mounting wells formed within the interior surface of the second housing member and a second plurality of bonding wells formed within the exterior surface of the second housing member, where the second plurality of cell mounting wells is adapted to receive a second end portion of a corresponding cell of the plurality of cells; (iii) a plurality of cells; (iv) a first adhesive introduced into the first plurality of bonding wells, the first adhesive forming a bond between the exterior surfaces of the first end portions of the cells and the first housing member; and (v) a second adhesive introduced into the second plurality of bonding wells, the second adhesive forming a bond between the exterior surfaces of the second end portions of the cells and the second housing member. Sag-resistant and/or high viscosity adhesives may be used for the first and second adhesives. The sag-resistant and/or high viscosity characteristic of the adhesive minimizes and/or prevents seepage of adhesive through the radial gap formed between the housing member mounting wells and the corresponding cells. A feature, such as a bonding well surface protrusion, may be used to reduce the volume within the first and second pluralities of bonding wells. The exterior surfaces of each of the first and second pluralities of cell mounting wells may include first and second pluralities of interconnect apertures, thereby providing access to the first and second cell end portions. The battery pack may further comprise a first connector plate bonded to the exterior surface of the first housing member and a second connector plate bonded to the exterior surface of the second housing member.

In a least one embodiment of the invention, a method of manufacturing a battery pack is provided, the method comprising the steps of (i) inserting a first end portion of each of a plurality of cells into a corresponding cell mounting well in an interior surface of a first housing member; (ii) inserting a second end portion of each of the plurality of cells into a corresponding cell mounting well in an interior surface of a second housing member; (iii) introducing a first adhesive into a first plurality of bonding wells within an exterior surface of the second housing member, where the first adhesive forms a bond between an exterior surface of the second end portions of the plurality of cells and the second housing member; (iv) rotating the battery pack; and (v) introducing a second adhesive into a second plurality of bonding wells within an exterior surface of the first housing member, where the second adhesive forms a bond between an exterior surface of the first end portions of the plurality of cells and the first housing member. The method may further comprise the steps of (i) bonding a first connector plate to the second housing member exterior surface and (ii) bonding a second connector plate to the first housing member exterior surface.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following text, the terms “battery”, “cell” and “battery cell” may be used interchangeably and may refer to any of a variety of different cell chemistries and configurations including, but not limited to, lithium ion (e.g., lithium iron phosphate, lithium cobalt oxide, other lithium metal oxides, etc.), lithium ion polymer, nickel metal hydride, nickel cadmium, nickel hydrogen, nickel zinc, silver zinc, or other battery type/configuration. The term “battery pack” as used herein refers to multiple individual batteries contained within a single piece or multi-piece housing, the individual batteries electrically interconnected to achieve the desired voltage and capacity for a particular application. The terms “connector plate” and “collector plate” may be used interchangeably and refer to a plate used to electrically connect to multiple batteries within a battery pack. It should be understood that identical element symbols used on multiple figures refer to the same component, or components of equal functionality. Additionally, the accompanying figures are only meant to illustrate, not limit, the scope of the invention and should not be considered to be to scale. Accordingly, not all battery elements and/or battery pack elements are shown in the illustrations.

FIG. 1illustrates a portion of a battery pack housing member100, this view providing both a perspective view of member100as well as a cross-sectional view of some of the plurality of battery cell mounting wells101. It will be appreciated that the present invention is not limited to a particular number of cell mounting wells or cells, nor is the invention limited to a particular cell packing density or cell layout. Member100may comprise either the outermost structural member of a battery pack, or member100may comprise an internal component of a battery pack. In the latter approach, in addition to the inclusion of a connector plate as preferred and as described further below, an outer battery pack housing is fit around member(s)100. An outer battery pack housing (not shown) provides additional environmental protection to the batteries and interconnects as well as increasing battery pack rigidity and strength. In some instances, the additional outer battery pack housing may be used to simplify battery pack mounting, for example by providing pack mounting structures.

In at least one preferred embodiment, a battery pack uses a pair of battery pack housing members100, one such member being coupled to one end portion of each of the cells, and a second such member being coupled to the opposite end portion of each of the cells. Accordingly, while the description and figures provided below describe the design and use of a single housing member100, it will be appreciated that preferably a battery pack in accordance with the invention would use a pair of complementary housing members to mount and hold the cells in place.

In the view of member100shown inFIG. 1, surface103is the interior surface of member100, this surface being oriented towards the inside region of the battery pack in which member100is used. Cell mounting wells101are configured to fit around the circumference of the cells with each mounting well101configured to accommodate a single battery cell. This aspect of the housing member is illustrated inFIG. 2in which a plurality of cells201are shown fitted within cell mounting wells101. Preferably cells201are lithium ion batteries utilizing an 18650 form-factor, although it will be appreciated that the invention is not limited to a specific cell chemistry, design, shape or configuration. As illustrated in these figures, interior housing member surface103is uninterrupted except for the inclusion of cell mounting wells101.

FIGS. 3 and 4provide perspective and cross-sectional views of the exterior surfaces of housing member100, without and with included cells, respectively. As shown inFIGS. 1-4, the housing member is designed such that the end surfaces401of cells201fit against surface105of the exterior structural layer of member100. Preferably, and as shown, surfaces105include an aperture107, thus providing a point of contact for electrically coupling the cells to a connector plate, wiring harness, or other electrical interconnect. The removal of interconnect apertures107from surfaces105has the added advantage of further reducing the weight of member100. It will be appreciated that the invention does not require apertures107, depending upon the means used to electrically connect to the cells. For example, in an alternate configuration (not shown) apertures107are eliminated and a wiring harness is integrated within the housing member.

As shown inFIGS. 3 and 4, located between adjacent cell mounting wells101are bonding wells301. Bonding wells301are accessed from the exterior side of housing member100. Within each bonding well301are one or more cell cutouts or windows109. As a result of cutouts109, when cells201are positioned within housing member100, each bonding well301is formed, in part, by exterior cell surfaces203. The remaining surfaces of each bonding well301are comprised of internal housing member surfaces303. As each bonding well is comprised of both cell exterior surfaces and housing member surfaces, when the bonding well is filled with an adhesive, a mechanical bond is formed between the housing member and the cells contained therein. Although not shown, if desired a third component, such as a cell interconnect connector plate, may be fitted on top of the exterior surface of housing member100, with the connector plate preferably being bonded to the housing member by the adhesive located on top of bond surfaces304.

Battery pack housing member100may be fabricated from any of a variety of materials. Preferably the selected material is not electrically conductive, thus preventing inadvertent cell shorting. In addition, preferably the selected material is light weight, easily manufactured, and capable of forming a strong bond with the selected adhesive. Exemplary materials include composite materials and any of a variety of polymers, e.g., a thermoplastic such as a polycarbonate/ABS (acrylonitrile/butadiene/styrene) blend.

During battery pack fabrication, after insertion of cells201into mounting wells101, the housing member is oriented in a manner such as that shown inFIG. 4, thus allowing direct access to bonding wells301. Typically housing member100is sized such that only a small portion of cells201are inserted into wells101, for example, less than 20% of the length of cells201, more preferably less than 10% of the length of cells201, and still more preferably less than 5% of the length of cells201. An adhesive is then introduced into the bonding wells. Due to the fit between the exterior surface of cells201and adjacent surface111of cell mounting wells101, little, if any, adhesive seeps through the radial gap between these surfaces. To aid in minimizing adhesive seepage through this gap, especially in light of the typical cell diameter variations encountered during manufacturing, preferably a high viscosity or non-sag or sag resistant adhesive is used. Exemplary non-sag and sag resistant adhesives include Loctite® E-120HP, Loctite® H3151, Loctite® 3414, and Loctite® H3300. It will be appreciated that the invention is not limited to these specifically-identified adhesives.

As previously noted, a connector plate may be bonded to the exterior surface of housing member100, preferably during the same bonding step as that used to bond cells201within mounting wells101. In such a configuration, preferably the connector plates include apertures that correspond to apertures107, thus allowing an interconnect such as a wire-bond to be coupled between the connector plate and the end surface401of the corresponding cell. Preferably such a connector plate also includes one or more indentations that provide positive positioning of the connector plate relative to the housing member, and also ensure one or more bonding surfaces that are aligned with the bonding wells, or with connector plate specific bonding wells (not shown).

As described above, using the housing member of the present invention allows the cell/housing adhesive to be introduced from outside the battery pack, or at least outside this portion of the battery pack, where the bond formed between the housing and the cells is clearly visible. This is in marked contrast to a battery pack, such as that disclosed in co-pending U.S. patent application Ser. No. 12/315,303, in which the battery pack adhesive, also referred to as an encapsulant, is introduced through housing member ports into the central region of the battery pack, thus preventing, or at least making it difficult, to inspect the bonds.

FIG. 5illustrates a minor modification of the previously described embodiment. As shown, within each bonding well301is located at least one bonding well feature501that is integral to housing member100. Preferably bonding well feature501is a protrusion(s) formed on a surface303of the housing member, for example during the fabrication of the housing member. Feature501reduces the volume of adhesive required within each bonding well101which, in turn, may decrease curing time, assembly weight, and assembly cost. Additionally, feature(s)501provide additional bonding surfaces, thereby increasing the mechanical strength of the bond formed between the cells and the housing member.

It will be appreciated that the present invention lends itself to both manual and automated battery pack manufacturing processes. For example, in one preferred process the first end portions of all of the cells are inserted into the corresponding cell wells within the first housing member, for example a housing member100such as that illustrated inFIG. 1. Once the cells are properly seated within the cell mounting wells of the housing member, a complementary housing member is positioned over the second end portions of the cells such that the second end portion of each cell is inserted within the corresponding cell well of the complementary housing member. As the housing members are preferably small relative to the overall cell length, as previously noted, after battery pack assembly there remains a gap between the complementary housing members. As a result of this configuration, the cells are the primary source of battery pack structural integrity. It should be understood that other configurations can also be used with the invention, for example configurations in which the housing members are large enough to completely encase the cells (i.e., where approximately half the length of each cell is within each housing member). In such a configuration, one or more latching mechanisms may be used to secure the two members together. In addition to using any of a variety of different latching mechanisms, other means can be used to secure the two housing members together in such a configuration. For example, the mating surfaces of the housing members can be ultrasonically welded together, or bonded together with a suitable adhesive.

Once the battery pack is assembled, the adhesive is added to the bonding wells of the uppermost housing member. Preferably the adhesive is introduced using an automated system. Because the individual bonding wells301are separated by bonding shelves304, the adhesive may be dispensed in a continuous bead, which may be easier to automate and control. This is in marked contrast to a battery pack, such as that disclosed in co-pending U.S. patent application Ser. No. 12/315,303, in which the battery pack adhesive, also referred to as an encapsulant, is introduced through individual housing member ports into the central region of the battery pack, thus requiring the adhesive to be dispensed in discreet shots.

After the adhesive is either sufficiently cured or sufficiently captured in place, the battery pack is rotated, i.e., flipped-over, and adhesive is then added to the bonding wells of the complementary housing member. The adhesive may be captured, for example, by adding a connector plate as previously described. In the preferred manufacturing process, after the adhesive is dispensed into the bonding wells and bonding shelves, the connector plate is mated to the housing member and fixtured in place, for example with snap or press-fit features on the connector plate and the housing member. Once fixtured, the connector plate seals the adhesive in the desired bonding regions, allowing the battery pack to be rotated without permitting the adhesive to seep out. Adhesive can then be dispensed into the bonding wells and bonding shelves of the complementary housing member. Assuming a complementary connector plate is fixtured in place, the adhesive linking the cells and connector plates to the housing members on both ends of the battery pack can be allowed to cure simultaneously. This is in marked contrast to a battery pack, such as that disclosed in co-pending U.S. patent application Ser. No. 12/315,303, in which the battery pack adhesive, also referred to as an encapsulant, is dispensed into an open cavity, thus requiring the adhesive to cure significantly or completely before the battery pack can be rotated.

In the preferred manufacturing process, and as described above, the battery pack is assembled prior to adding adhesive to either housing member. In an alternate manufacturing process, cell mounting fixtures are used to position the cells during the positioning and bonding of the first housing member. Once the adhesive is sufficiently cured, the structure is rotated, thus allowing the complementary housing member to be positioned and bonded to the cells. A disadvantage of this approach, however, is that a cell may be out of alignment when it is bonded to the first housing member, thereby preventing a straightforward integration of the cells into the second, complementary housing member.

As will be understood by those familiar with the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.