[0001 ] The invention relates to a composite structure for delivering electric power, for example as a structural battery.

[0002] The Applicant has developed composite and composite sandwich structures suitable as a structural battery comprising a container of a first material; and a core for accommodating a plurality of electric cells provided within said container wherein the container and the core of the composite structure together form a structural member having resistance to shear forces, compression forces, tension forces, torsional forces and longitudinal and transverse bending forces imposed on said structural member by the application. Further description of one embodiment is provided in the Applicant's co-pending Interrnational Patent Application filed 8 August 2018 under Attorney Docket No. P42453PCAU, the contents of which are hereby incorporated herein by reference.

[0003] Delivery of electric power from the electric cells to the application involves a number of considerations. The electrical connection means needs to organise the electric cells in series or parallel or more preferably both to deliver the voltage and battery capacity required by the application to reduce the number of electric cells required, each electric cell representing a cost. Further, the electrical connection means should ideally be provided in a manner that improves or at least does not adversely impact on the service of the structural battery as a structural member.

[0004] It is an object of the present invention to provide a composite structure useful as a structural battery that facilitates the efficient use of electric power in a range of applications, particularly through inclusion of a useful electrical connection means from the electrical cells to the application. [0005] With this object in view, the present invention provides a composite structure for delivering electric power to an application requiring electric power comprising:

a container of a first material resistant to longitudinal and transverse bending forces imposed on the container by the application;

a core of a second material resistant to compression and shear loads for accommodating a plurality of electrically connected electric cells provided within said container; and

an electrical connection means for connecting said plurality of electric cells enabling delivery of power from said plurality of connected electric cells to said application wherein the container and the core of the composite structure together form a structural member having resistance to shear forces, compression forces, tension forces, torsional forces and longitudinal and transverse bending forces imposed on said structural member by the application.

[0006] The composite structure includes electrical connection means, such as a bus, for connecting the electric cells enabling delivery of electric power from the composite structure to the application so that it functions as a structural battery. The electrical connection means desirably also enables recharging of electric cells included within the battery. The structural battery need not be made replaceable at least under normal circumstances and it may be advantageous not to allow replacement since the battery is preferably rechargeable. To either end, the composite structure conveniently includes an electrical connection bus comprising conductors for organising parallel and series connections for the plurality of electric cells included within the housing. The electric cells may be connected in series, in parallel or preferably in both series and parallel. A series/parallel connection allows achievement of both the desired voltage and current ratings with a standard cell size.

[0007] The electrical connection means or bus may be fixed to another electrical connection member such as a rigid electrical connection board. Such member or electrical connection board, while electrically insulating, could also serve a structural function, for example acting as a tension or compression layer, forming a composite sandwich structure. In such case, the electrical connection bus could be located on a rigid board forming a tension or compression loaded member for the composite sandwich structure. This tension or compression loaded member may conveniently act as an upper or lower layer of the container. Such member need not necessarily carry an electric connection bus.

[0008] The core advantageously accommodates the electric cells within spaces pre-formed within a second material or a sub-structure resistant to compression and shear loads. The second material may include a combination of materials. A portion of the material or sub-structure could be made electrically conductive to enable parallel connection of a group of electric cells, series connection of a group or string of cells or series connection of a group or string of parallel connected electric cell sub-groups, or parallel connection of a group or string of series connected electric cell sub-groups.

[0009] Honeycomb or like core structures of lightweight material such as a conductive light metal or light metal alloy; for example aluminium, are advantageous. Such a structure has high strength and stiffness yet is cost effective to produce. Suitable core structures are also described in the Applicant's co-pending International Patent Applications filed 8 August 2018 under Attorney Docket Nos. P42453PCAU, P43190PCAU and P43209PCAU, the contents of which are hereby incorporated herein by reference.

[0010] Accommodation for electric cells in such core structures is provided by spaces formed by the layout or framework of core elements or layers forming the core structure. The electric cells, in one embodiment, may be insulated from the elements of the core structure to achieve the desired connectivity. Such spaces are columnar and conveniently of hexagonal geometry (to allow close packing of electric cells) though other geometries, for example cylindrical geometry (which may provide spaces of circular section and a core structure resembling a wine rack viewed end on), can be adopted. [001 1 ] In another embodiment, the core sub-structure may comprise a framework of core elements comprising alternating layers of conductive material, for example aluminium or copper e.g. in the form of sheets, and insulating material, for example a ceramic or an insulating polymer such as a polyamide polymer. Ceramic or insulating material may be coated on to the conductive material. Where the core structure is made up of a plurality of layers of conductive material, such as aluminium or copper e.g. in the form of sheets, the layers may be separated by a layer or pad of insulating material which, though electrically isolating, may be thermally conducting if required. The layers may be disposed to form a laminated structure such as a laminated sheet.

[0012] Electrical cells may be connected in a range of ways, the preferable arrangement including both series and parallel connections between discrete electric cells. The parallel connections are conveniently between individual electric cells within a group or string of electric cells. The series connections are conveniently between electric cell groups or strings including a plurality of electric cells. Series connections require positive to negative terminal connection between discrete electric cells or groups or strings of parallel connected electric cells. Parallel connections require positive to positive terminal connection between discrete electric cells or groups of series connected electric cells and negative to negative connection between discrete electric cells or groups of series connected cells. These connections are preferably made in a manner that eases fabrication and reduces cost of materials for making the connections and maximising the number of electric cells that can be packed in a given housing volume. Where a honeycomb core structure is used, the positive to negative terminal connections between the electric cells may follow a zig-zag type pattern as the honeycomb core structure is viewed in plan though such an arrangement is not intended to be limiting. The electric cells in rows, groups or strings, such as parallel rows or tiers, within the core may have their positive terminal oriented up in one row and down in the next adjacent row or the cells may be constructed to have both the positive and negative terminal accessible from one end only. Adoption of the zig-zag pattern is advantageous for minimising weight and facilitating high volume manufacture by minimising welds and component count.

[0013] The number of electric cells and number of spaces selected to accommodate such electric cells is determined with reference to the electric power requirements of the application. The electric cells most desirably each have the same current and voltage rating. The cell type is not critical though suitable batteries could be selected from rechargeable batteries, such as from the lithium ion battery class, such as for example 18650 type cylindrical cell batteries or 2170 type cylindrical cell batteries rated at 3.7v approximately. The selected electrical cells would enable the structural battery, while having the required structural properties to act as a structural member, to have a relatively shallow depth in relation to length and breadth.

[0014] The battery may generate heat during operation or, alternatively, may require heating under some operating conditions. To control battery operating temperature, the housing or sub-structure may include thermal control means. Suitable thermal control means are described in the Applicant's co-pending International Patent Application filed 8 August 2018, under Attorney Docket P42683PCAU, the contents of which are hereby incorporated herein by reference. In such case, core elements are constructed, for example as described above, to enable efficient heat transfer.

[0015] The composite structure and composite sandwich structure, as alluded to above, is a structural member typically forming part of the structural framework required by the application and a range of applications are possible. For example, the composite structure could - without limitation - form part of the chassis of a vehicle, a part of a fuselage or wing of an aircraft or the hull or bulkheads of a watercraft, boat or ship, all requiring electric power for some purpose, for example using an electric motor as prime mover. The composite structures could form part of a portable device or a structure such as a building or a device such as a mobility device. The composite structures may be connected to other load bearing structures or structural members as required for applications such as those described above. Further description of the composite structures is provided in the Applicant's International Patent Application filed 8 August 2018 under Attorney Docket No. P42453PCAU, the contents of which are incorporated by reference. Whilst acting as a structural member, this is done without the weight involved with metal and metal alloy battery containers, frames and trays thereby meeting an important objective, of reduced weight and added strength especially important for electric motor powered vehicles.

[0016] The composite structure and structural battery of the invention may be more fully understood from the following description of exemplary embodiments thereof made with reference to the drawings in which:

[0017] Fig. 1 is an orthogonal view of a composite sandwich structure to be a structural battery in accordance with one embodiment of the present invention [0018] Fig. 2A is an orthogonal view of one embodiment of the composite sandwich structure on extraction from a fabrication mould and prior to connection of the electrical connection means.

[0019] Fig. 2B is an orthogonal view of a further embodiment of the composite sandwich structure on extraction from a fabrication mould and prior to connection of the electrical connection means.

[0021 ] Fig. 3 shows a schematic plan view of a space formed between the elements forming the honeycomb core structure of Fig. 2A or 2B showing positive and negative terminals for the electric cell.

[0022] Fig. 4 is a schematic side sectional view of a space of the honeycomb core structure along section line A-A of Fig. 3 showing a single electric cell in position within the space.

[0023] Fig. 5 shows a cutaway view of the space and electric cell as shown in Figs. 3 and 4.

[0024] Fig. 6 shows an alternative core configuration for accommodating electric cells.

[0025] Fig. 7 schematically shows how series and parallel connections are made between electric cells accommodated in the core of Fig. 6. [0026] Fig. 8 shows an orthogonal view of an electric cell included in the core shown in Figs. 6 and 7.

[0027] Fig. 9 shows an insulating member as included in the honeycomb structure core of Figs. 6 and 7.

[0028] Fig. 10 schematically shows a power board carrying electric connection means for the structural battery illustrated with reference to Figs. 1 to 5.

[0029] Referring now to Fig. 1 , there is shown a composite sandwich structure in the form of a structural battery 10 for delivering electric power to an application requiring electric power such as an electric motor vehicle (not shown) but not limited to this. Structural battery 10 includes a container 12; and a core 30 for accommodating a plurality of electric cells 34 provided within the container 12. The structural battery 10 forms a structural member having resistance to shear, compression, tension, torsion and longitudinal and transverse bending forces imposed on the structural member by the application.

[0030] The container 12 and so the structural battery 10 has a rectangular box shape and is in the form of a beam, similar to an Ί" beam, suitable as a structural member. To achieve this, the walls 22 and 26 and base and upper layer (not shown) of the container 10 must be constructed from suitable first material such as a fibre reinforced material such as CFRP of low electric conductivity compared to metallic materials employed for the core 30. The first material may also include other materials resistant to longitudinal and transverse bending forces, preferably lightweight materials which may include light metals or metal alloys such as aluminium alloys.

[0031 ] Core or sub-structure 30 must be resistant to compression and shear loads. In one example, the core 30 - as shown in Figs. 2A and 2B - is a honeycomb core structure 30 of a second lightweight material which may include a combination of materials. Such a core structure has high strength and stiffness yet is cost effective to produce. Accommodation for the electric cells 34 is provided by spaces 32 formed between the elements 31 forming the honeycomb structure 30 as made using an expansion process described in further detail in the Applicant's co-pending International Patent Application filed 8 August 2018 under Attorney Docket No. P42453PCAU, incorporated herein by reference. Such spaces 32 are columnar and here of hexagonal geometry, with dimensions to allow closely packed accommodation of electric cells 34, though other geometries could be adopted. For example, the spaces could be of circular section and cylindrical volume as are the spaces 132 between the framework of core elements 131 of the core structure 130 shown in Figs. 6 and 7. In this case, a corrugation moulding process of multiple plies of aluminium sheet may conveniently be used to form the core structure 130 from corrugated sheets which become laminated core elements 131 of the structure 130 separated by spaces 132 of circular section so resembling a wine rack viewed end on.

[0032] Core elements 31 or 131 are electrically insulated from each other. For the honeycomb structure core 30 of Fig. 2A, the layers may be separated by sheets or pads of insulating material 41 in the manner schematically illustrated in Fig. 3. Referring to Fig. 2B, hexagonal honeycomb structure 30 may be made, using an expansion process, from alternating sheets of material to become layers 31 A and 31 B of elements 31 of honeycomb structure 30. One set of sheets become layers 31 A of conductive material, for example aluminium or copper sheet. The other set of sheets become layers 31 B of insulating material such as a ceramic. Alternating layers 31 B are bolded in Fig. 2B to ease illustration. It will be understood that, where the space walls are double thickness, the insulating material must be selected for ease of bonding to the conductive material.

[0033] Referring to Figs. 6, 7 and 9, the core elements 131 are again formed of laminated sheets of conductive material, aluminium, these core elements 131 being separated by elongate insulating spacers 141 with arcuate or concave surfaces 141 A and 141 B and having a dogbone shape when viewed end on or in plan. Conductive elements 131 form part of an electric connection means or bus in this embodiment. The dimensions of concave surfaces 141 A and 141 B are selected to neatly accommodate electric cells 134. A ceramic insulating material or a polymeric insulating material, such as polyamide, may be used. Spacers 141 may be comprised of a material that absorbs heat or swells and forms a char in a thermal runaway situation. Spacers 141 may also include information links, such as a thermistor, for sensing battery parameters such as temperature.

[0034] The core structures 30 and 130 include fluid passage means to enable battery temperature control by heat exchange between electric cells 34, 134 and a heat transfer fluid selected not to interfere with battery operation under normal operating conditions. Suitable thermal control means are described in the Applicant's co-pending International Patent Application filed 8 August 2018, under Attorney Docket P42683PCAU, the contents of which are incorporated herein by reference. Heat transfer fluid flow may be controlled dependent on actual battery temperature, as sensed by information links as described above and, for example, embedded in insulating spacers 141 for core structure 130.

[0035] Electric cells 34 or 134 are accommodated in cylindrical spaces 32 or 132, with a high close packing factor, in a manner avoiding short circuiting and other electrical malfunctions. This may require electric cells 34 (134) to be spaced, by insulating medium, from conductive layers of core structures 30 and 130. The insulating medium may include electric cell insulation or another insulating material.

[0036] The number of electric cells 34 (134) and number of spaces 32 (132) selected to accommodate such electric cells 34 (134) is determined with reference to the electric power requirements of the application and further description is included in the Applicant's co-pending International Patent Application filed 8 August 2018 under Attorney Docket No. P42453PCAU, incorporated herein by reference.

[0037] Electric cells 34,134 of various types could be selected and this is not critical though suitable batteries, each of the same rating, could be selected from rechargeable batteries especially from the lithium ion battery class, such as for example 18650 or 2170 type batteries which have a cylindrical geometry and are rated at 3.7v per cell. In the case of an electric motor vehicle, the selected electrical cells 34,134 would enable the structural battery 10, while having the required structural properties to act as a structural member, to have a relatively shallow depth in relation to length and breadth.

[0038] Referring to Figs. 3 to 5, electrical connections are described for a structural battery 10 having the honeycomb core structure 30 of Fig. 2A. Each electric cell 34 is accommodated within hexagonally shaped space 32, the hexagonal section selected to maximise packing factor of electric cells 34 within core 30. Hexagonal packing enables most efficient use of core volume. Each space 32 is defined by conductive (aluminium) core elements 31 C and 31 D which are separated from each other by ceramic insulating pads 41 . Core elements 31 C and 31 D extend above the electric cell 34 and connect to a rigid electrical connection board 40 and its electrical connection means in the form of an electric bus 44 comprising conductors 45 and 46 enabling series and parallel connections between electric cells 34, arranged in parallel rows, strings or groups P1 , P2, P3, P4 as schematically shown in Fig. 10. Electric cells 34 within groups P1 to P4 are connected in parallel. Electric cell groups P1 to P4 are connected in series. Electric cells 34 would typically require closer packing than Fig. 10 would indicate. Board 40 also provides an upper tension or compression layer for the structural battery 10 and so is of suitable material, here CFRP, for this duty.

[0039] Electric cell 34 includes a positive electrode 35 and a negative electrode 36. A conductive tab (not shown) is used to connect the negative base 38 of electric cell 34 to negative electrode 36 at spot welds 37. The positive electrode 35 is also connected to the positive terminal of electric cell 34 by spot welds 37. Electric cell 34 is then, through positive and negative electrodes 35 and 36, connected to negative and positive terminals of other electric cells 34 within its group in the honeycomb structure 30 and ultimately to other electric cell groups to provide both parallel and series connections providing the required voltage and current ratings for the battery application. Series connections are made between groups of electric cells 34 and parallel connections are made between individual electric cells 34, resulting in a combined parallel/series connection system.

[0040] Layers 31 C and 31 D, as described previously, are separated by insulating pads 41 included during fabrication. However, thermal control for battery 10 is desired so the insulating pads 41 do not extend the full length of layers 31 C and 31 D, rather leaving inter-connected galleries 50 through which heat transfer fluid can be circulated in heat transfer contact with electric cell 34 without interfering with the operation of structural battery 10 under normal operating conditions. This enables battery temperature to be controlled, say within the 15 ^Q C to 35 ^Q C range. Direction of heat transfer fluid flow is indicated by arrows C in Fig. 5.

[0041 ] Referring to Figs. 6 to 8, electrical connections are made between electric cells 134 accommodated within honeycomb core structure core 130 in a different manner to that for electric cells 34 accommodated within core structure 30. Positive electrode 135 is connected to the positive terminal of electric cell 134 and spaced from battery core 134C by insulating pad 139. The negative electrode 136 is connected, via electric tab 138A, to the negative terminal located at base 138 of electric cell 134. Negative electrode is also spaced from battery core 134C by insulating pad 139. Electric cell 134 is then, through positive and negative electrodes 135 and 136, connected to negative and positive terminals of other electric cells 134 within the honeycomb structure core 130, as above described, involving conductive core elements 131 to provide both series and parallel connections between electric cells 134 and cell groups providing the required voltage and current ratings for the battery application.

[0042] Such combination of series and parallel connection is schematically illustrated with reference to Fig. 7. Connection of positive to negative electrodes 135, 136 provides a series connection. One example is connection of negative electrode 136' to positive electrode 135'. Connection of negative electrode 136' to negative electrode 136" makes a parallel connection. Connections of positive electrodes 135 of electric cells 134 within a cell group would also make parallel connections.

[0043] Each electric cell 134 shown in Fig. 7 is analogously interconnected to form series and parallel connections with other electric cells 134 to maximise the electrical output of the illustrated core 130 at the required voltage and current ratings.

[0044] Honeycomb core structure 130 also includes temperature control means which operates as described above. Further detail about the temperature control method is described in the Applicant's co-pending International Patent Application, filed 8 August 2018 under Attorney Docket P42683PCAU, the contents of which are incorporated herein by reference.

[0045] As described above, the structural battery 10 can be used in a range of applications including in fixed structures, mobility devices and portability devices. A potential application is to electric motor vehicles. In such case, a bank of structural batteries 10 could accommodate a very large number of electric cells 34, potentially thousands, and form a floor pan for an the electric motor vehicle. Weight, which is significantly lower than that involved with conventional metal and metal alloy battery containers or trays, would then be focussed in the lowest point of the vehicle where one or a bank of structural batteries provides a load bearing beam between front and rear wheels, left and right wheels (where provided) and a torsionally rigid member between all wheels.

[0046] Structural battery 10 is rechargeable and not intended for replacement under normal circumstances. However, it could be made replaceable if desired. This itself could depend on the application. [0047] Modifications and variations to the composite structure and structural battery described herein may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present invention.