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

[0002] With a drive to minimise the use of fossil fuels, there is an increasing trend towards using electric motors for various applications, for example to drive a variety of devices including vehicles, aircraft and other mobility devices. Electric motors require power from a battery and much work has been done to develop batteries with greater efficiency with a particular focus on the chemistry of the battery. One consequence of this has been a surge in interest in lithium ion batteries and a search for lithium resources to support the anticipated demand for lithium ion batteries. Other battery materials such as cobalt have also attracted interest.

[0003] However, the drive to efficient use of electrical power needs more than a focus on battery chemistry. For many applications which can adopt battery power, especially for portable and mobile battery powered devices, it is important to reduce weight. As weight is reduced, torque to weight ratio increases and power to weight ratio increases. Weight can, in theory, be reduced simply by adopting lighter weight materials but there are further complications. The lightweight device must also be a safe device and structural rigidity is also important.

[0004] US Patent No. 8739907 discloses an electrically powered car with a battery pack intended to become a structural member of the vehicle. The problem is that this structure, while doubtless meeting strength requirements, admits issues with weight. Specifically, the battery pack is connected to the vehicle chassis in such a way as to increase the strength of the chassis. The battery pack is made up of a plurality of cells, a control system and a housing. The housing includes structural members, a lower housing member and an upper housing member. The structural members are used to stiffen the battery pack and support the relatively high weight of the cells contained therein. The structural members may include 2"x3" rectangular tubes which extend about the periphery of the lower housing member, in addition to a plurality of 1 " square tubes and other smaller tubes that extend about the periphery of one or both of the lower and upper housing members. The structural members are made of a suitable material such as carbon steel.

[0005] One response to material weight is to attempt substitution of typically used metals with fibre reinforced materials, typically in a composite structure. However, it has been recognised that - where composite structures are used - whether fixed or mobile - re-design is likely to be necessary. The need for such redesign imposes a time and financial cost burden that favours conservative or conventional design and materials selection approaches. In addition, manufacturing processes for fibre reinforced materials and composite structures are quite distinct from those used for mass production of metallic components and fibre reinforced materials are anisotropic with mechanical properties not being identical in all directions.

[0006] It is an object of the present invention to provide a composite structure that facilitates the efficient use of electric power in a range of applications, whether for home use or use in a range of vehicles including automotive vehicles, aircraft including drones and mobility devices.

[0007] 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; 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. [0008] The container may include upper and lower layers or panels, possibly acting as closures for the container, which form tension and compression members of a composite sandwich structure. These layers conveniently have flat upper and lower surfaces.

[0009] The container may conveniently be provided in a rectangular box shape. Such a rectangular box shape, being in the form of a beam, particularly an Ί" beam, will often be advantageous and suitable as a structural member. The walls of such a container - being subject to in-plane stresses - are advantageously comprised of single composite material webs of monolithic structure, preferably including reinforcing fibres oriented longitudinally and laterally. Carbon fibre reinforced polymer (CFRP) would be a suitable first material. Woven mats and/or lightweight metal sheets could also be used as a first material. Combinations of materials may be used. However, the container may be designed in other shapes provided it has the required resistance to longitudinal and transverse bending forces imposed on the container by the application. Fabrication techniques may be adjusted, if required, with the assistance of simulation tools which enable appropriate selection of the structural element shape, choice of plies orientation of fibres in the material and stacking.

[0010] The core, which is desirably bonded or adhered to the container, advantageously accommodates the electric cells within a second material or a substructure of second material resistant to compression and shear loads. A suitable second material may include a polymer foam such as polyurethane or polystyrene foam which could be formed around electric cell(s). However, a particularly preferred and convenient sub-structure includes a honeycomb structure comprising elements of lightweight material such as a light metal or light metal alloy; for example aluminium. Combinations of materials may be used, for example in elements having laminated structure. Such a core structure has high strength and stiffness yet is cost effective to produce. Accommodation for electric cells is provided by spaces within the honeycomb core structure. One or more electric cells may be accommodated per space though one electric cell per space is preferred. Such spaces may be columnar and conveniently of polygonal, for example hexagonal, geometry though other geometries, for example cylindrical geometry (which may provide a honeycomb structure with spaces of circular section and resembling a wine rack viewed end on), can be adopted. 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. Electric cells are desirably close packed within the core, desirably with a packing factor approaching that for hexagonal geometry.

[001 1 ] Such a composite structure may include power distribution means for delivering electric power from the composite structure to the application so that it functions as a structural battery. The power distribution means desirably also enables recharging of the battery. To either end, the composite structure conveniently includes a power distribution bus comprising conductors and control circuitry for distributing power from the plurality of electric cells included within the housing of the composite structure and preferably controlling the recharging process. The power distribution bus may be fixed to another power distribution member such as a rigid power distribution board. Such member or power distribution board could also serve a structural function, for example acting as a tension or compression layer, forming part of a composite sandwich structure. In such case, the power distribution 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 could act as an upper or lower layer of the container as previously described. In any event, electric cells may be connected to the power distribution means, and more particularly to the conductors, through tabs electrically connected with cell terminals. Electric cells may be connected in series, parallel or preferably both.

[0012] The composite structure or 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 of an aircraft or the hull of a watercraft, boat or ship, all requiring electric power for some purpose, for example using an electric motor as prime mover. The composite structure could form part of a portable device or a structure such as a building or a device, such as a mobility device, or an electric vehicle. The composite structure may be connected to other load bearing structures or structural members as required for applications such as those described above. The container may include other stiffening members if required. For example, where the container is in the form of a box, the corners of the box may be provided with stiffening members which may also be connected to other structural members used within the application. Such structural members, including stiffening members, may enable electrical connections to be made if required.

[0013] Suitable composite materials for use as the first material of the container may be fibre reinforced materials, especially those based on long and continuous reinforcing fibres such as CFRP. Such materials typically have very low electrical conductivity relative to the metallic materials desirably used for the core. Such long and continuous fibres typically represent 50% or more of the material, the other approximately 50% or less consisting of a matrix, generally a heat setting resin, of epoxy (EP), diallylphthalate (DAP), polyester or vinyl ester type, for example. Thermoplastic resins may be used in some instances. The fibres may be selected with regard to cost and the properties required of the container. Mineral or organic fibres may be used. Mineral fibres include glass and carbon fibres among others. Organic fibres of various types, for example aramid fibres, may be selected. Lightweight metals or metal alloys could also be used. The first material selection will depend on required properties and cost.

[0014] Electric cells are included in number required to provide the required power for the composite structure so it functions as a structural battery. A potentially very large number of electric cells, perhaps thousands, could be included within a vehicle, with a single structural battery or bank of structural batteries as described herein being used. 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 batteries rated at 3.7v approximately or 2170 type batteries rated at a higher voltage. 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. 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 rechargeable.

[0015] Another embodiment of the invention provides a method for constructing a composite structure for delivering electric power to an application comprising the steps of:

forming a stock of a first material;

forming said stock of first material into a container; and

forming a core of a second material for accommodating a plurality of electric cells within said container such that said composite structure forms 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. The first and second materials may be selected from the materials described above.

[0016] A suitable stock of first material, for example a fibre reinforced material, may include pre-pregs of fibres impregnated with resin, such as a resin described above. The pre-pregs may be in planar form and may be foldable to form walls of the container.

[0017] Forming the stock into a container conveniently involves a moulding process in which the stock of composite material is placed into the mould to form the desired shape of container. Where such stock is of pre-pregs, a curing step may be required to complete the moulding process.

[0018] At this stage, the core which may comprise a filler material or, more advantageously and desirably, a honeycomb core structure or core sub-structure as above described may be formed and installed within the container. The honeycomb core structure can be fabricated from a second lightweight material such as a light metal or light metal alloy, for example aluminium (especially from aluminium foil) or other materials such as fibreglass and suitable polymers such as fibre reinforced polymers or other composite materials. The lightweight material is desirably electrically conductive. Honeycomb structures, whether having spaces for example of polygonal, for example hexagonal, or circular shape, are conveniently manufactured by an expansion or corrugation process, the former being suitable for light metals such as aluminium. Other manufacturing methods could be used. The core is desirably bonded or adhered to the container.

[0019] A power distribution means, such as a power distribution bus as above described, may then be conveniently connected to the honeycomb structure core and container. The power distribution bus may be fixed to another power distribution member with insulating properties such as a rigid power distribution board serving a structural function, for example acting as a tension or compression layer, for the composite structure, more specifically being a composite sandwich structure. In such case, the power distribution bus could be located on a rigid board forming a tension or compression loaded member for the composite structure. The rigid board could conveniently be formed from the stock of fibre reinforced material with insulating properties. This tension or compression loaded member conveniently acts as an upper or lower layer of the container as previously described. In any event, electric cells may be connected to the power distribution means, and more particularly to the conductors, through tabs electrically connected with cell terminals. Electric cells may be connected in series, parallel or both. Conveniently, the connection of such power distribution member to the honeycomb structure core and housing is by adhesion with an adhesive.

[0020] As described above, the composite structure can be used in a range of applications. Any application that can draw electric power from electric cells could adopt the composite structure as a structural battery. A potential application is to electric motor vehicles. In such case, the composite structure could accommodate a very large number of electric cells conveniently in the form of a floor pan for an electric motor vehicle. Weight is then focussed in the typically lowest point of the vehicle where it may provide a beam between front and rear wheels, left and right wheels (where provided) and a torsionally rigid member between all wheels.

[0021 ] The composite structure as described above may be conveniently fabricated to form a structural battery and structural member which may cost effectively be used in a range of applications. Whilst acting as a structural member, this is done without the weight involved with metal and metal alloy containers and trays meeting an important objective, especially for electric motor powered vehicles.

[0022] 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:

[0023] Fig. 1 is an orthogonal view of the composite structure for delivering electric power in accordance with one embodiment of the present invention and prior to connection of the circuit board.

[0024] Fig. 2 is a mould for forming a container of the composite material structure as shown in Fig. 1 .

[0025] Fig. 3 shows a stock of composite material for moulding into the container of the composite structure as shown in Fig. 1 using the mould shown in Fig. 2.

[0026] Fig. 4 shows the stock of composite material of Fig. 3 shown in position within the mould shown in Fig. 2.

[0027] Fig. 5 shows the stock of composite material and mould of Fig. 4 with further structural members inserted.

[0028] Fig. 6 shows the stock of composite material and mould of Fig. 4 with still further structural members inserted.

[0029] Fig. 7 shows the stock of composite material and mould of Fig. 6 with a housing or core of a hexagonal honeycomb structure for accommodating electric cells inserted.

[0030] Fig. 8 shows an alternative housing or core configuration with a circular (wine rack shape) honeycomb structure for accommodating electric cells. [0031 ] Fig. 9 shows the composite structure according to the first embodiment of the present invention and ready for extraction from the mould.

[0032] Figs. 10a to 10c schematically show the steps in fabricating the honeycomb structure shown in Fig. 7.

[0033] Fig. 1 1 shows a plan view of a power distribution bus for the composite structure shown in Fig. 9.

[0034] Fig. 12 shows an orthogonal view showing one possible arrangement of the power distribution bus of Fig. 1 1 in relation to the honeycomb core structure shown in Figs. 7 or 8.

[0035] Fig. 13 shows a front view of the composite structure ready for use as a structural battery.

[0036] Fig. 14 shows a bank of structural batteries, each as shown in Fig. 13.

[0037] Fig. 15 shows a detail orthogonal view of a further structural member as inserted and illustrated according to Figs. 6 and 14.

[0038] Fig. 16 shows a detail orthogonal view of a electrical connector for inclusion within the structural battery as shown in Fig. 12.

[0039] Fig. 17 shows a detail of an extruded structural member included in the composite material structure shown in Figs. 9 and 13.

[0040] Fig. 18 shows detail of an extruded structural member included in the composite structure shown in Figs. 9 and 13.

[0041 ] Referring now to Figs. 1 , 7, 9, 13 and 14 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 of a first, fibre reinforced composite material; 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, tension, compression, torsion and longitudinal and transverse bending forces imposed on the structural battery 10 by the electric motor vehicle whether stationary or in operation. [0042] The container 12 and the structural battery 10 has a rectangular box shape and so is in the form of a beam, similar to an "I" beam, suitable as a structural member. To achieve this, the walls 22 and 26 and base 24 of the container 10 must be constructed from suitable material. Further, the walls 22 and 26 and base 24 of container 10 being subject to in-plane stresses - are comprised of single fibre reinforced CFRP or epoxy material webs of monolithic structure, including aramid reinforcing fibres oriented longitudinally. Woven mats or metal sheets, for example aluminium or other metal or alloy, could also be used.

[0043] Container 12 accommodates the electric cells 34 within pre-formed spaces within a core or sub-structure 30 resistant to compression and shear loads. In this case, the core structure is a honeycomb structure 30 comprising a lattice or framework of elements 31 of a second, lightweight material, here aluminium. Such a 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 elements 31 of the honeycomb structure 30. Such spaces 32 are columnar and here of hexagonal geometry, with dimensions to allow accommodation of cells 34, though other geometries could be adopted. Hexagonal geometry may be selected to achieve a high electric cell 34 packing factor. For example, the spaces could be of circular section geometry as are the spaces 132 of the structure 130 shown in Fig. 8. In this case, a corrugation moulding process of multiple plies of aluminium sheet may conveniently be used to form the honeycomb structure from corrugated laminated sheets 131 which provide spaces 132 of circular section and so resemble a wine rack viewed end on. Suitable core structures are also described in the Applicant's co-pending International Patent Applications filed 8 August 2018 under Attorney Docket Nos. P43190PCAU and P43209PCAU, the contents of which are hereby incorporated herein by reference. Honeycomb core structure 30 is bonded or adhered to container 12 by an adhesive layer of a polymer resin, conveniently an epoxy resin. [0044] Electric cells 34 or 134 are accommodated in spaces 32 or 132 in a close packed manner avoiding short circuiting and other electrical malfunctions. One electric cell 34 or 134 is accommodated per space 32 or 132.

[0045] 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, for example as included in the table below.

In an electric motor vehicle, the aim would be to reach a cost effective balance between weight, vehicle range and battery cost.

[0046] Electric cells 34 (134) of various types could be selected and this is not critical though suitable batteries 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 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.

[0047] The container 12 is, in this embodiment, adhered to a rigid board 40, of insulating material such as glass fibre reinforced epoxy, for accommodating power distribution means in the form of power distribution bus 44 and control circuitry (not shown) for distributing power from the electric cells 34 included within structural battery 10 and controlling the re-charging process. The power distribution board 40 is important in providing a tension or compression layer for the structural battery 10 of composite sandwich structure, as shown the upper layer. Cells 34 are connected to the power distribution board 40 through conductive tabs 42 electrically connected with both positive and negative cell terminals, though not through soldering, and with complementary conductors 45 and 46. Flat conductors 45 and 46 may be fabricated from copper placed on to the rigid board 40 by a conventional method. Parallel arranged banks of electric cells 34 are schematically shown connected both in series and parallel connections may be employed. Further description of options for possible electrical layouts for structural batteries as described herein are described in the Applicant's co-pending International Patent Applications, filed 8 August 2018 under Attorney Docket Nos. P42682PCAU and P43209PCAU, the contents of which are hereby incorporated herein by reference.

[0048] Container 12 includes other stiffening members. In this case, the corners of the box container 12 are provided with stiffening members 120 of fibre reinforced nylon or polyamide which may be connected to other structural members used within the application. Such structural members, including stiffening members 220, 230, may enable electrical connections to be made through metal portions 232 if required. Suitable connectors and stiffening members are shown in Figs. 14 to 17.

[0049] The construction method for structural battery 10 will now be described with reference to Figs. 2 to 10(c).

[0050] In a first step, a stock 20 of aramid (or Kevlar) fibre reinforced epoxy resin material in the form of pre-pregs 22, 23, 24 and 26 shaped as planar elements, which will as the reference numbering indicates, will form the walls of container 12, is formed in a manner known in the art of composite material fabrication. Suitable composite materials for inclusion in the container 12 are so-called structural composite materials, especially those based on long and continuous reinforcing fibre such as CFRP. Such long and continuous fibres typically represent 50% or more of the material, the other approximately 50% or less consisting of a matrix, generally a heat setting resin, of epoxy (EP), diallylphthalate (DAP), polyester or vinyl ester type, for example.

[0051 ] The container 12 is formed using an aluminium mould 90 having walls 92 and base 94 of 10mm thickness as shown in Figs. 2 and 4 to 7 and 9.

[0052] First, the stock 20 of fibre reinforced material is accommodated within mould 90 with its various walls 22 and 24 and base 26 located as shown in Fig. 4.

[0053] Second, corner stiffening members 220A are inserted at each corner of the mould 90 (and so the container 12). The lower corner is glued into place and fibre is lapped over and glued to the fibre face as schematically illustrated in Fig. 5.

[0054] Third, corner extrusions 220 are inserted, lower corner is glued in place. Then fibre is lapped over and glued to the recesses cut for the fibre. This stage is schematically illustrated in Fig. 6.

[0055] At this stage, the core in the form of honeycomb core structure 30 - with structure and functionality as described above - is installed within the container 12. For this purpose, the composite material surfaces 22, 24 and 26 of container 12 are coated with adhesive so that the honeycomb structure core 30 can be inserted and adhered or bonded to the container 12. Ears are removed, texture is corrected and dimensions checked. The honeycomb structure 30 to form the core is fabricated from aluminium foil using an expansion process involving the steps schematically shown in Figs. 10(a) to 10(c).

[0056] The power distribution board 40 is then conveniently connected to one face 30A of the honeycomb structure core 30 and container 12 by gluing them together with a suitable adhesive, conveniently the same as used for adhering the honeycomb structure core 30 to the container 12. The structural battery 10 is ready for use and may be used alone or in a bank of structural batteries 10 as shown in Figs. 13 and 14 and acting as a structural member that can be connected to other structural members through connectors having structural form such as connector 220 shown in Fig. 15. Connectors 230 may be configured with a structural member 128 to conduct electricity where required for the application through metal portions 232 connected to member 128 as shown in Fig. 16.

[0057] Referring to Figs. 10(a) to 10(c), there is shown a conventional expansion process for fabricating a honeycomb structure and suitable also for fabricating honeycomb structure 30 to form the core of the structural battery 10. Layers of aluminium foil 290, 292 and 294 are glued together at staggered points as shown by arrows G. Adhesion of layers 290 to 292 takes place at points staggered from the adhesion of layers 292 to 294 as shown in Fig. 10(a). Expansion starts as shown in Fig. 9(b) and hexagonal columnar spaces 320 are formed. Dimensions of void spaces 320 which will become spaces 32 are selected to be sufficient to accommodate electrical cells 34. At points of adhesion, the walls 322 defining the spaces 320 have double thickness. At Fig. 10(c), the sandwich construction of layers 291 , 292 and 293 becomes evident through further expansion. Honeycomb structure 300 is ready for deployment as honeycomb structure core 30.

[0058] 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.

[0059] 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. [0060] 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.