GB2541756A

GB2541756A - Coated substrate and method of fabrication thereof

Info

Publication number: GB2541756A
Application number: GB1519430.1A
Authority: GB
Inventors: Dossett Simon; Lewis John; Archer John
Original assignee: Tata Motors European Technical Centre PLC; Tata Motors Ltd
Current assignee: Tata Motors European Technical Centre PLC; Tata Motors Ltd
Priority date: 2015-08-28
Filing date: 2015-11-03
Publication date: 2017-03-01
Anticipated expiration: 2035-11-03
Also published as: GB2541756C; GB2541756B; GB201519430D0; WO2017037597A1

Abstract

Method comprising providing a metallic substrate with at least a portion of the surface being a porous metal oxide and providing a layer of medium over at least a portion of the porous oxide surface such that the medium impregnates at least a portion of the pores. The medium is then cured to form an electrically insulating layer. The oxide may be formed through an anodic process or may be a layer of native oxide, the medium may be a sol-gel material and may comprise a polysiloxane. Solvent may be removed from the medium which may densify the gel where the medium is sol-gel. The substrate may comprise aluminium, magnesium or their alloys. The substrate may comprise passages therein. The coated substrates may be used to form heat-sinks for electrochemical cells which may be pouch cells and an array or stack of cells may be formed. The substrate may form a cable tray. Included are product claims for the results of the methods above and a further claim to a motor vehicle comprising a plurality of cell units.

Description

COATED SUBSTRATE AND METHOD OF FABRICATION THEREOF

TECHNICAL FIELD

The present invention relates to heat sinks and to a method of fabrication thereof. In particular but not exclusively embodiments of the present invention relate to heat sinks for use in power storage devices such as battery packs.

BACKGROUND

It is known to provide a heat sink arrangement for a battery pack in which sheets of material of relatively high thermal conductivity such as aluminium are sandwiched between a stack of flat power storage cells of lithium Ion (Li-ion) type.

Anodised aluminium is commonly used as a heatsink but suffers disadvantage that the oxide layer is inherently porous and can result in dielectric failure through water absorption.

The cells may be in the form of hermetically sealed pouches containing the lithium-ion cell structure and having an outer layer formed from an insulating plastics material. Each of the aluminium sheets acts as a heat sink, conducting away from the cells heat generated by charging or discharging of the cells.

Cell manufacturers state that no portion of each cell should contact electrically conductive material. Exposure of a cell to high voltage without proper dielectric isolation can cause internal damage to cell. Cells must also meet legislative requirements. Under BS EN 1989 -1:1997 (Electrically propelled road vehicles. Specific safety requirements. On board energy storage) the dielectric isolation must be capable of withstanding a potential difference of twice the battery voltage plus 1000V.

Each aluminium heat sink is provided in planar face contact with a storage cell so as to enable good thermal conduction from the cell to the heat sink. However, in order to maintain a sufficiently high electrical isolation resistance between the cell and metallic heat sink material, each sheet is coated with an electrical insulator in order to prevent the establishment of a current path from the storage cell to the aluminium sheet. Typically, multiple layers of insulating material are applied in order to obtain sufficient electrical isolation of the sheet.

In some alternative known arrangements, a film of a plastics material is applied to a heatsink in order to provide an electrically insulating layer. Typically the plastics material is Kapton (RTM). A disadvantage of using such a film is that a film cannot conform easily to irregularly shaped surfaces. Gaps between the film and surface can easily form when the film is applied, reducing still further the thermal conductivity between cell and heatsink. In some further alternative known arrangements, an insulating layer is formed by overmoulding a glass-filled nylon material, at a temperature of around 290°C.

Coatings such as filled organic resin have been used, but the thickness required to provide sufficient electrical insulation detracts from thermal performance.

It is desirable to provide improved conduction of heat away from cells of the battery whilst also providing sufficient electrical isolation of the heat sink material. This will enable more rapid charging and discharging of a battery of cells to be effected.

SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to the appended claims.

Aspects of the present invention provide an apparatus, a vehicle and a method.

In one aspect of the invention for which protection is sought there is provided a method of fabricating a coating comprising: providing a substrate comprising a metallic material, at least a portion of a surface of the metallic material having an exposed porous metal oxide layer; and providing a layer of a first medium over at least a portion of the exposed porous metal oxide layer, whereby the exposed porous metal oxide layer is at least partially impregnated with the first medium; and curing the layer of first medium to form an electrically insulating coating layer.

Embodiments of the present invention have the advantage that they enable a substantially continuous, electrically insulating coating to be fabricated having reduced thickness compared with some known coatings, allowing a coating with reduced thermal resistance to be provided. In some embodiments this is believed to be at least in part because the electrically insulating coating layer at least partially impregnates the surface oxide layer, enabling the coating to remain substantially continuous at a lower thickness than in known coating methods. The layer of first medium is able to impregnate the oxide layer to establish a stronger bond thereto upon curing. Consequently, following curing, the electrically insulating coating layer is more strongly bound to the substrate. Some embodiments of the invention are ideally suited to applications in which thin, highly insulating coatings having low thermal resistance are required, such as in the fabrication of heat sinks in electrical applications such as electrochemical energy storage devices.

Optionally, the step of providing a substrate comprising a metallic material having an exposed porous metal oxide layer comprises forming a layer of porous metal oxide before providing the layer of first medium.

Forming the layer of porous metal oxide over the surface of the metallic material may comprise forming the layer of oxide being a layer than is in addition to any native oxide layer already present. The layer of oxide being formed may result in an increase in the thickness of an existing oxide layer.

The porous metal oxide layer may be a substantially continuous layer. The porous metal oxide layer may cover substantially the entire surface of the metallic material, or only a portion of the surface.

Optionally, forming a layer of oxide comprises forming a layer of native oxide.

By native oxide is meant an oxide formed by oxidation of a surface of the substrate. The formation of a native oxide can advantageously provide a layer having a strong bond with the substrate.

Optionally, forming a layer of oxide comprises subjecting the substrate to an anodic process.

The anodic process may be a hard anodic process or a soft anodic process.

Anodic processes can be particularly advantageous for industrial mass-production processes.

In some embodiments, a portion of the surface of the metallic material may be masked prior to forming the layer of oxide by an anodic process such that oxide formation by the anodic process is substantially prevented in the masked areas.

Optionally, forming a layer of oxide comprises subjecting the substrate to an anodic oxidation process.

Other processes may be useful in addition or instead including exposure of the metallic material to an oxidizing agent.

Optionally, providing a layer of a first medium comprises providing a layer of a sol-gel material over the substrate.

Optionally, the layer of first medium comprises a solvent, the method comprising removing at least some solvent from the layer of first medium.

The method may comprise removing at least some solvent to form a layer of a gel material.

The method may comprise subjecting the gel material to a drying operation to remove at least some of the solvent.

Optionally, the drying operation comprises densifying the layer of gel by removal of at least some solvent.

This feature may advantageously result in the formation of a stronger, more scratch-resistant layer.

Optionally, curing the layer of first medium comprises heating the gel to form the electrically insulating coating layer.

Optionally, the substrate comprises or consists essentially of one selected from amongst aluminium, an aluminium alloy, magnesium, a magnesium alloy, an aluminium magnesium alloy, an aluminium lithium alloy and an aluminium beryllium alloy.

Aluminium, magnesium, and alloys thereof have the advantage that they are conductive materials of relatively low weight. They also allow the formation of a native oxide that is strongly bonded to the underlying metallic material. A porous native oxide may be formed by anodic oxidation of the metallic material.

Other metallic substrate materials may be useful in some embodiments.

Optionally, providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness of no more than 100 micrometres.

Thus, the cured layer may have a thickness of no more than 100 micrometres.

Optionally, providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness in the range from 1 micrometre to 500 micrometres.

Optionally, providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness in the range from 1 micrometre to 100 micrometres.

Optionally, providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of no more than 500 micrometres.

Optionally, providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of in the range from 1 micrometre to 500 micrometres.

Optionally, providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of in the range from 1 micrometre to 100 micrometres.

Optionally, the electrically insulating coating layer comprises a polysiloxane.

Optionally, the gel material comprises a polysiloxane.

The gel material may be in the form of particles, and the particles may be in the form of micelles of polysiloxane. Other arrangements may be useful in some embodiments.

The method may comprise forming the substrate to have one or more passages therein for flow of coolant therethrough.

In one aspect of the invention for which protection is sought there is provided a method of forming a heat sink, comprising the method of a preceding aspect.

In another aspect of the invention for which protection is sought there is provided a method of forming a heat sink of an electrochemical battery, the method comprising forming a heat sink according to the method of the preceding aspect.

The method may comprise providing a piuraiity of eiectrochemicai ceiis each in thermai contact with a heat sink.

The method may comprise providing the eiectrochemicai ceii in the form of a pouch ceii.

The method may comprise providing a piuraiity of ceii moduies, each moduie comprising a heat sink in thermai contact with a respective eiectrochemicai ceii, the method comprising providing the ceii moduies in the form of an array or stack of ceii moduies.

Optionaiiy, the substrate comprises a metai piate having a substantiaiiy fiat face in thermai contact with the eiectrochemicai ceii.

The stack of ceii moduies may be a verticai stack or a horizontai stack. Other arrangements may be usefui.

The method may comprise forming an eiectrochemicai battery comprising forming a heat sink according to the method of a preceding aspect.

In an aspect of the invention for which protection is sought there is provided a method of forming a cabie tray, comprising performing the method of a preceding aspect.

In a further aspect of the invention for which protection is sought there is provided a method of forming a coated substrate comprising performing the method of a preceding aspect.

In a still further aspect of the invention for which protection is sought there is provided a method of forming a heat sink comprising performing the method of a preceding aspect.

In one aspect of the invention for which protection is sought there is provided a method of forming a cable tray comprising performing the method of a preceding aspect.

In an aspect of the invention for which protection is sought there is provided a coated substrate comprising: a substrate comprising a metallic material, at least a portion of a surface of the metallic material having a porous metal oxide layer over at least a portion thereof: and an electrically insulating coating layer over at least a portion of the porous metal oxide layer, the porous metal oxide layer being at least partially impregnated with the coating layer, the electrically insulating coating layer being formed by curing a layer of a first medium.

Optionally, the electrically insulating coating layer is formed from a layer of a sol-gel material.

Optionally, the porous metal oxide layer comprises a layer formed by an anodic oxidation process.

Further optionally, the electrically insulating coating layer comprises a polysiloxane.

In one aspect of the invention for which protection is sought there is provided an energy storage device comprising a heat sink comprising a coated substrate according to a preceding aspect.

Optionally, the heat sink comprises a panel, the panel being provided substantially in abutment with an electrochemical cell for storing electrical charge, the heat sink in combination with the cell forming a cell unit.

Optionally, the device comprises a plurality of cell units in the form of a stack.

In an aspect of the invention for which protection is sought there is provided a motor vehicle comprising a device according to a preceding aspect.

In a further aspect of the invention for which protection is sought there is provided a cable tray or heat sink comprising a coated substrate according to a preceding aspect.

In one aspect of the invention for which protection is sought there is provided a method of fabricating a heat sink comprising: providing a heat sink substrate comprising a metallic material; and forming layer of an electrically insulating material over the substrate, the step of forming the layer of an electrically insulating material comprising forming a layer of a sol-gel material.

Some embodiments of the present invention provide a method of fabricating a coating. The method may comprise providing a substrate comprising a metallic material. At least a portion of a surface of the metallic material may have an exposed porous metal oxide layer. The method may comprise providing a layer of a first medium over at least a portion of the substrate, for example over at least a portion of an exposed porous metal oxide layer. whereby the exposed porous metal oxide layer is at least partially impregnated with the first medium. The method may comprise curing the layer of first medium to form an electrically insulating coating layer.

Use of a sol-gel material has the advantage that a layer of electrically insulating material of higher thermal conductivity (or lower thermal resistance) than known heat sinks may be formed on the substrate. In some embodiments this is at least in part because a substantially continuous layer of insulating material offering sufficiently high electrical isolation may be formed having a thickness that is lower than that of an insulating material formed by known techniques offering similarly high electrical isolation. Some embodiments of the invention have the advantage that, at least in part because the thickness may be made lower, a weight of the coating may be made lower than known coatings.

In some embodiments, a layer of electrically insulating material may be formed having improved bonding to the substrate.

Embodiments of the present invention have the advantage that they enable a heat sink to be fabricated having improved thermai conductivity. For some embodiments this is believed to be at least in part because the layer of electrically insulating material may be formed to be substantially continuous at a lower thickness than in known methods.

Forming the layer of sol-gel material may be accomplished by dip-coating, spin-coating, spraying or any other suitable technique.

The sol-gel material may comprise predominantly particles having a size in the range of up to around fOOnm. Such particles may be referred to as nanoparticles. The particles may be in the form of micelles. The particles may be predominantly in the size range from 5 to 100nm, optionally predominantly in the range from lOnm to fOOnm. Other size ranges are also useful. The colloidal material may comprise agglomerates of particles predominantly in this size range, at least some of the agglomerates being larger than lOOnm in some examples.

Advantageously the step of providing a heat sink substrate comprises forming a layer of oxide over a surface of the substrate before forming the layer of electrically insulating material.

This can improve bonding of the layer of electrically insulating material to the substrate and enable a thinner layer of insulating material to be formed more reliably.

Advantageously the layer of oxide may comprise a plurality of pores. That is, the oxide layer may be porous.

This feature has the advantage that the electrically insulating material is able to key into the oxide layer to establish a stronger bond thereto. Thus, particles of the sol-gel material may migrate into the pores in some embodiments. Furthermore, in some embodiments the presence of the insulating material in the pores may prevent ingress of moisture into the pores. The present applicant considers that moisture ingress into the pores of a native oxide film may result in an increase in electrical conductivity of the oxide layer, which is deleterious to the electrical performance of the heat sink. Some embodiments of the present invention have the feature that because the pores may be occupied by the electrically insulating material, a rate of Ingress of moisture may be reduced and in some embodiments ingress may be substantially prevented.

In some embodiments, the presence of pores facilitating bonding of the Insulating layer to the substrate has the advantage that surface Imperfections such as burrs, scratches and the like are less problematic to the Integrity of the Insulating layer. This Is because the sol-gel material Is able to conform to a topography of the substrate surface, when It Is applied, ccntacting the substrate surface over substantially the whole exposed surface area of the substrate, even where surface Imperfections are present. This reduces a likelihood that the resulting Insulating layer formed by the colloidal material loses Its Integrity resulting In the formation of one or more holes or voids in the layer.

The enhanced bonding between the porous oxide film and the insulating layer or coating formed by the colloidal material also prevents shrinkage of the insulating coating away from topographical surface imperfections such as sharp corners present at burrs or scratches. Such shrinkage is common in known coating technologies and results in extremely thin coatings in these areas that do not provide adequate electrical insulation.

Forming a layer of oxide may comprise forming a layer of native oxide.

By native oxide is meant an oxide formed by oxidation of a surface of the substrate. The formation of a native oxide can advantageously provide a layer having a relatively strong bond with the substrate.

Forming a layer of oxide may comprise subjecting the substrate to an anodic process.

It is to be understood that certain metals such as aluminium and magnesium are naturally coated with a native oxide layer when unoxidised metal is exposed to air. Accordingly, the anodic process may increase a thickness of an existing oxide layer.

Forming a layer of oxide may advantageously comprise subjecting the substrate to an anodic oxidation process.

The anodic oxidation process may be a hard anodic process or a soft anodic process.

For example, in the case of aluminium, a relatively hard anodic oxide may be formed by anodising in sulphuric acid at relatively low temperatures or by anodising in a sulphuric acid/oxalic acid mixture at room temperature.

Soft anodic films can be produced by anodising in sulphuric acid at room temperature. Other acids are also useful such as chromic acid and phosphoric acid. A hard anodic process is preferable to a soft anodic oxide in some embodiments.

Other processes are also useful including exposure to an oxidizing agent such as an acid.

The method may comprise subsequently removing a solvent from the layer of colloidal solution. It is to be understood that the solvent is present at least in part to provide a carrier allowing the sol-gel material to be applied to the substrate in a convenient manner, such as by spraying or dipping.

The method may comprise removing the solvent to form a layer of a gel material.

The method may comprise subjecting the gel to a drying operation to remove the solvent.

The drying operation may comprise densifying the layer of gel.

The method may comprise heating the gel to form the layer of electrically insulating material. This process may be referred to as curing in some embodiments.

It is to be understood that the drying step may be performed in addition to the curing step in particular where multiple layers of sol-gel material are to be formed before curing.

The substrate may comprise one selected from amongst aluminium, an aluminium alloy, magnesium, a magnesium alloy and an aluminium magnesium alloy. Other materials may also be useful such as an alumlnlum/lithium alloy or an aluminium/beryllium alloy.

Aluminium and magnesium and alloys thereof have the advantage that they are thermally conductive materials of relatively low weight and relatively low cost compared with some other materials. They also allow the formation of a native oxide that is strongly bonded to the metal. A porous native oxide may be formed by anodic oxidation of these metals.

Other metallic substrate materials are also useful.

The layer of electrically Insulating material may comprise a polyslloxane or polysiloxane-based material.

The polyslloxane material may In some embodiments be formed using the two-part PSX700A clear engineered slloxane coating manufactured by PPG Industries.

Advantageously the gel material may comprise particles of polyslloxane or a polyslloxane-based material.

The particles may be In the form of micelles of polyslloxane or a polyslloxane-based material. Other arrangements may also be useful.

The method may comprise forming the substrate to have one or more passages therein for flow of coolant therethrough. The coolant may be arranged to be air, a liquid, a phase change material or any other suitable coolant. The passages may be arranged to allow a heat pipe device to be provided therein, or pass therethrough.

The method may comprise masking an area of the substrate prior to forming the layer of electrically insulating material thereon.

In a further aspect of the invention for which protection is sought there is provided a heat sink comprising: a substrate comprising a metallic material; and a layer of electrically insulating material over the substrate, the layer of electrically insulating material being formed from a layer of a colloidal material.

The substrate may advantageously have a surface that has been subject to an anodic oxidation process to form a layer of a native oxide thereover, the native oxide having a plurality of pores therein.

Advantageously the electrically insulating material may be arranged to penetrate the plurality of pores.

The electrically insulating material may comprise a polysiloxane.

In a still further aspect of the invention for which protection is sought there is provided an energy storage device comprising a heat sink according to the preceding aspect.

Optionally the heat sink comprises a substantially flat panel, the heat sink being provided substantially in abutment with a substantially flat electrochemical cell for storing electrical charge.

Other shapes of heat sink are also useful. It is to be understood that embodiments of the present invention are ideally suited to a range of different heat sink sizes and shapes. This is because, in the case of anodic oxidation, formation of an anodic oxide over a relatively complex shape can be accomplished relatively easily. Coating of the substrate with an insulating layer by means of a wet chemical technique also allows coating of relatively complex shapes in a relatively straightforward manner, such as by spraying or dipping. Other coating methods may be used such as roller coating, squeegee coating, doctor blading, transfer printing, electrophoretic methods or any other suitable method.

The device may comprise a piuraiity of heat sinks and a piurality of ceiis, each heat sink being provided substantially in contact with a respective electrochemical cell.

It is to be understood that some embodiments of the present invention may be useful in heatsinks for applications other than electrochemical cell applications, for example applications in the cooling of electronic devices, electric machines such as electric motors, cooling of heating, ventilation and/or air conditioning (HVAC) systems or any other suitable application in which thermally conductive, electrically insulating coatings are useful or required.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle comprising a device according to the preceding aspect.

Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

For the avoidance of doubt, it is to be understood that features desoribed with respeot to one aspect of the invention may be included within any other aspect of the invention, alone or in appropriate combination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures in which: FIGURE 1 is a schematic illustration of a heat sink plate according to an embodiment of the present invention in cross-section; FIGURE 2 is a schematic illustration of an interface between a coating and substrate of the heat sink; FIGURE 3 is a flow chart illustrating a method according to an embodiment of the invention; FIGURE 4 shows (a) an electrochemical cell according to an embodiment of the present invention for use in a battery module, and (b) a battery module according to an embodiment of the invention; and FIGURE 5 is a perspective view of a cable tray according to an embodiment of the present invention.

DETAILED DESCRIPTION FIG. 1 is a cross-sectional view of a heat sink 100 according to an embodiment of the present invention. The heat sink 100 has a substrate 110 form from a sheet of aluminium (Al) coated with an electrically insulating layer 120. The insulating layer 120 is formed from a polysiloxane material. FIG. 2 is an enlarged view of a portion of FIG. 1 showing the structure of the interface between the aluminium substrate 110 and insulating layer 120 in more detail. The aluminium substrate 110 is an anodised substrate, having been subject to an anodic oxidation process to form a porous layer of aluminium oxide (AI2O3) 115 thereover. The porous layer 115 has a plurality of pores 115P provided therein and provides an anodised surface layer 115 over the substrate 110. In the present embodiment the anodic layer is around 20 micrometres in thickness although other thicknesses may be useful, such as thicknesses in the range from 10 micrometres to 50 micrometres. The insulating layer 120 can be seen to penetrate the pores 115P of the porous surface layer 115, enabling good adhesion to be established between the insulating layer 120 and porous surface layer 115.

The method by which the heat sink 100 of the present embodiment (FIG.1 and FIG. 2) may be formed will now be described.

As noted above, the layer of porous oxide was formed by an anodic oxidation process to a thickness of around 3-200 microns. The porous oxide layer 115 was then coated with a first layer in the form of a layer of a polysiloxane sol-gel material by spraying.

Following spraying the formulation was allowed to dry in air at 20°C for 1 hour to form a gel, before being fired at 150°C in air for 1 hour to form a second layer, being a final layer.

It is believed that when the polysiloxane sol-gel material is applied to the substrate 100, polysiloxane particles migrate into the pores formed in the porous oxide layer 115. It is believed that this enables the insulating layer 120 to better adhere to the substrate 100, since it is able to ‘key’ into the pores provided over the substrate 100.

The polysiloxane material as-fired is understood to be in the form of substantially continuous layer of insulating material. FIG. 3 is a flow-chart of a process of fabricating a heat sink according to an embodiment of the present invention.

At step SI01, a substrate of aluminium in the form of a sheet in this example is prepared for anodising. Preparation may include degreasing of the substrate. Light abrasion of the surface thereof may be performed in some embodiments.

At step SI 03 the sheet is subject to an anodic oxidation process to form a layer of porous native oxide thereover.

At step SI 05 the sheet is spray-coated in a polysiloxane sol-gel solution to form a first layer of solution thereover. It is to be understood that other coating methods may also be employed in embodiments of the present invention, such as dip-coating or any other suitable technique.

At step SI 07 the sheet is dried to convert the first layer to a polysiloxane gel layer. The gel layer is subsequently fired to convert the gel layer into a second layer in the form of a layer of electrically insulating material of relatively high scratch resistance that is highly thermally conducting and suitable for use as an electrically isolated heat sink. During firing to convert the first layer to the second layer, the first layer is densified, and it is believed that chemical bonds are formed between particles of polysiloxane. Other process may occur in some arrangements in addition or instead.

In some embodiments, more than one layer of gel material may be formed before curing. Thus in some embodiments a layer of sol-gel material may be formed and dried to form a gel layer. A second layer of sol-gel material may be formed over the gel layer, and again dried to form a second gel layer over the first. This process may be repeated as required to form a gel coating of the required total thickness although the present applicant has found that a single coating is sufficient for applications in which an electrical potential across the coating is expected to be up to 500V. Single coatings may also be suitable for higher potential differences such as 1000V or more in some embodiments. The gel coating may then be fired to form a layer of electrically insulating material of relatively high scratch resistance and which is highly thermally conducting, as described above.

In some embodiments, one or more regions of a substrate may be masked with a mask materiai such as a poiymer material before the anodic oxidation process or before coating with the sol-gel material. The mask material may be removed before or after curing of the sol-gel material in order to prevent the formation of a tightly bonded, electrically insulating polysiloxane layer in the one or more regions. This may be useful where it is required to make an electrical connection to the substrate, for example an earth connection.

Example 1 A substrate in the form of a substantially square sheet of aluminium approximately 1 mm in thickness and of side 200mm was degreased and subject to an anodic oxidation process. The anodic oxidation process was carried out according to BS EN ISO 7599 - “Anodizing of aluminium and its alloys”.

This process resulted in the formation of a layer of oxide approximately 30 microns in thickness.

The substrate was then coated in a solution of a polysiloxane sol-gel material by a dipcoating process.

The substrate was allowed to stand with its major faces in a substantially vertical plane to ‘dry’ the sol-gel material and convert the sol-gel layer to a gel layer. The substrate was then fired in order to cure the gel by heating to a temperature in the range from around 150°C to around 300°C, optionally in the range from 200°Ο to around 250°C in air. The substrate may be fired for any suitable period of time, for example a period of from 10 minutes to 100 minutes or more. Other temperatures and time periods may be useful in some embodiments.

The firing process resulted in the formation of an electrically insulating layer 120 having a thickness of approximately 50 microns.

Following fabrication of the structure, electrical testing of the structure was performed to test the integrity of the insulating layer. An electrical contact was made to the heat sink substrate by removal of a portion of the insulating layer 120. A further electrode was applied to the insulating layer 120 away from the electrical contact and a potential difference established across the insulating layer 120 between the substrate 100 and the electrode. A potential of 2kV was applied and it was found that current flow through the insulating layer 120 was negligible.

In some embodiments, other metals may be employed. For example, magnesium, titanium, niobium, zirconium, hafnium and tantalum may be used. These metals allow a native oxide to be formed thereover by anodic oxidation. Other methods of forming an oxide are also useful.

In some embodiments, zinc, iron or a carbon steel may be employed as the substrate and a coating of a sol-gel material formed thereon. In the case of a ferrous metal, a ferric oxide layer may be formed by exposure to red fuming nitric acid before depositing the sol-gel layer thereover.

It is to be understood that embodiments of the present invention find application in a wide range of situations where heat exchangers with low electrical conductivity and high thermal conductivity are required. These include applications such as microelectronic device cooling, for example cooling of microchips.

Embodiments of the present invention allow the fabrication of a heat sink 100 having a higher thermal conductivity than known heat sinks whilst still providing excellent electrical insulation between the metallic substrate 110 and electrical components that may be in contact therewith. FIG. 4(a) is a schematic illustration of a cell unit 440 of a battery module 450 illustrated schematically in FIG. 4(b). The cell unit has a heat exchange plate 445 that forms a tray for receiving an electrochemical pouch cell 447. The pouch cell 447 has electrical terminals 447T, being a positive terminal and a negative terminal. The battery module has a stack of six cell units 440 sandwiched between end plates 450P of the module 450. In use, the heat exchange plates 445 conduct heat generated in the pouch cells 447 during charging or discharging of the cells 447 away from the cells 447 to top and bottom plates 450TP, 450BP of the module 450. Cooling of the end plates 450P and top and bottom plates 450TP, 450BP therefore facilitates cooling of the pouch cells 447. In the embodiment shown the end plates 450P and top and bottom plates 450TP, 450BP are formed from cast aluminium. Other materials may be useful in some embodiments, and other methods of forming the plates 450P, 450TP, 450BP. The battery module 450 of FIG. 4(b) is a motor vehicle propulsion battery module for a motor vehicle having an electrical propulsion motor. It is to be understood that battery modules 450 incorporating substrates according to embodiments of the present invention may be useful in applications other than motor vehicle technologies such as the aircraft and aerospace industries, uninterruptable power supply (UPS) installations, and so forth.

It is to be understood that the stack may, in use, be a substantially horizontal stack, in which the plates 445 lie in a substantially vertical plane, or a vertical stack, in which the plates lie in a substantially horizontal plane.

Some embodiments of the present invention are suitable for use with a range of battery technologies including lithium ion battery technologies. Cells other than pouch cells may be employed in some embodiments. FIG. 5 is a perspective view of a further embodiment of the present invention in the form of a cable tray 560. The cable tray 560 is formed from rolled aluminium sheet bent into a substantially U-shaped tray structure. The aluminium sheet has been subject to anodic oxidation, followed by coating with a polysiloxane sol-gel material and curing to form a relatively thin, hard, tenacious, scratch-resistant coating that has provides excellent electrical insulation of the underlying aluminium sheet and yet allows good heat condition though the film, due at least in part to the relatively low thickness of the film.

The tray 560 is shown supporting multi-core cabling 562 and may be used in any suitable application such as domestic, commercial or industrial buildings, automotive, aircraft or aerospace applications.

It is to be understood that the some embodiments of the present invention allow a relatively highly scratch resistant, electrically insulating coating of relatively low thermal resistance to be formed on a metallic substrate in a reliable, convenient, industrially applicable and cost effective manner. The relatively low thermal resistance of the coating may be made possible at least in part because a relatively thin, substantially continuous coating may be provided having good electrical insulation properties.

Embodiments of the invention provide a convenient method of formation of a heat sink, cable tray or other metal fabrications allowing scale-up in a mass production process.

Other advantages of embodiments of the present invention will be apparent to the skilled person.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS:

1. A method of fabricating a coating comprising: providing a substrate comprising a metaiiic material, at least a portion of a surface of the metallic material having an exposed porous metal oxide layer; and providing a layer of a first medium over at least a portion of the exposed porous metal oxide layer, whereby the exposed porous metal oxide layer is at least partially impregnated with the first medium; and curing the layer of first medium to form an electrically insulating coating layer.

2. A method according to claim 1 whereby the step of providing a substrate comprising a metallic material having an exposed porous metal oxide layer comprises forming a layer of porous metal oxide before providing the layer of first medium.

3. A method according to claim 2 whereby forming a layer of oxide comprises forming a layer of native oxide.

4. A method according to claim 2 or 3 whereby forming a layer of oxide comprises subjecting the substrate to an anodic process.

5. A method according to claim 4 whereby forming a layer of oxide comprises subjecting the substrate to an anodic oxidation process.

6. A method according to any preceding claim wherein providing a layer of a first medium comprises providing a layer of a sol-gel material over the substrate.

7. A method according to any preceding claim wherein the layer of first medium comprises a solvent, the method comprising removing at least some solvent from the layer of first medium.

8. A method according to claim 7 as dependent on claim 6 comprising removing at least some solvent to form a layer of a gel material.

9. A method according to claim 8 comprising subjecting the gel material to a drying operation to remove at least some of the solvent.

10. A method according to claim 9 wherein the drying operation comprises densifying the layer of gel by removal of at least some solvent.

11. A method according to any one of claims 8 to 10 whereby curing the layer of first medium comprises heating the gel to form the electrically insulating coating layer.

12. A method according to any preceding claim whereby the substrate comprises or consists essentially of one selected from amongst aluminium, an aluminium alloy, magnesium, a magnesium alloy, an aluminium magnesium alloy, an aluminium lithium alloy and an aluminium beryllium alloy.

13. A method according to any preceding claim whereby providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness of no more than 100 micrometres.

14. A method according to any preceding claim whereby providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness in the range from 1 micrometre to 500 micrometres.

15. A method according to any preceding claim whereby providing the layer of first medium comprises forming an electrically insulating coating layer having a thickness in the range from 1 micrometre to 100 micrometres.

16. A method according to any preceding claim whereby providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of no more than 500 micrometres.

17. A method according to any preceding claim whereby providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of in the range from 1 micrometre to 500 micrometres.

18. A method according to claim 17 whereby providing a substrate having an exposed porous metal oxide layer comprises providing an exposed porous metal oxide layer having a thickness of in the range from 1 micrometre to 100 micrometres.

19. A method according to any preceding claim whereby the electrically insulating coating layer comprises a polysiloxane.

20. A method according to claim 6 or any one of claims 7 to 19 depending therethrough wherein the gel material comprises a polysiloxane.

21. A method according to any preceding claim comprising forming the substrate to have one or more passages therein for flow of coolant therethrough.

22. A method of forming a heat sink, comprising performing the method of any preceding claim.

23. A method of forming a heat sink of an electrochemical battery, the method comprising forming a heat sink by the method of claim 22.

24. A method according to claim 23 comprising providing a plurality of electrochemical cells each in thermal contact with a heat sink.

25. A method according to claim 24 comprising providing the electrochemical cell in the form of a pouch cell.

26. A method according to any one of claims 24 or 25 comprising providing a plurality of cell modules, each module comprising a heat sink in thermal contact with a respective electrochemical cell, the method comprising providing the cell modules in the form of an array or stack of cell modules.

27. A method according to any one of claims 23 to 26 wherein the substrate comprises a metal plate having a substantially flat face in thermal contact with an electrochemical cell.

28. A method of forming an electrochemical battery comprising forming a heat sink according to the method of any one of claims 23 to 27.

29. A method of forming a cable tray, comprising performing the method of any one of claims 1 to 21.

30. A coated substrate formed by the method of any one of claims 1 to 21.

31. A heat sink formed by the method of any one of claims 1 to 21.

32. A cable tray formed by the method of any one of claims 1 to 21.

33. A coated substrate comprising: a substrate comprising a metallic material, at least a portion of a surface of the metallic material having a porous metal oxide layer over at least a portion thereof; and an electrically Insulating coating layer over at least a portion of the porous metal oxide layer, the porous metal oxide layer being at least partially impregnated with the coating layer, the electrically insulating coating layer being formed by curing a layer of a first medium.

34. A coated substrate according to claim 33 wherein the electrically insulating coating layer is formed from a layer of a sol-gel material.

35. A coated substrate according to any one of claims 33 or 34 wherein the porous metal oxide layer comprises a layer formed by an anodic oxidation process.

36. A coated substrate according to any one of claims 33 to 35 wherein the electrically insulating coating layer comprises a polysiloxane.

37. An energy storage device comprising a heat sink comprising a coated substrate according to any one of claims 33 to 36.

38. An energy storage device according to claim 37 wherein the heat sink comprises a panel, the panel being provided substantially in abutment with an electrochemical cell for storing electrical charge, the heat sink in combination with the cell forming a cell unit.

39. A device according to claim 38 comprising a plurality of cell units in the form of a stack.

40. A motor vehicle comprising a device according to any one of claims 37 to 39.

41. A cable tray or heat sink comprising a coated substrate according to any one of claims 33 to 36.

42. A method, a coated substrate, a heat sink, a cable tray or an energy storage device substantially as hereinbefore described with reference to the accompanying drawings.