Connector with graphene composite material

Abstract

An electrical connector (figure 1, 10) comprises an electrical contact 16, the electrical contact 16 comprises a metal-graphene composite 30. Additionally, a wireless power transmission system (figure

Description

Technical Field

[0001] The present disclosure relates generally to electrical connectors and conductive materials for use in electrical connectors and related systems. Related art

[0002] These days, electrical connectors are among the most important components in electrical engineering. Although they have been on the market for a long time, they are constantly being developed and improved. There are a number of problems for which solutions have been found, but which are not satisfactory for many applications.

[0003] In particular, solutions have been found for electrical contact elements that allow a high number of mating cycles but still have serious disadvantages in terms of current carrying capacity. During development, a compromise must therefore often be found between the durability / abrasion resistance of the electrical contact elements and the current-carrying capacity. Furthermore, the temperature dependence of the electrical contact elements, in particular the expansion coefficient under high current load, also plays a decisive role. Electrical contact elements are particularly subject to high loads when high currents with a high frequency are conducted through them, as the alternating current mainly flows on the surface of the electrical contact elements. This leads to warming or heating of the electrical contacts, causing them to expand. If such disadvantageous electrical connectors are used in wireless power transmission systems, in which currents in the double-digit (e.g. 80 ampere) or even triple-digit (e.g. 110 ampere) range flow across the electrical contact elements at a frequency of a few kilohertz to a few hundred kilohertz, the electrical contact elements and also the cable connected to them can heat up and exhibit additional mechanical stress. The heating of the electrical contact elements and the cables can also lead to additional losses in the contactless charging system, as the tuning of the charging system (resonant circuit) can change due to the variation in resistance. All the disadvantages mentioned are not desirable. Short summary of the invention

[0004] An aim of the present invention is the provision of an electrical connector, a wireless power transmission system and a method for making a metal-graphene composite material, each with the objective to overcome the shortcomings and limitations of the state of the art.

[0005] Another aim of the invention is the provision of an electrical connector with enhanced features. In particular, the improved electrical connector may have electrical contacts with reduced interdiffusion, resulting in a temperature coefficient of resistivity close to zero. This can lead to low friction and tribologically favorable surfaces, which can have a positive effect in particular with regard to abrasion and the long-term durability of the connector.

[0006] A further aim of the invention is the provision of a wireless power transmission system with improved temperature stability, while conducing high frequency currents in cables and / or electrical connectors of said wireless power transmission system.

[0007] A further aim of the invention is the provision of a method for making a metal graphene composite material, which can be used in a simple and cost-effective fashion in the manufacture of the electrical contacts and / or the cable to produce said composite material.

[0008] According to the invention, these aims are attained by the object of the attached claims. In a first aspect of the invention, an electrical connector is disclosed.

[0009] The electrical connector includes an electrical contact comprising a metalgraphene composite.

[0010] Compared to electrical contacts know from prior art, the metal graphenecomposite can result in a near-zero temperature coefficient of resistivity, even under high current conditions. The durability of the electrical contact when mating and unmating is improved in equal measure.

[0011] The electrical contact of the electrical connector can be substantially free from nickel due to environmental, cost, and sustainability concerns.

[0012] The diffusivity of the metal-graphene composite into a noble metal of the electrical contact can be less than a diffusivity of copper into the noble metal.

[0013] A temperature coefficient of resistance of the metal-graphene composite of the electrical contact can be less than 1%, more preferably less than 0.5%, most preferably less than or equal to 0.38% per degree Celsius.

[0014] The metal-graphene composite of the electrical contact can be a copper-graphene composite. This could be advantageous for three reasons. First, this composite could have a lower temperature coefficient of resistivity, i.e., the material will not increase its resistance as rapidly as pure copper with increasing temperature. Second, the temperature coefficient of elasticity could be improved, so the material would not soften at higher temperatures to the same extent as copper. Finally, the actual Young's modulus could be higher, making the composite a better spring material. This is important in electrical contacts because mechanical springs are often used as part of the electrical contact design to apply a contact pressure that lowers the contact resistance between the male and female contacts, for example.

[0015] The metal-graphene composite of the electrical contact can be a noble metalgraphene composite.

[0016] The metal-graphene composite of the electrical contact can define at least a portion of a contact surface of the electrical contact configured to abut a contact surface of a mating electrical connector.

[0017] The electrical contact can further comprise a metal layer disposed over a layer of the metal-graphene composite, wherein the metal layer can define at least a portion of a contact surface of the electrical contact configured to abut a contact surface of a mating electrical connector.

[0018] The electrical connector can be a first of a pair of mating electrical connectors, wherein a second electrical connector of the pair can comprise an electrical contact having a thermal expansion coefficient greater than a thermal expansion coefficient of the electrical contact of the first electrical connector. The temperature coefficient of thermal expansion is the amount by which the coefficient of thermal expansion changes with increasing temperature. It can be desirable to keep this effect as small as possible in a spring-loaded electrical contact, as this minimizes the thermally induced relaxation of the spring force, which in turn reduces the contact pressure, which in turn increases the contact resistance.

[0019] The electrical connector can be a first of a pair of mating electrical connectors, wherein a second electrical connector of the pair can comprise an electrical contact having an elastic modulus less than an elastic modulus of the electrical contact of the first electrical connector.

[0020] In a second aspect of the invention, a wireless power transmission system is disclosed. The wireless power transmission system comprising a cable for conducting alternating current, wherein the cable comprises a metal-graphene composite.

[0021] By incorporating the metal-graphene composite into the cable, this cable is foreseen to transmit high frequencies and high power without the electrical resistance changing due to ohmic heating. If such a cable is used to supply a transmitting coil of a wireless power transmission system, detuning of the matching network (resonant circuit) is prevented. In addition, heating of the cable during operation of the wireless power transmission system is prevented, thereby increasing the safety of users of the wireless power transmission system when they come into contact with the cable or its insulation. In addition, it can reduce resistive electrical losses.

[0022] The cable of the wireless power transmission system can comprise a central substrate and a layer of the metal-graphene composite disposed over the substrate.

[0023] The alternating current can be conducted between a power circuit and an induction coil of said wireless power transmission system, and can thereby be conducted by said cable.

[0024] In a third aspect of the invention, a method for making a metal-graphene composite material is disclosed. The method comprises the step of electroplating a substrate in an aqueous solution comprising a metal salt and graphene to form a metalgraphene composite plating layer.

[0025] This is advantageous because the metal-graphene composite plating layer can be produced in a simple manner and therefore economically for high production volumes. Furthermore, this is a process that has been proven and results in metal-graphene composite plating layers that have a low degree of dimensional variability. Basically electrochemistry is a proven, scalable, low-risk, cost-effective production process.

[0026] The metal-graphene composite obtained by the method can be a copper-graphene composite.

[0027] Alternatively, the metal-graphene composite obtained by the method can be a noble metal-graphene composite.

[0028] Although all of the foregoing aspects (including embodiments thereof) are independently exemplified, these aspects may be combined where useful and technically feasible for one skilled in the art. Brief Description of the Drawings

[0029] The following detailed description of preferred implementations and best mode will be set forth with regard to the accompanying drawings, in which:

[0030] FIG. 1 is a partial cross-sectional view of an illustrative pair of mating electrical connectors;

[0031] FIG. 2 is a cross-sectional view of an illustrative electrical contact including a metal-graphene composite;

[0032] FIG. 3 is a cross-sectional view of another illustrative electrical contact including a metal-graphene composite;

[0033] FIG. 4 is an elevation view and a partial cross-sectional view of an illustrative wireless power transmission system in form of a wireless charging system for an electric vehicle; and

[0034] FIG. 5 is a schematic view of an illustrative method of making a metal-graphene composite. Examples of embodiments of the present invention

[0035] FIG. 1 is a partial cross-sectional view of an illustrative pair 10 of mating electrical connectors 12, 12’ shown in a disconnected condition. Each connector 12, 12’ includes a housing 14 and at least one electrical contact 16, 16’ located in the housing 14 at a fixed position relative to the respective housing. The connectors 12, 12’ can be moved toward each other so that a portion of one housing 14 is received by the other housing to assume a connected condition, in which the connectors 12, 12’ may be removably attached to each other (e.g., via a snap feature) to form an electrical connection between aligned pairs of electrical contacts 16, 16’. When the electrical connection is formed, the electrical contacts 16, 16’ are in physical contact with each other at respective and opposing contact surfaces 18, 18’ to form a contact interface. In the connected condition, the mating connectors 12, 12’ electrically connect conductors 20 (e.g., wires) of separate devices to carry electric current or signals between the connected devices.

[0036] In the illustrated example, the connectors 12, 12’ are respective plug and socket connectors and the contacts 16, 16’ are respective pin and receptacle contacts. Each electrical contact 16, 16’ is formed from or includes a surface layer of an electrically conductive material (e.g., metal) and is at least partly embedded in an electrically insulative material (e.g., plastic, glass, or ceramic), such as an insert 22 carried by the respective housing 14 or the housing itself. In addition to the connector housings 14 being removably attached to each other in the connected condition, portions of the respective contacts 16’ at the contact interface may be biased toward each other to ensure physical contact is maintained and / or to provide a frictional force opposing their separation. For example, the receptacle contacts 16’ may have an inner diameter less than the outer diameter of the pin contacts 16 when disconnected and be configured to radially expand against a biasing force of the material of the receptacle contact 16’. The biasing force in that case helps “grip” the mating pin connector 16 by providing a frictional force opposing separation.

[0037] It is noted that the connectors 12, 12’ and electrical contacts 16, 16’ of FIG. 1 are merely examples of multitudes of styles of electrical connectors and contacts. The discussion below is related to materials for use in the electrical contacts of any type of connector or connection or, in some cases, conductors 20 interconnected by other connectors. These materials may be particularly suitable for use in connectors or conductors through which relatively large amounts of power are transferred, through which relatively high-frequency AC current is carried, and / or in applications in which the electrical connection is subject to vibration, thermal cycling, or frequent connecting and disconnecting.

[0038] FIG. 2 is an enlarged cross-sectional view of one of the electrical contacts 16 of FIG. 1, which is not necessarily to scale. The contact 16 includes a substrate 24 and a layer 26 of conductive material disposed on or over the substrate that defines at least a portion of the contact surface 18. The substrate 24 may be formed from an electrically conductive material, such as copper, a copper alloy, or any other suitable material. The layer 26 of conductive material includes graphene 28 and at least one other material. In FIG. 2, the graphene 28 is represented only schematically for purposes of discussion, and this depiction is not intended to limit the shape, size, distribution, etc. of the graphene. Graphene is an allotrope of carbon formed from a single layer of atoms arranged in a hexagonal lattice nanostructure. As used herein, “graphene” includes single-layer graphene (SLG), multilayer graphene (MLG) having more than one layer of graphene, few layer graphene (FLG) having from 2 to 10 layers of graphene, and graphene nanoplatelets. “Graphene” also encompasses functionalized graphene, such as graphene oxide containing functional groups such as hydroxyl, epoxy, carboxyl, carbonyl, or phenol groups, to name a few. Embodiments of the graphene include reduced graphene oxide (rGO).

[0039] In the example of FIG. 2, the conductive layer 26 includes multiple discrete layers, including a first or inner layer 30 disposed over the substrate 24 and a second or outer layer 32 disposed over the first layer 30, with the second layer 32 providing the contact surface 18.

[0040] The illustrated first layer 30 is a metal-graphene composite layer formed directly on the substrate and includes the graphene 28 and a metal 34. The graphene 28 and metal 34 may be co-deposited on the substrate 24 such that the graphene and metal of the composite are interspersed with one another. The graphene 28 and metal 34 of the composite layer 30 may form a solid solution, or the graphene may form discrete phases within a metal phase or within a metal-graphene solid solution. The metal 34 of the composite layer 30 may have a high electrical conductivity, for example, greater than 4 x 107 S / m, greater than 5 x 107 S / m, or greater than 6 x 107 S / m. Suitable metals for the metal-graphene composite include copper, silver, and gold. The composite material layer 30 may have a thickness in a range from 1 pm to 100 pm, in a range from 1 pm to 50 pm, or in a range from 1 pm to 10 pm.

[0041] The outer layer 32 of the conductive layer 26 is also electrically conductive and may be a metal having a high electrical conductivity as defined above. The outer layer 32 may function as a protective layer for the metal-graphene composite layer 30 and / or may provide the contact 16 with a contact resistance lower than that of the composite layer or the metal 34 of the composite layer. The outer layer 32 may be or may include a noble metal, such as gold or silver. Other noble metals include the platinum group metals ruthenium, rhodium, palladium, osmium, iridium, and platinum. Noble metals can reduce or prevent oxidation or other corrosion at the contact surface 18. The thickness of the outer layer 32 depends on the application but may be in a range from 0.25 pm to 5 pm, from 0.25 pm to 1.5 pm, from 0.50 pm to 1.5 pm, or from 1.0 pm to 1.5 pm.

[0042] The composite layer 30 may function as a barrier layer that prevents or helps slow interdiffusion of the materials of the substrate 24 and outer layer 32. Certain combinations of materials interdiffuse when arranged as adjacent layers, which detracts from the material properties the individual layers are intended to have. For instance, when an electrical contact is made from gold-plated copper (or copper alloy), the copper of the underlying layer will diffuse into the relatively thin gold plating, eventually making its way to the contact surface where it may oxidize or otherwise corrode, thus defeating the purpose of the gold plating.

[0043] The solid-state diffusivity of the metal-graphene composite of the inner layer 30 with respect to the outer layer 32 may be less than the diffusivity of the material of the substrate 24 with respect to the outer layer. In some cases, the metal 34 of the metalgraphene composite 30 is the same metal as the substrate 24, e.g., a copper-based material such as copper or a copper alloy. In this manner, the presence of the graphene 28 in the inner layer 30 can change the metal 34 (e.g., copper), which otherwise easily diffuses into a noble metal (e.g., gold) outer layer 32, into a barrier layer that reduces the amount of diffusion into the outer layer. The graphene 28 may be present in the composite layer 30 in an amount from 25 to 50 atomic percent. This range is non-limiting and is intended only to provide an example that provides superior barrier properties without detrimentally sacrificing electrical conductivity. Stated in terms of a specific example, a layer 30 of copper-graphite composite material between a copper substrate 22 and a gold outer layer 32 reduces the rate of diffusion of the underlying copper into the gold layer. Embodiments of the electrical contact 16 include a barrier layer 30 between the substrate 24 and the outer layer 32, where the barrier layer is substantially free of nickel.

[0044] FIG. 3 is an enlarged cross-sectional view of one of the electrical contacts 16 of FIG. 1, also not necessarily to scale. Here, the layer 26 of conductive material and the layer 30 of the metal-graphene composite are one and the same such that the metal -graphene composite defines at least a portion of the contact surface 18. As in the embodiment of FIG. 2, the substrate 24 may be formed from an electrically conductive material (e.g., a copper-based material), and the metal-graphene composite layer 30 is formed directly on the substrate and includes the graphene 28 and a metal 34. The graphene 28 and metal 34 may be co-deposited on the substrate 24 such that the graphene and metal of the composite are interspersed with one another. The graphene 28 and metal 34 of the composite layer 30 may form a solid solution, or the graphene may form discrete phases within a metal phase or within a metal-graphene solid solution. The metal 34 of the composite layer 30 may have a high electrical conductivity as defined above.

[0045] In the absence of the outer layer 32 of FIG. 2, the metal-graphene composite layer 30 of FIG. 3 may be configured to perform the individual functions of the multiple layers of FIG. 2. For instance, the metal 34 of the composite layer 30 may have an oxidation resistance and / or a corrosion resistance greater than that of the material of the substrate 24 to function as a protective layer. In some embodiments, the metal 34 of the composite layer 30 includes or is a noble metal as defined above. The presence of the graphene 28 in the composite layer 30 may also reduce the diffusivity rate of metal material from the substrate 24 into the composite layer 26 compared to its diffusivity rate into the metal 34 of the composite layer alone. The composite material layer 30 may have a thickness in a range from 1 pm to 100 pm, in a range from 1 pm to 50 pm, or in a range from 1 pm to 10 pm.

[0046] The composite layer 30 may function as a lubricity layer that reduces wear at the contact surface 18 when subjected to multiple or frequent connect-disconnect cycles with the contact surface 18’ of a mating connector 12’ (FIG. 1) or when subjected to vibration in the intended application. Such a lubricity layer can also reduce fretting at the contact interface, which is a phenomenon involving both wear and corrosion caused by small oscillatory motions at the interface. In fretting, a protective layer (e.g., gold plating) wears and generates loose particles at the contact interface, which can increase abrasiveness while also exposing the underlying metal (e.g., copper). The underlying metal may then form an oxide layer, which may temporarily slow further oxidation. But the continued relatively movement breaks down the oxide layer, exposing the bare substrate metal and producing more abrasive particles at the interface.

[0047] The metal-graphene composite layer 30 wears differently. First, the presence of graphene 28 provides the contact surface 18 with a lower coefficient of friction than the metal 34 of the composite material alone. This leads to reduced wear at the contact surface 18, which means less particulates at the contact interface. Even if particulates are formed, they may contain graphene and therefore be less abrasive than metal particles. Second, the materials within the composite layer may wear at different rates. For example, the metal 34 of the composite layer 30 may wear at a greater rate than the graphene, effectively forming a dry graphene film at the contact surface 18 with very high lubricity. The graphene 28 may be present in the composite layer 30 in an amount from 25 to 50 atomic percent. This range is non-limiting and is intended only to provide an example that provides superior diffusion resistance with respect to the underlying substrate and greater lubricity than an all-metal layer without detrimentally sacrificing electrical conductivity or surface resistance. In one particular embodiment, the metal-graphene composite is a graphene-silver composite layer formed on or over a copper substrate.

[0048] FIG. 4 schematically illustrates another application for the above-described metal-graphene composite material. In this example, a wireless charging system 100 for an electric or hybrid vehicle includes a cable 102 interconnecting a power circuit 104 and a wireless charging pad 106. The power circuit 102 receives power from an external power supply (not shown) and supplies power to the charging pad 106 through the cable 102. The power circuit 104 may include additional components, such as an electronic controller, switches, a human-machine interface, etc., and the charging pad 106 may include one or more induction coils configured to link-up with a wireless receiver of the vehicle and induce a charging current to charge a battery or other electric storage component of the vehicle. The cable 102 thus conducts AC power at a frequency that is dependent on the particular charging system.

[0049] The cable 102 includes one or more electrical conductors 108 in the form of a wire (e.g., copper wire), wire bundle, or wire braid. Each conductor 108 may be configured similarly to the example of FIG. 3, with a conductor substrate 24 (e.g., copper) and a conductive layer 26 comprising a metal-graphene composite layer 30 as a surface layer defining at least a portion of the outer surface 18 of the conductor 108 or defining a near-surface layer (e.g., as in FIG. 2). The metal of the graphene-metal composite layer 30 may be selected in the same manner discussed above. The cable 102 can be connected to the power circuit 104 and / or the wireless charging pad 106 using electrical connectors and / or electrical contacts as described in conjunction with FIGS. 1-3. Each of the cable and the electrical connectors can include graphene-metal composite layers, which can provide advantages according to the present disclosure.

[0050] The presence of the graphene in the metal-graphene composite layer 30 effectively reduces the temperature coefficient of resistance of the composite material relative to the metal portion of the composite alone. The metal-graphene composite may, for example, have a temperature coefficient of resistance less than 0.38% per degree Celsius. This takes advantage of the fact that graphene has a temperature coefficient of resistance that is essentially zero or, in some cases, negative over a range of useful engineering temperatures (e.g., -60°C to 60°C). The metal-graphene composite may therefore have a temperature coefficient of resistance less than that of copper or silver, even with only a small percentage of graphene, such as 1 to 5 wt%, which can reduce ohmic losses at elevated temperatures, particularly when the frequency of the AC power transmitted through the cable 102 is of a relative high frequency, such as greater than 10 kHz or in a range from 10 kHz to 100 kHz.

[0051] In such charging systems, the bulk of the electric current is transmitted through the conductor 108 at or near its outer surface 18 in what may be referred to as an electromagnetic skin depth. This electromagnetic skin depth decreases with increasing AC frequency. This means that the current-carrying cross-sectional area of the conductor 108 is effectively reduced at high frequencies such that the conductor behaves as if it has a smaller cross-section: with higher electrical resistance. This leads to heating of the conductor 108, which increases the electrical resistance of the contacts, which leads to even more ohmic losses to additional heat. The reduced temperature coefficient of resistance of the metal-graphene composite layer 30 mitigates increases m resistance due to ohmic heating. While shown here as part of a charging system 100 for a personal automotive vehicle, the system 100 may be applied to any type of wireless charging system for various other types of mobile applications that require charging between uses, such as forklifts, AGVs, mobile robots, agricultural and mining equipment, drones, etc.

[0052] The reduced temperature coefficient of resistance is also advantageous in electrical connectors such as those discussed above in conjunction with FIGS. 1-3, particularly in high temperature applications and in high power transmission applications in which the electrical contacts typically experience ohmic heating.

[0053] The metal-graphene composite material may include additional benefits, such as a reduced thermal expansion coefficient of the composite material 30 relative to the metal portion 34 of the composite alone, and an effective increase in the elastic modulus of the composite material 30 relative to the metal portion 34 of the composite alone.

[0054] In electrical connector applications, thermal expansion can affect the contact forces (i.e., biasing forces) at the contact interface formed at the opposing surfaces 18, 18’ of mated contacts 16, 16’. Such changes in contact force can change the effective contact resistance, especially in the presence of a thermal gradient. With reference to FIG. 1, for example, the electrical contact 18 of one connector 12 may a solid pin with very good conductive heat sinking through the respective conductor 20 providing the power, whereas the receptacle contact 18’ may have a smaller cross-sectional area and an accompanying lower ability to conduct heat away from the contact interface. As a result, the hotter receptacle 18’ may thermally expand more than the cooler pin 18, leading to loosening of the connection and an associated higher contact resistance. Higher contact resistance can of course lead to reduced power transmission, ohmic heating, and / or unwanted noise when the connector transmits control signals.

[0055] The lower coefficient of thermal expansion (CTE) of the metal-graphene composite can be used to engineer a pair of mating connectors to reduce the thermal gradient that normally occurs when one side of the connection has different thermal boundary conditions than the other side of the connection. For instance, the individual connectors 12, 12’ of a pair 10 of mating connectors can be designed with electrical contacts 16, 16’ having different thermal expansion coefficients. Graphene alone has a negative thermal expansion coefficient relative to metals. In the example of FIG. 1, the solid pin electrical contacts 16 of the first connector 12 may be made from a metal (e.g., copper), while the hollow receptacle contacts 16’ may be made as in FIG. 2 or 3 to include graphene in at least one layer. The effective thermal expansion coefficient of the metalgraphene may be tailored via graphene content, with higher graphene content (relative to metal content) providing a greater reduction in the CTE of the composite. For example, a metal-graphene composite layer with only 1 to 3 wt% graphene can reduce the CTE of the composite relative to the metal alone by 20% to 25%. This concept is not limited to pinreceptacle connectors or contacts and may be applied in other applications in which the heat transfer rates within a single conductor or contact or a mated pair of conductors or contacts are inherently different based on component geometry and / or available heat sink capacity of surrounding components. Graphene may be added to the metal of the component with the inherently higher thermal expansion in the application to mitigate the resulting thermal gradient.

[0056] The higher elastic modulus of the metal-graphene composite can be used to reduce material relaxation or creep over time, which is the tendency for a material under load to exhibit less strain over time. Such reduced strain may reduce the biasing force with which mated electrical contacts 16, 16’ of mated connectors 12, 12’ are pressed together. The higher elastic modulus of the metal-graphene composite can mitigate time-dependent material relaxation. In some cases, as with the thermal expansion differential discussed above, one side of an electrical connection, such as the hollow or split-wall receptacle contact 16’ of FIG. 1, is inherently less stiff than the other side, such as the solid pin 16 of FIG. 1, due to individual feature geometry. Creep mitigation may be provided by forming the solid pin contacts 16 of the first connector 12 from a metal (e.g., copper), while the hollow receptacle contacts 16’ are formed as in FIG. 2 or 3 to include graphene in at least one layer. The effective elastic modulus of the metal-graphene may be tailored via graphene content, with higher graphene content (relative to metal content) providing an increased elastic modulus. For example, a metal-graphene composite layer with only 0.5 to 10 wt% graphene can improve the elastic modulus of the composite relative to the metal alone by 25% to 75%. Similar improvements in hardness and yield strength are also abtained. This concept is not limited to pin-receptacle connectors or contacts and may be applied in other applications in which the stiffness of one feature is inherently less than that of another feature (if made from the same material) due to component geometry.

[0057] FIG. 5 schematically illustrates a portion of a method of making a metalgraphene composite material 30. The illustrated method is an electroplating process 200 in which a substrate 24 is immersed in a plating solution 202 along with a plating anode 204. The plating solution 202 includes a solvent and a metal salt or other electrolyte that results in ionic species that facilitate current transport as well as reduction / oxidation processes. FIG. 4 illustrates an example using a metal salt that dissociates in the solvent to form cations M+ and anions M- in the solution 202. The solvent may include water such that the plating solution 202 is an aqueous solution. The plating solution 202 also includes graphene or graphene oxide 28 as a solute. The substrate 24 is electrically connected to one side of a power source 206, and the plating anode 204 is electrically connected to the opposite side of the power source. The substrate 24 acts as a plating cathode, and the metal ions M+ are attracted to and deposited onto the oppositely charged surface of the substrate 24 to form a solid plating layer. In this example, the plating anode 204 is made from the metal M of the metal salt in the plating solution 202 such that the plating anode replenishes the metal cations removed from solution to form the plating layer. In other embodiments, the plating anode is a different non-sacrificial metal and the metal salt is continuously replenished in the solution.

[0058] Ionic flow in the plating solution is somewhat directional in that the difference in electrical potential between the substrate 24 and the plating anode 204 induces an ionic flow field 208 therebetween. The electrically conductive graphene 28 is thus attracted and co-deposited on the surface of the substrate 24 with the plating metal M to form the metalgraphene composite 30 as the plating layer.

[0059] In the case of an electrical contact 16, 16’ of a connector 12, 12’, as in FIG. 1, or a cable conductor 108, as in FIG. 3, the metal substrate 24 is the plating cathode such that the metal-graphene composite 30 is electroplated onto the substrate to form the respective contact 16, 16’ or conductor 108. FIG. 5 is schematic, and there may be additional components supporting and / or electrically linking the metal plating anode 204 and the substrate 24 to be plated. For instance, multiple substrates 24 in the shape of the desired electrical contact 16, 16’ may be carried by an internally conductive plating rack onto which the substrates are clipped prior to being immersed in the solution 202 and from which the metal-graphene composite plated contacts 16, 16’ substrates are removed after plating.

[0060] In a particular example, the plating anode 204 is copper metal and the metal salt of the plating solution 202 is a copper salt, such as copper sulfate, which dissociates into Cu2+ cations and SO2- anions in solution such that the metal-graphene composite 30 is a graphene-copper composite. Copper salts other than sulfates may be used as well. In another example, the plating anode 204 is silver metal and the metal salt of the plating solution 202 is a silver salt, such as silver sulfamate, silver cyanide, silver nitrate, or silver chloride, which dissociates into Ag+ cations and respective anions in solution such that the metal-graphene composite 30 is a graphene silver composite. The metal salt may be any metal salt based on the desired metal 34 in the graphene metal composite.

[0061] The graphene 28 may be placed in solution in the plating solution as an aqueous dispersion of graphene. For instance, the plating solution 202 may include graphene 28 at a concentration in a range from 1 g / L to 10 g / L. Embodiments of the process employ pure graphene, graphene oxide, or a mixture of pure graphene and graphene oxide. Graphene is consumed in the electroplating process such that the graphene content of the plating solution may require continuous replenishing.

[0062] The above-described electrical contacts 16 and other conductors 108 comprising graphene in a conductive layer 26 and / or a metal-graphene composite 30 are not limited to production by the disclosed electroplating process as, now that the benefits of metal-graphene composites are disclosed here, other techniques may be developed to realize the advantages of these materials. In one example, graphene can be disposed onto a metal substrate to form the metal-graphene composite by dip coating. Dip coating may include removing oxides from (or otherwise cleaning) an outer surface of a metal substrate 24 (e.g., copper) via acid etching, for example. Then, the cleaned substrate 24 can be immersed in a concentrated graphene solution (e.g., 10 g / L graphene). Coating of the metal substrate with the graphene and / or graphene oxide can be accentuated by temperature and / or ultrasonic agitation.

[0063] All terms used in the claims are intended to be given their broadest reasonable construction and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.

Claims

1. An electrical connector comprising an electrical contact, the electrical contact comprising a metal-graphene composite.

2. The electrical connector of claim 1, wherein the electrical contact is substantially free from nickel.

3. The electrical connector of claim 1, wherein a diffusivity of the metal-graphene composite into a noble metal is less than a diffusivity of copper into the noble metal.

4. The electrical connector of claim 1, wherein a temperature coefficient of resistance of the metal-graphene composite is less than 0.38% per degree Celsius.

5. The electrical connector of claim 1, wherein the metal-graphene composite is a copper-graphene composite.

6. The electrical connector of claim 1, wherein the metal-graphene composite is a noble metal-graphene composite.

7. The electrical connector of claim 1, wherein the metal-graphene composite defines at least a portion of a contact surface of the electrical contact configured to abut a contact surface of a mating electrical connector.

8. The electrical connector of claim 1, the electrical contact further comprising a metal layer disposed over a layer of the metal-graphene composite, wherein the metal layerdefines at least a portion of a contact surface of the electrical contact configured to abut a contact surface of a mating electrical connector.

9. The electrical connector of claim 1, wherein the electrical connector is a first of a pair of mating electrical connectors, wherein a second electrical connector of the pair comprises an electrical contact having a thermal expansion coefficient greater than a thermal expansion coefficient of the electrical contact of the first electrical connector.

10. The electrical connector of claim 1, wherein the electrical connector is a first of apair of mating electrical connectors, wherein a second electrical connector of the pair comprises an electrical contact having an elastic modulus less than an elastic modulus of the electrical contact of the first electrical connector.

11. A wireless power transmission system comprising a cable for conducting alternating current, wherein the cable comprises a metal-graphene composite.

12. The wireless power transmission system of claim 11, wherein the cable comprises a central substrate and a layer of the metal-graphene composite disposed over the substrate.

13. The wireless power transmission system of claim 11, wherein the alternating current is conducted between a power circuit and an induction coil of the wireless power transmission system.

14. A method of making a metal-graphene composite material, comprising immersing a substrate in an aqueous graphene solution to deposit a surface layer comprising graphene on the substrate.

15. The method of claim 14, further comprising electroplating the substrate in the aqueous graphene solution, wherein the graphene solution comprises a metal salt such that the deposited surface layer is a metal-graphene composite plating layer.

16. The method of claim 15, wherein the metal-graphene composite is a copper-graphene composite.

17. The method of claim 15, wherein the metal-graphene composite is a noble metalgraphene composite.

Images