WELDABLE COMPOSITE CONDUCTORS

FIELD OF THE INVENTION

[0001] The present disclosure is in the field of composite materials and, more specifically, directed to composite conductors and stacks formed for composite conductors. Some aspects relate to the field of battery technology and, more specifically, to current collectors using composite conductors or stacks of composite conductors.

BACKGROUND

[0002] Conductive materials are found in a significant portion of modern products, from consumer electronics to electric vehicles and aerospace applications. There is therefore an ongoing desire for strong and lightweight conductive materials with application dependent properties. Current collectors are a fundamental component of every battery product available on the market, from mobile phones to electric vehicles. Applications are driven by the automotive sector and increased electrical vehicle (EV) adoption among the general population, grid storage of electricity, avionics, train, marine and other transport electrification.

[0003] Commercially available current collectors are made of thin foils of copper metal that is either rolled at high pressure into shape or deposited using electrochemical methods. The main issue with traditional manufacturing techniques is the minimum thickness of copper that can be used reliably as a mechanical substrate in subsequent production steps. Currently, standard foil thicknesses between 10 pm and 120 pm are used. From an electrical conductivity point of view, even 10 pm of copper is more than what might be used to make a functional battery. Hundreds of nanometers of copper are enough for electrical conduction purposes.

[0004] Copper metal is considered an abundant and easily recyclable material. However, the production of thin copper foils is an energy intensive process that uses prolonged steps at high temperature (greater than 750 °C) and high pressure to create a substrate with the desired properties. The bill of materials of modem Li-ion packs, for example, represents the largest portion of the manufacturing cost. Rare or environmentally damaging materials such as chromium, nickel and magnesium are driving the total materials cost. Technological solutions that utilize less material, or replace expensive ones with cheaper, more environmentally friendly alternatives are of great interest to the market. Thus, a current collector that is lighter, safer, and more sustainable than the presently available current collectors, and methods of their manufacture which are scalable, are desirable. Similar considerations apply to next generation fuses and cables, which are generally made from similar materials such as copper. Thus, lighter, safer, and more sustainable materials for these technologies are also desirable.

[0005] Irrespective of the particular application of modern materials, to facilitate the adoption of such materials with desirable properties, it is desirable that such materials integrate readily with existing manufacturing processes such as welding. A particular example of such a manufacturing process is laser welding of current collectors to form electrical connections in a battery, for example a battery for use in an EV.

SUMMARY

[0006] It has been discovered that the composite conductors and stacks of the present disclosure address the above issues, and that their composite nature allows properties like strength, conductivity, weight, frequency response and more to be controlled at least to some extent independently, while integrating well with manufacturing techniques such as welding and in particular laser welding. This discovery has been exploited to develop the present disclosure, which, in part, is directed to composite conductors and their stacks, as well as a method of forming such stacks.

[0007] In some aspects, a stack of composite conductors is provided. Each composite conductor comprises a carrier polymer layer and a conductor layer disposed on one side of the carrier polymer layer. The stack comprises a welding region with a single conductor layer between adjacent polymer layers.

[0008] In some examples, each composite conductor comprises a conductor layer on only one side of the carrier polymer layer.

[0009] In some examples, each composite conductor comprising a conductor layer on only one side of the carrier polymer layer in the welding region of the stack and a conductor layer on both sides of the carrier polymer layer outside the welding region of the stack. In some examples, the stack extends in a transverse direction across the carrier polymer layers from one stack face to another and in a lateral direction along the polymer layers from one stack side to another and the welding region defines a welding tab on one of the stack sides.

[0010] In some examples, each composite conductor comprising a conductor layer on both sides of the carrier polymer layer, the stack comprising a spacer polymer layer between a pair of adjacent composite conductors. In some examples, the spacer polymer layer is provided between each pair of composite conductors in the stack. In some examples, the spacer polymer layer has a thickness of about at least about 1 pm, at least about 5 pm, at least about 10 pm, or at least about 50 pm. In some examples, the spacer polymer layer has a thickness of less than about 250 pm, less than about 100 pm, or less than about 50 pm. In some examples, the spacer polymer layer has a thickness in a range defined by any pair of these upper and lower limits. In some examples, the spacer polymer layer comprises one or more of of polyethylene terephthalate) (PET); poly(ethylene 2,6-naphthalate) (PEN); Polypropylene(PP); Polyimide (PI); polystyrene (PS); and their bi-axially oriented variants (boPET, boPEN, boPP, etc.).

[0011] In some examples, each carrier polymer layer has a thickness of at least about 1 pm, at least about 5 pm, at least about 10 pm, or at least about 50 pm. In some examples, the carrier polymer layer has a thickness of less than about 250 pm, less than about 100 pm, or less than about 50 pm. In some examples, the carrier polymer layer has a thickness in a range defined by any pair of these upper and lower limits. In some examples, the carrier polymer layer comprises one or more of PET; PEN; PP; PI; PS; and their bi-axially oriented variants (boPET, boPEN, boPP, etc.).

[0012] In some examples, each conductor layer comprises a metal, for example copper. In some examples, the conductor layer has a thickness of less than about 1pm, 0.5 pm, 0.25 pm or 0.1 pm. In some examples, the conductor layer has a thickness between these upper bounds and 1 nm or 5 nm. In some examples, the diameter of the conductive paths is at least about 10 nm, at least about 100 nm, or at least about 500 nm, and/or less than about 1 pm, less than about 10 pm, less than about 100 pm, or less than about 500 pm.

[0013] In some examples, one or more of the composite conductors, in some examples each composite conductor, comprises conductive paths extending from the conductor layer to the other side of the carrier polymer layer.

[0014] In some further aspects, a composite conductor is provided. The composite conductor comprises a carrier polymer layer and a respective conductor layer disposed on each side of the polymer layer. The composite conductor comprises a welding region comprising an exposed portion of the carrier polymer layer free of the conductor layer on one side of the carrier polymer layer and a covered portion of the carrier polymer opposite the exposed portion and covered by the conductor layer on the other side of the carrier polymer.

[0015] In some examples, the conductor layer on the one side of the carrier polymer is patterned to provide a plurality of welding regions. In some examples, the composite conductor comprises a plurality of strips of exposed carrier polymer on the one side of and along the carrier polymer to provide the plurality of welding regions. In some examples, the strips extend along some or all of the length of the carrier polymer.

[0016] In some examples, multiple conductive paths extend through the carrier polymer layer from one of the conductor layers to the other. [0017] In some examples, the stack of the some aspects and their examples is formed by composite conductors according to the some further aspects and their examples.

[0018] In yet some further aspects, there is provided a method of forming a welded stack of composite conductors. The method comprises providing a stack as described above and heating at least a portion of the welding region to weld the composite conductors of the stack together.

[0019] In some examples, the method comprises forming an electrically conductive path between any two conductor layers in the stack or between all conductor layers in the stack.

[0020] In some examples, the method comprises providing the stack on a metallic foil or tab and heating the at least a portion of the welding region to weld the composite conductors of the stack the foil or tab.

[0021] The method, in some examples, comprising heating the at least a portion of the welding region to form a weld across the stack and to one side of the stack, for example using a laser beam.

[0022] Aspects extend to the above stack welded together and/or to a conductive tab in the welding region or to the composite conductor welded to a conductive tab.

[0023] In yet further aspects, a battery is provided. In some aspects, the battery comprises the above composite conductor or stack of composite conductors, welded at the welding region to a conductive tab, for example to provide a current collector of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The foregoing and other objects of the present disclosure, the various features thereof, as well as the disclosure itself may be more fully understood from the following description, when read together with the accompanying drawings in which:

[0025] Figure 1 depicts a composite conductor;

[0026] Figure 2 depicts a stack of the composite conductors of claim 1 about to be welded;

[0027] Figure 3 depicts the stack of Figure 2 after welding;

[0028] Figure 4 depicts a stack of the composite conductors of Figure 1 with a spacer polymer layer for improved welding;

[0029] Figure 5 depicts the stack of Figure 4 after welding;

[0030] Figure 6 depicts a stack of composite conductors with an exposed polymer region on the composite conductors forming a welding region for improved welding;

[0031] Figure 7 depicts the stack of Figure 6 after welding;

[0032] Figure 8A depicts top view of a composite conductor with an alternative configuration of a welding regions suitable for roll-to-roll manufacture; [0033] Figure 8B depicts a side view of the composite conductor of Figure 8 A;

[0034] Figure 9 depicts metal deposition on one side of the composite conductor of Figure 8A;

[0035] Figure 10 depicts metal deposition on another side of the composite conductor of Figure 8A;

[0036] Figure 11 is a cross-sectional electron micrograph of a welded stack of composite conductors;

[0037] Figure 12 is an enlarged cross-sectional electron micrograph of the welded stack of Figure 11; and

[0038] Figure 13 is an another enlarged cross-sectional electron micrograph of the welded stack of Figure 11.

DESCRIPTION

[0039] The disclosures of these patents, patent applications, and publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein. The instant disclosure will govern in the instance that there is any inconsistency between the patents, patent applications, and publications and this disclosure.

[0040] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The initial definition provided for a group or term herein applies to that group or term throughout the present specification individually or as part of another group, unless otherwise indicated.

[0041] For the purposes of explaining the invention well-known features of composite materials and metal deposition technology known to those skilled in the art of applied material science have been omitted or simplified in order not to obscure the basic principles of the invention. Parts of the following description will be presented using terminology commonly employed by those skilled in the art of material science and industrial design and manufacturing techniques. It should also be noted that in the following description of the invention repeated usage of the phrase “in one example” does not necessarily refer to the same example.

[0042] As used herein, the articles “a” and “an” refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. Furthermore, use of the term “including” as well as other forms, such as “include,” “includes,” and “included,” is not limiting. [0043] As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, including ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. [0044] Reference will now be made to specific examples illustrating the disclosure. It is to be understood that the examples are provided to illustrate exemplary embodiments and that no limitation to the scope of the disclosure is intended thereby.

[0045] The present disclosure provides stacks of composite conductors and composite conductors with a welding region, and methods of producing and welding the same. It also provides equipment that can contain such composite conductors, including batteries. Such equipment containing such composite conductors is lighter, safer, and more sustainable compared to conventional presently available examples using metallic foils. The production of such conduits may utilize a roll-to-roll line, followed by the preparation of medium sized rolls, ready to be deployed into standard industrial production and testing lines for batteries and other equipment.

[0046] A cross-sectional view of a composite conductor 100 is depicted in FIG. 1 The composite conductor 100 comprises a polymer layer 101 and a conductive layer 103 made of copper. In some non-limiting examples, conductive paths (not shown) extend through the polymer layer 101 and are also made of copper. However, the conductive layer 103 and conductive paths are not limited to copper. The polymer layer 101 is made of PET but not limited to this material. The conductive paths may comprise a convex end portion extending radially on a face of the polymer layer 101 at one end of the path, mechanically and electrically connected to the conductive layers 103. The conductive paths can have different forms and shapes, e.g., but not limited to, having for example an inclination with respect to polymer layer. The conductive paths may also comprise a concave end portion at the other end of one of the conductive paths.

[0047] Conductive surface layers on each side of the polymer layer can be made of different materials,. In one nonlimiting example, for example one side can be Al and the other side can be Cu. Also, any of conductive layers or the polymer layer may consist of multiple numbers of layers of different materials. In a nonlimiting example, for example, the conductive layer can consist of 150 nm thick Cu and 10 nm of Al or other material or number of materials in different combinations. The combination of materials can be used for altering a surface property (e.g., but not limited to, like wettability, or adhesion, or other functionality). [0048] The polymer layer 101 may be about 6 pm thick, but it is not limited to this thickness. The exemplified conductive layers are each about 150 nm thick but are not limited to this thickness. The conductive channels 105 may have an average diameter of about 1000 nm but are not limited to this diameter. The diameter of the conductive paths may be at least about 10 nm, at least about 100 nm, or at least about 500 nm, and/or less than about 1 pm, less than about 10 pm, less than about 100 pm, or less than about 500 pm. The end portions may have a diameter of about 10 pm and a height of about 2 pm but are not limited to these dimensions.

[0049] While a specific composite conductor has been described, it will be appreciated that many different configurations or composite conductors having a polymer layer sandwiched between two conductive layers with composite conductors between the conductive layer and through the conduit are possible and can be manufactured using a number of techniques. One such non-limiting example technique is disclosed in US application 63/398853 from which this application claims priority and in International application PCT/EP2023/072792 claiming the same priority, both of which are incorporated by reference. For example, in one non-limiting manufacturing method. The polymer layer may be coated with the conductive layer by deposition of a metal vapor with simultaneous emission of metal droplets that form the conductive paths on impact on the polymer layer. For example, using plasma deposition, such as virtual cathode deposition, with high enough plasma energies, can be used for the simultaneous emission of metal vapor and droplets. Naturally, a plethora of micro or nano patterning techniques may be used to form the conductive paths in conjunction with various metal deposition techniques.

[0050] The composite conductors can be provided in many different form factors, for example as sheets or having an elongated form factor with a high aspect ratio. The former may be most suitable for, for example, current collectors in batteries. The latter may be most suitable for use as cabling. In either case, in many applications it is desirable to weld conductive paths together and/or to a conductive tab for connection to other components of a system, for example using lase welding.

[0051] Figure 2 illustrates a stack 200 of composite conductors 100 as described with reference to Figure 1, about to be welded by a laser beam 201, for example a visible or nearinfrared laser beam. As can be understood and seen in Figure 2, where the two composite conductors 100 meet, the stack comprises two conductive layers 103 directly adjacent each other between the two respective polymer layers 101. Figure 3 illustrates the result of the welded stack, with the conductive layers 103 fused together in a welded region 300. However, to weld through and fuse the two adjacent conductive layers 103 in between the polymer layers 101, a high level of energy needs to be deposited by the laser. The resulting connections are mechanically weak and have high resistance, such as more than IQ. At higher weld powers, the composite conductor can become extremely brittle and can even deteriorate into ash.

[0052] A stack 400 that improves the ability of the composite conductors in the stack to be welded together and/or to a conductive tab is illustrated in Figure 4. The stack 400 comprises a spacer polymer layer 401, for example a PEN and/or PET layer of similar or different thickness to that of the polymer layer 101, sandwiched between two composite conductors 100. As can be seen, there are now no directly adjacent conductive layers 103, each pair of conductive layers 103 is separated by a spacer polymer layer 401 and there are no directly adjacent conductive layers 103 in the stack 400.

[0053] The result of welding the stack 400 with the laser beam 201 is illustrated in Figure 5. Since the are no double layers of conductive layer 101 to weld through, a successful weld can be formed using lower weld energies and the conductive layers 103 fuse together across the polymer layers 101, 401 in a weld region 500. With this arrangement, it has been found that mechanically strong welds with up to 10-fold reduced resistance can be formed by laser welding, for example weld resistance of less than 1 Q. As will be appreciated from inspection of Figure 5, a similar arrangement and effect can be achieved by stacking together composite conductors as described above but which have a polymer layer 101 covered only on one side with a conductive layer 103.

[0054] In many applications, welding of the composite conductor will only be needed in a defined region of the composite conductor. A stack 600 of composite conductors defining a welding region 601 to be welded to a metal tab or foil 603 is illustrated in Figure 6. Each polymer layer 101 of the composite conductors 100 comprises an exposed region 605 free of conductive material of the conductive layers 103 on one side of the polymer layers 101, which is covered with conductive material outside the exposed region 605. The opposite side of the polymer layers 101 is covered with respective conductive layers 103, including the regions across from the exposed regions 605. Collectively, the exposed regions 605 define the welding region 601 free of directly adjacent conductive layers 103. The exposed regions 605 may be formed during deposition of the conductive layers 103 by masking the corresponding regions of the polymer layers 103 or may be formed after deposition of the conductive layers 103 by removal, for example mechanical or chemical, of the conductive layer 103 from the corresponding region. The weld formed by laser welding using a laser beam 201 is illustrated in Figure 7.

[0055] While a welding region 603 to one side of a stack of composite conductors 100 has been described with refence to Figures 6 and 7, it will be appreciated that there are many possible configurations of a welding region 603, which can be employed as suitable depending on the application. An example of an alternative welding region 603 arrangement comprising a plurality of exposed regions 603 on the polymer layer 101 is illustrated in Figures 8A and 8B. Figures 8 A and 8B depict a composite conductor 100 with polymer layer 101 that is fully covered by a conductive layer 103 on one side and has a patterned conductive layer 801, comprising strips of conductive material, on the other, opposed side. The strips of conductive material cover the polymer layer 101 only partially, leaving exposed regions 605 of the polymer layer 101 in between the strips. In this arrangement, a stack of the composite conductors will have only single layer conductive material in between adjacent polymer layers 101 forming a welding region 605 that extends in strips along a dimension, for example a length of the stack of composite conductors 100.

[0056] In some examples, the composite conductor 100 described above with reference to Figures 8 A and 8B is manufactured using a roll to roll process in which the polymer layer 101 is provide as a film on one roll and paid out to be taken up by another roll, moving the polymer layer 101 past metal deposition guns, for example plasma deposition guns 901 in a direction 903 as illustrated in Figure 9 and 10. Figure 9 illustrates depositing a conductive film 103 over the entire polymer layer 101 on one side and Figure 10 illustrates depositing a conductive film 103 in a pattern on the other side of polymer layer 101, leaving the exposed regions 603 free of conductive material. The two sides can be covered processed simultaneously in arrangements in which the metal deposition guns are provided on both sides of the polymer layer, or sequentially by depositing on one side, reversing the role and orientation of the paying out and taking up rolls, and depositing on the other side. The patterned deposition on the other side of the polymer layer, in some examples, is achieved by placing a mask 1001 in between the metal deposition guns 901 and the polymer layer 101, for example in contact with the other side of the polymer layer 101, leaving one or more exposed regions 603 along the length (along the direction of movement of the polymer layer 101, arrow 903) of the polymer layer 101 exposed and substantially free of deposited metal to form conductive strips 801 in between the exposed regions 605.

EXAMPLE

[0057] A stack of 60 single-sided composite conductors comprising a PET film with Cu deposited on one was welded and found to have good mechanical stability and a resistance between the top and middle conduit of 0.7Q. Figure 11 presents and electron micrograph of a cross-section 1101 of the stack cast in resin and cut and polished to form the cross-section. A hole 1103 from laser welding is apparent. Figures 12 and 13 present enlarged and rotated portions of the stack cross-section 1101 at higher magnification, in which the bonds between layers of the composite conductor are clearly visible.

EQUIVALENTS

[0058] Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific embodiments described specifically herein. Such equivalents are intended to be encompassed in the scope of the following claims.