System for powder coating with non-contact dispersion

Abstract

A system for powder coating is provided. The system includes an electrode connected to a first voltage source configured to apply a first potential to the electrode. The system includes a powder transfer device configured to receive powder particles thereon and transfer the powder particles towards the electrode. An outer surface of the powder transfer device is spaced from the electrode to form a gap. The first voltage source is configured to generate an alternating current (AC) electrostatic field in the gap with the electrode to indirectly remove the powder particles from the outer surface of the powder transfer device.

Description

Attorney Docket No. 137174.00109SYSTEM FOR POWDER COATING WITH NON-CONTACT DISPERSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 716,946, filed on November 6, 2024. The entire content of the foregoing provisional application is incorporated herein by reference in its entirety.BACKGROUND

[0002] A variety of batteries are available in the industry for different uses. Lithium- ion (Li-ion) batteries have generally become the predominant type of battery used in portable consumer electronics and electric vehicles. Fabrication of Li-ion batteries involves numerous steps, each of which can affect the quality of the battery itself, as well as the cost involved in manufacturing the battery. A conventional manufacturing process generally includes formation of an electrode slurry having an active material, a conductive additive, and a binder, mixed in an organic solvent, and the electrode slurry is applied to a metal foil material. Once applied to the foil material, the solvent is dried out or evaporated while the active electrode mixture remains attached to the metal foil material surface. In some instances, the solvent may be toxic and can necessitate additional steps for handling / discarding that increase the overall cost of the manufacturing process. The cost of removing the solvent from the coated material on the metal foil therefore involves an additional step that also increases the overall cost of the manufacturing process.

[0003] An alternative manufacturing technique used in the industry is electrostatic deposition (ESD), which is a solvent-free manufacturing process for electrode coating for Li-ion batteries. (See, e.g., B. Ludwig et al., Solvent-Free Manufacturing of Electrodes for Lithium-ion Batteries, Sci. Rep. 6, Article No. 23150, doi: 10.1038 / srep23150 (2016); M. Wang et al., The Influence of Polyvinylidene Fluoride (PVDF) Binder Properties on LiNio.33Coo.33Mno.33O2 (NMC) Electrodes Made by a Dry-Powder-Coating Process, J. Electrochem. Soc., Vol. 166, No. 10, A2151 (2019); H. Abe et al., Electrostatic Spray Deposition for Fabrication of Li-ion Batteries, Transactions of JWRI, Vol. 44, No. 2 (2015); and U.S. Patent No. 10,547,044). Rather than relying on a solvent mixture, the ESD process uses a dry powder of the active electrode mixture which is applied to the metal foil material. By removing the solvent from the mixture and the drying step from the manufacturing process, the overall process is simplified and becomes more economical,1MEl\58928088.vlAttorney Docket No. 137174.00109 resulting in a viable alternative for large-scale manufacturing. In particular, the solvent- free electrode coating technology is an attractive alternative to traditional manufacturing since it can significantly reduce energy consumption in the manufacturing process and thus significantly reduces the manufacturing cost of batteries.

[0004] In a conventional continuous dry powder ESD coating system, a web (e.g., a grounded electrically conductive substrate) passes continuously through a coating chamber while the dry powder mixture is fluidized and pneumatically conveyed from a hopper to an electrostatic spray gun. The electrostatic spray gun electrostatically charges the powders using tribo-charging or corona charging, and sprays the charged powders onto the web where they are deposited.

[0005] In some instances, a dry powder mixture is transferred from hopper using a roller and a brush is subsequently used to remove and scatter the powder mixture from the roller through mechanical interaction with the powder particles. Such mechanical interaction with the powder particles can result in damage to the powder particles, as well as mechanical wear of the equipment used for scattering of the powder particles. As such, the resulting electrode may not produce optimal results and the equipment for production of the electrode may necessitate additional maintenance, thereby increasing the manufacturing process.SUMMARY

[0006] Embodiments of the present disclosure provide an exemplary system for battery electrode fabrication including a powder coating process involving non-contact dispersion and charging of powder particles. The system relies on an alternating cunent electrostatics approach to fluidize the powder from a source, e.g., a hopper and a roller assembly, or the like. The system includes an electrostatic roll transfer approach to coating a dry battery electrode material, e.g., a foil web, by generating an alternating current (AC) between a roller and an electrode to both fluidize and (in some instances) charge the powder particles. In some embodiments, an electrostatic charging assembly (e.g., a corona wire, or the like) can be used to charge the powder particles in a non-contact manner. The powder particles can thereby be removed or dispersed from the roller without using a mechanical, direct contact means typically used in the industry, avoiding potential damage to the powder particles. As the powder particles are removed from the roller, the electrode may charge the powder particles and the electrostatic fields guide the charged electrodes for coating of2MEl\58928088.vlAttorney Docket No. 137174.00109 the continuously moving web. The non-contact approach to dispersion and charging ensures no damage to the powder particles, uniformity in coating, and optimal performance from the resulting electrode.

[0007] In accordance with embodiments of the present disclosure, an exemplary system for powder coating with non-contact dispersion and charging is provided. The system includes an electrode connected to a first voltage source configured to apply a first potential to the electrode. The system includes a powder transfer device configured to receive powder particles thereon and transfer the powder particles towards the electrode. An outer surface of the powder transfer device is spaced from the electrode to form a gap. The first voltage source is configured to generate an alternating current (AC) electrostatic field in the gap with the electrode to indirectly remove the powder particles from the outer surface of the powder transfer device.

[0008] In some embodiments, the powder particles can include (i) an anode powder with an active material, a binder, and a conductive material, and (ii) a cathode powder with an active material, a binder, and a conductive material. In some embodiments, the electrode can define a substantially planar or flat configuration on opposing surfaces with a lack of curvature in a surface facing the outer surface of the powder transfer device. In some embodiments, the electrode can define a concave or curved surface facing the outer surface of the powder transfer device. In such embodiments, the concave surface can define a curvature complementary to a curvature of the outer surface of the powder transfer device. In some embodiments, the electrode can include a casing at least partially surrounding the electrode. In some embodiments, the casing can block transfer of current and / or the casing can be electrically insulating. In such embodiments, the system can include a second voltage source connected to the casing and configured to apply a second potential to the casing.

[0009] The system can include a second voltage source connected to the powder transfer device and configured to apply a second potential to the powder transfer device. The first and second potentials can be offset and different. The second potential can be constant in time via direct current (DC) or variable in time via alternating current (AC). Indirectly removing the powder particles from the outer surface of the powder transfer device can include removing the powder particles without physical contact of the powder particles with a mechanical structure (e.g., an oscillating brush, or the like).3MEl\58928088.vlAttorney Docket No. 137174.00109

[0010] In some embodiments, the system can include an electrostatic charging assembly (e.g., a corona wire, or the like) configured to electrostatically charge the powder particles removed from the outer surface of the powder transfer device. In some embodiments, the system can include a web connected to a second voltage source configured to apply a second potential to the web. The first and second potentials can be different to attract the electrostatically charged powder particles to the web for coating. In some embodiments, the system can include an air flow device configured to generate an air stream through the gap to guide the powder particles towards the web. In some embodiments, the air flow device can, e.g., inject air by pushing the air stream through the gap, withdraw air by pulling the air stream through the gap, or both.

[0011] In some embodiments, the system can include a powder source configured to receive a powder particle mixture and further configured to dispense the powder particles from the powder particle mixture onto the outer surface of the powder transfer device. In some embodiments, the system can include a leveling feature disposed above the outer surface of the powder transfer device. The leveling feature can be configured to limit a size of the powder particles received on the outer surface of the powder transfer device to generate a substantially uniform height coverage of the powder particles on the outer surface of the powder transfer device. In some embodiments, the powder transfer device can include features on the outer surface configured to at least partially receive and retain the powder particles on the powder transfer device.

[0012] In accordance with embodiments of the present disclosure, an exemplary method of powder coating is provided. The method includes positioning powder particles on an outer surface of a powder transfer device. The method includes transferring the powder particles towards an electrode with the powder transfer device. The outer surface of the powder transfer device is spaced from the electrode to form a gap. The method includes applying a first potential to the electrode with a first voltage source connected to the electrode. The method includes generating an alternating current (AC) electrostatic field in the gap with the electrode to indirectly remove the powder particles from the outer surface of the powder transfer device.

[0013] Any combination and / or permutation of embodiments is envisioned. Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood,4MEl\58928088.vlAttorney Docket No. 137174.00109 however, that the drawings are designed as an illustration only and not as a definition of the limits of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] To assist those of skill in the art in making and using the system for powder coating with non-contact charging, reference is made to the accompanying figures, wherein:

[0015] FIGS. 1 A and IB are diagrammatic views of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including non-contact charging and dispersion through an electrode and an air system with a powder transfer device rotating in a counterclockwise direction (FIG. 1A) and rotating in a clockwise direction (FIG. IB).

[0016] FIG. 2 is a diagrammatic view of an exemplary system for powder coating of FIG. 1 A, including voltage sources for application of voltage to a roller, and electrode, and a web.

[0017] FIG. 3 is a chart of varying potential applied to an electrode of an exemplary system for powder coating of FIG. 2.

[0018] FIG. 4 is a chart of varying potential applied to a roller of an exemplary system for powder coating of FIG. 2.

[0019] FIG. 5 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including a push air system.

[0020] FIG. 6 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including a pull air system.

[0021] FIG. 7 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including an electrode defining an arc or concave cross-section.

[0022] FIG. 8 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including an electrode defining a cylindrical cross-section.5MEl\58928088.vlAttorney Docket No. 137174.00109

[0023] FIG. 9 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, including an electrode with a case having different potentials.

[0024] FIG. 10 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, oriented with a roller disposed above a web.

[0025] FIG. 11 is a diagrammatic view of an exemplary system for powder coating in accordance with embodiments of the present disclosure, oriented with a roller disposed below a web.DETAILED DESCRIPTION

[0026] An exemplary system for powder coating with electrostatic actuation is provided. The system focuses on deposition and coating of powdered materials onto a moving web where an electrostatic force is used. In the manufacturing of unitary battery objects from powder particles (which generally include an active component, a conductive component, a binder component, and any other additive(s)), it is desired to control the deposition of the various powder particles to achieve a desired loading (mass per area), thickness, and / or pattern of the powder particles on a web / substrate. The web / substrate can be, e.g., a metal foil (typically aluminum or copper).

[0027] Various existing approaches for substrate coating techniques have failed to fully enable the manufacturing of battery electrodes with comparable quality and speed to state-of-the-art slurry-based manufacturing techniques. Enabling such state-of-the-art performance will generally necessitate high throughput with web speeds in excess of about 100 m / min, controllable heights of deposited powder materials of between about 10 and 500 um, inclusive, and as-deposited porosities of between about 20% and 50%, inclusive, (volume basis), among other characteristics. These requirements or thresholds are not trivial to achieve, and the exemplary system discussed herein provides a novel manufacturing approach that is capable of achieving these performance thresholds.

[0028] Electrostatics-based approaches (e.g., ESD coating) are attractive for several reasons. Electrostatic forces can actuate fine particles (both conductive and insulative) in a directed manner based upon at least two of (i) the charge of the fine particles, (ii) the direction of an electric field, (iii) the shape of an electric field, and (iv) the material properties of the powder particles, among others. Generally, electrostatic forces depend6MEl\58928088.vlAttorney Docket No. 137174.00109 upon a property of the powder particles and a property of the field. By independently controlling each (the field and the particle), a strong degree of performance can be designed into and extracted from various electrostatics-based systems.

[0029] The exemplary system discussed herein relies on an electrostatic roll transfer approach to coat a dry battery electrode material (e.g., powder particles) onto a thin metal foil, also known as a web. The system operation can be referred to as “alternating current electrostatics”. The system can include a roller and an electrode with an alternating current (AC) applied to the electrode to generate an AC electrostatic field between the roller and the electrode to remove and disperse / fluidize the powder from the roller, and further charging the powder for deposition onto the moving web.

[0030] In particular, the AC electrostatic powder roller assembly coats a dry battery powder material onto a thin foil. To begin the process, the dry powder material can be staged within a powder source, e.g., a hopper, or the like. The hopper can be disposed adjacent to a rotating roller, which conveys powder from the hopper. The surface of the rotating roller can include features, e.g., a set of grooves or scores in an arranged pattern, to assist with receiving and maintaining a portion of the powder particles thereon. The hopper exit or outlet produces a thin powder layer on the roller, which can be created via a precision leveling element, e.g., a doctor blade, or the like.

[0031] Powder continues to rotate with the roller until the powder is radially brought into a deposition region where powder is removed from the roller and directed towards the web for coating. Within the deposition region, an AC electrostatic field is generated between the roller and an electrode to fluidize the powder. The AC electrostatic field removes the powder particles from the surface of the roller in a non-contact, indirect manner, thereby avoiding mechanical damage to the powder particles and / or roller (including the roller texture or surface features).

[0032] The AC electrostatic field can be created between the electrode and roller by applying a potential and AC waveform to the electrode. In some embodiments, the roller can also have a potential and waveform applied to the roller, which can match or be different from the amplitude, frequency, and / or phase of the waveform associated with the electrode. In contrast, the web can be held at a fixed potential so that powder particles are directed towards the web using electrostatic force. In some embodiments, the web’s fixed potential may be earth ground.7MEl\58928088.vlAttorney Docket No. 137174.00109

[0033] In some embodiments, in addition to the AC electrostatic field, the system can optionally include an air source and / or sink configured to create an air stream to assist in directing or guiding the powder particles towards the web for coating. The air stream can be a push system (such as an air knife), a pull system (utilizing vacuum), or both. After the powder particles have been deposited on the web surface to form a coating, the web can continuously move to convey the coated section of the web out of the AC electrostatic field to avoid further fluidization and adherence of powder particles to the web.

[0034] FIG. 1A is a diagrammatic view of an exemplary system 100 for powder coating (hereinafter “system 100”). The system 100 can be used to manufacture a coated substrate usable in, e.g., Li-ion batteries, solid state batteries, or the like. The system 100 can be incorporated into a containment enclosure (e.g., a containment chamber) for deposition of the powder coating onto a substrate or web 102, e.g., a continuously moving substrate or web 102. The web 102 includes a top surface and an opposing bottom surface, both of which can be powder coated. In some embodiments, the top and bottom surfaces of the web 102 can be simultaneously coated. In some embodiments, the top surface can be coated first while the web 102 travels along direction 104, and subsequently the bottom surface can be coated while the web 102 travels along the same direction 104 or a different direction. The powder coating includes at least a cathode material or an anode material, e.g., for rechargeable lithium batteries, or the like. In some embodiments, a binder material can be included in the powder coating mixture.

[0035] The system 100 uses an alternating current between opposing electrodes to establish a field which is sensed by powder particles to be coated on the web 102. As discussed herein, powder particles can be initially conveyed from a storage hopper onto a roller, and the roller is rotated to position the powder particles to interact with an electrode opposing the roller. The powder particles sense and interact with the AC electrostatic field, resulting in a first interaction (e.g., levitation, lift-off, or otherwise actuation) of the powder particles to a region between the opposing electrodes. Once powder particles are actuated or guided to this region, additional field, forces, and the like, can actuate, bias, or otherwise transport the powder particles with a second interaction. The second interaction can move the powder particles toward or onto a nearby web surface.

[0036] FIG. 1A shows the general orientation of the components of the system 100. The system 100 includes a powder source 106, e.g., a hopper, configured to receive the powder particle mixture 108. The system 100 includes a powder transfer device 110, e.g.,8MEl\58928088.vlAttorney Docket No. 137174.00109 a roller, or the like, disposed adjacent to and below the powder source 106. Although illustrated as rotating in a counterclockwise direction, it should be understood that the device 110 could operate similarly by rotation in a clockwise direction. For example, FIG. IB shows the system 100 having a substantially similar configuration as the system 100 of FIG. 1A, except the device 110 rotates in a clockwise direction. In such embodiment, the leveling feature 116 and the cleaning feature 132 (discussed in more detail below) can be disposed on opposite sides of the powder source 106 as compared to the configuration of FIG. 1 A. Further, due to the clockwise rotation of the device 1 10, the powder particles 114 engage or adhere to the outer surface 112 of the device 110 traveling towards the web 102 and are therefore illustrated on the opposing side of the device 110 as compared to FIG. 1 A. It should be understood that although the systems discussed herein and illustrated in the figures are shown with a device rotating in a counterclockwise direction (similar to FIG. 1 A), each of the systems can be adjusted to rotate the device in a clockwise direction (similar to FIG. IB).

[0037] The outer surface 112 of the device 110 can include various features, e.g., grooves, slits, or the like, with patterns configured to engage or receive a portion of the powder particles 114 from the mixture 108. Thus, as the device 110 rotates about its axis, powder particles 114 attach to remain on the outer surface 1 12, and are radially transferred towards a region having the AC electrostatic field. For example, the powder particles 114 can fall at least partially into the features on the outer surface 112 of the device 110, and can remain engaged in the features during rotation of the device 110. In some embodiments, the powder particles 114 can adhere, stick, or otherwise attach to or on the outer surface 112 of the device 110, and can remain in this position until the device 110 rotates and repositions the powder particles 114 at or near the electrode 118.

[0038] The surface 112 features of the device 110 can be in a variety of forms, with the ultimate goal being to control and meter the amount of powder particles 114 accepted onto the device 110 from the powder source 106. The features can include, e.g., random roughness with defined average parameters (such as an Ra or Rz value), machined grooves that may be arranged in a randomized, patterned, or a regular configuration (including circumferentially, longitudinally, wavy features, knurls, or the like), gravure-style and / or anilox-style features, including honeycomb features, square features, linear features (lines or trenches), pyramid features, or the like the like) which may be formed by engraving and / or machining processes, adhered components to form a texture or roughness (including9MEl\58928088.vlAttorney Docket No. 137174.00109 adhered particles (which may be of spherical, angular, or any other shape or form), wound wires, or the like), or combinations thereof.

[0039] The size, shape, and / or orientation of the surface features may be selected based upon a size and / or range of sizes of the powder particles 114. For example, it may be desired to size the features of a size above which powder particles 114 (or collection of particles 114) will be excluded from the features after interaction with a leveling feature 116 (discussed below). For example, if the features include a hemispherical cavity with a depth of about 100 um, and a leveling feature 116 mates with or near the surface of the device 110, the cavity and the leveling feature 114 can exclude powder particles 114 and agglomerates of particles 114 larger than the depth of the hemispherical cavity. In particular, it is generally undesired to disperse agglomerated particles 114 towards the web 102. Therefore, the leveling feature 116 can assist with breaking up particles 114 and avoiding agglomerated particles 114 from passing on the device 110 towards the electrode 1 18.

[0040] In some embodiments, it may generally be desirable to select a finer size of the surface features to limit the largest size of agglomerates permitted on the surface of the device 110. In some embodiments, it may be desirable to maintain a characteristic length scale of the features (such as a depth into the device 110 or length along the surface of the device 100) larger the average powder particle 114 size of the, but also smaller than a multiple of the average particle 1 14 size. In some embodiments, the range of the multiple can be between about, e.g., 1-3 inclusive, 2-5 inclusive, 3-10 inclusive, 5-20 inclusive, or the like.

[0041] In some embodiments, the system 100 can include a height adjustment or leveling structure / feature 116, e.g., a blade, plate, flange, comb, screed, or the like, at the output of the powder source 106. For example, the leveling feature 116 can extend from the powder source 106 over the outer surface 1 12 of the device 1 10, with a distance between the leveling feature 116 and the outer surface 112 selectively preset based on the desired amount or height of the powder particles 114 on the device 110. In some embodiments, the distance between the leveling feature 116 and the outer surface 112 can be adjustable. The leveling feature 116 sets a height of the powder particles 114 on the outer surface 112 of the device 110. As the device 110 rotates with the powder particles 114 on its outer surface 112, the leveling feature 116 can limit the amount of the powder particles 114 passing through the gap between the leveling feature 116 and the outer surface 112,10MEl\58928088.vlAttorney Docket No. 137174.00109 ensuring a substantially uniform height and / or amount of the powder particles 114 is radially carried by the device 110 away from the powder source 106.

[0042] The leveling feature 116 can be located on the output side of the powder source106 to provide the height adjustment or leveling functionality as the device 110 rotates and collects powder particles 1 14 on its surface 112. The opposing side or end of the powder source 106 can include a cleaning structure or feature 132 extending up to or near the surface 112 of the device 110. As the device 110 rotates in the counterclockwise direction and powder particles 114 are removed from the surface 112 for coating of the web 102, the device 110 continues to rotate back towards the powder source 106 to repeat the process. The feature 132 can function as a cleaning element (e.g., a brush, or the like) that cleans the surface 112 from any residual powder particles 114, such that there is no build-up in powder particles 114. This avoids mass transfer non-uniformities with time, ensuring consistent powder particle 114 metering.

[0043] In some embodiments, the feature 132 can further function as a sealing element, helping to maintain the powder particles 108 within the powder source 106 and ensuring powder particle 108 output is only permitted at the leveling feature 116 section of the powder source 106. It should be understood that if the device 110 is rotated in the opposing clockwise direction, the position of the leveling feature 116 and the cleaning feature 132 can be reversed to perform their intended functions (see, e.g., FIG. IB). The feature 132 can prevent the leakage, motion, transport, and / or egress of powder particles 108 from the powder source 106. In some embodiments, the sealing feature 132 can include a rigid material at tight clearance between a side wall of the powder source 106 and the outer surface 112 of the device 110. In some embodiments, the sealing feature 132 can include a flexible, fibrous, and / or otherwise compliant material to form a substantially closed or mated interface between a surface of the sealing feature 132 and the outer surface 112 of the device 110. In some embodiments, a compliant sealing feature 132 can include a silicone elastomer, plastic (such as Teflon, poly(vinylidene fluoride), poly(ethylene), poly(propylene), or the like), a substantially polymeric fibrous material, or any other material constructed to exhibit compliance on the outer surface 112.

[0044] The system 100 includes an electrode 118 disposed adjacent and offset from the device 110. The electrode 118 can be, e.g., metal, a conductive material, or the like. In some embodiments, the electrode 118 can include a non-conductive material insulative cover that partially covers the electrode 118. The non-conductive material insulative cover11MEl\58928088.vlAttorney Docket No. 137174.00109 can completely block contact between a conductive surface of the electrode 118 and the powder particles 114, 120. In some embodiments, rather than a cover, a non-conductive, field permeable coating can be used on the electrode 1 18 to completely block contact between the conductive surface of the electrode 118 and the powder particles 114, 120. The electrode 118 can be positioned radially offset from the powder source 106, with the device 110 transferring the powder particles 114 towards the area surrounding the electrode 118 (e.g., a gap between the device 110 and the electrode 118). Although illustrated as having a planar, rectangular cross-sectional area, in some embodiments, the electrode 118 can be, e.g., arc-shaped, oval, or the like, in cross-section. The electrode 118 creates an AC electrostatic field which fluidizes the powder particles 114, thereby removing and guiding the powder particles 114 away from the device 110 in a non-contact manner.

[0045] Simultaneously (or immediately after), the electrode 118 induces electrostatic forces in the powder particles 114, 120 (which may or may not induce a net charge), the powder particles 114 120 may be guided toward the web 102 or creating a powder particle coating 122. The electrodes 118 can be driven to the web 102 by the presence of a converging / di verging field. In some embodiments, the system 100 can include an electrostatic charging assembly 119 for actuation and charging of the powder particles. For example, the electrostatic charging assembly 119 can be in the form of a single corona wire, an array of corona wires, an array of corona points, or the like, maintained at a positive or negative potential. In some embodiments, the corona wire can be configured integral to an air source or sink, such that ions generated by the corona wire can be entrained in a gas flow generated by the source or sink.

[0046] The web 102 passes through or near a gap 160 between the device 110 and the electrode 118 such that the charged powder particles 120 (e.g., particles 120 charged by the electrode 118, the corona wire 119, or both) can be guided towards the web 102 without passing over a significant distance. In some embodiments, the gap 160 distance between the device 110 and the web 102 can be dimensioned equal or close to the gap 162 distance between the device 110 and the electrode 118. In some embodiments, the device 110, electrode 118, web 102, and any other supporting mechanisms (e.g., brackets, frames, or the like) can be set at a potential which can vary in time. The web 102 can be grounded.

[0047] In some embodiments, the system 100 can include an electrode 118 that is in the form of a non-blocked electrode, e.g., where powder particles 114 contact a conductive surface of the electrode 118 for charging. In some embodiments, the opposing electrode12MEl\58928088.vlAttorney Docket No. 137174.00109118 can be constructed as a blocked electrode 118 to prevent the passage of current from the electrode 118 to other objects (such as the powder particles 114). As the electrode 118 necessarily includes a conductive material (such as a metal), the blocked electrode 118 can be constructed using a dielectric material of defined thickness over and around a conductive material within the electrode 118. The thickness of the dielectric material can be selected based upon the electrical potential at which the electrode 118 is to operate, such that the dielectric (or breakdown) strength of the dielectric material is not exceeded. The dielectric material can be, e.g., a glass, ceramic, polymer (such as polyimide or polyamide), or any combination thereof. The thickness of the dielectric material can be between about, e.g., 10-200 um, inclusive, 100 um-1 mm, inclusive, 500 um-10 mm, inclusive, greater than 10 mm, or the like. Thus, in the blocked electrode 118 configuration, the powder particles 114 do not make direct contact with the conductive surface of the electrode 118. The process can be used to coat an electrode which is a dielectric / insulator and which cannot be assigned a potential. As a comparison, FIG. 9 discusses an electrode (which may have a coating) embedded in a casing 148 that can exhibit a case voltage.

[0048] The opposing electrode 118 can be arranged in a variety of positions and configurations. When the electrode 118 is planar / linear, the gap 162 between the electrode 118 and the device 110 is necessarily variable, e.g., the region or gap 162 will converge and / or diverge resulting in a non-uniform electric field due to the rounded nature of the device 110. In each of these instances, the electrode 118 can be a blocking electrode. The non-uniform electric field can be utilized to focus or bias an amount of powder particles 114 based upon the shape of the field formed. In some embodiments, the electrode 118 can be curved (see, e.g., FIG. 7). The curve can substantially follow the shape of the outer surface 112 of the device 110, e.g., the curve can be a circular section. The circular section can maintain a substantially uniform gap (or offset) between the surface 112 of the device 110 and the electrode 118 face. The curve can establish a converging, diverging, or any combination of converging diverging gaps between the curve and the surface 1 12 of the device 110.

[0049] In some embodiments, the system 100 can include an air source 124 configured to apply an air stream 126 for directing the powder particles 114 towards the web 102. As discussed herein, the air source 124 can provide a blowing air stream 126 onto the powder particles 114, although the system 100 can similarly include only a vacuum suction source to guide the powder particles 114, or both blowing and suction. The air stream 126 can be13MEl\58928088.vlAttorney Docket No. 137174.00109 supplied to the in-between location (e.g., gap) established by the placement of the device 110 and the electrode 118. In this way, the levitated powder particle 120 cloud can be biased in a direction of the air flow, e.g., towards the web 102. Blowing and / or suction air flows can be used either alone or in combination. The blowing and / or suction can be localized near the web 102, and can be directed with, e.g., ducting, baffles, combinations thereof, or the like. In some embodiments, the blowing and / or suction can be performed within a duct where the web 102 forms at least a portion of the duct, to more carefully confine the powder particles 120. The electrostatic forces discussed herein are configured to remove the powder particles 114 from the device 110, and the air stream 126 is configured to guide the powder particles 114, 120 through charging and towards the web 102. Thus, the air stream 126 is not used to remove the powder particles 114 from the device 110.

[0050] One or more rollers 128, 130 can be used to continuously move the web 102 adjacent to the electrode 118, such that the coating 122 can be substantially continuously formed on the web 102 and the web 102 can subsequently be moved away from the electrode 118 for further processing. The web 102 can be positioned adjacent to an inbetween location (e.g., a gap) established by the placement of the device 110 and the electrode 118. In this way, the levitated powder particle 120 cloud can be located adjacent to the web 102. The direction 104 of travel of the web 102 can be aligned or counteraligned with the direction of gravity. For example, the web 102 can move parallel to and with the direction of gravitational acceleration, or the web 102 can move parallel to and against the direction of gravitational acceleration. In some embodiments, the system 100 can be configured to permit a horizontal motion of the web 102, such that the web 102 travels in a direction orthogonal to the direction of gravitational acceleration. When oriented orthogonal to the direction of gravitational acceleration, the web 102 can be coated on the top side or the bottom side (or both).

[0051] FIG. 2 shows the system 100 of FIG. 1 A, including voltage sources which were excluded from FIG. 1A for clarity. The system 100 can include a voltage source 134 connected to the electrode 118 to apply a potential (ve) to the electrode 118. The system 100 can include a voltage source 136 connected to the device 1 10 to apply a potential (vr) to the device 110. In some embodiments, the potential applied to the device 110 can act as a direct charging means to partially charge the powder particles 114 on the surface 112 of the device 110 before dispersion towards the electrode 118. In some embodiments, rather than charging the particles 114, the potential applied to the device 110 can be used to create14MEl\58928088.vlAttorney Docket No. 137174.00109 the AC electrostatic field to guide the powder particles 114 away from the device 110. The voltage applied to the electrode 118 can be offset from the voltage applied to the device 110, such that a direct current (DC) voltage can be imposed on the AC voltage. Thus, both DC and AC could be used. In some embodiments, the DC voltage can be used to provide a net charge of a particular sign, e.g., positive or negative with respect to ground, in cases where the magnitude of the DC is larger than one half of the peak-to-peak voltage provided by the AC signal. The system 100 can include a voltage source 138 connected to the web 102 to apply a potential (vw) to the web 102. Tn some embodiments, the web 102 can be grounded instead of receiving a potential. As shown in the charts of FIGS. 3 and 4, in some embodiments, the potential applied to the device 110 and / or the electrode 118 can be varying / oscillating.

[0052] Therefore, various objects (or combinations of objects) in the system 100 can be configured with electrical potentials to actuate the powder particles 114, 120. The applied potentials initially levitate the powder particles 1 14, 120 by generating an electrostatic force to oppose adhesive forces constraining the powder particles 114 to the surface 112 of the device 110, and any other forces which would oppose the motion of the powder particles 114 in the direction of the electrode 118. The powder particles 114 can be uncharged or slightly charged at this stage. For example, the system 100 can use converging / diverging fields in the gap 162, which necessarily require that the field lines are curved. Powder particles 114 accelerate along the field lines, but are unable to follow the field lines from their finite momentum, and can be thrown out of the curved field lines, some in the direction of the grounded web 102. The converging / diverging fields are thereby used to remove the powder particles 114 from the surface 112 of the device 110.

[0053] Thus, initially the electrostatic forces (e.g., AC electric field) generated between components of the system 100 (e.g., the device 110 and the electrode 118) force removal of the powder particles 114 from the device 110 surface 112 in a non-contact manner, i.e., there is no direct physical contact between a removal mechanism, such as a brush, to remove the powder particles 114 from the device 110. Due to the attraction of the powder particles 114 to the electrostatic forces, the AC electric field guides, forces, or otherwise propels the powder particles 114 away from the device 110 and towards the electrode 118 (or the gap between the device 110 and the electrode 118). After removal of the powder particles 114 from the device 110, passage of the particles 114 near the electrode 118 can (in some embodiments) charge the powder particles 114 in a non-contact manner15MEl\58928088.vlAttorney Docket No. 137174.00109 as the particles 114 move through the gap between the electrode 118 and the device 110. In some embodiments, the electrostatic charging assembly 119 (e.g., a corona wire, or the like) can be used to charge the particles 114 with the electrode 118 providing only minimal charging or no charging and only usable for removal of the particles 114 from the device 110. The potentials applied to the electrode 118 and the web 102 can further guide the powder particles 120 towards the surface of the web 102 for coating. In some embodiments, the air stream 126 can help guide the charged powder particles 120 towards the web 102 for coating.

[0054] The system 100 therefore relies on generation of an AC electric field to disperse and move the particles 114, 120 from the device 110 without contact. As such, the system 100 avoids mechanical means of agitating particles 114 (such as fine needles, brushes, or air) from the device 110. It should be noted that the air stream 126 of the system is optionally used after the particles 114 have been removed from the surface 112 of the device 1 10 in order assist with guiding of the particles 120 towards the web 102. In particular, the air stream 126 is not used to remove the particles 114 from the surface 112 of the device 110. Conventional systems that may rely on an air stream to dislodge the particles from a roller surface, for example, can create high speed flow patterns with irregular, unpredictable, or otherwise chaotic characteristics. Such conventional flow patterns can produce undesirable distribution of the powder particles after the particles are carried by the fluid flow and deposit onto the moving web 102. Therefore, the system 100 relies on the electrostatic field to indirectly remove the particles 114 from the surface 112 of the device 110 without relying on the air stream 126. It is noted that having a non-contact means of dispersing the powder particles 114 is beneficial, because the powder particles 114 do not need to be as free flowing as those for conventional systems. Further, the system 100 does not necessitate secondary transfer particles (e.g., a brush, or the like) movable relative to the device 110 surface to remove particles 114, which simplifies the complexity and need for separation. Further still, the balancing of the electric potentials between the electrode 118, the device 110, and the web 102, along with the waveforms, is critical to fluidizing the powder particles 114, 120.

[0055] The electrode 118 can be set at a potential which varies in time. The potential can be characterized by a bias (or offset) voltage, a frequency, a waveform shape, and a peak-to-peak amplitude (the magnitude of the largest to the smallest voltage). The potential can be periodic (e.g., sinusoidal, pulsed, sawtooth, or the like) and can further be biased16MEl\58928088.vlAttorney Docket No. 137174.00109 with respect to a reference potential, such as a ground potential. The web 102 can generally be held at a ground potential, although in some embodiments, the web 102 can feasibly be held at a potential different than ground.

[0056] The device 110 can be held at a potential different than the electrode 118 and the web 102. In some embodiments, it may be desired for the web 102 to be maintained at a ground potential, and for both the device 110 and the electrode 118 to be maintained at a characteristic voltage (such as may be determined by computing a root mean squared voltage) larger than the web 102 voltage. In some embodiments, it may be desirable to maintain the electrode 118 at a higher potential than the device 110 at all times, even if the electrode 118 and device 110 both exhibit a time-varying and / or spatially -varying potential. The different potentials applied to components of the system 100 can therefore be used to initially remove the powder particles 114 from the device 110 in a non-contact manner, charges the powder particles 120 with the electrode 118, and subsequently attracts / guides the charged powder particles 120 towards the web 102 for coating.

[0057] In some embodiments, the system 100 can include a feedback control loop formed by a controller 152 in communication with each of the voltage sources 134, 136, 138 (see, e.g., FIG. 1A). For example, the controller 152 can receive feedback from a sensor 154 disposed over the web 102 and detecting a quality metric of the powder particle 120 coating on the web 102. The quality metric may be based upon at least one of: a thickness of the coated material, a continuity in thickness of the coated material, a mass loading of the coated material (such as an areal mass density, for example), a reflectivity of the coated material, a thermal response of the coated material (such as a reflected amount of power in response to an input power), a roughness, or characteristic of a roughness, of the coated material, or any other sensed characteristic. Determination, or measurement, of a quality metric may produce a sensed (or measured) value corresponding to the measured characteristic. These sensed values may be compared to at least one threshold value for the corresponding quality metrics. A comparison may produce a determination where (1) a measured value exceeds a set minimum value (or lower limit), (2) a measured value is less than a set maximum value (or upper limit), (3) a measured value is within a predetermined percentage of a set reference value, a combination of the above, or any other comparison of a measured value as compared to a reference value or set of values. The comparison may also result in different control behaviors based upon a degree of a deviation between a measured value and a reference value. According to some embodiments, a control system17MEl\58928088.vlAttorney Docket No. 137174.00109 may modify an aspect of the system in response to the comparison or determination. According to some embodiments, a determination may produce a continuously changing quantity (such as a deviation between a desired value and a measured value), and a control system may operate to modify an aspect of the system in response to the determination.

[0058] In some embodiments, the sensor 154 can be, e.g., vision based, laser based, mass based (x-ray, beta particle, or the like), radiofrequency, terahertz, or the like. In some embodiments, the sensor 154 can produce an integrated output to determine a total mass of material deposited on the web 102, and / or to reveal a mass distribution across and along the web 102. For example, and according to some embodiments, if the coating on the web 102 results in a determination that a measured value violates a set range or ranges, an aspect of the system may be modified. For example, and according to some embodiments, the controller 152 can adjust the potentials applied to the respective voltage sources 134, 136,138 to improve the coating quality and rectify the difference between a sensed and desired value or values. As a further example, and according to some embodiments, the controller 152 may be used to (1) adjust aspects of powder transport and metering, including a height (or spacing) between the leveling device 116 and the surface 112 such that an amount of powder particles 114 may be increased (if the spacing between the leveling device 1 16 and the surface 112 is made large) or decreased (if the spacing between the leveling device 116 and the surface 112 is decreased), (2) adjust a rate of rotation of the surface 112, (3) adjust the speed of the web 102, or any other modification to affect a characteristic of the deposited powder.. The controller 152 can similarly be in communication with a sensor disposed at or near the device 110 surface 112, which indicates whether a sufficient percentage of particles 114 have been removed from the surface 112 by the generated AC electric field. If not, the controller 152 can regulate the varying potentials to ensure the AC electric field sufficiently removes the particles 114 from the device 110.

[0059] Different configurations of the system 100 are envisioned. For example, FIG. 5 illustrates the system 100 including an air source 124 configured to apply a push of the air stream 126. In some embodiments, the air source 124 position can be adjustable (e.g., translatable and / or rotatable) to allow for the direction of the air stream 126 to be controlled and precisely directed towards the gap between the device 110 and the electrode 118. Thus, after the powder particles 114 can been removed from the surface 112 of the device 110, the air stream 126 can assist in guiding the powder particles 1 14 past the electrode 118 for18MEl\58928088.vlAttorney Docket No. 137174.00109 charging and towards the web 102 for coating. FIG. 6 is substantially similar to the system 100 of FIG. 5, except the air source 140 is provided as a pull style system (e.g., a vacuum or suction system). Rather than pushing air through the gap, the air source 140 is configured to create a suction air stream 142 that pulls the air through the gap and towards the web 102. In some embodiments, the system 100 can include both push and pull style air systems.

[0060] FIGS. 7 and 8 show the system 100 with different types of electrodes 144, 146. In particular, the electrode used with the system 100 can be any shape and / or configuration. As an example, the electrode 144 defines an arc or concave cross-section, and the electrode 146 defines an oval or cylindrical cross-section. However, other cross-sections are also envisioned and can be used with the system. The shape of the electrode 144 can be substantially complementary to the surface 112 of the device 110, thereby providing a more uniform gap between the device 110 and the electrode 144. However, for the arc-shaped electrode 144 can generate a non-uniform electric field at the endpoints, as compared to the planar or oval electrodes. The air source 124 can be pivoted such that the air stream 126 can be directed towards the gap between the device 110 and the electrode 144. A similar positioning of the air source 124 can be performed for the electrode 146.

[0061] In some embodiments, as shown in FIG. 9, the electrode 118 can include a casing 148 that substantially surrounds the electrode 118. In some embodiments, the casing 148 can entirely surround the electrode 1 18. In some embodiments, the casing 148 can partially surround the electrode 118 while maintaining some portions of the electrode 118 exposed, e.g., the surface facing the device 110 exposed. For a cuboidal electrode 118, the casing 148 can surround five sides of the electrode 118. In some embodiments, the casing 148 can surround a substantially cylindrical electrode 118 permitting a section of the electrode 118 to protrude. In some embodiments, the casing 148 can be separated from the electrode 118 by a dielectric layer, blocking passage of the electrical current. In such embodiments, the electrode 118 and the casing 148 can receive the same or differing potentials via respective voltage sources (e.g., voltage source 134 for the electrode 118 and voltage source 150 (vc) for the casing 148. The varying potential between the electrode 118 and the casing 148 can thereby be selectively regulated depending on the desired electric field generation.

[0062] In some embodiments, the casing 148 may be different than a dielectric / insulative covering over the electrode 118, such that an electrode 118 may be19MEl\58928088.vlAttorney Docket No. 137174.00109 embedded in the casing 148 and the electrode 118 may have a dielectric / insulative covering (which would make electrode 118 a blocking electrode, the block referring to the passage of current). In some embodiments, the casing 148 can include a blocked electrode and the potential of the casing 148 and the electrode 118 may be held differently without passage of current between them (the electrode 118 and the casing 148 can be separated by an insulator / dielectric) .

[0063] The orientation of one or more portions of the system 100 can also be varied. For example, FIG. 10 shows the electrode 118 disposed relatively below the device 110, with the air source 124 disposed to the left of the electrode 118 and guiding powder particles towards the web 102 disposed on the right side of the device 110. In contrast, FIG. 11 shows the electrode 118 disposed to the right of the device 110, the air source 124 disposed relatively below the electrode 118 and the device 110, and the web 102 passing above the electrode 118 and the device 110. Thus, it should be understood that the system 100 can operate in a variety of configurations.

[0064] While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein, without departing from the spirit and scope of the invention.20MEl\58928088.vl

Claims

Attorney Docket No. 137174.00109CLAIMS:

1. A system for powder coating, the system comprising: an electrode connected to a first voltage source configured to apply a first potential to the electrode: and a powder transfer device configured to receive powder particles thereon and transfer the powder particles towards the electrode, wherein an outer surface of the powder transfer device is spaced from the electrode to form a gap; wherein the first voltage source is configured to generate an alternating current (AC) electrostatic field in the gap with the electrode to indirectly remove the powder particles from the outer surface of the powder transfer device.

2. The system of claim 1, wherein the powder particles include (i) an anode powder with an active material, a binder, and a conductive material, and (ii) a cathode powder with an active material, a binder, and a conductive material.

3. The system of claim 1, wherein the electrode defines a planar or flat configuration on opposing surfaces with a lack of curvature in a surface facing the outer surface of the powder transfer device.

4. The system of claim 1, wherein the electrode defines a concave surface facing the outer surface of the powder transfer device.

5. The system of claim 4, wherein the concave surface defines a curvature complementary to a curvature of the outer surface of the powder transfer device.

6. The system of claim 1, wherein the electrode includes a casing at least partially surrounding the electrode, and wherein at least one of (i) the casing blocks transfer of current or (ii) the casing is electrically insulating.

7. The system of claim 6, comprising a second voltage source connected to the casing and configured to apply a second potential to the casing.

8. The system of claim 1, comprising a second voltage source connected to the powder transfer device and configured to apply a second potential to the powder transfer device.

9. The system of claim 8, wherein the first and second potentials are offset and21MEl\58928088.vlAttorney Docket No. 137174.00109 different, and wherein the second potential is constant in time via direct current (DC) or variable in time via alternating current (AC).

10. The system of claim 1, wherein indirectly removing the powder particles from the outer surface of the powder transfer device includes removing the powder particles without physical contact of the powder particles with a mechanical structure.

11. The system of claim 1, comprising an electrostatic charging assembly configured to electrostatically charge the powder particles removed from the outer surface of the powder transfer device.

12. The system of claim 11, comprising a web connected to a second voltage source configured to apply a second potential to the web.

13. The system of claim 12, wherein the first and second potentials are different to attract the electrostatically charged powder particles to the web for coating.

14. The system of claim 12, comprising an air flow device configured to generate an air stream through the gap to guide the powder particles towards the web.

15. The system of claim 14, wherein the air flow device injects air by pushing the air stream through the gap, withdraws air by pulling the air stream through the gap, or both.

16. The system of claim 1, comprising a powder source configured to receive a powder particle mixture and further configured to dispense the powder particles from the powder particle mixture onto the outer surface of the powder transfer device.

17. The system of claim 16, comprising a leveling feature disposed above the outer surface of the powder transfer device.

18. The system of claim 17, wherein the leveling feature is configured to limit a size of the powder particles received on the outer surface of the powder transfer device to generate a substantially uniform height coverage of the powder particles on the outer surface of the powder transfer device.22MEl\58928088.vlAttorney Docket No. 137174.0010919. The system of claim 1 , wherein the powder transfer device includes features on the outer surface configured to at least partially receive and retain the powder particles on the powder transfer device.

20. A method of powder coating, comprising: positioning powder particles on an outer surface of a powder transfer device; transferring the powder particles towards an electrode with the powder transfer device, wherein the outer surface of the powder transfer device is spaced from the electrode to form a gap; applying a first potential to the electrode with a first voltage source connected to the electrode; and generating an alternating current (AC) electrostatic field in the gap with the electrode to indirectly remove the powder particles from the outer surface of the powder transfer device.23MEl\58928088.vl

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