Method and system for dry battery electrode fabrication

Abstract

An electrode fabrication system is provided. The system includes a powder feeding unit, a powder charging unit, a carrier roller, a carrier roller charging unit and a calendering unit. The dry powder particles applied from the powder feeding unit are charged and attached onto the carrier roller surface through an electrostatic process by applying a proper bias voltage. The charged powder attached on the surface of carrier roller are released and deposited onto a moving foil web to form a powder coating layer through an electrostatic process by applying a proper bias voltage. The powder coating layer is conveyed to the calendering unit and densified with or without heat to form an electrode.

Description

METHOD AND SYSTEM FOR DRY BATTERY ELECTRODE FABRICATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of a co-pending, commonly assigned U.S. Provisional Patent Application No. 63 / 614,771, which was filed on December 26, 2023. The entire content of the foregoing provisional application is incorporated herein by reference.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 spray 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 Poly vinylidene 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 asolvent 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 economic, 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 reduce the manufacturing cost of batteries.

[0004] In a conventional 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 dispensed from a hopper. An air supply system provides a high velocity air stream into the coating chamber to fluidize the dispensed powder and carry the fluidized powder particles to the electric field for electrostatically charging and to deposit on the web for distribution and coating. However, the use of high velocity air leads to an inherent kinetic energy of the power particles in the air stream as being a dominant force during deposition, which diminishes the ESD capability to produce a highly uniform coating of the powder particles on the web. This lack of uniform coating is typically because the entire mass of powder particles must be diluted and carried in the air stream, which requires a high velocity to obtain a reasonable mass flow rate for production needs. As such, conventional ESD coating systems are unable to offer a high degree of controlled uniformity of the powder particles on the web at high mass flow rates.SUMMARY

[0005] Embodiments of the present disclosure provide an electrostatic coating system capable of being used for coating a moving substrate or foil web with dry powder. The exemplary system achieved high uniformity in the powder particle coating of the web, even under high mass flow rates. The electrostatic coating system includes a powder feeding unit, powder charging unit, a carrier roller, and a carrier roller charging unit.

[0006] The powder feeding unit provides powder to the system. The powder feeding unit can include, e.g., rollers, fluidized beds, belts, spray guns, electrostatic feeders, combinations thereof, or the like. For example, the powder feeding unit can include a reservoir that receives a mixture of the powder particles for dispersion onto the web. In some embodiments, the powder feeding unit can include one or more powder dispersion systems, e.g., nozzles, rollers, dispensing tubes, mechanical feeders, electrostatic powderfeeders, dispersion based on gravimetric or volumetric meter basis, vibratory and / or acoustic dispersion systems, or the like.

[0007] The powder charging unit applies charges through, e.g., tribo-charging, corona charging, or other ways of charging, to charge the powder particles. For example, the powder charging unit can include any one or combination of the following charging mechanisms, e.g., corona discharge (positive or negative), tribo-charging, direct conduction charging, induction charging, dielectric barrier discharges, other non-thermal plasmas, or the like. In some embodiments, the powder deposition and / or charging unit can include one or more features of those disclosed in International Patent Publication No. WO24 / 006235, filed on June 27, 2023; International Patent Publication No. WO24 / 123857, filed on December 6, 2023; and International Patent Publication No. WO24 / 182808, filed on March 4, 2024, each of which is incorporated herein by reference.

[0008] The carrier roller is made of, e.g., conductive material, photoconductive material, magnetic material, or the like. The carrier roller can be charged by the carrier roller charging unit to attract the charged powder to the surface of the carrier roller. In some embodiments, the carrier roller can attract magnetic carrier particles to its surface. The charged powder particles are attached to the carrier roller via applying proper bias voltage (e.g., voltage for contact charging), the voltage difference between the charged particles and the surface of carrier roller, and transported to near the moving foil web, which is transported by a foil transportation unit. The powders are transferred from the surface of the carrier roller to the moving foil by applying the proper bias voltage. In some embodiments, the proper bias voltage can be in the range of about, e.g., 0-1000 V, inclusive. The foil is either grounded or charged to attract the charged powder by adjusting the bias voltage, e.g., with a controller communicatively connected to the foil. The foil is typically a metal foil, such as Al foil or Cu foil.

[0009] The powder includes composite powder particles as disclosed in, e.g., U.S. Non-Provisional Patent Application Serial No. 17 / 713,722, entitled Electrode for Energy Storage Device, which is incorporated herein by reference. The powder can refer to a mixture of (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 certain embodiments, these mixtures may be homogeneous mixtures. A number of smaller dielectric charging particles attach on a larger active material particle surface to form acomposite powder particle. The dielectric charging particles with a resistivity of 1011ohm cm or higher attach on the active material particles, which increases the relaxation time for charge dissipation. This enables the charged particles to be effectively attached onto the carrier roller. In some embodiments, the dielectric charging particles can be polymeric materials, such as PVDF. In some embodiments, the dielectric charging particles can be inorganic materials, such as AI2O3. In some embodiments, the dielectric charging particles can be a combination of polymeric and inorganic materials. In some embodiments, the active material particles can be battery cathode materials, such as LiCoCh, LiNixCoyMnzO2, LiFePCh, or battery anode materials, such as graphite, Si composite anode materials. Although the magnetic carrier particles may be included in the powder, it is preferred not to have the magnetic carrier particles due to the concern of contamination of the electrode, which may have a negative effect on the electrode performance.

[0010] In one embodiment, the exemplary system or apparatus includes one or more dry powder feeding units, one or more dry powder charging units, one or more carrier rollers, one or more calendering rollers, and one or more foil transportation units. Powder feeding unit feeds powders into a powder hopper. The powders in the hopper are charged by powder charging units. The powder charging unit apply charges through, e.g., tribocharging, corona charging or other ways of charging. Tribo-charging can be realized with or without carrier particles. The charged powders are attached to carrier rollers via an electrostatic process and transported to near the foil. The surface of the carrier is conductive, and can be positively or negatively charged by the carrier roller charging unit. The foil can be grounded or charged with opposite charge of the charged particles. The powders are transferred from the surface of carrier roller to the foil by applying proper bias voltage to form a powder coating layer. The charging unit and carrier roller are operated in a way to allow precise metering and uniform transfer of powders. The powder coating layer is conveyed to a calendering unit via a foil conveying unit where the powder coating layer is densified with pressure with or without heat to form an electrode. The above coating process can occur on one side of the foil in horizontal direction. The foil can be also fed vertically or with an angle relative to the vertical direction. The coating can be at either one side or both side of the foil to form single side or dual side coated electrodes. The coating on the two sides of the foil can occur simultaneously or sequentially.

[0011] In another embodiment, the charged powder particles are first attracted ontothe surface of a supplemental carrier roller via an electrostatic process. The charged particles attached on the supplemental carrier roller surface are transferred to the surface of the carrier roller via an electrostatic process involving applying a proper bias voltage. The powders are transferred from the carrier roller to the foil by applying proper bias voltage to form a powder coating layer. The powder coating layer is conveyed to a calendering unit where the powder coating layer is densified with pressure with or without heat to form an electrode.

[0012] In another embodiment, the carrier roller can be a photoconductive drum. In the embodiment, the powder includes composite powder particles. No carrier particles for certain electronic and magnetic properties are needed. Light is used to trigger conductivity, similar to photography.

[0013] The electrophotography process performed by the exemplary system / apparatus can include a series of process steps oriented radially around a photoconductive drum. The first step is to charge the surface of the photoconductive drum uniformly. Typically, corona generators including corotron / scorotron / shields or charging rollers are utilized. Afterwards, an image is imprinted onto the uniformly charged photoconductor surface using laser or other optical means. Next the charged composite powder particles are precisely transferred onto the oppositely charged sections of the photoconductive drum using powder feeding mechanisms, such as rollers, fluidized beds, belts, spray guns, electrostatic feeders, or others. The composite powder particles are charged using, e.g., corona discharges, tribo-charging, direct conduction charging, or AC induction charging. The charged particles are then transferred from the surface of the photoconductive drum to the foil with a proper bias voltage. The foil is grounded. However, in some cases, the foil can be charged with the opposite charge of the charged particles to adjust the bias voltage. The bias voltage is intended to guide the particles to the intended surface or component of the system, and adjustability of the bias voltage (in real-time or substantially real-time) can assist with ensuring optimal guidance of the particles in the intended direction. In some embodiments, a feedback control loop can be used, including one or more sensors detecting the particle movement in the system and a controller associated with the voltage source(s), with the controller operating / adjusting the voltage source(s) in real time based on sensor readings to ensure optimal bias voltage is generated to improve particle movement in the system. Any powder that did not transfer can bereclaimed and reused. The photoconductive drum is cleaned off before the process repeats. Lastly, the powder coating layer is conveyed to a calendering unit where the powder coating layer is densified with pressure and heat if needed and forms an electrode.

[0014] In an embodiment, the powder coating units are arranged in series to allow for thicker or higher speed coating.|0015 | In accordance with embodiments of the present disclosure, an exemplary electrode fabrication system is provided. The system includes a powder feeding unit configured to receive and dispense dry powder particles. The system includes a powder charging unit configured to apply a first charge to the dry powder particles dispensed from the powder feeding unit. The system includes a carrier roller assembly (e.g., a first carrier roller, a supplemental carrier roller, or both), and a carrier roller charging unit configured to apply a second charge to the carrier roller assembly. The dry powder particles with the first charge are guided toward and attached to a surface of the carrier roller assembly through a first electrostatic process based on a first bias voltage between the first charge of the dry powder particles and the second charge of the carrier roller assembly. The system includes a foil moving in a foil direction, and a foil charging unit configured to apply a third charge to the foil. The dry powder particles attached to the surface of the carrier roller assembly are released and deposited onto the foil to form a powder coating layer through a second electrostatic process based on a second bias voltage between the first charge of the dry powder particles and the third charge of the foil.

[0016] The system can include a calendering unit. The foil with the powder coating layer is configured to be conveyed through the calendering unit for densification with or without heat to form an electrode. Each of the dry powder particles can include high resistivity dielectric particles on a surface of an active material particle. A size of each of the high resistivity dielectric particles is dimensioned smaller than a size of the active material particle. The active material particle can be a cathode active material particle and / or an anode active material particle. The high resistivity dielectric particles can be a polymeric material particle, an inorganic material particle, or a combination thereof.

[0017] The carrier roller assembly can include a first carrier roller. In some embodiments, an entire area of the surface of the first carrier roller capable of receiving the dry powder particles with the first charge is conductive. The surface of the first carrier roller can be positively or negatively charged with the carrier roller charging unit. In someembodiments, the surface of first carrier roller can define an area capable of receiving the dry powder particles with the first charge, and a portion of the area is conductive and a portion of the area is nonconductive. In some embodiments, the first carrier roller can be a photoconductive drum. In some embodiments, the system can include means for forming uncharged regions on the surface of the first carrier roller.

[0018] The at least one of the powder charging unit or the carrier roller charging unit can provide the respective first or second charge through at least one of corona charging or tribo-charging. In some embodiments, the carrier roller assembly can include a first carrier roller and a supplemental carrier roller disposed adjacent to the first carrier roller. In such embodiments, the system can include a supplemental carrier roller charging unit configured to apply a fourth charge to the supplemental carrier roller. The dry powder particles with the first charge are released from a surface of the first carrier roller and guided towards a surface of the supplemental carrier roller through a third electrostatic process based on a third bias voltage between the first charge of the dry powder particles and the fourth charge of the supplemental carrier roller.

[0019] In some embodiments, the foil can include a Al foil or a Cu foil. In some embodiments, the calendering unit can include at least one pair of calendering rollers. In some embodiments, the at least one of the first or second bias voltage can be in a range of about 100-1000V, inclusive.

[0020] In accordance with embodiments of the present disclosure, an exemplary method of electrode fabrication is provided. The method includes receiving and dispensing dry powder particles with a powder feeding unit. The method includes applying a first charge to the dry powder particles dispensed from the powder feeding unit with a powder charging unit. The method includes applying a second charge to a carrier roller assembly with a carrier roller charging unit. The method includes guiding and attaching the dry powder particles with the first charge to a surface of the carrier roller assembly through a first electrostatic process based on a first bias voltage between the first charge of the dry powder particles and the second charge of the carrier roller assembly. The method includes applying a third charge to a foil moving in a foil direction. The method includes releasing the dry powder particles from the surface of the carrier roller assembly and depositing the released dry powder particles onto the foil to form a powder coating layer through a secondelectrostatic process based on a second bias voltage between the first charge of the dry powder particles and the third charge of the foil.

[0021] In some embodiments, the carrier roller assembly can include a first carrier roller and a supplemental carrier roller disposed adjacent to the first carrier roller. In such embodiments, the method includes applying a fourth charge to the supplemental carrier roller with a supplemental carrier roller charging unit. The method includes releasing the dry powder particles with the first charge from the surface of the first carrier roller and guiding the dry powder particles towards a surface of the supplemental carrier roller through a third electrostatic process based on a third bias voltage between the first charge of the dry powder particles and the fourth charge of the supplemental carrier roller.

[0022] 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, 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

[0023] To assist those of skill in the art in making and using the dry battery electrode fabrication system, reference is made to the accompanying figures, wherein:

[0024] FIG. 1 is a diagrammatic view of an exemplary dry battery electrode fabrication system including a carrier roller;

[0025] FIG. 2 is a diagrammatic view of an exemplary dry battery electrode fabrication system including a carrier roller and a supplemental carrier roller;

[0026] FIG. 3 is a diagrammatic view of an exemplary composite powder particle;

[0027] FIG. 4 is a diagrammatic view of an exemplary dry battery electrode fabrication system with an electrophotographic process;

[0028] FIG. 5 is a diagrammatic view of an exemplary dry battery electrode fabrication system in a vertical orientation for dual side simultaneous coating.

[0029] FIG. 6 is a diagrammatic view of an exemplary dry battery electrode fabrication system with coating setup in series.DETAILED DESCRIPTION

[0030] The exemplary electrostatic coating system 100 of FIG. 1 includes a powder feeding unit 102 to load with powder 101 (e.g., a powder particle mixture), a carrier roller 103, a carrier roller charging unit 110, and a charge unit 104. The system 100 can include a cleaning unit 105, a calendering unit 106, foil 107 (e.g. a web), and an idle roller 108. The powder 101 can include composite particles, such as the composite powder particle 300 of FIG. 3. The composite powder particle 300 of FIG. 3 is formed by attaching smaller high resistivity dielectric particles 302 onto the active material particle surface 301. For example, the active material particle surface 301 can be substantially circular or spherical, and the dielectric particles 302 can radially coat or attach to the surface 301. The attached high resistivity dielectric particles 302 enable the composite powder particle 300 to have a sufficient long relaxation time for charge depletion to allow the coating process to be successfully performed. In particular, the sufficiently long relaxation time ensures that the particles 300 are charged enough to be attracted to the foil 107 for coating formatting. In some embodiments, one or more portions of the system 100 can include walls, boundaries, or the like, which do not permit the passage of a charge from a charged particle 302 or assemblage of particles 302. In such embodiments, the electrical resistance of the particles 302 may not matter. In some embodiments, the relaxation time can be, e.g., more than 3 seconds. In some embodiments, the relaxation time can be dependent on the conductivity of the particles 302 and can be, e.g., as low as 10"12seconds, more than 3 seconds, more than 10 seconds, 1 minute or more, or the like. In some embodiments, the composite powder particle 300 can include some small conductive particles, such as conductive carbon, Si, or the like.

[0031] The composite powder particles are applied from the powder feeding unit 102 and charged by the charging unit 104 as the particles are dispensed from the feeding unit 102. The powder charging unit 104 applies charges to the powder particles through, e.g., corona discharges, tribo-charging, direct conduction charging, AC induction charging, combinations thereof, or the like. In embodiments where corona discharges are used, corona generators can include corotron / scorotron / shields or charging rollers. The outer surface of the carrier roller 103 can be charged by the carrier roller charging unit 110, which can be connected to a voltage source. The powder charging unit 104 applies charges and the carrier roller charging unit 110 through, e.g., corona discharges, tribo-charging, direct conduction charging, AC induction charging, combinations thereof, or the like. The coronagenerators can include corotron / scorotron / shields or charging rollers. The charged powder particles attach onto the surface of carrier roller 103 via an electrostatic process due to application of a proper bias voltage. In particular, the charge applied to the powder particles and the charge applied to the carrier roller 103 creates a proper bias voltage resulting in an attraction of the powder particles to the carrier roller 103 surface. The bias voltage can be adjusted by changing the charge applied on the carrier roller 103 to allow the best or optimal effect. In some embodiments, the charge applied can be in the range of, e.g., 0-1000 V, less than 1000 V, or the like. The charge is intended to pull or guide the particles towards the charged roller 103. Higher or lower potentials can be selected to achieve the intended bias towards the roller 103. In some embodiments, the bias voltage between the charged particles and the carried roller 103 can be between, e.g., 100V to 1000V, inclusive. The surface of the carrier roller 103 is typically oppositely charged against the charged particles to ensure the voltage bias guides the charged particles towards the surface of the carrier roller 103.

[0032] The charged particles attached onto the surface of carrier roller 103 are transported to a position close to or adjacent to the foil 107 surface, and are transferred to the foil 107 surface via an electrostatic process by applying a proper bias voltage to form a uniform powder coating layer on the foil 107. In particular, the carrier roller 103 rotates about its longitudinal axis to position the coated surface of the carrier roller 103 adjacent to the foil 107 surface. In some embodiments, the distance between the carrier roller 103 surface and the foil 107 surface can be about, e.g., 100-500 um, inclusive, or the like. In some embodiments, the distance between the carrier roller 103 surface and the foil 107 surface can be as close as possible without direct contact between the surfaces. In some embodiments, the distance between the carrier roller 103 surface and the foil 107 surface can allow minimal contact to assist with particle transfer to the foil 107. The foil 107 can be connected to a voltage source to charge the foil 107, thereby creating a bias voltage between the charged particles on the carrier roller 103 and the foil 107. The bias voltage between the foil 107 and the particles attached onto the carrier roller 103 can be in the range of about, e.g., 100V to 1000V, inclusive. The voltage bias guides the particles from the carrier roller 103 to the foil 107, and can dislodge the particles from the surface of the carrier roller 103 to initiate the transfer of the particles to the foil 107 surface. In some embodiments, a mechanical device (e.g., a brush, or the like) can be in contact with the carrier roller 103 to assist with removal of the particles from the carrier roller 103.

[0033] After releasing the powder, any residual powder on the carrier roller 103 surface can be removed by the cleaning unit 105. In some embodiments, the cleaning unit 105 can be blade, brush, vacuum, a combination thereof, or the like. Any powder that is not transferred to the foil 107 and is cleaned off by the cleaning unit 105 can be reclaimed and reused.

[0034] The powder coating layer on the foil 107 is conveyed to the calendering unit106 and densified at a specified pressure with or without heat. In some embodiments, a conditioning unit can be disposed between the calendering unit 106 and the carrier roller 103 to spread the powder particles on the oil 107, resulting in a uniform coating. The foil conveying units 120 include foil unwinding and winding assemblies, and maintains the foil107 moving in the web moving direction. After the calendering process, the powder coating layer adheres on the foil 107 to form an electrode. The compression force applied between the two calendering rollers can be typically between about, e.g., 25-2000N / mm, inclusive, or the like. In some embodiments, the compression force applied by the two calendering rollers can be about, e.g., 10-2000 N / mm or higher, inclusive, 10-1900 N / mm inclusive, 10-1800 N / mm inclusive, 10-1700 N / mm inclusive, 10-1600 N / mm inclusive, 10-1500 N / mm inclusive, 10-1400 N / mm inclusive, 10-1300 N / mm inclusive, 10-1200 N / mm inclusive, 10- 1100 N / mm inclusive, 10-1000 N / mm inclusive, 10-900 N / mm inclusive, 10- 800 N / mm inclusive, 10-700 N / mm inclusive, 10-600 N / mm inclusive, 10-500 N / mm inclusive, 10-400 N / mm inclusive, 10-300 N / mm inclusive, 10-200 N / mm inclusive, 10-100 N / mm inclusive, 10-50 N / mm inclusive, 10-20 N / mm inclusive, 20-2000 N / mm inclusive, 30-2000 N / mm inclusive, 40-2000 N / mm inclusive, 50-2000 N / mm inclusive,100-2000 N / mm inclusive, 200-2000 N / mm inclusive, 300-2000 N / mm inclusive, 400-2000 N / mm inclusive, 500-2000 N / mm inclusive, 600-2000 N / mm inclusive, 700-2000N / mm inclusive, 800-2000 N / mm inclusive, 900-2000 N / mm inclusive, 1000-2000 N / mm inclusive, 1100-2000 N / mm inclusive, 1200-2000 N / mm inclusive, 1300-2000 N / mm inclusive, 1400-2000 N / mm inclusive, 1500-2000 N / mm inclusive, 1600-2000 N / mm inclusive, 1700-2000 N / mm inclusive, 1800-2000 N / mm inclusive, 1900-2000 N / mm inclusive, 20-1500 N / mm inclusive, 20-1000 N / mm inclusive, 20-500 N / mm inclusive, 20- 300 N / mm inclusive, 10 N / mm, 20 N / mm, 30 N / mm, 40 N / mm, 50 N / mm, 60 N / mm, 70 N / mm, 80 N / mm, 90 N / mm, 100 N / mm, 200 N / mm, 300 N / mm, 400 N / mm, 500 N / mm, 600 N / mm, 700 N / mm, 800 N / mm, 900 N / mm, 1000 N / mm, 1100 N / mm, 1200 N / mm, 1300 N / mm, 1400 N / mm, 1500 N / mm, 1600 N / mm, 1700 N / mm, 1800 N / mm, 1900 N / mm,2000 N / mm or above, or the like. The idler roller 108 can provide support for the foil 107. In some embodiments, the idler roller 108 can be used as a charge providing roller (e.g., a foil charging unit) to adjust the bias voltage between the foil 107 and the charged particles (e.g., with the roller 108 connected to a voltage source to charge the foil 107). In some cases, the idler roller 108 is not needed.

[0035] FIG. 2 illustrates another exemplary electrostatic coating system 200. The system 200 can be substantially similar in structure and function to the system 100, except for the distinctions noted here. The system 200 includes a powder feeding unit 202 configured to receive powder 201, a charge unit 204 configured to apply a charge to a supplemental carrier roller 203a, and a charging unit 210 configured to apply a charge to a carrier roller 203. The rollers 203a, 203 can be referred to collectively as a carrier roller assembly.

[0036] The composite particles 201 can be charged by the charge unit 204, as shown in FIG. 2. These charged particles are attracted onto the surface of supplemental carrier roller 203a by applying a proper voltage bias between the particles and the roller 203a. The surface of supplemental carrier roller 203a can be grounded or charged with the opposite charge of the charged composite particles. The charged particles attached on the surface of supplemental carrier roller 203 a are transferred to the surface of carrier roller 203 with application of a proper voltage bias between the rollers 203 a, 203. In particular, the rollers 203a, 203 can rotate in opposite directions with a small gap between the surfaces of the rollers 203a, 203 (as illustrated in FIG. 2). The small gap between the rollers 203a, 203 ensures that the voltage bias guides the particles from the roller 203a to the roller 203. In some embodiments, the gap distance between the rollers 203a, 203 can be about, e.g., 100- 500 um, inclusive, or the like. In some embodiments, the gap distance can be selected to ensure a sufficient enough distance to avoid arcing, while ensuring particle transfer with diffusion is permitted between the rollers 203a, 203. In some embodiments, if a range of about 1-1000 V is used for the voltage bias, breakdown will generally not occur over the 100-500 um distance range.

[0037] The surface of carrier roller 203 is typically charged with the opposite charge of the charged composite particles by the carrier roller charging unit 210, which is connected to a voltage source. The typical voltage bias range can be about, e.g., 100-1000V, inclusive. As the roller 203 rotates and brings its surface close to or adjacent to the surfaceof the foil 207, the charged particles are transferred from the surface of the carrier roller 203 to the foil 207 via electrostatic process with application of a proper bias voltage. The foil 207 can be ground or charged to adjust the voltage bias (e.g., via the roller 208 disposed under the foil 207). The typical voltage bias can be in the range of about, e.g., 100-1000V, inclusive. The supplemental carrier roller 203a and carrier roller 203 can be cleaned by the cleaning unit 205 before the process repeats. For example, each carrier 203a, 203 can include a dedicated cleaning unit 205 disposed adjacent to the respective surface, thereby removing any powder particles which have not been transferred to the foil 207. Thus, any powder that is not transferred and cleaned off by the cleaning unit 205 can be reclaimed and reused. The powder coating layer is conveyed via the foil conveying unit 220 to the calendering unit 206, where the layer is densified with pressure and (optionally) heat to form an electrode.

[0038] The surface of carrier roller 103, 203 is conductive. However, in some embodiments, the carrier roller 103, 203 can have some select nonconductive surface regions in the outer surface of the roller 103, 203. Since the nonconductive regions cannot be charged by the carrier roller charging unit 110 or 210, the charged composite particles cannot be attached onto these regions, which produces a coating pattern with uncoated regions of powder coating layer on the foil 107, 207.

[0039] FIG. 4 illustrates another exemplary electrostatic coating system 300. The system 400 can be substantially similar in structure and function to the system 100, 200 except for the distinctions noted here. The system 400 includes a powder feeding unit 402 configured to receive powder 401, a charge unit 404 configured to apply a charge to a supplemental carrier roller 403a, and a charging unit 410 configured to apply a charge to a carrier roller 403. Cleaning units 405 can be used to clean powder particles adhered to the surface of the respective rollers 403 a, 403. After coating of the foil 407 with the powder particles, the foil 407 can be passed through a calendering unit 407 for compression (with or without heat) to create the electrode. Conveying unit 420 can maintain motion and support of the foil 407, and an idler roller 408 can support the foil 407 (and optionally apply a charge to the foil 407).

[0040] In an embodiment, the carrier roller 403 shown in FIG. 4 can be in the form of a photoconductive drum. The surface of the photoconductive drum is first charged uniformly by a charge unit 410. Typically, corona generators can includecorotron / scorotron / shields or charging rollers are utilized. After charging of the roller 403, an image 412 is imprinted onto the uniformly charged photoconductor surface using laser or other optical means 411. The image 412 can be in the form of a pattern on the surface of the roller 403. The pattern imprinted on the surface of the roller 403 does not cover the entire surface area of the roller 403. The image 412 creates uncharged regions of the roller 403 which do not attract the powder 401 particles. In particular, the image is in the form of a stimulus to discharge the charge imparted in the previous step of charging the roller 403. Typically, a photoconductor is used, e.g., a light is shined on the charged region to enable the drum to discharged in the region where the light has been applied. In some embodiments, the light can be applied with, e.g., a laser, LED, or other optical source.

[0041] The composite powder 401 particles that are charged by the charge unit 404 using, e.g., corona discharges, tribo-charging, direct conduction charging, AC induction charging, combinations thereof, or the like, are precisely transferred onto the oppositely charged sections of the photoconductive drum using powder feeding mechanisms such as rollers, fluidized beds, belts, spray guns, electrostatic feeders, or the like. In an embodiment, the charged powder particles are first attracted to the surface of the supplemental carrier roller 403a via electrostatic force or magnetic force, then transferred onto the oppositely charged sections of the photoconductive drum 403. In particular, upon being dispensed out of the powder feeding unit 402, the powder 401 is charged with the unit 404 which guides the powder 401 to the surface of the rollers 403a. The roller 403a rotates in a direction opposite from the roller 403, with surfaces of the rollers 403a, 403 spaced by a small gap. Based on the proper bias voltage between the charge applied to the roller 403 by the unit 410 and the charge applied to the roller 403a by the unit 404, as well as the charge of the powder 401 itself, the powder 401 is guided from the surface of the roller 403 a to the surface of the roller 403.

[0042] As the roller 403 rotates and brings the particles on its surface adjacent to the foil 407, the charged particles are transferred from the surface of the photoconductive drum to the grounded foil 407 via electrostatic process with application of a proper bias voltage. For example, the foil 407 can be charged and the bias voltage guides the particles from the roller 403 onto the web 407. The photoconductive drum is cleaned off by a cleaning unit 405 before the process repeats. Any powder that is not transferred from the roller 403a, 403 and cleaned by the cleaning unit 405 can be reclaimed and reused. As a last step, the powdercoating layer is conveyed to a calendering unit 406 via the foil conveying unit 420 where the layer is densified with pressure and heat to form an electrode.

[0043] FIG. 5 illustrates another exemplary electrostatic coating system 500. The system 500 can be substantially similar in structure and function to the systems 100, 200, 400, except for the distinctions noted here. The system 500 includes powder feeding units 502a, 502b configured to be loaded with powder 501a, 501b, carrier rollers 503a, 503b, carrier roller charging units 510a, 510b, charge unit 504a, 504b configured to charge respective powder 501a, 501b, cleaning units 505a, 505b configure to clean respective rollers 503a, 503b, a calendering unit 506, and foil 507. The foil 507 is orientated vertically and the system 500 is configured to coat both sides of the foil 507 simultaneously, although it should be understood that a similar process could be used to coat both sides of the foil 507 sequentially. In some embodiments, the system 500 can be oriented horizontally and performs the same function, depending on the constraints of the surrounding environment.

[0044] The powder 501a, 501b is applied or dispensed through the powder feeding unit 502a, 502b and charged by the respective charging unit 504a, 504b. These charged composite powder 501a, 501b particles are guided toward and attached to the surface of respective carrier roller 503a, 503b. The surface of the carrier roller 503a, 503b is charged by the respective charging roller charging unit 510a, 510b. The bias voltage between the charged powder 501a, 501b particles and the carrier roller 503a, 503b can be in the range of about, e.g., 100V to 1000V, inclusive, and can be selectively adjusted by charging the carrier roller 403a, 403b with the opposite charge. In some embodiments, the system 500 can include a sensor configured to detect the process and quality of attachment of the powder 501a, 501b to the surface of the respective roller 503a, 503b. If the attachment is below a predetermined threshold, the sensor can signal a controller to adjust the bias voltage to optimize the attachment of the powder 501a, 501b to the rollers 503a, 503b.

[0045] The charged powder 501a, 501b particles attached onto the carrier roller 503 a, 503b are released from the carrier roller 503a, 503b and deposited onto the foil 507 via an electrostatic process with application of a proper bias voltage. The bias voltage between the foil 507 and charged powder 501a, 501b particles attached on the carrier roller 503a, 503b can be in the range of about, e.g., 100V to 1000V, inclusive, and can be selectively adjusted by charging the foil 507 with the opposite charge. In particular, the foil 507 can receive a charge from, e.g., a charging unit, unit 520, or the like, to guide the powder 501a,501b from the rollers 503a, 503b to the respective opposing surfaces of the foil 507. As illustrated in FIG. 5, substantially similar structures and set-ups for coating are located on opposite sides of the foil 507. This allows dual side simultaneous coating of the foil 507. To obtain a uniform dual side coating, the mirror symmetric setup is used. The powder coating layer on the foil 507 is conveyed via the foil conveying unit 520 to the calendering unit 506 and densified at a specified pressure with or without heat. After the calendering process, the powder coating layer adheres on the foil to form an electrode. The powder coating unit with the photoconductive drum can also be arranged along both sides of the foil 507 to produce a dual side coated electrode.

[0046] The exemplary electrostatic coating systems 100, 200, 400, 500 discussed herein can be arranged in series to achieve a thicker coating or higher speed coating using multiple layers. Different types of systems 100, 200, 400, 500 can be used in combination. For example, FIG. 6 illustrates an electrostatic coating system 600 including the series arrangement of two systems 400, although it should be understood that two or more of the same or different systems could be set up in this manner, as well as on opposite sides of the foil 407.

[0047] 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.

Claims

CLAIMS:

1. An electrode fabrication system, comprising: a powder feeding unit configured to receive and dispense dry powder particles; a powder charging unit configured to apply a first charge to the dry powder particles dispensed from the powder feeding unit; a carrier roller assembly; a carrier roller charging unit configured to apply a second charge to the carrier roller assembly, wherein the dry powder particles with the first charge are guided toward and attached to a surface of the carrier roller assembly through a first electrostatic process based on a first bias voltage between the first charge of the dry powder particles and the second charge of the carrier roller assembly; a foil moving in a foil direction; and a foil charging unit configured to apply a third charge to the foil, wherein the dry powder particles attached to the surface of the carrier roller assembly are released and deposited onto the foil to form a powder coating layer through a second electrostatic process based on a second bias voltage between the first charge of the dry powder particles and the third charge of the foil.

2. The electrode fabrication system of claim 1 , comprising a calendering unit, wherein the foil with the powder coating layer is configured to be conveyed through the calendering unit for densification with or without heat to form an electrode.

3. The electrode fabrication system of claim 1 , wherein each of the dry powder particles includes high resistivity dielectric particles on a surface of an active material particle.

4. The electrode fabrication system of claim 3, wherein a size of each of the high resistivity dielectric particles is smaller than a size of the active material particle.

5. The electrode fabrication system of claim 3, wherein the active material particle is a cathode active material particle or an anode active material particle.

6. The electrode fabrication system of claim 3, wherein the high resistivity dielectric particles are a polymeric material particle, an inorganic material particle, or acombination thereof.

7. The electrode fabrication system of claim 1, wherein the carrier roller assembly includes a first carrier roller, and wherein an entire area of the surface of the first carrier roller capable of receiving the dry powder particles with the first charge is conductive.

8. The electrode fabrication system of claim 7, wherein the surface of the first carrier roller is positively or negatively charged with the carrier roller charging unit.

9. The electrode fabrication system of claim 1, wherein the carrier roller assembly includes a first carrier roller, wherein the surface of first carrier roller defines an area capable of receiving the dry powder particles with the first charge, and wherein a portion of the area is conductive and a portion of the area is nonconductive.

10. The electrode fabrication system of claim 1, wherein the carrier roller assembly includes a first carrier roller, and wherein the first carrier roller is a photoconductive drum.

11. The electrode fabrication system of claim 1, comprising means for forming uncharged regions on the surface of the first carrier roller.

12. The electrode fabrication system of claim 1, wherein the at least one of the powder charging unit or the carrier roller charging unit provides the respective first or second charge through at least one of corona charging or tribo-charging.

13. The electrode fabrication system of claim 1, wherein the carrier roller assembly includes a first carrier roller and a supplemental carrier roller disposed adjacent to the first carrier roller.

14. The electrode fabrication system of claim 13, comprising a supplemental carrier roller charging unit configured to apply a fourth charge to the supplemental carrier roller, wherein the dry powder particles with the first charge are released from a surface of the first carrier roller and guided towards a surface of the supplemental carrier roller through a third electrostatic process based on a third bias voltage between the first charge of the dry powder particles and the fourth charge of thesupplemental carrier roller.

15. The electrode fabrication system of claim 1, wherein the foil includes a Al foil or a Cu foil.

16. The electrode fabrication system of claim 2, wherein the calendering unit comprises at least one pair of calendering rollers.

17. The electrode fabrication system of claim 1, wherein at least one of the first or second bias voltage is in a range of about 100-1000 V, inclusive.

18. A method of electrode fabrication, comprising: receiving and dispensing dry powder particles with a powder feeding unit; applying a first charge to the dry powder particles dispensed from the powder feeding unit with a powder charging unit; applying a second charge to a carrier roller assembly with a carrier roller charging unit; guiding and attaching the dry powder particles with the first charge to a surface of the carrier roller assembly through a first electrostatic process based on a first bias voltage between the first charge of the dry powder particles and the second charge of the carrier roller assembly; applying a third charge to a foil moving in a foil direction; and releasing the dry powder particles from the surface of the carrier roller assembly and depositing the released dry powder particles onto the foil to form a powder coating layer through a second electrostatic process based on a second bias voltage between the first charge of the dry powder particles and the third charge of the foil.

19. The method of claim 18, wherein the carrier roller assembly includes a first carrier roller and a supplemental carrier roller disposed adjacent to the first carrier roller.

20. The method of claim 19, comprising: applying a fourth charge to the supplemental carrier roller with a supplemental carrier roller charging unit; and releasing the dry powder particles with the first charge from the surface of the first carrier roller and guiding the dry powder particles towards a surface of the supplemental carrier roller through a third electrostatic process based on a third biasvoltage between the first charge of the dry powder particles and the fourth charge of the supplemental carrier roller.

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