WO2022094539A1

WO2022094539A1 - Roll-to-roll carbon coating by discharge methods

Info

Publication number: WO2022094539A1
Application number: PCT/US2021/072011
Authority: WO
Inventors: Martti Kaempgen
Original assignee: Novelis Inc.
Priority date: 2020-10-27
Filing date: 2021-10-25
Publication date: 2022-05-05

Abstract

Described herein is a surface-modified current collector. The surface-modified current collector may include a metallic foil. The metallic foil may include an electrically conductive material having a contact surface. The metallic foil may have a thickness from 1 µm to 50 µm. The surface-modified current collector may also include a carbon-containing material having an amorphous microstructure. The carbon-containing material may include a thickness from 0.05 µm to 5.0 µm, a porosity from 0.05 cm³/g to 0.5 cm³/g, and a surface roughness (Ra) from 0.01 µm to 0.8 µm. The carbon-containing material may extend the surface of the metallic foil to form a closed layer. The closed layer may extend the contact surface of the metallic foil with less than 10.0 % variation of coverage.

Description

ROLL-TO-ROLL CARBON COATING BY DISCHARGE METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63/198,548, filed October 27, 2020, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] Sustainable energy, efficient and economical energy conversion, and storage technologies have become increasingly important in light of rising environmental issues. Electrical energy storage technologies play a significant role in the demand for green and sustainable energy. Specifically, rechargeable batteries or secondary batteries, such as lithium-ion batteries, which allow for reversible conversion between electrical and chemical energy, are increasingly relied upon by numerous technologies requiring portable and uninterrupted power sources. One possible drawback of rechargeable batteries, however, is their reduced energy/power densities and shorter life cycles. Because various applications, such as portable electronics or electric vehicles (EV), have limited volume and/or weight available for batteries, the amount of batteries within an application is often restricted. Moreover, current battery production practices may pose environmental and safety concerns due to hazardous solvents and excess material usage. Current battery production is also expensive. Hence, energy/power capacity, size, safety, and cost are important considerations for rechargeable batteries and their production methodologies.

BRIEF SUMMARY OF THE INVENTION

[0003] The term embodiments and The term embodiment and like terms are intended to refer broadly to all of the subject matter of this disclosure and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the claims below. Embodiments of the present disclosure covered herein are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the disclosure and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings and each claim. [0004] Described herein is a surface-modified current collector. The surface-modified current collector may include a metallic foil having a thickness from 1 pm to 50 pm. The metallic foil may include an electrically conductive material having a contact surface. For example, the metallic foil may include copper, aluminum, titanium, or nickel. In some embodiments, the contact surface may include an interfacial contact between the metallic foil and an electrode. In such embodiments, the interfacial contact may have reversible electrochemical capabilities to allow for electron exchange with the electrode. Optionally, the metallic foil may maintain stability at a working potential from 0.1 V to 5.0 V.

[0005] The surface-modified current collector may also include a carbon-containing material. For example, the carbon-containing material may include a carbon allotrope. The carbon-containing material may have an amorphous microstructure. The carbon-containing material may have a thickness from 0.05 pm to 5.0 pm, a porosity from 0.05 cm³/g to 0.5 cm³/g, and a surface roughness (Ra) from 0.01 pm to 0.8 pm. The carbon-containing material may extend the contact surface of the metallic foil to form a closed layer. The closed layer may continuously extend the contact surface of the metallic foil with less than 10% variation of coverage. Optionally, the surface-modified current collector may further include a current-collecting tab.

[0006] In some embodiments, the surface-modified current collector may be a positive current collector. Optionally, the contact surface of the metallic foil including the closed layer may be contacted by a positive electrode. In other embodiments, the surface-modified current collector may be a negative current collector. In such embodiments, the contact surface of the metallic foil including the closed layer may be contacted by a negative electrode. In embodiments, the surface-modified current collector may be part of a battery. In such embodiments, the battery may have a specific capacity from 25 mAh/g to 50 mAh/g. Optionally, a lithium-ion battery including an anode, a cathode, and an electrolyte, may also include the current collector as described herein.

[0007] In an aspect, described are methods for continuously modifying a surface of a current collector to make a surface-modified current collector. The methods may include providing a pair of roller units. The pair of roller units may be part of a continuous roller-to- roll system. The pair of roller units may include a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between. The first roller unit may include a length from 0.5 meters to 3.0 meters. In some embodiments, the method may include controlling the space gap between the first roller unit and the second roller unit. For example, controlling the space gap between the first roller unit and the second roller unit may include maintaining the space gap between the first roller unit and the second roller unit at a distance from 1 mm to 50 mm. Optionally, the second roller unit may be oriented to bring the metallic foil into the space gap formed between the second roller unit and the first roller unit. A transferrable carbon-containing material may be on a surface of the first roller unit. In some embodiments, the carbon-containing material extending the surface of the first roller unit may be characterized by an amorphous microstructure. The method may include feeding a metallic foil including an electrically conductive material having a contact surface to the pair of roller units. In some embodiments, feeding the metallic foil to the pair of roller units may include continuously feeding the metallic foil to the pair of roller units.

[0008] The method may also include supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit. In some embodiments, supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit may include controlling a voltage between the first roller unit and the second roller unit and/or controlling a current between the first roller unit and the second roller unit. Optionally, controlling the voltage between the first roller unit and the second roller unit may include maintaining the voltage from 50 V to 300 V. In some embodiments, controlling the current between the first roller unit and the second roller unit may include maintaining a working current from 0.5 A/cm² to 10.0 A/cm².

[0009] The method may also include transferring at least a portion of the carbon-containing material onto the contact surface of the metallic foil to form a closed layer on the metallic foil. In some embodiments, transferring at least the portion of the carbon-containing material to the metallic foil to form the closed layer includes bringing the contact surface of the metal foil into the space gap with the surface of the first roller unit such that the carbon-containing material on the surface of the first roller unit transfers onto the contact surface of the metallic foil. In some embodiments, the closed layer may continuously extend the surface of the metallic foil with less than 10 % variation of coverage. The closed layer may include a thickness from 0.05 pm to 5 pm, a porosity of from 0.05 cm³/g to 0.5 cm³/g, and a surface roughness (Ra) from 0.01 pm to 0.8 pm. [0010] In another aspect, described herein is an apparatus for continuously modifying a surface of a current collector. The apparatus may include a pair of roller units. The pair of roller units may include a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between. In some embodiments, the second roller unit may be oriented to bring a metallic foil including an electrically conductive material into a space gap that is formed between the second roller unit and the first roller unit. A transferrable carbon-containing material may extend a surface of the first roller unit parallel to the second roller unit. The apparatus may include a power source having a positive terminal and a negative terminal. The power source may be operably coupled with the pair of roller units to supply a current and a voltage to the pair of roller units to form an electrical field between the first roller unit and the second roller unit. The positive terminal may be in electrical communication with the first roller unit and the negative terminal may be in electrical communication with the second roller unit. Optionally, the power source may be a direct current (DC) source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 illustrates a lithium-ion battery according to some embodiments as disclosed herein.

[0012] FIG. 2A illustrates an exemplary current collector.

[0013] FIG. 2B illustrates the current collector of FIG. 2A contacting an electrode.

[0014] FIG. 2C illustrates an interface between the current collector and the electrode of FIG. 2B

[0015] FIG. 3A illustrates a surface-modified current collector contacting an electrode according to some embodiments as disclosed herein.

[0016] FIG. 3B illustrates an interface between the surface-modified current collector and the electrode of FIG. 3A.

[0017] FIG. 4 illustrates an apparatus for continuously surface modifying a current collector according to some embodiments as disclosed herein.

[0018] FIG. 5 illustrates an electro-discharge process for continuously surface modifying a current collector according to some embodiments as disclosed herein. [0019] FIG. 6 illustrates a continuous system for surface modifying a current collector according to some embodiments as disclosed herein.

[0020] FIG. 7 illustrates a flowchart of a method for continuously surface modifying a current collector according to some embodiments as disclosed herein.

DETAILED DESCRIPTION

[0021] Described herein are surface-modified current collectors including a metallic foil and a carbon-containing material. Apparatuses and methods for making surface-modified current collectors by applying a carbon-containing material onto a metallic foil are also described herein. The apparatuses and methods for making the surface-modified current collectors may allow for continuous transfer of the carbon-containing material onto the metallic foil by generating an electric field between a pair of rollers. By utilizing the electric field to perform an electro-discharge process, the transferred carbon-containing material on the metallic foil may form a closed layer having less than 10 % variation of coverage. The resulting surface-modified current collector, when utilized as part of a battery, may provide for increased energy/power capacity during charging and discharging cycles and extend the overall lifespan of the battery.

[0022] As battery technology has become more advanced, so has the use of batteries within a wide range of applications. Rechargeable batteries, also known as secondary batteries, have become the power source of choice for many portable applications ranging from laptops to personal digital assistants, cellular phones, and electric vehicles (EV). As the use of rechargeable batteries increases within portable applications, however, so has the demand for increased performance of the rechargeable battery. With the rapid development of portable applications, demands are placed on rechargeable batteries for greater energy/power density, reduced size and weight requirements, and longer lifespans.

[0023] One type of rechargeable battery at the forefront of battery technology is the lithium-ion (Li-ion) battery. Li-ion batteries are leading the charge for battery technology advancement because of their electrochemical capabilities which allow for the battery to recharge after use. Reversible conversion between electrical and chemical energy within the Li-ion battery allows Li-ion batteries to undergo multiple charging and discharging cycles during their lifespans.

[0024] Improving the electrochemical properties of the electrode and electrolyte materials has been a primary focus of battery development over recent years. Li-ion batteries, however, are integrated systems, and as such their electrochemical performances are not determined by only the electrode and electrolyte materials. Other components and features of the Li-ion batteries also play a role in the electrochemical performance of Li-ion batteries. Current collectors are one such component that may impact the electrochemical performance of Li-ion batteries.

[0025] Current collectors are important and indispensable components of Li-ion batteries. Generally, a Li-ion battery includes two current collectors: one for the positive electrode, also known as a cathode, and one for the negative electrode, also known as the anode. Current collectors contact the electrode materials, which include active materials, binders and conductive additives, to electrically connect the electrode materials to an external circuit. Therefore, the surface characteristics of current collectors may play a vital role in improving the energy/power density and lifespan of Li-ion batteries.

[0026] During a charging or discharging cycle, electrons transfer between the current collector and the electrode, thereby generating a current. Thus, it is important that electrons can move between the current collector and the electrode with little-to-no impedance. Within present battery technologies, however, high electric polarization may occur at the interface between the current collector and the electrodes. Polarization may be undesirable because it can cause increased electrical resistance or impedance. Electrical resistance, also known as electrical contact resistance, at the interface between the electrode and current collector can cause significant energy loss. In addition to potentially significant energy loss, electrical resistance in extreme cases may lead to temperatures that can melt the battery electrodes and current collectors in a phenomenon similar to spot welding. Moreover, polarization may cause degradation of the current collector by, for example, corrosion. Corrosion products may separate the current collectors from the electrode materials, further impacting the performance of the battery. In some cases, corrosion products reduce the overall lifespan of the battery.

[0027] Accordingly, as provided herein, the performance, specifically the energy/power density and lifespan of Li-ion batteries, may be improved by reducing polarization and electrical resistance at the current collectors. More specifically, the current collectors as provided herein include surface-modified current collectors. The surface-modified current collectors may include a layer of carbon-containing material that reduces the polarization and electrical resistance between the electrode and the current collector. A Li-ion battery employing a surface-modified current collector as provided herein may have improved energy/power capacity during charging and discharging cycles and increased lifespans due to the surface-modified current collector.

[0028] Moreover, methodologies and apparatuses for making surface-modified current collectors are provided herein. To make surface-modified current collectors, an apparatus including a pair of roller units is provided. The apparatus may be configured to apply a carbon-containing material onto a metallic foil during an electro-discharge process in which an electric field is generated between the pair of roller units. The process and apparatus for applying the carbon-containing material onto the metallic foil to make the surface-modified current collector may be more environmentally friendly, safer, and cost effective than conventional processes. The methods and associated apparatus disclosed herein may not require additional materials such as binders, solvents, and/or additives to apply the carbon- containing material onto the metallic foil. Generally, these additional materials are hazardous and may pose safety concerns due to flammability and toxicity levels. Moreover, the process and apparatus provided herein may allow for the application process to be continuous, thus increasing production efficiency for making surface-modified current collectors.

[0029] Further detail regarding such embodiments and additional embodiments is provided in relation to the figures. FIG. 1 depicts a battery 100 that may be implemented by one or more embodiments. Battery 100 may be a lithium-ion battery and produce electrical energy through electrochemical and/or chemical reactions. Battery 100 may be a rechargeable battery (i.e., a secondary battery) having reversible electrochemical capabilities to allow for repeated charging and discharging cycles of battery 100.

[0030] Battery 100 may include a cathode 102, an anode 108, and an electrolyte 112. Battery 100 may also include an electron path 114 and two current collectors (terminals) 104 and 110. The arrangement of battery 100 and respective components may vary depending on the configuration of battery 100. Cathode 102 may be a positive electrode and anode 108 may be a negative electrode. Cathode 102 may, prior to the initiation of a charging process, contain a plurality of lithium ions 120 (i.e., Li⁺). During the charging process, lithium ions 120 intercalated within cathode 102 may flow, via electrolyte 112, to anode 108. During the discharging process, the opposite may take place and lithium ions 120 intercalated within anode 108 may flow, via electrolyte 112, back to cathode 102. [0031] As used herein, the terms intercalation, intercalated, and intercalate may refer to a reversible inclusion or insertion of an ion (e.g., lithium ions 120) into a material having a layered or crystalline structure (lattices), such as anode 108 or a cathode 102. Similarly, the terms deintercalation, deintercalated, and deintercalate may refer to the reversible exclusion or expulsion of an ion (e.g., lithium ions 120) out of a material having a layered or crystalline structure (lattices).

[0032] Current collector 104 may be a surface-modified current collector attached to cathode 102. Current collector 104 may be a positive current collector. Current collector 110 may be a surface-modified current collector attached to anode 108. Current collector 110 may be a negative current collector. Current collectors 104 and 110 may include various materials including, but not limited to, aluminum, copper, gold, silver, nickel coated steel, and/or compounds/alloys based on aluminum, copper, nickel, or any other suitable metal. In some embodiments, current collectors 104 and 110 may include platinum, palladium, titanium, any other noble metals, and/or any compounds/alloys or combination thereof.

[0033] During the charging process, when lithium ions 120 within cathode 102 flow from cathode 102 to anode 108 via electrolyte 112, electrons 122 may be simultaneously “released” from cathode 102. Electrons 122 may flow from cathode 102 to current collector 104 and then from current collector 104, via electron path 114, to current collector 110. Because current flows in the opposite direction of electrons, current collector 104 may collect current during the charging process.

[0034] During a discharging process, the converse may happen. During a discharging process, lithium ions 120 within anode 108 may flow from anode 108, via electrolyte 112, to cathode 102. Electrons 122 may also flow from anode 108 to cathode 102. In particular, electrons 122 may flow through current collector 110 via electron path 114 to current collector 104 and eventually cathode 102. In embodiments, device 116 may be attached to electron path 114 and, during a discharging process, electrons 122 flowing through electron path 114 (from anode 108 to cathode 102) may power device 116. In one embodiment, device 116 may only be attached to electron path 114 during a discharging process. In such an embodiment, during a charging process when an external voltage is applied to battery 100 by an external power source, device 116 may be directly powered or partially powered by the external power source. [0035] Device 116 may be a parasitic load atached to batery 100. Device 116 may operate based at least in part off of power produced by batery 100. Device 116 may be any of various devices such as an electronic motor, a laptop, a computing device, a processor, and/or one or more other electronic devices. Device 116 may not be a part of battery 100, but instead relies on batery 100 for electrical power. For example, device 116 may be an electronic motor that receives electric energy from batery 100 via electron path 114 and device 116 may convert the electric energy into mechanical energy to perform one or more functions such as acceleration in an EV. During a charging process, when an external power source is connected to batery 100, device 116 may be powered by the external power source (e.g., external to batery 100). During a discharging process, when an external power source is not connected to batery 100, device 116 may be powered by batery 100.

[0036] Electrolyte 112 may separate cathode 102 and anode 108 and prevent the electrodes from directly contacting one another. In some embodiments, a separator may hold the electrolyte and separate the electrodes from one another. For example, the separator may be made from a non-conductive material, such as a polymer. During the charging and discharging cycles, electrolyte 112 separating cathode 102 and anode 108 may prevent electrons 122 from flowing between the electrodes. By preventing electron flow through electrolyte 112, electrons 122 may be forced to flow via electron path 114. Electron path 114 may be a path through which electrons 122 flow between cathode 102 and anode 108 because electrons 122 cannot flow through electrolyte 112.

[0037] In embodiments, electrolyte 112 may be a liquid electrolyte. For example, electrolyte 112 may include soluble salts, acids or other bases in liquid or gelled formats. Exemplary electrolytes 112 may include a solution of lithium salts with organic solvents such as ethylene carbonate. However, in other embodiments, electrolyte 112 may be a solid electrolyte. For example, when electrolyte 112 is a solid electrolyte, electrolyte 112 may include a polymer solid-state electrolyte, a solid electrolyte powder, such as an inorganic solid-state electrolyte, or a sulfur based electrolyte. Exemplary polymer solid-state electrolytes may include polyethylene oxide (POE), which may contain a lithium salt, such as lithium hexafluorophosphate (LiPFe), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate)borate (LiBOB), lithium tetrafluoroborate (LiBF4), and lithium perchlorate (LiClO4). Exemplary inorganic solid-state electrolytes may include an oxide such as lithium aluminum titanium phosphate (LATP; Lii_+xAl_yTi_2-yPO4.), for example Lii.3Alo.3Tii.7(P04)3, a lithium aluminum germanium phosphate (LAGP), for example Li i.sAlo.sGei.sPsOn, Lii.sAlo.sGei PC s or Lii.5Alo.5Gei.5(P04)3, a lithium phosphorous oxy-nitride (LiPON), for example Li2.9PO3.3N04, or a lithium lanthanum zirconate oxide (LLZO), for example LivLasZnOn. Inorganic solid- state electrolytes may also include complex hydrides, such as iodide substitution in lithium borohydride (LiBFL-Lil) or lithium nitride (L43N). In embodiments, electrolyte 112 may include a sulfur-based solid electrolyte. Exemplary sulfur-based solid electrolytes may include a lithium germanium phosphorous sulfide (LGPS), such as LiioGeP2Si2, or a lithium phosphorus sulfide (LPS), such as Li2S-P2S5. In embodiments where electrolyte 112 is a solid electrolyte, the configuration of battery 100 may vary since cathode 102 and anode 108 may no longer be submerged in electrolyte 112.

[0038] Current collectors, such as current collectors 104 and 110, play a key role in transporting electrons 122 between electrodes 122 and external device 116. To allow movement of electrons 122 during the charging and discharging cycles, current collectors 104 and 110 need to be electrically conductive. Although often not the focus of battery development, current collectors are vital to Li-ion battery technology. Current collectors 104 and 110 may electronically connect cathode 102 and anode 108, respectively, to electron pathway 114 and thereby device 116. Therefore, the characteristics and properties of current collectors 104 and 110 may impact the overall performance of battery 100. For example, electrical resistance, also known as electrical contact resistance, at the electrode-collector interface, can significantly reduce the discharge/charge capacity of battery 100. Electrical resistance loss can be as high as 20% of the total energy flow in and out of battery 100 in some cases.

[0039] FIG. 2A depicts an illustration of a current collector 200. Current collector 200 may be a conventional current collector. Current collector 200 may be a positive current collector, or a negative current collector. Current collector 200 may include a metallic foil 202. Metallic foil 202 may be made at least partially or completely from an electrically conductive material. Conductive material may be material that allows for the movement or transfer of electrons 122 and electric current. For example, metallic foil 202 may include, but without limitation, aluminum, copper, gold, silver, nickel coated steel, and/or compounds/ alloys based on aluminum, copper, nickel, or any other suitable metal. In some embodiments, current collectors 104 and 110 may include platinum, palladium, titanium, any other noble metals, and/or any compounds/alloys or combination thereof. Metallic foil 202 may be electrically conductive to allow for the movement or transfer of electrons 122 from an electrode to an external circuit, such as electron pathway 114.

[0040] Metallic foil 202 may have a thickness 205. For example, in some embodiments, metallic foil 202 may have a thickness from 1 pm to 50 pm (e.g., from 1 pm to 40 pm, from 5 pm to 30 pm, from 5 pm to 25 pm, or from 5 pm to 20 pm). For example, metallic foil 202 may have a thickness of 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 15 pm, 16 pm, 17 pm, 18 pm, 19 pm, 20 pm, 21 pm, 22 pm, 23 pm, 24 pm, 25 pm, 26 pm, 27 pm, 28 pm, 29 pm, 30 pm, 31 pm, 32 pm, 33 pm, 34 pm, 35 pm, 36 pm, 37 pm, 38 pm, 39 pm, 40 pm, 41 pm, 42 pm, 43 pm, 44 pm, 45 pm, 46 pm, 47 pm, 48 pm, 49 pm, and/or 50 pm.

[0041] In some embodiments, metallic foil 202 may include a contact surface 206. Contact surface 206 may be a surface of metallic foil 202 that is configured (prepared, manufactured, or otherwise) to contact an electrode or material from which electrons 122 may flow into and out of. For example, contact surface 206 may be formed by known surface preparation techniques to enhance the surface of metallic foil 202 contacting the electrode. Exemplary surface preparation techniques may include cleaning, soaking, etching, current assisted etching, electrolytic polishing, coating, electrolytic cleaning, galvanization, and/or surface texturing, among others. The surface of metallic foil 202 may be prepared to enhance the electrical conductivity of metallic foil 202. In embodiments, metallic foil 202 may have more than one contact surface 206.

[0042] FIG. 2B illustrates contact surface 206 of metallic foil 202 contacting an electrode 204. FIG. 2B may represent a current collector situated in a battery or battery assembly, such as battery 100. Electrode 204 may be a cathode, such as cathode 102, or an anode, such as anode 108. When metallic foil 202 contacts electrode 204, an interfacial contact 208 may form at the electrode-collector interface. The primary purpose of interfacial contact 208 may be to allow for an uninterrupted passage of electric current, and reciprocally electrons in the opposite direction, across the contact interface. In some embodiments, interfacial contact 208 may form across the entirety of contact surface 206. However, in other embodiments, interfacial contact 208 may form along only a portion of contact surface 206.

[0043] FIG. 2C illustrates a close-up view of interfacial contact 208 of FIG. 2B. As shown, contact between electrode 204 and metallic foil 202 may occur only at discrete points which are formed by the mechanical contact of asperities on both surfaces due to the surface roughness and surface irregularities of the contact surface 206 of metallic foil 202. This may mean that the actual contact area of interfacial contact 208 may be only a small percentage of the nominal surface area of electrode 204 and contact surface 206 of metallic foil 202. For example, the actual contact surface area of interfacial contact 208 formed by the discrete points of contact may often be less than 2 % of the nominal surface area of electrode 204 and contact surface 206. In exemplary cases, the actual contact surface area of interfacial contact 208 formed by discrete points of contact may be less than 1.9 %, less than 1.8 %, less than 1.7 %, less than 1.6 %, less than 1.5 %, less than 1.4 %, less than 1.3 %, less than 1.2 %, less than 1.1 %, less than 1.0 %, less than 0.9 %, less than 0.8 %, less than 0.7 %, less than 0.6 %, less than 0.5 %, less than 0.4 %, less than 0.3 %, less than 0.2 %, or even less than 0.1 % of the nominal surface area of electrode 204 and contact surface 206.

[0044] Electrode 204 and current collector 200 containing metallic foil 202 may each have a voltage V2 and VI, respectively. As represented and discussed herein, it is understood that voltage V2 and VI represent voltage potential between two given points. For ease of discussion, V2 and VI are referred to as voltages. Voltages VI and V2 may occur far from the electrode-collector interface within the respective body of metallic foil 202 and electrode 204. The voltage difference between VI and V2 may cause an electric current from the high voltage body to the low voltage one. Electric current lines 214 may illustrate the path of the electric current from the high voltage body to the low voltage body. In FIG. 2C, metallic foil 202 may be the high voltage body and electrode 204 may be the low voltage body. An exemplary scenario that FIG. 2C may depict may be a positive current collector contacting a cathode during a charging cycle. During a charging cycle, electrons within the cathode, here represented by electrode 204, may flow from the low voltage anode through metallic foil 202 having a slightly greater voltage to a greater voltage anode. Because current flows in the opposite direction of electrons, an electrical current, indicated by electric current lines 214, may form flowing from metallic foil 202 to electrode 204.

[0045] At the electrode-current interface, electric current lines 214 may bundle together to pass through the discrete contact points between electrode 204 and metallic foil 202. Convergence of electrical flow as a result of the micro-contact points may reduce the volume of material used for electrical conduction. This may cause electrical resistance, also known as electrical contact resistance. The contact resistances at each of the discrete contact spots may apply a resistance to electric current lines 214 traveling through each spot due to the limited surface area of the discrete contact spots. Because electrical resistance is a measure of the amount of impedance to the flow of electric current, the greater the electrical resistance, the lower the electric current may be at a given voltage determined by battery chemistry. In general, greater electric current may be desirable for batteries because it directly corresponds to the speed of a discharging/charging cycle of the battery.

[0046] Electrical contact resistance may involve three main factors: (i) surface topology of the current collector at the interfacial contact 208, (ii) contact mechanics at the interfacial contact 208, and (iii) electrical transport at the electrode-collector interface. Factors (i) and (ii) may be strongly correlated since the contact mechanic analysis strongly depends on the surface topology. During the use of a battery, the surface topology and the contact mechanics may change. Heat generation at the electrode-collector interface due to electrical resistance may cause the material properties of both the current collector and the electrode along the interfacial contact 208 to change, and consequently so may the surface topology and the contact mechanics. Additionally, over time, oxide layers may form along contact surface 206. Oxide layers, also known as corrosion deposits, may significantly increase electrical contact resistance along the electrode-collector interface. Current collectors used within Li- ion batteries may also be susceptible to environmental degradation. For example, metallic foils, such as aluminum foils, may be susceptible to pitting corrosion while copper foils may be susceptible to environmentally assisted cracking. Localized corrosion of a metallic foil, such as metallic foil 202, may occur due to high oxidizing potential associated with the electrode charge condition. Corrosion to a current collector, specifically the metallic foil, may result in detrimental changes to surface topography and impact the interfacial contact at the electrode-collector interface.

[0047] Electrical contact resistance may be reduced by several methods, such as, for example, by modifying the surface of the current collector. The surface of the current collector may be modified by depositing a layer of material onto the contact surface. Modifying the surface of the current collector may increase the actual contact area. Adding a layer of material onto the contact surface of the current collector may also reduce electrical resistance because the layer may act as an electrical grease or lubricant, conforming to the imperfect surface features of the mating surfaces at the interface contact point. Moreover, modifying the surface of the current collector may prevent formation of oxide layers on the contact surface of a current collector by reducing exposure of the metallic foil to the electrode and the electrolyte. [0048] The processes and apparatuses described herein may provide for continuously modifying the surface of a current collector to reduce electrical contact resistance at the electrode-collector interface and prevent environmental degradation or corrosion. The processes and apparatuses herein may provide numerous advantages over conventional processes for modifying the surface of current collectors. Conventional processes typically use wet coating processes in which a slurry is applied to a metallic foil. The slurry must be dried before the coating is formed. To ensure adhesion, conventional processes contain binders. Binders, however, are known to decrease the overall performance of the current collector. Moreover, the dispersion/application of the slurry onto the metallic foil often requires organic solvents to improve wetting of the metallic foil. Organic solvents may be hazardous and often come with maximum allowable concentrations in breathable air due to toxicity concerns. Moreover, organic solvents are flammable and thus equipment used within a process may require heightened safety measures.

[0049] The continuous surface modification process for current collectors (hereinafter referred to as the modification process) described herein may address many of the issues of conventional processes. First, the modification process may be a dry coating process that does not use any binders or organic solvents. By omitting binders, the performance of the resulting surface-modified current collectors may have improved conductivity. Additionally, no organic solvents are required in the modification process and thus the safety concerns corresponding to the solvents may be negated. Second, the modification process may reduce overall operating costs. The modification process may be more cost effective than conventional processes because it does not use binders or organic solvents, and can be done in a single modification stage. Additionally, because the modification process is a dry coating process, there is no need for equipment to make, apply, and dry the wet (slurry) material. Third, the modification process may be done continuously, thereby reducing processing time. This may allow for optimization of the production process for surface- modified current collectors from both a financial perspective and a time perspective.

[0050] FIG. 3A illustrates a surface-modified current collector 300 made according to a modification process described herein. Surface-modified current collector 300 may have reduced electrical contact resistance at the electrode-collector interface (i.e., at interfacial contact 308). Surface-modified current collector 300 may include a metallic foil 302 and a layer 316. In some embodiments, surface-modified current collector 300 may include a current-collecting tab 303. Metallic foil 302 may be the same as or similar to metallic foil 202. In FIG. 3A, however, contact surface 306 of metallic foil 302 may be modified to include a layer 316. Metallic foil 302 may be electrically conductive to facilitate the movement of electrons and current to and from an electrode, such as electrode 304. In some embodiments, metallic foil 302 may have the electro-mechanical properties to maintain stability at a working potential from 0. 1 Volts (V) to 5.0 V. When metallic foil 302 is part of a positive current collector, metallic foil 302 may have a working potential from 3.0 V to 4.7 V. When metallic foil 302 is part of a negative current collector, metallic foil 302 may have a working potential from 0.5 V to 2.5 V. Stability or passivation may mean that metallic foil 302 does not corrode or degrade at a given working potential. Corrosion may include discoloration, pitting, holes, and/or cracking of a surface area of metallic foil 302. In some embodiments, corrosion or degradation of metallic foil 302 may include mass loss. When metallic foil 302 maintains stability at a working potential, then metallic foil 302 may have little to no mass loss after repeated charging/discharging cycles. Repeated charging/discharging cycles may include more than 1 charging and/or discharging cycles, more than 5 charging and/or discharging cycles, more than 10 charging and/or discharging cycles, more than 15 charging and/or discharging cycles, more than 20 charging and/or discharging cycles, more than 25 charging and/or discharging cycles, more than 50 charging and/or discharging cycles, more than 75 charging and/or discharging cycles, or more than 100 charging and/or discharging cycles. During and after extended charging/discharging cycles, metallic foil 302 maintaining stability at a given working potential may exhibit less than 1.0 % mass loss, less than 0.9 % mass loss, less than 0.8 % mass loss, less than 0.7 % mass loss, less than 0.6 % mass loss, less than 0.5 % mass loss, less than 0.4 % mass loss, less than 0.3 % mass loss, less than 0.2 % mass loss, less than 0.1 % mass loss, less than 0.09 % mass loss, less than 0.075 % mass loss, or less than 0.05 % mass loss. Additionally, when a metallic foil does not maintain stability or is unstable at a given working potential, the metallic foil may form a lithium alloy which can reduce the working lifespan of the overall battery itself. In some cases, a metallic foil that does not have electrochemical stability at a given working potential may dissolve during repeated charging or discharging cycles. Because every metal may have a different electrochemical stability range, the type of material used for metallic foil 302 may vary depending on the working potential of the current collector.

[0051] In some embodiments, when a battery, such as those described herein, utilize surface-modified current collector 300, the battery may have a specific capacity from 25 mAh/g to 50 mAh/g (e.g., from 30 mAh/g to 50 mAh/g, from 30 mAh/g to 45 mAh/g, from 35 mAh/g to 45 mAh/g, or from 35 mAh/g to 40 mAh/g). For example, surface-modified current collector 300 may have a specific capacity of 25 mAh/g, 26 mAh/g, 27 mAh/g, 28 mAh/g, 29 mAh/g, 30 mAh/g, 31 mAh/g, 32 mAh/g, 33 mAh/g, 34 mAh/g, 35 mAh/g, 36 mAh/g, 37 mAh/g, 38 mAh/g, 39 mAh/g, 40 mAh/g, 41 mAh/g, 42 mAh/g, 43 mAh/g, 44 mAh/g, 45 mAh/g, 46 mAh/g, 47 mAh/g, 48 mAh/g, 49 mAh/g, and/or 50 mAh/g.

[0052] Layer 316 may be a surface modification to metallic foil 302 along contact surface 306. For example, layer 316 may be a coating or nano-coating applied to contact surface 306. In some embodiments, layer 316 may include one or more carbonaceous materials. For example, layer 316 may include a carbon-containing material. The carbon-containing material may include any type of carbon allotrope. For example, the carbon-containing material may include carbon, graphite, graphene, carbon (nano)tubes, carbon rods, carbon fibers, carbon flakes, glassy carbon or diamond-like-carbon, among others. In some embodiments, the carbon-containing material may be characterized by an amorphous microstructure. Amorphous microstructure as used herein may refer to the irregularity of a solid’s structure. If the atoms that make up the solid material are periodic and well-ordered, then the microstructure may be considered crystalline or less amorphous. If the atoms are irregular and haphazard, the microstructure may be considered amorphous. In other embodiments, layer 316 may be or include one or more other materials, such as silicon. In some embodiments, layer 316 may include any suitable metal such as but not limited to aluminum, nickel, titanium, gold, platinum, tungsten, copper, chromium, vanadium, zirconium, molybdenum, silver, or iridium.

[0053] In some embodiments, layer 316 includes a thickness 315. In some embodiments, thickness 315 may be from 0.005 pm to 20.0 pm (e.g., from 0.01 pm to 20.0 pm, from 0.1 pm to 20.0 pm, from 1.0 pm to 18.0 pm, from 5.0 pm to 15.0 pm, or from 7.0 pm to 12.0 pm). For example, thickness 315 may be 0.005 pm, 0.006 pm, 0.007 pm, 0.008 pm, 0.009 pm, 0.01 pm, 0.02 pm, 0.03 pm, 0.04 pm, 0.05 pm, 0.06 pm, 0.07 pm, 0.08 pm, 0.09 pm, 0.1 pm, 0.2 pm, 0.3 pm, 0.4 pm, 0.5 pm, 0.6 pm, 0.7 pm, 0.8 pm, 0.9 pm, 1.0 pm, 1.1 pm,

1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm, 1.6 pm, 1.7 pm, 1.8 pm, 1.9 pm, 2.0 pm, 2.1 pm, 2.2 pm,

2.3 pm, 2.4 pm, 2.5 pm, 2.6 pm, 2.7 pm, 2.8 pm, 2.9 pm, 3.0 pm, 3.1 pm, 3.2 pm, 3.3 pm,

3.4 pm, 3.5 pm, 3.6 pm, 3.7 pm, 3.8 pm, 3.9 pm, 4.0 pm, 4.1 pm, 4.2 pm, 4.3 pm, 4.4 pm,

4.5 pm, 4.6 pm, 4.7 pm, 4.8 pm, 4.9 pm, 5.0 pm, 5.1 pm, 5.2 pm, 5.3 pm, 5.4 pm, 5.5 pm,

5.6 pm, 5.7 pm, 5.8 pm, 5.9 pm, 6.0 pm, 6.1 pm, 6.2 pm, 6.3 pm, 6.4 pm, 6.5 pm, 6.6 pm,

6.7 pm, 6.8 pm, 6.9 pm, 7.0 pm, 7.1 pm, 7.2 pm, 7.3 pm, 7.4 pm, 7.5 pm, 7.6 pm, 7.7 pm, 7.8 pm, 7.9 pm, 8.0 pm, 8.1 pm, 8.2 pm, 8.3 pm, 8.4 pm, 8.5 pm, 8.6 pm, 8.7 pm, 8.8 pm,

8.9 pm, 9.0 pm, 9.1 pm, 9.2 pm, 9.3 pm, 9.4 pm, 9.5 pm, 9.6 pm, 9.7 pm, 9.8 pm, 9.9 pm,

10.0 pm, 10.1 pm, 10.2 pm, 10.3 pm, 10.4 pm, 10.5 pm, 10.6 pm, 10.7 pm, 10.8 pm, 10.9 pm, 11.0 pm, 11.1 pm, 11.2 pm, 11.3 pm, 11.4 pm, 11.5 pm, 11.6 pm, 11.7 pm, 11.8 pm,

11.9 pm, 12.0 pm, 12.1 pm, 12.2 pm, 12.3 pm, 12.4 pm, 12.5 pm, 12.6 pm, 12.7 pm, 12.8 pm, 12.9 pm, 13.0 pm, 13.1 pm, 13.2 pm, 13.3 pm, 13.4 pm, 13.5 pm, 13.6 pm, 13.7 pm,

13.8 pm, 13.9 pm, 14.0 pm, 14.1 pm, 14.2 pm, 14.3 pm, 14.4 pm, 14.5 pm, 14.6 pm, 14.7 pm, 14.8 pm, 14.9 pm, 15.0 pm, 15.1 pm, 15.2 pm, 15.3 pm, 15.4 pm, 15.5 pm, 15.6 pm,

15.7 pm, 15.8 pm, 15.9 pm, 16.0 pm, 16.1 pm, 16.2 pm, 16.3 pm, 16.4 pm, 16.5 pm, 16.6 pm, 16.7 pm, 16.8 pm, 16.9 pm, 17.0 pm, 17.1 pm, 17.2 pm, 17.3 pm, 17.4 pm, 17.5 pm,

17.6 pm, 17.7 pm, 17.8 pm, 17.9 pm, 18.0 pm, 18.1 pm, 18.2 pm, 18.3 pm, 18.4 pm, 18.5 pm, 18.6 pm, 18.7 pm, 18.8 pm, 18.9 pm, 19.0 pm, 19.1 pm, 19.2 pm, 19.3 pm, 19.4 pm,

19.5 pm, 19.6 pm, 19.7 pm, 19.8 pm, 19.9 pm, and/or 20.0 pm.

[0054] Layer 316 may contact electrode 304. Electrode 304 may be the same as or similar to electrode 204, though it need not be. In some embodiments, electrode 304 may be an anode, such as anode 108, while in other embodiments, electrode 304 may be a cathode, such as cathode 102. An interfacial contact 308 may form along the electrode-collector interface, at the contacting point between electrode 304 and layer 316. FIG. 3B illustrates a close-up view of interfacial contact 308 at the electrode-collector interface. Surface-modified current collector 300 and electrode 304 may both have a voltage. As noted herein, voltage can mean voltage potential at a given point; however, for ease of discussion the term voltage is used. Surface-modified current collector 300 containing metallic foil 302 may have a voltage VI and electrode 304 may have a voltage V2. As illustrated in FIG. 3B, VI may be a greater voltage than V2. As such, electric current may flow from the current collector containing metallic foil 302 to electrode 304, while electrons simultaneously flow from electrode 304 to surface-modified current collector 300. Electrical current lines 314 illustrate the path that the electric current may take between metallic foil 302 and electrode 304.

[0055] Layer 316 may reduce electrical contact resistance at interfacial contact 308. As illustrated in FIG. 3B, electrical current lines 314 may not be forced through limited discrete contact points between electrode 304 and metallic foil 302. In contrast to interfacial contact 208 illustrated in FIG. 2C, interfacial contact 308 includes many contact points. By splitting the electrical current, illustrated by electrical current lines 314, over a larger area and contact points, the electrical contact resistance may be reduced. Additionally, decreasing the relative distance of the contact points also reduces the electrical contact resistance by providing more easily accessible pathways for the electrical current to flow. In some embodiments, increasing the contact area of interfacial contact 308 may also decrease electrical contact resistance.

[0056] Layer 316 may reduce electrical contact resistance between metallic foil 302 and electrode 304 by modifying the surface topology of metallic foil 302 and improving the contact mechanics at the electrode-collector interface to facilitate electrical conductivity. Layer 316 may uniformly extend or on contact surface 306 of metallic foil 302 to form a closed layer. The closed layer may be a continuous layer extending on contact surface 306 of metallic foil 302 with less than 20.0 % variation in coverage, such as, for example, from 0.1 % to 20.0 % variation in coverage. For example, the closed layer may continuously extend contact surface 306 of metallic foil 302 with less than 19.0 %, less than 18.0 %, less than 17.0 %, less than 16.0 %, less than 15.0 %, less than 14.0 %, less than 13.0 %, less than 12.0 %, less than 11.0 %, less than 10.0 %, less than 9.0 %, less than 8.0 %, less than 7.0 %, less than 6.0 %, less than 5.0 %, less than 4.0 %, less than 3.0 %, less than 2.0 %, or less than 1.0 % variation in coverage. In some cases, the amount of variation in coverage of the closed layer (e.g., layer 316) on contact surface 306 may be so small as to be considered negligible (e.g., less than 1.0%, less than 0.9 %, less than 0.8 %, less than 0.7 %, less than 0.6 %, less than 0.5 %, less than 0.4 %, less than 0.3 %, less than 0.2 %, or less than 0.1 % variation in coverage).

[0057] Variation in coverage may include gaps or holes or other discontinuities in layer 316 in which contact surface 306 of metallic foil 302 is exposed and/or contacts electrode 304. Variation in coverage may also include changes in the surface topography and contact mechanics. Surface topography may be mainly characterized by surface roughness. Surface roughness is a measure of the texture of a surface. Roughness may play a key role in formation of interfacial contact 308 between electrode 304 and surface-modified current collector 300. A widely used parameter to measure the roughness of a surface is the arithmetic average of the measured profile height deviations, defined by the following equation. Surface roughness (Ra) is calculated as a roughness average of a surface containing N ordered, equally spaced points along a trace, and x_; which is the vertical distance from a mean line to the z^th data point. Height is assumed to be positive in the up direction, away from the bulk material.

[0058] In some embodiments, layer 316 may have or be characterized by a surface roughness (Ra) from 0.001 gm to 1.0 gm (e.g., from 0.01 gm to 1.0 gm, from 0.05 gm to 1 gm, from 0. 1 gm to 1.0 gm, or from 0. 1 gm to 0.75 gm). For example, layer 316 may have a surface roughness (Ra) of 0.001 gm, 0.002 gm, 0.003 gm, 0.004 gm, 0.005 gm, 0.006 gm, 0.007 gm, 0.008 gm, 0.009 gm, 0.01 gm, 0.011 gm, 0.012 gm, 0.013 gm, 0.014 gm, 0.015 gm, 0.016 gm, 0.017 gm, 0.018 gm, 0.019 gm, 0.02 gm, 0.021 gm, 0.022 gm, 0.023 gm, 0.024 gm, 0.025 gm, 0.026 gm, 0.027 gm, 0.028 gm, 0.029 gm, 0.03 gm, 0.031 gm, 0.032 gm, 0.033 gm, 0.034 gm, 0.035 gm, 0.036 gm, 0.037 gm, 0.038 gm, 0.039 gm, 0.04 gm, 0.041 gm, 0.042 gm, 0.043 gm, 0.044 gm, 0.045 gm, 0.046 gm, 0.047 gm, 0.048 gm, 0.049 gm, 0.05 gm, 0.051 gm, 0.052 gm, 0.053 gm, 0.054 gm, 0.055 gm, 0.056 gm, 0.057 gm, 0.058 gm, 0.059 gm, 0.06 gm, 0.061 gm, 0.062 gm, 0.063 gm, 0.064 gm, 0.065 gm, 0.066 gm, 0.067 gm, 0.068 gm, 0.069 gm, 0.07 gm, 0.071 gm, 0.072 gm, 0.073 gm, 0.074 gm, 0.075 gm, 0.076 gm, 0.077 gm, 0.078 gm, 0.079 gm, 0.08 gm, 0.081 gm, 0.082 gm, 0.083 gm, 0.084 gm, 0.085 gm, 0.086 gm, 0.087 gm, 0.088 gm, 0.089 gm, 0.09 gm, 0.091 gm, 0.092 gm, 0.093 gm, 0.094 gm, 0.095 gm, 0.096 gm, 0.097 gm, 0.098 gm, 0.099 gm, 0.1 gm, 0.11 gm, 0.12 gm, 0.13 gm, 0.14 gm, 0.15 gm, 0.16 gm, 0.17 gm, 0.18 gm, 0.19 gm, 0.2 gm, 0.21 gm, 0.22 gm, 0.23 gm, 0.24 gm, 0.25 gm, 0.26 gm, 0.27 gm, 0.28 gm, 0.29 gm, 0.3 gm, 0.31 gm, 0.32 gm, 0.33 gm, 0.34 gm, 0.35 gm, 0.36 gm, 0.37 gm, 0.38 gm, 0.39 gm, 0.4 gm, 0.41 gm, 0.42 gm, 0.43 gm, 0.44 gm, 0.45 gm, 0.46 gm, 0.47 gm, 0.48 gm, 0.49 gm, 0.5 gm, 0.51 gm, 0.52 gm, 0.53 gm, 0.54 gm, 0.55 gm, 0.56 gm, 0.57 gm, 0.58 gm, 0.59 gm, 0.6 gm, 0.61 gm, 0.62 gm, 0.63 gm, 0.64 gm, 0.65 gm, 0.66 gm, 0.67 gm, 0.68 gm, 0.69 gm, 0.7 gm, 0.71 gm, 0.72 gm, 0.73 gm, 0.74 gm, 0.75 gm, 0.76 gm, 0.77 gm, 0.78 gm, 0.79 gm, 0.8 gm, 0.81 gm, 0.82 gm, 0.83 gm, 0.84 gm, 0.85 gm, 0.86 gm, 0.87 gm, 0.88 gm, 0.89 gm, 0.9 gm, 0.91 gm, 0.92 gm, 0.93 gm, 0.94 gm, 0.95 gm, 0.96 gm, 0.97 gm, 0.98 gm, 0.99 gm, and/or 1.0 gm.

[0059] Contact mechanics influencing the electrical conductivity at interfacial contact 308 may include the porosity and material of layer 316. Layer 316 may have electro-mechanical properties to prevent oxidization and/or corrosion along interfacial contact 308 over the lifespan of the battery. For example, layer 316 may prevent lithium alloying of metallic foil 302 by minimizing contact of metallic foil 302 with electrode 304. Layer 316 may also reduce electrical contact resistance because of its porosity. The porosity of layer 316 may increase utilization of the electrode active materials by increasing the contact area of the current collector. The porosity of layer 316 may increase the contact area of surface- modified current collector 300 without forming gaps or vacancies of no contact (i.e., areas between discrete contact points) between electrode 304 and current collector 300, such as illustrated by interfacial contact 308.

[0060] Porosity, or void fraction, may be a measure of the void spaces within layer 316. Porosity is a fraction of the volume of voids per unit weight of layer 316. In some embodiments, layer 316 may have a porosity from 0.05 cm³/g to 0.5 cm³/g (e.g., from 0.06 cm³/g to 0.4 cm³/g, from 0.08 cm³/g to 0.3 cm³/g, or from 0.09 cm³/g to 0.2 cm³/gFor example, layer 316 may have a porosity of 0.05 cm³/g, 0.06 cm³/g, 0.07 cm³/g, 0.08 cm³/g , 0.09 cm³/g, 0.1 cm³/g, 0.11 cm³/g, 0.12 cm³/g, 0.13 cm³/g, 0.14 cm³/g, 0.15 cm³/g, 0.16 cm³/g, 0.17 cm³/g, 0.18 cm³/g, 0.19 cm³/g, 0.2 cm³/g, 0.21 cm³/g, 0.22 cm³/g, 0.23 cm³/g, 0.24 cm³/g, 0.25 cm³/g, 0.26 cm³/g, 0.27 cm³/g, 0.28 cm³/g, 0.29 cm³/g, 0.3 cm³/g, 0.31 cm³/g, 0.32 cm³/g, 0.33 cm³/g, 0.34 cm³/g, 0.35 cm³/g, 0.36 cm³/g, 0.37 cm³/g, 0.38 cm³/g, 0.39 cm³/g, 0.4 cm³/g, 0.41 cm³/g, 0.42 cm³/g, 0.43 cm³/g, 0.44 cm³/g, 0.45 cm³/g, 0.46 cm³/g, 0.47 cm³/g, 0.48 cm³/g, 0.49 cm³/g, and/or 0.5 cm³/g.

[0061] FIG. 4 illustrates an apparatus 400 for continuously making a surface-modified current collector according to some embodiments of the present disclosure. The surface- modified current collector formed by apparatus 400 may be surface-modified current collector 300. The surface-modified current collector may include a metallic foil 402 and a layer 416, which may be similar to metallic foil 302 and layer 316 described above. To form the current collector, apparatus 400 may include a pair of roller units. The pair of roller units may include a first roller unit 420 and a second roller unit 430. First roller unit 420 may be cylindrical in nature, having at least one curved surface 422. In some embodiments, however, first roller unit 420 may be a blade or rod (not shown) instead of a roller unit. First roller unit 420 may have an axis 424 along a length 426. First roller unit 420 may rotate axis 424 towards second roller unit 430. In some embodiments, first roller unit 420 may have a length 426 from 0.5 m (meters) to 5.0 m (e.g., from 0.75 m to 5.0 m, from 1.0 m to 5.0 m, from 1.0 m to 4.0 m, or from 2.0 m to 3.0 m). For example, first roller unit 420 may have a length 426 of 0.5 m, 0.6 m, 0.7 m, 0.8 m, 0.9 m, 1.0 m, 1.1 m, 1.2 m, 1.3 m, 1.4 m, 1.5 m, 1.6 m, 1.7 m, 1.8 m, 1.9 m, 2.0 m, 2.1 m, 2.2 m, 2.3 m, 2.4 m, 2.5 m, 2.6 m, 2.7 m, 2.8 m, 2.9 m, 3.0 m, 3.1 m, 3.2 m, 3.3 m, 3.4 m, 3.5 m, 3.6 m, 3.7 m, 3.8 m, 3.9 m, 4.0 m, 4.1 m, 4.2 m, 4.3 m, 4.4 m, 4.5 m, 4.6 m, 4.7 m, 4.8 m, 4.9 m, and/or 5.0 m.

[0062] Similarly, second roller unit 430 may be cylindrical in nature, having at least one curved surface 432. Second roller unit 430 may also include an axis 434 which second roller unit 430 rotates towards first roller unit 420. Second roller unit 430 may also have a length. The length of second roller unit 430 may be the same as length 426. In some embodiments, the length of second roller unit 430 may be greater than length 426 of first roller unit 420, while in other embodiments, the length of second roller unit 430 may be less than length 426 of first roller unit 420.

[0063] Metallic foil 402 may be fed between first roller unit 420 and second roller unit 430. In some embodiments, metallic foil 402 may be a sheet of material that is continuously fed to the pair of roller units. First roller unit 420 and second roller unit 430 may be positioned parallel to each other to form a space gap 414 between them. Space gap 414 may be uniform along length 426 of the pair of roller units. Space gap 414 may correspond to the amount of current flow between first roller unit 420 and second roller unit 430 that allows for transfer (or deposition) of carbon-containing material 412 onto metallic foil 402. If space gap 414 is too small or too large, burning and/or oxidation may occur during the transfer process. The amount of current flow may vary depending on the material of metallic foil 402 and/or carbon-containing layer 412 and environmental conditions, such as humidity, temperature, pressure, oxygen content, or gas type if processing in an inert atmosphere. In some embodiments, space gap 414 may be from 1.0 mm to 100.0 mm (e.g., from 5.0 mm to 90.0 mm, from 10.0 mm to 80.0 mm, from 20.0 mm to 70.0 mm, or from 30.0 mm to 60.0 mm). For example, space gap 414 may be 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, 8.5 mm, 9.0 mm,

9.5 mm, 10.0 mm, 10.5 mm, 11.0 mm, 11.5 mm, 12.0 mm, 12.5 mm, 13.0 mm, 13.5 mm,

14.0 mm, 14.5 mm, 15.0 mm, 15.5 mm, 16.0 mm, 16.5 mm, 17.0 mm, 17.5 mm, 18.0 mm,

18.5 mm, 19.0 mm, 19.5 mm, 20.0 mm, 20.5 mm, 21.0 mm, 21.5 mm, 22.0 mm, 22.5 mm,

23.0 mm, 23.5 mm, 24.0 mm, 24.5 mm, 25.0 mm, 25.5 mm, 26.0 mm, 26.5 mm, 27.0 mm,

27.5 mm, 28.0 mm, 28.5 mm, 29.0 mm, 29.5 mm, 30.0 mm, 30.5 mm, 31.0 mm, 31.5 mm,

32.0 mm, 32.5 mm, 33.0 mm, 33.5 mm, 34.0 mm, 34.5 mm, 35.0 mm, 35.5 mm, 36.0 mm,

36.5 mm, 37.0 mm, 37.5 mm, 38.0 mm, 38.5 mm, 39.0 mm, 39.5 mm, 40.0 mm, 40.5 mm,

41.0 mm, 41.5 mm, 42.0 mm, 42.5 mm, 43.0 mm, 43.5 mm, 44.0 mm, 44.5 mm, 45.0 mm,

45.5 mm, 46.0 mm, 46.5 mm, 47.0 mm, 47.5 mm, 48.0 mm, 48.5 mm, 49.0 mm, 49.5 mm, 50.0 mm, 50.5 mm, 51.0 mm, 51.5 mm, 52.0 mm, 52.5 mm, 53.0 mm, 53.5 mm, 54.0 mm,

54.5 mm, 55.0 mm, 55.5 mm, 56.0 mm, 56.5 mm, 57.0 mm, 57.5 mm, 58.0 mm, 58.5 mm,

59.0 mm, 59.5 mm, 60.0 mm, 60.5 mm, 61.0 mm, 61.5 mm, 62.0 mm, 62.5 mm, 63.0 mm,

63.5 mm, 64.0 mm, 64.5 mm, 65.0 mm, 65.5 mm, 66.0 mm, 66.5 mm, 67.0 mm, 67.5 mm,

68.0 mm, 68.5 mm, 69.0 mm, 69.5 mm, 70.0 mm, 70.5 mm, 71.0 mm, 71.5 mm, 72.0 mm,

72.5 mm, 73.0 mm, 73.5 mm, 74.0 mm, 74.5 mm, 75.0 mm, 75.5 mm, 76.0 mm, 76.5 mm,

77.0 mm, 77.5 mm, 78.0 mm, 78.5 mm, 79.0 mm, 79.5 mm, 80.0 mm, 80.5 mm, 81.0 mm,

81.5 mm, 82.0 mm, 82.5 mm, 83.0 mm, 83.5 mm, 84.0 mm, 84.5 mm, 85.0 mm, 85.5 mm,

86.0 mm, 86.5 mm, 87.0 mm, 87.5 mm, 88.0 mm, 88.5 mm, 89.0 mm, 89.5 mm, 90.0 mm,

90.5 mm, 91.0 mm, 91.5 mm, 92.0 mm, 92.5 mm, 93.0 mm, 93.5 mm, 94.0 mm, 94.5 mm,

95.0 mm, 95.5 mm, 96.0 mm, 96.5 mm, 97.0 mm, 97.5 mm, 98.0 mm, 98.5 mm, 99.0 mm,

99.5 mm, and/or 100.0 mm. Additionally, the size of space gap 414 may vary depending on the thickness of metallic foil 402. Space gap 414 may allow for metallic foil 402 to be evenly fed between the pair of roller units without allowing for contact of metallic foil 402 with both rollers 420 and 430.

[0064] A carbon-containing material 412 may be on surface 422 of first roller unit 420. In some embodiments, carbon-containing material 412 may be coated or applied to surface 422 of first roller unit 420. In other embodiments, carbon-containing material 412 may be part of first roller unit 420. For example, first roller unit 420 may be made from carbon-containing material 412 or a portion of first roller unit 420 may be made from carbon-containing material 412. In some embodiments, carbon-containing material 412 may be a powder or in an otherwise solid form compacted onto surface 422 of first roller unit 420.

[0065] Second roller unit 430 may be oriented and operationally configured to continuously feed metallic foil 402 in rotation with first roller unit 420. Specifically, second roller unit 430 may be oriented and operationally configured to continuously generate an electrical current between contact surface 406 of metallic foil 402 and carbon-containing material 412 on first roller unit 420. When an electrical current is generated between metallic foil 402 and carbon-containing material 412, a portion of carbon-containing material 412 may transfer onto metallic foil 402 to form a layer 416 on contact surface 406 of metallic foil 402. In some embodiments, metallic foil 402 and contact surface 406 and/or metallic foil 402 and first roller unit 420 may not physically contact each other. Layer 416 may be the same as or similar to layer 316 or may be different than layer 316. In some cases, layer 416 is a closed layer as described above with respect to FIGs. 3A-3B. [0066] Apparatus 400 may include a power supply 440 having a positive terminal and a negative terminal. Power supply 440 may supply an electrical current or charge to each of first roller unit 420 and second roller unit 430. Power supply 440 may be an alternating current (AC) power supply or a direct current (DC) power supply. For example, power supply 440 may be an outlet, a battery, a generator, or any other means of power supply. In some embodiments, first roller unit 420 may be in electrical communication with the positive terminal via line 442 and second roller unit 430 may be in electrical communication with the negative terminal via line 444. An electrical field may be formed between first roller unit 420 and second roller unit 430 using the positive charge and the negative charge supplied by power supply 440.

[0067] Apparatus 400 may be used to continuously make surface-modified current collectors. The continuous surface modification process performed by apparatus 400 may be a process similar to an electro-discharge coating process. FIG. 5 illustrates an electrodischarge process for continuously modifying a surface of a current collector to form a closed layer 416 on metallic foil 402. A cutaway and simplified version of apparatus 400 as discussed with respect to FIG. 4 is illustrated in FIG. 5 to depict how the electro-discharge process is performed using apparatus 400.

[0068] As discussed above, power supply 440 may supply an electrical current to the pair of roller units. Line 442 may supply a positive charge to first roller unit 420, while line 444 may supply a negative charge to second roller unit 430. When the positive charge is supplied to first roller unit 420, first roller unit 420 may act as a positive electrode. When the negative charge is supplied to second roller unit 430, metallic foil 402 may act as a negative electrode. An electrical field may be formed between first roller unit 420 and second roller unit 430 by supplying the electrical charges to the roller units, respectively. The electrical field may be uniform between first roller unit 420 and second roller unit 430 along the length of the roller units. To form a uniform electrical field between first roller unit 420 and second roller unit 430, space gap 414 may be constant along the length of both roller units. The electrical field may form along space gap 414 between first roller unit 420 and second roller unit 430.

[0069] As first roller unit 420, acting as a positive electrode, approaches (due to rotation) second roller unit 430, acting as a negative electrode, the electric field intensity between the two roller units may increase sharply. The spike in electric field intensity may release energy. The release in energy may cause carbon-containing material 412 to transfer/deposit onto contact surface 406 of metallic foil 402. For example, at a specific current density (i.e. , working current) flowing in space gap 414 between first roller unit 420 and the second roller unit 430 carbon-containing material 412 may transfer onto contact surface 406. As depicted, particles 510 of carbon-containing material 412 may transfer off of first roller unit 420 and onto contact surface 406 of metallic foil 402 when second roller unit 430 brings metallic foil 402 within space gap 414 range of first roller unit 420. Simultaneously, when the electric field is generated between the pair of roller units, electrons 122 may flow from the second roller unit 420, acting as the negative electrode, to the first roller unit 410, acting as the positive electrode. The operating parameters for the electro-discharge process are provided in more detail with respect to FIG. 7.

[0070] The electro-discharge process may be performed in the presence of a dielectric fluid. For example, first roller unit 420 and second roller unit 430, or a portion thereof, may be submerged in the dielectric fluid. However, in other embodiments, the electro-discharge process may be performed in a specialized environment. For example, apparatus 400 may be operated in aN2, Ar, or He rich atmosphere. Performing the electro-discharge process in an inert environment may reduce oxidation of metallic foil 402 as well as oxidation of the carbon-containing material 412.

[0071] In some embodiments, apparatus 400 may be part of a continuous roll-to-roll system. FIG. 6 illustrates an exemplary continuous roll-to-roll system 600 including apparatus 601. Continuous roll-to-roll system 600 may be part of a continuous casting and rolling system. Apparatus 601 may be the same as or similar to apparatus 400, or it may be different. Apparatus 601 may include a pair of roller units: first roller unit 620 and second roller unit 630. First roller unit 620 and second roller unit 630 may be the same as or similar to first roller unit 420 and second roller unit 430, or may be different. A surface of first roller unit 620 may include a carbon-containing material 612. Carbon-containing material 612 may be the same as or similar to carbon-containing material 412 or 312, or may be different. Apparatus 601 may include a power supply 640. Power supply 640 may be the same as or similar to power supply 440, or may be different. Power supply 640 may supply a positive charge to first roller unit 620 via line 642 and supply a negative charge to second roller unit 630 via line 644.

[0072] Second roller unit 630 may be oriented to bring a metallic foil 602 into a space gap, such as space gap 414, formed between second roller unit 630 and first roller unit 620. Metallic foil 602 may be the same as or similar to metallic foil 402 or 302, or may be different. Metallic foil 602 may be supplied from a coil 608. A set of rolling stands 626 may provide metallic foil 602 from coil 608 to apparatus 601 by rolling in direction 628. The set of rolling stands 626 may include a single rolling stand; however, any number of rolling stands may be used, such as two, three, or more. In some embodiments, rolling stands 626 may reduce the thickness of metallic foil 602 to a desired gauge. In some cases, the use of a larger number of rolling stands (e.g., three, four, or more) may result in better surface quality for a given total reduction of thickness (e.g., reduction of thickness from before the first rolling stand to after the last rolling stand) because each rolling stand therefore needs to reduce the thickness of metallic foil 602 by a smaller amount, and thus fewer surface defects may be generally imparted on metallic foil 602. The desired gauge may be the thickness of metallic foil as discussed above, such as thickness 205, although it need not be. In some embodiments, some of rolling stands 626 may be hot rolling stands. Some or all of rolling stands 626 may further perform other processing of metallic foil 602, such as surface treatment (e.g., texturing), quenching, preheating, and heat treating. Surface treatments may include cleaning, etching, and/or pretreatment. In some embodiments, such processes may be either wet processes requiring baths or dry processes requiring heat, flame, or plasma.

[0073] Rolling stands 626 may allow for metallic foil 602 to be continuously provided to apparatus 601 for application of carbon-containing material 612 onto metallic foil 602. For example, rolling stands 626 may continuously feed metallic foil 612 to apparatus 601. This may allow for apparatus 601 to continuously operate an electro-discharge process to form closed layer 616 on metallic foil 602.

[0074] FIG. 7 illustrates a flowchart of an exemplary method 700 according to some embodiments. Method 700 will be discussed with reference to apparatus 400 of FIGs. 4 and 5. Method 700 may include step 710. At step 710, a pair of roller units may be provided. The pair of roller units may include first roller unit 420 and second roller unit 430. First roller unit 420 may include carbon-containing material 412 on a surface 422. Metallic foil 402 may be provided to the pair of roller units at block 720. In some embodiments, the metallic foil 402 may be fed to the pair of roller units. As previously described, second roller unit 430 may be oriented to bring metallic foil 402 within space gap 414.

[0075] At step 730, space gap 414 formed between first roller unit 420 and second roller unit 430 may be controlled. Controlling space gap 414 may be important for achieving sufficient transfer of particles 510 from first roller unit 420 onto metallic foil 402. If space gap 414 is too wide, then a higher voltage may be required to establish an electric field but establishing a stable electric field during the electro-discharge process to effectively transfer particles 510 of carbon-containing material 412 onto metallic foil 402 may be difficult. If space gap 414 is too small then a reduced voltage may be required, however, at lower voltages there may not be enough voltage to adequately form an electric field and transfer sufficient particles 510 of carbon-containing material 412. Additionally, space gap 414 that is too small may cause for reduced transfer of particles 510 during the electro-discharge process, causing uneven or undesirable transfer of particles 510 of carbon-containing material 412 onto metallic foil 402.

[0076] In some embodiments, a compaction process may follow the electro-discharge process. In such embodiments, metallic foil 402 with the transferred carbon-containing material 412 forming closed layer 416 may be subjected to compaction to improve the film properties. By applying a compaction pressure to the metallic foil 402 after the electrodischarge process the adhesion and conductivity of closed layer 416 may be improved. In some embodiments, the density and porosity of closed layer 416 may be modified. For example, when the compaction pressure increases, then the density of closed layer 416 may increase and/or the porosity of closed layer 416 may decrease.

[0077] Method 700 may also include step 740. At step 740, an electrical charge may be supplied to the pair of roller units. The electrical charge may be supplied by power supply 440. A positive charge may be supplied to first roller unit 420 via line 442 and a negative charge may be supplied to second roller unit 430 via line 444. An electrical field may be formed between first roller unit 420 and second roller unit 430. The voltage and the current between first roller unit 420 and second roller unit 430 may control the intensity of the electrical field. The voltage and the current between first roller unit 420 and second roller unit 430 may play a vital role in the deposition (transfer) of particles 510 of carbon- containing material 412 onto metallic foil 402, and the ultimate formation of closed layer 416.

[0078] At block 742, method 700 may include controlling the voltage and current between first roller unit 420 and second roller unit 430. The voltage and current may be controlled by adjusting the electrical charge supplied by power supply 440 to the pair of roller units.

During the electro-discharge process, as the current, also known as working current, increases more material (particles 510) may transfer onto metallic foil 402. However, when the working current is too high then the working current may cause degradation of metallic foil 402. For example, a strong spark caused by high currents may remove some of metallic foil 402 or cause damage to metallic foil 402. Too high of working current may also cause oxidation of metallic foil 402 and/or carbon-containing material 412. Since current depends on the surface area of the material forming the gap, current density may be used to quantify the working current. The optimal working current may depend on process conditions and materials used. In some embodiments, the working current may be from 0.5 A/cm² to 10.0 A/cm² (e.g., from 0.8 A/cm² to 10.0 A/cm², from 1.0 A/cm² to 9.0 A/cm², from 2.0 A/cm² to 8.0 A/cm², or from 3.0 A/cm² to 7.0 A/cm²). For example, the working current may be 0.5 A/cm², 0.6 A/cm², 0.7 A/cm², 0.8 A/cm², 0.9 A/cm², 1.0 A/cm², 1.1 A/cm², 1.2 A/cm², 1.3

A/cm², 1.4 A/cm², 1.5 A/cm², 1.6 A/cm², 1.7 A/cm², 1.8 A/cm², 1.9 A/cm², 2.0 A/cm², 2.1

A/cm², 2.2 A/cm², 2.3 A/cm², 2.4 A/cm², 2.5 A/cm², 2.6 A/cm², 2.7 A/cm², 2.8 A/cm², 2.9

A/cm², 3.0 A/cm², 3.1 A/cm², 3.2 A/cm², 3.3 A/cm², 3.4 A/cm², 3.5 A/cm², 3.6 A/cm², 3.7

A/cm², 3.8 A/cm², 3.9 A/cm², 4.0 A/cm², 4.1 A/cm², 4.2 A/cm², 4.3 A/cm², 4.4 A/cm², 4.5

A/cm², 4.6 A/cm², 4.7 A/cm², 4.8 A/cm², 4.9 A/cm², 5.0 A/cm², 5.1 A/cm², 5.2 A/cm², 5.3

A/cm², 5.4 A/cm², 5.5 A/cm², 5.6 A/cm², 5.7 A/cm², 5.8 A/cm², 5.9 A/cm², 6.0 A/cm², 6.1

A/cm², 6.2 A/cm², 6.3 A/cm², 6.4 A/cm², 6.5 A/cm², 6.6 A/cm², 6.7 A/cm², 6.8 A/cm², 6.9

A/cm², 7.0 A/cm², 7.1 A/cm², 7.2 A/cm², 7.3 A/cm², 7.4 A/cm², 7.5 A/cm², 7.6 A/cm², 7.7

A/cm², 7.8 A/cm², 7.9 A/cm², 8.0 A/cm², 8.1 A/cm², 8.2 A/cm², 8.3 A/cm², 8.4 A/cm², 8.5

A/cm², 8.6 A/cm², 8.7 A/cm², 8.8 A/cm², 8.9 A/cm², 9.0 A/cm², 9.1 A/cm², 9.2 A/cm², 9.3

A/cm², 9.4 A/cm², 9.5 A/cm², 9.6 A/cm², 9.7 A/cm², 9.8 A/cm², 9.9 A/cm², and/or 10.0 A/cm²-.

[0079] At block 742, the voltage may also be controlled. To form a uniform closed layer 416 having less than 20 % variation of coverage for metallic foil 402, the voltage may be controlled from 100 V to 300 V. The greater the voltage between the pair of rollers, the stronger the electrical field may be. Up to a certain point, a stronger electrical field may be advantageous because it may facilitate transfer of particles 510 from carbon-containing material 412 onto metallic foil 402. However, beyond a certain voltage, such as 300 V, the electrical field may become too intense, causing high temperatures which may lead to oxidation of metallic foil 402 and/or degradation of metallic foil 402. The voltage may depend on process conditions and material used. In general, the voltage may be adjusted to maintain a stable total current at a given current density. In exemplary cases, the voltage may be controlled from 100 V to 300 V A (e.g., from 125 V to 300 V, from 150 V to 300 V, from 150 V to 250 V, or from 175 V to 225 V).

[0080] In some embodiments, the voltage may be 50 V, 51 V, 52 V, 53 V, 54 V, 55 V, 56

V, 57 V, 58 V, 59 V, 60 V, 61 V, 62 V, 63 V, 64 V, 65 V, 66 V, 67 V, 68 V, 69 V, 70 V, 71

V, 72 V, 73 V, 74 V, 75 V, 76 V, 77 V, 78 V, 79 V, 80 V, 81 V, 82 V, 83 V, 84 V, 85 V, 86

V, 87 V, 88 V, 89 V, 90 V, 91 V, 92 V, 93 V, 94 V, 95 V, 96 V, 97 V, 98 V, 99 V. 100 V,

101 V, 102 V, 103 V, 104 V, 105 V, 106 V, 107 V, 108 V, 109 V, 110 V, 111 V, 112 V, 113 V, 114 V, 115 V, 116 V, 117 V, 118 V, 119 V, 120 V, 121 V, 122 V, 123 V, 124 V, 125 V, 126 V, 127 V, 128 V, 129 V, 130 V, 131 V, 132 V, 133 V, 134 V, 135 V, 136 V, 137 V, 138 V, 139 V, 140 V, 141 V, 142 V, 143 V, 144 V, 145 V, 146 V, 147 V, 148 V, 149 V, 150 V, 151 V, 152 V, 153 V, 154 V, 155 V, 156 V, 157 V, 158 V, 159 V, 160 V, 161 V, 162 V, 163 V, 164 V, 165 V, 166 V, 167 V, 168 V, 169 V, 170 V, 171 V, 172 V, 173 V, 174 V, 175 V, 176 V, 177 V, 178 V, 179 V, 180 V, 181 V, 182 V, 183 V, 184 V, 185 V, 186 V, 187 V, 188 V, 189 V, 190 V, 191 V, 192 V, 193 V, 194 V, 195 V, 196 V, 197 V, 198 V, 199 V, 200 V, 201 V, 202 V, 203 V, 204 V, 205 V, 206 V, 207 V, 208 V, 209 V, 210 V, 211 V, 212 V, 213 V, 214 V, 215 V, 216 V, 217 V, 218 V, 219 V, 220 V, 221 V, 222 V, 223 V, 224 V, 225 V, 226 V, 227 V, 228 V, 229 V, 230 V, 231 V, 232 V, 233 V, 234 V, 235 V, 236 V, 237 V, 238 V, 239 V, 240 V, 241 V, 242 V, 243 V, 244 V, 245 V, 246 V, 247 V, 248 V, 249 V, 250 V, 251 V, 252 V, 253 V, 254 V, 255 V, 256 V, 257 V, 258 V, 259 V, 260 V, 261 V, 262 V, 263 V, 264 V, 265 V, 266 V, 267 V, 268 V, 269 V, 270 V, 271 V, 272 V, 273 V, 274 V, 275 V, 276 V, 277 V, 278 V, 279 V, 280 V, 281 V, 282 V, 283 V, 284 V, 285 V, 286 V, 287 V, 288 V, 289 V, 290 V, 291 V, 292 V, 293 V, 294 V, 295 V, 296 V, 297 V, 298 V, 299 V, and/or 300 V.

[0081] The pulse (time-pulse) at which the electrical charge is supplied by power supply 440 to the pair of roller units may also impact the deposition (transfer) of particles 510 onto metallic foil 402. When the time-pulse increases then the deposition rate may also increase. At greater time-pulse rates, the amount of energy input into the process increases, which may lead to greater temperatures. At greater temperatures, carbon-containing material 412 may more readily transfer from first roller unit 420. However, when the time-pulse increases above a certain point (i.e., 150 ps, 250 ps, 350 ps, 450 ps, 550 ps, 650 ps) then the deposition rate may decrease. Above a certain point, closed layer 416 formed on metallic foil 402 may be uneven (nonuniform) and/or brittle. Moreover, particles 510 transferred onto metallic foil 402 may not properly bond with metallic foil 402 at high time-pulse rates, leading to ineffective formation of closed layer 416. In some embodiments, the pulse may form as a sinus wave, rectangular, or triangle shape waves.

[0082] At step 750, carbon-containing material 412 may transfer onto metallic foil 402 to form a closed layer 416. Specifically, particles 510 of carbon-containing material 412 may transfer from surface 422 of first roller unit 420 onto contact surface 406 of metallic foil 402. Contact surface 406 of metallic foil 402 may contact carbon-containing material 412 at block 752. When contact surface 406 and carbon-containing material 412 both come within space gap 414, particles 510 of carbon-containing material 412 may transfer from first roller unit 420 onto metallic foil 402, at block 754. Second roller unit 430 may be operationally configured (e.g., oriented, positioned, aligned) to bring metallic foil 402 into space gap 414 with carbon-containing material 412. Due to the electrical field, carbon-containing material 412 may readily transfer onto metallic foil 402.

[0083] When particles 510 of carbon-containing material 412 transfer onto metallic foil 402, a closed layer 416 may be formed. Because closed layer 416 is formed from solid material (i. e. , carbon-containing material 412) as opposed to a slurry or liquid, the resulting surface-modified current collector may be achieved without further processing, such as, for example, drying. The resulting surface-modified current collector by method 700 may be surface-modified current collector 300 or 400, or may be another surface-modified current collector.

[0084] In the foregoing specification, aspects of the invention are described with reference to specific embodiments thereof, but those skilled in the art will recognize that the invention is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, embodiments can be utilized in any number of environments and applications beyond those described herein without departing from the broader spirit and scope of the specification. The specification and drawings are, accordingly, to be regarded as illustrative rather than restrictive. Additionally, for the purposes of explanation, numerous specific details were set forth in the foregoing description in order to provide a thorough understanding of various embodiments of the present invention. It will be apparent, however, to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details. In other instances, well-known structures, components, and methods are shown in illustrative form. [0085] It should be appreciated that that any described values may be part of a range. For example when a list of values is provided, a range may be made using any of the values as the upper bound and the lower bound. A range may also be made using any value provided herein with a lower bound of 0. It should also be appreciated that any provided value or range may have a standard deviation of up to 10% percent.

[0086] The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and/or various stages may be added, omitted, and/or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.

[0087] Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, an apparatus for continuously modifying the surface of a current collector has been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations will provide those skilled in the art with an enabling description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

[0088] Also, configurations may be described as a process which is depicted as a flow diagram or block diagram. Although each may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may have additional steps not included in the figure. Furthermore, examples of the methods may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the necessary tasks may be stored in a non- transitory computer-readable medium such as a storage medium. Processors may perform the described tasks.

[0089] Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of the invention. Also, a number of steps may be undertaken before, during, or after the above elements are considered.

ILLUSTRATIONS

[0090] As used below, any reference to a series of illustrations is to be understood as a reference to each of those examples disjunctively (e.g., “Illustrations 1-4” is to be understood as “Illustrations 1, 2, 3, or 4”).

[0091] Illustration 1 is a surface-modified current collector, the surface-modified current collector comprising: a metallic foil comprising an electrically conductive material having a contact surface, wherein the metallic foil has a thickness from 1 pm to 50 pm; a carbon- containing material having an amorphous microstructure, wherein the carbon-containing material comprises: a thickness from 0.05 pm to 5.0 pm; a porosity from 0.05 cm³/g to 0.5 cm³/g; and a surface roughness (Ra) from 0.01 pm to 0.8 pm; and wherein the carbon- containing material extends the contact surface of the metallic foil to form a closed layer, and wherein the closed layer continuously extends the contact surface of the metallic foil with less than 10 % variation of coverage.

[0092] Illustration 2 is the surface-modified current collector of any previous or subsequent illustration, wherein the metallic foil comprises copper, aluminum, titanium, or nickel.

[0093] Illustration 3 is the surface-modified current collector of any previous or subsequent illustration or 2, wherein the surface-modified current collector is a positive current collector and wherein the contact surface of the metallic foil comprising the closed layer is contacted by a positive electrode.

[0094] Illustration 4 is the surface-modified current collector of any one of any previous or subsequent illustration, wherein the surface-modified current collector is a negative current collector and wherein the contact surface of the metallic foil comprising the closed layer is contacted by a negative electrode. [0095] Illustration 5 is the surface-modified current collector of any one of any previous or subsequent illustration, wherein the surface-modified current collector further comprises a current-collecting tab.

[0096] Illustration 6 is the surface-modified current collector of any one of any previous or subsequent illustration, wherein the contact surface comprises an interfacial contact between the metallic foil and an electrode and wherein the interfacial contact has reversible electrochemical capabilities to allow for electron exchange with the electrode.

[0097] Illustration 7 is the surface-modified current collector of any one of any previous or subsequent illustration, wherein the carbon-containing material comprises a carbon allotrope.

[0098] Illustration 8 is the surface-modified current collector of any one of any previous or subsequent illustration, wherein a battery including the surface-modified current collector has a specific capacity from 25 mAh/g to 50 mAh/g.

[0099] Illustration 9 is the surface modified current collector of any one of any previous or subsequent illustration, wherein the metallic foil maintains stability at a working potential from 0.1 V to 5.0 V.

[0100] Illustration 10 is a lithium-ion battery comprising the current collector of any one of any previous or subsequent illustration, wherein the lithium-ion battery comprises an anode, a cathode, and an electrolyte.

[0101] Illustration 11 is a method for continuously modifying a surface of a current collector, the method comprising: providing a pair of roller units comprising a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between, wherein a transferrable carbon-containing material is on a surface of the first roller unit; feeding a metallic foil comprising an electrically conductive material having a contact surface to the pair of roller units; supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit; and transferring at least a portion of the carbon-containing material onto the contact surface of the metallic foil to form a closed layer on the metallic foil.

[0102] Illustration 12 is the method of any previous or subsequent illustration, wherein the second roller unit is oriented to bring the metallic foil into a space gap formed between the second roller unit and the first roller unit. [0103] Illustration 13 is the method of any previous or subsequent illustration or 12, wherein the method further comprises controlling the space gap between the first roller unit and the second roller unit.

[0104] Illustration 14 is the method of any one of any previous or subsequent illustration, wherein supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit comprises: controlling a voltage between the first roller unit and the second roller unit and/or controlling a current between the first roller unit and the second roller unit.

[0105] Illustration 15 is the method of any one of any previous or subsequent illustration, wherein transferring at least a portion of the carbon-containing material to the metallic foil to form the closed layer comprises bringing the contact surface of the metallic foil into the space gap with the surface of the first roller unit such that the carbon-containing material on the surface of the first roller unit transfers onto contact surface of the metallic foil.

[0106] Illustration 16 is the method of any one of any previous or subsequent illustration, wherein controlling the space gap between the first roller unit and the second roller unit comprises maintaining the space gap between the first roller unit and the second roller unit at a distance from 1 mm to 50 mm.

[0107] Illustration 17 is the method of any one of any previous or subsequent illustration, wherein the first roller unit comprises a length from 0.5 meters to 3.0 meters.

[0108] Illustration 18 is the method of any previous or subsequent illustration, wherein controlling the voltage between the first roller unit and the second roller unit comprises maintaining the voltage from 50 V to 300 V.

[0109] Illustration 19 is the method of any previous or subsequent illustration, wherein controlling the current between the first roller unit and the second roller unit comprises applying maintaining a working current from 0.5 A/cm2 to 10 A/cm2.

[0110] Illustration 20 is the method of any one of any previous or subsequent illustration, wherein the carbon-containing material extending the surface of the first roller unit is characterized by an amorphous microstructure.

[oni] Illustration 21 is the method of any one of any previous or subsequent illustration and 20, wherein the closed layer continuously extends the contact surface of the metallic foil with less than 10.0 % variation of coverage and wherein the closed layer comprises: a thickness from 0.05 pm to 5.0 pm; a porosity of from 0.05 cm³/g to 0.5 cm³/g; and a surface roughness (Ra) from 0.01 pm to 0.8 pm.

[0112] Illustration 22 is the method of any one of any previous or subsequent illustration, 20, and 21, wherein providing the metallic foil to the pair of roller units comprises continuously feeding the metallic foil to the pair of roller units.

[0113] Illustration 23 is the method of any previous or subsequent illustration and 20-22, wherein the pair of roller units are part of a continuous roll-to-roll system.

[0114] Illustration 24 is an apparatus for continuously modifying a surface of a current collector, the apparatus comprising: a pair of rollers units comprising a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between, wherein a transferrable carbon-containing material extends a surface of the first roller unit parallel to the second roller unit; and a power source comprising a positive terminal and a negative terminal, wherein the power source is operably coupled with the pair of roller units to supply a current and a voltage to the pair of roller units to form an electrical field between the first roller unit and the second roller unit, wherein the positive terminal is in electrical communication with the first roller unit and the negative terminal is in electrical communication with the second roller unit.

[0115] Illustration 25 is the apparatus of any previous or subsequent illustration, wherein the second roller unit is oriented to bring a metallic foil comprising an electrically conductive material into a space gap that is formed between the second roller unit and the first roller unit.

[0116] Illustration 26 is the apparatus of any one of any previous or subsequent illustration, wherein the power source is a direct current (DC) source.

[0117] All patents, publications and abstracts cited above are incorporated herein by reference in their entirety. The foregoing description of the embodiments, including illustrated embodiments, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or limiting to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. A surface-modified current collector, the surface-modified current collector comprising: a metallic foil comprising an electrically conductive material having a contact surface, wherein the metallic foil has a thickness from 1 pm to 50 pm; and a carbon-containing material having an amorphous microstructure, wherein the carbon-containing material comprises: a thickness from 0.05 pm to 5.0 pm; a porosity from 0.05 cm³/g to 0.5 cm³/g; and a surface roughness (Ra) from 0.01 pm to 0.8 pm; and wherein the carbon-containing material extends the contact surface of the metallic foil to form a closed layer, and wherein the closed layer continuously extends the contact surface of the metallic foil with less than 10.0 % variation of coverage.

2. The surface-modified current collector of claim 1, wherein the metallic foil comprises copper, aluminum, titanium, or nickel.

3. The surface-modified current collector of claim 1 or 2, wherein the surface-modified current collector is a positive current collector and wherein the contact surface of the metallic foil comprising the closed layer is contacted by a positive electrode.

4. The surface-modified current collector of any one of claims 1-3, wherein the surface-modified current collector is a negative current collector and wherein the contact surface of the metallic foil comprising the closed layer is contacted by a negative electrode.

5. The surface-modified current collector of any one of claims 1-4, wherein the surface-modified current collector further comprises a current-collecting tab.

6. The surface-modified current collector of any one of claims 1-5, wherein the contact surface comprises an interfacial contact between the metallic foil and an electrode and wherein the interfacial contact has reversible electrochemical capabilities to allow for electron exchange with the electrode.

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7. The surface-modified current collector of any one of claims 1-6, wherein the carbon-containing material comprises a carbon allotrope.

8. The surface-modified current collector of any one of claims 1-7, wherein a battery including the surface-modified current collector has a specific capacity from 25 mAh/g to 50 mAh/g.

9. The surface modified current collector of any one of claims 1-8, wherein the metallic foil maintains stability at a working potential from 0.1 V to 5.0 V.

10. A lithium-ion battery comprising the current collector of any one of claims 1-9, wherein the lithium-ion battery further comprises an anode, a cathode, and an electrolyte.

11. A method for continuously modifying a surface of a current collector, the method comprising: providing a pair of roller units comprising a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between, wherein a transferrable carbon-containing material is on a surface of the first roller unit; feeding a metallic foil comprising an electrically conductive material having a contact surface to the pair of roller units; supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit; and transferring at least a portion of the carbon-containing material onto the contact surface of the metallic foil to form a closed layer on the metallic foil.

12. The method of claim 11, wherein the second roller unit is oriented to bring the metallic foil into the space gap formed between the second roller unit and the first roller unit.

13. The method of claim 11 or 12, wherein the method further comprises controlling the space gap between the first roller unit and the second roller unit.

14. The method of any one of claims 11-13, wherein supplying an electrical charge to the first roller unit to form a uniform electrical field between the first roller unit and the second roller unit comprises: controlling a voltage between the first roller

36 unit and the second roller unit and/or controlling a current between the first roller unit and the second roller unit.

15. The method of any one of claims 11-14, wherein transferring at least the portion of the carbon-containing material to the metallic foil to form the closed layer comprises bringing the contact surface of the metallic foil into the space gap with the surface of the first roller unit such that the carbon-containing material on the surface of the first roller unit transfers onto the contact surface of the metallic foil.

16. The method of any one of claims 11-15, wherein controlling the space gap between the first roller unit and the second roller unit comprises maintaining the space gap between the first roller unit and the second roller unit at a distance from 1 mm to 50 mm.

17. The method of any one of claims 11-16, wherein the first roller unit comprises a length from 0.5 meters to 3.0 meters.

18. The method of any one of claims 14-17, wherein controlling the voltage between the first roller unit and the second roller unit comprises maintaining the voltage from 50 V to 300 V.

19. The method of any one of claims 14-18, wherein controlling the current between the first roller unit and the second roller unit comprises maintaining a working current from 0.5 A/cm² to 10.0 A/cm².

20. The method of any one of claims 11-17, wherein the carbon-containing material extending the surface of the first roller unit is characterized by an amorphous microstructure.

21. The method of any one of claims 11-17 and 20, wherein the closed layer continuously extends the contact surface of the metallic foil with less than 10 % variation of coverage and wherein the closed layer comprises: a thickness from 0.05 pm to 5.0 pm; a porosity of from 0.05 cm³/g to 0.5 cm³/g; and a surface roughness (Ra) from 0.01 pm to 0.8 pm.

22. The method of any one of claims 11-17, 20, and 21, wherein feeding the metallic foil to the pair of roller units comprises continuously feeding the metallic foil to the pair of roller units.

23. The method of claim any one of claims 11-17 and 20-22, wherein the pair of roller units are part of a continuous roll-to-roll system.

24. An apparatus for continuously modifying a surface of a current collector, the apparatus comprising: a pair of rollers units comprising a first roller unit and a second roller unit positioned parallel to each other to form a space gap there between, wherein a transferrable carbon-containing material extends a surface of the first roller unit parallel to the second roller unit; and a power source comprising a positive terminal and a negative terminal, wherein the power source is operably coupled with the pair of roller units to supply a current and a voltage to the pair of roller units to form an electrical field between the first roller unit and the second roller unit, wherein the positive terminal is in electrical communication with the first roller unit and the negative terminal is in electrical communication with the second roller unit.

25. The apparatus of claim 24, wherein the second roller unit is oriented to bring a metallic foil comprising an electrically conductive material into a space gap that is formed between the second roller unit and the first roller unit.

26. The apparatus of any one of claims 24-25, wherein the power source is a direct current (DC) source.