Smoothing film stack layers with induction heating

Abstract

A method for forming smooth film stack layers for energy storage devices is disclosed herein. In one example, a method of smoothing an outer layer of a film stack of an energy storage device comprises forming the outer layer on a current collector of the film stack and energizing a heat source disposed over the outer layer of the film stack to heat the outer layer. The heating of the outer layer of the film stack causes reflow of the outer layer to reduce defects on an outer layer surface.

Description

SMOOTHING FILM STACK LAYERS WITH INDUCTION HEATINGBACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to methods and apparatus for processing a substrate, and more specifically to smoothing film stack layers with induction heating.Description of the Related Art

[0002] Substrate independent direct transfer (SIDT) is a method to pre-lithiate anodes in energy storage devices in order to improve the life cycles of the batteries. In SIDT processes, lithium is first deposited on a support layer composed of one or more materials such as polyethylene terephthalate (PET), paper, or combinations thereof. The materials on the support layer are directly transferred to the anode for pre-lithiation. A release layer enables transferring lithium and other materials off of the support layer and onto the anode.

[0003] Following SIDT, imperfections on processing equipment may imprint defects onto or within a surface of the lithium of the formed film stack, revealing a rough lithium surface with undesired defects. Such rough lithium surfaces can be a source location for crystal growth. These crystal growth locations are problematic as they may be uncontrolled and degrade the lithium film quality for use in electrochemical devices. For example, the defects on the lithium surfaces may lead to non-uniformity of the surface of the lithium film. As a result, SIDT is not utilized in the battery and capacitor industries, among other industries, as such industries require high-quality alkali metal films (e.g., Li films) that can be used for device integration.

[0004] There is a need for improving the quality of film stack layers for energy storage devices.SUMMARY

[0005] Embodiments of the present disclosure generally relate to methods and apparatus for processing a substrate, and more specifically to smoothing film stack layers with induction heating.

[0006] In one aspect, a method of smoothing an outer layer of a film stack of an energy storage device comprises forming the outer layer on a current collector of the film stack and energizing a heat source disposed over the outer layer of the film stack to heat the outer layer. The heating of the outer layer of the film stack causes reflow of the outer layer to reduce defects on an outer layer surface.

[0007] Implementations can include one or more of the following. The heat source is configured to provide a temperature gradient less than a thickness of the outer layer of the film stack. The heat source is coupled to a platform configured to move the heat source along the outer layer of the film stack. The method further includes actuating the platform across a film stack width. The outer layer is an alkali metalcontaining layer comprising lithium or sodium. The current collector is an anode. A first film stack is formed by substrate independent direct transfer. The heat source does not contact the film stack. The heat source is an inductive heater. The reflow of the outer layer yields a surface roughness of about 6 Ra to about 30 Ra. The surface roughness is about 6 Ra to about 12 Ra.

[0008] In another aspect, a method of smoothing an outer layer of a film stack for an energy storage device comprises forming the outer layer on a current collector of the film stack and energizing an inductive heater disposed over the outer layer of the film stack to heat a surface of the outer layer. The inductive heater is configured to provide a temperature gradient less than a thickness of the outer layer of the film stack. Further, heating the surface of the outer layer causes reflow of the outer layer to reduce defects and form a smoothed surface of the outer layer having a surface roughness of 6 Ra to about 30 Ra.

[0009] Implementations can include one or more of the following. The outer layer is an alkali metal-containing layer. The alkali metal-containing layer comprises lithium or sodium. The film stack is formed by substrate independent direct transfer. The thickness of the outer layer of the film stack is about 1 micron to about 20 microns.The method further includes actuating the inductive heater disposed on a platform across the film stack in a back and forth overlapping pattern.

[0010] In yet another aspect, a method of smoothing an outer layer of a film stack for an energy storage device comprises forming the outer layer on a current collector of the film stack, actuating a platform with a heat source disposed thereon along the outer lithium layer of the film stack traversing a substrate independent direct transfer system, and energizing an inductive heater disposed over and not contacting the outer layer of the film stack to heat a surface of the outer layer. The outer lithium layer is disposed on a current collector layer comprising graphite or copper. The lithium layer has a surface roughness less than 10 micron. The inductive heater is configured to provide a temperature gradient less than a thickness of the outer lithium layer of the film stack. Further, heating the surface of the outer lithium layer causes reflow of the outer lithium layer to reduce defects on an outer lithium layer surface forming a smoothed surface of the outer lithium layer with a surface roughness of 6 Ra to about 12 Ra.

[0011] In another aspect, a non-transitory computer readable medium has stored thereon instructions, which, when executed by a processor, causes the process to perform operations of the above apparatus and / or method.

[0012] In yet another aspect, a flexible substrate processing system is provided. The system includes a pickup hub, a supply hub, a calendaring unit, and a heating unit. The calendering unit includes a calender roller, and is positioned downstream from the supply hub and upstream from the pickup hub. The heating unit has an interior volume. The pickup hub is configured to rotate and assist in conveying a flexible substrate through the interior volume of the heating unit. The heating unit is positioned downstream from the supply hub and upstream from the pickup hub. The heating unit includes one or more heating sources configured to generate and direct thermal energy toward the flexible substrate when the flexible substrate is conveyed through the interior volume of the heating unit.

[0013] Implementations can include one or more of the following. The one or more heating sources include a first heat source and a second heat source, the first heat source is positioned to direct thermal energy to a first portion of the interior volume on a first side of the flexible substrate when the flexible substrate is conveyed throughthe interior volume of the heating unit and the second heating source positioned to direct thermal energy to a second portion of the interior volume on a second side of the flexible substrate opposite to the first side when the flexible substrate is conveyed through the interior volume of the heating unit. The heating unit is positioned downstream from the calendering unit and upstream from the pickup hub. The one or more heating sources are capable of melting, liquefying, and reflowing an alkali metal-containing layer disposed over a current collector layer while not thermally affecting the current collector layer. The one or more heating sources are capable of heating lithium up to or beyond a melting temperature of 181 degrees. The one or more heating sources comprise an induction heater capable of about 1 ,000 BTU / hr to about 50,000 BTU / hr. The one or more heating sources are disposed on a movable platform. The movable platform is actuatable or capable of scanning along a length of the flexible substrate, across a width of the flexible substrate, or both along the length of the flexible substrate and across the width of the flexible substrate.

[0014] In yet another aspect, a flexible substrate processing system for transferring a film from a substrate is provided. The system includes a heating unit and a system controller. The heating unit has an interior volume. The heating unit includes one or more inductive heating sources configured to generate and direct thermal energy toward a flexible substrate when the flexible substrate is conveyed through the interior volume of the heating unit. The system controller is configured to cause the processing system to perform a process. The process includes conveying a flexible carrier from a supply hub toward a pickup hub, the flexible carrier having an alkali metal-containing layer formed thereover, contacting the flexible carrier with the flexible substrate, wherein the alkali metal-containing layer contacts the flexible substrate, separating the flexible carrier from the alkali metal-containing layer, and exposing the alkali metal-containing layer disposed over the flexible substrate to the thermal energy to heat the alkali metal-containing layer.

[0015] Implementations can include one or more of the following. Exposing the alkali metal-containing layer to the thermal energy includes energizing the one or more inductive heating sources disposed over the alkali metal-containing layer to heat a surface of the alkali metal-containing layer, one or more inductive heating sources configured to provide a temperature gradient less than a thickness of the alkali metalcontaining layer. Heating the surface of the alkali metal-containing layer causesreflow of the alkali metal-containing layer to reduce defects and form a smoothed surface of the alkali metal-containing layer having a surface roughness of 6 Ra to about 30 Ra. The alkali metal-containing layer comprises lithium or sodium. The thickness of the alkali metal-containing layer is about 1 micron to about 20 microns. The process further includes actuating the one or more inductive heating sources disposed on a platform across the alkali metal-containing layer disposed over the flexible substrate in a back and forth overlapping pattern. The flexible carrier includes a polymer material and the alkali metal-containing layer includes lithium. The flexible substrate includes a current collector substrate, an anode film, or the anode film formed on the current collector substrate. Contacting the flexible carrier with the flexible substrate includes laminating the alkali metal-containing layer to the flexible substrate.

[0016] In another aspect, a non-transitory computer readable medium has stored thereon instructions, which, when executed by a processor, causes the process to perform operations of the above apparatus and / or method.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the disclosure and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0018] FIG. 1 illustrates a schematic cross sectional view of a film stack according to at least one embodiment of the present disclosure.

[0019] FIG. 2A is a flowchart showing selected operations of a method of smoothing a film stack layer according to at least one embodiment of the present disclosure.

[0020] FIG. 2B-2D illustrate a schematic cross sectional view of a film stack that is processed with operations of the method of FIG. 2A according to at least one embodiment of the present disclosure.

[0021] FIG. 3 illustrates a cross-sectional side view of a flexible substrate processing system according to at least one embodiment of the present disclosure.

[0022] FIG. 4 illustrates a cross-sectional side view of a heating unit included in the flexible substrate processing system of FIG. 3 according to at least one embodiment of the present disclosure.

[0023] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0024] Embodiments of the present disclosure generally relate to techniques for forming smooth film stack layers for energy storage devices. Film stacks described herein can have superior device performance relative to conventional technologies. Methods described herein are reproducible and can yield uniform lithium layers. Further, embodiments described herein can enable streamlined material handling and integration and longer shelf life for the lithium film stacks (e.g., lithium film rolls) than conventional technologies.

[0025] Although embodiments of the present disclosure are described with respect to lithium, it is contemplated that embodiments described herein apply to other materials, such as other alkali metals (e.g., sodium).Example Film Stack

[0026] FIG. 1 illustrates a schematic cross-sectional view of one implementation of a film stack 100. The film stack 100 can be or include a device or a portion of a device. The film stack 100 includes a current collector (CC) layer 102 having a bottom surface 102a and a top surface 102b. The film stack 100 further includes an alkali metal-containing layer 104 (for example, a lithium-containing layer, a sodium-containing layer, a lithium alloy, or a sodium alloy) having a bottom surface 104a disposed on the top surface 102b of the CC layer 102. The alkali metal-containing layer 104 further has a top surface 104b. In some embodiments, the film stack 100 includes non-alkali metals and alloys.

[0027] The top surface 104b may be smoothed to form an alkali metal-containing layer 104 having a substantially uniform thickness across the substrate length, resulting in a smooth and level alkali metal-containing layer 104. After the smoothing operation, the surface roughness (Ra) of the top surface may be about 6 Ra to about 30 Ra, such as about 6 Ra to about 12 Ra, which may exhibit a mirror-like finish.

[0028] In some embodiments, an optional high-purity passivation layer can be disposed on the top surface 104b of the alkali metal-containing layer 104 to, for example, protect the alkali metal-containing layer 104 from unwanted reactions that can affect the performance of the film stack, when, for example, the film stack 100 is used as a battery (or a portion of a battery).

[0029] The film stack 100 can be used in an energy storage device, such as a battery. For example, an energy storage device can include an anode and the film stack 100 disposed over the anode.Example Methods

[0030] Embodiments described herein also relate to methods of forming one or more smooth alkali metal-containing layers. Generally, and in some embodiments, smoothing and / or planarization methods described herein include heating a surface of an alkali metal-containing layer to reflow the surface material of the alkali metalcontaining layer.

[0031] The alkali metal-containing layer can be part of a film stack such as those made by substrate independent direct transfer (SIDT). SIDT is a method for forming electrode device stacks by transferring one or more layers including an alkali metal layer, for example, a lithium metal layer, to a receiving substrate, for example, a current collector in implementations where lithium metal functions as an anode or for pre-lithiating (or pre-sodiating) an anode material which is already formed on the current collector. The alkali metal includes an alkali metal, for example, lithium metal,sodium, potassium, rubidium, cesium, francium, an alloy including the alkali metal, or a combination thereof. The already formed anode material can include or be, but is not limited to, graphite, silicon, silicon graphite, silicon oxide graphite, silicon, tin, hard carbon, metal oxide, or combinations thereof. The alloy including the alkali metal can include an alloy of the alkali metal and the anode material. The current collector can include or be metalized plastic, copper, or combinations thereof. In SIDT processes, alkali metal is formed over a carrier substrate composed of one or more materials such as a polymer substrate, for example, polyethylene terephthalate (PET), paper, or combinations thereof. The materials formed on the carrier substrate are directly transferred to a receiving substrate. The receiving substrate can include or be a current collector, a current collector having anode material formed thereover, a metallized plastic substrate, a separator, or a metallized plastic substrate having alkali metal formed thereover. A release layer may be formed between the alkali metal layer and the carrier substrate. The release layer enables transferring the alkali metal and other materials from the carrier substrate to the receiving substrate.

[0032] Following SIDT, imperfections on processing materials and / or processing equipment, such as the PET, the release layer, or a roller, may imprint defects onto a surface of the lithium of the formed film stack revealing a rough lithium surface with undesired defects. Such rough lithium surfaces can be a source location for crystal growth. These crystal growth locations are problematic as they may be uncontrolled and degrade the desired lithium film quality for use in electrochemical devices. That is, the defects on the lithium surfaces may lead to non-uniformity of the lithium film. As a result, SIDT is not utilized in the battery and capacitor industries, among other industries, as such industries require high-quality alkali metal films (for example, Li films) that can be used for device integration. Utilization of SIDT for such industries, however, can be beneficial because SIDT can enable wider substrate deposition and high throughput. Furthermore, commodity plastic substrates are widely available and are recyclable. Additional benefits include streamline production independent of customer substrate and electrode pattern requirements, good Li edge control by lamination and build device stack thin film layers needed to augment functionality before SIDT, preferably under vacuum, and use of the same deposition system to allow a highest quality interface. In contrast, methods of depositing lithium by evaporation, molten lithium slot die, and molten lithium hot roll transfer, among others,can be problematic for most substrates due to heat exposure during deposition causing warpage. SIDT transfer can remove any thermal issues related to the actual substrate.

[0033] As described herein, a post-SIDT smoothing operation can achieve, for example, improved qualities of metal films for superior device performance.

[0034] FIG. 2A is a flowchart showing selected operations of a method 200 for forming a smooth film stack layer (e.g., an alkali metal-containing layer 104) according to at least one embodiment of the present disclosure. FIG. 2B-2D illustrate a schematic cross sectional view of the film stack 260 that is processed with operations of the method 200 of FIG. 2A according to at least one embodiment of the present disclosure.

[0035] The method 200 can be a continuous process where the film stack 100 is in continuous motion, such that film stack 260 is smoothed continuously.

[0036] The method 200 begins with film stack 260, which may contain a rough top surface 104b having defects 208 (such as pin holes), as illustrated in FIG. 2B. In some embodiments, the film stack 260 has undergone a cleaning operation (not shown) to remove harmful materials on the top surface 104b. As shown in FIG. 2C, at operation 205, heat is applied to film stack 260 to melt and reflow the top surface 104b of the alkali metal-containing layer 104. The alkali metal-containing layer 104 is disposed on the top surface 102b of the CC layer 102. As illustrated in FIG. 2B, the top surface 104b is initially rough and uneven. For example, after an SIDT operation, the top surface 104b may exhibit defects 208 (such as pin holes) imprinted from the PET, release layer, and / or rollers. In some instances, the surface roughness (Ra) of the top surface 104b may be up to about 10 urn, or less than about 9 urn, such as less than about 8 urn, such as less than about 7 urn, such as less than about 6 urn, such as less than about 5 urn. In some embodiments, the pin holes may substantially extend into the alkali metal-containing layer 104. In some embodiments, the thickness of the alkali metal-containing layer 104 varies from about 1 micron (urn) to about 120 urn, such as about 1 urn to about 100 urn along the width of the substrate.

[0037] The heating process of operation 205 can include performing an adjustable heat treatment 254 on film stack 260 using a heat source 252 to form the film stack100. The term “adjustable” means the ability to manipulate the thermal energy provided to the film stack. For example, providing a greater or lesser power to the heater, moving the position of the heater along a length, width, closer and / or farther from the film stack, and the like. As shown in FIG. 2C, the transitional film stack 270 is undergoing a heating operation 205. Here, the defects 208 and / or the roughness of the top surface 104b are softened, partially liquefied, and reflowed, by gravitational force, to create a uniform top surface 104b of the alkali metal-containing layer 104.

[0038] The heating process of operation 205 can be a continuous process where the film stack 260 is in continuous motion such that film stack 100 is produced continuously. In some embodiments, the film stack 260 is continuously traversing below a static heated source 252. In some embodiments, the heat source 252 is mounted on a movable platform capable of scanning the top surface 104b of the alkali metal-containing layer 104 across the width of the film stack. The platform is configured to allow thermal energy to pass to the alkali metal-containing layer 104. In other embodiments, the heat source 252 is configured to scan the top surface 104b of the alkali metal-containing layer 104 along the length of the moving film stack 270 in a predetermined back and forth distance in an overlapping pattern. The film stack 260 may traverse the heat source 252 at a film processing rate of about 0.1 meters / min (m / min) to about 100 m / min, such as about 2 m / min to about 90 m / min, such as about 1 m / min to about 75 m / min, about 1 m / min to about 50 m / min, such as about 1 m / min to about 25 m / min, such as about 1 m / min to about 10 m / min, such as about 2 m / min to about 8 m / min, such as about 3 m / min to about 6 m / min.

[0039] The heating process of operation 205 can be performed in-line as the substrate traverses below an exposed heat source 252. An exposed heat source may be defined as accessible for maintenance without necessitating a stop of production. In some embodiments, heating process is performed in a contained heating chamber configured to perform heating operations such as, for example, a cleaning chamber with heating capabilities. The heating process of operation 205 may utilize a heater capable of melting, liquefying, and reflowing the alkali metal-containing layer 104 while not thermally affecting the CC layer 102. In some embodiments, for example, the heater may be capable of heating lithium up to or beyond the melting temperature of 181 degrees Celsius, such as about 160 degrees Celsius to about 250 degrees Celsius, such as about 170 degrees Celsius to about 230 degrees Celsius, such asabout 180 degrees Celsius to about 220 degrees Celsius, such as about 200 degrees Celsius to about 210 degrees Celsius. Furthermore, the heater may also be capable of adjusting the heating rate for dynamic heat rate fluctuations. For example, the heater may be capable of a higher heating rate for a faster film stack processing rate and a lower heat rate for a slower film stack processing rate. For example, the heating process may be performed by a non-contacting induction heater capable of about 1 ,000 BTU / hr to about 50,000 BTU / hr. In other embodiments, a resister type, a graphite based resistive type, or a radiation source type heater, such as xenon lamp, may be utilized for causing softening, liquefying, and / or reflowing only the alkali metalcontaining layer 104. In some embodiments, the heater may be mounted to a roller that contacts the film stack as the flexible substrate is processed. The heated roller may provide sufficient heat to the traversing substrate to enable reflow and thus smooth the top surface 104b.

[0040] The heating treatment process of operation 205 can be performed for a duration of less than about 10 minutes (min), such as less than about 5 min, such as less than about 2 min, such as less than about 1 min, such as less than about 30 seconds (s), such as less than about 20 s, such as less than about 10 s, or from about 1 s to about 30 s, such as from about 5 s to about 20 s, though other values are contemplated. Adjustment of heat treatment process duration enables further adjustments of the processing rate and the heating rate of the heater. Any of the foregoing numbers can be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0041] In some embodiments, the heating treatment can include a radiofrequency (RF) power source to energize, for example, an inductive heater. The RF power source may provide alternating current (AC) power to be utilized to energize the heater for processing the film stack 270. The RF power source can be set to a frequency range that is from about 400 kilohertz (kHz) to about 20 megahertz (MHz), such as about 1 MHz to about 13.56 MHz, such as about 1 MHz to about 5 MHz, though other values are contemplated. Any of the foregoing numbers can be used singly to describe an open-ended range or in combination to describe a close-ended range.

[0042] The heating treatment at operation 205 is configured to heat the alkali metal-containing layer 104 while not thermally affecting the CC layer 102. Forexample, the heat source 252 applies a temperature gradient within alkali metalcontaining layer 104. However, in various embodiments, the temperature gradient does not substantially penetrate beyond the thickness of the alkali metal-containing layer 104. In some embodiments, the top surface 104b exhibits an elevated temperature while the interface between the bottom surface 104a and the top surface 102b of the CC layer 102 is not significantly affected by the heating treatment. In various embodiments, the following equation may be used to configure the temperature gradient to a depth equal to or less than the thickness of the alkali metalcontaining layer 104.D = 5000(— )1 / 2Equation (1 ) -f wherein:D = depth in centimeters (cm) p = material resistivity in Ohm-cm = relative magnetic permeability of the material f = AC field frequency in hertz (Hz)Equation (1 ) relates the material properties to the applied heat provided to specific depths. Therefore, dynamic heat controls may be configured to target specific depths so as the CC layer 102 remains undamaged from heat while the alkali metalcontaining layer 104 can be conditioned to soften and reflow providing a smoothing operation 210. For example, the thickness of the alkali metal-containing layer 104 can be about 1 micron to about 20 microns and, therefore, the depth can be set below the thickness of the alkali metal-containing layer 104.

[0043] The method 200 further includes smoothing a surface (for example, top surface 104b) of the alkali metal-containing layer 104 at operation 210. FIG. 2D illustrates the resulting film stack 100 after film stack 270 of FIG. 2C has undergone operation 210 as illustrated in FIG 2C. Here, surface smoothing can include actively or passively reflowing of the top surface 104b to close and / or reduce the defects 208 present on film stack 260. Moreover, by smoothing the film stack 260, the crystal growth of, for example, lithium crystals, is reduced to increase the longevity of the filmstack 100 resulting in longer storage options and increased performance of the electronic device, such as a battery.Example Processing Chamber

[0044] Embodiments of the present disclosure generally relate to flexible substrate processing systems that include one or more heating units to treat a recently exposed surface of a film positioned on a flexible substrate. One exemplary use of the processing methods provided in this disclosure include heating a surface of a lithium film that can be used as part of an electrode in a lithium ion-battery. For example, a lithium film can be transferred from a flexible carrier (for example, a polymer-based carrier) to a flexible substrate (for example, a flexible copper substrate) by having the flexible carrier and the flexible substrate pass through a calendering unit and then peeling away the flexible carrier. Transferring the lithium film to the flexible substrate exposes a new surface of the lithium film to the surrounding environment when the flexible carrier is peeled away from the flexible substrate. This newly exposed surface can be rough, uneven, and contain defects from the processing that can negatively affect the performance of the lithium film in a lithium-ion battery. For example, non- uniform surfaces of the lithium layers can negatively affect the performance of using a lithium film on the anode of a lithium-ion battery.

[0045] FIG. 3 illustrates a cross-sectional side view of a flexible substrate processing system 300 according to at least one embodiment of the present disclosure. The processing system 300 includes equipment for transferring lithium films on a first flexible carrier 310 and a second flexible carrier 320 to each side of a flexible substrate 330, so that the flexible substrate 330 with the lithium films can be used as an electrode (for example, an anode) in a lithium-ion battery. The processing system 300 includes a calendering unit 340 to transfer the lithium films on the flexible carriers 310, 320 to the flexible substrate 330. The processing system 300 further includes a heating unit 400 for smoothing the top surface of lithium films before the lithium films are transferred onto the flexible substrate 330.

[0046] The processing system 300 includes a first flexible carrier supply hub 315. A supply roll 311 of the first flexible carrier 310 is positioned on the first flexible carrier supply hub 315. In some embodiments, the first flexible carrier 310 can be formed of a polymer material, such as polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polyimide (PI), or combinations thereof. A lithium film (not shown in FIG. 3) is positioned on the lower side 31 OL of the first flexible carrier 310, so that this lithium film faces an upper surface 330LI of the flexible substrate 330 as the first flexible carrier 310 and the flexible substrate 330 are conveyed through the calendering unit 340. This lithium film is shown as the lithium film 401 in FIG. 4 after being transferred to the flexible substrate 330. The upper surface 330LI of the flexible substrate 330 is on an opposite side relative to a lower surface 330L of the flexible substrate 330. The upper surface 330LI is also referred to as the first surface or the first side of the flexible substrate 330 while the lower surface is also referred to as the second surface or the second side of the flexible substrate 330.

[0047] The processing system 300 includes a second flexible carrier supply hub 325. A supply roll 321 of the second flexible carrier 320 is positioned on the second flexible carrier supply hub 325. In some embodiments, the second flexible carrier 320 can be formed of a same material (for example, PET) as the first flexible carrier 310. A lithium film (not shown in FIG. 3) is positioned on the upper side 320LI of the second flexible carrier 320, so that this lithium film faces the lower surface 330L of the flexible substrate 330 as the second flexible carrier 320 and the flexible substrate 330 are conveyed through the calendering unit 340. This lithium film is shown as the lithium film 402 in FIG. 4 after being transferred to the flexible substrate 330.

[0048] In some embodiments, the lithium films on the first flexible carrier 310 and the second flexible carrier 320 can be formed of lithium metal, another alkali metals or an alloy including an alkali metal.

[0049] The processing system 300 includes a flexible substrate supply hub 335. A supply roll 331 of the flexible substrate 330 is positioned on the flexible substrate supply hub 335. In some embodiments, the flexible substrate 330 can be formed of one or more of copper, graphite, silicon, silicon graphite, silicon oxide graphite, silicon, metalized plastic, or other materials.

[0050] The processing system 300 further includes the calendering unit 340. The calendering unit 340 includes a first calender roller 341 and a second calender roller 342. The first flexible carrier 310, the second flexible carrier 320, and the flexible substrate 330 are arranged to be conveyed along a path that extends between the first calender roller 341 and the second calender roller 342. The flexible substrate330 is positioned between the first flexible carrier 310 and the second flexible carrier 320 when the first flexible carrier 310, the second flexible carrier 320, and the flexible substrate 330 are conveyed between the first calender roller 341 and the second calender roller 342. The calender rollers 341 , 342 exert a high amount of pressure on the flexible carriers 310, 320 and the flexible substrate 330 that causes the lithium film on each of the flexible carriers 310, 320 to be transferred to the flexible substrate 330. In some embodiments, a release layer is disposed on each of the flexible carriers 310, 320 between the corresponding flexible carrier 310, 320 and the lithium film on that flexible carrier. In some embodiments, the release layer can be formed of siloxane.

[0051] The processing system 300 includes a first flexible carrier pickup hub 316. A pickup roll 312 of the first flexible carrier 310 is positioned on the first flexible carrier pickup hub 316. The lithium film is no longer on the first flexible carrier 310 when the first flexible carrier 310 is wound onto the first flexible carrier pickup hub 316 because the lithium film previously on the first flexible carrier 310 is transferred onto the flexible substrate 330 by the calendering unit 340.

[0052] The processing system 300 includes a second flexible carrier pickup hub 326. A pickup roll 322 of the second flexible carrier 320 is positioned on the second flexible carrier pickup hub 326. The lithium film is no longer on the second flexible carrier 320 when the second flexible carrier 320 is wound onto the second flexible carrier pickup hub 326 because the lithium film previously on the second flexible carrier 320 is transferred onto the flexible substrate 330 by the calendering unit 340.

[0053] The processing system 300 includes a flexible substrate pickup hub 336. A pickup roll 332 of the flexible substrate 330 is positioned on the flexible substrate pickup hub 336. The flexible substrate 330 includes a lithium film on each of the upper surface 330LI and the lower surface 330L of the flexible substrate 330. These lithium films are transferred from the respective flexible carriers 310, 320 onto the flexible substrate 330 by the calendering unit 340.

[0054] The processing system 300 further includes a plurality of rollers 381 -388. In some embodiments, each of the rollers 381-388 can be passive rollers. The rollers 381-388 can assist in applying proper tension to and assist in changing the direction of the flexible carriers 310, 320 and the flexible substrate 330 during the movement of each of the flexible carriers 310, 320 and the flexible substrate 330 through thedifferent portions of the processing system 300. Some of the rollers 381 -388 can also assist in moving the flexible carriers 310, 320 closer to or further away from the flexible substrate 330. For example, the second and third rollers 382, 383 assist in bringing the flexible carriers 310, 320 into contact with the flexible substrate 330 before the flexible carriers 310, 320 and the flexible substrate 330 are conveyed through the calendering unit 340. Additionally, the fourth and fifth rollers 384, 385 provide a location at which tension can be applied to the flexible carriers 310, 320 to peel these flexible carriers 310, 320 away from the flexible substrate 330. In some embodiments, one or more of the rollers 381 -388 can instead be a bar, such as metal bar, that can apply tension to the carrier or flexible substrate during the movement of the carrier or flexible substrate.

[0055] In some embodiments, the heating unit 400 is placed within a short distance from the rollers 384, 385 to increase the duration of the time for the smoothing to occur after heating the flexible substrate. In some embodiments, the corresponding heating unit 400 can be positioned within two feet of the rollers 384, 385, such as within one foot, such as within six inches of the rollers 384, 385. Similarly, in some embodiments, the corresponding heating unit 400 can be positioned within two feet of the calender rollers 341 , 342, such as within one foot, such as within six inches of the rollers 341 , 342.

[0056] The processing system 300 can further include actuators (not shown) configured to rotate each of the hubs 315, 316, 325, 326, 335, 336, so that the flexible carriers 310, 320 and the flexible substrate 330 can be conveyed from the corresponding supply hub 315, 325, 335, through the calendering unit 340, and to the corresponding pick hub 316, 326, 336. The processing system 300 can further include one or more actuators (not shown) to rotate the calender rollers 341 , 342 of the calendering unit 340. The rotational speed of the actuators can be adjusted to control the speed at which the flexible substrate 330 and flexible carriers 310, 320 are conveyed through the processing system 300.

[0057] In the processing system 300, the flexible substrate 330 is conveyed along a path from the supply roll 331 that is supported by the supply hub 335, past the first roller 381 , between the second and third rollers 382, 383, between the calender rollers 341 , 342, between the fourth and fifth rollers 384, 385, through the heating unit 400past the eighth roller 388, and to the pickup roll 332 around the pickup 336. The flexible substrate pickup hub 336 is configured to rotate and assist in conveying the flexible substrate through the interior volume of the corresponding heating unit 400 after the flexible substrate 330 passes between the first calender roller 341 and the second calender roller 342. Similarly, the pickup hubs 316, 326 are configured to rotate and assist in conveying the flexible carriers along paths between the flexible carrier supply hubs 315, 325 and the pickup hubs 316, 326.

[0058] The processing system 300 can also include a controller 305 for controlling processes performed by the processing system 300. The controller 305 can be any type of controller used in an industrial setting, such as a programmable logic controller (PLC). The controller 305 includes a processor 307, a memory 306, and input / output (I / O) circuits 308. The controller 305 can further include one or more of the following components (not shown), such as one or more power supplies, clocks, communication components (for example, network interface card), and user interfaces typically found in controllers for semiconductor equipment.

[0059] The memory 306 can include non-transitory memory. The non-transitory memory can be used to store the programs and settings described below. The memory 306 can include one or more readily available types of memory, such as read only memory (ROM) (for example, electrically erasable programmable read-only memory (EEPROM), flash memory, floppy disk, hard disk, or random access memory (RAM) (for example, non-volatile random access memory (NVRAM).

[0060] The processor 307 is configured to execute various programs stored in the memory 306 such as a program configured to execute methods described herein. During execution of these programs, the controller 305 can communicate to I / O devices through the I / O circuits 308. For example, during execution of these programs and communication through the I / O circuits 308, the controller 305 can control outputs (for example, the actuators connected to the different hubs and the calendering unit 340). The memory 306 can further include various operational settings used to control the processing system 300. For example, the settings can include speed settings for the actuators connected to the hubs as well as settings to control the heating unit 400 described below.

[0061] FIG. 4 illustrates a cross-sectional side view of the heating unit 400 included in the flexible substrate processing system of FIG. 3 according to at least one embodiment of the present disclosure. In FIG. 4, an upper lithium film 401 (first lithium film) is positioned on the upper surface 330LI of the flexible substrate 330, and a lower lithium film 402 (second lithium film) is positioned on the lower surface 330L of the flexible substrate 330. The flexible substrate 330 and the lithium films 401 , 402 can be conveyed in a direction D through the heating unit 400 and towards the flexible substrate pickup hub 336 (see FIG. 3). The upper lithium film 401 includes an outer surface 403. The lower lithium film 402 includes an outer surface 404. The outer surfaces 403, 404 may be a rough surface 412 and / or contain defects 208 when the first flexible carrier 310 and the second flexible carrier 320 are peeled away from the flexible substrate 330 after being conveyed through the calendering unit 340 and passing the rollers 384, 385 (see FIG. 3).

[0062] The heating unit 400 comprises a plurality of heating sources, for example, 452LI and 452L, configured to heat lithium films 401 , 402 as the flexible substrate 330 is conveyed in a direction D. The heating sources 452LI and 452L are disposed on movable platforms 410, 411. Each movable platform 410, 411 may be movable independently or in synchronization with each other. The movable platform 410, 411 is illustrated as actuatable (or capable of scanning) along the length of the flexible substrate 330 however, the movable platform 410, 411 may actuate across the width of the flexible substrate 330. As depicted, the movable platform 410, 411 moves in directions B, F for a predetermined distance to encourage adequate heat treatments to lithium film 401 , 402.

[0063] As illustrated in the embodiment of Figure 4, rough surface 412 and / or defects 208 are disposed on or within the lithium films 401 , 402. Smooth surfaces 420 are the resulting surfaces after the lithium films 401 , 402 have been heat treated to soften and uniformly level the lithium to create a smoothed surface.

[0064] Implementations and all of the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of them. Implementations described herein can be implemented as one or more non-transitorycomputer program products, i.e. , one or more computer programs tangibly embodied in a machine readable storage device, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.

[0065] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0066] Embodiments of the present disclosure generally relate to film stacks for electronic devices and to methods of forming film stacks. Film stacks described herein can have superior device performance relative to conventional technologies. Methods described herein are reproducible and can yield uniform passivation layers. Further, embodiments described herein can enable, for example, streamlined material handling and integration and longer shelf life for the passivated film stacks (passivated film rolls) than conventional technologies.

[0067] As is apparent from the foregoing general description and the specific aspects, while forms of the aspects have been illustrated and described, various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, it is not intended that the present disclosure be limited thereby. Likewise, the term “comprising” is considered synonymous with the term “including.” Likewise whenever a composition, process operation, process operations, an element or a group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “Is” preceding the recitation of the composition, process operation, process operations, element, or elements and vice versa, such as the terms “comprising,” “consisting essentially of,” “consisting of” also include the product of the combinations of elements listed after the term.

[0068] For purposes of this present disclosure, and unless otherwise specified, all numerical values within the detailed description and the claims herein are modified by“about” or “approximately” the indicated value, and consider experimental error and variations that would be expected by a person having ordinary skill in the art. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the subranges 1 to 4, 1 .5 to 4.5, 1 to 2, among other subranges. As another example, the recitation of the numerical ranges 1 to 5, such as 2 to 4, includes the subranges 1 to 4 and 2 to 5, among other subranges. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the numbers 1 , 1.5, 2, 2.75, 3, 3.80, 4, 5, among other numbers. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0069] As used herein, the indefinite article “a” or “an” shall mean “at least one” unless specified to the contrary or the context clearly indicates otherwise. For example, aspects comprising “a layer” includes aspects comprising one, two, or more layers, unless specified to the contrary or the context clearly indicates only one layer is included.

[0070] While the foregoing is directed to aspects of the present disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

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