Patent Publication Number: US-2021193986-A1

Title: Method and apparatus for making lithium ion battery electrodes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/951,398, filed Dec. 20, 2019, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This specification relates to methods and equipment for making electrodes and electrode assemblies of lithium-ion cells. 
     INTRODUCTION 
     This section provides information helpful in understanding the invention but that is not necessarily prior art. 
     Assemblies of lithium-ion battery cells are used in many applications, from rechargeable batteries for laptops and other personal devices to use in providing motive power in automotive vehicles. Each lithium-ion cell of a battery may provide an electrical potential of about three to four volts and a direct electrical current, depending on the composition and mass of the electrode materials in the cell. Lithium-ion battery cells can be discharged and re-charged over many cycles. A battery may be assembled by combining a suitable number of individual cells in a combination of electrical parallel and series connections to satisfy voltage and current requirements for an electric device or motor. For example, the assembled battery for an automotive vehicle may have perhaps three hundred individually packaged cells that are electrically interconnected to provide forty to four hundred volts and sufficient electrical power to an electrical traction motor to drive a vehicle. 
     Each lithium-ion cell typically comprises a negative electrode layer (anode, during cell discharge), a positive electrode layer (cathode, during cell discharge), a thin, porous separator layer interposed in face-to-face contact between parallel, facing, electrode layers, a liquid, lithium-containing, electrolyte solution filling the pores of the separator and contacting the facing surfaces of the electrode layers for transport of lithium ions during repeated cell discharging and re-charging cycles, and a thin layer of a metallic current collector. It is desirable to have a manufacturing process that does not waste the expensive materials used in making the lithium ion components. Because a battery requires such a great number of lithium-ion cells to provide sufficient electrical power to an electrical traction motor to drive a vehicle, an efficient, high quality production method is a key commercial consideration for this end use. 
     Present production methods have several drawbacks. For example, electrodes are made by spreading or spraying a liquid slurry composition containing electrode material, conductive carbon materials, and a polymeric binder in a solvent system onto one or both sides of a thin metal foil, which serves as the current collector for the electrode. Thus, the electrodes have been made by dispersing mixtures of binders and active particulate materials in a suitable liquid and depositing the wet mixture as a coating layer of controlled thickness on the surface of a current collector metal foil. The deposited slurry layer must then be dried, e.g. in an oven, to force off the solvent, then pressed between calendering rollers to fix the resin-bonded electrode particles to their respective current collector surfaces. The electrodes formed on conductive metal current collector foil sheets of a suitable area and shape may then be cut (if necessary), folded, rolled, or otherwise shaped for assembly into lithium-ion cell containers with suitable porous separators and a liquid electrolyte. 
     This current process requires a large manufacturing footprint for producing the liquid slurry mixture and for the separate coating, drying, calendering, and assembly stations, and it requires high capital investment for the equipment as well as high energy costs, particularly in the drying step. Further, use of solvents may introduce health and fire hazards and produce regulated emissions. 
     Gayden, US Patent Application Publication 2016/0254533 describes manufacturing electrode members using an atmospheric plasma stream to heat the electrode material and deposit it on thin sheet substrates. The plasma stream containing the particles is directed on a substrate supported on a flat working surface. There is a significant loss of electrode material in this deposition arrangement due to overspray. 
     It would, therefore, be desirable to improve the process for manufacture of lithium-ion cells. 
     SUMMARY 
     This need is met by a method now disclosed of depositing particles of an active electrode material and a metal (referred to together as “electrode material”) from an atmospheric plasma onto a lithium-ion cell substrate, e.g. a metal foil or separator film, as the substrate enters a gap between opposing calendering rolls. The active electrode material and the metal may be deposited as separate particles, whether from the same or from different atmospheric plasma deposition devices, or may be deposited as composite particles comprising particles of the metal and the active electrode material adhered together. The electrode material particles may be deposited from the atmospheric plasma directly into the gap or be directed onto the substrate in the gap. The metal particles (or metal portions of the composite particles) are surface-activated, surface-softened, and/or surface-melted (hereinafter referred to together as “surface-activated”) by the atmospheric plasma such that the deposited electrode material is compressed between the calendering rolls into a coherent electrode layer adhering to the substrate. The calendering rolls need not be heated or may optionally be heated. The method may be used with cathode or anode materials deposited from the atmospheric plasma and may be used to make an electrode layer on a single side or on both sides of the substrate and/or sandwiched between substrates. The substrate may be sheetfed sheets or may be in the form of a continuous roll (also called a web). 
     One or more than one atmospheric plasma deposition device may be used to deposit the electrode material particles, depending on factors such as the size and deposition rate of the atmospheric plasma deposition device, the width of the substrate, and the desired electrode layer thickness and density. For example, for a thicker or denser electrode layer, a plurality of atmospheric plasma deposition devices may be positioned to deposit the electrode material particles in generally a same area of the gap as the substrate passes in between the calendering rolls such that more electrode material is deposited per unit area of substrate than could be deposited with fewer atmospheric plasma deposition devices. In another example, for a wider substrate a plurality of atmospheric plasma deposition devices may be positioned to deposit the electrode material particles in generally adjacent or overlapping areas width-wise across the substrate to prepare a generally uniform electrode layer across the width of the substrate. Electrode layer thickness and/or density may be controlled through setting the width of the gap into which the electrode material is deposited. 
     In an embodiment of the process, the lithium-ion cell substrate may be drawn through a gap between an opposing pair of calendering rolls with a first side against a first one of the calendering rolls, with deposition of electrode material from an atmospheric plasma deposition device into the gap between the second side of the substrate and the second calendering roll, the calendering rolls pressing the deposited electrode material into an electrode layer that adheres on the second side of the substrate. A second lithium-ion cell substrate may be concurrently drawn through the gap with a first side against the second calendering roll and a second side facing the first lithium-ion cell substrate, the atmospheric plasma deposition device depositing the electrode material between the two substrates, and the calendering rolls pressing the two substrates and deposited electrode material together to sandwich the electrode layer between the two lithium-ion cell substrates. Surface activation in the atmospheric plasma deposition of the metal particles of the electrode material or metal regions of composite electrode material particles causes the surface activated metal to adhere to other particles and to the substrates. For example, the lithium-ion cell substrate drawn through the gap with a first side against a first one of the opposing pair of calendering rolls may be a metal foil and the second lithium-ion cell substrate drawn through the gap with a first side against a second one of the opposing pair of calendering rolls may be a separator sheet, or vice versa. After leaving the calendering rolls, the electrode layer-substrate assembly, optionally with the second substrate on the opposite side of the electrode layer, may be cut into a shape to be assembled into lithium ion cells, e.g. slit into strips that may be further cut such as with a laser into individual lithium ion cell assemblies, or collected, e.g., by rolling the electrode layer-substrate assembly up on an uptake roller, for later fabrication into lithium ion cells. 
     In another embodiment of the process, an electrode layer may be built up by passing through successive pairs of calendering rolls, each succeeding pair of calendering rolls being separated by a greater gap width between the rolls than the previous pair of calendering rolls, so that an additional amount of electrode material may be deposited by atmospheric plasma deposition into the gap between the rolls and pressed onto the existing electrode layer by the rolls to make a thicker electrode layer. In this embodiment, the lithium-ion cell substrate may be drawn through a gap of a first width with a first side against a first one of a first opposing pair of calendering rolls, with deposition of electrode material from an atmospheric plasma deposition device into the gap of the first width between the second side of the substrate and the second calendering roll, the calendering rolls pressing the deposited electrode material into an electrode layer of a first thickness adhered on the second side of the substrate. The substrate is then drawn through a second, wider gap having a second width greater than the first width, with a first side against a first one of a second opposing pair of calendering rolls, with deposition of electrode material from a second atmospheric plasma deposition device into the second gap between the electrode layer already on the substrate and the second calendering roll of the second pair of calendering rolls, the second pair of calendering rolls pressing the electrode material deposited from the second plasma deposition device to form an electrode layer of a second thickness greater than the first thickness on the second side of the substrate. The substrate may pass through further pairs calendering rolls set progressively further apart, with additional electrode material being deposited by atmospheric plasma deposition into a gap between the calendering rolls and onto the electrode layer so as to continue to build up the thickness of the electrode layer on the first substrate until a desired final electrode layer thickness is reached between a final pair of calendering rolls. Optionally, a second lithium-ion cell substrate may be concurrently drawn through the gap between the final pair of calendering rolls with a first side of the second substrate against a calendering roll and a second side facing the electrode layer on the first lithium-ion cell substrate, an atmospheric plasma deposition device depositing the final amount of electrode material, and the calendering rolls pressing the two substrates and deposited electrode material together to sandwich the electrode layer of the final desired thickness between the two lithium-ion cell substrates, which may be (as described above) a metal foil and a separator sheet. In a further method, after the electrode layer of the final desired thickness is formed on the first substrate, the assembly of electrode layer-first substrate may be drawn between a pair of calendering rolls with the electrode layer facing a gap between the rolls, and metal particles may be deposited from an atmospheric plasma into the gap and calendered between the rolls to form a metal current collector layer on the electrode layer. The electrode layer-substrate assembly, optionally with the second substrate or plasma-deposited current collector layer on the opposite side of the electrode layer or current collector layer, may (as described above) be cut into a final shape to be assembled into lithium ion cells or collected, e.g., by rolling the electrode layer-substrate assembly up on an uptake roller, for later further fabrication steps. 
     In another embodiment, a lithium ion cell substrate may be drawn through the gap with a first layer of a first electrode material applied by atmospheric plasma deposition to a first side of the substrate and a second layer of a second electrode material applied by atmospheric plasma deposition to a second side of the substrate; wherein, passing between the opposing calendering rolls, the first layer is pressed between a first calendering roll and the first side into a first electrode layer and the second layer is pressed between a second calendering roll and the second side into a second electrode layer. The first electrode material may be the same as the second electrode material or the first electrode material may have a different active electrode material and/or metal than the second electrode material. In an embodiment, the first electrode material is an anode material, the second electrode material is a cathode material, and the substrate is a porous separator sheet. In this embodiment, there may be a partition between the cathode material and anode material sides to prevent cross-contamination. Also in this embodiment, a first metal foil may be drawn through the gap against a first one of the calendering rolls and a second metal foil may be drawn through the gap against a second one of the calendering rolls to be pressed into an assembly of metal foil-anode layer-porous separator-cathode layer-metal foil. In another embodiment, the first electrode material and the second electrode materials are either both anode materials or are both cathode materials, and the substrate is a metal foil (e.g., current collector for the lithium ion cell). In a further method, the first electrode layer is an anode layer, the second electrode layer is a cathode layer, and the anode layer-substrate-cathode layer assembly may be drawn between a second pair of calendering rolls with one or both of the electrode layers facing a gap between the rolls, and metal particles may be deposited from an atmospheric plasma into the gap and calendered between the rolls to form a metal current collector layer on the one or both electrode layers. After leaving the calendering rolls, the product lithium ion cell assembly may be cut into a final shape to be assembled into lithium ion cells and batteries, e.g. slit into strips that may be further cut such as with a laser into individual lithium ion cell assemblies, or collected, e.g., by rolling the electrode layers-substrate(s) assembly up on an uptake roller, for later further fabrication steps. 
     In another embodiment of the process in which a lithium ion cell substrate is drawn through the gap with a first layer of a first electrode material applied by atmospheric plasma deposition to a first side of the substrate and a second layer of a second electrode material applied by atmospheric plasma deposition to a second side of the substrate, the electrode layer on the first side or on the second side or on both sides may be built up by passing through successive pairs of calendering rolls, each succeeding pair of calendering rolls having a greater gap width between the substrate and the calendering roll on the substrate side of the electrode layer being built up than that provided by the previous pair of calendering rolls so that an additional amount of electrode material may be deposited by atmospheric plasma deposition into the gap between the substrate and the calendering roll and pressed by the calendering rolls to make a thicker electrode layer. In this embodiment, the lithium-ion cell substrate may be drawn through a gap between a first opposing pair of calendering rolls, with deposition of electrode material from an atmospheric plasma deposition device into a gap of a first width between one side of the substrate and a first calendering roll and deposition of electrode material from an atmospheric plasma deposition device into a gap of a second width between the second side of the substrate and a second calendering roll, the calendering rolls pressing the deposited electrode materials into an electrode layer of a first thickness adhered on the first side and an electrode layer of a second thickness adhered on the second side of the substrate. The first width and the second width may be the same or different, and first thickness and the second thickness may be the same or different. The substrate is then drawn through a second, wider gap between a second opposing pair of calendering rolls, in which there is a further gap between electrode layer and calendering roll on one side or on both sides of the substrate to allow deposition of more electrode material from an additional atmospheric plasma deposition device into the gap between the electrode layer already on the substrate and a calendering roll of the second pair of calendering rolls, the second pair of calendering rolls pressing the electrode material deposited to form an electrode layer of a greater thickness on the substrate on the one side or on both sides of the substrate. The substrate may pass through further pairs calendering rolls set progressively further apart, with additional electrode material being deposited by atmospheric plasma deposition into a gap between a calendering roll of each further pair and the electrode layer on one or both sides of the substrate so as to continue to build up the thickness of the electrode layer or to build up the thickness of both electrode layers until a desired final electrode layer thickness is reached between a final pair of calendering rolls. A second lithium-ion cell substrate may be concurrently drawn through a gap between a first one of the final pair of calendering rolls and a first electrode layer with a first side of the second substrate against a calendering roll and a second side facing the electrode layer already on the first lithium-ion cell substrate, an atmospheric plasma deposition device depositing the final amount of electrode material between the second substrate and the electrode layer on the first substrate; optionally a third substrate being concurrently drawn through a gap between a second one of the final pair of calendering rolls and a second electrode layer with a first side of the third substrate against the second calendering roll and a second side facing the second electrode layer already on the first lithium-ion cell substrate, an atmospheric plasma deposition device depositing the final amount of electrode material between the third substrate and the second electrode layer on the first substrate; and the calendering rolls pressing the substrates and deposited electrode material together to sandwich the electrode layer(s) of the final desired thickness between the two lithium-ion cell substrates. For example, the first substrate may be a porous separator layer on which an anode layer is built up on one side and a cathode layer is built up on the other side, and the second and third substrates may be metal foils. In another example, the first substrate may be a metal foil on which anode layers are built up on both sides or cathode layers are built up on both sides, and the second and optionally a third substrate is a porous separator sheet. In a further variation of the process, when the first substrate is a porous separator layer on which an electrode layer is built up on one side and a cathode layer is built up on the other side, this assembly may be drawn through a gap between a further pair of calendering rolls and metal particles may be deposited from an atmospheric plasma on one or both electrode layers and calendered between the rolls to form a current collector layer on the electrode layer or on both electrode layers. The electrode layers-substrate(s) assembly may (as described above) be cut into a final shape to be assembled into lithium ion cells or collected, e.g., by rolling the electrode layer-substrate assembly up on an uptake roller, for later further fabrication steps. 
     Also disclosed is an apparatus having a path for advancing a lithium ion cell substrate between at least one pair of opposing calendering rolls, which may optionally be heated. At least one atmospheric plasma deposition device is positioned to deposit by atmospheric plasma deposition particles of electrode material comprising an active electrode material and a metal, supplied from a reservoir or reservoirs of the particles connected to the plasma deposition device, into a gap between a first side of the substrate and one of the pair of calendering rolls. The pair of calendering rolls serve to press the deposited particles into an electrode layer on the first side of the substrate. The path may include an unwinding roll for the substrate and an uptake roll for the product substrate with an electrode layer on the first side. Instead of the uptake roll, the apparatus may include a cutting table for slitting and/or cutting the product substrate with the electrode layer into a desired shape for assembly into a lithium ion cell. The apparatus may include a plurality of atmospheric plasma deposition devices arranged along the width of the substrate, each positioned to deposit particles of electrode material from a connected reservoir or connected reservoirs. The active electrode material and a metal may be co-deposited from the plasma deposition devices (as separate particles of metal and particles of active electrode material or as composite particles containing both active electrode material and metal) or separately from different plasma deposition devices, preferably generally uniformly and in a desired volume proportion of metal to active electrode material into the gap across a desired part of the width of the substrate with the calendering rolls being of a length suitable to press deposited electrode layer into an electrode layer on the substrate. In one embodiment, the path advances the substrate, which may be a metal foil or a porous separator sheet, against a first calendering roll of the pair, and the apparatus may further include a path for advancing a second substrate, which may be the other of a metal foil or a porous separator sheet, against a second calendering roll of the pair so that the electrode layer is formed between the first substrate and the second substrate. In another embodiment, the path advances the substrate through one or more pairs of calendering rolls, each succeeding pair of calendering rolls having a greater gap width than the immediately preceding pair of calendering rolls, wherein one or more further atmospheric plasma deposition devices is or are positioned to deposit by atmospheric plasma deposition particles of electrode material comprising an active electrode material and a metal, supplied from a reservoir or reservoirs of the particles connected to the plasma device, into the gap between the electrode layer and one of the pair of calendering rolls, such that the thickness of the electrode layer is increased as the substrate passes through each succeeding pair of calendering rolls. Both in the embodiment having one pair of calendering rolls equipped with at least one plasma deposition device to deposit electrode material and in the embodiment having a plurality of pairs of calendering rolls equipped with plasma deposition devices to deposit electrode material, the disclosed apparatus may include a final pair of calendering rolls equipped with plasma deposition device(s) to deposit electrode material and a path for advancing a second lithium ion cell substrate between one of the final pair of calendering rolls and the electrode layer being formed between the final pair calendering rolls, and optionally equipped with plasma deposition device(s) to deposit electrode material and a path for advancing a third lithium ion cell substrate between the other roll of the final pair of calendering rolls and an electrode layer on the other side of the substrate being formed between the final pair calendering rolls. In other embodiments, the apparatus may include a final pair of calendering rolls equipped with at least one plasma deposition device to deposit metal particles from a supply of metal particles suitable to form a current collector layer on the electrode layer or, if the substrate has an electrode layer on both sides, at least one plasma deposition device to deposit metal particles from a supply into a gap between each electrode layer and one of the final pair of calendering rolls, the deposited metal particles being pressed by the final pair of calendering rolls into a current collector layer on the electrode layer. 
     Also disclosed is an apparatus having a path for advancing a lithium ion cell substrate between a plurality of pairs of calendering rolls, the rolls optionally capable of being heated, each pair of calendering rolls equipped with one or more atmospheric plasma deposition devices equipped to supply particles of electrode material comprising an active electrode material and a metal, from a reservoir or reservoirs of the particles connected to the plasma device, into a gap between a first side of the substrate and one of the pair of calendering rolls as previously described, in which each succeeding pair has a greater gap width as previously described, wherein, after an electrode layer of desired thickness is formed on one side of the substrate, the substrate path advances the substrate through the next pair of calendering rolls with the electrode layer against a first one of the calendering rolls and the one or more atmospheric plasma deposition devices positioned to deposit particles of electrode material into a gap between the substrate face opposite the electrode layer and a second one of the calendering rolls. The apparatus of this embodiment can apply an electrode layer to a first side of the substrate and then apply an electrode layer to the second side of the substrate. As previously described, the apparatus may optionally have a plurality of pairs of calendering rolls depositing electrode material on each side to build up the thickness of the electrode layer on each side; the apparatus may optionally have a path for providing a further substrate between the electrode layer being formed and the calendering roll facing the electrode layer being formed to sandwich the electrode layer being formed between lithium ion cell substrates or a pair of calendering rolls equipped with at least one plasma deposition device to deposit metal particles from a supply of metal particles suitable to form a current collector layer on the electrode layer. In these embodiments, the electrode material in the supply to the plasma deposition devices positioned on either side of lithium ion cell substrate may have the same composition or different compositions. 
     Also disclosed is an apparatus for advancing a lithium ion cell substrate between at least one pair of opposing calendering rolls in which at least one atmospheric plasma deposition device having a supply of particles of electrode material comprising an active electrode material and a metal is positioned to deposit the particles of electrode material by atmospheric plasma deposition into a gap between a first side of the substrate and the first calendering roll and at least one further atmospheric plasma deposition device having a supply of particles of electrode material comprising an active electrode material and a metal is positioned to deposit the particles of electrode material by atmospheric plasma deposition into a second gap between a second side of the substrate and the second calendering roll. The pair of calendering rolls serve to press the deposited particles into an electrode layer on the first side of the substrate and a second electrode layer on the second side of the substrate. The path may include an unwinding roll for the substrate and an uptake roll for the product substrate with the electrode layers on either side. Instead of the uptake roll, the apparatus may include a cutting table for slitting and/or cutting the product substrate with the electrode layers on either side into a desired shape for assembly into a lithium ion cell. The apparatus may include a plurality of atmospheric plasma deposition devices having a supply of particles of electrode material comprising an active electrode material and a metal is positioned to deposit the particles of electrode material, whether together from the same deposition devices or separately from different deposition devices, generally evenly into the gaps across a desired part of the width of the substrate such that the calendering rolls can press deposited electrode layer into an electrode layer or the substrate. When the substrate is a metal foil, the electrode material type (cathode or anode) can be the same on both sides of the metal foil (i.e., anode material supply for the plasma deposition devices on both sides or cathode material supply for the plasma deposition devices on both sides) and the apparatus may further include, on one or both sides of the metal foil, a path for providing a porous separator sheet between the electrode layer being formed and the calendering roll facing the electrode layer being formed to sandwich the electrode layer being formed between the metal foil and the separator sheet. When the substrate is a porous separator sheet, the electrode material type in supply (cathode or anode) can be different on the first and second sides of the porous separator sheet (i.e., a cathode layer on one side and an anode layer on the other side), and the apparatus may optionally further include a path for providing a metal foil between the electrode layer being formed and the calendering roll facing the electrode layer being formed to sandwich the electrode layer being formed between the metal foil and the separator sheet or, alternatively, the apparatus may optionally further include at least one further pair of opposing calendering rolls in which at least one further atmospheric plasma deposition device having a supply of metal particles suitable to form a current collector layer is positioned to deposit the metal particles by atmospheric plasma deposition into a third gap between a first side of the substrate and one of the pair of calendering roll and at least one further atmospheric plasma deposition device having a supply of metal particles suitable to form a current collector layer is positioned to deposit the metal particles by atmospheric plasma deposition into a fourth gap between a second side of the substrate and the other of the pair of calendering roll to form current collector layers on the electrode layers. 
     Also disclosed is an apparatus configured as in any of the embodiments described above in which the pair of opposing calendering rolls equipped with the atmospheric plasma deposition device(s) are configured with a guard or closure for the gap positioned near or at the ends of the calendering rolls to contain deposited electrode material and either prevent deposition of material on an outer edge of the substrate or prevent loss of electrode material from the ends of the calendering rolls. The guard or closure may be fixed into the gap between the calendering rolls or may be attached to or integral with one or both of the calendering rolls. In one such embodiment, at least one roll of the pair has a raised ring or ridge at or near one or both of its ends, which may be part of the roll or may be a separate article fit over the end of the roll such as a gasket which may comprise, for example, a rubber such as silicone rubber, that extends toward the second roll of the pair so as to close off or at least partially close off the gap between that roll and the substrate. The apparatus may further include a brush or scraping edge outside the gap (e.g., in an area away from the gap) to remove any accumulated electrode material from the raised ring, ridge, or gasket. In another such embodiment, a stationary guard or closure is fit into the gap between substrate and a calendering roll near or at an end of the calendering roll to contain deposited electrode material, optionally with a path for a second substrate between the stationary guard and the calendering roll. 
     The disclosed methods and equipment advantageously minimizes wasteful overspray of the active electrode material to efficiently and economically produce electrodes and combined electrodes for lithium ion batteries. Because the application of the electrode material to the substrate is a solid state coating method, the disclosed methods and equipment avoids using any solvent. As a further advantage, the disclosed methods and equipment provide high throughput of electrodes, assemblies of multiple electrodes, half-cell assemblies, and full-cell assemblies for economical production than previous methods that require separate coating and assembly steps and allow for easy control of thickness and density of the applied electrode material layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being place upon illustrating the principles of the embodiments. The drawings for illustrative purposes only of selected aspects and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic illustration of a first aspect of the invention; 
         FIG. 2  is a schematic illustration of a second aspect of the invention; 
         FIG. 3  is a schematic illustration of a third aspect of the invention; 
         FIG. 4  is a schematic illustration of a fourth aspect of the invention; 
         FIG. 5A  is a cross-sectional detail showing schematically one arrangement for an integral raised ring at an end of one roll of a pair of the calendering rolls; and 
         FIG. 5B  is a cross-sectional detail showing schematically an arrangement for a gasket over the end of each roll of a pair of calendering rolls to contain electrode material while allowing center passage of a substrate. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     “A,” “an,” “the,” “at least one,” and “one or more” are used interchangeably to indicate that at least one of the item is present; a plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range. 
     “Active electrode material” means a lithium intercalation material that is in either an anode or a cathode during operation of a lithium ion cell or battery. 
     “Adhered” when used to describe attachment of metal particles surface-energy activated, surface-softened, or surface-melted (together, “surface-activated”) in an atmospheric plasma to other metal particles, active electrode material particles, or a lithium-ion cell substrate means a surface attachment of the metal particles. The metal particles adhere as they return to their original state after the surface energy activation by the atmospheric plasma. The metal particles do not fully or substantially melt. The active electrode material particles do not undergo any change in the atmospheric plasma. 
     “Atmospheric plasma” refers to a plasma produced at a temperature up to about 3500° C. and at a pressure at or about at atmospheric pressure. In an atmospheric plasma, the peak temperature reached by the active electrode material particles are typically less than about 1200° C. 
     The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used in this specification, the term “or” includes any and all combinations of one or more of the associated listed items. 
     “Particle size” refers to average particle size as determined by the ISO 13320 test method. 
     Each of the disclosed methods includes depositing from an atmospheric plasma deposition device particles of a lithium-ion cell electrode material, which particles include an active electrode material and a metal, into a gap between an opposing pair of calendering rolls. At least one sheet of a lithium-ion cell substrate is drawn through the gap, and the calendering rolls press the deposited particles into an electrode layer on a side of the sheet of the lithium-ion cell substrate to make an electrode assembly for a lithium-ion cell. The metal is surface-activated in the atmospheric plasma, causing the electrode material to cohere and adhere to the substrate. The rate at which the particles are deposited from the atmospheric plasma deposition device or deposition devices and the width of the gap are selected to produce an electrode layer of the particles of a desired thickness and density in the electrode assembly. 
     A detailed description of exemplary, non-limiting embodiments, with reference to the figures, follows. 
     In  FIG. 1 , opposing calendering rolls  6 ,  8  define an interior gap  18 . Calendering rolls  6 ,  8  are placed such that gap  18  will produce a desired thickness of electrode layer  2  between separator sheet  25  and metal foil  20  in the separator-electrode-metal foil assembly  4  exiting from calendering rolls  6 ,  8 . In  FIG. 1 , separator sheet  25  is pulled over calendering roll  6 , and metal foil  20  is pulled over calendering roll  8 . The lengths of calendering rolls  6 ,  8  along their rotational axes and the widths of separator sheet  25  and metal foil  20  may be generally the same or about the same for efficient production of the separator-electrode-metal foil assembly and to forestall build-up of electrode material on calendering rolls  6 ,  8 . There may be guards (not shown) against either end of calendering rolls  6 ,  8  that may extend upward to the top of or above gap  18  to prevent spillage of electrode material  16  (i.e., prevent electrode material  16  from spilling out from gap  18 ). In the example of  FIG. 1 , separator sheet  25  and metal foil  20  are shown as webs that may be drawn from unwind rolls (not shown), optionally drawn through a delivery pathway that includes tensioning rolls (not shown), with the product separator-electrode-metal foil assembly  4  being wound on uptake roller  30 . The product separator-electrode-metal foil assembly  4  may instead be cut into individual electrode shapes rather than being wound on uptake roller  30 . 
     Atmospheric plasma deposition device  12  and atmospheric plasma deposition device  14  deposit particulate electrode material  16  into the gap  18  via atmospheric plasma deposition. Electrode material  16  comprises a particulate electrode material comprising active electrode material and a metal surface-activated by the plasma. In one embodiment, particulate active electrode material and particulate metal surface-activated by the plasma are co-deposited from each atmospheric plasma deposition device, either as individual particles or as composite particles containing active electrode material and metal adhered together. The rate of deposition of the electrode material from each atmospheric plasma deposition device may be from about 0.5 gram to about 20 grams per minute, or may be from about 1 gram to about 15 grams per minute. A sufficient number of the atmospheric plasma deposition devices may be located along the length of the calendering rolls  6 ,  8  to deposit the electrode material  16  along a desired length of the open gap. Depending on the rate at which each atmospheric plasma deposition device deposits the electrode material  16 , the rate at which the separator sheet  25  and metal foil  20  are moving through the gap  18 , and the desired thickness of electrode layer  2  in the product separator-electrode-metal foil assembly  4 , a plurality of atmospheric plasma deposition devices may be positioned to deposit the electrode material  16  in a given area or in overlapping areas to supply a desired amount of the electrode material  16  per unit volume into the gap between the separator sheet  25  and metal foil  20 . A portion of the electrode material  16  may be deposited by the atmospheric plasma deposition onto one or both of the separator sheet  25  and metal foil  20  at a point before the gap  18 , but at least a portion, preferably substantially all, and particularly preferably all of the electrode material  16  is deposited by the atmospheric plasma deposition into gap  18  or onto one or both of the separator sheet  25  and metal foil  20  at a point after the substrates enter the gap  18 . The gap  18  begins at an imaginary plane A-A passing through the outermost circumference points of calendering rolls  6 ,  8 . Thus, the plasma deposition device jet(s) may be located so that the opening emitting the particles is past plane A-A and into the gap  18 . 
     In an alternative embodiment, particulate metal surface-activated by the plasma may be deposited by a first atmospheric plasma deposition device jet and particulate active electrode material may be deposited from a second atmospheric plasma deposition device jet into a same area of the gap  18 . 
     The apparatus illustrated in  FIG. 1  may be oriented vertically as shown, or may be oriented horizontally or at any angle between vertical and horizontal. 
     Atmospheric plasma generators and spray deposition devices are commercially available. The plasma deposition device typically has a metallic tubular housing which provides a flow path of suitable length for receiving the flow of a working gas carrying dispersed particles of the electrode material and for enabling the formation of the plasma stream in an electromagnetic field established within the flow path of the tubular housing. The tubular housing typically terminates in a conically tapered outlet shaped to direct the contained, particle-carrying plasma stream toward the substrate (e.g., separator sheet  25  or metal foil  20 ) to be coated. An electrically insulating ceramic tube is typically inserted at the inlet of the tubular housing such that it extends along a portion of the flow passage. A stream of a working gas, such as air, carrying the dispersed particles of electrode material is introduced into the inlet of the deposition device. The flow of the air-particle mixture may be caused to swirl turbulently in its flow path by use of a swirl piece with flow openings inserted near the inlet end of the deposition device. A linear (pin-like) electrode may be placed at the ceramic tube site along the flow axis of the deposition device at the upstream end of the tubular housing. During plasma generation the electrode is powered by a high frequency generator, for example at a frequency of about 50 to 60 kHz, and to a suitable potential such as a few kilovolts. The metallic housing of the plasma deposition device is grounded, and an electrical discharge can be generated between the axial pin electrode and the housing. When the generator voltage is applied, the frequency of the applied voltage and the dielectric properties of the ceramic tube produce a corona discharge at the stream inlet and the electrode. As a result of the corona discharge, an arc discharge from the electrode tip to the housing is formed. This arc discharge is carried by the turbulent flow of the air/particulate electrode material stream to the outlet of the deposition device. A reactive plasma of the air (or other carrier gas) and suspended particulate electrode material is formed at a relatively low temperature and at atmospheric pressure. The outlet of the plasma deposition device is shaped to direct the particle-carrying plasma stream into the gap between the calendering rolls. 
     The width of the separator sheet  25  and the metal foil  20  may be from about 1 mm to about 800 mm, preferably from about 5 mm to about 300 mm, and more preferably from about 30 mm to about 200 mm. The thickness of the separator sheet  25  may be from about 5 micrometers to about 30 micrometers, preferably from about 10 micrometers to about 25 micrometers, and more preferably from about 15 micrometers to about 20 micrometers. The thickness of the metal foil  20  may be from about 5 micrometers to about 25 micrometers, preferably from about 10 micrometers to about 20 micrometers, and more preferably from about 12 micrometers to about 15 micrometers. The thickness of the electrode layer  2  may be from about 5 micrometers to about 500 micrometers, preferably from about 30 micrometers to about 300 micrometers, and more preferably from about 60 micrometers to about 200 micrometers. The thickness of the separator-electrode-metal foil assembly  4  may be from about 15 micrometers to about 550 micrometers, preferably from about 60 micrometers to about 300 micrometers, and more preferably from about 85 micrometers to about 225 micrometers. The separator sheet  25  and the metal foil  20  may enter the gap  18  at a rate of from about 5 to about 150 meters per minute. 
     The particulate active electrode material may have particle sizes in the range from about 100 nanometers to about 100 micrometers. In an example embodiment the active electrode material may have a particle size in the range from about one micrometer to about fifty micrometers. The deposited electrode layer containing the active electrode material and the metal may typically from about 5 micrometers to about 500 micrometers thick. In an example embodiment the deposited electrode layer is from about 5 micrometers to about 350 micrometers thick. 
     Suitable examples of active anode materials include, without limitation, lithium titanate (LTO), graphite, and silicon-based materials such as silicon, silicon alloys, SiOx, and LiSi alloys. Suitable examples of active cathode materials include, without limitation, lithium manganese nickel cobalt oxide (NMC), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), and other lithium-complementary metal(s) oxides and phosphates. More than one active anode material may be deposited from the atmospheric plasma deposition in making a deposited anode layer, and more than one active cathode material may be deposited from the atmospheric plasma deposition in making a deposited cathode layer. When more than one active electrode material is deposited, the different active electrode materials may be deposited from separate atmospheric plasma deposition devices or may be deposited from a same atmospheric plasma deposition device. If deposited from a same atmospheric plasma deposition device, the different active electrode materials may be introduced into the atmospheric plasma as a pre-made mixture or may be introduced into the atmospheric plasma from separate feed lines. 
     The plasma-deposited particulate electrode material also comprises a particulate metal that is surface-activated by the plasma, which serves to adhere the electrode layer to the substrate. In the case of particulate metal for the cathode layer, the metal particles may have a particle size less than the particle size of the active cathode material or up to about the same as the particle size of the active cathode material. For example, the metal particles deposited in making a cathode layer may have particle sizes in the range from about 1 nanometer to about 100 micrometers or from about 10 nanometers to about 50 micrometers or from about 100 nanometers to about 5 micrometers. In the case of particulate metal for the anode layer, the metal particles may have a particle size about the same as or greater than the particle size of the active anode material. For example, the metal particles deposited in making an anode layer may have particle sizes in the range of from about 100 nanometers to about 100 micrometers or from about 10 nanometers to about 50 micrometers or from about 100 nanometers to about 5 micrometers. In making an anode layer, the metal particles may comprise a metal or metals selected from, without limitation, copper, tin, silver, gold, nickel, palladium, platinum, and alloys of these. In making a cathode layer, the metal particles may comprise a metal or metals selected from, without limitation, aluminum, indium, thallium, titanium, zirconium, hafnium, nickel, palladium, platinum, silver, gold, and alloys thereof. 
     The metal particles and the active electrode materials may be deposited from separate atmospheric plasma deposition devices or may be deposited from a same atmospheric plasma deposition device. If deposited from a same atmospheric plasma deposition device, the metal particles and active electrode materials may be introduced into the atmospheric plasma as a pre-made mixture (in which the metal particles are either mixed with or adhered in composite particles with the active anode material) or may be introduced into the atmospheric plasma from separate feed lines. 
       FIG. 2  illustrates coating both sides of a metal foil  120  with cathode or anode material in which a series of plasma deposition devices and calendering roll pairs are used to build up electrode layer thickness through successive atmospheric plasma depositions of electrode material with deposited electrode material being calendered to an increasing thickness with each successive pair of calendering rolls. Plasma deposition devices  112 ,  114  deposit electrode material  116  on their respective opposite sides of metal foil  120 . The metal foil passes through first calendering rolls  106 ,  108 , which press the deposited electrode material into electrode layer thicknesses B-B. Plasma deposition devices  152 ,  154  deposit additional electrode material on their respective opposite sides of metal foil  120 . The metal foil passes through second calendering rolls  156 ,  158 , which press the deposited electrode material into electrode layer thicknesses C-C that is greater than thickness B-B. Plasma deposition devices  172 ,  174  deposit an additional amount of electrode material on their respective opposite sides of metal foil  120 . The metal foil passes through third calendering rolls  176 ,  178 , which press the deposited electrode material into electrode layer thicknesses D-D that is greater than thickness C-C. The gap (also called nip) between second calendering rolls  156 ,  158  is greater than the gap between first calendering rolls  106 ,  108 , and the gap between third calendering rolls  176 ,  178  is greater than the gap between second calendering rolls  156 ,  158  such that the electrode thickness steadily increases as the metal foil  120  advances through each succeeding pair of calendering rolls. It should be apparent that further plasma deposition devices and calendering roll pairs can be used to build up the electrode layer on one or both sides of a substrate as desired, and that the gaps between each face of the metal foil  120  or other substrate and the calendering rolls may be independently selected to independently produce a desired thickness of electrode on each major face of the substrate. 
       FIG. 3  illustrates an arrangement for making a lithium ion cell component of a porous separator sheet having a cathode layer on a first side and an anode layer on a second side and optionally further including a cathode current collector deposited on the outward side of the cathode layer and an anode current collector deposited on the outward side of the anode layer. A roll of porous separator sheet  228  is unwound and drawn past a separating structure  200 , which may be made of a material such as polymer or metal, configured to keep anode and cathode materials separate during the atmospheric plasma depositions of those materials to prevent cross-contamination. Although shown as a simple flat barrier, separating structure  200  may comprise compartments or housings that wrap at least partially around at the ends of at least one of calendering rolls  206 ,  208  to prevent any passage of the electrode material from that side to the other side of porous separator sheet  228 . A first atmospheric plasma deposition device  212  deposits cathode material onto one side of the porous separator sheet  228  in a gap between it and calendering roll  206 ; a second atmospheric plasma deposition device  214  deposits anode material onto a second side of the porous separator sheet  228  in a gap between it and calendering roll  208 . The porous separator sheet  228  then passes through opposing calendering rolls  206 ,  208 , which compress the electrode layers to a desired thickness. The lithium ion cell assembly may then be cut into final shape (not shown) or may be wound on an uptake roll (not shown) for later fabrication and incorporation into lithium ion batteries. 
     As shown in  FIG. 3 , metal particles  233  of an appropriate metal for a cathode current collector may be applied from an atmospheric plasma deposition device  252  onto the formed cathode layer, and metal particles  235  of an appropriate metal for an anode current collector may be applied from an atmospheric plasma deposition device  254  onto the formed anode layer. The porous separator sheet  228  then passes through opposing calendering rolls  256 ,  258 , which compress the current collector layers to a desired thickness. The product lithium ion cell component  290  may then be cut into final shape (not shown) or may be wound on uptake roll (not shown) for later forming and incorporation into lithium ion batteries. 
       FIG. 4  shows a further embodiment for making a lithium ion cell component of a porous separator sheet having a cathode layer on a first side sandwiched between the porous separator sheet and a cathode current collector layer and an anode layer on a second side sandwiched between the porous separator sheet and an anode current collector. A porous separator sheet  310  is unwound from roll  328  and drawn past a separating structure (not shown) configured to keep anode and cathode materials separate during the atmospheric plasma depositions of those materials to prevent cross-contamination. The porous separator sheet  310  passes between calendering rolls  306 ,  308 , not touching either calendering roll. A cathode current collector foil  337  is unwound from roll  333  and drawn around calendering roll  306 , with one side of cathode current collector foil  337  against calendering roll  306 . A first atmospheric plasma deposition device  312  deposits cathode material  302  into the gap between the porous separator sheet  310  and cathode current collector foil  337 . An anode current collector foil  327  is unwound from roll  323  and drawn around calendering roll  308 , with one side of anode current collector foil  327  against calendering roll  308 . A second atmospheric plasma deposition device  314  deposits anode material  304  into the gap between the porous separator sheet  310  and anode current collector foil  327 . The porous separator sheet  310  then continues through opposing calendering rolls  306 ,  308 , which compress the electrode layers to a desired thickness between the porous separator sheet  310  and the respective current collector foils  327 ,  337 . The lithium ion cell assembly  390  may then be cut into final shape (not shown) or may be wound on uptake roll  330  for later forming and incorporation into lithium ion batteries. 
     In some embodiments, one or more calendering rolls may include an integral or non-integral guard or closure at or near the one or both roll ends. The guard or closure may prevent spillage of the particles of electrode material out of the sides of the gap and/or may provide a sharp edge to the electrode layer formed on the substrate. When the substrate is a foil, a guard or closure may keep one end of the foil uncoated by the electrode material for electrical connection when assembled in a battery. When the substrate is a porous separator, guards or closures may keep both ends of the separator uncoated by the electrode material or provide a sharp edge for the electrode layer at both ends of the separator.  FIG. 5A  shows such an arrangement, in which calendering rolls  406 ,  408  are separated by a gap  410 . Calendering roll  406  has a terminal, integral ring  450 . Substrate  413  passes between roll  408  and ring  450 . The apparatus may further include a brush or scraper (not shown) located at a non-engaged area of ring  450  to remove any clinging electrode material from ring  450 .  FIG. 5B  shown an alternative arrangement in which calendering roll  506  has a non-integral gasket  550  and calendering roll  508  has a non-integral gasket  540  around their respective ends. Substrate  513  fits between gaskets  540 ,  550  and defines a gap  510  between one face of substrate  513  and roll  508  and a gap  511  between the opposite face of substrate  513  and roll  506 . Gaskets  540 ,  550  contain electrode material deposited into gaps  510 ,  511  by atmospheric plasma deposition and thus produce sharp edges for the electrode layers formed in gaps  510 ,  511 . The gaskets  540 ,  550  can be cleaned as they rotate through non-engaged areas or can be removed for cleaning. 
     Suitable porous separators have been made of polymers such as polyethylene, polypropylene, polyethylene oxide, polyvinylidene difluoride (PVDF), and ethylene-propylene copolymers, which may be filled with particulate ceramic material such as alumina (Al 2 O 3 ), silica (SiO 7 ), magnesium oxide (MgO), or lithium-containing materials such as Li 2 O-P 2 O 5 -B 2 O 3 , g-Li 3 PO 4 , Li 2 O-Li 2 SO 4 -B 2 O 3 , Li 4 GeO 4 /Li 3 VO 4 , Li 3 PO 4 -Li 2 S-SiS 2 , Li 2 S-SiS 2 -Li 4 SiO 4 , SiS 2 -P 2 S 5 -Li 2 S-LiI, LIPON (lithium phosphorous oxynitride): xLi 2 O:yP 2 O 5 :zPON, where x ranges from about 2.8 to 3.8, y ranges from about 3.2 to 3.9, and z ranges from about 0.2 to 0.9, Li x La 2/3-x3 1/3-2x3 TiO 3 , Li 7-x La 3 Zr 2 O 12-0.5x (LLZO), NASICON type glass-ceramic such as Li 1+x M x Ti 2-x (PO 4 ) 3  (M=Al, In), or LISICON type glass-ceramic: Li 2+2x Zn 1-x GeO 4 . 
     A battery is assembled for an application by combining a suitable number of individual cells in a combination of electrical parallel and series connections to satisfy voltage and current requirements for a specified electric motor. In a lithium-ion battery application for an electrically powered vehicle, the assembled battery may, for example, comprise up to three hundred individually packaged cells that are electrically interconnected to provide forty to four hundred volts and sufficient electrical power to an electrical traction motor to drive a vehicle. The direct current produced by the battery may be converted into an alternating current for more efficient motor operation. The separator is infiltrated with a suitable electrolyte for the lithium ion cell. The electrolyte for the lithium-ion cell is often a lithium salt dissolved in one or more organic liquid solvents. Examples of salts include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (Li ClO 4 ), lithium hexafluoroarsenate (Li AsF 6 ), and lithium trifluoroethanesulfonimide. Some examples of solvents that may be used to dissolve the electrolyte salt include ethylene carbonate, dimethyl carbonate, methylethyl carbonate, propylene carbonate. There are other lithium salts that may be used and other solvents. But a combination of lithium salt and liquid solvent is selected for providing suitable mobility and transport of lithium ions in the operation of the cell. The electrolyte is carefully dispersed into and between closely spaced layers of the electrode elements and separator layers. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.