Patent Publication Number: US-2020280104-A1

Title: Anode Subassemblies for Lithium-Metal Batteries, Lithium-Metal Batteries Made Therewith, and Related Methods

Description:
RELATED APPLICATION DATA 
     This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 62/812,472, filed Mar. 1, 2019, and titled “NEW STACK JELLY-ROLL STRUCTURE USING LAMINATION ON LITHIUM-METAL ANODE”, and U.S. Provisional Patent Application Ser. No. 62/830,620, filed Apr. 8, 2019, and titled “NEW STACK JELLY-ROLL STRUCTURE USING LAMINATION ON LITHIUM-METAL ANODE”, and U.S. Provisional Patent Application Ser. No. 62/832,665, filed Apr. 11, 2019, and titled “NEW STACK JELLY-ROLL STRUCTURE USING LAMINATION ON LITHIUM-METAL ANODE”, each of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of electrochemical devices. In particular, the present invention is directed to anode subassemblies for lithium-metal batteries, lithium-metal batteries made therewith, and related methods. 
     BACKGROUND 
     Because of their high gravimetric and volumetric energy densities, lithium-metal batteries have the potential of becoming the batteries of choice for many applications where such properties are desirable, including electric vehicles and mobile electronic devices, among others. However, the manufacturing of lithium-metal batteries has challenges that must be overcome to make the costs of producing lithium-metal batteries economically viable. Several challenges stem from inherent properties of lithium metal. Lithium metal is a pyrophoric metal that is challenging to work with, especially in the context of large-scale manufacturing, due to its “stickiness,” lightness, and softness, particularly when handling and processing the thin layers (e.g., less than 20 microns) that can be desirable to use in commercial-grade lithium-metal batteries. 
     SUMMARY OF THE DISCLOSURE 
     In some aspects, the present disclosure is directed to a method of making a lithium-metal battery. The method includes assembling a stacked jellyroll, the assembling of the stacked jellyroll including: providing a plurality of anode-subassembly sheets each comprising a lithium-metal layer pressure laminated between a first separator and a second separator; providing a plurality of cathode sheets; and alternatingly stacking the anode-subassembly sheets and the plurality of cathode sheets with one another so as to form the stacked jellyroll. 
     In one or more embodiments of the method, forming the anode-subassembly sheets, wherein the forming includes: forming a laminated web comprising the first separator, the lithium-metal layer, and the second separator; and cutting the laminated web so as to form the anode-subassembly sheets. 
     In one or more embodiments of the method, forming the laminated web includes contacting the first and second separators with the lithium-metal to form a multilayer structure, and applying pressure to the multilayer structure to form the laminated web. 
     In one or more embodiments of the method, applying pressure to the multilayer structure includes feeding the multilayer structure through pinch rollers. 
     In one or more embodiments of the method, the first separator includes a functional coating for the lithium-metal layer and the functional coating is in contact with the lithium-metal layer. 
     In one or more embodiments of the method, the functional coating includes a ceramic material. 
     In one or more embodiments of the method, the functional coating includes lithium fluoride. 
     In one or more embodiments of the method, the functional coating includes lithium carbonate. 
     In one or more embodiments of the method, forming the anode-subassembly sheets, wherein the forming includes: forming a laminated web comprising the first separator, the lithium-metal layer, and the second separator, wherein the first separator includes functional coating in contact with the lithium-metal layer; and cutting the laminated web so as to form the anode-subassembly sheets. 
     In one or more embodiments of the method, forming the laminated web includes contacting the first and second separators with the lithium-metal to form a multilayer structure, and applying pressure to the multilayer structure to form the laminated web. 
     In one or more embodiments of the method, applying the functional coating to a porous separator body so as to form the first separator. 
     In one or more embodiments of the method, the functional coating includes a ceramic material. 
     In one or more embodiments of the method, the functional coating includes lithium fluoride. 
     In one or more embodiments of the method, the functional coating includes lithium carbonate. 
     In one or more embodiments of the method, applying pressure to the multilayer structure includes feeding the multilayer structure through pinch rollers. 
     In one or more embodiments of the method, placing the stacked jellyroll in an interior of a casing. 
     In one or more embodiments of the method, adding an electrolyte to the interior of the casing and sealing the casing. 
     In one or more embodiments of the method, the lithium-metal layer has a thickness less than 20 microns. 
     In one or more embodiments of the method, the lithium-metal layer has a thickness less than 10 microns. 
     In one or more embodiments of the method, the lithium-metal layer has a sheet area and the anode-subassembly sheet further comprising a current-collector layer in contact with the lithium-metal layer across the sheet area. 
     In one or more embodiments of the method, the current-collector layer is embedded in the lithium-metal layer so that lithium metal is present on both sides of the current-collector layer. 
     In some aspects, the present disclosure is directed to a method of making an anode subassembly. The method includes providing a lithium-metal layer having a first side and a second side opposite the first side; providing a first separator having a functional coating for the lithium metal layer; contacting the functional coating and the first side of the lithium-metal layer with one another; and pressure laminating the first separator and the lithium-metal layer with one another to form the anode subassembly. 
     In one or more embodiments of the method, applying the functional coating to a porous separator body so as to form the first separator. 
     In one or more embodiments of the method, the pressure laminating uses pinch rollers. 
     In one or more embodiments of the method, the method is performed in a roll-to-roll process. 
     In one or more embodiments of the method, the functional coating includes a ceramic material. 
     In one or more embodiments of the method, the functional coating includes lithium fluoride. 
     In one or more embodiments of the method, the functional coating includes lithium carbonate. 
     In one or more embodiments of the method, providing a second separator; contacting the second separator and the second side of the lithium-metal layer with one another; and pressure laminating the first separator, the lithium-metal layer, and the second separator with one another to form the anode subassembly. 
     In one or more embodiments of the method, the lithium-metal layer has a sheet area and the anode-subassembly sheet further comprising a current-collector layer in contact with the lithium-metal layer across the sheet area. 
     In one or more embodiments of the method, the current-collector layer is embedded in the lithium-metal layer so that lithium metal is present on both sides of the current-collector layer. 
     In some aspects, the present disclosure is directed to an anode assembly, including a lithium-metal layer having a first side and a second side opposite the first side; and a first separator having a face and a functional coating for the lithium-metal layer applied to the face, wherein the first separator is pressure laminated to the lithium-metal layer on the first side of the lithium-metal layer with the functional coating in contact with the lithium-metal layer. 
     In one or more embodiments of the anode, the functional coating includes a ceramic material. 
     In one or more embodiments of the anode, the functional coating includes lithium fluoride. 
     In one or more embodiments of the anode, the functional coating includes lithium carbonate. 
     In one or more embodiments of the anode, the lithium-metal layer has a thickness less than 20 microns. 
     In one or more embodiments of the anode, the lithium-metal layer has a thickness less than 10 microns. 
     In one or more embodiments of the anode, a second separator pressure laminated with the lithium-metal layer on the second side of the lithium-metal layer. 
     In one or more embodiments of the anode, the lithium-metal layer has a sheet area and the anode-subassembly sheet further comprising a current-collector layer in contact with the lithium-metal layer across the sheet area. 
     In one or more embodiments of the anode, the current-collector layer is embedded in the lithium-metal layer so that lithium metal is present on both sides of the current-collector layer. 
     In some aspects, the present disclosure is directed to a lithium-metal battery, including a core stack that includes a plurality of anode-subassembly sheets and a plurality of cathode sheets alternatingly stacked with the anode-subassembly sheets; wherein each of the anode-subassembly sheets includes: a lithium-metal layer having a first side and a second side opposite the first side; a first separator pressure laminated to the lithium-metal layer on the first side of the lithium metal layer; and a second separator pressure laminated with the lithium metal layer on the second side of the lithium-metal layer; an electrolyte solution; and a casing containing the core stack and the electrolyte solution so that the electrolyte solution saturates the first and second separators of the anode assembly sheets. 
     In one or more embodiments of the lithium-metal battery, the first separator includes a functional coating for the lithium-metal layer, and the first separator is pressure laminated to the lithium-metal layer so that the functional coating is in contact with the lithium-metal layer. 
     In one or more embodiments of the lithium-metal battery, the functional coating includes a ceramic material. 
     In one or more embodiments of the lithium-metal battery, the functional coating includes lithium fluoride. 
     In one or more embodiments of the lithium-metal battery, the functional coating includes lithium carbonate. 
     In one or more embodiments of the lithium-metal battery, the lithium-metal layer has a thickness less than 20 microns. 
     In one or more embodiments of the lithium-metal battery, the lithium-metal layer has a thickness less than 10 microns. 
     In one or more embodiments of the lithium-metal battery, the lithium-metal layer has a sheet area and the anode-subassembly sheet further comprising a current-collector layer in contact with the lithium-metal layer across the sheet area. 
     In one or more embodiments of the lithium-metal battery, the current-collector layer is embedded in the lithium-metal layer so that lithium metal is present on both sides of the current-collector layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustrating examples of the present disclosure, the drawings show aspects of one or more embodiments of the invention(s). However, it should be understood that the present invention(s) is/are not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
         FIG. 1  is a diagram illustrating a conventional Z-fold stacking process for making a Z-fold stacked jellyroll for a lithium-metal battery; 
         FIG. 2A  is a diagram illustrating an example direct-stacking process for making a directly stacked jellyroll for a lithium-metal battery, wherein the stacking process includes alternatingly stacking anode-subassembly sheets and cathode sheets with one another; 
         FIG. 2B  is an enlarged partial cross-sectional view of an example of the anode-subassembly sheets of  FIG. 2A  illustrating the first and second separator layers pressure laminated to the lithium-metal layer; 
         FIG. 2C  is a diagram illustrating an example method of making an anode-subassembly web that can be a precursor to the anode-subassembly sheets of  FIGS. 2A and 2B ; 
         FIG. 2D  is an enlarged partial cross-sectional view of an example of the cathode sheet of  FIG. 2A ; 
         FIG. 2E  is an enlarged partial cross-sectional view of an example alternative anode-subassembly sheet that includes a current-collector layer; 
         FIG. 3A  is an exploded side view of an example anode-assembly sheet that includes a functional coating for a lithium-metal layer applied to at least one separator layer prior to pressure-laminating the separator layer(s) and lithium-metal layer with one another; 
         FIG. 3B  is a longitudinal cross-sectional view of the anode-assembly sheet of  FIG. 3A  after the separator layer(s) and the lithium-metal layer have been pressure laminated with one another; 
         FIG. 3C  is a diagram illustrating an example method of making a precursor anode-subassembly web to the anode-subassembly sheet of  FIG. 3B ; and 
         FIG. 4  is a cross-sectional view of an example lithium-metal battery having a directly stacked jellyroll made in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In some aspects, the present disclosure is directed to methods of making directly stacked jellyrolls for lithium-metal batteries and making lithium-metal batteries using such stacked jellyroll. In some aspects, the present disclosure is directed to the stacked jellyrolls and batteries themselves. In some aspects, the present disclosure is directed to methods of making anode subassemblies that have one or more functional coatings for a lithium metal layer pre-applied to one or more separators prior to contacting the functional coating with the lithium metal layer to make an anode subassembly. In some aspects, the present disclosure is directed to such anode subassemblies themselves. Examples of these and other methods are presented below. It is noted that while the examples presented in this disclosure are largely directed to lithium metal batteries having lithium metal anodes, the general methods, techniques, structures, etc., are applicable to other lithium-metal-based electrochemical devices, such as supercapacitors. In addition, the lithium metal in any of the present examples and embodiments may be replaced by one or more other active alkali metals, such as sodium magnesium, and/or aluminum, among others, and any suitable alloy thereof. 
     Example Directly Stacked Jellyroll 
       FIG. 1  depicts a conventional stacking process  100  for making stacked jellyrolls for lithium-metal batteries. This conventional stacking process  100  involves alternatingly stacking cathode sheets  104  with anode sheets  108  while feeding out a continuous separator web  112  from a roll  112 A to form a stacked jellyroll  116 , with a portion of the separator web sandwiched between each pair of the cathode and anode sheets. The stacking is accomplished by alternatingly adding individual cathode sheets  104  and anode sheets  108  (the adding represented by arrows  120 ( 1 ) and  120 ( 2 ), respectively) and moving one, the other, or both of the growing stacked jellyroll  116  and roll  112 A back and forth (in this example, arrow  124  represents back-and-forth movement of the stacked jellyroll) so that the separator web  112  wraps around one lateral side of each of the cathode and anode sheets and becomes sandwiched between pairs of the cathode sheets and anode sheets as the stacking continues. As one can readily envision, due to the zig-zag shape of the continuous separator web  112  in the finished stacked jellyroll  116 , this process is often referred to as a “zigzag stacking process” or a “Z-fold stacking process.” 
     The machinery (not shown) required to perform this conventional stacking process  100  is fairly complex not only due to the machinery needing to move the stacked jellyroll  116  and/or roll  112 A of the continuous separator web  112  to create the zigzag configuration, but also due to the machine needing to do this in coordination with placing of the cathode and anode sheets  104  and  108 , respectively, into the growing stack. For contemporary and future lithium-metal batteries that utilize quite-thin layers of lithium metal (e.g., on the order of 20 microns or 10 microns or less), the machinery for performing a conventional Z-fold stacking process, such as the conventional stacking process  100  of  FIG. 1 , must also be designed to handle extremely delicate lithium-metal anode sheets. As mentioned in the Background section above, lithium metal has a number of physical properties that make it extremely challenging to handle and process. Indeed, the fragility of contemporary and future lithium-metal anodes often requires specialized components and the need to limit the speed at which the machinery can operate. This fact, along with the complexity of operation concomitant the complexity of the machinery results in the machinery taking a fair amount of time to complete the stacking process for each stacked jellyroll it makes. 
       FIG. 2A  illustrates an example direct-stacking method  200  that can be used to make a directly stacked jellyroll  204 . As will become apparent from reading this section, machinery (not shown) for performing the direct-stacking method  200  can be far less complex than machinery for performing the Z-folding process of the conventional stacking method  100  of  FIG. 1 . This is so because the machinery for the direct-stacking method  200  does not provide a separator as a separate and distinct component in the stacking process. Consequently, separator-handling components are not needed, nor are actuators and/or other components/features for moving the stacked jellyroll  116  ( FIG. 1 ) and/or the separator roll  112 A ( FIG. 1 ). In addition, and as described below, machinery for the direct-stacking method  200  of  FIG. 2B  does not directly handle a lithium-metal anode and thus does not need to be specially designed to handle the fragility of such an anode. 
     Referring to  FIG. 2A , the example direct-stacking method  200  involves alternatingly adding only two types of components to the growing stacked jellyroll  204 , namely cathode sheets  208  and anode-subassembly sheets  212  (the adding represented by arrows  216 ( 1 ) and  216 ( 2 ), respectively). Stacking only two types of components with one another greatly simplifies the process of making stacked jellyrolls for use in batteries, especially lithium-metal batteries but also other types of active-metal batteries. 
     This highly simplified stacking process of the direct-stacking method  200  is enabled by the construction of the anode-subassembly sheets  212  that, as seen in  FIG. 2B , includes a lithium-metal layer  212 A sandwiched between two separator layers  212 B and  212 C. It is noted that for convenience, the two separator layers  212 B and  212 C may also be referred to herein and in the appended claims, respectively, as a “first separator” or a “first separator layer” and a “second separator” or a “second separator layer”. No meaning should be given to “first” and “second” in these terms other than providing a convenient way to identify the two as being separate from one another. As illustrated in  FIG. 2C , in some embodiments, the separator layers  212 B and  212 C are pressure laminated onto the lithium-metal layer  212 A, for example, in a continuous web-forming process  220  utilizing pinch rollers, such as pinch rollers  224 ( 1 ) and  224 ( 2 ). The pinch rollers  224 ( 1 ) and  224 ( 2 ) and/or their corresponding support mechanisms (not shown) are adjusted to provide an amount of pressure sufficient to adhere the separator layers  212 B and  212 C to the lithium-metal layer  212 A. Typically, the adhesion is a direct adhesion of separator layers  212 B and  212 C to the lithium-metal layer  212 A; no separate adhesive or other bonding agent is used for direct adhesion. Such direct adhesion is promoted by the relative softness of the lithium metal in the lithium-metal layer. In some embodiments, the ranges of pressure and temperature that optimize results are 10° C. to 60° C. and 100 lbf/in (175 N/cm) to 1000 lbf/inch (1750 N/cm), respectively. Generally, the optimal values typically depend on the coated materials. 
     In the continuous-web forming process  220  illustrated in  FIG. 2C , the lithium-metal layer  212 A is paid-out from a lithium-metal roll  212 A(R), and each of the first and second separator layers  212 B and  212 C are paid-out, respectively from a first separator roll  212 B(R) and a second separator roll  212 C(R). As the layers  212 A,  212 B, and  212 C are paid out, they are brought into contact with one another and pinch-rolled by pinch rollers  224 ( 1 ) and  224 ( 2 ) so that they are pressure laminated to or with one another so as to form a continuous anode-subassembly web  228 . The anode-assembly web  228  may then be cut, for example, punched, die cut, sheared, etc., to form the anode-assembly sheets  212  for using in the direct-stacking process  200  of  FIG. 2A . 
     Referring to  FIG. 2B , as those skilled in the art know, each of the first and second separator layers  212 B and  212 C provide physical and electrical separation between an anode, here, the lithium-metal layer  212 A, and a cathode, here, one of the cathode sheets  208  ( FIG. 2A ) in the stacked jellyroll  204 , while allowing for ionic flow within an electrolyte (not shown) between the anode and cathode. Each of the separator layers  212 B and  212 C may be made of any suitable material(s), such as polyethylene, polypropylene, and/or a mixture of ceramic blended polyolefin materials, and any combination thereof, among others. Though not illustrated, in some embodiments each of the separator layers  212 B and  212 C may incorporate thermal-shutdown capability. In some embodiments, the thickness of each separator layer  212 B,  212 C may be in a range of 10 to 30 um, though other thicknesses may be used to suit a particular design. As noted above, the use of anode-subassembly sheets having separator layers adhered to a lithium-metal layer, such as anode-subassembly sheets  212 , is particularly desirable for use with thin layers of lithium metal, such as lithium-metal layers having thicknesses of 50 microns or less, 20 microns or less, or 10 microns or less. However, the lithium-metal layer  212 A may be greater than 50 microns for other applications. 
     In one example in which each of the first and second separator layers  212 B and  212 C are made of a porous blend of an inorganic material (e.g., Al 2 O 3 ) and polyethylene, providing the lithium-metal layer  212 A in the composite anode-subassembly sheet  212  greatly increases the ease with which the lithium-metal layer can be handled. Lithium metal has a very low tensile modulus of 0.81 MPa, which is a result of its physical softness (melting temperature of 180° C.). After pressure laminating the lithium-metal layer  212 A with the first and second separator layers  212 B and  212 C, the tensile modulus of the composite anode-assembly sheet  212  is on the order of 30 MPa to 50 MPa, an increase of over 2 orders of magnitude over the corresponding bare lithium-metal anodes used in a conventional Z-fold stacking process, such as conventional stacking process  100  of  FIG. 1 . 
     In addition, a bare lithium-metal anode is difficult to cut and stack due to its sticky nature. During die cutting and stacking, the bare lithium-metal anodes tend to stick to cutting and handling components of cutting and stacking machinery and are thereby easily damaged. Due to its fragility, cutting and handling machines need to be run at relatively low speeds to enhance the control of the very fragile lithium metal. However, when utilizing anode-subassembly sheets, such as anode-subassembly sheets  212  of  FIGS. 2A and 2B , the lithium metal (e.g., lithium-metal layer  212 A) is covered by the separator layers, here separator layers  212 B and  212 C, on both sides (see, e.g., first and second sides  212 A( 1 ) and  212 A( 2 ) of  FIG. 2C ) of the lithium-metal layer generally across the entire sheet area. This minimizes the extent of the lithium metal exposed to cutting, handling, and stacking machinery, thereby minimizing detrimental interactions between the lithium metal and such machinery. This, in conjunction with the robustness of the anode-subassembly sheets  212 , allows the machinery to operate at much greater speeds as compared to machinery handling bare lithium-metal anodes, as in conventional stacking processes. The Table below illustrates the beneficial effects of the higher-speed operations and simplified stacking of a direct-stacking process of the present disclosure, such as direct-stacking process  200  of  FIG. 2A , versus a conventional Z-fold stacking process, such as conventional process  100  of  FIG. 1 . 
                             TABLE                   Bare Li-Metal Anodes   Anode Subassemblies       Task   (parts per minute)   (parts per minute)                  Cutting to form anode   30   100       structures       Complete stacks of 23 anodes   0.2 (Z-fold separator)   2 (direct stacking)       and 24 cathodes                    
As can be seen in the Table above, in this example the speed of cutting the anode structures is more than tripled when using the composite anode-subassembly sheets of the present disclosure, such as the anode-subassembly sheets  212  of  FIGS. 2A and 2B . The Table also shows that, when using the composite anode-subassembly sheets of the present disclosure to make a directly stacked jellyroll having 23 anodes and 24 cathodes, the stacking speed is ten times faster than when using conventional bare lithium-metal anodes.
 
     Referring to  FIGS. 2A and 2B , each cathode sheet  208  may be made of any material(s) suitable for providing a cathode compatible with the lithium-metal-based anode assembly sheet  212  and the particular electrolyte used in the final battery (not shown) utilizing the stacked jellyroll  204 . In one example, illustrated in  FIG. 2D , each cathode sheet  208  includes an aluminum foil layer  208 A as a positive substrate. The foil layer  208 A is coated on both sides with a slurry containing a high-nickel NMC811 (88% lithium nickel, 11% manganese, and 11% cobalt), a polymer binder (here, polyvinylidene difluoride (PVDF), and a conductive carbon to provide active cathode layers  208 B on both sides of the foil layer. Other than suitability of the particular chemistry at issue, there are generally no constraints on the construction and manufacture of the cathode sheets  208 . 
     It is noted that while  FIG. 2C  illustrates a particular arrangement of a pair of pinch rollers  224 ( 1 ) and  224 ( 2 ), those skilled in the art will readily understand that other arrangements are possible, including arrangements that include more than one set of pinch rollers. For example, one or more additional sets of pinch rollers may be provided that sequentially increase the pressure applied to the anode-subassembly web  228 . It is further noted the pressure laminating may be performed in a manner other than using pinch rollers. For example, the lithium-metal layer  212 A and the first and second separator layers  212 B and  212 C may be pressure laminated with one another using a stationary press (not shown). In this example, the stationary press may be configured to pressure laminate the first and second separator layers  212 B and  212 C to the lithium-metal layer  212 A in discrete lengths. For example and referring to  FIG. 2C , the three layers  212 A,  212 B, and  212 C may be paid-out from corresponding rolls  212 A(R),  212 B(R), and  212 C(R) to form a loose stack (not shown), and the loose stack may then be pressed in the stationary press to form the anode-subassembly web  228 . In some embodiments, the anode-subassembly web  228  may then be cut as described above to form the anode-subassembly sheets  212  ( FIGS. 2A and 2B ). 
     While the example anode-subassembly sheet  212  of  FIGS. 2A and 2B  have only a lithium-metal layer  212 A, other embodiments may include one or more additional layers sandwiched between the first and second separator layers  212 B and  212 C. For example,  FIG. 2E  shows an anode-subassembly sheet  212 ′ that includes a current-collector layer  212 D located within the lithium-metal layer  212 A. The current-collector layer  212 D may be made of any suitable conductive material, such as copper or aluminum, among others. In addition, the current collector may be solid or perforated, depending on the particular design at issue. In some embodiments, an optional bonding agent  212 E ( FIG. 2E ) may be used to assist with securing one or both of the separator layers  212 B and  212 C to the lithium-metal layer  212 A. This alternative anode-subassembly sheet  212 ′ may be substituted for the anode-subassembly sheet  212  in the direct-stacking process  200  of  FIG. 2A . 
     In connection with embodiments of the anode-subassembly sheets having one or more additional layers, such as the embodiment of  FIG. 2E  that has a current-collector layer  212 D located between the first and second separator layers  212 B and  212 C, it is noted for clarity that various terms have particular meanings. Regarding the term “lithium-metal layer”, for convenience, this term shall mean the totality of the lithium metal present between the first and second separator layers  212 B and  212 C. This is straightforward in the context of the embodiments of  FIG. 2B  in which each lithium-metal layer  212 A is either the only layer between the first and second separator layers  212 B and  212 C ( FIG. 2B ) or is only on one side of the current-collector layer  212 D. However, the term “lithium-metal layer” is deemed to also apply to the embodiment of  FIG. 2E  to describe the total thickness of the lithium metal between the first and second separator layers  212 B and  212 C, despite the fact that when the current-collector layer  212 D is a solid layer, the lithium metal forms two discrete layers, one on either side of the current-collector layer. In this case, each such separate lithium-metal layer may be considered a sublayer and/or the current-collector layer  212 D may be considered to be embedded in the lithium-metal layer  212 A. 
     Example Indirect Functional Coatings for Lithium-Metal Layers 
     Lithium metal and its oxides are not easily wetted with liquids having surface tension in excess of 25 dynes/cm. Consequently, it is difficult to apply, directly to a lithium-metal layer, a functional coating that is beneficial for the lithium-metal layer. Examples of functional coatings for a lithium-metal layer include a ceramic coating, lithium fluoride coating, and lithium carbonate coating, among others. Referring to  FIGS. 3A and 3B , to ameliorate this problem, one or more functional coatings, such as functional coating  300 , may be applied to a separator layer  304  prior to the separator layer being laminated to a lithium-metal layer  308  ( FIG. 3A ). The coated separator layer  304 ′ is then pressure laminated to the lithium-metal layer  308  to form an anode-subassembly  312  ( FIG. 3B ), which may either be in a continuous web form or a sheet form, depending on the circumstances. When in sheet form, the anode-subassembly  312  can be used in the direct-stacking process  200  of  FIG. 2A . 
     The process of applying a functional coating for benefiting a lithium-metal layer, such as functional coating  300  applied for lithium-metal layer  308 , may be referred to as an “indirect coating process”, since the functional coating is applied directly to a separator layer, here separator layer  304 , and then the functional coating is finally contacted with the lithium-metal layer when the separator layer is pressure laminated to the lithium-metal layer. As illustrated in  FIGS. 3A and 3B , in some embodiments this indirect coating process may involve only a single (or “first”) separator layer  304  pressure laminated to the lithium-metal layer  308  on only one side of the lithium-metal layer. However, as also illustrated, a second separator layer  316  may be optionally provided, with or without a second functional coating  320 . Indeed, one can readily envision modifying the anode-subassembly web-forming process of  FIG. 2C  to include one or more coating applicators upstream of the pinch rollers  224 ( 1 ) and  224 ( 2 ). Such a modified process is illustrated in  FIG. 3C . 
     Referring to  FIG. 3C , each of the first separator layer  304 , the lithium-metal layer  308 , and optional second separator layer  316  may be paid-out from corresponding rolls  304 R,  308 R, and  316 R. Prior to pressure laminating via a pair of pinch rollers  324 ( 1 ) and  324 ( 2 ), one, the other, or both of the first and second separator layers  304  and  316  may be coated with at least one corresponding functional coating for the lithium-metal layer  308 , here functional coatings  300  and  320 , respectively, using one or more coating applicators, here separate coating applicators  328  and  332 . Each of the coating applicators  328  and  332  may be of the same or differing type. In some embodiments in which the functional coatings  300  and  320  are composed of the same material(s), a single applicator (not shown) may be used. Each of the coating applicators  328  and  332  may be of any suitable type, such as a spray applicator, brush applicator, dip applicator, etc., depending on the type(s) of functional coating being applied as functional coatings  300  and  320 , if present. For convenience only, the coating applicators  328  and  332  are illustrated as spray applicators. 
     In a specific example, one, the other, or both of the functional coating  300  and  320  may be made using a slurry containing nano-sized aluminum oxide (Al 2 O 3 , particle size D50=50 nm) and one or more polymer binders, such as poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP), polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and/or carboxymethyl cellulose (CMC), among others. In some embodiments, the formulation of this alumina may be more than 70% and less than 95%. The slurry may then be dried before further processing, such as pressure lamination as described below. 
     Example Lithium-Metal Batteries Made Using a Directly Stacked Jellyroll and/or an Indirect Functional Coating 
       FIG. 4  illustrates an example lithium-metal battery  400  made using a directly stacked jellyroll  404  made in accordance with aspects of the present disclosure. In this example, the directly stacked jellyroll  404  is sealed within a casing, here, a pouch-type casing  408 , along with a suitable electrolyte (not illustrated, but present in at least the separator layers  416 B( 1 ) and  416 B( 2 )). In other embodiments, the pouch-type casing  408  may be replaced with a casing of a differing type, such as a rigid-wall housing, among others. Fundamentally, the type of casing is important only to the extent that it provides the requisite functionalities, including providing a sealed volume for containing the directly stacked jellyroll  404  and the electrolyte. Those skilled in the art are familiar with techniques and materials for constructing the pouch-type casing  408  or other type of casing that a particular design may include. Consequently, further details on the casing are not necessary herein for those skilled in the art to instantiate the lithium-metal battery  400  without undue experimentation. 
     Regarding the electrolyte, since in this example the battery  400  is a lithium-metal battery, meaning that the anodes  416  comprise lithium metal to which lithium ions are deposited and stripped during, respectively, charging and discharging cycles, the electrolyte contains lithium ions (not shown) that flow between the anodes and cathodes  420  within the directly stacked jellyroll  404  during the charging and discharging cycles. Consequently, in this example the electrolyte includes one or more lithium-based salts in a suitable form, such as in a solution, an eutectic mixture, or a molten form, among others. In some embodiments, the electrolyte may contain one or more solvents, one or more performance and/or property enhancing additives, and/or one or more polymers, among other things. The electrolyte may be in any suitable state of matter, such as liquid, gel, or solid state. The composition of the electrolyte can be any composition suitable for the particular application at issue and can be determined by the designer of the particular instantiations of the lithium-metal battery  400 . 
     The anodes  416  are provided to the directly stacked jellyroll  404  in anode-subassembly sheets  416 S, and the cathodes are provide to the directly stacked jellyroll as cathode sheets  420 S. Each anode-subassembly sheet  416 S generally includes a lithium-metal layer  416 A pressure laminated between first and second separator layers  416 B( 1 ) and  416 B( 2 ), respectively (only labeled in one of the anode-subassembly sheets  416 S to avoid clutter; the others are the same). Each of the anode-subassembly sheets  416 S may be the same as or similar to any of the anode subassembly sheets described above, such as any of the embodiments described above in connection with anode subassembly sheets  212  and  212 ′, which includes a version containing one or more functional coatings for the lithium-metal layer  416 A as described above in connection with  FIGS. 3A to 3C . In this embodiment, each anode subassembly sheet  416 S also includes a current collector layer  416 C. Each cathode sheet  420 S may be the same as or similar to the cathode sheet  208  of  FIG. 2A . The directly stacked jellyroll  404  of  FIG. 4  may be made using the direct stacking process  200  of  FIG. 2A . Each anode-subassembly sheet  416 S may be made using any suitable pressure laminating process, such as the pinch-roller process described above in connection with  FIG. 2C . If one or more functional coatings (not shown) for the lithium-metal layer  416 A are provided, the coatings may be applied to the corresponding separator layer(s)  416 B( 1 ) and  416 B( 2 ) in any suitable manner, such as the application process described above in connection with  FIG. 3B . It is noted that the number ( 4 ) of each of the anode-subassembly sheets  416 S and the number ( 5 ) of cathode sheets  420 S shown are only for convenience. More or fewer of each of the anode-subassembly sheets  416 S and cathode sheets  420 S may be provided to suit a particular design. 
     Referring still to  FIG. 4 , the lithium-metal battery  400  also includes a positive terminal  424  electrically connected to each of the cathodes  420  via corresponding electrodes  428 ( 1 ) to  428 ( 5 ). Similarly, the lithium-metal battery further includes a negative terminal  432  electrically connected to each of the anodes  416 , here to the current-collector layers  416 C, via corresponding electrodes  436 ( 1 ) to  436 ( 4 ). 
     The foregoing has been a detailed description of illustrative embodiments of the invention. It is noted that in the present specification and claims appended hereto, conjunctive language such as is used in the phrases “at least one of X, Y and Z” and “one or more of X, Y, and Z,” unless specifically stated or indicated otherwise, shall be taken to mean that each item in the conjunctive list can be present in any number exclusive of every other item in the list or in any number in combination with any or all other item(s) in the conjunctive list, each of which may also be present in any number. Applying this general rule, the conjunctive phrases in the foregoing examples in which the conjunctive list consists of X, Y, and Z shall each encompass: one or more of X; one or more of Y; one or more of Z; one or more of X and one or more of Y; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y and one or more of Z. 
     Various modifications and additions can be made without departing from the spirit and scope of this invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present invention. Additionally, although particular methods herein may be illustrated and/or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention. 
     Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.