Patent Publication Number: US-9887403-B2

Title: Thin film encapsulation battery systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/801,217, filed Mar. 15, 2013, entitled “Thin Film Encapsulation Battery Systems,” the entirety of which is incorporated by reference as if fully recited herein. 
    
    
     TECHNICAL FIELD 
     The subject matter of this disclosure relates generally to battery systems, and in particular to battery systems suitable for a range of different electronics applications including, but not limited to, computer systems, portable electronics and mobile devices. More specifically, the disclosure relates to battery systems and related methods of manufacture, utilizing encapsulation techniques to provide improved energy storage and performance. 
     BACKGROUND 
     Battery systems are utilized in a wide range of electronics applications, including computers, mobile devices, media players, personal digital assistants, power tools, navigational and communications equipment, and power storage and management systems for automotive, rail, shipping and industry use. Depending on application, these systems are traditionally configured around a cellular anode and cathode battery structure, for example in a cylindrical rod-and-tube type dry cell or flat plate flooded cell design. More advanced battery systems may utilize a “Jelly roll” or “Swiss roll” configuration, in which the anode and cathode layers are provided on opposite sides of a flat sheet or flexible substrate, which can be rolled up folded inside a battery pouch or enclosure. 
     Battery system design is driven by a number of competing factors, including size, weight, energy capacity, storage density, cost, safety, reliability, durability, and ease of manufacture. In rechargeable battery systems, thermal loading, recharge rate and other cycling considerations may also be important concerns, particularly as they relate to service life and suitability for particular electronics applications. These design and engineering factors may also be weighted differently based on intended usage, for example as directed to larger scale battery systems for transportation and industrial power systems, as compared to smaller scale batteries for computers and consumer electronic devices. 
     As a result, there is a continual need for improved battery system designs, with increased service life and performance over a wide range of different operational configurations and demands. In particular, there is a need for improved thin film, laminar, and encapsulated battery technologies, with increased energy capacity and storage density suited to the ever-increasing service requirements of modern electronics and power system environments. 
     SUMMARY 
     Exemplary embodiments of the disclosure include battery systems, methods of making battery systems, and electronic devices utilizing battery systems. The battery systems include anode and cathode layers having one or more encapsulated structures. 
     Representative processing methods may include forming a base layer on a substrate, and forming a thin film battery stack on the base. The battery stack may include an anode layer, a cathode layer, and an electrolyte layer between the anode and cathode, and can be encapsulated. The battery system typically includes a connector or electrodes for making power connections to the battery stack, for example anode and cathode electrodes coupled to the anode and cathode layers, respectively. 
     Depending on application, the battery stack may be thermally processed to generate a phase transition in the cathode layer. For example, a crystal phase transition may be thermally generated. 
     In stacked battery applications, a number of thin film battery cells are stacked for assembly into the battery system. For example, each stack may include a cathode collector layer adjacent the cathode layer, and adjacent cells can be inverted so that the cathode collector layers are electrically coupled within the battery assembly. Alternatively, bare cathode or anode layers can be stacked adjacent to one another, and a conducting adhesive can be used to form the collector layers. 
     The battery cells can be encapsulated with a polymer or organic film. Alternatively, a multilayer encapsulation system can be used, with an inner ceramic layer positioned toward the cell stack, an outer polymer layer arranged about the inner ceramic layer, and a metallic layer between the inner ceramic layer and the outer polymer layer. 
     In battery system applications, a number of thin film battery cells may be arranged in a stacked configuration, where each of the cells includes an anode layer, a cathode layer, and an electrolyte layer between the anode and cathode layers. The encapsulant surrounds the stacked configuration, providing a substantially continuous chemical and mechanical barrier about the thin film battery cells. 
     Suitable encapsulants can be formed of organic liquid and polymer materials. A three-layer encapsulation system can also be used, with an inner ceramic layer, an outer polymer layer, and a metallic layer in between. In some designs, a space or gap is left between the encapsulant and the stacked thin film cell configuration, in order to accommodate thermal expansion and contraction, or the stack of battery cells can be formed with slanted or nonparallel opposing sides, to allow for relative movement. 
     These battery systems can be utilized in electronic devices, for example a smartphone, tablet computer, or other mobile device. In these applications, the battery assembly is typically coupled to a controller, and configured to power a display. The assembly itself includes a number of thin film battery cells arranged in a stacked configuration, where each of the thin film battery cells has an anode, cathode, and electrolyte layer. The encapsulant can be disposed about the stacked configuration of cells, to provide a chemical and mechanical barrier for the battery cells. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a battery system with improved thin film, laminar and/or encapsulation structures for increased energy density, as described herein. 
         FIG. 1B  is a perspective view of the battery system, with an alternate form factor. 
         FIG. 2  is a process flow diagram for making a battery system or battery assembly, utilizing a process substrate layer. 
         FIG. 3  is a process flow diagram for a battery system or assembly, utilizing an etched substrate and permanent base layer. 
         FIG. 4  is a process flow diagram for a battery system or assembly, in a stacked cellular design. 
         FIG. 5  is a process flow diagram for a battery system or assembly, with a conducting adhesive collector layer. 
         FIG. 6  is a process flow diagram for a battery system or assembly, with multiple cell encapsulation. 
         FIG. 7  is a process flow diagram for a battery system or assembly, with conducting adhesive anode and cathode collector layers. 
         FIG. 8A  is a cross-sectional illustration of a battery system, in an encapsulated stacked cell configuration. 
         FIG. 8B  is an alternate cross-sectional illustration of the battery system, in an encapsulated configuration with internal spacing. 
         FIG. 8C  is a cross-sectional illustration of a battery system with a sloped sidewall configuration. 
         FIG. 9  is a block diagram of a method for forming a battery system or assembly. 
         FIG. 10  is a schematic illustration of a representative electronic device incorporating a battery system or assembly. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is directed to battery systems and assemblies for electronic devices and power management systems. The batteries can be formed in a thin film process, for example by forming a base layer on a substrate, and forming a battery stack on the base layer. Suitable thin film processing techniques include, but are not limited to, those described in METHOD FOR TRANSFERRING THIN FILM TO SUBSTRATE, U.S. Publication No. 2010/0066683, published Mar. 18, 2010, the entirety of which is incorporated by reference herein. 
     The battery stacks can also be assembled into a multi-cell battery system, with or without permanent substrate layers. Depending on stacking configuration, the anode and cathode collectors layers may be eliminated, or replaced with a conducting adhesive, decreasing the inactive mass and increasing power and performance, within a given form factor or size and weight envelope. 
       FIG. 1A  is a perspective view of a battery (or battery system)  10  with improved thin film, laminar and/or encapsulation structures. These structures provide battery system  10  with increased energy density for improved service life and performance, suitable for a range of different electronic and power system applications, as described herein. 
     As shown in  FIG. 1A , battery system  10  is provided as a laminated anode/cathode structure within enclosure  11 , for example a battery pouch, casing or encapsulation layer. Protective film wrap  12  may be provided over battery enclosure  11  to protect battery  10  during shipping and storage. Film wrap  12  can also include a label, barcode, or other informational indicia for inventory control, which is typically removed before insertion of battery system  10  into an electronic device. 
     One or more connectors  13  provide power, sensor and control connections to battery system  10 , for example in a “pigtail” configuration with a connector board or manifold  14  coupled to battery system  10  via flex circuit  15 . The flex circuit connection can be made through a side  16  or end  17  of battery enclosure  11 , as shown in  FIG. 1A , or a major surface  18  (e.g., top or bottom surface) of enclosure  11 . Flex circuit  15  also allows the connector board or manifold  14  to be relocated away from battery enclosure  11  during installation and removal, and for wrapping and unwrapping of protective film  12 . 
     Length L, width W and thickness T of enclosure  11  define the shape or form factor of battery  10 , typically excluding protective wrapper  12  and any other components that are removed before installation. In the particular configuration of  FIG. 1A , for example, battery system  10  has a substantially rectangular or oblong form factor, with width W defined between opposite sides  16  of enclosure  11 , and length L defined between opposite ends  17 . Thickness T is typically defined between the major surfaces of battery  10 , for example between the bottom of battery enclosure  11  and top surface  18 . 
       FIG. 1B  is alternate perspective view of battery system  10 , with a different form factor. In this configuration, battery thickness T is relatively greater, as compared to the thin-profile embodiment of  FIG. 1A , and as a fraction of battery length L and width W. This may provide battery system  10  with greater storage capacity, within a given area L×W, in exchange for more weight and a larger volume envelope. Battery system  10  may also utilize a three-connector configuration, as shown in  FIG. 1B , with control or sensor connector  13  and separate (e.g., positive and negative) electrodes  19  for charging and power delivery. 
     Enclosure  11  is sometimes formed of a laminated pouch structure, for example using a relatively thin or flexible metal such as aluminum or steel, sandwiched between polymer protective layers or other coatings. Alternatively, enclosure  11  may be formed as a rigid case, using a relatively thicker metal or plastic material, or as an encapsulation layer or encapsulated enclosure system, as described below. In advanced battery systems, the internal structure (or battery core) of battery system  10  may be formed as a thin film or laminated anode/cathode structure. In particular, a thin film lithium ion battery structure may be utilized, in order to provide increased potential energy density and a higher power/weight ratio for battery system  10 . 
     To achieve these advantages, the proportion of active battery materials should be increased or maximized, including lithium ion utilization in the cathode layers, as compared to inactive materials and “overhead,” which should be decreased or minimized. To achieve high lithium ion utilization, particular crystalline structures or orientations may also be selected. For example, a substantially uniform or single-crystal structure may provide greater energy density in the cathode layers, as compared to a more amorphous structure. In addition, particular crystal plane orientations may be preferred, for example a (104), (101) or (012) crystal plane orientation, as compare to other possible orientations, such as (003). 
     In order to produce the desired crystal structures, the thin film battery layers are typically subjected to heating and other physical and chemical processes after deposition, in order to achieve the desired phase transitions. For example, both the film battery layers and the substrate may be heated to relatively high temperatures of up to 700 C or more, for extended periods of time, in order to achieve thermal crystallization. Thus, the process substrate must be thermally, chemically and mechanically stable, even at high temperatures. This requirement tends to limit the selection of suitable substrate materials, raising costs and reducing design options. 
     To address this problem, battery system  10  may utilize a thin film transfer process, in which the battery layers are deposited and processed on a substrate material, then transferred to a new (permanent) substrate, or into a battery stack, after the desired phase transformations have been achieved. This approach also reduces or minimizes overhead and inactive materials. Flexible substrates, for example, are typically fabricated in roll-to-roll form, where each roll may be 1-2 meters wide, and up to thousands of meters long. In order to withstand typical jelly roll (and other standard battery) processing techniques, however, a minimum substrate thickness must be maintained. For example, up to 25 μm thick substrates may be utilized in display panel and touch screen applications, while the typical active layer thicknesses may be as low as 3-5 μm. Actual production parameters vary, but representative numbers suggest a potential material overhead of 500% or more, based on the substrate thickness, as compared to the active (e.g., cathode) layers. Thin film transfer techniques can be used to substantially reduce this overhead, increasing the active material fraction and corresponding potential energy density, as described below. 
       FIG. 2  is a flow diagram illustrating a representative method or process  20  for producing a battery stack  40 , for example utilizing a thin film technique. Method  20  may utilize one or more steps including, but not limited to, providing a substrate (step  21 ), providing a base layer on the substrate (step  22 ), forming battery layers in a stack on the base layer (step  23 ), processing the battery stack (step  24 ). The stack may be formed on a permanent or target substrate, or attached to a transfer plate (step  25 ), which is released (step  26 ) for transferring the battery stack to a permanent substrate (step  27 ), and removing the transfer plate (step  28 ). Process method  20  may thus be utilized to form one or more thin film battery stacks or cells  40  for use a battery assembly such as battery system  10 , above. 
     In step  21 , process substrate or carrier layer  31  is provided in the form of a glass wafer or other suitable process substrate material  31 . Generally, the composition and thickness of process substrate  31  are selected for thermal, chemical and mechanical stability. 
     In step  22 , release or base layer  32  is provided on process substrate  31 . Base layer  32  may be formed, for example, of a silicon base or etch stopping material on which the battery layers are formed, and which is retained when process substrate  31  is removed. A seed layer or seed material may also be provided, in order to encourage a particular crystal plane orientation in an adjacent anode, cathode or collector layer, for example a lithium cobalt (LiCo) seed layer for forming a lithium cobalt cathode or cathode collector with a selected crystal plane structure. Base layer  32  can also be provided as a sacrificial layer, which is removed from the final battery assembly to release process substrate  31 , or as a base layer, which is retained in the final battery assembly. 
     In step  23 , laminar battery stack  40  is formed on base layer  32  and process substrate  31 , for example using thin film deposition and masking techniques. In particular, battery stack  40  is formed of one or more battery layers selected from the following: cathode current collector layers  33 , cathode layers  34 , electrolyte layers  35 , anode layers  36 , and anode collector layers  37 . 
     Suitable anode and cathode layer materials include, but are not limited to, lithium, lithium cobalt oxide, lithium iron phosphate and other lithium metal phosphates, lithium manganese oxide, carbon, and graphite, or graphite infused with lithium ions. In one particular configuration, for example, anode layer  36  may be formed of lithium, and cathode layer  34  may be formed of lithium cobalt oxide. Alternatively, anode layer  36  may be formed of lithium cobalt oxide, or another lithium phosphate or metal oxide material, and cathode layer  34  may be formed of graphite, or lithium ion infused graphite, or a lithium-based material. 
     Suitable materials for electrolyte layer  35  include, but are not limited to, ethylene carbonate and diethyl carbonate containing lithium ion complexes, and other (e.g., acid or alkali) electrolytes having suitable ion transport properties. In lithium ion applications of battery  10 , the electrolyte is typically non-aqueous, in order to avoid reacting with lithium metal components in the anode and cathode layers. A separator material may also be provided in electrolyte layer  35 , for example a porous or microporous ion transport material, a glassy or thin film solid electrolyte separator, or a paper, polymer, or fibrous composite membrane material with selected ion transport properties. Suitable electrolyte and separator materials also include, but are not limited to, polyethylene lithium ion transport materials, lithium phosphate, lithium phosphorous, and lithium phosphorous oxynitride (LiPON or LiPOxNy) materials, polymer, carbon (e.g., carbon nanotube) and composite membrane materials, and lithium-salt type electrolytes in a substantially solid polymer composite, for example in a lithium polymer battery configuration. 
     The particular configuration of battery stack  40  is merely representative, and the number and order of the individual anode, electrolyte, cathode and collector layers  33 - 37  may vary. For example, the layers may be reversed or inverted with respect to base layer  32  and process substrate  31 , and collector layers  33  and  37  may be provided either as separate metal or conduction layers, or combined with the anode and cathode layers. Depending on the charging or discharging state, moreover, the charge flow in anode and cathode layers  36  and  34  may be reversed, and these designations may be modified accordingly, without loss of generality. 
     In step  24 , battery stack  40  is processed to obtain selected material properties. For example, battery stack  40  may be heat treated to obtain crystallization or another phase change in cathode layer  34 , or in other layers of battery stack  40 . Generally, the crystallization temperature may be relatively high, for example up to 700 C or more. In applications where a seed layer or seed material is provided, the crystallization temperature may be somewhat lower, for example about 400 C or above. In additional examples, the relevant phase change temperature varies, depending upon the desired properties of battery stack  40 , and the corresponding material composition and configuration of battery layers  31 - 37 . 
     Processing step  24  may also include encapsulation of battery stack  40  within encapsulation layer  38 . Encapsulation layer  38  provides a relatively thin, electrically insulating, chemical and mechanical barrier for battery stack  40 , protecting from environmental effects including electrical contact, mechanical stress, and moisture intrusion. 
     Encapsulation layer  38  may be provided before or after heating and other processing steps on battery stack  40 . For example, suitable materials for encapsulation layer  38  include ceramics and other high temperature or refractory materials, which may be applied before or after thermal crystallization of cathode layers  34  (or anode layers  36 ). Additional suitable materials include polymer coatings and epoxy resins, for which the application sequence may depend upon the processing temperature and heating time, as compared to the thermal stability of the encapsulating material. 
     In transfer step  25 , battery stack  40  is bonded to a transfer plate or transfer layer  41 , for example using an easy release adhesive or other releasable bonding material  39 . Alternatively, battery stack  40  is formed directly on the target or final substrate. 
     Suitable materials for transfer layer  41  include, but are not limited to, flexible polymer materials such as polyethylene terephthalate (PET) and other flexible polymers, and rigid materials such as glass, and silicon wafer materials. Suitable materials for adhesive or bonding material  39  include soluble glues and adhesive, which can be selected to temporarily adhere battery stack  40  to transfer layer  41 , and which can later be dissolved or otherwise removed. 
     In release step  26 , process substrate  31  is removed or released and battery stack  40  is transferred to transfer layer  41 . Alternatively, battery stack  40  is formed on the target or permanent substrate, and the release step is not required. 
     Depending upon application, base layer  32  may also be removed, for example when using a sacrificial release material. Alternatively, base layer  32  can also be retained in the final battery assembly. For example, a chemical etching process may be utilized, which is stopped by base layer  32  as formed with an etch-resistant material, such as silicon. Alternatively, a sacrificial base or release layer  32  may be used, which undergoes a phase change when subject to an additional processing step, for example using an XeCl excimer laser or other radiation source to crystallize an amorphous silicon base layer  32 . Base layer  32  can also be ablated, or vaporized in an annealing process or other heat treatment. Depending on removal technique, moreover, process substrate layer  31  may either be destroyed, or preserved for reuse in a subsequent processing method  20 . 
     In step  27 , battery stack  40  is attached to the target or permanent (intended) substrate  42 , for example using an adhesive layer  43  laminated between the bottom of battery stack  40  (e.g., cathode collector layer  33 , and/or other battery layers), and target substrate  42 . Alternatively, battery stack  40  is formed on the target or permanent substrate. 
     Suitable materials for adhesive layer  43  include, but are not limited to, permanent adhesives such as thermosetting adhesives, epoxy adhesives, and radiation-cured adhesive materials, and other bonding agents. In additional applications, target substrate  42  may be provided in the form of a patterned film, which can be laminated onto battery stack  40 , or onto a thin film stackup including multiple battery cells  40 . 
     In step  28 , any transfer plate (or layer)  41  may be removed, for example by dissolving or otherwise removing temporary adhesive layer  39 . After completion of processing method  20 , battery stack  40  is released from process substrate  31  (and transfer layer or plate  41 ), and battery stack  40  can be bonded to permanent or target substrate  42 . One or more individual battery stacks  40  may then be utilized in a battery system  10 , for example in a stacked arrangement inside a battery enclosure  11 , as shown in  FIGS. 1A and 1B . Alternatively, the battery enclosure may incorporate an encapsulation layer  38  and the target substrate  42 . 
     This stacked configuration results in a battery system  10  with substantially more active material, as a fraction of total battery height, and provides a corresponding increase in potential energy density and storage capacity, as compared to other battery systems with similar overall dimensions, but larger substrate thicknesses. In very thin substrate applications, moreover, the thickness of target substrate  42  may be even less, for example about 5 μm or less, or about 2-3 μm, providing a further increase in battery capacity and performance. 
       FIG. 3  is a process flow diagram illustrating method  20  for producing battery stack  40 , in an alternate technique with a permanent base layer  32 . In this example, processing steps  21 ,  22 ,  23 ,  24 , and  25  may be similar to those of  FIG. 2 , above, or other thin film techniques may be used, as known in the art. In step  26 , base layer  32  is retained as a permanent base layer for battery stack  40 . 
     In this example, base layer  32  may be provided in the form of a silicon etch block or base layer, as described above, with or without a seed layer for generating a particular crystal plane orientation in one or more thin film battery layers  33 - 37 . After processing battery stack  40  to provide the desired crystalline structure and other material properties, process substrate layer  31  may be etched away, leaving thin film battery stack attached to base layer  32 . Alternatively, a mechanical process such as grinding can be used, avoiding the harsh chemical environment typically associated with etching. 
     In step  27 , battery stack  40  is attached to target substrate  42 , for example using a layer of permanent adhesive  43  to bond base layer  32  to target substrate  42 . In step  28 , temporary adhesive  39  and transfer layer  41  are removed, preparing battery stack  40  for use in a battery system  10 , as described above. Alternatively, the process substrate can also be used as the permanent substrate. 
       FIG. 4  is a process flow diagram illustrating method  20  for processing a plurality of battery stacks  40 , in a multiple stacked cell design. In this example, processing steps  21 - 25  may also be similar to those described above, with base layer  32  provided in the form of a sacrificial release layer, which is removed along with process substrate layer  31  in release step  26 . Instead of bonding battery stack  40  directly to a target substrate, however, a number of battery stacks  40  are assemble into a multi-cell stack configuration, as shown in step  29 . 
     Adjacent battery stacks  40  may also be inverted with respect to one another, with a layer of conducting adhesive  44  provided between adjacent cathode layers  34  or cathode collectors  33  (or both), forming a single cathode connector  33  for two adjacent battery stacks  40 . Alternatively, a non-conducting adhesive may be used, with separate (e.g. parallel) electrical connections between individual cathode collector layers  33 . 
     The order of individual thin film battery layers  33 - 37  can also be reversed or otherwise modified in individual battery stacks  40 , so that conducting adhesive  44  (or an insulating bonding agent) is provided between adjacent anode layers  36  and/or anode collectors  37 . A variety of different electrode couplings are also contemplated, for example with anode collectors  37  and cathode collectors  33  exiting from opposites sides of the stacked battery cell assembly, with additional conductive adhesive  44  between adjacent portions of the respective collector layers. 
     In step  30 , temporary adhesive  39  and transfer layers  41  are removed (see step  28 , above), and stacked battery cells  40  are provided for use in a battery system  10 . Additional battery stacks or cells  40  may also be added, to provide a multi-cell stacked battery design with an arbitrary number of battery stacks  40 . One or more substrate layers  42  and encapsulation layers  38  may also be included at the top or bottom of the individual battery cell stacks  40 , or eliminated altogether, depending upon the desired chemical and mechanical properties of battery system  10 . 
       FIG. 5  is a process flow diagram illustrating method  20  for processing multiple layered battery stacks or cells  40 , with a conducting adhesive cathode collector layer  33 . In this example, no separate cathode collector layer is formed in battery stack  40  (step  23 ). Both process substrate  31  and base (or release) layer  32  may be removed (step  26 ) before bonding adjacent (inverted) battery stacks  40  (step  29 ). 
     Thus, conductive adhesive  44  is provided directly between adjacent cathode layers  34 , and serves as both a bonding layer and a cathode current collector, as shown in step  28 . This design eliminates the need for conventional separate or distinct cathode collector layers, reducing battery height (or z-height) without removing active materials, and further increasing the potential energy density, with respect to other designs. 
       FIG. 6  is a process flow diagram illustrating method  20  for processing battery stacks or cells  40 , with multiple cell encapsulation. In this example, a sacrificial base or release layer  32  is utilized (step  22 ), and there is no encapsulation layer in either thin-film deposition (step  23 ) or subsequent processing of battery stack  40  (step  24 ). Depending on application, a separate cathode collector layer  33  may also be avoided, as described above with respect to  FIG. 5 . Using a suitable conducting adhesive layer  44  to form cathode collector  33  when adjacent battery stacks  40  are bonded together (step  29 ). 
     In stacking step  30 , any top or bottom transfer layers  41  that are used can be removed and pairs of adjacent battery stacks or cells  40  are bonded along the cathode collector interfaces, for example with additional conducting adhesive  44  between adjacent cathode collectors  37 . Alternatively, the individual cell stacking order can be reversed, as described above, and additional temporary adhesive  39  and transfer layers  41  may also be removed, in order to stack an arbitrary number of battery cells  40 . The multiply stacked cells  40  can then either be enclosed in a traditional battery casing, or encapsulated as a unit, as described below. 
     In some designs, all the cathode collector layers  33  in a particular battery system or assembly  10  are connected in parallel, as are the anode collector layers  37 . Alternatively, individual battery stacks  40  (or pairs or stacks of cells  40 ) may have a reversed orientation, in order to provide one or more series couplings for higher output voltage. Thus, a wide range of different stacking configurations are encompassed, including different vertical layer ordering, and different horizontal (left and right) anode and cathode collector orientations, as long as shorts and other direct couplings across the anode and cathode layers are avoided in individual battery cells or stacks  40 . 
       FIG. 7  is a process flow diagram illustrating method  20  for processing battery stacks  40 , with conducting adhesive anode and cathode collector layers. In this example, no separate cathode collector or anode collector layers  33  and  37  are formed in deposition step  23 , and both process substrate  31  and sacrificial base layer  32  are removed in release step  25 , before bonding adjacent battery stacks  40  (step  29 ). 
     In stacking step  30 , pairs of adjacent battery stacks or cells  40  may be bonded together, as described above with respect to the example of  FIG. 6 . As shown in  FIG. 7 , however, there are no separate anode collector structures, and conducting adhesive  44  serves as both the cathode collector  33  and the anode collector  37 . This provides a further decrease in the stacking height of the battery assembly, with an additional increase in power capacity and potential energy density, as compared to a more traditional design with the same form factor, or with the same mass and size envelope. 
     As shown in  FIGS. 2-7 , film transfer processing methods provide substantial advantages in the manufacture and structure of individual battery stacks  40 , and for assembled multi-cell or multi-stack battery systems  10 . The use of a thin film encapsulated structure substantially reduces the inactive material in battery system  10 , and increases the potential energy density. Alternatively, the z-height of the battery system can be reduced, within a given area, while maintaining or even increase total power output and storage capacity. 
       FIG. 8A  is a cross-sectional illustration of battery system  10 , in an encapsulated, stacked cell configuration. As shown in  FIG. 8A , any number of individual battery stacks or cells  40  can be stacked in a parallel plane orientation within battery system  10 . Different stacking orders and orientations are possible for the individual battery layers  33 - 37  in each stack  40 , and the anode and cathode collectors layers  37  and  33  can either be provided as independent structures, or combined the corresponding anode and cathode layers  36  and  34 , for example utilizing a conducting adhesive  44 . 
     In the particular configuration of  FIG. 8A , a substantially continuous encapsulation system  50  is provided over the outside surfaces of stacked cell battery assembly  10 . Depending on design goals, encapsulation system  50  may also function as the battery casing, in lieu of a separate enclosure, with connections to anode and cathode collectors  37  and  33  provided via electrodes  19 . 
     Generally, encapsulation system  50  is formed of a chemically inert and mechanically durable material, which is resistant to environmental effects. Suitable encapsulation materials include polymers and organic insulating materials, for example a plastic or laminated film, as described above for encapsulation layer  38 . Alternatively, one or both of encapsulation layer  38  and encapsulation system  50  may be formed of a thin liquid coating barrier layer, for example siloxane. Encapsulation system  50  may also be provided as a patterned layer, or a layer that is patterned before curing, in order to provide access for electrodes  19 , collector layers  33  and  37 , or both. 
     Encapsulation of battery system  10  reduces the non-active material content, and minimizes material overhead. This contrasts with other thin film and jelly roll battery designs, where a protective pouch or metal casing is utilized, and the nonactive mass and volume are greater. Alternatively, both an encapsulant (layer  38  or system  50 ) and an enclosure  11  may be provided, for example by inserting an encapsulated battery assembly  10  into an enclosure  11 , as shown in  FIG. 1A or 1B , in order to provide additional protection for mission-critical systems applications, or for use in harsh operating environments. 
     Suitable techniques for applying encapsulation system  50  include spray application, dip coating, and roll-to-roll or sheet-to-sheet film coating and application methods. Encapsulation system  50  may also be UV or thermally cured, for example at a temperature of about 180 C or lower. In particular applications, the curing temperature of encapsulation system  50  (or encapsulation layer  28 ) may be selected to be substantially below the melting point of lithium, and substantially below the crystallization temperature of the cathode layer, in order to avoid potential phase transitions in the materials of battery layers  33 - 37 , target substrate materials  42 , adhesives  43  and  44 , and the other components of processed battery stacks  40 . 
     In some designs, a multi-layer encapsulation system  50  is provided, for example with an inner layer  51  adjacent the stack of battery cells  40 , a middle layer  52  disposed about inner layer  51 , and an outer layer  53  disposed about middle layer  52 , with middle layer  52  located between inner layer  51  and outer layer  53 . Together, inner layer  51 , middle layer  52  and outer layer  53  provide a flexible covering and chemical/mechanical barrier, which expands and contracts during operation of battery system  10 , for example due to thermal effects during charging and discharging. 
     In one particular configuration, inner layer  51  is formed of a ceramic such as silicon nitride (SiN), or other ceramic material selected for bonding properties and density and to provide a chemical barrier. Middle layer  52  may be formed of a meteor metallic material selected for tensile strength and structural support, and outer layer  53  may be formed of a polymer such as parylene, or another polymer selected for density and ability to act as a moisture and oxygen barrier. 
       FIG. 8B  is an alternate cross-sectional illustration of battery system  10 , in an encapsulated configuration with internal spacing. In this configuration, a gap, internal diaphragm, or compressive spacer material  54  is provided between inner layer  51  of encapsulation system  50  and battery stacks  40 . An internal encapsulation layer  38  may also be provided, with spacer or gap  54  disposed between internal encapsulation layer  38  and layer  51  of outer encapsulation system  50 . 
       FIG. 8C  is a cross-sectional illustration of battery system  10  in a sloped sidewall configuration. In this configuration, sidewalls  55  of one or more individual battery stacks  40  are sloped at an angle with respect to the vertical; thus, sidewalls  55  are slanted with respect to the vertical or stacking direction, and not necessarily parallel to one another. 
     For example, sidewalls  55  may define a triangular or trapezoidal shape for the multi-cell stack, in which the lengths of the anode and cathode layers may be different. Encapsulation system  50  may also be provided in the form of a relatively thick encapsulation layer  38 , for example a liquid coating material, which can travel along the sloped outer surfaces or sidewalls  55  of the multilayer cell assembly, and may be more resistant to cracking when cured. 
       FIG. 9  is a block diagram of method  70  for forming a battery assembly, for example battery system  10  with one or more individual battery stacks or cells  40 , as described above. Method  70  may include one or more steps including, but not limited to, forming a base layer (step  71 ), forming a thin film battery stack on the base layer (step  72 ), processing the battery stack to achieve desired physical properties, and assembling the thin film battery stack into a battery system (step  80 ). Method  70  may also include one or more intermediate processing steps  74 - 79  and additional assembly steps  81 - 83 , as described below. 
     Forming a base layer (step  71 ) and forming a thin film battery stack on the base layer (step  72 ), and other steps of method  70 , may be performed according to any of the different examples of processing method  20 , as described above with respect to  FIGS. 2-7 , or using other thin film processing steps known in the art. For example, the battery stack may comprise anode, cathode, and electrolyte layers with or without distinct collector layers, and the base layer may be formed on a temporary process substrate or a permanent substrate material, such as a pattern film substrate. 
     After the battery layers are deposited, the battery stack (or stacks) can be processed (step  73 ) to generate a crystalline structure in the anode or cathode layers, or other desired property, for example by thermal treatment or annealing. Additional chemical, thin film, and mechanical processes may also be applied, including encapsulation of the individual battery stacks or cells. 
     Depending on embodiment, the thin film battery stack may be bonded to a transfer layer (step  74 ), for transfer from the process substrate (step  75 ). The process substrate can be remove by etching, or by generating a phase transition in the base layer, in order to release the process substrate from the battery stack. The base layer can either be removed along with the process substrate, or kept together with the battery stack, for assembly into the completed battery system. 
     The battery stack is typically transferred to the transfer layer for bonding to a target or permanent substrate (step  76 ), or for assembly into a multi-cell stack (step  77 ). Generally, the permanent target substrate materials are retained with the battery stack, in the final assembly, but a permanent substrate is not required. Any remaining transfer layers can also be removed (step  78 ), either during the stacking process (step  77 ), or during final assembly of the battery system (step  80 ). A pattern film lamination can also be applied (step  79 ), as described above. 
     In some examples, the thin film battery cells are stacked bottom-to-bottom, with a pair of cathode collectors placed in an adjacent and electrically coupled relationship. Alternatively, one or more collector layers may be omitted, and the bare cathode layers themselves may be adjacent. In this technique, a bond can be formed between adjacent pair of cathode layers, for example using a conducting adhesive, which forms a (single) cathode collector for the two adjacent cathode layers. 
     Similarly, battery cells can also be stacked top-to-top, or with a reversed layer structure, so that the anode collector (or bare anode) layers are adjacent. A conducting bond can be formed between the adjacent collector layers, or between adjacent bare anode layers. Thus, the conducting bonds can be formed with a direct electrical connection between adjacent anode or cathode layers, with no other intervening collector layers. 
     Assembling the battery system (step  80 ) may include encapsulating the battery stack (step  81 ), inserting the battery stack into a pouch or casing (step  82 ), or both. Typically, the battery assemblies also provides additional features, for example electrodes or other connectors, which are configured for connecting the battery stack (or multilayer stack of cells) to an electronic device (step  83 ), as described below. 
     The battery stacks can either be individually encapsulated (step  81 ), or encapsulated as a multilayer stack. For example, a multilayer encapsulation system may be provided to form a substantially continuous barrier, surrounding the stack of individual thin film battery cells. Typical multilayer systems include a ceramic inner layer oriented toward or proximate the multilayer stack of cells, and an outer polymer layer disposed about the inner ceramic layer, and oriented away from the stack. A metallic layer can also be included, for example between the inner ceramic layer and the outer polymer layer. 
     The battery stack (or stacks) can also be laminated together with a patterned film (step  79 ). The patterned film may include precut or patterned openings for accessing the connector, for example as described above with respect to  FIG. 2 , in order to make power connections to the electronic device. 
       FIG. 10  is a block diagram illustrating representative electronic device  100 , for example with housing  102  and controller  104  coupled to battery system  10 , in order to provide power management and operational control of device  100 . In some applications, electronic device  100  is configured for use as a smartphone, tablet computer, or other mobile device. Alternatively, device  100  may be configured as a media player, digital assistant, game player, personal computer or computer display; a laptop, desktop, notebook, or handheld computer; a navigational or communications system; a power tool or other power equipment; or a power management component for use in a commercial, industrial, or transportation power system. 
     Housing  102  is provided to protect the internal components of device  100 , and may be formed of a durable material such as aluminum and steel, or from metal, plastic, glass, ceramic, and composite materials, and combinations thereof. Cover glass  106  is typically formed of a glass or transparent ceramic material, for example silica glass or sapphire, or a clear plastic polymer such as acrylic or polycarbonate. In mobile device applications, cover glass  106  may include a display window for a touch screen, graphical interface or other display component  108 . 
     Device  100  may also include a number of additional components powered by battery system  10 , including, but not limited to, a motion sensor and other internal accessories  110 , audiovisual and sensor features  112  including speakers, microphones, cameras, and lighting/indicator features (e.g., a light emitting diode or flash device), and various control devices  114 , such as home, menu and hold buttons, volume controls, and other control elements, arranged variously with respect to housing  102  and cover glass  106 . 
     As shown in  FIG. 10 , controller  104  is coupled in signal and power communication with battery system  10 , and one or more of display  108 , internal accessories  110 , audiovisual features  112 , and control devices  114 . Controller  104  includes microprocessor and memory components configured to execute a combination of operating system and application firmware and software, in order to provide power management and device functionality including, but not limited to, data display, voice communications, voice control, media playback and development, internet access, email, messaging, gaming, security, navigation, transactions, and personal assistant functions. Controller  104  may also include additional input/output (I/O) components configured to support hard-wired, wireless, audio, visual, infrared (IR), and radio frequency (RF) connections  116 , for one or more external accessories  118 , host devices  120  and networks  122 . 
     While this invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents may be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, modifications may be made to adapt the teachings of the invention to particular situations and materials, without departing from the essential scope thereof. Thus, the invention is not limited to the particular examples that are disclosed herein, but encompasses all embodiments falling within the scope of the appended claims.