Abstract:
A co-extrusion print head capable of extruding at least two layers vertically in a single pass having a first inlet port connected to a first manifold, a first series of channels connected to the first inlet port arranged to receive a first fluid from the first inlet port, a second inlet port connected to one of either a second manifold or the first manifold, a second series of channels connected to the second inlet port arranged to receive a second fluid from the second inlet port, a merge portion of the print head connected to the first and second series of channels, the merge portion arranged to receive the first and second fluids, and an outlet port connected to the merge portion, the outlet port arranged to deposit the first and second fluids from the merge portion as a vertical stack on a substrate.

Description:
RELATED APPLICATIONS 
     The application is related to US Patent Publication No. 20120156364; US Patent Publication No. 20120153211; U.S. patent application Ser. Nos. 13/727,937; 13/727,960; and 13/727,993. 
     BACKGROUND 
     Battery manufacturing requires disparate processing of the cathode, anode and separator materials. This causes high production costs that remain a barrier to adoption in key electric vehicles and grid storage markets. Conventional lithium ion cell production consists of slurry coating the anode and cathode materials onto the current collectors that may be referred to as foils, typically in separate rooms. They are then calendared, which involves pressing them flat, drying them and re-reeling the foils. The foils are then slit to the size required and re-reeled. During cell assembly, the anode and cathode are subsequently laminated together with the separator material in between and packaged into a can or case during final assembly. This process typically involves 6 or more wind/unwind (reeling) operations, each having their own costs and possible yield losses. 
     Current methods of multilayer coating typically employ a slot or slide coater. These tools can coat up to 3 layers simultaneously by stacking the dies or distributions plates. However, lower viscosity pastes with lower particulate loading do not have adequate control of layer boundaries. Depending upon the viscosities of the pastes, the dies or print heads used in these methods may also have speed limitations, as discussed in U.S. Pat. No. 7,700,019. 
     The approach in U.S. Pat. No. 7,700,019 proposes a method of using multi-layer extrusion with slot dies for fabricating vertical layers of electrode material on current collectors with a sheet of polymer electrolyte. This patent discloses slot coating and cannot handle high particulate loading or viscosity of paste that provide better battery structures. 
     Another approach is disclosed in U.S. Pat. No. 7,799,371 in which a multi-layer metal stack fabricated by individual orifice outlets such that layers of dispensed paste lie on top of each other. In this approach, the materials merge together and form the multi-layer structure outside the printhead. This may cause issues with registration between the layers if the substrate or the print head shifts during deposition. 
     A co-extrusion print head, as opposed to a slot coater, and a co-extrusion process has been discussed in several US Patents and US Patent Applications. Examples of these types of battery electrodes are discussed in U.S. Pat. Nos. 7,765,949; 7,780,812; 7,922,471; and US Patent Publications 20120156364 and 20120153211. U.S. Pat. No. 7,765,949 discloses a device for extruding and dispensing materials on a substrate, the device has at least two channels for receiving materials and an exit port for extruding the materials onto the substrate. U.S. Pat. No. 7,780,812 discloses another such device having a planarized edge surface. U.S. Pat. No. 7,922,471 discloses another such device for extruding materials that have an equilibrium shape that does not settle after deposition onto the substrate. US Patent Publications 20120156364 and 20120153211 disclose a co-extrusion head that combines streams of two or more materials into an interdigitated structure on a substrate, where there are multiple stripes of the materials. None of these discussions address co-extruding multi-layer structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a method of manufacturing batteries in accordance with the prior art. 
         FIG. 2  shows an embodiment of a slot coating system to coat a current collector. 
         FIG. 3-6  show embodiments of co-extruded materials. 
         FIG. 7  shows a flowchart of an embodiment of a method of making a vertically stacked battery structure. 
         FIG. 8  shows an embodiment of a co-extrusion print head capable of extruding three vertically stacked materials. 
         FIG. 9  shows a side view of an embodiment of a co-extrusion print head capable of extruding a vertically stacked battery structure in one pass. 
         FIG. 10  shows a side view of a fully assembled multi-layer co-extrusion print head. 
         FIG. 11  shows an embodiment of a multi-layer co-extrusion print head consisting of a set of plates. 
         FIG. 12  shows an exploded view of a portion of a multi-layer co-extrusion print head consisting of a set of plates. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows an example of a process to manufacture batteries. The two processes are very similar but occur in separate clean rooms. For example, the process begins with formation of the cathode or anode slurries at  10  and  11 . The current collectors are then unreeled and coated at steps  12  and  13 . The coated collectors are then calendared for thickness at  14  and  15 . The calendared collectors are then dried at  16  and  17  to remove the solvents. The calendared and dried collectors are then rewound. The collectors are then unwound and slit to the size required for a particular cell at  18  and  19 , and then rewound. The foils are then unwound again and laminated together with a separator between them at  20 . The finished product is then packaged into a can or case during final cell assembly. 
     Currently, the preferred method of multilayer coating uses a slot or slide coater in a system  30  shown in  FIG. 2 . In these systems, a coating head  24  coats the substrate  22  with a material  28  as it passes by a transport roller  26 . The slot coater generally deposit single material layers that are thinner with lower viscosity than pastes that have sufficient particle loading to make efficient battery structures. Further, the slot coaters cannot fabricate both electrodes and separator in a single pass from the same print head apparatus, nor can a slot coating machine produce interdigitated cathodes and anodes. 
       FIGS. 3-6  show embodiments of co-extruded materials.  FIG. 3  shows a prior art embodiment of co-extruded materials. The substrate, which may or may not consist of current collector, receives stripes of interdigitated materials  40  and  42 . In one embodiment, the material  40  may be the same material or two different materials, one for the cathode and anode, or may consist of the same material. Alternatively, it may be a highly porous material that can be filled with an electrolyte, or a sacrificial material that can be replaced with an electrolyte, as examples. One should note that the materials here will be referred to as fluids, which includes slurries and pastes or any type of material that can be flowed, however slowly, through a print head. 
     In contrast, the embodiments disclosed here stack the materials vertically, rather than dispensing them side by side.  FIG. 4  shows the materials  40  and  42 , to demonstrate the differences, stacked vertically on the substrate  44 . These materials are deposited simultaneously in one pass from a print head subject to the discussion here. The embodiments of  FIGS. 3 and 4  may be of different scales. 
     Using this print head, further modifications become possible.  FIG. 5  shows a first embodiment of a vertically stacked battery structure having an anode  40 , a separator  42 , and an interdigitated cathode  46 . The interdigitated cathode  46  in this embodiment consists of an active material  48  and an intermediate material  50 . The intermediate material  50  may be a sacrificial material that is burned off or otherwise removed and then replaced with a liquid or gel electrolyte. Another possibility is that the material  50  may be a highly porous material that would then be filled with a liquid or gel electrolyte. Other types of materials are of course possible. 
       FIG. 6  shows another possible modification of the vertically stacked materials. In this embodiment, both the anode and cathode are interdigitated. The anode  40  consists of interdigitated stripes of an active material  52  and an intermediate material  54 . The active material would typically be different than the active material of the cathode, but the intermediate material may be a sacrificial material or a highly porous anode material that would then be filled with a liquid or gel electrolyte. Any aspects of these embodiments may be mixed with aspects of the other embodiments, such as having an interdigitated anode but not an interdigitated cathode, or variations on materials, etc. In addition, the process of manufacturing these structures is far simpler than the process of  FIG. 1 . 
       FIG. 7  shows an embodiment of a manufacturing process  60  for vertically stacked structures. Similar to the process of  FIG. 1 , the anode, cathode and separator slurries are formed at  62 . A difference here lies in the formation of the separator slurry, since the previous process put the separator sheet in as a final step. In addition, the slurries themselves will typically be different. As mentioned previously, the anode and cathode liquid materials used in slot coating generally have lower viscosity and lower levels of particle loading that the slurries that can be used here. Higher particle loading and viscosities enable different structures that lead to better electrical performance. 
     At  64 , the slurries are loaded into a multi-layer co-extrusion print head and all three materials are deposited onto the substrate in one pass. The substrate in this embodiment would be one of the two current collectors in a battery structure. One should note that the embodiments here are directed to a battery structure having three materials, but more or less than 3 materials could be used, and could be used in structures other than batteries. 
     Once the materials are deposited onto the substrate, the substrate and materials may be calendared for thickness control at  66 . Depending upon the materials and process used, calendaring may not be necessary. The calendared substrate is then dried at  68  to get rid of solvents and other extraneous materials. The resulting structure is then assembled into its final form with the remaining current collector. Again, this is merely one example of one structure that can result from this print head and process. 
       FIG. 8  shows an example of such a print head  80 . In this embodiment, the print head has 3 material paths, but may employ more or fewer materials. In this example, the print head has a lower material  88  that flows from a first fluid path. A middle material  86  flows from a second fluid path, and a top material  84  flows from a third fluid path. The three materials are deposited in simultaneously onto the substrate  82 . One aspect of these embodiments is that the materials are flowed together inside the print head, rather than after the fluids leave the print head. When the materials flow together into their layers outside the print head, there is a tail portion in which the lowest material protrudes from under the middle material, and the middle material will protrude from under the top layer of material. Further, if there is any kind of agitation in the movement of the print head, the layers may lose registration between themselves. 
       FIG. 9  shows a side view of an embodiment of a multi-layer co-extrusion print head  80  using four materials, where two of the materials are horizontally interdigitated when the vertically stacked materials are deposited. Materials  90  and  92  are horizontally interdigitated by the flow paths from the inlet ports  91  and  93  to form an interdigitated layer at the exit orifice  98 . In one embodiment, this interdigitated layer would form the cathode of a battery structure. The separator material  94  flows from a second flow path and inlet port  95  and the anode material  96  from a third path and inlet port  97 . These materials will exit the orifice  98  together to form a vertically stacked structure as seen in  FIG. 5 .  FIG. 10  shows an embodiment of a print head  80  after it has been fully assembled such that one can only see the exit orifice  98 . 
       FIG. 11  shows a particular embodiment of a multi-layer co-extrusion print head. The term ‘multi-layer’ refers to the resulting stacked structure, although the print head consists of multiple layers. The embodiment here has a first plate  100 , which may be referred to a fixture plate. In one embodiment, the fixture plate consists of a steel plate but any rigid material that can put enough pressure on the plates to keep them flat will suffice. A sealing gasket  102  resides next to the fixture plate. The dual side manifold  104  distributes 2 cathode or anode materials to form the interdigitated cathode or anode structure. The sheets or plates in a first subset  106  of the sheets of the print head form fluid channels for the interdigitated cathode or anode. In this embodiment the first set  106  consists of sheets  108 ,  110  and  112 . One should note that while some of this discussion may assume the cathode is produced by the lower sheets, but they could also produce the anode. 
     Sheet  114  is a merge or transition sheet for the cathode or anode and separator fluids. The sheets in another subset  116 , in this case sheets  118  and  120 , form the fluid channels for the separator. The separator material merges with the anode material in the channels of sheet  122 . The subset of sheets  124 , consisting of sheets  126 ,  128  and  130 , provide the fluid channels for the anode. A dual side manifold  132  provides fluid distribution for the anode and the separator. The set of sheets is then sealed on the top with a sealing gasket  134  and a top plate  136 . Typically the set of sheets that form the print head is held together by bolts that can be tightened to ensure sealing of the stack. The registration between the layers is ensured by alignment features on the plates or sheets. 
       FIG. 12  shows an exploded view of one of the subsets of sheets, in this case the subset  106  that combines the two fluids for the cathode or anode that result in an interdigitated cathode or anode. Plate  110  has channels  143  towards the back of the plate, as oriented in the drawing, and plate  108  has channels  142 . These channels  142  and  143  take the first cathode material from the manifolds such as  204  in plate  104 . Similarly, plate  110  has channels  144  and plate  108  has channels  140 . These channels  144  and  140  take the second cathode material from the manifold. Plate  112  has channels  146  that merge the first and second cathode materials into the interdigitated cathode layer. As discussed above, the interdigitated cathode materials then flow up to the merge and transition sheet  114  to merge with the materials from the separator flow path. 
     Many variations and modifications of the print head are of course possible. One of the possible modifications is that the anode sheets set  124  in  FIG. 11  could be replaced with sheets similar to the sheets in set  106  to form an interdigitated anode. An additional distribution path would need to be added to the anode/separator manifold or the cathode manifold, forming a print head that takes in 5 separate fluids and merges them into the battery structure. Another modification would simplify the sheets to a 2 layer structure, meaning that only 2 materials are used to form the structure. This would be accomplished by removing the appropriate sheets and manifolds from the assembly. 
     In this manner, a structure of vertically stacked materials can be formed on a substrate. The stack may be of two or more layers and the stack may form a battery structure or other types of structures. The layers may consist of one or more layers of interdigitated materials. In one embodiment, the structure is a battery consisting of three layers, an anode, a cathode and a separator. In another embodiment, the cathode consists of two materials interdigitated. In yet another embodiment, the anode consists of two materials interdigitated as well. Regardless of the structure or the number of layers, the resulting structure has vertically stacked layers that are deposited in one pass. 
     It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.