Patent Publication Number: US-2019181431-A1

Title: Solid film as binder for battery electrodes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/596,035, filed Dec. 7, 2017. The entirety of the above referenced application is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to electrochemical cells and electrodes used in electrochemical cells. In particular, the present disclosure relates to electrodes and electrochemical cells for use in batteries, including methods of forming electrodes and electrochemical cells. 
     Description of the Related Art 
     A lithium ion battery typically includes a separator and/or electrolyte between an anode and a cathode. In one class of batteries, the separator, cathode and anode materials are individually formed into sheets or films. Sheets of the cathode, separator and anode are subsequently stacked or rolled with the separator separating the cathode and anode (e.g., electrodes) to form the battery. For the cathode, separator and anode to be rolled, each sheet must be sufficiently deformable or flexible to be rolled without failures, such as cracks, brakes, mechanical failures, etc. Typical electrodes include electro-chemically active material layers on electrically conductive metals (e.g., aluminum and copper). For example, electrochemically active material can be deposited onto a current collector along with an inactive binder material. Electrodes can be rolled or cut into pieces which are then layered into stacks. The stacks are of alternating electro-chemically active materials with the separator between them. 
     SUMMARY 
     Example methods of forming electrodes are provided. The method can include providing a current collector, providing a substantially solid layer of electrode attachment substance on a side of the current collector, and providing electrochemically active material adjacent the substantially solid layer of the electrode attachment substance. The electrochemically active material can be provided in powder form. The method can also include adhering the electrochemically active material to the side of the current collector via the electrode attachment substance. 
     In various methods, providing the electrochemically active material adjacent the layer of electrode attachment substance can comprise sandwiching the layer of electrode attachment substance between the electrochemically active material and the current collector. Some such methods can further comprise providing a second layer of electrode attachment substance adjacent the electrochemically active material such that the electrochemically active material is sandwiched between the two layers of electrode attachment substance. In some methods, providing the electrochemically active material adjacent the layer of electrode attachment substance can comprise sandwiching the electrochemically active material between the layer of electrode attachment substance and the current collector. 
     In some methods, the layer of electrode attachment substance can comprise a thermoplastic film. The layer of electrode attachment substance can be insoluble in solvent at a temperature below about 200° C. The layer of electrode attachment substance can comprise a polyphenylene sulfide film, a polyether ether ketone film, a polyether sulfone film, a polysulfone film, or a polyethylene terephthalate film. 
     The electrochemically active material can comprise a silicon carbon composite material. In some examples, the electrochemically active material can include at least about 50% to about 100% by weight of silicon. For instance, the electrochemically active material can include the silicon at about 60% to about 100% by weight, at about 70% to about 100% by weight, or at about 80% to about 100% by weight. 
     In some methods, adhering can comprise applying pressure to the electrode attachment substance and/or the electrochemically active material to adhere the electrochemically active material to the current collector. In some methods, adhering can comprise applying heat to the electrode attachment substance and/or the electrochemically active material to adhere the electrochemically active material to the current collector. In some methods, adhering can include an extrusion process. The current collector can be provided in roll form. The layer of electrode attachment substance can be provided in roll form. The method can comprise a roll to roll process. 
     Various methods can further include providing a second layer of electrode attachment substance on second side of the current collector, providing a second electrochemically active material adjacent the second layer of electrode attachment substance, and adhering the second electrochemically active material to the second side of the current collector via the second layer of electrode attachment substance. In some methods, providing the second electrochemically active material adjacent the second layer of electrode attachment substance can comprise sandwiching the second layer of electrode attachment substance between the second electrochemically active material and the current collector. The methods can further include providing a third layer of electrode attachment substance adjacent the second electrochemically active material such that the second electrochemically active material is sandwiched between the two layers of electrode attachment substance. In some methods, providing the second electrochemically active material adjacent the second layer of electrode attachment substance can comprise sandwiching the second electrochemically active material between the second layer of electrode attachment substance and the current collector. 
     In some methods, the second layer of electrode attachment substance can be provided in a substantially solid state. The second layer of electrode attachment substance can comprise a thermoplastic film. The second layer of electrode attachment substance can be insoluble in solvent at a temperature below about 200° C. The second layer of electrode attachment substance can comprise a polyphenylene sulfide film, a polyether ether ketone film, a polyether sulfone film, a polysulfone film, or a polyethylene terephthalate film. 
     In some instances, the second layer of electrode attachment substance can comprise a different material than the substantially solid layer of electrode attachment substance. The second electrochemically active material can be provided in powder form. The second electrochemically active material can comprise a silicon carbon composite material. In some examples, the second electrochemically active material can include at least about 50% to about 100% by weight of silicon. For instance, the second electrochemically active material can include the silicon at about 60% to about 100% by weight, at about 70% to about 100% by weight, or at about 80% to about 100% by weight. 
     In some methods, adhering the electrochemically active material and adhering the second electrochemically active material can occur simultaneously. The electrode can be a negative electrode. 
     Additional example methods of forming electrodes are provided. The method can include providing a current collector, providing a layer comprising electrochemically active material on a side of the current collector, and providing a substantially solid layer of electrode attachment substance adjacent the layer comprising electrochemically active material such that the electrochemically active material is between the substantially solid layer of electrode attachment substance and the current collector. The method can also include adhering the electrochemically active material to the side of the current collector via the electrode attachment substance. 
     Various methods can further comprise providing a second substantially solid layer of electrode attachment substance between the layer comprising electrochemically active material and the current collector such that the electrochemically active material is sandwiched between both of the provided layers of electrode attachment substance. The electrochemically active material can be provided in powder form. The electrochemically active material can be provided as a film. The film can comprise a silicon carbon composite film. In some examples, the electrochemically active material can comprise at least about 50% to about 100% by weight of silicon. For instance, the electrochemically active material can include the silicon at about 60% to about 100% by weight, at about 70% to about 100% by weight, or at about 80% to about 100% by weight. 
     In some methods, the layer of electrode attachment substance can comprise a thermoplastic film. The layer of electrode attachment substance can be insoluble in solvent at a temperature below about 200° C. The layer of electrode attachment substance can comprise a polyphenylene sulfide film, a polyether ether ketone film, a polyether sulfone film, a polysulfone film, or a polyethylene terephthalate 
     In some methods, adhering can comprise applying pressure to the electrode attachment substance and/or the electrochemically active material to adhere the electrochemically active material to the current collector. In some methods, adhering can comprise applying heat to the electrode attachment substance and/or the electrochemically active material to adhere the electrochemically active material to the current collector. In some methods, adhering can include an extrusion process. The current collector can be provided in roll form. The layer of electrode attachment substance can be provided in roll form. The layer of electrochemically active material can be provided in roll form. The method can comprise a roll to roll process. 
     Various methods can further include providing a layer comprising a second electrochemically active material on a second side of the current collector, providing a substantially solid layer of a second electrode attachment substance adjacent the layer comprising the second electrochemically active material such that the second electrochemically active material is between the second electrode attachment substance and the current collector, and adhering the second electrochemically active material to the second side of the current collector via the second electrode attachment substance. The methods can further include providing a substantially solid layer of a third electrode attachment substance between the layer comprising the second electrochemically active material and the current collector such that the second electrochemically active material is sandwiched between the second and third electrode attachment substance. 
     In some methods, the second electrochemically active material can be provided in powder form. The second electrochemically active material can be provided as a film. In some instances, the second electrochemically active material can comprise a silicon carbon composite film. In some examples, the second electrochemically active material can include at least about 50% to about 100% by weight of silicon. For instance, the second electrochemically active material can include the silicon at about 60% to about 100% by weight, at about 70% to about 100% by weight, or at about 80% to about 100% by weight. 
     In some methods, the second electrode attachment substance can comprise a thermoplastic film. The second electrode attachment substance can comprise a different material than the electrode attachment substance. 
     In some methods, adhering the electrochemically active material and adhering the second electrochemically active material can occur simultaneously. The electrode can be a negative electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  schematically illustrates an example electrode in accordance with certain embodiments described herein. 
         FIGS. 1B, 1C, and 1D  schematically illustrate examples of various configurations to prepare layers of current collector, electrode attachment substance, and electrode active material to form an electrode. 
         FIG. 2  shows an example method of forming an electrode in accordance with certain embodiments described herein. 
         FIG. 3  shows another example method of forming an electrode in accordance with certain embodiments described herein. 
         FIG. 4  is a plot of the discharge capacity versus the number of cycles for electrodes made using a binder in N-Methyl-2-pyrrolidone (NMP) solution compared to example electrodes made in accordance with certain embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Commercial lithium-ion battery electrodes are commonly fabricated by casting a slurry onto a metallic current collector. The slurry typically includes active material, conductive additive (e.g., carbon), and binder in a solvent (e.g., N-Methyl-2-pyrrolidone (NMP)). In general, the slurry after being uniformly mixed is cast onto the current collector and the solvent is dried off. The drying process time can be consuming and costly, with the added cost of the sacrificial solvent which in most cases can come with risks of pollution and/or safety hazards. In addition, the use of a cast slurry as electrode material can limit the number of binders that can be used to fabricate such electrode. For example, generally, the binder must be chemically inert to the electrolyte within the battery, but at the same time, it needs to be fairly easily dissolvable in the solvent used for the slurry mix. 
     Certain implementations described herein utilize one or more substantially solid layers of electrode attachment substance to adhere the electrochemically active material to the current collector. For example, a single solid film or multiple solid films (e.g., one or more thermoplastic films) can be used as the binder/adhesive of the electrode active material by binding together active material powders or other active material (e.g., an active material film) to the current collector. In various instances, using a solid film as adhesive/binder material for active material can allow fabrication of battery electrodes in a roll to roll process. In some embodiments, using a solid film as adhesive/binder material can also allow for fabrication without any solvent for slurry mixes and/or without coating of slurry mixes. By adhering active material to a current collector without the use of a slurry mix, there is no need to dissolve the binder materials in a solvent in order to make the slurry mix. Some such embodiments can be solvent free, e.g., solvent free roll to roll fabrication of battery electrodes, which can reduce production time and lower production cost (e.g., due to no solvent for slurry mixes, no coating of slurry mixes, and/or no drying of slurry mixes). Some such processes can be based on pressure and/or temperature to allow adhesion/binding. 
       FIG. 1A  schematically illustrates an example electrode in accordance with certain embodiments described herein. The electrode  100  can be used as a negative electrode (e.g., an anode), a positive electrode (e.g., a cathode), or both. Various embodiments of the electrode  100  can be used in an electrochemical cell. The electrode  100  can be used in either secondary batteries (e.g., rechargeable) or primary batteries (e.g., non-rechargeable). The electrochemical cell can include a lithium ion battery. 
     With continued reference to  FIG. 1A , the example electrode  100  can include a current collector  110 , a substantially solid layer of electrode attachment substance  120 , and a layer comprising electrochemically active material  130 . The current collector  110  can include any current collector material known in the art or yet to be developed. For example, the current collector  110  can include a metal. Example metals include, but are not limited to, copper, nickel, iron, titanium, molybdenum, stainless steel, chromium, aluminum, or a combination thereof. In some instances, copper and/or nickel can be used for an anode, and aluminum can be used for a cathode. In some embodiments, the current collector  110  can include non-metallic materials. An example non-metallic conductive material includes carbon. 
     The electrode attachment substance  120  (e.g., adhesive) can be used to couple or adhere the electrochemically active material  130  to the current collector  110  (e.g., to prevent delamination between them). In various embodiments, the attachment substance  120  is in a substantially solid state. For example, the attachment substance  120  can be a thermoplastic film/foil. Since certain embodiments do not coat a slurry mix on a current collector, the attachment substance  120  is not limited to binders which are soluble in solvents. For example, the attachment substance  120  can include a polyphenylene sulfide (PPS) film, which typically is insoluble in solvent at a temperature below about 200° C./392° F. Some other examples of attachment substance  120  can include films/foils of polyether ether ketone (PEEK), polyether sulfone (PES), polysulfone (PSU), or polyethylene terephthalate (PET). 
     With continued reference to  FIG. 1A , the layer comprising electrochemically active material  130  can include any electrochemically active material in any form (e.g., powder or film form). In some examples, the electrochemically active material can include silicon, germanium, tin, oxide, carbon, graphite, or a combination thereof. Various embodiments can include a silicon-carbon (or carbon-silicon) composite material. U.S. patent application Ser. No. 13/008,800, filed Jan. 18, 2011, and published on Jul. 21, 2011 as U.S. Patent Application Publication No. 2011/0177393, entitled “Composite Materials for Electrochemical Storage;” U.S. patent application Ser. No. 13/601,976, filed Aug. 31, 2012, and published on Jun. 19, 2014 as U.S. Patent Application Publication No. 2014/0170498, entitled “Silicon Particles for Battery Electrodes;” and U.S. patent application Ser. No. 13/799,405, filed Mar. 13, 2013, and published on Jun. 19, 2014 as U.S. Patent Application Publication No. 2014/0166939, entitled “Silicon Particles for Battery Electrodes,” each of which is incorporated by reference herein, describe certain embodiments of carbon-silicon composite materials using carbonized polymer and silicon material. In various embodiments, the layer of electrochemically active material  130  can include a film, e.g., a silicon-carbon composite film. 
     The layer of electrochemically active material  130  can include electrode active material with or without additives. For example, the layer of electrochemically active material  130  can include from greater than 0% to about 100% by weight of electrochemically active material. For example, the amount of electrochemically active material by weight of the layer of electrochemically active material  130  can include any weight percent within this range (e.g., about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, etc.), or any range within this range such as any range formed by the example values (e.g., greater than about 0% to about 25% by weight, greater than about 0% to about 35% by weight, greater than about 0% to about 50% by weight, greater than about 0% to about 70% by weight, greater than about 0% to about 90% by weight, greater than about 0% to about 95% by weight, from about 10% to about 35% by weight, from about 10% to about 50% by weight, from about 10% to about 90% by weight, from about 10% to about 95% by weight, from about 10% to about 100% by weight, from about 30% to about 85% by weight, from about 30% to about 90% by weight, from about 30% to about 95% by weight, from about 30% to about 100% by weight, from about 50% to about 85% by weight, from about 50% to about 90% by weight, from about 50% to about 95% by weight, from about 50% to about 100% by weight, from about 60% to about 85% by weight, from about 60% to about 90% by weight, from about 60% to about 95% by weight, from about 60% to about 100% by weight, from about 70% to about 85% by weight, from about 70% to about 90% by weight, from about 70% to about 95% by weight, from about 70% to about 100% by weight, from about 80% to about 90% by weight, from about 80% to about 95% by weight, from about 80% to about 100% by weight, etc.). 
     As an example, the layer of electrochemically active material  130  can include at least about 50% to about 100% by weight of silicon, at least about 60% to about 100% by weight of silicon, at least about 70% to about 100% by weight of silicon, at least about 80% to about 100% by weight of silicon. In some examples, the layer of electrochemically active material  130  can include 100% silicon. 
       FIGS. 1B, 1C, and 1D  schematically illustrate various example configurations to prepare the layers of current collector  110 , electrode attachment substance  120  (e.g., binder/adhesive), and electrode active material  130  to form an electrode. In  FIG. 1B , a substantially solid layer of electrode attachment substance  120  is sandwiched between a layer of electrochemically active material  130  and the current collector  110 . In  FIG. 1C , the layer of electrochemically active material  130  is sandwiched between two layers electrode attachment substance  120 ,  125 . In  FIG. 1D , the layer of electrochemically active material  130  is sandwiched between the layer of electrode attachment substance  120  and the current collector  110 . In some instances, the layers in  FIGS. 1B, 1C, and 1D  can be extruded, heat laminated, roll pressed, flat pressed, etc. to form the example electrode illustrated in  FIG. 1A . The attachment substance  120  can bind to the active material  130  and current collector  110 . 
       FIG. 2  illustrates an example method of forming an electrode (e.g., the electrode  100  schematically illustrated in  FIG. 1A ). The method  200  of forming can include providing a current collector, as shown in block  210 , and providing a substantially solid layer of electrode attachment substance on a side of the current collector, as shown in block  220 . The method  200  can also include providing electrochemically active material adjacent the substantially solid layer of electrode attachment substance, as shown in block  230 . Further, the method  200  can include adhering the electrochemically active material to the side of the current collector via the electrode attachment substance, as shown in block  240 . 
     With reference to block  210 , the current collector (e.g., current collector  110  in  FIGS. 1A-1D ) can be provided as a sheet (e.g., foil, film, etc.). In some instances, the current collector can be provided in roll form. With reference to block  220 , the substantially solid layer of electrode attachment substance (e.g., attachment substance  120  in  FIGS. 1A-1D ) can be provided in roll form as well to allow a roll to roll process. With reference to block  230 , the electrochemically active material can be provided in powder (e.g., particles, fibers, etc.) or film (e.g., sheet, foil, etc.) form. 
     When provided in powder form, the electrochemically active material can be dispersed on the solid layer of electrode attachment substance (e.g., as in  FIGS. 1B  and  1 C) or on the current collector (e.g., as in  FIG. 1D ). When provided in film form, the active materials can be pre-processed and available in sheets or in roll form (e.g., allowing for roll to roll processing). The film can be placed on the solid layer of electrode attachment substance (e.g., as in  FIGS. 1B and 1C ) or on the current collector (e.g., as in  FIG. 1D ). 
     As shown in  FIG. 1B , the electrochemically active material  130  can be provided adjacent the layer of electrode attachment substance  120  such that the layer of electrode attachment substance  130  is between the electrochemically active material  130  and the current collector  110  (e.g., the layer of electrode attachment substance  120  sandwiched between the layer of electrochemically active material  130  and the current collector). In some instances, as shown in  FIG. 1C , a second layer of electrode attachment substance  125  can be provided adjacent the electrochemically active material  130  such that the electrochemically active material  130  can be sandwiched between the two layers of electrode attachment substance  120 ,  125 . In some embodiments, as shown in  FIG. 1D , the electrochemically active material  130  can be provided adjacent the layer of electrode attachment substance  120  such that the electrochemically active material  130  can be sandwiched between the layer of electrode attachment substance  120  and the current collector  110 . 
     With reference to block  240 , the electrochemically active material can be adhered to the side of the current collector via the electrode attachment substance (e.g., to form  FIG. 1A ). In some embodiments, the layers can undergo an extrusion process to adhere the layers together. In some instances, the layers can be adhered mechanically by applying pressure and/or adhered thermally by applying heat to one or more of the layers. For example, a pressure from about 10 MPa to about 45 MPa (e.g., any pressure within this range such as about 10 MPa, about 15 MPa, about 20 MPa, about 25 MPa, about 30 MPa, etc.), or any range within this range (e.g., any range formed by the example values such as about 10 MPa to about 40 MPa, about 10 MPa to about 35 MPa, about 15 MPa to about 45 MPa, about 15 MPa to about 40 MPa, about 20 MPa to about 45 MPa, about 20 MPa to about 40 MPa, about 20 MPa to about 35 MPa, about 25 MPa to about 35 MPa, etc.) can be applied. As another example, a temperature from about 150° C. to about 350° C. (e.g., any temperature within this range such as about 150° C., about 175° C., about 200° C., about 225° C., about 250° C., about 275° C., about 300° C., about 325° C., about 350° C., etc.) or any range within this range (e.g., any range formed by the example values such as about 150° C. to about 325° C., about 150° C. to about 300° C., about 200° C. to about 350° C., about 200° C. to about 325° C., about 200° C. to about 300° C., etc.) can be applied. As another example, the layers can be adhered with a two-step process, such as applying a first lower temperature (e.g., from about 150° C. to about 250° C., from about 160° C. to about 250° C., from about 170° C. to about 250° C., from about 180° C. to about 230° C., from about 180° C. to about 240° C., from about 180° C. to about 250° C., etc.) followed by a higher temperature (e.g., from about 260° C. to about 300° C., from about 260° C. to about 310° C., from about 260° C. to about 325° C., from about 260° C. to about 350° C., etc.). In some instances, the attachment substance  120  can be adhered to the current collector  110  at a lower temperature, and the electrochemically active material  130  can be adhered to the current collector  110  at a higher temperature. Other examples are possible. 
     Although  FIGS. 1A-1D  illustrate active material on one side of the current collector, electrochemically active material can also be placed on the other side of the current collector, e.g., using one or more similar processes. For example, a layer of electrode attachment substance can be provided on the other side of the current collector, and electrochemically active material can be provided adjacent that layer of electrode attachment substance. The electrochemically active material can be adhered to that side of the current collector via the layer of electrode attachment substance. In some instances, the layer of electrode attachment substance can be sandwiched between the electrochemically active material and the current collector. In some instances, the electrochemically active material can be sandwiched between two layers of electrode attachment substance. In some instances, the electrochemically active material can be sandwiched between the layer of electrode attachment substance and the current collector. 
     The electrode attachment substance can be the same as or different from the electrode attachment substance on the other side of the current collector. The electrode attachment substance can include any of the attachment substances described herein. For example, the electrode attachment substance can be provided in a substantially solid state. The attachment substance can be a thermoplastic film. In some instances, the attachment substance can be polyphenylene sulfide or any other polymer that is insoluble in a solvent e.g., at a temperature below about 200° C. Some other examples of attachment substance  120  can include films/foils of polyether ether ketone (PEEK), polyether sulfone (PES), polysulfone (PSL), or polyethylene terephthalate (PET). 
     The electrochemically active material can be the same as or different from the electrochemically active material on the other side of the current collector. The electrochemically active material can include any of the electrochemically active material described herein. For example, the electrochemically active material can be in powder or film form. The active material can include a silicon carbon composite material. In some examples, the active material can include at least about 50% to about 100% by weight of silicon, at least about 60% to about 100% by weight of silicon, at least about 70% to about 100% by weight of silicon, at least about 80% to about 100% by weight of silicon, or 100% by weight of silicon. 
     The electrochemically active material can be adhered to the current collector as described herein (e.g., by applying pressure and/or heat). In some instances, adhering the electrochemically active material on both sides of the current collector can occur simultaneously. In some instances, the electrochemically active material can be adhered sequentially on one side of the current collector and then on the other side of the current collector. 
       FIG. 3  illustrates another example method of forming an electrode (e.g., the electrode  100  schematically illustrated in  FIG. 1A ). The method  300  of forming can include providing a current collector, as shown in block  310 , and providing a layer comprising electrochemically active material on a side of the current collector, as shown in block  320 . The method  300  can also include providing a substantially solid layer of electrode attachment substance adjacent the layer comprising electrochemically active material such that the electrochemically active material is between the substantially solid layer of electrode attachment substance and the current collector, as shown in block  330 . Further, the method  300  can include adhering the electrochemically active material to the side of the current collector via the electrode attachment substance, as shown in block  340 . 
     With reference to block  310 , in some instances, the current collector (e.g., current collector  110  in  FIGS. 1C and 1D ) can be provided as a sheet (e.g., foil, film, etc.). In some instances, the current collector can be provided in roll form. With reference to block  320 , the electrochemically active material can be provided in powder or film form. When provided in film form, the active material can also be available in sheets or in roll form (e.g., allowing for roll to roll processing). As in  FIGS. 1C and 1D , in some embodiments, when provided in powder or film form, the electrochemically active material  130  can be placed directly or indirectly on the current collector  110 . With reference to block  330 , the substantially solid layer of electrode attachment substance (e.g., attachment substance  120  in  FIGS. 1C and 1D ) can also be provided in roll form to allow a roll to roll process. As in  FIG. 1D , the layer of electrode attachment substance  120  can be provided on the electrochemically active material  130 . As in  FIG. 1C , the electrochemically active material  130  can be sandwiched between two layers of electrode attachment substance  120 ,  125 . 
     With reference to block  340 , the electrochemically active material can be adhered to the side of the current collector via the electrode attachment substance (e.g., to form  FIG. 1A ). Similar to method  200  in  FIG. 2 , the layers can undergo an extrusion process in some embodiments to adhere the layers together, the layers can be adhered by applying pressure and/or heat to one or more of the layers, and electrochemically active material can be placed on both sides of the current collector (e.g., using one or more similar processes as described herein). For example, a layer comprising electrochemically active material can be provided on the other side of the current collector, and a layer of electrode attachment substance can be provided adjacent that layer comprising electrochemically active material. The electrochemically active material can be adhered to that side of the current collector via the layer of electrode attachment substance. In some instances, the layer of electrode attachment substance can be placed between the electrochemically active material and the current collector. In some instances, the electrochemically active material can be placed (e.g., sandwiched in some instances) between the electrode attachment substance and the current collector. In some instances, the electrochemically active material can be sandwiched between two layers of electrode attachment substance. 
     The electrode attachment substance can be the same as or different from the electrode attachment substance on the other side of the current collector. The electrode attachment substance can include any of the attachment substances described herein. For example, the electrode attachment substance can be provided in a substantially solid state. The attachment substance can be a thermoplastic film. In some instances, the attachment substance can be polyphenylene sulfide or any other polymer that is insoluble in a solvent e.g., at a temperature below about 200° C. Some other examples of attachment substance  120  can include films/foils of polyether ether ketone (PEEK), polyether sultone (PES), polysulfone (PSU), or polyethylene terephthalate (PET). 
     The electrochemically active material can be the same as or different from the electrochemically active material on the other side of the current collector. The electrochemically active material can include any of the electrochemically active material described herein. For example, the electrochemically active material can be in powder or film form. The active material can include a silicon carbon composite material. In some examples, the active material can include at least about 50% to about 100% by weight of silicon, at least about 60% to about 100% by weight of silicon, at least about 70% to about 100% by weight of silicon, at least about 80% to about 100% by weight of silicon, or 100% by weight of silicon. 
     The electrochemically active material can be adhered to the current collector as described herein (e.g., by applying pressure and/or heat). In some instances, adhering the electrochemically active material on both sides of the current collector can occur simultaneously. In some instances, the electrochemically active material can be adhered sequentially on one side of the current collector and then on the other side of the current collector. 
     In various embodiments, after the electrode is formed, the electrode can be punched and processed. In certain embodiments, an electrode can be attached to a separator using an attachment substance similar to the electrode attachment substance described herein. For example, a separator and an electrode can be provided. A substantially solid layer of attachment substance can also be provided on the separator and/or the electrode. The separator and electrode can be adhered together via the attachment substance (e.g., by applying pressure and/or heat). 
     EXAMPLES 
     The following examples are provided to demonstrate the benefits of some embodiments of electrodes, electrochemical cells, and methods of forming the same. These examples are discussed for illustrative purposes and should not be construed to limit the scope of the disclosed embodiments. 
     Sample electrodes (e.g., anodes) were made in accordance with certain embodiments described herein. For example, two samples of silicon dominant electrochemically active material (i.e., carbon-silicon composite films made using pyrolyzed polymer and silicon material) were attached to copper foil using thermoplastic film (Torelina® 4 μm Polyphenylene sulfide (PPS) film) with a solvent free, high temperature and pressure method. The samples were pressed at about 28 MPa (e.g., about 4000 psi). The PPS film was adhered to the copper foil at about 220° C., and the silicon dominant electrochemically active material was adhered thereon at about 300° C. Electrodes were also made using binder in N-Methyl-2-pyrrolidone (NMP) solution. For example, two samples of the same silicon dominant electrochemically active material were attached to copper foil by coating it in a slurry of binder in NMP solution.  FIG. 4  is a plot of the discharge capacity versus the number of cycles for the electrodes. The performance of the electrodes made using thermoplastic film is shown in black solid lines, while the performance of the electrodes made using binder in NMP solution is shown in gray dashed lines. The cycling data shows that certain embodiments described herein have results that at least match that of using solvent based binder, with potential improvement of battery performance. 
     As described herein, new binders/adhesives (e.g., insoluble in solvents) can be tested and used to prepare battery electrodes. Certain embodiments described herein can attach electrochemically active material to a current collector using a roll to roll process and in some instances, be solvent free. Various embodiments can reduce manufacturing time and costs by not requiring a solvent in a slurry mix, coating of a slurry mix, and/or drying of a slurry mix. 
     Various embodiments have been described above. Although the invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.