Abstract:
The invention provides, in preferred embodiments, methods, systems, and devices arising therefrom for making battery electrodes, in particular, for lithium-ion batteries. Unlike conventional slurry coating methods that use mechanical means to coat thick pastes of active material, other materials, and solvent(s) onto a substrate, the invention provides for a method to produce electrode coatings onto support in a multi-layer approach to provide highly uniform distribution of materials within the electrode. Problems of differential sedimentation of particles in slurries found in conventional methods are minimized with the methods of the present invention. Also included are systems for producing in large-scale the battery electrodes of the invention. Further included are electrodes produced by the methods and systems described herein.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention generally relates to the field of battery electrode manufacturing, preferably lithium-ion battery electrode manufacturing. The invention generally pertains to the field of energy storage, batteries, lithium-ion (Li-ion) batteries, advanced vehicles technology, and reduction of national reliance upon foreign petroleum products. The invention also relates to manufacturing systems for applying a coating or coatings to surfaces of substrates. The invention further relates to the field of energy efficiency, and environmental protection. 
       BACKGROUND 
       [0002]    Lithium ion batteries play an important part in today&#39;s high-technology world. Reaching new markets, lithium ion batteries offer the promise of high energy capacity/high power output in relatively lightweight and compact formats when compared to traditional lead acid, nickel metal anhydride, or nickel cadmium batteries. 
         [0003]    Traditional methods for making lithium ion batteries generally include the formation of a slurry comprising a solvent and a mixture of particles. The slurry is then spread out upon the surface of a substrate, typically a metal foil, then dried and calendared to a desired thickness and density. Problems exist with the slurry coating method, whether by doctor blade or by slot die process, in that generally only one layer can be deposited upon the surface of the substrate. Depositing additional layers using doctor blade and slot die methods runs the risk of delaminating the earlier deposited layers due to the forces applied against the substrate as it is pulled across the doctor blade or slot die head. 
         [0004]    Another problem with traditional battery making methods is that because thick layers are deposited to achieve the desired energy density for the electrode, the period of time it takes for the solvent to evaporate from the deposited slurry is considerable. During this time while the slurry is wet, particles of differing sizes and rheological behavior will sediment at different rates thus causing a stratification of the soon to solidify electrode matrix. Stratification leads to less than optimal performance because the different particles within the electrode matrix are not spatially distributed evenly. 
         [0005]    There has been a trend towards using nanometer scale sized active material particles for electrodes. Not wishing to be bound by theory, it is believed that nano-scale particles present a problem, however, because they have a greater number of particles per unit mass than micrometer scale particles typically used in commercially available cells. Unless higher than average amounts of conductive particles like carbon black are used, the increased number of active material particles increases the internal resistance of the electrode. Internal resistance causes power loss through heating and can contribute to thermal runaway and flame. Nanoparticles, however, can be used by substituting carbon nanotubes instead of or in combination with carbon black. The inside diameter of carbon nanotubes, compared to their outside dimension, greatly reduces the number of effective interfaces in the electrical conductive path. A problem exists, however, in using carbon nanotubes in that they tend to aggregate. Likewise, active material nano-scale particles tend to aggregate as well. Aggregation can pose a problem with coating surfaces to form electrodes using a slurry based process. 
         [0006]    Accordingly, there is a need for a method for depositing materials onto a substrate for the purposes of making battery electrodes that provides for uniform distribution of particles within the electrode matrix. There is also a need for a method for depositing materials onto a substrate that avoids the need for using toxic organic chemical as a solvent. Embodiments of the invention address the above noted problems and other problems, individually and collectively. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    Among addressing other problems, it is an object of the invention to address the problems mentioned above in making advanced battery components. Towards this end, the invention aims to provide superior methods for manufacturing electrodes for use in batteries, preferably lithium ion batteries. The invention provides, in one aspect, a method for coating a substrate using multi-coat spraying. In preferred embodiments, the method comprises the steps of: providing a substrate having a surface; providing an active material suspension comprising: active material particles; and, electrically conductive particles; a solvent; spraying the active material suspension onto the substrate surface to form a first coating layer; evaporating at least 50% of the solvent, if any, from the first coating layer; repeating the steps (c) through step (e) for at least two repetitions. 
         [0008]    In preferred embodiments, the steps (c) and (d) are repeated at least five times. In more preferred embodiments, steps (c) and (d) are repeated at least ten times. And, in highly preferred embodiments, steps (c) and (d) are repeated at least twenty times. 
         [0009]    In certain embodiments, the active material suspension is sprayed using an aerosol sprayer, more preferably, an airless sprayer, and yet even more preferably an ultrasonic sprayer. It is highly preferred to use a pulse width modulated sprayer, and wherein the active material suspension is sprayed in a volumetrically controlled manner. 
         [0010]    In another embodiment, the invention provides for a method wherein the evaporating step further comprises detecting the amount of solvent in the coating layer. In preferred embodiments, the coating layer is dried to a content level of about less than 20% w/w prior to repeating the spraying step. In particularly preferred embodiments, the thickness of the coating layer is measured prior to the repeating of the spraying and evaporating steps. In some embodiments, the density of the coating layer is measured prior to the repeating of the spraying and evaporating steps. 
         [0011]    In highly preferred embodiments, the active material particles comprise a battery electrode active material. In some embodiments, the electrically conductive particles comprise carbon, more preferably, carbon comprises carbon nanotubes, and yet more preferably, carbon comprises graphitic carbon, and yet other embodiments, the carbon is carbon black. In highly preferred embodiments, the electrically conductive particles comprise a mixture of carbon particles mentioned above. 
         [0012]    In highly preferred embodiments, the solvent is a non-organic solvent, and in some embodiments, the solvent is an organic solvent. In particularly preferred embodiments, the solvent comprises water. In some embodiments, the solvent comprises ethanol. In certain preferred embodiments, the solvent comprises acetone, and/or N-methylpyrrolidone. 
         [0013]    In particularly preferred embodiments, the battery active material reversibly stores lithium ions. 
         [0014]    In one aspect of the invention, the spraying step is operationally linked to a detector monitoring at least one attribute of the coating layer so that the spray volume is adapted in real-time in response to control, wholly or partly, a degree of the attribute. 
         [0015]    In certain embodiments of the invention, the substrate is wound about an axis to form a substrate roll and the substrate is unwound from the roll and is traversed through a spraying region wherein the first spraying step occurs. In highly preferred embodiments, the substrate first traverses through the spraying region and then traverses through a evaporating region where the first evaporating step occurs. In highly preferred embodiments, the substrate subsequently traverses through a second spraying region then a second evaporating region and so forth until a desired number of coating layers are built upon the substrate surface. In some embodiments, the substrate further comprises a second surface on a side of the substrate opposite the first substrate surface. In particularly preferred embodiments, the spraying step and the evaporating step are applied simultaneously to the first and the second substrate surfaces to form a first coating layer upon the substrate first surface and a second coating layer upon the substrate second surface to yield a double-sided coating on the substrate surfaces. In some embodiments, the spraying step and the evaporating step are applied alternately to the first and the second substrate surfaces to form a first coating layer upon the substrate first surface and a second coating layer upon the substrate second surface to yield a double-sided coating on the substrate surfaces. In some embodiments, a subsequent coating layer comprises materials different from the active material particles and the electrically conductive particles. 
         [0016]    In preferred embodiments, the evaporating step further comprises providing a heat source, preferably where the heat source comprises an infrared heating element, and/or a where the heat source comprises a gas-catalytic heat source, and/or where the heat source comprises a radio frequency transmitter, and/or the heat source comprises a convective heat element. 
         [0017]    In certain embodiments, the evaporating step further comprises providing an air flow apparatus for passing air across the surface of the substrate during the evaporating step, preferably where the air passing across the surface of the substrate surface is heated, and/or the air passing across the surface of the substrate is not heated, and/or the air passing across the surface of the substrate is cooled. 
         [0018]    In some embodiments, the heat source further comprises two or more air flow apparatuses wherein at least one air flow apparatus passed heated air across a portion of the surface of the substrate at one point in time and then passes cooled air across the portion of the surface of the substrate at another point in time. 
         [0019]    In certain embodiments, the active material particles comprise nanometer scale sized active material particles, preferably where the active material particles comprise nano-structured materials, and/or where the active material particles contain micrometer scale sized active material particles. In highly preferred embodiments, the active material particles comprise a cathode active material capable of reversibly storing an ion. In some embodiments, the cathode active material comprises a cathode active material selected from the group consisting of: LiFePO 4 ; LiCoO 2 ; LiMnO 2 ; LiMn 2 O 4 ; LiMn 1/2 Ni 1/2 O 2 ; and, Li (Ni 1/3 Mn 1/3 CO 1/3 )O 2 . 
         [0020]    In some embodiments, the active material particles comprise an anode active material capable of reversibly storing an ion, preferably where the anode active material may be carbon; graphite; graphene; carbon nanotubes; silicon; porous silicon; nanostructured silicon; nanometer scale silicon; micrometer scale silicon; alloys containing silicon; carbon coated silicon; carbon nanotube coated silicon; tine; alloys containing tin; and/or Li 4 Ti 5 O 12 . In highly preferred embodiments, the active material particles further comprise lithium ions stored therein. 
         [0021]    In some embodiments, the electrically conductive particles comprise carbon, whereas in some embodiments, the electrically conductive particles comprise at least one metal element. In certain embodiments, the carbon may be carbon; amorphous carbon; carbon black; carbon nanotubes; single-walled carbon nanotubes; multi-walled carbon nanotubes; carbon nanorods; carbon nanofoam; nanostructured carbon; carbon nanobuds; Buckminster fullerenes; linear acetylenic carbon; metallic carbon; Lonsdaleite; diamond; graphite; and/or, graphene. 
         [0022]    In certain embodiments, the metal element may be ruthenium; rhodium; palladium; silver; osmium; iridium; platinum; and/or, gold. 
         [0023]    In preferred embodiments, the solvent comprises water, the solvent comprises an organic solvent, and/or the solvent comprises a mixed solvent comprising at least two different solvents. In certain embodiments, the solvent may be a polar solvent, polar aprotic solvent; and/or, a non-polar solvent. In some embodiments, the solvent may be water; methanol; ethanol; propanol; isopropanol; butanol; tert-butanol; pentane; hexane; heptane; acetone; dimethylformamide; n-methyl-2-pyrrolidone; and/or, 1,3-dimethyl-2-imidazolidinone. 
         [0024]    In some embodiments, the substrate comprises a metal, a non-metal, or both. In certain embodiments, the substrate comprises a woven material, a non-woven material, or both. In some embodiments, the substrate is porous or non-porous, or comprises both porous and non-porous portions. In particularly preferred embodiments, the substrate is a foil. In some embodiments, the substrate comprises a film. In certain embodiments, the substrate comprises a plurality of layers, preferably two or more of the plurality of layers are different, and/or two or more of the plurality of layers are the same. In highly preferred embodiments, the substrate comprises copper, aluminum, or both. 
         [0025]    The invention provides, in another aspect, a system for making a battery electrode comprising: an unwinder; a rewinder; a plurality of spray/dry regions disposed between the unwinder and the rewinder, each spray/dry region comprising: a sprayer in liquid communication with a liquid suspension source; a dryer in fluid communication with a gas source, the dryer being immediately preceded the spray region. 
         [0026]    In preferred embodiments, the plurality of spray/dry regions comprises at least two spray/dry regions. In even more preferred embodiments, the plurality of spray/dry regions comprises at least five spray/dry regions. In still more preferred embodiments, the plurality of spray/dry regions comprises at least ten spray/dry regions. In particularly preferred embodiments, the plurality of spray/dry regions comprises at least twenty spray/dry regions. 
         [0027]    These and other embodiments of the invention are described in further detail below with reference to the Figures and the Detailed Description 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0028]      FIGS. 1A and 1B  depict a substrate traversing from a spraying region to a drying region in an embodiment of the invention. 
           [0029]      FIG. 2  depicts a roll-to-roll spray/dry embodiment of the invention. 
           [0030]      FIG. 3  depicts a roll-to-roll multiple spray/dry region embodiment of the invention. 
           [0031]      FIG. 4  depicts a roll-to-roll multiple spray/dry/cool embodiment of the invention. 
           [0032]      FIG. 5  depicts a roll-to-roll multiple heat/spray/dry embodiment of the invention. 
           [0033]      FIG. 6  depicts a typical pulse wave signal used to control a pulse-width modulated spray head embodiment of the invention. 
           [0034]      FIGS. 7A and 7B  depict a preferred spray head of the invention in two different states. 
           [0035]      FIG. 8  depicts an ultrasonic multi-orifice spray head employed in a preferred embodiment of the invention. 
           [0036]      FIG. 9  depicts a flow-chart showing the logic flow of a feedback-loop operated spray deposition system of a preferred embodiment of the invention. 
           [0037]      FIGS. 10A-10C  depict images of sample electrodes produced using a preferred method of the invention. 
           [0038]      FIGS. 11A-11C  depict scanning microscopic images of sample electrodes produced using a preferred method of the invention. 
           [0039]      FIG. 12  depicts charge/discharge curves graphically for a sample electrode produced using a preferred method of the invention. 
           [0040]      FIGS. 13A-13B  depict a capacity profile for two sample electrodes produced using a preferred method of the invention. 
           [0041]      FIG. 14  depicts a voltage v. time profile for a sample electrode produced using a preferred method of the invention. 
           [0042]      FIG. 15  depicts charge v. current profiles for two sample electrodes produced using a preferred method of the invention and a commercially available electrode. 
           [0043]      FIG. 16  depicts a capacity v. current profile for two sample electrodes produced using a preferred method of the invention. 
           [0044]      FIG. 17  depicts a capacity v. half-cycle number graph for two sample electrodes produced using a preferred method of the invention. 
           [0045]      FIG. 18  depicts a scanning electron micrograph of a sample electrode produced using a preferred method of the invention. 
           [0046]      FIGS. 19A-19B  depict images of sample electrodes produced using a preferred method of the invention. 
           [0047]      FIG. 20  depicts a voltage v. time profile for a sample electrode produced using a preferred method of the invention. 
           [0048]      FIG. 21  depicts charge and discharge curves for a sample electrode produced using a preferred method of the invention. 
           [0049]      FIGS. 22A-22B  depict capacity v. half-cycle number graphs for two sample electrodes produced using a preferred method of the invention. 
           [0050]      FIG. 23  depict a power curve for two sample electrodes produced using a preferred method of the invention. 
           [0051]      FIG. 24  depicts a power curve for two sample electrodes produced using a preferred method of the invention and a commercially available electrode. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    The invention provides for methods for making battery electrode and systems, apparatuses for making battery electrodes and devices arising there from. Preferred embodiments of the invention provides for methods, systems, and apparatuses for making electrodes for use in lithium-ion batteries. 
         [0053]    The invention provides for, in one aspect, for a coating system that sprays a suspension of battery electrode materials onto a substrate, preferably a metal foil substrate. The preferred embodiments of the invention differ from the prior art in at least one fundamental way. These embodiments build up an electrode matrix in numerous layers rather than by one relatively thick slurry coating. The problem with the latter includes, but is not limited to differential sedimentation of electrode materials (particle) during the drying process that creates an electrode having an inhomogeneous composition with respect to the thickness dimension of the coated electrode. 
         [0054]    Currently, there is a trend towards using smaller and smaller sized active material particles in battery electrodes for lithium-ion cells. Not wishing to be bound by theory, the inventors believe that as the particle size lessens, the tendency for the particles to aggregate and sediment out of the wet curing electrode made by slurry coating will result in losing the benefits of the smaller sized particles, for example, but not limited to, higher surface area to mass ratio and better ion diffusion rates. Moreover, it is believed that differential sedimentation causes inefficient distribution of conductive materials and active materials within the electrode matrix thus causing some parts of the electrode matrix to have lower conductivity than others while yet other parts of the electrode matrix have different amounts and characteristics of active material particles. 
         [0055]    To address these problems, and others, applicants have invented a system that provides for a higher level of intra-electrode homogeneity when compared to standard slurry coating methods using one-step doctor blade or slot die type application of the electrode coating to the substrate foil current collector. By applying thin layers by spray and rapidly drying each layer, a plurality of layers of electrode material are built up to form an electrode matrix having a high degree of homogeneity with respect to spatial particle distribution and minimized homo-particle aggregation. 
         [0056]    Turning now to  FIG. 1A , an exemplary embodiment of the invention is shown. Spray/Dry System  1000  operates by traversing Substrate  1010  from Spraying Region  1015  to Drying Region  1018 . Spraying Region  1015  and Drying Region  1018  are separated from each other and external of Spray/Dry System  1000  by several Partitions  1040 . Sprayer  1050  is supported inside Spraying Region  1015  and aimed towards Surface  1020  of Substrate  1010 . Adjacent Spraying Region  1015  is Drying Region  1018  having therein Dryer  1080  in fluid communication with Dryer Manifold  1090  and Dryer Jets  1100 . 
         [0057]    Substrate  1010  is introduced into Spray System  1000  by way of Support Stage  1030  that passes under Partitions  1040  with Substrate  1010  thereupon. Once in Spray Region  1015 , a coating is applied to Surface  1020  of Substrate  1010  by Sprayer  1050 . Sprayer  1050  comprises Spray Tip  1060  from which Spray Mist  1070  emanates therefrom and travels towards Surface  1020  to form a layer of electrode material. 
         [0058]    Depicted in  FIG. 1B , Substrate  1020  traverses into Dryer Region  1018 , Hot Air or Gas  1120  of Dryer Flow  1130  is passed through Dryer  1080  and Dryer Manifold  1090  out towards Surface  1020  of Substrate  1010 . After impinging upon Surface  1010 , the Hot Air or Gas  1120  is deflected upward and is scavenged from Dryer Region  1018  through Exhaust  1150  as Exhaust Flow  1055 . After Substrate  1010  Surface  1020  is sufficiently dried, Substrate  1010  is traversed out of Dryer Region  1080  upon Support Stage  1030  onward to potentially further spray/dry steps or onto some other processing. 
         [0059]    In highly preferred embodiments, the invention provides for a continuous coating system that relies on roll-to-roll type material handling similar to that of newspaper printing presses.  FIG. 2  depicts a roll-to-roll spray/dry embodiment of the invention wherein Spray System  1000  is equipped with Unwinder  1160  and Rewinder  1190  where supported thereon are Unwind Roll  1170  and Rewind Roll  1200  loaded with Continuous Substrate  1210  that is in the form of a long ribbon-like material that arrives at Sprayer System  1000  wound upon Unwind Roll  1070  and wherein Continuous Substrate  1210  traverses Spray System  1000  ultimately terminating on Rewind Roll  1200  wherein Continuous Substrate  1210  is wound thereupon during a coating run. When finished, Rewind Roll  1200  should have wound thereabouts Continuous Substrate  1210  with Surface  1020  coated with electrode material. The continuous process generally has both Spray  1050  and Dryer  1080  active simultaneously or near simultaneously. 
         [0060]    In highly preferred embodiments, the invention provides for a continuous coating system similar to that depicted in  FIG. 2 , except that a plurality of Spray Systems  1000  are arranged serially between Unwinder  1160  and Rewinder  1190  to form Spray Line  1001 . 
         [0061]      FIG. 3  depicts a roll-to-roll multiple spray/dry region embodiment of the invention. Each Spraying Region  1015  and Drying Region  1018  is arranged in alternating fashion to permit multiple layers to be applied to Surface  1020  of Continuous Substrate  1210 . The rate for which Continuous Substrate  1210  is fed through Spray Line  1001  is preferably set to a speed wherein a substantial amount of solvent is removed from the coating prior to each subsequent coating cycle. This is believed to help minimize segregation of particles within the electrode coating during the drying process. In certain embodiments, a preceding layer is allowed to dry to a point that sedimentation is substantially halted even though some amount of solvent may still be present within the preceding layer prior to applying a subsequent layer of electrode material. 
         [0062]      FIG. 4  depicts a roll-to-roll multiple spray/dry/cool embodiment of the invention. In some embodiments, it may be desirable to reduce the temperature of Surface  1020  prior to spraying on an additional layer of electrode material. This is to ensure that the freshly sprayed material has some period of time in liquid form to self level. If dried prematurely due to Surface  1020  being too hot from a preceding drying step, Cooling Region  1019  may be further incorporated into the Spray Line  1001  depicted in  FIG. 3 . Here, Spraying Region  1015  is followed by Drying Region  1018 , and then by Chilling Region  1019  wherein the temperature of Surface  1020  is lowered to a desired level to facilitate spraying in a subsequent Spraying Region  1015 . 
         [0063]      FIG. 5  depicts a roll-to-roll multiple heat/spray/dry embodiment of the invention. In some embodiments, it may be desirable to reduce the temperature of Surface  1020  prior to spraying on an additional layer of electrode material. This is to ensure that the freshly sprayed material has some period of time in liquid form to self level. If dried prematurely due to Surface  1020  being too hot from a preceding drying step, Heating Region  1021  may be further incorporated into the Spray Line  1001  depicted in  FIG. 3 . Here, Spraying Region  1015  is preceded by Heating Region  1021 , and then by Drying Region  1018  wherein the temperature of Surface  1020  is raised to a desired level. 
         [0064]    In certain embodiments, Sprayer  1050  is controlled in a pulsatile manner to control flow rates without altering spray patterns.  FIG. 6  depicts a typical pulse wave signal used to control a pulse-width modulated spray head embodiment of the invention. Pulse Train  1220  comprises a series of voltage pulses organized in Pulse Trains  1240 , Pulse Train Intervals  1290 , and Pulse Profiles  1250 . Within a Pulse Train  1240  are Pulses  1280  having a time dimension width between the leading edge of Pulse  1280  and the trailing edge of Pulse  1280 , a Pulse Interval  1260  having a time dimension width between the trailing edge of a preceding Pulse  1280  and the leading edge of a immediately subsequent Pulse  1280 , and Frequency  1270  having a time dimension width between the leading edge of two consecutive Pulses  1280 . Each Pulse  1280  has Amplitude  1230  which can represent voltage amplitude or current flow. 
         [0065]    As depicted in  FIG. 7A , in preferred embodiments, Spray System  1000  comprises a Pulse-Width Modulated (“PWM) Sprayer  1300  to precisely regulate coating flow rates while maintaining a consistent Spray Pattern  1445 . Pulse-Width Modulated Sprayer  1300  comprises: Spray Head  1310  that includes, but is not limited to, Valve Body  1340  having associated therewith: Solenoid Actuator  1350  housing Coil  1360  and a portion of Plunger  1370 ; Spray Nozzle  1320  with Spray Guides  1330 . Coil  1360  is in electrical communication through Leads  1380  with Pulse Generator  1390  that produces electrical pulses that actuate Solenoid Actuator  1350  to move Plunger  1370  into and out of Valve Body  1340  thus permitting and restricting the flow of coating suspension through Spray Head  1310  and forming Spray Pattern  1445 . Tank  1400  is in fluid communication with Spray Head  1310  through Delivery Tube  1420 . Coating Suspension, not shown, can be pumped to Spray Head  1310  using any pumping system.  FIG. 7A  depicts a gas pressure pumping system wherein Tank  1400  is placed under gas pressure from a pressurized gas source through Pressurized Gas Tube  1410  to act as a gas spring to force the coating suspension in Tank  1400  through Delivery Tube  1420  to Spray Head  1310 . In  FIG. 7A , Plunger  1370  is shown in the actuated position where a portion of Plunger  1370  is urged into Valve Body  1340  to stop the flow of coating suspension through Spray Head  1310 .  FIG. 7B  depicts Plunger  1370  in a refracted position that permits flow of coating suspension through Spray Head  1310  and Spray Nozzle  1320  to emit Spray  1440  forming Spray Pattern  1445  to coat a substrate, not shown. In certain embodiments, Tank  1400  may further include a device for mixing a suspension contained therein. In preferred embodiments, the mixer employs sonication and/or ultrasonication. In some embodiments, the mixer may include an impeller and/or mixing paddle. 
         [0066]      FIG. 8  depicts an ultrasonic multi-orifice spray head employed in a preferred embodiment of the invention. Ultrasonic Spray Head  1500  comprises, in preferred embodiments, Spray Body  1510  preferably has an internal flow control valve therein, not shown. Attached to Spray Body  1510  is Piezo Element  1520  to which Nozzle Array  1530  is attached thereto. Nozzle Array  1530  is in fluid communication with Spray Body  1510  such that when coating suspension is pumped into Spray Body  1510 , and the valve, if any, is open, coating suspension can flow to Nozzle Array  1530  to be emitted through a plurality of Ports  1540 . Piezo Element  1520  is energized by a power source to cause Piezo Element  1540  to experience the reverse piezo electricity effect achieving a volumetric displacement along an axis perpendicular to Nozzle Array  1530 . The result is that Nozzle Array  1530  is moved back and forth along the axis perpendicular to Piezo Element  1540 . In preferred embodiments, Piezo Element  1520  is energized and de-energized by the power source at frequencies between 10,000 Hz and 100,000 Hz. By varying the frequency applied to Piezo Element  1520 , different drop sizes may be achieved for a given viscosity and pressure of the coating suspension. In preferred embodiments, strain-thinning coating suspensions are used to provide low viscosity under pressure and high viscosity once deposited upon a substrate. In some embodiments, the valve body is instead simply a body to permit flow of fluid and to support other parts of the spray head. In some embodiments, the Piezo element is located inside the valve body with a tube for transporting coating suspension to a nozzle and the element, in conjunction with the tube, act to pump and control the flow of coating suspension towards the nozzle or nozzles. 
         [0067]      FIG. 9  depicts a flow-chart showing the logic flow of a proportional-integral-derivative controller (PID controller) feedback-loop operated spray deposition system of a preferred embodiment of the invention. The PID controller initially sets the first 75 percent of the spray regions to apply 75 percent of the final density specified for the coating. To establish a baseline for the substrate&#39;s density, the substrate&#39;s density is measured prior to spray coating. Then, after the substrate has passed through 75 percent of the spray regions, a second (interim) density measurement is made. From the second density measurement, the first density measurement is subtracted to determine the density of the coating thus far applied. The substrate is then coated at the pre-set flow rate to achieve the specified density. If the density of the coating thus far is too low, the flow rate of the final 25 percent of the spray regions is increased to provide for a final density according to specification. Also, the initial spray flow rate is increased to yield a coating density of 75 percent of specification at the second density measurement for subsequent substrate(s) coating. If the density of the coating at the second density measurement is too high, the flow rate for the final 25 percent of the spray regions is decreased to provide for a final density according to specification. Also, the initial flow fate is decreased to yield a coating density of 75 percent of specification at the second density measurement for subsequent substrate(s) coating. Variations of this system may, in some embodiments, further include including moisture detection to monitor drying rates in the drying regions to ensure that the coating is at the specified dryness prior to subsequent sprayings or final drying. Drying rates may, in some embodiments, may be altered by increasing temperature, air flow, or both in the drying regions. 
         [0068]    Images of coated electrodes are depicted in  FIGS. 10A through 10C , wherein  FIG. 10A  depicts an electrode material loading of 2.5 mg/cm 2 ,  10 B is loaded at 5.0 mg/cm 2 , and  10 C is loaded at 10 mg/cm 2 . The coating is evenly distributed as evidenced by the consistent darkness across each electrode surface. 
         [0069]      FIGS. 11A through 11D  depict Scanning Electron Micrograph (SEM) images at 100×, 1,000×, 10,000×, and 100,000× magnification of an anode made using a preferred method of the invention. Of interest is  FIG. 11D  where Carbon Nanotubes  1800  can be seen among graphite particles having an average diameter of about 150 μm. 
         [0070]    Turning to  FIG. 12 , an exemplary Charge &amp; Discharge Curves are depicted for an anode produced using a preferred embodiment of the invention. The dashed line represents the 1 st  discharge of the half-cell. The solid line represents the 1 st  charge of the half-cell. The anode comprised graphite as the active material and carbon nanotubes for conductive particles. The binder Styrene-Butadiene Rubber (SBR) was also included in the coating suspension. According to the graph, the anode had a capacity of about 270mAh/g. 
         [0071]    Anode capacity profiles we conducted on two replicate anodes as depicted in  FIGS. 13A and 13B . Here, the half-cell data shows the anodes to be resistant to significant fade over about 100 cycles 
         [0072]    A voltage time curve is presented in  FIG. 14  wherein the graph depicts approximately equal charge and discharge times suggesting that irreversible loss is relatively minimal. 
         [0073]    When compared to a commercially available graphite based anode, an anode produced by the preferred method of the invention yields an electrode with a higher power capacity by a margin of about 2× to 5× over the commercially available anode.  FIG. 15  depicts a Current v. Charge graph wherein the lines represented by the circles and triangles are data derived from an anode produced using the preferred method of the invention. The line represented with squares was derived from a commercially available graphite anode. 
         [0074]    A Capacity v. Current graph for two replicate anodes is depicted in  FIG. 16 . Charge over a wide-range of current rates was well maintained. 
         [0075]    A Capacity v. Half-Cycle data is presented in  FIG. 17  for two replicate anodes. 
         [0076]    Images of coated electrodes made using a preferred method of the invention are depicted in  FIGS. 18A and 18B , wherein  FIG. 18A  depicts an electrode material loading of 2.5 mg/cm 2 ,  18 B is loaded at 15 mg/cm 2 , and  10 B is loaded at 30 mg/cm 2 . The coating is evenly distributed as evidenced by the consistent darkness across each electrode surface. 
         [0077]    A 10,000× SEM of a cathode made using a preferred method of the invention in 
         [0078]      FIG. 19 . The cathode comprised LiFePO 4 , carbon nanotubes, and SBR binder. 
         [0079]    Charge and discharge data for a cathode made using a preferred method of the invention is depicted in  FIG. 20 . Of interest is that the time distances between the peak and valley of each cycle are approximately equal indicating good levels of reversible charge capacity.  FIG. 21  represents the same data in a different format to better illustrate the charge time/discharge time differential, again indicating good reversible charge capacity. 
         [0080]    Fade was studied for a cathode made by a preferred method of the invention. Replicate cathodes were tested and the results depicted in  FIGS. 22A and 22B , the latter showing minimal fade over 80 cycles. 
         [0081]      FIGS. 23 and 24  depict power curves for sample electrodes produced using a preferred method of the invention, the latter figure showing a commercially available electrode for comparison. 
         [0082]    While the present invention has been described with reference to specific embodiments, it should be understood by those skilled in the art that obvious changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt the methods and devices of the present invention to particular situations, materials, compositions of matter, processes, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto. 
       EXAMPLES 
     Example 1 
     Basic Spray/Dry Process 
       [0083]    Basic spray/dry method was tested using an airbrush filled with a suspension containing: 
         [0084]    Spraying was performed manually with a back and forth motion of the spray head parallel to the surface of the substrate. Approximately 40 passes were made to load the surface to a desired amount. 
       Example 2 
     Multi-step Spray/Dry Process 
     Example 3 
     Fabrication of Electrodes into a Cell 
       [0085]    Circles were cut from each type of electrode (cathode/anode) in a size to fit into a pouch. A porous polymer sheet was placed between the electrodes as they were layered into the pouch. Electrolyte (LiPF 6 ) was added prior to vacuum sealing the pouch to form a pouch cell. 
       Example 4 
     Testing of Cell 
       [0086]    The following protocol was followed to test cells made with the electrodes of the invention:
       a) Measure open circuit voltage (OCV) (10 sec)   b) Apply 1 sec current pulse (0.5 mA for coin cells, 5-10 mA for pouch cells)   c) Measure voltage drop between OCV and the first 10 msec of applied pulse   d) Impedance testing: A few special cells, especially large pouch cells:   e) Measure impedance from 1000 kHz to 0.01 Hz       
 
         [0092]    Anode Half-cells
       a) Resistance test   b) Initial capacity test in constant current mode (3 cycles, starting with discharge cycle, each cycle running at 25 mA/g and then lowering to 12.5 mA/g until voltage limit is reached—designated “25+12.5 mA/g”)
           (a) For graphite ½-cells, voltage limits are 0.01V and 1.5V   (b) For silicon ½-cells, voltage limits 0.07V to 1.0V   
           c) Resistance test
           i) Power test* up to 10 mA total current   ii) followed by power test up to 20 mA, if charge withdrawn at 10 mA step is ≧70% total capacity   iii) followed by power test up to 30 mA, if charge withdrawn at 10 mA step is ≧80% total capacity   
           d) fade testing: capacity test in constant current mode (100 cycles at “25+12.5 mA/g”, with a resistance and a power test every 25 cycles)       
 
         [0102]    *Power test:
       a) discharge down to lower voltage limit at “25+12.5” mA/g   b) charge at highest current until upper voltage limit   c) rest 5 minutes   d) charge at half the previous current   e) rest 5 minutes   f) etc., until the current is at or below 25 mA/g       
 
         [0109]    Cathode Half-cells
       a) Resistance test   b) Initial capacity test in constant current mode (3 cycles, starting with charge cycle, each cycle running at 12.5 mA/g and then lowering to 6.25 mA/g until voltage limit is reached—designated “12.5+6.25 mA/g”)
           i) For LiFePO4 ½-cells, voltage limits are 4.1V and 2.0V   ii) For other cathode chemistries, voltage limits may be a few 0.1&#39;s of volts higher   
           c) Resistance test   d) Power test* up to 10 mA total current
           i) followed by power test up to 20 mA, if charge withdrawn at 10 mA step is ≧70% total capacity   ii) followed by power test up to 30 mA, if charge withdrawn at 10 mA step is ≧80% total capacity   
           e) Fade testing: capacity test in constant current mode (100 cycles at “12.5+6.25 mA/g”, with a resistance and a power test every 25 cycles)       
 
         [0119]    *Power Test:
       a) charge up to upper voltage limit at “12.5+6.25 mA/g”   b) discharge at highest current until lower voltage limit   c) rest 5 minutes   d) discharge at half the previous current   e) rest 5 minutes   f) etc., until the current is at or below 12.5 mA/g       
 
         [0126]    Full Cells (matched)
       a) Resistance test   b) Initial capacity test in constant current mode (3 cycles, starting with discharge cycle, each cycle running at either “25+12.5 mA/g” (anode weight) or “12.5+6.25 mA/g” (cathode weight), whichever is smaller)
           i) For graphite anode and LiFePO4 cathode full cells, voltage limits are 2.0 and 4.1 V   ii) For cells with other cathodes, voltage limits may be a few 0.1V higher   
           c) Resistance test   d) Power test* up to 10 mA total current
           i) followed by power test up to 20 mA, if charge withdrawn at 10 mA step is ≧70% total capacity   ii) followed by power test up to 30 mA, if charge withdrawn at 10 mA step is ≧80% total capacity   
           e) Fade testing: capacity test in constant current mode (100 cycles at “25+12.5 mA/g” (anode) or “12.5+6.25 mA/g” (cathode), whichever is smaller, with a resistance and a power test every 25 cycles)       
 
         [0136]    Test Equipment 
         [0137]    For resistance and impedance tests: potentiostat/galvanostat
       a) Princeton Applied Research: Versastat V3       
 
         [0139]    For capacity and power: battery testers:
       a) Manufacturer: Neware Technology Limited   b) Models (for different current ranges):
           i) BTS-5V10A(8CH) 10 mA limit   ii) BTS-5V100A(8CH) 100 mA limit   iii) BTS-5V200A(8CH) 200 mA limit