Devices and methods for preparing slurry for coating onto substrate

Abstract

To provide devices and methods for preparing slurry for coating onto a substrate and providing the slurry in a closed space with at least one passage.SOLUTION: A slurry includes a solvent, a powder, and a binder. The slurry can also include a dispersion agent. The slurry is forced to move repeatedly under high pressure through at least one passage in a first flow direction and then back through the at least one passage in a second flow direction opposite to the first flow direction. The forced movement homogenously disperses the powder and the binder within the solvent. Both sides of the substrate are then coated simultaneously with the slurry extruded from the closed space after the forced movement. Curing of the coated slurry includes freeze drying to preserve the porosity of the slurry on the substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 15 / 964,651, filed April 26, 2018, which is incorporated by reference in its entirety.

[0002] The present disclosure relates to an apparatus and method for preparing a slurry and coating a substrate with the slurry. [Background technology]

[0003] The formation of slurries containing powders dispersed in a solvent and optional binders involves significant energy and equipment. This is the case when forming slurries for the manufacture of substrates used in forming electrodes for batteries. For example, in a conventional electrode wet coating process, a viscous slurry containing powders such as carbon black powder or other active / inactive materials and organic polymers as binders is applied onto a substrate to form a current collector by unwinding or feeding either the slurry or the substrate by various methods such as doctor blades, roll-to-roll coaters, etc. Conventional equipment used in wet coating requires large space due to the need for the use of doctor blades, roll-to-roll coaters, etc. All the equipment and workstations involved in conventional mixing, kneading, coating, and drying are large in scale.

[0004] Mixing the slurry using a conventional planetary mixer takes a long time. In addition, in conventional wet coating, a large amount of toxic solvents are also typically used in the slurry to aid in the formation and application of the slurry to the substrate. Such toxic solvents include, for example, n-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, etc. After the slurry is coated onto the substrate, the toxic solvent must be removed. This requires advanced evaporation techniques during the drying process to prevent environmental pollution and explosion. The drying process to evaporate the toxic solvent requires a large dryer that includes a combination of a long belt conveyor and a heating system. Along with the drying system, a system to recover the evaporated toxic solvent must also be installed to prevent environmental pollution.

[0005] The dry coating process is an alternative to wet coating for electrode manufacturing. However, dry coating has some drawbacks. For example, it requires grinding the dry carbon composite powder into a fine powder for coating, which requires two machines, one to grind the powder and the other to spread it on the substrate. Special hoppers and complex coater configurations are also required to distribute the powder on the substrate.

[0006] Dry coating also has the problem of inconsistent battery performance due to the irregular distribution of fine powder on the substrate. The resulting non-uniform powder density on the substrate directly affects the adhesion between the coating and the substrate, the uniformity of pores and many other issues, which ultimately leads to a lack of uniform reaction. Even with specially designed coating machines with advanced dispersion devices, the same kind of problem of inconsistent cell performance still exists. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need for a coating apparatus and process applied to the manufacture of battery electrodes that generally alleviates the above-mentioned problems in slurry formation. [Means for solving the problem]

[0008] Certain aspects of the present disclosure include a process for coating a substrate with a slurry to form an electrode. The slurry includes a powder. In some aspects, the powder can be formed of carbon black powder or any conductive / non-conductive material or mixtures thereof. The slurry further includes one or more solvents and binders. The slurry can optionally include one or more dispersants. The process further includes freeze-drying the coated substrate and heating the freeze-dried coated substrate under vacuum at an elevated temperature to remove residual solvent. The process further includes calendering the resulting coated substrate for use as a battery electrode.

[0009] A further aspect of the present disclosure is an apparatus configured to mix and knead a slurry and then coat the slurry on both sides of a substrate simultaneously. The apparatus includes two cylinders connected via a capillary tube, with a piston in each cylinder configured to repeatedly force the slurry back and forth between the cylinders and within the tube. The repeated movement of the slurry through the tube applies shear forces to the slurry, which mix and knead it. In some embodiments, the apparatus includes a die configured to extrude the slurry onto the substrate such that the slurry contacts both sides of the substrate simultaneously.

[0010] Another aspect of the disclosure includes a method of coating a substrate, comprising providing a slurry in an enclosed space having at least one passageway. The slurry comprises a solvent, a powder, a binder, and a dispersant. The method further comprises forcing the slurry under high pressure repeatedly in a first flow direction in the at least one passageway and then again in a second flow direction opposite the first flow direction in the at least one passageway to uniformly disperse the powder and binder in the solvent. The method further comprises simultaneously coating both sides of the substrate with the slurry extruded from the enclosed space after the forcing step.

[0011] Aspects of the present disclosure also include electrodes coated according to the above methods, batteries having electrodes coated according to the above methods, and battery systems having a plurality of battery cells, each battery cell having an electrode coated according to the above methods.

[0012] Another aspect of the present disclosure includes a method of curing a coated substrate, comprising providing a substrate coated on both sides with a slurry. The slurry includes a solvent, a powder, a binder, and a dispersant. The method further includes freezing at least the solvent and the dispersant coated on the substrate, and sublimating at least the solvent and the dispersant frozen on the substrate. The method further includes heating the substrate under vacuum to a temperature above the freezing point of at least one of the solvent and the dispersant after the sublimating step, and calendering the substrate after the heating step.

[0013] A further aspect of the disclosure includes a system having a first cylinder assembly including a first cylinder and a first piston. The first piston is configured to reciprocate within the first cylinder. The system also includes a second cylinder assembly including a second cylinder and a second piston. The second piston is configured to reciprocate within the second cylinder. The system also includes a passageway connecting the first cylinder assembly to the second cylinder assembly. During operation of the system, the first cylinder assembly and the second cylinder assembly are configured to apply alternating compression and suction to a slurry in the first cylinder and the second cylinder causing the slurry to reciprocate within the passageway.

[0014] These and other capabilities of the disclosed devices, systems, and methods will become more fully understood with reference to the following drawings, detailed description, and claims. [Brief description of the drawings]

[0015] [Figure 1]FIG. 1 illustrates a cross-sectional view of an apparatus used to prepare a slurry according to an aspect of the present disclosure. [Figure 2A] FIG. 1 illustrates a perspective view of a die assembly according to an aspect of the present disclosure. [Figure 2B] FIG. 2B illustrates an exploded view of the die assembly of FIG. 2A having two die pieces, according to an embodiment of the present disclosure. [Figure 2C] FIG. 2B illustrates a top view of the die assembly of FIG. 2A according to an embodiment of the present disclosure. [Figure 2D] FIG. 2B illustrates a bottom view of the die assembly of FIG. 2A according to an embodiment of the present disclosure. [Figure 3A] 2 illustrates a cross-sectional view of the apparatus of FIG. 1 configured to apply a slurry to a substrate according to an embodiment of the present disclosure. [Figure 3B] FIG. 3B illustrates an optically transparent perspective view of the die of FIG. 3A applying a slurry to a substrate, according to an embodiment of the present disclosure. [Figure 3C] FIG. 3B illustrates a cross-sectional view of the substrate of FIG. 3B being coated with a slurry, taken along line 3B-3B, according to an embodiment of the present disclosure. [Figure 4] 1 is a flow chart of a process for coating a substrate according to an aspect of the present disclosure. [Diagram 5] 1 is a flow chart of a process for curing a coated substrate according to an aspect of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] While the devices, systems, and methods described herein are susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings. It should be understood, however, that the description is not intended to be limited to the particular forms disclosed. Rather, the description is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0017] Although one or more embodiments of the devices, systems, and methods are shown in the drawings and described in detail herein, it should be understood that the disclosure is considered an illustration of the principles disclosed herein and is not intended to limit the broad aspects to only the illustrated embodiments. For the purposes of this detailed description, the singular includes the plural and vice versa (unless expressly disclaimed), the word "or" is both conjunctive and disjunctive, the word "all" means "any and all," the word "any" means "any and all," and the word "including" means "including, but not limited to." Additionally, singular terms (a, an, the) also include the plural unless the context clearly requires otherwise. All numerical ranges disclosed herein include all rational numbers, including the upper and lower numerical limits and all integers therebetween.

[0018] Apparatus and processes are disclosed for preparing a slurry and then applying the slurry to a substrate. The disclosed apparatus and processes significantly reduce and shorten the complexity and time required to form a slurry and apply it to a substrate. A process for curing a substrate coated with the slurry is also disclosed. The disclosed apparatus and processes can be used in the manufacture of electrodes for batteries. However, the apparatus and processes can be used to form any type of slurry and apply it to any type of substrate, and are not particularly limited to substrates intended for electrodes.

[0019] When applied to the manufacture of battery electrodes, the disclosed apparatus and methods reduce or eliminate the use of toxic chemicals such as NMP, DMF, acetone, etc. as solvents and / or dispersants in forming slurries for electrodes. The apparatus and methods also shorten and simplify the overall process of manufacturing battery electrodes by eliminating complex conventional processes in slurry preparation, substrate handling, equipment operation, etc. The apparatus and methods also miniaturize and eliminate the use of expensive and large equipment used for concentrating, grinding, and powder distribution for the processes discussed in the background section above.

[0020] In particular, the method of the present disclosure uses only one apparatus, which does all the mixing, kneading, and coating. The apparatus coats the slurry directly on the substrate in situ, eliminating the hassle of transporting the slurry from, for example, a mixing apparatus to a coating apparatus. The apparatus also coats both sides of the substrate simultaneously. The method also includes a step of freeze-drying the coated substrate, thereby eliminating the need for a solvent. The freeze-drying step helps reduce damage or alteration of the pore structure of the formed slurry and substrate during coating. The present disclosure also provides a slurry coating process together with a coating apparatus for producing electrodes for electrochemical cells. The electrode cells can be primary or secondary cells, such as, for example, lithium cells or fuel cells.

[0021] The slurry of the present disclosure is formed of a solvent, a powder, and a binder. The slurry may also include a dispersant. In one or more embodiments, the solvent may be any chemical capable of dissolving the binder, and any chemical may be selected depending on the desired binder properties. For example, the solvent may be water containing a water-soluble binder, such as polytetrafluoroethylene (PTFE). Alternatively, the solvent may be acetone (or nearly pure acetone), NMP, or DMF, and a water-insoluble binder, such as polyvinylidene fluoride (PVDF) powder or resin. In one or more alternative embodiments, the solvent may be any chemical capable of forming a dispersion of the binder and powder.

[0022] The powder can be any powder used in the manufacture of dispersions. In one or more embodiments, the powder can be any powder used in the manufacture of electrodes. For example, the powder can be any inorganic or organic material, electrochemically active, active, or inactive, or a combination thereof. If the powder is a conductive powder, it serves as an electrode or conductive additive in an electrode for an electrochemical cell. The conductive powder can be carbon black powder, graphite, carbon fiber, etc., or a mixture thereof. Other non-carbon powders can be, for example, silicon carbide (SiC), barium sulfate (BaSO), lithium iron phosphate (LiFePO), lithium iron manganese phosphate (LiMnFePO), and various oxides, such as, for example, silicon dioxide (SiO), aluminum oxide (AlO), lithium nickel cobalt aluminum oxide (LiNiCoAlO), lithium nickel cobalt manganese oxide (LiNiCoMnO), lithium manganate (LiMnO), lithium nickel manganese spinel (LiNiMnO), lithium cobalt oxide (LiCoO), and other naturally occurring minerals, and combinations thereof.

[0023] All of the above non-carbon powders are water soluble and hydrophilic. Therefore, in the use of water soluble hydrophilic powders as described above, the ratio of aqueous solvent to powder in the slurry can be further reduced to about 0.6:1 by weight, due to the mixing step and the hydrophilicity of the materials as described below. This is in contrast to the weight ratio of hydrophobic powder to aqueous solvent of about 1.25:1 in the conventional wet method. For carbon-based powders, the weight ratio of solvent to powder in the slurry can be about 4.5-8:1. This provides an advantage over conventional slurries that require a solvent to powder weight ratio of about 24-27:1. Therefore, significantly less solvent can be used in the disclosed method, thereby reducing the amount of solvent that must be removed during curing.

[0024] The binder helps the powder adhere to the substrate after coating and curing. In one or more embodiments, the binder can be a resin binder. The binder can be soluble in a solvent, e.g., water-soluble, or can be in the form of a dispersion, e.g., an aqueous polytetrafluoroethylene emulsion. Specific binders that can be used in battery manufacturing include, for example, sodium carboxymethylcellulose (Na-CMC), poly(sodium acrylate) (PAA-Na), poly(ethylene oxide) (PEO), poly(vinylpyrrolidone) (PVP), polyethylene glycol (PEG), poly(3,4-ethylenedioxythiophene), water soluble acrylates (Acryl S020), polyvinyl alcohol (PVA), polyacrylamides and polymethylacrylamides, divinyl ether maleic anhydride, polyoxazolines, various polyphosphates used in tissue engineering, starch, liquid glucose, hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), carnauba wax, guar gum, xanthan gum (XG), pectin, and the like, and combinations thereof.

[0025] In the manufacture of electrodes, the amount of binder used in the slurry depends on how the binder affects the electrical conductivity of the final electrode. In one or more embodiments, the binder to powder ratio in the slurry can be from about 0.02:1 to about 0.1:1. However, binder contents greater than about 10 wt. % with respect to the total weight of binder and powder are not suitable for large-scale electrode production due to viscosity and energy density considerations.

[0026] The dispersant aids in mixing the hydrophobic inorganic component, e.g., carbon powder, with the aqueous solvent and binder. In one or more preferred embodiments, the dispersant is selected to have, in the liquid state, similar or lower physical properties than the solvent, e.g., a lower melting point / precipitation temperature. By having similar or lower physical properties of the dispersant compared to the solvent, the dispersant evaporates with or before the solvent, so that the thin film remaining on the substrate after freeze-drying mainly comprises the powder. As an example, isopropyl alcohol, which has a precipitation temperature of -89°C, can be used as a solvent together with water. Excess solvent residues, including non-aqueous solvents, can be extracted during freeze-drying, e.g., in a freeze-drying condenser at -60°C to -80°C, or during subsequent heating of the coated substrate at higher temperatures, as described further below.

[0027] Dispersants that can be used in the slurry include, for example, isopropyl alcohol, ethanol, methanol, acetic acid, acetonitrile, acetone, NMP, DMF, and the like. Additionally, in one or more embodiments, some dispersants can also function as both dispersants and solvents. Additionally, while dispersants such as NMP and DMF are preferably not used due to their toxicity, they can still be used in the slurries of the present disclosure due to the much lower concentrations required. For example, due to the advantages of mixing and associated equipment described below, the amount of these dispersants can be much less than in traditional wet processes, which further reduces the costs associated with their use.

[0028] The amount of dispersant used in the slurry depends on the other components in the slurry, such as the solvent. However, the dispersant in the slurry can be as low as 0.01 weight percent (wt%). This is in contrast to conventional slurries mixed using conventional methods that require up to 30 wt% of dispersant in an aqueous solvent. For example, in the presently disclosed slurry of carbon powder, water as the solvent, and PTFE emulsion as the binder, if isopropyl alcohol is used as the dispersant, the isopropyl alcohol content of the slurry is about 1 wt%. If NMP is used as the dispersant, the NMP content of the slurry can be as low as 0.01 wt%.

[0029] Referring to FIG. 1, a cross-sectional view of an apparatus 100 used to prepare a slurry 102 and coat the slurry 102 on a substrate is shown, according to an embodiment of the present disclosure. The apparatus 100 includes a pair of cylinders 104a, 104b and a pair of pistons 106a, 106b. Each piston 106a, 106b is within one of the cylinders 104a, 104b (e.g., piston 106a is within cylinder 104a and piston 106b is within cylinder 104b). The pistons 106a, 106b are connected to one or more devices (not shown) that are configured to impart linear reciprocating motion to the pistons 106a, 106b along the length (e.g., stroke length or direction) of the cylinders 104a, 104b, as shown by line A. In one or more embodiments, the device or devices driving the pistons 106a, 106b can be one or more linear actuators that can be controlled by a programmable device. However, the device or devices can be any type of mechanical and / or electromechanical device capable of imparting reciprocating linear motion to the pistons 106a, 106b. The actuation of the pistons 106a, 106b is synchronized such that when one piston is exerting a compressive force on the slurry 102, the other piston exerts a suction force.

[0030] The cylinders 104a, 104b are fluidly connected via a capillary tube 108. The capillary tube 108 allows the slurry 102 to flow between the cylinders 104a, 104b under compressive forces generated by actuation of the pistons 106a, 106b. By actuating the pistons 106a, 106b to reciprocate within the cylinders 104a, 104b, the slurry 102 can repeatedly pass through the tube 108. Thus, the slurry 102 flows in a first flow direction from cylinder 104a through the tube 108 to cylinder 104b, e.g., from left to right in the direction of line A in FIG. 1. The slurry 102 then flows from cylinder 104b through the tube 108 to cylinder 104a, e.g., from right to left in the direction of line A in FIG. 1. The second flow direction is opposite to the first flow direction. Although the flow direction shown in FIG. 1 is linear along line A, in one or more embodiments, the flow direction can be non-linear. For example, the tube 108 may be U-shaped, S-shaped, or may have any number of the same and / or different bends that create a tortuous path for the slurry 102 to travel.

[0031] As the slurry 102 moves repeatedly through the tube 108, it mixes. Mixing is further aided by the small diameter of the tube 108 in the stroke direction or flow direction of the pistons 106a, 106b (e.g., line A) compared to the diameter of the cylinders 104a, 104b, for example. The slurry 102 passing through the tube 108 is subjected to high shear forces resulting from non-uniformity in the velocity of the particles in the slurry 102 with the particles at the edges of the tube 108 experiencing a lower velocity than the particles in the center of the tube 108, according to Bernoulli's principle. The shear forces exerted while the slurry 102 is filling and / or discharging from the cylinders 104a, 104b result in high mixing efficiency and a large kneading effect.

[0032] The mixing efficiency depends on the flow rate of the slurry 102 through the tube 108, the diameter of the tube 108, and the mixing time. The smaller the diameter of the tube 108 and the faster the flow rate of the slurry 102 through the tube 108, the more effective the mixing and kneading. For example, a 3 / 8 inch inner diameter tube with a flow rate of 430 millimeters per second will take only 15 minutes to mix. A 3 / 8 inch inner diameter tube with a flow rate of 380 millimeters per second will take only 25 minutes to mix. And a 1 / 8 inch inner diameter tube with a flow rate of 170 millimeters per second will take only 10 minutes to mix. In practice, the diameter of the tube 108 can be about 1 / 16 to 1 / 2 inch. Therefore, the configuration of the apparatus 100 provides a higher mixing efficiency than conventional devices, such as conventional planetary mixers. For example, the energy required to mix 30 grams of carbon black powder is only about 0.3 kilowatt hours (kWh). For larger amounts of mixed material, power consumption can be up to about 10-15 kilowatt-hours per kilogram of powder.

[0033] According to one example, the apparatus 100 was formed with cylinders (i.e., cylinders 104a, 104b) with an inside diameter of 3 inches. The cylinders were connected with a tube (i.e., tube 108) with a length of 7 inches and an inside diameter of 1 / 8 inch. The slurry (i.e., slurry 102) was forced between the cylinders by pistons (i.e., pistons 106a, 106b) with a stroke of 6 inches and a piston speed of 1 millimeter per second. The slurry formed with the carbon black polymer mixture was thoroughly mixed and kneaded by the reciprocating motion of the pistons and passed through the tubes in less than 30 minutes, ready for coating. However, the actual mixing and kneading time can vary depending on the particle size, the size (e.g., inside diameter, length) of the tubes 108 and the speed of the pistons 106a, 106b and therefore the speed of the final slurry 102 passing through the tubes 108.

[0034] Although only one tube 108 is shown connecting the cylinders 104a, 104b, in one or more embodiments, there may be multiple tubes 108 connecting the cylinders 104a, 104b. Multiple tubes 108 may be used when the diameter of the cylinders 104a, 104b is larger relative to the diameter of the tube 108 in the stroke direction.

[0035] The apparatus 100 can be made of one or more metals, metal alloys, or other materials (e.g., plastics). The materials used for the apparatus 100 can depend on the solvent used to form the slurry. If water is used as the primary solvent for the slurry, the apparatus 100 can be made of a material that is resistant to corrosion by water and other dispersants, such as 316 stainless steel.

[0036] In one or more embodiments, the apparatus 100 can include a third cylinder. The third cylinder can be attached to one of the cylinders 104a, 104b and / or the tube 108. The third cylinder can be used to contain the slurry prior to coating the slurry onto a substrate, as described further below. In one embodiment, the effective space of the third cylinder can be larger than that of the cylinders 104a or 104b, such that the third cylinder can contain the slurry 102 after mixing for later coating, as described further below.

[0037] 2A-2D, a die 200 used to apply the slurry 102 to a substrate is shown, according to an aspect of the present disclosure. As shown in FIGS. 2A and 2B, the die 200 is formed from two die parts 202a, 202b. The die parts 202a, 202b may be symmetrical or identical as shown. Alternatively, the die parts 202a, 202b may be asymmetric. Also, while the die parts 202a, 202b are shown and described as being one piece each, in one or more embodiments, the die parts 202a, 202b may each be formed from multiple pieces. The die parts 202a, 202b are configured to apply a thin, flat layer of the slurry 102 to both sides of the substrate simultaneously, as will be further described below. The die 200 includes a junction 204 (FIG. 2A) configured to connect the die 200 to the cylinders 104a, 104b or to the tube 108 (or to a third cylinder, if present). The junction 204 includes two slurry inlet ports 206a, 206b, one inlet port 206a, 206b for each die part 202a, 202b. The inlet ports 206a, 206b are configured to receive the slurry 102 extruded from the apparatus 100, either from the cylinders 104a, 104b or from the tube 108, depending on where the die 200 is mounted.

[0038] 2B, each die part 202a, 202b further includes a slurry exit port 208a, 208b configured to evenly distribute the slurry 102 onto the substrate as the substrate passes through the exit port 208a, 208b. The exit port 208a, 208b is approximately the same width as the substrate, but can be wider or narrower than the substrate.

[0039] The passages 210a, 210b connect the outlet ports 208a, 208b to the inlet ports 206a, 206b. The inlet ports 206a, 206b are configured to split the slurry 102 into two separate streams. The passages 210a, 210b are then configured to evenly distribute the slurry 102 to the outlet ports 208a, 208b for subsequent distribution of the slurry to a substrate.

[0040] 2C and 2D, die parts 202a, 202b are joined together to form die 200 and define a slit 212 through die 200. As will be described further below, slit 212 allows a substrate to pass through die 200. As the substrate passes through die 200, slurry 102 extruded from exit ports 208a, 208b is simultaneously applied to both sides of the substrate passing through slit 212.

[0041] Referring to FIG. 3A, a cross-sectional view of an apparatus configured to coat a substrate 300 with a slurry 102 is shown, according to an embodiment of the present disclosure. The apparatus 100 has been modified by decoupling the tube 108 from the cylinder 104a. Instead of the tube 108, a die 200 is connected to the cylinder 104a via a joint 204. However, in one or more embodiments, the die 200 can instead be connected to the tube 108 or the cylinder 104b (or a third cylinder). For example, the tube 108 can have a joint that connects to the joint 204 of the die 200. The ability to reconfigure the apparatus 100 from the mixing and kneading configuration of FIG. 1 to the application configuration of FIG. 3A allows for easy, in-situ coating without the need to transport the slurry 102 from one apparatus (i.e., the apparatus 100) to another apparatus.

[0042] Before connecting the die 200, as much of the slurry 102 as possible can be collected in the cylinder 104a. The slurry 102 in the cylinder 104a is then extruded from the cylinder 104a via the action of the piston 106a. The extruded slurry 102 passes into the die 200 and is simultaneously applied to both sides of the substrate 300 through the exit ports 208a, 208b. The substrate 300 can be any substrate, such as a substrate used in forming an electrode. For example, the substrate can be a foam, a mesh, or any type of porous, semi-porous, or non-porous material.

[0043] 3B shows the slurry 102 entering the inlet ports 206a, 206b, being directed into the passages 210a, 210b, exiting the die 200 through the outlet ports 208a, 208b, and then passing to the substrate 300. The pressure of the slurry 102 exiting the outlet ports 208a, 208b forces the slurry 102 into the substrate 300, for example, into small holes in the substrate 300.

[0044] In one or more embodiments, applying the slurry 102 to the substrate 300 also advances the substrate 300 through the slit 212 and into the die 200. In other words, applying the slurry 102 to the substrate 300 can cause the substrate 300 to move in a desired direction, e.g., downward in the orientation of FIG. 3B. Alternatively, or in addition, the substrate 300 can be driven through the die 200 using other driving forces, such as a take-up device (not shown).

[0045] FIG. 3C shows the slurry 102 applied onto the substrate 300. Specifically, the slurry 102 forms thin films 302a, 302b on both sides of the substrate 300. The thin films can be about 8 μm to about 25 μm (micrometers) thick. By applying the thin films 302a, 302b by the disclosed process, a uniform thickness is obtained on both sides of the substrate 300. Furthermore, the thickness can be controlled by the speed of the piston 106a while the slurry 102 is being extruded from the cylinder 104a, as well as the speed of the substrate 300 passing through the die 200 and through the slit 212.

[0046] In one or more embodiments, after mixing the slurry 102, the slurry 102 can be exposed to a vacuum in one or both of the cylinders 104a, 104b (or a third cylinder) before coating the slurry 102 onto the substrate 300. The vacuum helps remove gases in the slurry 102 before coating. The gases in the slurry 102 can affect the surface uniformity and adhesion of the final thin film 302a, 302b of the slurry 102 on the substrate 300. Therefore, removing the gases improves the uniformity and adhesion of the slurry 102.

[0047] FIG. 4 is a flow chart of a process 400 for coating a substrate according to an embodiment of the present disclosure. The process 400 is performed using the apparatus 100 described above. The process 400 begins in step 402 with a slurry in the apparatus 100. The apparatus 100 has an enclosed space with at least one passageway defined by the cylinders 104a, 104b and the tube 108, as described above. The slurry can be any slurry described herein and can include a solvent, a powder, a binder, and a dispersant. In one or more embodiments, the slurry can be dispersant-free. As previously disclosed, the binder in the slurry cannot exceed 10 wt % with respect to the total weight of the binder and powder. The ratio of aqueous solvent to powder in the slurry can be about 4.5-8:1 by weight. The amount of dispersant in the slurry can be as low as 0.01 wt %. However, if a dispersant is included in the slurry, the amount is typically about 1-2 wt %. By way of example, the slurry may be formed with water as the solvent, carbon black as the powder, polytetrafluoroethylene emulsion as the binder, and alcohol as the dispersant, although any of the components disclosed above may be used. Importantly, the slurry does not require n-methyl-2-pyrrolidone or other toxic dispersants based on the ability of the apparatus 100 to disperse the slurry without the use of toxic dispersants.

[0048] In step 404, the slurry is repeatedly forced at high pressure through at least one passage in a first flow direction and then again through at least one passage in a second flow direction opposite the first flow direction to uniformly disperse the powder and binder in the solvent. As disclosed above, each of the two cylinders includes a piston, and the reciprocating action of the two pistons forces the slurry to flow in the first flow direction and the second flow direction. The cylinders are configured such that the cross-sectional area of ​​at least one passage is smaller than the cross-sectional area of ​​the cylinder in the stroke direction of the two pistons. This imparts high shear forces to the slurry as it passes through the tube, which causes the slurry to mix. For example, the inner diameter of each passage can be about 1 / 16 inch to 1 / 2 inch, and the inner diameter of the cylinder can be much larger, such as about 3 inches or more. In one or more embodiments, the inner diameter can be smaller than 3 inches depending on the speed of the pistons in the cylinder.

[0049] In step 406, both sides of the substrate are simultaneously coated with the slurry extruded from the enclosed space. The coating can be a thin film of slurry of a desired thickness, as described above. In one or more embodiments, prior to step 406, a vacuum can be applied to the slurry in the apparatus 100 after step 404 to remove any gasses that may have been generated in the slurry during previous process steps.

[0050] Depending on the solvent and dispersant used to form the slurry, a curing process of the slurry on the substrate can be used that is different from the conventional process. Specifically, since a small amount of a volatile organic solvent, such as the aforementioned alcohol, is used to disperse a hydrophobic material, such as carbon powder, in a predominantly aqueous solution, a freeze-drying step can be used to remove the solvent and dispersant and dry the coating. The freeze-drying process reduces the possibility of problems found in conventional electrode manufacturing processes. These problems include uncontrolled deformation of the pore structure during drying and degradation of the thin film morphology and porosity.

[0051] 5 is a flow chart of a process 500 for curing a coated substrate as a final product according to an embodiment of the present disclosure. The process 500 begins at step 502, where a substrate is coated on both sides with a slurry. The substrate can be coated according to process 400 described above, and the slurry can be any slurry according to an embodiment of the present disclosure.

[0052] In step 504, the solvent and dispersant coated on the substrate are frozen. Freezing can be done by any process that reduces the temperature of the solvent and dispersant below their freezing points. However, in one or more embodiments, when the amount of dispersant used is negligible relative to the amount of solvent, such as in the case of 1 wt % isopropyl alcohol of the present invention, it is not necessary to freeze the dispersant.

[0053] After freezing the solvent and dispersant, the solvent and dispersant within the coated substrate are sublimated to freeze-dry the substrate in step 506. Sublimation can be accomplished by any process that sublimes the solvent and dispersant.

[0054] After sublimating the solvent and dispersant, the substrate is heated under vacuum to a temperature above the normal freezing point of the solvent and dispersant in step 508. The heating and vacuum further aid in removing any remaining solvent and dispersant in the substrate.

[0055] At step 510, after heating, the substrate is calendered. In one or more embodiments, the calendering includes cold calendering the substrate to stabilize the coating on the substrate. In one or more embodiments, the calendering also includes hot rolling the substrate after cold calendering. The hot rolling can be at about 100° C. to about 150° C. to improve adhesion of the thin film onto the substrate. In addition to improving adhesion, hot rolling also enhances electrical conductivity through improved adhesion.

[0056] Although porosity within the film may be lost during the calendaring process, the pore structure characteristics of the film after freeze drying are still superior in terms of porosity and uniformity to any coating made by conventional methods in battery electrode manufacturing. Thus, the coating method produces a uniform coating on the substrate with better porosity than previously achieved by conventional methods. The coating is relatively defect-free compared to conventional approaches, with very low occurrence of pinholes, blisters, divots, burrs, striping, foreign material contamination, excessively non-uniform coated areas, or lumps on the coating surface.

[0057] In this manner, the disclosed method and apparatus reduces or entirely eliminates the use or amount of toxic materials in forming the slurry, such as toxic solvents that generate undesirable vapors during the production of battery electrodes. The reduction or elimination of toxic materials reduces or eliminates the dedicated equipment required to prevent the release of toxic materials into the environment and other problems such as explosions. The disclosed method and apparatus also reduces the workspace required for electrode production compared to conventional processes.

[0058] While the present disclosure is directed to one or more particular embodiments disclosed, those skilled in the art will recognize that many modifications may be made thereto without departing from the spirit and scope of the invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the invention. It is also contemplated that additional embodiments according to aspects of the invention may combine any number of features of any of the embodiments disclosed herein.

Claims

1. 1. A method for coating a substrate, comprising the steps of: providing a slurry into an enclosed space having at least one passageway, the enclosed space including two cylinders connected by at least one passageway, the two cylinders each including a piston, the slurry including a solvent, a powder, and a binder, the slurry being used to form an electrode of a battery cell when applied to the substrate; homogeneously dispersing the powder and the binder in the solvent by repeatedly forcing the slurry through the at least one passage in a first flow direction and then again through the at least one passage in a second flow direction opposite to the first flow direction under high pressure based on reciprocating motion of the piston; simultaneously coating opposite non-facing surfaces of the substrate with the slurry expelled from the enclosed volume after forcing the slurry to travel through the at least one passageway; freezing at least the solvent applied onto the substrate; sublimating at least the solvent frozen on the substrate; After sublimation, heating the substrate under vacuum above the freezing point of at least one of the solvents; calendering the substrate after heating; forming a battery cell electrode on the calendared substrate; The weight ratio of said binder to said powder is from 0.02:1 to 0.1:

1.

2. 2. The method of claim 1, wherein in each of the at least one passage, a cross section of the passage in the first flow direction is smaller than a cross section of the cylinder in a stroke direction of the piston.

3. The method of claim 1, wherein the at least one passage has a diameter between 1 / 16 inch (1.58 mm) and 1 / 2 inch (12.7 mm).

4. The method of claim 1, wherein the slurry is free of n-methyl-2-pyrrolidone.

5. The method of claim 1 , wherein the solvent is water.

6. The method of claim 5 wherein the binder is a polytetrafluoroethylene emulsion.

7. The method of claim 6 , wherein the slurry includes a dispersant, the dispersant being an alcohol.

8. 10. An electrode coated by the method of claim 1.

9. A battery having electrodes coated by the method of claim 1.

10. 13. A battery system having a plurality of battery cells, each of said battery cells having an electrode coated according to the method of claim 1.

11. The method of claim 1 , wherein the step of calendering comprises cold calendering the substrate to stabilize the coating on the substrate and then hot rolling the substrate.

12. 1. A method for coating a substrate, comprising the steps of: Providing a slurry into an enclosed volume having at least one passageway, the slurry including a solvent, a powder, and a binder; homogeneously dispersing the powder and the binder in the solvent by repeatedly forcing the slurry under high pressure through the at least one passage in a first flow direction and then again through the at least one passage in a second flow direction opposite to the first flow direction; applying a vacuum to the enclosed space to remove gas from the slurry; simultaneously coating both sides of the substrate with the slurry expelled from the enclosed space after the forcing step; The method includes:

13. The method of claim 12, wherein the ratio of the binder to the powder is between 0.02:1 and 0.1:1 by weight.

14. 13. The method of claim 12, wherein the powder comprises a non-carbon powder that is not carbon, and the ratio of the solvent to the non-carbon powder is between 0.6:1 and 1.25:1 by weight.

15. 13. The method of claim 12, wherein the powder comprises carbon powder and the ratio of the solvent to the carbon powder is between 4.5:1 and 8:1 by weight.

16. 13. The method of claim 12, wherein the enclosed space includes two cylinders connected by the at least one passageway, each of the two cylinders including a piston, the reciprocating motion of the pistons forcing the slurry to flow in the first flow direction and the second flow direction.

17. 13. The method of claim 12, wherein 10-15 kWh of energy is required per kilogram of solid powder to form a dispersion of the powder and the binder in the slurry.

18. The method of claim 12, wherein the solvent is water.

19. 13. The method of claim 12, wherein the powder is carbon black powder and the substrate forms an electrode for a battery cell.

20. The method of claim 12 wherein the binder is a polytetrafluoroethylene emulsion.

21. The method of claim 12, wherein the slurry is free of n-methyl-2-pyrrolidone.

22. The method of claim 12 , wherein the slurry includes a dispersant.

23. The method of claim 22, wherein the slurry comprises 0.01 to 2 wt % of the dispersant.

24. 23. The method of claim 22, wherein the dispersant is an alcohol.

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