Apparatus and method for preparing a slurry and coating a substrate with the slurry

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 the priority of U.S. Patent Application No. 15 / 964,651, filed on April 26, 2018, and the entire disclosure of the same is incorporated herein by reference.

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

Background Art

[0003] The formation of a slurry containing powders dispersed in a solvent and optionally a binder involves a great deal of energy and equipment. This is applicable when forming a slurry for the manufacture of a substrate used in forming an electrode for a battery. For example, in a conventional electrode wet - coating process, a highly viscous slurry containing powders such as carbon black powder or other active / inactive materials and an organic polymer as a binder is applied onto a substrate by feeding either the slurry or the substrate by various methods such as a doctor blade, roll - to - roll coater, etc., and a current collector is formed. Conventional apparatuses used in wet - coating require a large space because they need to use devices such as doctor blades, roll - to - roll coaters, etc. All of the conventional apparatuses and workstations related to mixing, kneading, coating, and drying are large - scale.

[0004] Mixing slurries using conventional planetary mixers is time-consuming. Furthermore, in conventional wet coating, large quantities of toxic solvents are typically used in the slurry to aid in its formation and application to the substrate. Such toxic solvents include, for example, n-methyl-2-pyrrolidone (NMP), dimethylformamide, and dimethylacetamide. After coating the substrate with the slurry, the toxic solvents must be removed. To prevent environmental pollution and explosions, advanced evaporation techniques are required during the drying process. The drying process to evaporate the toxic solvents requires a large dryer, including a combination of a long conveyor belt and a heating system. Along with the drying system, a system for recovering the evaporated toxic solvents is also necessary to prevent environmental pollution.

[0005] The dry coating process is an alternative to wet coating for electrode manufacturing. However, dry coating has several drawbacks. For example, it requires grinding the dry carbon composite powder into a fine powder for coating, which necessitates two machines: one for grinding the powder and another for spreading it onto the substrate. Special hoppers and coaters with complex layouts are also required to disperse the fine powder onto the substrate.

[0006] Dry coating also presents the problem of inconsistent battery performance due to the irregular distribution of fine powder particles on the substrate. The resulting uneven powder density directly impacts adhesion between the coating and the substrate, pore uniformity, and many other issues, ultimately leading to a lack of uniform reaction. Even specially designed coating machines equipped with advanced dispersion devices suffer from the same problem of inconsistent cell performance. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Therefore, there is a need for coating equipment and processes that can be applied to the manufacture of battery electrodes and that can alleviate the aforementioned problems in slurry formation. [Means for solving the problem]

[0008] Certain aspects of this disclosure include a process of coating a substrate with a slurry to form electrodes. The slurry comprises a powder. In some embodiments, the powder may be formed of carbon black powder or any conductive / non-conductive material or a mixture thereof. The slurry further comprises one or more solvents and a binder. The slurry may optionally contain one or more dispersants. The process further comprises the steps of freeze-drying the coated substrate and heating the freeze-dried coated substrate under a high-temperature vacuum to remove any residual solvent. The process further comprises the step of calendrizing the resulting coated substrate for use as battery electrodes.

[0009] Further aspects of the present disclosure relate to an apparatus configured for mixing and kneading a slurry and then simultaneously coating both sides of a substrate with the slurry. The apparatus includes two cylinders connected via a capillary tube, each cylinder having a piston configured to repeatedly force the slurry back and forth between the cylinders and within the tube. The repeated motion of the slurry through the tube applies a shear force to the slurry, which mixes and kneads it. In some embodiments, the apparatus includes a die configured to push the slurry onto the substrate so that the slurry contacts both sides of the substrate simultaneously.

[0010] Other aspects of the present disclosure include a method for coating a substrate, which includes the step of providing a slurry in a closed space having at least one passage. The slurry comprises a solvent, a powder, a binder, and a dispersant. The method further includes the step of uniformly dispersing the powder and binder in the solvent by repeatedly forcing the slurry to move under high pressure in a first flow direction in at least one passage, and then again in a second flow direction opposite to the first flow direction in at least one passage. The method further includes the step of simultaneously coating both sides of the substrate with the slurry as it is pushed out of the closed space after the forcing step.

[0011] Aspects of the present disclosure also include electrodes coated according to the above method, a battery having electrodes coated according to the above method, and a battery system having a plurality of battery cells, each of which has electrodes coated according to the above method.

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

[0013] Further aspects of the present disclosure include a system having a first cylinder assembly comprising a first cylinder and a first piston, the first piston being configured to reciprocate within the first cylinder. The system also includes a second cylinder assembly comprising a second cylinder and a second piston, the second piston being configured to reciprocate within the second cylinder. The system also includes a passage connecting the first cylinder assembly to the second cylinder assembly. During operation of the system, the first and second cylinder assemblies are configured to alternately compress and suction the slurry in the first and second cylinders, causing the slurry to reciprocate within the passage.

[0014] The above and other capabilities of the disclosed apparatus, system, and method will be better understood by referring to the following drawings, detailed description, and claims. [Brief explanation of the drawing]

[0015] [Figure 1]A cross-sectional view of an apparatus used for preparing slurry according to an aspect of this disclosure is shown. [Figure 2A] A perspective view of a die assembly according to an aspect of this disclosure is shown. [Figure 2B] Figure 2A shows an exploded view of a die assembly having two die components according to an aspect of the present disclosure. [Figure 2C] Figure 2A shows a top view of the die assembly according to an aspect of this disclosure. [Figure 2D] Figure 2A shows a bottom view of the die assembly according to an aspect of this disclosure. [Figure 3A] Figure 1 shows a cross-sectional view of the apparatus configured to apply slurry to a substrate according to an aspect of this disclosure. [Figure 3B] Figure 3A shows an optically transparent perspective view of the die used to coat a substrate with slurry, according to an aspect of this disclosure. [Figure 3C] This shows a cross-sectional view along line 3B-3B of the substrate of Figure 3B, which is coated with slurry, according to an aspect of this disclosure. [Figure 4] This is a flowchart of the process for coating a substrate according to the embodiments of this disclosure. [Figure 5] This is a flowchart of the process for curing a coated substrate according to an aspect of the present disclosure. [Modes for carrying out the invention]

[0016] While various modifications and alternative forms are possible for the apparatus, systems, and methods described herein, specific embodiments are illustrated in the drawings as examples. However, it should be understood that the description is not limited to the specific forms disclosed. Rather, the description covers all modifications, equivalents, and alternatives that fall within the spirit and scope of this disclosure as defined by the accompanying claims.

[0017] One or more embodiments of apparatuses, systems, and methods are shown in the drawings and described in detail herein. It should be understood, however, that the present disclosure is considered an exemplification of the principles disclosed herein and is not intended to be limited to the embodiments shown, which exemplify broad aspects. For the purposes of this detailed description, the singular forms include the plural forms and vice versa (except where expressly denied), the word "or" is both conjunctive and disjunctive, the word "all" means "all and every," the word "any" means "any and all," and the phrase "comprising" means "including, but not limited to." Also, terms in the singular form (a, an, the) include the plural form as well, unless the context clearly requires otherwise. All numerical ranges disclosed herein include all rational numbers, including the upper and lower numbers and all integers between them.

[0018] Apparatuses and processes for preparing a slurry and then applying the slurry to a substrate are disclosed. According to the apparatuses and processes of the present disclosure, the complexity and time required to form and apply the slurry to a substrate are significantly reduced. A process for curing a substrate coated with the slurry is also disclosed. The disclosed apparatuses and processes can be used in the manufacture of electrodes for batteries. However, the apparatuses and processes can be used for the formation of any type of slurry and its application to any type of substrate, and are not particularly limited to substrates used for electrodes.

[0019] When applied in the manufacture of battery electrodes, the apparatuses and methods of the present disclosure reduce or eliminate the use of toxic chemicals such as NMP, DMF, acetone, etc. as solvents and / or dispersants in the formation of electrode slurries. The apparatuses and methods also shorten and simplify the entire process of manufacturing battery electrodes by eliminating complex conventional processes in slurry preparation, substrate treatment, equipment operation, etc. According to the apparatuses and methods, the large and expensive apparatuses used for concentration, grinding, and powder spraying for the processes described in the background section above are miniaturized and their use is eliminated.

[0020] In particular, the method of the present disclosure uses only one device, which performs all of mixing, kneading, and coating. The device directly coats the slurry onto the substrate in situ, eliminating the need to transport the slurry, for example, from a mixing device to a coating device. The device also coats both sides of the substrate simultaneously. The method also includes the step of lyophilizing the coated substrate, thereby eliminating the need for a solvent. The lyophilization step helps to reduce damage or changes to the pore structure of the formed slurry and the substrate during coating. The present disclosure also provides a slurry coating process for manufacturing an electrode for an electrochemical cell, together with a coating device. The electrode cell can be, for example, a primary cell or a secondary cell such as a lithium cell or a fuel cell.

[0021] The slurry of the present disclosure is formed of a solvent, powder, and binder. The slurry can also include a dispersant. In one or more embodiments, the solvent can be any chemical capable of dissolving the binder and can be selected with any chemical according to the desired properties of the binder. For example, the solvent can be water containing a water-soluble binder, such as polytetrafluoroethylene (PTFE). Alternatively, the solvent can be acetone (or, substantially 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 can be any chemical capable of forming a dispersion system of the binder and powder.

[0022] The powder can be any powder used in the manufacture of the dispersion system. In one or more embodiments, the powder can be any powder used in the manufacture of the electrode. For example, the powder can be any inorganic or organic material, or a combination thereof, that is electrochemically activatable, active, or inert. If the powder is a conductive powder, it serves as an electrode for an electrochemical cell or as a conductive additive within the electrode. The conductive powder can be carbon black powder, graphite, carbon fiber, etc., or a mixture thereof. Other non-carbon powders can include, for example, silicon carbide (SiC), barium sulfate (BaSO4), lithium iron phosphate (LiFePO4), lithium iron manganese phosphate (LiMnFePO4), and various oxides such as silicon dioxide (SiO2), aluminum oxide (Al2O3), lithium nickel cobalt aluminum oxide (LiNiCoAlO2), lithium nickel cobalt manganese oxide (LiNiCoMnO2), lithium manganate (LiMn2O4), lithium nickel manganese spinel (LiNi0.5Mn1.5O4), lithium cobalt oxide (LiCoO2), and other natural minerals, as well as combinations thereof.

[0023] All of the non-carbon powders described above 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 described later and the hydrophilicity of the material. This is in contrast to the weight ratio of hydrophobic powder to aqueous solvent of about 1.25:1 in conventional wet methods. In the case of carbon-based powders, the weight ratio of solvent to powder in the slurry can be about 4.5 to 8:1. This provides an advantage over conventional slurries that require a solvent-to-powder weight ratio of about 24 to 27:1. Therefore, the method of this disclosure requires significantly less solvent, thereby reducing the amount of solvent that must be removed during curing.

[0024] The binder helps to adhere the powder to the substrate after coating and curing. In one or more embodiments, the binder may be a resin binder. The binder may be soluble in a solvent, for example, water-soluble, or in the form of a dispersion, for example, an aqueous polytetrafluoroethylene emulsion. Specific binders usable 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 acrylate (Acryl SiO20), polyvinyl alcohol (PVA), polyacrylamide and polymethylacrylamide, divinyl ether maleic anhydride, polyoxazoline, various polyphosphates used in tissue engineering, starch, liquid glucose, hydroxypropyl methylcellulose (HPMC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), carnauba wax, guar gum, xanthan gum (XG), pectin, and combinations thereof.

[0025] In electrode manufacturing, the amount of binder used in the slurry is determined by how the binder affects the conductivity of the final electrode. In one or more embodiments, the binder-to-powder ratio in the slurry can be approximately 0.02:1 to approximately 0.1:1. However, binder content exceeding approximately 10 wt% of the total weight of binder and powder is unsuitable for large-scale electrode production, considering viscosity and energy density.

[0026] The dispersant assists in mixing hydrophobic inorganic components, such as carbon powder, with the aqueous solvent and binder. In one or more preferred embodiments, the dispersant is selected to have properties similar to or lower than those of the solvent in its liquid state, e.g., a lower melting point / precipitation temperature. By having properties similar to or lower than those of the solvent, the dispersant evaporates with or before the solvent, thereby ensuring that the thin film remaining on the substrate after freeze-drying consists mainly of powder. As an example, isopropyl alcohol with a precipitation temperature of -89°C can be used as a solvent along with water. Excess solvent residue, including non-aqueous solvents, can be extracted during freeze-drying, for example, in a freeze-drying condenser at -60°C to -80°C, or during subsequent heating of the coated substrate at higher temperatures, as will be discussed further.

[0027] Dispersants that can be used in the slurry include, for example, isopropyl alcohol, ethanol, methanol, acetic acid, acetonitrile, acetone, NMP, DMF, etc. Furthermore, in one or more embodiments, some dispersants can also function as both a dispersant and a solvent. In addition, dispersants such as NMP and DMF are preferably not used due to their toxicity, but in the slurry of this disclosure, they can still be used because the required concentrations are much lower. For example, due to the advantages of mixing and the associated apparatus described later, the amount of these dispersants can be much less than in conventional wet methods, which further reduces the costs associated with this use.

[0028] The amount of dispersant used in a slurry depends on other components in the slurry, such as the solvent. However, the amount of dispersant in a slurry can be as low as 0.01 wt%. This is in contrast to conventional slurries mixed using conventional methods that require a maximum of 30 wt% of dispersant in the aqueous solvent. For example, in the slurry of this disclosure of carbon powder, water as the solvent, and PTFE emulsion as the binder, when isopropyl alcohol is used as the dispersant, the isopropyl alcohol content of the slurry is approximately 1 wt%. When NMP is used as the dispersant, the NMP content of the slurry can be as low as 0.01 wt%.

[0029] Referring to Figure 1, a cross-sectional view of an apparatus 100 used to prepare a slurry 102 and to coat the slurry 102 onto a substrate, according to an aspect of the present disclosure, is shown. The apparatus 100 includes a pair of cylinders 104a, 104b and a pair of pistons 106a, 106b. Each piston 106a, 106b is located in one of the cylinders 104a, 104b (for example, piston 106a is in cylinder 104a and piston 106b is in cylinder 104b). The pistons 106a, 106b are connected to one or more apparatuses (not shown) which are configured to cause the pistons 106a, 106b to reciprocate linearly along the length (e.g., stroke length or direction) of the cylinders 104a, 104b, as indicated by line A. In one or more embodiments, the device driving the pistons 106a, 106b may be one or more linear actuators controllable by a programmable device. However, the device may be any kind of mechanical and / or electromechanical device capable of imparting reciprocating linear motion to the pistons 106a, 106b. The operation of the pistons 106a, 106b is synchronized such that when one piston applies a compressive force to the slurry 102, the other piston applies an attractive force.

[0030] Cylinders 104a and 104b are fluidly connected via a capillary tube 108. Through the capillary tube 108, slurry 102 can flow between cylinders 104a and 104b under the compressive force generated by the operation of pistons 106a and 106b. By operating pistons 106a and 106b to reciprocate within cylinders 104a and 104b, slurry 102 can repeatedly pass through tube 108. Thus, slurry 102 flows from cylinder 104a through tube 108 to cylinder 104b in a first flow direction, for example, from left to right in the direction of line A in Figure 1. Slurry 102 then flows from cylinder 104b through tube 108 to cylinder 104a, for example, from right to left in the direction of line A in Figure 1. The second flow direction is the opposite of the first flow direction. Although the flow directions shown in Figure 1 are linear along line A, in one or more embodiments the flow directions can be nonlinear. For example, the pipe 108 can be U-shaped, S-shaped, or have several identical and / or different bends that create a meandering passage for the slurry 102 to move through.

[0031] As the slurry 102 repeatedly moves through the pipe 108, the slurry 102 is mixed. Mixing is further aided by the fact that the pipe 108 has a smaller diameter compared to the diameter of the cylinders 104a, 104b, for example, in the stroke direction of the pistons 106a, 106b or in the flow direction (e.g., line A). The slurry 102 moving through the pipe 108 is subjected to high shear forces resulting from the non-uniformity of particle velocity within the slurry 102, based on particles at the edges of the pipe 108 having a lower velocity than particles in the center of the pipe 108, according to Bernoulli's principle. The shear forces generated while the slurry 102 is filling and / or discharging from the cylinders 104a, 104b increase the mixing efficiency and produce a large kneading effect.

[0032] The mixing efficiency depends on the flow velocity 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 velocity of the slurry 102 through the tube 108, the greater the mixing and kneading effect. For example, with a tube with an inner diameter of 3 / 8 inch and a flow velocity of 430 mm per second, mixing takes only 15 minutes. With a tube with an inner diameter of 3 / 8 inch and a flow velocity of 380 mm per second, mixing takes only 25 minutes. Also, with a tube with an inner diameter of 1 / 8 inch and a flow velocity of 170 mm per second, mixing takes only 10 minutes. In reality, the diameter of the tube 108 can be approximately 1 / 16 to 1 / 2 inch. Therefore, the configuration of the apparatus 100 provides a higher mixing efficiency than conventional apparatuses 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 quantities of mixed materials, power consumption can reach up to approximately 10-15 kilowatt-hours per kilogram of powder.

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

[0034] Although it is shown that only one tube 108 connects cylinders 104a and 104b, in one or more embodiments, there may be multiple tubes 108 connecting cylinders 104a and 104b. Multiple tubes 108 can be used when the diameters of cylinders 104a and 104b are larger than the diameter of 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 material used for the apparatus 100 can be determined depending on the solvent used to form the slurry. If water is used as the main solvent for the slurry, the apparatus 100 can be made of a material resistant to corrosion by water and other dispersants, such as 316 stainless steel.

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

[0037] Referring to Figures 2A to 2D, a die 200 used for coating a substrate with slurry 102 according to an aspect of the present disclosure is shown. As shown in Figures 2A and 2B, the die 200 is formed from two die components 202a and 202b. The die components 202a and 202b may be symmetrical or identical, as shown in the figures. Alternatively, the die components 202a and 202b may be asymmetrical. Although the die components 202a and 202b are illustrated and described as each being a single component, in one or more embodiments, the die components 202a and 202b may each be formed from multiple components. The die components 202a and 202b are configured to simultaneously coat a thin, flat layer of slurry 102 on both sides of the substrate, which will be further described later. The die 200 includes a joint 204 (Figure 2A) configured to connect the die 200 to cylinders 104a, 104b, or to tube 108 (or to a third cylinder, if there is one). The joint 204 includes two slurry inlet ports 206a, 206b, i.e., one inlet port 206a, 206b for each die component 202a, 202b. The inlet ports 206a, 206b are configured to receive slurry 102 extruded from the apparatus 100, from cylinders 104a, 104b, or from tube 108, depending on where the die 200 is mounted.

[0038] Referring to Figure 2B, each die component 202a, 202b further includes slurry outlet ports 208a, 208b. The outlet ports 208a, 208b are configured to uniformly distribute the slurry 102 onto the substrate as the substrate passes through the outlet ports 208a, 208b. The outlet ports 208a, 208b are approximately the same width as the substrate, but can be wider or narrower than the substrate.

[0039] Passages 210a and 210b connect exit ports 208a and 208b to inlet ports 206a and 206b. Inlet ports 206a and 206b are configured to split the slurry 102 into two separate streams. Passages 210a and 210b are then configured to uniformly distribute the slurry 102 to exit ports 208a and 208b for subsequent distribution onto the substrate.

[0040] Referring to Figures 2C and 2D, die components 202a and 202b are integrally connected to form a die 200, which defines a slit 212 through which the die 200 passes. As will be further explained later, the slit 212 allows the substrate to pass through the die 200. As the substrate passes through the die 200, the slurry 102 extruded from the exit ports 208a and 208b is simultaneously applied to both sides of the substrate as it passes through the slit 212.

[0041] Referring to Figure 3A, a cross-sectional view of an apparatus configured to coat a substrate 300 with slurry 102 according to an aspect of the present disclosure is shown. Apparatus 100 is modified by detaching tube 108 from cylinder 104a. Instead of tube 108, die 200 is connected to cylinder 104a via joint 204. However, in one or more embodiments, die 200 may instead be connected to tube 108 or cylinder 104b (or a third cylinder). For example, tube 108 may have a joint that connects to joint 204 of die 200. By being able to reconfigure apparatus 100 from the mixing and kneading configuration of Figure 1 to the coating configuration of Figure 3A, coating can be easily performed in situ and directly, without having to transport slurry 102 from one apparatus (i.e., apparatus 100) to another.

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

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

[0044] In one or more embodiments, by applying the slurry 102 to the substrate 300, the substrate 300 is also advanced through the slit 212 into the die 200. In other words, by applying the slurry 102 to the substrate 300, the substrate 300 can be moved in a desired direction, for example, downward in the orientation shown in Figure 3B. Alternatively, or in addition to the above, the substrate 300 can be driven through the die 200 using other driving forces, such as a winding device (not shown).

[0045] Figure 3C shows the slurry 102 applied to the substrate 300. Specifically, the slurry 102 forms thin films 302a and 302b on both sides of the substrate 300. The thin films can have a thickness of approximately 8 μm to 25 μm (micrometers). By applying the thin films 302a and 302b using 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 substrate 300 as it passes through the die 200 and the slit 212, as well as by the speed of the piston 106a while the slurry 102 is being pushed out from the cylinder 104a.

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

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

[0048] In step 404, the slurry is repeatedly forced under high pressure to move through at least one passage in a first flow direction, and then again through at least one passage in a second flow direction opposite to the first flow direction, so that the powder and binder are uniformly dispersed in the solvent. As previously disclosed, each of the two cylinders contains a piston, and the reciprocating motion of the two pistons forces the slurry to flow in the first and second flow directions. The cylinder is 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 a high shear force to the slurry as it passes through the tube, which mixes the slurry. 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, for example, 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 piston in the cylinder.

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

[0050] The solvent and dispersant used to form the slurry allow for a different slurry curing process on the substrate than conventional processes. Specifically, since a small amount of volatile organic solvent such as the aforementioned alcohol is used to disperse hydrophobic materials such as carbon powder in a solution that is mostly water, it is possible to use a freeze-drying step to remove the solvent and dispersant and dry the coating. The freeze-drying process reduces the likelihood of problems seen in conventional electrode manufacturing processes. These problems include uncontrollable deformation of the pore structure during drying and degradation of the thin film morphology and pores.

[0051] Figure 5 is a flowchart of process 500 for curing a coated substrate as a final product according to an embodiment of the present disclosure. Process 500 begins in step 502, in which both sides of the substrate are coated with slurry. The substrate may be coated according to process 400 described above, and the slurry may 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 carried out by any process that lowers 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 with respect to the amount of solvent, for example, in the case of 1 wt% isopropyl accord of the present invention, it is not necessary to freeze the dispersant.

[0053] In step 506, after the solvent and dispersant are frozen, the solvent and dispersant in the coating substrate are sublimated, and the substrate is freeze-dried. Sublimation can be carried out by any process that sublimes the solvent and dispersant.

[0054] In step 508, after the solvent and dispersant have sublimated, the substrate is heated under vacuum to a temperature above the standard freezing point of the solvent and dispersant. The heating and vacuum further help to remove all remaining solvent and dispersant from the substrate.

[0055] In 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. Hot rolling, at about 100°C to about 150°C, can improve the adhesion of the thin film to the substrate. In addition to improving adhesion, hot rolling also improves conductivity through improved adhesion.

[0056] Although porosity within the thin film may be lost during the calendering process, the porosity of the thin film after freeze-drying remains superior in terms of pore uniformity and homogeneity compared to any coating produced by conventional methods in battery electrode manufacturing. Therefore, this coating method produces a uniform coating on the substrate with superior pores compared to those achieved by conventional methods. The coating is relatively defect-free compared to conventional methods, with very low rates of pinholes, blisters, divots, burrs, striping, foreign matter inclusion, excessively non-uniform coating areas, or clumping on the coating surface.

[0057] Thus, the methods and apparatus of the present disclosure reduce or completely eliminate the use or amount of toxic materials in slurry formation, 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 need for dedicated equipment to prevent the release of toxic materials into the environment and other problems such as explosions. The methods and apparatus of the present disclosure also reduce the workspace required for electrode production compared to conventional processes.

[0058] While this disclosure relates to one or more specific embodiments disclosed, those skilled in the art will see that many modifications can be made without departing from the spirit and scope of the invention. Each of these embodiments and its obvious variations is assumed to fall within the spirit and scope of the invention. Furthermore, additional embodiments according to aspects of the invention may combine any number of features of the embodiments disclosed herein.

Claims

1. A method for coating a substrate, A step of providing a slurry in a closed space having at least one passage, the closed space comprising two cylinders connected by at least one passage, each of the two cylinders comprising a piston, and the slurry comprising a solvent, a powder, and a binder, A step of homogeneously dispersing the powder and the binder in the solvent by repeatedly forcibly moving 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 the reciprocating motion of the piston, After forced movement, the slurry is pushed out from the closed space to simultaneously coat both sides of the substrate that do not face each other, and A step of freezing at least the solvent applied to the substrate, A step of sublimating at least the solvent frozen on the substrate, After sublimation, the substrate is heated under vacuum to a temperature above the freezing point of at least one of the solvents. The steps include: calendering the substrate after heating, The process includes the step of forming battery cell electrodes on the substrate after calendering, The aforementioned powder is a conductive powder, The method wherein the binder is soluble in the solvent.

2. The method according to claim 1, wherein the calendering process comprises cold calendering the substrate to stabilize the coating on the substrate, and then hot rolling the substrate.

3. The method according to claim 1, wherein the weight ratio of the binder to the powder is 0.02:1 to 0.1:

1.

4. The method according to claim 1, wherein in each of the at least one passages, the cross-section of the passage in the first flow direction is smaller than the cross-section of the cylinder in the stroke direction of the piston.

5. The method according to claim 4, wherein the diameter of each of the at least one passage is between 1 / 16 inch (1.6 mm) and 1 / 2 inch (12.7 mm).

6. The method according to claim 1, wherein the slurry does not contain n-methyl-2-pyrrolidone.

7. The method according to claim 1, wherein the solvent is water.

8. The method according to claim 5, wherein the binder is a polytetrafluoroethylene emulsion.

9. The method according to claim 1, wherein a vacuum is applied to the enclosed space before the coating in order to remove gas from the slurry.

10. The method according to claim 1, wherein the powder comprises at least one of carbon black powder, graphite, carbon fiber, and combinations thereof.

11. The method according to claim 10, wherein the powder is carbon black powder, and the weight ratio of the solvent to the carbon black powder is 4.5:1 to 8:

1.

12. The method according to claim 1, wherein the powder is a non-carbon powder, and the weight ratio of the solvent to the non-carbon powder is 0.6:1 to 1.25:

1.

13. The non-carbon powder is silicon carbide (SiC), barium sulfate (BaSO ４ ), lithium iron phosphate (LiFePO ４ ), lithium manganese iron phosphate (LiMnFePO ４ ), silicon dioxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), lithium nickel cobalt aluminum oxide (LiNiCoAlO ２ ), lithium nickel cobalt manganese oxide (LiNiCoMnO ２ ), lithium manganese oxide (LiMn ２ O ４ ), lithium nickel manganese spinel (LiNi ０．５ Mm １．５ O ４ ), lithium cobalt oxide (LiCoO ２ ), and at least one combination thereof, the method according to claim 12.

14. The method according to claim 1, wherein the binder is in the form of a water-soluble binder or a dispersion.

15. The method according to claim 14, wherein the binder comprises at least one of the following: 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 acrylate (Acryl S020), polyvinyl alcohol (PVA), polyacrylamide, polymethylacrylamide, divinyl ether-maleic anhydride, polyoxazoline, various polyphosphates used in tissue engineering, starch, liquid glucose, hydroxypropyl methylcellulose (HPMC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), carnauba wax, guar gum, xanthan gum (XG), pectin, and combinations thereof.

16. The method according to claim 1, wherein the binder is a water-insoluble binder.

17. The method according to claim 1, wherein the slurry further comprises a dispersant selected to form the battery cell electrodes after being applied to the substrate.

18. The steps include at least coating the substrate with the solvent and the dispersant and freezing it, The steps include sublimating at least the frozen solvent and the dispersant on the substrate, The method according to claim 17, comprising the step of heating the substrate under vacuum to a standard freezing point or higher for at least one of the solvents and the dispersant after sublimation.

19. The method according to claim 18, wherein the slurry is 0.01 to 2% by weight of the dispersant.

20. The method according to claim 17, wherein the dispersant is an alcohol.

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