Dry electrode preparation

Abstract

Approaches for preparing a dry electrode are described. In one example, a method of preparing a dry electrode comprises mixing a binder element and a primary conductive element to obtain a first mixture. The first mixture may then be cooled by a milling process to obtain a second mixture. Further, the second mixture may be mixed with an active element to a first temperature obtain a third mixture. The second mixture comprises a partially fibrillated binder element. In one example, the particle size of the binder element in the second mixture may be lying in the range of about 80 to 100 microns. The second mixture may be mixed with the secondary binder element to form a third mixture. The obtained third mixture may be mixed with the first mixture to obtain a fourth mixture comprising partially fibrillated first mixture.

Description

DRY ELECTRODE PREPARATIONBACKGROUND

[0001] Secondary energy storage devices, for example, rechargeable batteries store energy through reversible electrochemical reactions. These devices play a central role in a wide range of applications, from portable electronics to electric vehicles (EVs), and are integral to the integration of renewable energy sources into the grid. The ability to store energy and release it upon demand makes these devices a cornerstone of modern energy infrastructure. The development of secondary energy storage devices is focused on improving energy density, safety, cost-effectiveness, and environmental sustainability. Innovations in electrode materials, electrolytes, and manufacturing processes are driving the evolution of these devices. Thus, secondary energy storage devices are a dynamic and rapidly evolving field, with ongoing research and development aimed at meeting the growing demand for efficient, reliable, and sustainable energy storage solutions.BRIEF DESCRIPTION OF DRAWINGS

[0002] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0003] FIG. 1 illustrates a method for preparing a dry electrode, in accordance with an embodiment of the present subject matter.

[0004] FIG. 2(A-B) represents the experimental results of fibrillation of binder element before milling process, in accordance with an embodiment of the present subject matter.

[0005] FIG. 3(A-B) represents the experimental results of fibrillation of binder element after milling process, in accordance with an embodiment of the present subject matter.

[0006] FIG. 4(A-C) represents experimental results of a comparison between fibrillation of binder element before and after milling process, in accordance with an embodiment of the present subject matter.

[0007] FIG. 5(A-B) illustrates experimental results of an anode with a percentage weight of carbon coated binder element and different carbon additive, in accordance with an embodiment of the present subject matter.

[0008] FIG. 6(A-B) illustrates a graphical representation of particle size distribution prior to milling process, in accordance with an embodiment of the present subject matter. FIG. 6(C-D) illustrates a graphical representation of particle size distribution post milling process, in accordance with an embodiment of the present subject matter.

[0009] FIG. 7(A-C) illustrates a graphical representation of effect of milling process on capacity retention, in accordance with an embodiment of the present subject matter.

[0010] FIG. 8(A-B) illustrates a graphical representation of electrode composition with respect to performance cycle and capacity retention, in accordance with an embodiment of the present subject matter.

[0011] It may be noted that throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and / or implementations consistent with the description; however, the description is not limited to the examples and / or implementations provided in the drawings.DETAILED DESCRIPTION

[0012] As may be understood, rapid advances in electric vehicles (EVs) have led to an increased demand for lithium-ion batteries, accompanied by escalating performance expectations, particularly in areas such as storage capacity and production costs. However, increased storage capacity has the potential to address predominantly existing issues related to poor battery life in EVs. In addition to development of efficient energy storage batteries, the aforementioned resolutionmay be achieved through optimization and innovation in the conventional batteries used in EVs.

[0013] One such optimization in the conventional batteries is the usage of dry electrodes in batteries. Dry electrode preparation is a manufacturing process for creating electrodes by eliminating or reducing the use of solvents, otherwise used in wet electrode preparation. The electrodes are generally prepared by directly compacting dry powder electrode materials containing active substances. Compared to the traditional wet electrode manufacturing processes using large amounts of volatile organic compounds (VOCs) and other solvents, which are harmful to the environment, dry electrodes are manufactured by eliminating the use of such toxic solvents, thereby reducing the environmental footprint of battery production.

[0014] Further, by removing a drying stage that is mandatory in traditional wet electrode manufacturing processes to evaporate solvent(s), dry electrode manufacturing processes reduces energy consumption and production costs that is particularly advantageous when scaling up for the high-volume production of EVs. The dry electrode manufacturing processes may produce electrodes with higher energy density because of an absence of solvent(s), allowing for compact and dense structures, which may be desirable for an improved performance of EVs. Often, dry electrode manufacturing aligns with offering a sustainable and an efficient production method due to the improved performance characteristics of batteries produced. Thus, it may be inferred that dry electrode manufacturing processes may play a pivotal role in making EVs an energy-efficient option for consumers.

[0015] Conventionally, dry electrode manufacturing processes begins with mixing of electrode's constituent materials, including a binder element, conductive elements, and an active material. The binder is a polymer that holds the electrode materials together, while the conductive elements ensure electrical connectivity throughout the electrode. The active material is what stores and releases the electrical charge (for example, lithium in lithium-ion batteries).

[0016] However, binder plays a pivotal role in dry electrode manufacturing and is integral to formation of a functional electrode structure by providing mechanical integrity. It acts as a glue that holds the active material particles and conductive elements together. The binder is fibrillated, generally, using a high shear milling process. During the milling process, the binder is fibrillated to create a network of fine fibers that interconnect the particles, thereby enhancing the structural support of the electrode, thus produced.

[0017] Conventional techniques for dry electrode preparation pose numerous disadvantages. Firstly, the fibrillation of the binder is non-uniform and dense for the electrodes prepared with bare binder element. Secondly, a number of particles of the binder element remain non-f ibril lated which may cause hindrance in the electrochemical properties of the dry electrode which may further reduce the efficiency of the battery. Further, the electrode may be brittle, mechanically unstable, and may not show desired performance characteristics. Accordingly, there is a need for preparing an electrode with uniformly distributed binder element particles throughout the electrode for overcoming the aforementioned disadvantages.

[0018] Approaches for preparing a dry electrode are described. In one example, a method of preparing a dry electrode comprises pre-mixing a binder element and a primary conductive element to obtain a first mixture. In one example, the binder element in the first mixture may have a particle size in a range of about 350 microns to 450 microns. Herein, the pre-mixing of the binder element and the primary conductive element to obtain the first mixture may be carried out at a speed in a range of about 600 to 1800 RPM, for a time period in a range of about 10-30 minutes.

[0019] The first mixture may then be cooled by a milling process to obtain a second mixture. The milling process may be implemented by applying pressure to the first mixture. By applying pressure to the first mixture, the particle size of the binder element may be reduced by at least 50-60 percent. For example, the milling process may help reduce the particle size of the binder element to less than 100 microns. It may be noted that pre-mixing refers to processing the binder element to reduce the particle size.

[0020] Further, the second mixture may be pre-mixed with an active element to a first temperature, having range of about 15°C to 25°C to obtain a third mixture. The second mixture comprises a partially fibrillated binder element. In one example, the particle size of the binder element in the second mixture may be lying in the range of about 80 to 100 microns.

[0021] Although, the first temperature has been mentioned to be in the range of 15°C to 25°C, the same should not be construed as a limitation. Other ranges in which the first temperature lies may also be considered without deviating from the scope of the present subject matter. For example, the first temperature may be lying within a range of about 17-19°C.

[0022] In another example, the first temperature may be lying within a range of about 14-17°C.

[0023] In yet another example, the first temperature may be lying within a range of about 10-14°C. It may be noted that other ranges falling within the abovedescribed ranges may also be applicable as ranges for the first temperature. Such other ranges or values of the first temperature are only further examples.

[0024] Continuing further, in one example, the pressure applied to the first mixture may be a feeding pressure and a milling pressure. Herein, feeding pressure and milling pressure refer to the pressures applied during the milling process to reduce the particle size of the binder element within the first mixture. Feeding pressure is a force applied to feed the mixture of binder and conductive element into a milling equipment (for example, a milling chamber). The feeding pressure may be typically set to ensure a consistent and controlled delivery of the first mixture to be milled. Further, milling pressure on the other hand refers to a force applied by the milling equipment to the first mixture to achieve particle size reduction. This pressure may be exerted by mechanical component(s) of the milling equipment (for example, rollers, balls, hammers) depending on the type of mill used (such as ball mill, hammer mill, jet mill, and more). The milling pressure is a determining factor regarding the fibrillation and reduction in particle size of the binder element in the first mixture.

[0025] In one example, the feeding pressure may be kept slightly higher than the milling pressure, during the milling pressure, to significantly reduce the particle size of the binder. Further, the feeding pressure may be in a range of about 1 to 3 kg / cm2, and the milling pressure may be in a range of about 1 to 2 kg / cm2. Other ranges of the feeding pressure and the milling pressure may be present, without deviating from the scope of the present subject matter.

[0026] Returning to the present subject matter, the method further comprises mixing the active element with a secondary conductive carbon and a secondary binder in the temperature range of about 15°C to 20°C for a time period of about 15 to 30 minutes.

[0027] The active element may be mixed with the secondary conductive element and a secondary binder element in two different steps. The process comprises mixing the active element with the secondary conductive element in the temperature range of about 15°C to 20°C at a speed of about 800 to 1200 RPM for about 15 to 30 minutes to form the second mixture. The second mixture may be pre-mixed with the secondary binder element in the temperature range of about 15°C to 20°C at a speed of about 800 to 1200 RPM for about 15 to 30 minutes to form a third mixture.

[0028] The obtained third mixture may be mixed with the first mixture to obtain a fourth mixture comprising partially fibrillated first mixture. Herein, mixing the first mixture with the active element comprises passing the fourth mixture through a high shear mixing process to a second temperature. For example, mixing the first mixture with the active element may be done until the second temperature is in a range of about 65°C to 85°C. The fourth mixture is the final electrode mixture prepared by the examples described herein.

[0029] Although, the second temperature has been mentioned to be in the range of about 65°C to 85°C, the same should not be construed as a limitation. Other ranges in which the second temperature lies may also be considered without deviating from the scope of the present subject matter. For example, the second temperature may be lying within a range of about 71 -73°C.

[0030] In another example, the second temperature may be lying within a range of about 68-69°C.

[0031] In yet another example, the second temperature may be lying within a range of about 70-72°C. It may be noted that other ranges falling within the abovedescribed ranges may also be applicable as ranges for the second temperature. Such other ranges or values of the second temperature are only further examples of the claimed subject matter. Continuing further, the high-shear mixing process ensures that the active material is evenly distributed throughout the binder and conductive element. The second temperature attained during the high-shear mixing process is controlled to ensure that the constituents integrate properly without damaging the structure of the electrode. In one example, the third mixture may correspond to formation of thin and dense fibrils of the binder element present in the first mixture due to reduction in the particle size during the milling process. In one example, the reduction in the particle size of the binder element during the milling process may increase the extent of fibrillation of the binder element. In one example, the high shear mixing process of the second mixture may be carried out at a speed in a range of about 3000 to 4000 RPM, for a time period of about 5-60 minutes.

[0032] In one example, the third mixture may further be cooled to a third temperature to obtain a fourth mixture. For example, the third mixture may be cooled to the third temperature in a range of about 15°C to 25°C. This may prevent the agglomeration of particles, which may lead to inconsistencies in the electrode structure. Further, cooling helps stabilize the second mixture and maintain a desired particle size distribution, wherein milling may help fibrillate the binder element, thereby creating a network of fine fibers. The network of fine fibers may enhance structural integrity and performance of the electrode.

[0033] Although, the third temperature has been mentioned to be in the range of about 15°C to 25°C, the same should not be construed as a limitation. Other ranges in which the third temperature lies may also be considered without deviating from the scope of the present subject matter. For example, the third temperature may be lying within a range of about 15-17°C. In another example, the thirdtemperature may be lying within a range of about 17-21 °C. In yet another example, the third temperature may be lying within a range of about 5-10°C. It may be noted that other ranges falling within the above-described ranges may also be applicable as ranges for the third temperature. Such other ranges or values of the third temperature are only further examples of the claimed subject matter.

[0034] In one example, the milling process may be one of a jet milling process, a cryogenic milling process, or combinations thereof. However, other milling processes for reducing the particle size of the binder element may also be employed, without deviating from the scope of the present subject matter.

[0035] In one example, the primary binder element may be selected from a group comprising one of polytetrafluoroethylene (PTFE), Polyether ether ketone (PEEK), poly(tetrafluoroethylene-co-perfluoro propyl vinyl ether) (PFA), polypropylene, Polyacrylonitrile (PAN), tetrafluoroethylene-co- hexafluoropropylene-co-vinylidene (THV), poly(tetrafluoroethylene-co- hexafluoropropylene) (FEP), and combinations thereof.

[0036] The secondary binder is selected from the group consisting of polyvinylidene fluoride (PVDF), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), sodium carboxymethyl cellulose (Na-CMC), carboxymethyl cellulose (CMC), styrene butadiene rubber, polyethylene glycol (PEG), polyacrylic acid (PAA), polyethylene oxide (PEO) or combinations thereof.

[0037] In one example the primary conductive element is selected form the group consisting of carbon nanofibers, super-p, vapor grown carbon fibers, carbon nanotubes or combinations thereof

[0038] In one example, the secondary conductive element may be selected from a group comprising one of carbon black, ketjenblack, acetylene black, activated carbon, or combinations thereof.

[0039] In one example, the active element may be selected from a group comprising one of one of natural graphite, synthetic graphite, silicon, Si-Carbon composites, nickel-manganese-cobalt oxide (NMC), lithium-nickel-cobalt-aluminium oxides (NCA), lithium iron phosphate (LFP), or lithium-manganese-rich (LMR), or combinations thereof.

[0040] In one example the weight percentage of the active element is in the range of 96 to 97%, the secondary conductive element is in the range of 0 to 1%, the secondary binder element is in the range of 0 to 1% and the first mixture is in the range of 1 to 4%.

[0041] In one example the ratio of the primary binder element to the primary conductive element is in the range of 95:5 to 99:1 .

[0042] In one example, mixing of the binder element and the conductive element may cause coating of the conductive element on the particles of the binder element, wherein the coating of the conductive element may be at least 5 percent.

[0043] The present approaches provide a number of technical advantages. For example, fibrillated binder element increases the surface area of the electrode. A higher surface area may allow for more active sites for electrochemical reactions, which may improve the battery's performance by enhancing its charge and discharge rates. While the primary conductive pathway in an electrode comes from the conductive elements, the fibrillated binder may also contribute to the overall electrical connectivity. The network of fibers helps maintain contact between the active material particles and the conductive elements, ensuring efficient electron transport throughout the electrode. Furthermore, the fibrillation process may influence the porosity of the electrode. A well-fibrillated binder creates a porous structure that facilitates the movement of ions within the electrode that is particularly beneficial for ion transport during the charge and discharge cycles of the battery. By creating a network of fibers, the binder enhances the structural integrity, electrical connectivity, and ion transport within the electrode, all of which are integral to the efficient functioning of a battery.

[0044] The above and other features, aspects, and advantages of the subject matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and should not be construed as a limitation to the present subject matter. Itis thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components. While aspects of the described method of dry electrode preparation may be implemented in any number of different systems, and / or implementation, the examples are described in the context of the following example system. It may be noted that drawings of the present subject matter shown here are for illustrative purposes and are not to be construed as limiting the scope of the subject matter claimed.

[0045] FIG. 1 illustrates a method 100 for preparing a dry electrode, in accordance with an embodiment of the present subject matter. The order in which method 100 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 100, or any alternative methods. Furthermore, method 100 may be implemented by apparatus(s) or machine(s) through any suitable hardware, or combinations thereof. The present method is described in relation to operation of one or more components, elements or stages implemented as part of an industrial and / or laboratory process for preparing a dry electrode.

[0046] At block 102, a first mixture is obtained by pre-mixing a binder element and a primary conductive element. The binder element in the first mixture has a particle size in a range of about 350 to 450 microns. In one example, the pre-mixing of the primary binder element and the conductive element may be done in a mixing chamber. The mixing of the binder element and the primary conductive element to obtain the first mixture may be carried out at a speed in a range of about 600 to 1800 RPM, for about 10-30 minutes. It may be noted that a mixing chamber may be a device or part of a machine where the binder element and the conductive element may be combined and homogenized before further processing. Examples of mixing chamber may include, but not limited to, planetary mixer, rotary drum mixer, V-blender, ribbon blender, and more. It may be noted that this is one of themany other examples by way of which the binder element and the primary conductive element may be mixed. Such other examples too fall within the scope of the present subject matter. Since, milling of bare binder element without premixing exhibits higher trends towards self-agglomeration due to increased surface energy and heat generated during the milling process, the pre-mixing of the binder element for passivating fibrillation sites before the milling process may increase milling efficiency.

[0047] At block 104, a second mixture may be obtained. In one example, the second mixture may be obtained by cooling the first mixture. The cooling may be affected through a cold milling processing by passing cold air through the first mixture. In such a case, the cold milling reduces the temperature of the first mixture comprising the binder element and the primary conductive element.

[0048] In one example, the cold milling process to which the first mixture is subject to may involve subjecting the first mixture to pressure. The milling process may be performed in a milling chamber. As may be understood, a milling chamber may be a component of a milling machine where various mechanical actions comprising grinding, crushing, or pulverizing of materials, takes place. Different types of milling chambers, such as a jet milling chamber, ball milling chamber, hammer milling chamber, cryogenic milling chamber, and more, may be used without deviating from the scope of the present subject matter.

[0049] Returning to the present subject matter, pressure is applied to the first mixture (e.g., during the milling process in the milling chamber), to achieve particle size reduction of the binder element in the first mixture. By applying pressure to the first mixture, the particle size of the binder element may be reduced by at least 50- 60 percent, to provide the second mixture. For example, the milling process may help reduce the particle size of the binder element to about less than 100 microns. The specific parameters of the pressure applied, such as magnitude, duration, and rate of application, may be accordingly controlled based on the quantity of the mixture undergoing cold milling. These parameters may be optimized for particular material(s) and desired end properties of the electrode, without deviating from the scope of the present subject matter.

[0050] In another example, the pressure applied to the first mixture may be one of a feeding pressure and a milling pressure. Herein, feeding pressure and milling pressure refer to the pressures applied during the milling process to reduce the particle size of the binder element within the first mixture. As may be understood, feeding pressure is a force applied to feed the mixture of binder and conductive element into a milling equipment (for example, a milling chamber). The feeding pressure may be typically set to ensure a consistent and controlled delivery of the first mixture to be milled. Further, milling pressure on the other hand refers to a force applied by the milling equipment to the first mixture to achieve particle size reduction. Such pressure may be exerted by mechanical component(s) of the milling equipment (for example, rollers, balls, hammers) depending on the type of mill used (such as ball mill, hammer mill, jet mill, and more). The milling pressure is a determining factor regarding the fibrillation and reduction in particle size of the binder element in the first mixture. In one example, the feeding pressure may be kept higher than the milling pressure, during the milling pressure, to significantly reduce the particle size of the binder. Further, the feeding pressure may be in a range of about 1 to 3 kg / cm2, and the milling pressure may be in a range of about 1 to 2 kg / cm2. The method also comprises mixing the active element with a secondary conductive carbon and a secondary binder in the temperature range of about 15°C to 20°C for a time period of about 15 to 30 minutes.

[0051] In yet another example, the active element may be mixed with the secondary conductive element and a secondary binder element in two different steps. The process comprises mixing the active element with the secondary conductive element in the temperature range of about 15°C to 20°C at a speed of about 800 to 1200 RPM for about 15 to 30 minutes to form the second mixture. The second mixture may be mixed with the secondary binder element in the temperature range of about 15°C to 20°C at a speed of about 800 to 1200 RPM for about 15 to 30 minutes to form a third mixture. It is again reiterated that the above approaches and different examples may be used as described or in different combinations. These examples, and their corresponding variations, are only otherexemplary embodiments and continue to fall within the scope of the present subject matter.

[0052] At block 106, a third mixture may be obtained by mixing the second mixture with an active element, in a first temperature range of about 15°C to 25°C. In one example, the second mixture comprises a partially fibril lated binder element. In another example, the particle size of the binder element in the second mixture may be lying in the range of about 80 to 100 microns. Herein, mixing the second mixture with the active element to obtain the third mixture may be implemented in a temperature range of about 15°C to 25°C. The mixing of the second mixture with the active element may be done in a mixing chamber (as explained previously). It may be noted that a mixing chamber may be a device or part of a machine where the binder element and the conductive element may be combined and homogenized before further processing. Examples of mixing chamber may include, but not limited to, planetary mixer, rotary drum mixer, V-blender, ribbon blender, and more.

[0053] At block 108, the third mixture may be subjected to a high shear mixing process which is performed at a second temperature which is in a range of about 65°C to 85°C. In an example, for high shear mixing, intense shear force may be applied to the third mixture to rapidly and thoroughly combine the constituents into a uniform substance and may be implemented in a high shear mixing chamber. As may be understood, this may involve a fast rotation or movement of a component within a mixer, such as a rotor, blade, or impeller, which creates high levels of shear. During the high shear mixing process in the high shear mixing chamber, the third mixture may be subjected to mechanical forces for breaking down particles, dispersing aggregates, and homogenizing the constituents. Herein, the mixing the third mixture with the active element may be done until the second temperature is in a range of about 65°C to 85°C. The high-shear mixing process ensures that the active material is evenly distributed throughout the binder and conductive element. The second temperature attained during the high-shear mixing process is controlled to ensure that the constituents integrate properly without damaging the structure of the electrode. In one example, the third mixture may correspond toformation of thin and dense fibrils of the binder element present in the first mixture due to reduction in the particle size during the milling process. In one example, the reduction in the particle size of the binder element during the milling process may increase the extent of fibrillation of the binder element.

[0054] At block 110, a fourth mixture may be obtained by cooling the third mixture after it has been subjected to high shear mixing. In one example, the obtained third mixture may be mixed with the first mixture to obtain a fourth mixture comprising partially fibrillated first mixture. In an example, the third mixture may further be cooled to a third temperature in a cooling chamber. The third mixture may be cooled to the third temperature in a range of about 15°C to 25°C. This may prevent the agglomeration of particles, which may lead to inconsistencies in the electrode structure. Further, cooling helps stabilize the second mixture and maintain a desired particle size distribution, wherein milling may help fibrillate the binder element, thereby, creating a network of fine fibers. The network of fine fibers may enhance structural integrity and performance of the electrode. In one example, the binder element and the conductive element may be mixed at a speed of about 600-1800 RPM, for a predefined time period. In one example, the predefined time period may be in the range of about 10-30 minutes. Other ranges of speed and predefined may also be present, without deviating from the scope of the present subject matter..EXPERIMENTAL RESULTS FIGS. (2-8)

[0055] FIGs. (2-8) illustrate experimental result(s) (including SEM images and graphical representations) in conjunction with the examples of the present subject matter in relation to preparation of the dry electrode. The same as explained with reference to the first mixture and second mixture disclosed in FIG. 1 and should not be construed as a limitation in any way.

[0056] FIG. 2(A-B) represents an example fibrillation of binder element before the milling process, in accordance with an embodiment of the present subject matter. FIG. 2(A-B) depicts a SEM image of a binder element mixed with a conductive element before the milling process. In an example, to preventagglomeration of particles in the binder element during the milling process, different milling media may be used. For example, the mixing of the binder element with different conductive elements at different weight percentages may produce varying results. The Table 1 shown below depicts an example of the material composition comprising the binder element and the conductive element and their particle size distribution in microns. In an example, the binder element may be PTFE and the conductive element may be carbon. Other examples may also be used without deviating from the scope of the scope of the present subject matter.TABLE 1

[0057] In another example, Table 2 below shows variation of particle size of the binder element on application of varying feeding pressure and milling pressure, for the purposes of explanation of optimization of process parameters to increase the size reduction efficiency along with minimizing the occurrence of agglomeration. As may understood, the optimization of feed rate, gas pressure, and classifier speed during the milling process for treatment of the binder element results in ensuring uniform particle size reduction and minimized agglomerations.TABLE 2

[0058] As explained previously, feeding pressure and milling pressure refer to the pressures applied during the milling process to reduce the particle size of the binder element within the first mixture. Feeding pressure is a force applied to feed the mixture of binder and conductive element into a milling equipment (for example, a milling chamber). The feeding pressure may be typically set to ensure a consistent and controlled delivery of the first mixture to be milled. Further, milling pressure on the other hand refers to a force applied by the milling equipment to the first mixture to achieve particle size reduction. This pressure may be exerted by mechanical component(s) of the milling equipment (for example, rollers, balls, hammers) depending on the type of mill used (such as ball mill, hammer mill, jet mill, and more). The milling pressure is a determining factor regarding the fibrillation and reduction in particle size of the binder element in the first mixture.

[0059] As may be seen from Table 2, the feeding pressure may be kept slightly higher than the milling pressure, during the milling pressure, to significantly reduce the particle size of the binder. Further, the feeding pressure may be in a range of about 1 to 3 kg / cm2, and the milling pressure may be in a range of about 1 to 2 kg / cm2. By maintaining a higher feeding pressure, the first mixture is continuously and forcefully pushed into the milling zone, where the actual size reduction occurs due to the milling pressure. The differential between the feeding pressure and the milling pressure helps to regulate the material throughput in the first mixture, ensuring that the milling chamber receives a steady supply of material withoutoverloading or underfeeding, which could compromise the quality of the milled product.

[0060] FIG. 3(A-B) represents an example fibrillation of binder element after the milling process, in accordance with an embodiment of the present subject matter. In an example, FIG. 3(A-B) represents a SEM image of the conductive element (for example, jet milled carbon coated PTFE powder with 5 percent weight). As may be understood, after the milling process of the binder element (for example, PTFE), average particle size is reduced due to uniform distribution of the binder element, which further increases extent of fibrillation and enhanced particle to particle attachment in the electrode. This improvement in fibrillation may further lead to a two-fold increase in peel strength for the electrode (anode or cathode) made with milled binder element.

[0061] FIG. 4(A-C) represents an example comparison between fibrillation of binder element (for example, PTFE) before and after the milling process with a SEM image of an anode having a percentage weight of carbon coated binder element, and with different conductive elements (for example, carbon), in accordance with an embodiment of the present subject matter. In an example, FIG. 4A represents a SEM image of an anode with bare binder element (without the milling process). In another example, FIG. 4B represent a SEM image of an anode with for example, jet milled 5 percent weight carbon coated binder element. As may be seen in FIG. 4B, dense and thin fibrils are uniformly present across the electrode after the milling process. FIG. 4G represents a SEM image of an anode with for example, jet milled 5 percent weight carbon coated binder element and a different conductive element for the purposes of establishing the comparison between the extent of fibrillation due to processing of the binder element for preparing the electrode for calendaring.

[0062] FIG. 5(A-B) illustrates an example SEM image of a cathode, in accordance with an embodiment of the present subject matter. As shown in FIG. 5A, the cathode with bare (without the milling process) binder element shows no dense fibrils present while thick fibrils may be observed at some areas. FIG. 5B shows a SEM image of a cathode with for example, jet milled 5 percent weightcarbon coated binder element wherein uniform, thin and dense fibrils are present across the electrode.

[0063] FIG. 6(A-B) illustrates an example graphical representation of particle size distribution before the milling process, in accordance with an embodiment of the present subject matter. FIG. 6(C-D) illustrates a graphical representation of particle size distribution after the milling process, in accordance with an embodiment of the present subject matter. As depicted in FIG. 6(A-D), the extent of fibrillation is inversely proportional to the particle size of the binder element (for example, PTFE) and its distribution into the powdered mixture.

[0064] FIG. 7(A-C) illustrates an example graphical representation of effect of milling process on capacity retention, in accordance with an embodiment of the present subject matter. In an example, the milling process of the binder element (for example, PTFE), shown by reference numerals 702 and 704, in the treatment process results in the improved discharge capacity and capacity retention as depicted from the graphical representations in FIG. 7(A-C). The uniform distribution of the binder element may be improved after reduction of their particle size due to which increases the extent of thin dense fibrillization and enhanced the electrochemical performance in terms of initial capacity and capacity retention.

[0065] FIG. 8(A-B) illustrates an example graphical representation of electrode composition, shown by reference numerals 802 and 804, with respect to performance cycle and capacity retention, in accordance with an embodiment of the present subject matter. In an example, due to the treatment of the binder element with the milling process, the performance is improved, and capacity is retained. In an example, the electrode cells binder elements after the milling process may retain 90% capacity after 28 cycles.

[0066] Although examples for the present disclosure have been described in language specific to structural features and / or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.

Claims

I / We Claim:1 . A method of preparing a dry electrode, the method comprising: pre-mixing of a binder element and a primary conductive element to obtain a first mixture, wherein the binder element in the first mixture has a particle size in a range of 350 to 450 microns; cooling the first mixture by passing the first mixture through a cold milling process, wherein passing the first mixture through the milling process comprises applying a pressure to the first mixture to obtain a second mixture, for attaining a particle size of the binder element less than 100 microns; mixing the second mixture with an active element, in a first temperature range of about 15°C to 25°C to obtain a third mixture; subjecting the third mixture through a high shear mixing process to a second temperature, wherein the second temperature is in a range of about 65°C to 85°C; and cooling the third mixture to a third temperature, wherein the third temperature is in a range of 15°C to 25°C, to obtain a fourth mixture.

2. The method as claimed in claim 1 , wherein the pressure applied to the first mixture during the cold milling process is a feeding pressure and a milling pressure, wherein the feeding pressure is greater than the milling pressure.

3. The method as claimed in claim 2, wherein the feeding pressure is in a range of about 1 to 3kg / cm2, and the milling pressure is in a range of about 1 to 2kg / cm2.

4. The method as claimed in claim 1 , wherein the second mixture comprises a partially fibrillated binder element.

5. The method as claimed in claim 1 , wherein the particle size of the binder element in the second mixture is in the range of 80 to 100 microns.

6. The method as claimed in claim 1 , wherein milling process is one of a jet milling process, a cryogenic grinder milling process, or combinations thereof.

7. The method as claimed in claim 1 , wherein the pre-mixing of the binder element and the primary conductive element to obtain the first mixture is carried out at a speed in a range of about 600 to 1800 RPM, for a time period in a range of about 10-30 minutes.

8. The method as claimed in claim 1 , wherein the high shear mixing process of the second mixture is carried out at a speed in a range of about 3000 to 4000 RPM, for a time period of about 5-60 minutes.

9. The method as claimed in claim 1 , wherein mixing the second mixture with the active element to obtain the third mixture further comprises pre-mixing the active element with a secondary conductive element and a secondary binder element.

10. The method as claimed in claim 9, wherein the pre-mixing is carried out in a temperature in the range of 15°C to 25°C at a speed of about 800 to 1200 RPM for a time period of about 10 - 30 min.1 1 . The method as claimed in claim 1 , wherein the primary conductive element is selected from the group consisting of carbon nanofibers, super-p, vapor grown carbon fibers, carbon nanotubes or combinations thereof.

12. The method as claimed in claim 1 , wherein the primary binder element is selected from a group comprising one of polytetrafluoroethylene (PTFE), Polyether ether ketone (PEEK), poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA), polypropylene, Polyacrylonitrile (PAN), tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene (THV), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), or combinations thereof.

13. The method as claimed in claim 9, wherein the secondary conductive element is selected from a group comprising one of carbon black, ketjenblack, acetylene black, activated carbon, or combinations thereof.

14. The method as claimed in claim 9, wherein the secondary binder element is selected from polyvinylidene fluoride (PVDF), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), sodium carboxymethyl cellulose (Na-CMC), carboxymethyl cellulose (CMC), styrene butadiene rubber, polyethylene glycol (PEG), polyacrylic acid (PAA), polyethylene oxide (PEO) or combinations thereof.

15. The method as claimed in claim 1 , wherein the active element is selected from a group comprising one of natural graphite, synthetic graphite, silicon, Si-Carbon composites, or combinations thereof.

16. The method as claimed in claim 1 wherein the ratio of the binder to the conductive carbon is in the range of 95:5 to 99:1 .

17. The method as claimed in claim 1 , wherein the active element is selected from a group comprising one of one of natural graphite, synthetic graphite, silicon, Si-Carbon composites, nickel-manganese-cobalt oxide (NMC), lithium-nickel-cobalt-aluminium oxides (NCA), lithium iron phosphate (LFP), or lithium-manganese-rich (LMR), or combinations thereof.

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