A process for preparation of an electrode film and implementations thereof

Abstract

The present disclosure provides a process of preparation of an electrode film, said process comprising: a mixing an active material with a conducting carbon to obtain a first mixture; b. blending a first portion of a binder having compressibility index of at least 10% with the first mixture to obtain a second mixture; c. mixing a second portion of the binder having compressibility index less than 10% with the second mixture to obtain a third mixture; and d. subjecting the third mixture to calendaring to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5% with respect to the total weight of the electrode film. The present disclosure also provides an electrode film and an electrochemical cell.

Description

A PROCESS FOR PREPARATION OF AN ELECTRODE FILM AND IMPLEMENTATIONS THEREOFFIELD OF INVENTION

[0001] The present disclosure broadly relates to the field of batteries. Particularly, the present disclosure relates to a dry process of preparing an electrode film, more particularly to a dry process of preparing a cathode film with high active material loading.BACKGROUND OF THE INVENTION

[0002] There is an increase in demand for safer and high performing energy storage solutions. The solvent free dry process preparation of electrodes is one such highly appealing and cost cutting strategy in order to attain high performing and safer battery technology.

[0003] The dry process encompasses the fibrillating polymer-based membrane development, which provides a thin and flexible film that can be used directly as an electrode material for the battery technology. However, most of the fibrillating polymer is fluorine based polymeric derivative, having significant reactivity with the active material and hence the electrochemical performances are degraded over the cycling. Further, the binder is ionically insulating and not contributing to the capacity, hence its higher content will further reduce the electrochemical performance of the system. Hence, reducing the amount of the binder is highly essential to maintain the electrochemical performance. Also, the binder content can be reduced only up to a certain limit and without compromising the formation of a flexible and freestanding film.

[0004] Therefore, there is an unmet need to develop a dry process with optimized amounts of binder and process parameters in order to achieve a robust and flexible electrode film with lower content of the fibrillating binder, and without compromising the electrochemical performance.SUMMARY OF THE INVENTION

[0005] In an aspect of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: (a) mixing an active material with a conducting carbon to obtain a first mixture; (b) blending a first portion of a binder having compressibility index of at least 10 % with the firstmixture to obtain a second mixture; (c) mixing a second portion of the binder having compressibility index less than 10% with the second mixture to obtain a third mixture; and (d) subjecting the third mixture to calendaring to obtain the electrode film; wherein the binder is in a weight of less than 0.5 % with respect to the total weight of the electrode film.

[0006] In another aspect of the present disclosure, there is provided an electrochemical cell comprising: (a) a cathode film obtained from the process as disclosed herein; (b) an anode; and (c) an electrolyte.

[0007] In yet another aspect of the present disclosure, there is provided an electrode film obtained by the process as disclosed herein, the electrode film comprising: (a) 98 to 99.5% by weight of an active material; (b) 0.4 to 1.9% by weight of a conducting carbon; and (c) 0.1 to 0.5 % by weight of a binder.

[0008] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the as claimed subject matter, nor is it intended to be used to limit the scope of the as claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following drawings form a part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.

[0010] Figure 1 depicts the schematic illustration of the dry process for the film formation, in accordance with an embodiment of the present disclosure.

[0011] Figure 2 depicts the SEM images of the first mixture prepared by mixing at A) 18.37 m / s, B) 20.42 m / s, and C) 25.52 m / s, in accordance with an embodiment of the present disclosure.

[0012] Figure 3 depicts the ED AX mapping for carbon element at for carbon coated cathode active material mixing carbon and cathode active material at a tip speed of25.52 m / s for A) Sl-10 mins, B) S2- 20 mins C) S3- 30 mins, D) S4- 40 mins, and E) S5- 50 mins, in accordance with an embodiment of the present disclosure.

[0013] Figure 4 depicts the SEM images of binder with A) low flowability or compressibility index higher than 10 (first portion of binder), B) high flowability or compressibility index less than 10 (second portion of binder), in accordance with an embodiment of the present disclosure.

[0014] Figure 5 depicts the SEM images showing the effect of different weight percentage of binder in the final electrode film after applying the shear force to understand the degree of fibrillation in terms of thick and slender threads wherein A) 0.5% by weight of binder B) 0.1% by weight of binder C) <0.2% by weight of binder and D) > 1% by weight of binder, in accordance with an embodiment of the present disclosure.

[0015] Figure 6 depicts the Nyquist plot for electrochemical impedance characteristics corresponding to the different amount of PTFE binder in the carbon coated sodium nickel-iron-manganese (NFM) cathode, wherein -1.5F, -0.5F and - 0.1 F represents the electrode film obtained by mixing at a speed of 25.52m / s and comprising a binder in a weight of 1.5%, 0.5% and 0.1% by weight respectively, in accordance with an embodiment of the present disclosure.

[0016] Figure 7 depicts the Young’s modulus evaluation result of electrode film prepared with (A) 1.5% binder and (B) 0.2% binder, in accordance with an embodiment of the present disclosure.

[0017] Figure 8 depicts the film formed by the dry process comprising two step addition of low flowable PTFE and high flowable PTFE binder with a total binder content of 0.2%, wherein A) the weight ratio of first and second portion of the binder is 10:90, B) the weight ratio of first and second portion of the binder is 80:20, and C) the weight ratio of first and second portion of the binder is 50:50, in accordance with an embodiment for the present disclosure.

[0018] Figure 9 depicts the cross-sectional SEM image of the thin electrode film having thickness less than 100 micron, in accordance with an embodiment of the present disclosure.

[0019] Figure 10 depicts the voltage vs specific capacity plots for NFM cathode film having different binder content A) -1.5F (1.5% binder), B) IF (1% binder), C) 0.5F (0.5% binder), and D) 0.2F (0.2% binder), in accordance with an embodiment of the present disclosure.DESCRIPTION OF THE INVENTION

[0020] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features. Definitions

[0021] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0022] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0023] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0024] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

[0025] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0026] The term "at least one" is used to mean one or more and thus includes individual components as well as mixtures / combinations.

[0027] The term “active material” refers to the active constituent of an electrode, which comprises the particles that undergo oxidation or reduction, resulting in reversible ion storage. The active material of the present disclosure is a cathode active material comprising oxides of lithium, manganese, cobalt, nickel, or combinations thereof. Examples of cathode active materials include but not limited to sodium nickel-iron-manganese (NFM) based compounds, sodium-vanadium- fluorophosphate (NVPF) based compounds, Prussian blue based cathode materials, Prussian white based cathode materials, lithium nickel-manganese-cobalt oxide (NMC) based compounds, lithium-nickel-cobalt-aluminium oxides (NCA), lithium-cobalt oxide (ECO) based compounds, lithium iron phosphate (EFP) based compounds, or lithium-manganese-rich (EMR) based compounds.

[0028] The term “conducting carbon” refers to carbon material which has conducting property and is used in combination with the active material of the present disclosure, to obtain a composite electrode material. Examples of conductive carbon includes but not limited to ketjen black (KB), graphite, KS6L, Super P, graphitic nanofiber, carbon nanofiber, carbon nanotubes, or combinations thereof.

[0029] The term “binder” refers to the binder constituent of an electrode, which has the property to form small fibrils under the application of shear force. The binder provides the mechanical integrity of the electrode during manufacturing and provide optimal dispersion and adhesion of the active material and conductive additive to the current collector. Examples of binder in the present disclosure includes but not limited to polytetrafluoroethylene (PTFE), polyamide, fluoroethylene vinyl ether (FEVE), polyethylene (PE), polyethylene oxide (PEO), or combinations thereof.

[0030] The term “thin electrode film” refers to the electrode film that is capable of being employed as an electrode in an electrochemical cell which has thickness in a range of 40 to 100 micrometres. In an aspect of the present disclosure, the thinelectrode film is obtained by calendering or multiple folding and pressing of the electrode film as disclosed herein, having a thickness of at least 40 pm.

[0031] The term “compressibility index CI (%)”, as used herein refers to the flowability of bulk solids. According to the present disclosure, the term is used to predict the propensity of a given binder sample to be compressed. The reference table for CI (%) and the corresponding flowability properties are provided in Table 1. The Hausner ratio (H) is another indication of flowability. A Hausner ratio of greater than 1.25 is considered to be an indication of poor flowability. According to the present disclosure, the binder is used with different flowability properties.

[0032] Table 1

[0033] The term “tip speed” refers to the tangential velocity of the blade at its tip in a rotating blender / mixer, impeller, propeller, cutter, or the like. It is a function of the rotation per minute (RPM) and diameter of the mixer blade. In case of a mixer / blender, tip speed = rotation speed x circumference of the mixer / blender (2?tr), wherein r is the blade radius, and 7t is 3.14151. In an aspect of the present disclosure, the mixing in step (a), blending in step (b) and mixing in step (c) are independently carried out at a tip speed in a range of 15 m / s to 31 m / s. In an aspect of the present disclosure, the blade radius is 97.5 mm, the blade circumference is 2x3.14x97.5 = 612.3 mm. In one revolution the blade covers 612.3 mm. At 2500 revolutions per minute, the blade covers 2500 x 612.3 which is equal to 15,30,750 mm or 1530.75 m. In one second, the blade covers 1530.75 -? 60 = -25.52 m. So, the tip speed is specified as the distance swept by the blade tip in one second which is -25.52 m / s in one experimental setup. As the blade diameter increases (as in large mixers), the m / s required to achieve the same tip speed will decrease as the larger blade radius has a higher circumference.

[0034] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, weight percentage in the range of 0.1% to 0.5% should be interpreted to include not only the explicitly recited limits of 0.1% to 0.5% but also to include sub-ranges, such as 0.15% to 0.2%, 1.5% to 0.49% and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 0.18%, 0.45%, and 0.3%.

[0035] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products, compositions, formulations, and methods are clearly within the scope of the disclosure, as described herein.

[0036] As discussed in the background, there are challenges in optimizing a dry process of preparing an efficient cathode. In particular, lowering the binder content as low as 1% by weight, while not compromising the flexible and free-standing film formation is a continuing challenge in the battery field. According to the present disclosure, the film with reduced binder content can be realized due to a sequential processing of the carbon coverage and the two-step addition of binder with different flowability. By reducing the amount of binder, very high amount such as 99.5 % of the active material loading can be achieved, which will further increase the energy density of the system. The formation of carbon coverage over the electrode material and the addition of the binder having different flowability at different stages are responsible to achieve the thin, flexible, robust, and high performing electrode film. The homogeneous carbon coverage confers the proper electronic networking for the charge kinetics and also supports the mutual adhesion between the particles during the addition of binder while preparing the electrode (as shown in Figure 1). This homogeneous carbon coverage further helps to fibrillate the binder in thinnerthreads up to a longer distance, and hence the thin film formation can be done with the much lower amount of the binder (0.1% by weight). The initial addition of a less flowable binder adheres over the surface of carbon coated cathode active material, conferring the high packing fraction to the carbon coated cathode active materials. The highly flowable binder is introduced in a later stage which spreads over the entire cathode material and fibrillate homogeneously with thinner threads to provide a robust free standing dry electrode film.

[0037] Accordingly, in the present disclosure, there is provided a dry process of preparation of an electrode film for an electrochemical cell, wherein the film has a homogenous coating of conductive carbon over the active material. The binder used in the preparation of electrode film comprises a high flowable binder and a less flowable binder.

[0038] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: (a) mixing an active material with a conducting carbon to obtain a first mixture; (b) blending a first portion of a binder having compressibility index of at least 10 % with the first mixture to obtain a second mixture; (c) mixing a second portion of a binder having compressibility index of less than 10% to the second mixture to obtain a third mixture; and (d) subjecting the third mixture to calendaring to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film.

[0039] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the active material is selected from sodium nickel-iron- manganese (NFM) based compounds, sodium-vanadium-fluorophosphate (NVPF) based compounds, Prussian blue based cathode materials, Prussian white based cathode materials, nickel-manganese-cobalt oxide (NMC) based compounds, lithium-nickel-cobalt-aluminium oxides (NCA), lithium-cobalt oxide (LCO) based compounds, lithium iron phosphate (LFP) based compounds, or lithiummanganese-rich (LMR) based compounds. In another embodiment of the present disclosure, the active material is selected from sodium nickel-iron-manganese (NFM) based compounds, sodium-vanadium-fluorophosphate (NVPF) basedcompounds, nickel-manganese-cobalt oxide (NMC) based compounds, lithium- nickel-cobalt-aluminium oxides (NCA), or combinations thereof. In yet another embodiment of the present disclosure, the active material is selected from sodium nickel-iron-manganese (NFM) based compounds, or nickel-manganese-cobalt oxide (NMC) based compounds. In still another embodiment of the present disclosure, the active material is sodium nickel-iron-manganese (NFM) based compounds.

[0040] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the active material is in a weight range of 98 to 99.5%, with respect to the total weight of the electrode film. In another embodiment of the present disclosure, the active material is in a weight range of 98 to 99%, with respect to the total weight of the electrode film. In yet another embodiment of the present disclosure, the active material is in a weight range of 98 to 98.5%, with respect to the total weight of the electrode film.

[0041] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the conducting carbon is selected fromketjen black (KB), graphite, KS6L, super P, graphitic nanofiber, carbon nanofiber, carbon nanotubes, or combinations thereof. In yet another embodiment of the present disclosure, the conducting carbon is selected from ketjen black (KB), graphite, KS6L, super P, or combinations thereof. In still another embodiment of the present disclosure, the conducting carbon is selected from ketjen black (KB), KS6L, or combinations thereof. In further embodiments, the conducting carbon is a combination of ketjen black (KB), and KS6L.

[0042] In an embodiment of the present disclosure, the conducting carbon is selected from ketjen black (KB), graphite, KS6L, super P, graphitic nanofiber, carbon nanofiber, carbon nanotubes, or combinations thereof. In another embodiment of the present disclosure, the conducting carbon is a combination of one or more conducting carbons. In yet another embodiment of the present disclosure, the conducting carbon is selected from ketjen black (KB), KS6L, or combinations thereof. In still another embodiment of the present disclosure, the conducting carbon is a combination of ketjen black (KB) and KS6L.

[0043] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the conducting carbon is a combination of two conducting carbons in a weight ratio range of 1:0.3 to 1:0.8, with respect to the total weight of the conducting carbon. In another embodiment of the present disclosure, the conducting carbon is a combination of ketjen black (KB) and KS6L in a weight ratio range of 1:0.3 to 1:0.8, with respect to the total weight of the conducting carbon.

[0044] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the conducting carbon is in a weight range of 0.4 to 1.9 %, with respect to the total weight of the electrode film. In another embodiment of the present disclosure, the conducting carbon is in a weight range of 0.9 to 1.7 %, with respect to the total weight of the electrode film. In yet embodiment of the present disclosure, the conducting carbon is in a weight range of 1.4 to 1.6 %, with respect to the total weight of the electrode film.

[0045] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: (a) mixing 98 to 99.5%, of an active material with 0.4 to 1.9 % of a conducting carbon to obtain a first mixture; (b) blending a first portion of a binder having compressibility index of at least 10 % with the first mixture to attain a temperature in a range of 60 to 75 °C followed by cooling to obtain a second mixture; (c) mixing a second portion of a binder having compressibility index of less than 10% with the second mixture to attain a temperature in a range of 60 to 75 °C followed by cooling to obtain a third mixture; and (d) subjecting the third mixture to calendaring at a temperature in a range of 25 to 35 °C to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film.

[0046] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the mixing in step (a) is carried out at a tip speed in a range of 15 m / s to 31 m / s for a time period in a range of 35 to 60 minutes. In another embodiment of the present disclosure, the mixing in step (a) is carried out at a tip speed in a range of 15 m / s to 31 m / s for a time period in a range of 40 to 50 minutes.

[0047] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the blending in step (b) is carried out at a tip speed in a range of 15 m / s to 31 m / s, for a time period in a range of 5 to 60 minutes to attain a temperature in a range of 60 to 75 °C. In another embodiment of the present disclosure, the blending is carried out for a time period in a range of 20 to 60 minutes to attain a temperature in a range of 65 to 73 °C. In yet another embodiment, the blending is carried out for a time period in a range of 45 to 55 minutes to attain a temperature in a range of 68 to 72 °C.

[0048] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the blending in step (b) is followed by cooling at a rate in a range of 2 to 5 °C / min, for a time period in a range of 5 to 40 minutes. In another embodiment of the present disclosure, the blending in step (b) is followed by cooling at a rate in a range of 2 to 5 °C / min, for a time period in a range of 10 to 30 minutes.

[0049] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: (a) mixing 98 to 99.5%, an active material with 0.4 to 1.9 % of a conducting carbon at a tip speed in a range of 15 m / s to 31 m / s to obtain a first mixture; (b) blending a first portion of a binder having compressibility index of at least 10 % with the first mixture at a tip speed in a range of 15 m / s to 31 m / s, to attain a temperature in a range of 60 to 75 °C followed by cooling to obtain a second mixture; (c) mixing a second portion of a binder having compressibility index of less than 10% with the second mixture at a tip speed in a range of 15 m / s to 31 m / s, to attain a temperature in a range of 60 to 75 °C followed by cooling to obtain a third mixture; and (d) subjecting the third mixture to calendaring at a temperature in a range of 25 to 35 °C to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film.

[0050] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the third mixture is subjected to multiple folding and pressing under a shear force in a range of 100-200 MPa to obtain the electrode film.

[0051] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the cooling is carried out at a rate in a range of 2 to 5 °C / min for a time period in a range of 5 to 40 minutes.

[0052] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the mixing in step (c) is carried out in a zeppelin mixer.

[0053] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein subjecting the third mixture to calendering results in formation of binder fibrils.

[0054] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the binder fibrils have diameter in a range of 10 to 50 nm.

[0055] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein subjecting the third mixture to calendaring is carried out at a roller speed in a range of 1 to 12 cm / s.

[0056] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: (a) mixing an active material with a conducting carbon at a tip speed in a range of 15 ms'1to 31 ms'1to obtain a first mixture; (b) blending a first portion of a binder having compressibility index of at least 10 % with the first mixture at a tip speed in a range of 15 ms1to 31 ms'1for a time period in a range of 5 to 60 minutes to attain a temperature in a range of 60 to 75 °C followed by cooling at a rate in a range of 2 to 5 °C / min for a time period in a range of 5 to 40 minutes to obtain a second mixture; (c) mixing a second portion of a binder having compressibility index of less than 10% with the second mixture at a tip speed in a range of 15 ms'1to 31 ms'1to attain a temperature in a range of 60 to 75 °C followed by cooling at a rate in a range of 2 to 5 °C / min for a time period in a range of 5 to 40 minutes, to obtain a third mixture; and (d) subjecting the third mixture to calendaring at a temperature in a range of 25 to 35°C and at a roller speed in a range of 1 to 12 cm / s to obtain the electrode film; wherein the binder is in a weight range of 0.1% to 0.5 % with respect to the total weight of the electrode film and the first portion and the second portion of the binder are in a weight ratio range of 0.95: 1 to 1: 1 with respect to the total weight of the electrode film.

[0057] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the first portion of the binder and the second portion of the binder are in a weight ratio range of 0.95 : 1 to 1 : 1 with respect to the total weight of the electrode. In an embodiment, the first portion of the binder and the second portion of the binder are in a weight ratio of 1: 1.

[0058] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the binder is selected from polytetrafluoroethylene (PTFE), polyamide, fluoroethylene vinyl ether(FEVE), polyethylene (PE), polyethylene oxide (PEO), or combinations thereof. In another embodiment of the present disclosure, the binder is selected from polytetrafluoroethylene (PTFE), polyamide, fluoroethylene vinyl ether(FEVE), or combinations thereof. In yet another embodiment of the present disclosure, the binder is polytetrafluoroethylene (PTFE).

[0059] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the electrode film has a thickness in a range of 40 to 100 pm.

[0060] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the electrode film is a cathode.

[0061] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the electrode film has a specific capacity in a range of 140 - 170 mAh / g for sodium ion battery. In another embodiment of the present disclosure, the electrode film has a specific capacity in a range of 180 - 270 mAh / g for lithium-ion battery.

[0062] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: (a) a cathode film obtained from the process as disclosed herein; (b) an anode; and (c) an electrolyte.

[0063] In an embodiment of the present disclosure, there is provided electrochemical cell as disclosed herein, wherein the electrochemical cell optionally comprises a separator.

[0064] In an embodiment of the present disclosure, there is provided an electrode film obtained by the process as disclosed herein, the electrode film comprising: (a)98 to 99.5% by weight of an active material; (b) 0.4 to 1.9% by weight of a conducting carbon; and (b) 0.1 to 0.5 % by weight of a binder.

[0065] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein step (a) is carried out by mixing at a speed in a range of 15 to 31 m / s. In another embodiment of the present disclosure, the step (a) is carried out by mixing at a speed in a range of 20 to 29 m / s. In yet another embodiment of the present disclosure, the step (a) is carried out by mixing at a speed in a range of 22 to 27 m / s.

[0066] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the first mixture possesses conductivity in a range of 2 x 10’4to 3 x 10’4S / cm and particle size in a range 1 to 10 microns. The conductivity measurement provides a clear idea about the uniform carbon coating over the active material. Higher the conductivity value of the first mixture, more uniform the coating of conductive carbon over the active material surface.

[0067] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein subjecting the third mixture to calendaring in step (d) at a temperature in a range of 25 to 35 °C results in formation of binder fibrils.

[0068] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the binder fibril has a diameter in a range of 10 to 70 nm. In another embodiment, as provided in Figure 5C, the binder fibrils have a diameter in a range of 10 to 50 nm.

[0069] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the first portion of the binder has a compressibility index of more than 10%; and the second portion of the binder has a compressibility index of less than 10%. In another embodiment of the present disclosure, the first portion of the binder has a compressibility index in a range of 10 to 12%; and the second portion of the binder has a compressibility index in a range of 8 to 10%.

[0070] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the process further comprises multiple folding and pressing of the electrode film to obtain a thin electrode film under a shear force in a range of 100-200 MPa.

[0071] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the thin electrode film has a thickness of at least 40 micrometres. In another embodiment of the present disclosure, the thin electrode film has a thickness in a range of 40 to 100 micrometres. In yet another embodiment of the present disclosure, the thin electrode film has a thickness in a range of 60 to 100 micrometres, as depicted in Figure 9.

[0072] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the process comprises multiple folding and pressing of the third mixture under a shear force in a range of 100-200 MPa to obtain a thin electrode film having a thickness of at least 40 micrometres. In another embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the process comprises multiple folding and pressing of the third mixture under a shear force in a range of 100-200 MPa to obtain a thin electrode film having a thickness of at least 40 micrometres instead of calendaring.

[0073] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the thin electrode film is a cathode.

[0074] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film as disclosed herein, wherein the thin electrode film has a specific capacity in a range of 140 -170 mAh / g for sodium ion battery and 180 to 270 mAh / g for lithium-ion battery with metal anodes.

[0075] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: a. mixing an active material with a conducting carbon at a speed in a range of 15.31 to 30.63 m / s for a time period in a range of 5 to 60 minutes to obtain a first mixture; b. adding a firstportion of a binder having low flowability into the first mixture by mixing at a tip speed in a range of 15.31 to 30.63 m / s for 5 to 30 mins to obtain a second mixture; and c., adding a second portion of the binder having high flowability to the second mixture to obtain the third mixture at a tip speed in the range of 15.31 to 30.63 m / s for 5 to 20 mins; and d. calender the third mixture to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film; wherein the first portion of the binder having compressibility index of at least 10 and the second portion of the binder having a compressibility index of less than 10 are in a weight ratio range of 0.95: 1 to 1: 1 with respect to the total weight of the binder.

[0076] In an embodiment of the present disclosure, there is provided a process of preparation of an electrode film, said process comprising: a. mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 m / s for a time period in a range of 5 to 60 minutes to obtain a first mixture; b. adding a first portion of a binder having low flowability into the first mixture by mixing at a speed in a range of 15.31 to 30.63 m / s to obtain a second mixture; c. adding a second portion of the binder having high flowability to the second mixture to obtain the third mixture at a tip speed in the range of 15.31 to 30.63 m / sand c. subjecting the third mixture to multiple folding and pressing for applying a shear force in a range of 100-200 MPa, at a temperature in a range of 20 to 35 °C to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film; the electrode film obtained is a thin electrode film having a thickness of at least 40 micrometres; wherein the thin electrode film is a NFM cathode having a specific capacity in a range of 140 - 170 mAh / g .

[0077] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) a cathode obtained from the process as disclosed herein; b) an anode; and c) an electrolyte.

[0078] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the electrochemical cell optionally comprises a separator.

[0079] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) a cathode obtained from the process as disclosed herein; b) an anode; c) an electrolyte; and d) optionally a separator.

[0080] In an embodiment of the present disclosure, there is provided electrode film obtained by the process as claimed in claim 1, the electrode film comprising: a) 98 to 99.5% by weight of an active material; b) 0.4 to 1.9% by weight of a conducting carbon; and c) 0.1 to 0.5 % by weight of a binder.

[0081] In an embodiment of the present disclosure, there is provided electrode film obtained by the process as claimed in claim 1, the electrode film comprising: a) 98 to 99.5% by weight of an active material; b) 0.4 to 1.9% by weight of a conducting carbon; and c) 0.1 to 0.5 % by weight of a binder, wherein the binder is in the form of fibrils having diameter in a range of 10 to 50 nm.

[0082] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.EXAMPLES

[0083] The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to the particular methods, and experimental conditions described, as such methods and conditions may apply.Materials and methods

[0084] For the purpose of the present disclosure, the following raw materials were used.1. Na, Ni, Fe, Mn precursors of the active material NaNixFeyMnzO2 (NFM) cathode was procured from sigma Aldrich, (>99% purity).2. Conducting carbon: first conductive carbon (Ketjen black) from Nouryon, and second conductive carbon (KS6L) from Imerys.3. Binder: polytetrafluoroethylene (PTFE) was procured from Gujarat Fluorochemicals Limited (GFL).EXAMPLE 1Preparation of electrode film

[0085] A dry process of preparation of an electrode film for an electrochemical cell was performed as explained below. Initially, 98.3% by weight of NaNixFeyMnzO2 (NFM, x=y=z=0.33) cathode powder (active material) was dried in a hot air oven at 120°C to avoid the presence of any moisture in the system. Then 1.5% by weight of Ketjen black (KB) and KS6L (conducting carbons) in a weight ratio of 1:0.5 were mixed with the cathode active material powder at a speed of 25.52 m / s, tip speed of 25.5 m / s, and for a time duration of 50 minutes to obtain a first mixture. A first portion of 0.2 % by weight of polytetrafluoroethylene (PTFE) binder having low flowability or compressibility index of 11.71% was added to the first mixture, by blending at a speed of 200 m / s and tip speed of 20.42 m / s for 15 minutes until the temperature reaches up to 70°C to obtain a second mixture. The mixture was cooled to room temperature at a rate of 2 °C / min. In a separate system, a second portion of the binder PTFE was heated to a temperature of 80°C to attain a PTFE with compressibility index of 9.01% and a high flowability. The pre-heated second portion of polytetrafluoroethylene (PTFE) binder was added to the second mixture at a tip speed of 20.42 m / s . . . ms'1to attain a temperature of 70 °C to obtain a third mixture. The first portion of the binder PTFE and the second portion of the binder PTFE were in a weight ratio of 1: 1. The third mixture was cooled to a temperature below 19°C for obtaining homogeneous fibrillation and flexible film formation. If the cooling was not carried out, the film obtained was found to be hard and brittle. The third mixture was then subjected to calendaring at room temperature and rollerspeed of 5 to 8 cm / s to obtain an electrode film. The obtained electrode film was observed to have the thickness of about 100 pm.. The thin electrode film thus obtained had a thickness of less than 100 pm (as shown in Figure 9), and a specific capacity of 150 mAh / g.EXAMPLE 2Characterization of the electrode film

[0086] The first mixture, second mixture and the electrode film obtained fromExample 1 were subjected to various characterization analysis to assess the effect of the disclosed process on the morphological, structural, and electrochemical properties of the dry electrode film.

[0087] Techniques, such as, scanning electron microscopic (SEM) analysis, and energy-dispersive x-ray (ED AX) were performed for the analysis of structural and morphological properties of the electrode film. First Mixture

[0088] The first mixture obtained by the mixing of a combination of conductive carbon (KB and KS6L) along with the cathode powder under different m / s were assessed using SEM analysis.Table 2

[0089] The first mixture samples of the category S4-a, S4-b, S4-c, S5-a, S5-b, and S5-c prepared at a mixing speed of 18.37 m / s to 25.52 m / s for a duration of 40 minutes and 50 minutes respectively, exhibited good coating on the active material.

[0090] The uniform coating of the conductive carbon on the active material was validated from the SEM monographs obtained for the first mixtures prepared by mixing at 25.52 m / s for 50 minutes (Figure 2C), when compared to mixtures prepared by mixing at 18.37 m / s (Figure 2A), and 20.42 m / s (Figure 2B).

[0091] ED AX mapping for carbon element determined for first mixture samples prepared by mixing at 25.52 m / s (Sl= after 10 mins, S2=after 20 mins , S3=after 30 mins, S4=after 40 mins, S5=after 50 mins), suggested that better carbon coating homogeneity was obtained with large mixing time (as shown in Figure 3).

[0092] Overall, it was observed that the first mixture S5-c prepared by mixing at a tip speed of 25.52 m / s for a duration of 50 minutes resulted in uniform coating of the conductive carbon on the active material.Second and Third Mixture

[0093] Different parameters, such as weight percentage and compressibility index of binder, blending speed, and duration of step (b) were compared to determine their effect in terms of homogeneous spread across the cathode system without any aggregation and hence on the properties of the film formed after further shear mixing.

[0094] The binder was used in its powder form in these varied processes. In the step (b) of the disclosed process to prepare second mixture, less flowable binder with compressibility index higher than 10 (Figure 4A) was used, which can adhere over the surface of the cathode particles, however in the step (c) of the disclosed process to prepare the third mixture, high flowable binder (Figure 4B) was used to spread over the entire surface of the carbon coated cathode active material. Further, the flowability property of the binder expressed in terms of the CI% or the Hausner Ratio used in various samples are provided in Table 3. It was observed that when the binder was added in a single step as against the disclosed process, resulted inthick fibrils with a diameter of 100 to 300 nm after calendaring in step (d). On the other hand, when binder was added partly in two steps (step b and step c) of the process resulted in thin fibrils with a diameter of 10 to 50 nm after calendaring in step (d), which helps to increase energy density of the battery in terms of high utilization of active materials (table 3). Similarly, Figure 5 (A-D) suggests that using less than 0.2% by weight of binder resulted in thin fibrils when compared to using more than 1% by weight of binder. Figure 5 depicts the SEM images showing the effect of different weight percentage of binder in the final film to understand the degree of fibrillation in terms of thick and slender threads wherein A) 0.5% by weight of binder B) 0.1% by weight of binder C) <0.2% by weight of binder and D) > 1% by weight of binder.

[0095] Also, the process for electrode film fabrication was performed by varying the weight ratios of the binder added in step (b) and step (c). Outside the disclosed range of 0.95: 1 to 1: 1 such as 1:9 and 8:2 , both of which resulted in breaking of films while lifting as shown in Figure 8 A and 8B. However, when the binder addition was carried out in two step and in varying flowability, the film was found to be uniform, thin, and free-standing flexible film (as shown in Figure 8C). Except binder ratios, all other process parameters were same as that of Example 1. Further, because of the lower binder content, two different flow property-based binder (High and low flow ability) have exhibited enhanced effect to attain the binding capability without compromising on the mechanical strength of the film. If a single type of binder such as low flowable with CI higher than 10% or high flowable with CI less than 10% was used, the electrode film was not of desirable characteristics such as less tensile strength, high thickness, and brittle with lower binder content of <0.2wt%.

[0096] The results of Nyquist plot for electrochemical impedance characteristics corresponding to the electrode films showed that (Figure 6) the electrode film prepared with 0.2% by weight of binder exhibited minimal resistance of less than 30 ohms.

[0097] The mixing of the different characteristics of the binder affects the flowability of the electrode mixture, which can be analysed by the compressibility index and Hausner ratio as tabulated in the following table.

[0098] Table 3

[0099] * refer table 1 for flow properties.

[0100] Table 3 illustrates the compressibility index of Bl) PTFE binder below 19°C, S2) PTFE after heat treatment at 80 °C referred to as high flowable PTFE, El) carbon coated cathode active material, E2) a mixture of carbon coated cathode active material with either low flowable (B l) or high flowable (B2) binder added in single step, and E3) third mixture obtained by blending carbon coated cathode active material with low flowable (Bl) and mixing with high flowable (B2) binder in two steps, by the process as claimed in the present disclosure. The two-step addition of binders and its flow characteristics variation affects the flowability and the properties of the third mixture, or the final dry electrode film . B 1 represents thePTFE binder that has a compressibility index of 11.71% and shows low flowability as such purchased. B2 represents the high flowable PTFE prepared by heating B 1 PTFE at 80°C for 3 h in vacuum. The high flowable PTFE has a compressibility index of 9.01%. El represents the carbon coated cathode active material which has a compressibility index of 19% obtained by mixing the active material NFM with conductive carbon KB and KS6L at 25.52 m / s for 50 minutes. The higher the compressibility index, lower the flowability. E2 represents the mixture comprising carbon coated cathode material and either one of low flowable or high flowable PTFE added in a single step. The compressibility index for the E2 mixture was 15.93% which was more flowable than carbon coated cathode active material El. E3 represents an electrode film mixture comprising carbon coated cathode material and low flowable PTFE and high flowable PTFE added in two steps showed a compressibility index of 9.47%, which was more flowable than each of El and E2. The E2 mixture, which was formed by the single step addition of PTFE with a single flow character PTFE such as either low flowable or high flowable, resulted the mixture having low flowability. This provides a poor dry electrode film with less tensile strength and high thickness. The E3 third mixture, which was formed by the two-step addition of low flowable and high flowable PTFE provided a third mixture having high flowability resulting in an electrode film with desirable thickness, thin binder fibrillation and enhanced electrochemical performance.Electrode film

[0101] An electrode film was obtained by calendaring the third mixture at a roller speed of 1 to 12 cm / s and at room temperature, obtained by the process as disclosed herein. The mechanical property of the electrode film fabricated using the disclosed process was assessed by evaluating its Young’s modulus. Figure 7 (A) shows that the electrode film prepared with 1.5% binder exhibited break point at above a load of 0.2 MPa, while the reduction in the amount of PTFE up to 0.2% provided an electrode film having tensile strength of 0.15 MPa, as shown in Figure 7(B), which is comparable with the electrode film having higher amount of PTFE. The electrode film prepared by the process as disclosed in the present disclosure which employedminimum amount of PTFE and still showed high mechanical stability, could be used for making electrodes which can be sustainable during winding process.

[0102] The results of voltage vs specific capacity plots for NFM cathode comprising low flowable PTFE binder and high flowable PTFE binder in the weight ratio of 1: 1 in two step addition at various binder content such as A) 1.5F, B) IF, C) -0.5F, and D) -0.2F showed that electrodes have proper ion migration and delivering desired capacity even with reduced PTFE content and high active material mass loading (Figure 10). This mainly attributed to the better and enhanced fibrillization even after reducing the binder content to a much significant value. The electrode film retained its specific capacity in the range of 140 - 170 mAh / g, depending on the mass loading. Due to the reduced binder content, higher mass loading was achieved. The higher the mass loading, higher the energy density.

[0103] Overall, it was observed that the second mixture prepared after mixing the first mixture with a portion of the binder of low flowability and the addition of binder with high flowability followed by calendaring resulted in thin fibrillation of the binder. The electrode film and the corresponding thin electrode film fabricated with the above said binder characteristics exhibited improved performance.

[0104] Collectively, a process for dry electrode film when carried out with the disclosed parameters resulted in an electrode film with superior performance. Any deviation from the disclosed weight ranges of the ingredients or process parameters ranges did not result in the desired performance of the electrode film.EXAMPLE 3Preparation of an electrochemical cell

[0105] The electrode film of Example 1 was arranged adjacent to an electrolyte NaPFe dissolved in a solvent mixture of EC-DEC-DMC and a sodium-based anode was arranged on the other end of the electrolyte. The electrodes, both cathode and anode were individually placed adjacent to the electrolyte using a Whatman filter paper as a separator in between them.

[0106] The electrochemical cells obtained were analyzed for their electrochemical performance, stability, and capacity. The prepared electrochemical cell exhibited a capacity of at least 150 mAh / g, as shown in Figure 10.ADVANTAGES OF THE PRESENT INVENTION

[0107] The present disclosure provides a process of preparation of an electrode film, which exhibits the following advantages.(a) With reduction of the binder content (0.1%), very high (99.5%) active material loading of the film was achieved.(b) The properties of carbon coverage over the electrode material and the addition of the binder into different stages of the disclosed process results in a thin, flexible, robust, and high performing electrode film.(c) The homogeneous carbon coverage confers the proper electronic networking for the charge kinetics and also supports the mutual adhesion between the particles after addition of the binder.(d) The homogeneous carbon coverage further helps to fibrillate the binder in thinner treads with a diameter of 10 to 50 nm, which further increases the energy density of the battery in terms of high utilization of active materials.(e) The electrode film prepared with 0.2% PTFE provide the tensile strength of 0.15 MPa, which is comparable with the higher amount of PTFE, showing high mechanical stability even by using low PTFE content. The disclosed process is a solvent free process, which does not require high energy mixture and or high temperature fibrillation technique, herein fibrillation is achieved at room temperature i.e., 20-35 °C.(f) The two-step addition of low flowable and high flowable with 1 : 1 ratio leads the formation of thin and robust free-standing film with enhanced electrochemical performance. g. The capacity is maintained with reduced binder content. Due to the lower binder content (up to 0.2 wt.%) of PTFE, the active material mass loading is high (up to 99.5%) and provides the improvement in energy density.

Claims

I / We Claim:

1. A process of preparation of an electrode film, said process comprising: a. mixing an active material with a conducting carbon to obtain a first mixture; b. blending a first portion of a binder having compressibility index of at least 10 % with the first mixture to obtain a second mixture; c. mixing a second portion of the binder having compressibility index less than 10% with the second mixture to obtain a third mixture; and d. subjecting the third mixture to calendaring to obtain the electrode film; wherein the binder is in a weight range of 0.1 to 0.5 % with respect to the total weight of the electrode film.

2. The process as claimed in claim 1 , wherein the active material is selected from nickel-iron-manganese (NFM) based compounds, sodium- vanadium-fluorophosphate (NVPF) based compounds, Prussian-blue based cathode materials, Prussian white based cathode materials, nickel- manganese-cobalt oxide (NMC) based compounds, lithium-nickel- cobalt-aluminium oxides (NCA), lithium-cobalt oxide (LCO) based compounds, lithium iron phosphate (LFP) based compounds, or lithiummanganese-rich (LMR) based compounds.

3. The process as claimed in claim 1, wherein the active material is in a weight range of 98 to 99.5%, with respect to the total weight of the electrode film.

4. The process as claimed in claim 1, wherein the conducting carbon is selected from ketjen black (KB), graphite, KS6L, super P, graphitic nanofiber, carbon nanofiber, carbon nanotubes, or combinations thereof.

5. The process as claimed in claim 1, wherein the conducting carbon is in a weight range of 0.4 to 1.9 %, with respect to the total weight of the electrode film.

6. The process as claimed in claim 1, wherein the mixing in step (a) is carried out at a tip speed in a range of23 to 27 m / s , and for a time period in a range of 35 to 60 minutes.

7. The process as claimed in claim 1, wherein the blending in step (b) is carried out at a tip speed in a range of 18 to 22 m / s , for a time period in a range of 5 to 60 minutes to attain a temperature in a range of 60 to 75 °C.

8. The process as claimed in claim 1, wherein the blending in step (b) is followed by cooling at a rate in a range of 2 to 5 °C / min, for a time period in a range of 5 to 40 minutes.

9. The process as claimed in claim 1, wherein the mixing in step (c) is carried out at a tip speed in a range of 18 to 22 m / s to attain a temperature in a range of 60 to 75 °C.

10. The process as claimed in claim 1, wherein the mixing in step (c) is followed by cooling at a rate in a range of 2 to 5 °C / min for a time period in a range of 5 to 40 minutes.

11. The process as claimed in claim 1, wherein subjecting the third mixture to calendering results in formation of binder fibrils.

12. The process as claimed in claim 1, wherein subjecting the third mixture to calendaring is carried out at a temperature in the range of 25 to 35°C and at a roller speed in a range of 1 to 12 cm / s.

13. The process as claimed in claim 1, wherein the first portion of the binder and the second portion of the binder are in a weight ratio range of 0.95: 1 to 1 : 1 with respect to the total weight of the electrode film.

14. The process as claimed in claim 1, wherein the binder is selected from polytetrafluoroethylene (PTFE), polyamide, fluoroethylene vinyl ether (FEVE), polyethylene (PE), polyethylene oxide (PEO), or combinations thereof.

15. The process as claimed in claim 1, wherein the electrode film has a thickness in a range of 40 to 100 pm.

16. The process as claimed in claim 1, wherein the electrode film is a cathode.

17. The process as claimed in claims 1, wherein the electrode film has a specific capacity in a range of 140 - 270 mAh / g for lithium-ion battery.

18. An electrochemical cell comprising: a. a cathode comprising the electrode film obtained from the process as claimed in claims 1 to 18; b. an anode; and c. an electrolyte.

19. The electrochemical cell as claimed in claim 19, wherein the electrochemical cell optionally comprises a separator.

20. An electrode film obtained by the process as claimed in claim 1, the electrode film comprising: a. 98 to 99.5% by weight of an active material; b. 0.4 to 1.9% by weight of a conducting carbon; and c. 0.1 to 0.5 % by weight of a binder.

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