DESC:FIELD OF INVENTION
[0001] The present disclosure broadly relates to the field of batteries. Particularly, the present disclosure relates to a dry manufactured composite cathode material, more particularly to a dry process of preparing a composite electrode material, and that of a free-standing electrode film.
BACKGROUND OF THE INVENTION
[0002] Ni-rich layered oxide (NMC) cathode materials with Ni content =60 mol% have been considered as promising cathodes of LIBs due to their high capacity, improved kinetics, and high stability at high operating voltage. Compared to the traditional wet coating process for making NMC electrode, there is high focus on an alternative dry electrode technology which involves mixing of active material and a binder, and then carrying out hot rolling to form an electrode film. Therefore, solvent addition and drying recovery process is not essential in the preparation process. The preparation is greatly simplified in a dry process and the battery manufacturing cost can be greatly reduced with absence of harmful solvents in the whole process.
[0003] Additionally, the problem of environmental pollution caused in the battery manufacturing process is also solved by avoiding solvent usage. However, there are challenges in preparing layered Ni-rich cathode electrodes by dry electrode processing. One of the major challenge is that the NMC material, the conductive carbon and the binder are difficult to be homogeneously mixed. The material has relatively higher hardness, resulting in the wear and tear of mixer blades. Moreover, the hardness makes it difficult to press the powder into a soft self-supporting film in the calendering rollers. Calendaring also results in cracks and dents on the rollers and cannot be laminated with a current collector. In addition, NMC materials suffer from poor conductivity.
[0004] Therefore there is a dire need in the state of art to develop a process to prepare an electrode material to address the processability issues such as internal friction, and also to provide improved conductivity.

BRIEF DESCRIPTION OF THE FIGURES
[0005] 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.
[0006] Figure 1 depicts SEM (scanning electron microscopic) images of the (a) pristine NMC material without graphene coating; (b) composite electrode material with uniform coating; and (c) composite electrode material top view with dense graphene coating, in accordance with various embodiments of the present disclosure.
[0007] Figure 2 depicts the SEM images of the (a) cross-sectional view, (b) top- view, and (c) surface morphology, of the free-standing electrode film, in accordance with one of the embodiment of the present disclosure.
[0008] Figure 3 depicts the specific charge-discharge plot of the cathode composite, in accordance with one of the embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0009] 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
[0010] 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.
[0011] 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.

[0012] 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”.
[0013] 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.
[0014] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.
[0015] The term "at least one" is used to mean one or more and thus includes individual components as well as mixtures/combinations.
[0016] 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.
[0017] 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 include but not limited to graphene, super P, ketjen black, graphite, and so on. The graphene could be selected from bilayered and multi- layered graphene having tap density in a range of 0.01-0.009 g/cc.
[0018] The term “fibrillating binder” refers to a type of the binder constituent of an electrode, which has the property to form small fibrils under the application of shear force. The fibrillating 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 fibrillating binder in the present disclosure includes but not limited to fluorinated ethylene propylene (FEP), polytetrafluoroethylene, polymers of FEP, polyethylene oxide (PEO), polyvinylidene difluoride (PVDF), or combinations thereof.

[0019] The term “free-standing electrode film” refers to the electrode film which is capable of being employed as an electrode in an electrochemical cell. In an aspect of the present disclosure, the free-standing electrode film obtained by the calendaring the composite electrode material as disclosed herein, having a thickness in a range of 100 to 200µm. The free-standing electrode film as disclosed in the present disclosure, may be coated over a current collector to be used as a cathode. The free-standing electrode film as disclosed in the present disclosure, may be combined with a separator to be used as a cathode.
[0020] The term “voltage window’ refers to the electrode potential range of a material between which the material does not undergo oxidation or reduction. 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 1% to 2% (w/w) should be interpreted to include not only the explicitly recited limits of 1% to 2% (w/w) but also to include sub-ranges, such as 1.1% to 2% (w/w), 1.5% to 2% (w/w) and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 1.8% (w/w), 1.5% (w/w), and 1.3% (w/w).
[0021] 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.
[0022] As discussed in the background, there are challenges in dry processing of cathode materials such as wear, and tear caused by the hard NMC materials over the rollers and machinery during processing. Also, calendaring of these materials to form films do not produce uniform and crack-free films out of the powdered samples. Hence in order to reduce the friction caused by the solid active materials, and to obtain a homogeneous mixture, it is essential to smoothen the surface of NMC by uniform and dense coating with lubricating or softening agents. Such dense coating over the NMC material with carbon-based materials such as graphene can also serve as a conductive additive to reduce the charge transfer and internal resistances. As per the cohesive force studies, there is a high affinity for a fibrillating binder to agglomerate, fibrillate and anchor on to the conductive carbon particles during the high shearing process. A dense carbon coating on the NMC surface facilitates a better anchoring of the binder particles during the addition of the fibrillating binder. In addition to that, NMC cathodes inherently suffer from poor conductivity. Therefore, carbon layers such as amorphous carbon, graphene, graphene oxide and carbon black can enhance the electronic conductivity and prevent any side reaction, resulting in a good physical/chemical barrier against electrolyte for NMC cathodes.
[0023] In light of the above, a conductive carbon such as graphene, super p, ketjen black, graphite, act as a lubricating agent and provide dense carbon coating on the NMC surface. In specific, graphene, in comparison to carbon blacks, which are spherical nanoparticles form plane-to-plane contact with NMC, instead of point-to- point contact. The hydrophobicity of graphene can also reduce the moisture sensitivity of the NMC cathode surface. Also, by applying a graphene coating on the surface of NMC primary particles, significant enhancements in the high-voltage cycle life and Coulombic efficiency upon electrochemical cycling can be achieved.
[0024] Accordingly, in the present disclosure, there is provided a dry manufactured composite cathode electrode material for an electrochemical cell, wherein the composite electrode material has a uniform, dense coating of conductive carbon over the active material.
[0025]
[0026] Accordingly, in the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, wherein the composite electrode material has a uniform, dense coating of conductive carbon over the active material.
[0027] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon to obtain a first mixture; b) adding a fibrillating binder to the first mixture to obtain a second mixture; and c) high shear mixing of the second mixture followed by cooling to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.
[0028] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein mixing an active material with conducting carbon is carried out at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes. In another embodiment of the present disclosure, wherein mixing an active material with conducting carbon is carried out at a speed in a range of 2000 to 3000 rpm and for a time period in a range of 30 to 120 minutes at a temperature less than 30?.
[0029] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein adding a fibrillating binder to the first mixture is carried out under stirring speed in a range of 1000 to 2000 rpm for a time period in a range of 10 to 30 minutes. In another embodiment of the present disclosure, wherein adding a fibrillating binder to the first mixture is carried out under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 15 to 30 minutes at a temperature less than 30?.
[0030] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein high shear mixing the second mixture is carried out at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes. In another embodiment of the present disclosure, wherein high shear mixing the second mixture is carried out at a speed in a range of 2000 to 3000 rpm for a time period in a range of 5 to 15 minutes. In another embodiment of the present disclosure, high shear mixing the second mixture is carried out at a speed of 3000 rpm to attain a temperature of 70°C.
[0031] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein high shear mixing the second mixture is carried out to attain a temperature in a range of 30 to 90°C. In another embodiment of the present disclosure, wherein high shear mixing the second mixture is carried out to attain a temperature in a range of 60 to 80°C.
[0032] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein cooling the second mixture is carried out while stirring at a speed in a range of 300 to 700 rpm for a time period in a range of 5 to 20 minutes. In another embodiment of the present disclosure, wherein cooling the second mixture is carried out while stirring at a speed in a range of 500 to 700 rpm for a time period in a range of 5 to 20 minutes.
[0033] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein cooling the second mixture is carried out at a temperature in a range of 15 to 25°C. In another embodiment of the present disclosure, cooling the second mixture is carried out to attain a temperature of 15 to 20°C.
[0034] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein cooling the second mixture is carried out using a chiller with the temperature set in the range of 0 to 7°C. In another embodiment of the present disclosure, the chiller is set at a temperature of 5°C. In another embodiment of the present disclosure, wherein cooling the second mixture is carried out using a chiller with the temperature set in the range of 0 to 7°C to attain a temperature of 15 to 20°C.
[0035] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture to obtain a second mixture; and c) high shear mixing of the second mixture followed by cooling to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.

[0036] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 10 to 30 minutes to obtain a second mixture; and c) high shear mixing of the second mixture followed by cooling to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.
[0037] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 10 to 30 minutes to obtain a second mixture; and c) high shear mixing of the second mixture at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes, followed by cooling to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.
[0038] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 10 to 30 minutes to obtain a second mixture; and c) high shear mixing of the second mixture at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes, to attain a temperature in a range of 60 to 80°C, followed by cooling to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.

[0039] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 10 to 30 minutes to obtain a second mixture; and c) high shear mixing of the second mixture at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes, to attain a temperature in a range of 60 to 80°C, followed by cooling at a temperature in a range of 15 to 25°C under stirring at a speed in a range of 300 to 700 rpm for a time period of 5 to 20 minutes, to obtain the composite electrode material, wherein the conducting carbon forms a uniform coating over the active material.
[0040] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the composite electrode material is calendered to obtain a free standing electrode film. In another embodiment of the present disclosure, wherein the free standing electrode film has the fibrillating binder anchored on the conducting carbon coated on the active material. In one another embodiment of the present disclosure, the free standing film has PTFE anchored on the graphene coated with the active material.
[0041] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the composite electrode material is calendered at a temperature in a range of 80 to 150°C to obtain a free standing electrode film. In another embodiment of the present disclosure, wherein the composite is calendered at a roll speed in a range of 0.34 to 3 meter/min. In one another embodiment of the present disclosure, the composite is calendered at a shear force in the range of 1 to 250%.
[0042] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the composite electrode material is calendered at a temperature in a range of 80 to 150°C, at a roll speed in a range of 0.34 to 3 meter/min, at a shear force in a range of 1 to 250% to obtain a free standing electrode film.
[0043] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material film for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon to obtain a first mixture; b) adding a fibrillating binder to the first mixture to obtain a second mixture; c) high shear mixing of the second mixture followed by cooling to obtain the composite electrode material; and d) calendering the composite electrode material to a free standing electrode film, wherein the conducting carbon forms a uniform coating over the active material.
[0044] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon to obtain a first mixture; b) adding a fibrillating binder to the first mixture to obtain a second mixture; c) high shear mixing of the second mixture followed by cooling to obtain the composite electrode material; and d) calendering the composite electrode material at a temperature in a range of 80 to 150°C, at a roll speed in a range of 0.34 to 3 meter/min, at a shear force in the range of 1 to 250%, to obtain a free standing electrode film, wherein the conducting carbon forms a uniform coating over the active material.
[0045] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell, said process comprising: a) mixing an active material with a conducting carbon at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes to obtain a first mixture; b) adding a fibrillating binder to the first mixture under stirring speed in a range of 1200 to 1500 rpm for a time period in a range of 10 to 30 minutes to obtain a second mixture; and c) high shear mixing of the second mixture at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes, to attain a temperature in a range of 60 to 80°C, followed by cooling at a temperature in a range of 15 to 25°C under stirring at a speed in a range of 300 to 700 rpm for a time period of 5 to 20 minutes, to obtain the composite electrode material; and d) calendering the composite electrode material at a temperature in a range of 80 to 150°C, at a roll speed in a range of 0.34 to 3 meter/min, at a shear force in the range of 1 to 250%, to obtain a free standing electrode film, wherein the conducting carbon forms a uniform coating over the active material; and the free standing electrode film has the fibrillating binder anchored on the conducting carbon coated on the active material.
[0046] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the composite electrode material has a particle size in a range of 8 to 12 µm.
[0047] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the free standing film is a cathode film.
[0048] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the active material is selected from oxides of lithium, nickel, manganese, cobalt, or combinations thereof. In another embodiment, the active material is selected from lithium-nickel-manganese cobalt oxides. In another embodiment of the present disclosure, wherein the lithium-nickel-manganese cobalt oxides comprises of 70-85% by weight of nickel, 5-15% by weight of manganese, 5-10% by weight of cobalt, or combinations thereof. In yet another embodiment of the present disclosure, the active material is preferably comprising 80% by weight of nickel, 10% by weight of manganese, and 10% by weight of cobalt. In still another embodiment, the active material is NMC composite material having Nickel content above 92% of the total weight of the composite. In one another embodiment of the present disclosure, the lithium-nickel-manganese cobalt oxide is LiNi0.8Mn0.1Co0.1O2.
[0049] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the active material is in a weight range of 96 to 98.5%, with respect to total weight of the composite. In another embodiment of the present disclosure, wherein the active material is in a weight range of 97 to 98.5%, with respect to total weight of the composite.
[0050] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the conducting carbon is selected from graphene, super P, ketjen black, graphite, or combinations thereof. In another embodiment of the present disclosure, wherein the conducting carbon is selected from bi- layered or multilayered sheets of graphene with a tap density of 0.01-0.009 g/cc, optionally in combination with one or more of super P, ketjen black, and graphite. In one another embodiment of the present disclosure, the conducting carbon is graphene or super P or ketjen black or graphite, or a combination.
[0051] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the conducting carbon is in a weight range of 0.1 to 1.5%, with respect to total weight of the composite. In another embodiment of the present disclosure, the conducting carbon is in a weight range of 0.1 to 0.5%, with respect to total weight of the composite.
[0052] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the conducting carbon forms a uniform coating having a thickness in a range of 10 to 1000 nm over the active material. In one another embodiment of the present disclosure, wherein the conducting carbon coats greater than or equal to about 50% of the exposed surface of the active material.
[0053] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the binder is selected from poly tetrafluoro ethylene (PTFE), fluorinated ethylene propylene (FEP), polyethylene oxide (PEO), polyvinylidene difluoride (PVDF), or combinations thereof. In another embodiment of the present disclosure, the fibrillating binder is poly tetrafluoro ethylene (PTFE).
[0054] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the fibrillating binder is in a weight range of 1 to 2%, with respect to total weight of the composite. In another embodiment of the present disclosure, the fibrillating binder is in a weight range of 1 to 1.5%, with respect to total weight of the composite.
[0055] In an embodiment of the present disclosure, there is provided a dry process of preparation of a composite electrode material for an electrochemical cell as disclosed herein, wherein the free standing film is a cathode film. In another embodiment of the present disclosure, wherein the free standing film has a thickness in the range of 100 to 200µm. In one another embodiment of the present disclosure, the free standing film has a moisture sensitivity in a range of 50 to 100 ppm with respect to the film thickness in a range of 100 to 200µm.
[0056] In an embodiment of the present disclosure, there is provided a cathode comprising the composite electrode material obtained by the process as disclosed herein, coated over a current collector. In another embodiment of the present disclosure, the current collector is an aluminum foil of thickness in the range of 10- 14 µm with a 1-2 µm of carbon pre-coating.
[0057] In an embodiment of the present disclosure, there is provided a cathode comprising the free standing film obtained by the process as disclosed herein, coated over a current collector.
[0058] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) an anode; b) cathode comprising a composite electrode material obtained by the process as disclosed herein; c) an electrolyte; and d) a separator.
[0059] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) an anode; b) a cathode comprising a free standing film obtained by the process as disclosed herein; and c) an electrolyte.
[0060] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) an anode; b) cathode comprising a composite electrode material obtained by the process as disclosed herein, coated over a current collector; c) an electrolyte; and d) a separator.
[0061] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: a) an anode; b) a cathode comprising a free standing film obtained by the process as disclosed herein coated over a current collector; and c) an electrolyte.
[0062] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the anode is selected from Li metal, graphite, silicon, graphite-silicon composites, lithium titanate or combinations thereof; the electrolyte is Lithium hexafluorophosphate dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) or combinations thereof; and the separator is a cellulose or a Whatman filter paper separator.
[0063] In an embodiment of the present disclosure, there is provided an electrochemical cell as disclosed herein, wherein the electrochemical cell has a voltage window of 2.5 – 4.3V, and a columbic efficiency in the range of 90- 99%. In another embodiment, the electrochemical cell has an initial columbic efficiency in the range of 90 to 98%. In yet another embodiment, the electrochemical cell has a columbic efficiency in the range of 98 to 99% in the subsequent cycles.
[0064] 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 particular methods, and experimental conditions described, as such methods and conditions may apply.

Materials and methods
[0065] For the purpose of the present disclosure, the following raw materials were used. LiNi0.8Mn0.1Co0.1O2, conducting carbons such as multilayered graphene, Super P, KS6L graphite, Ketjen black and polytetrafluoroethylene.

EXAMPLE 1
Preparation of composite
[0066] A dry process of preparation of a composite electrode material for an electrochemical cell was carried as explained below. 97% by weight of NMC 811 (LiNi0.8Mn0.1Co0.1O2) (active material) was mixed with 1.5% by weight of graphene (conducting carbon), at a speed in a range of 1500 to 3000 rpm and for a time period of 30 to 120 minutes in a Zeppelin mixer to obtain a first mixture. To the first mixture, 0.75% by weight of polytetrafluoroethylene (PTFE) and 0.75 % by weight of polyvinylidene fluoride (PVDF) was added while stirring at a speed of 1200 to 1500rpm for 10 to 15 minutes to obtain a second mixture. Throughout the PTFE addition step, it was ensured that temperature does not exceed 30°C. The second mixture was then subjected to high shear mixing at a speed of 3000rpm for about 2 hours until a temperature of 70°C was achieved. The high shear mixed mixture was then rapidly cooled using a chiller which was set to a temperature of 5°C, until the temperature of the mixture was 19°C, to obtain the composite electrode material. The composite electrode material hence obtained has uniform and dense coating of graphene over the active material. The composite electrode material thus obtained by the process explained above, was then subjected to calendering at a temperature of 80 to 150°C. The rollers were distanced between each other in the range of 40 to 250 µm and the gap increment was set in the range of 20 to 150%. The composite material was calendered at a rolling speed of 0.34 to 3 meter/min and a shearing force of up to 250% to obtain a free-standing electrode film with PTFE anchoring on the graphene coated particles. The free-standing PTFE electrode film has a thickness in the range of 100 to 200µm.
EXAMPLE 2
Scanning electron microscopic (SEM) analysis

[0067] Scanning electron microscopic (SEM) analysis of the composite electrode material and free-standing electrode film was performed to analyze the density and uniformity of graphene coating over the active material along with the particle size and thickness of the material obtained. Figure 1(a) depict the active material NMC 811 without graphene coating.
[0068] The composite electrode material obtained by the process as explained in the Example 1 was found to have a dense and uniform coating of graphene over the active material NMC 811, as shown in Figures 1 (b) and 1(c). The particle size of the composite electrode material was found to be in a range of 8 to 12 µm
[0069] The free-standing electrode film obtained by the process as explained in Example 1, was found to possess a thickness of 111.8µm, as shown in Figure 2 (a). SEM images (Figures 2b and c) of the free-standing electrode film confirmed the fibrillation of PTFE binder after calendaring. The surface morphology of the free- standing electrode film is shown in Figure 2 (c). Therefore, it is evident that the process of present disclosure resulted in a composite electrode material with an uniformly graphene coated active material. The process also enabled incorporation of the fibrillating binder with the formation of fibrils which held the coated active material together and rendered electrode stability.
EXAMPLE 3
Preparation of an electrochemical cell
[0070] The composite electrode material of Example 1 was arranged adjacent to an electrolyte 1M Lithium hexafluorophosphate (LiPF6) dissolved in a solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) or combinations thereof and a lithium-based anode was arranged on the other end of the electrolyte. The electrodes, both cathode and anode was individually placed adjacent to the electrolyte using a Whatman filter paper as a separator in between them.
[0071] In a similar manner, an electrochemical cell was prepared with the free- standing cathode film obtained by the process as explained in example 1 as cathode, 1M LiPF6 dissolved in EC/EMC/DMC as electrolyte and Li metal as anode.

[0072] The electrochemical cells obtained were analyzed for their electrochemical performance, and capacity.
[0073] Fig 3 depicts the Specific charge-discharge cycle data of the graphene coated NMC811 cathode. The electrode showed a discharge capacity of 212 mAh/g with the ICE of 92.31%. These result supplement the fact that the dense coating of graphene over the NMC improves the conductivity thereby enhancing the ICE and discharge capacities of the Li-ion cell.
ADVANTAGES OF THE PRESENT INVENTION
[0074] The present disclosure provides a dry process of preparation of a composite electrode material with uniform graphene coating on the surface of the active material. The dry process disclosed herein provides uniform coating of graphene in a thickness in the range of 10 to 1000 nm after 2 hours of high shear mixing at 3000 rpm. After high shear mixing, fibrils of PTFE are formed which are seen to hold polycrystalline and single crystals of NMC. The dry process provides a step of calendering by which strong and flexible free-standing film is obtained. The rollers of the calendering machine is not affected due to uniform graphene coating over NMC in the composite electrode material. A dense graphene coating on the NMC surface facilitates a better anchoring of the PTFE particles on the NMC surface during PTFE mixing rather than the formation of PTFE agglomerates. The dense coating of graphene on the NMC particles is intact and the PTFE fibrils are connecting the particles together in the free-standing film.

,CLAIMS:I/We Claim:
1. A dry manufactured cathode for use in secondary battery, the cathode comprising
a) 96 to 97.5 % cathode active material
b) 0.1 to 1.5% of conductive carbon and
c) 0.5 to 2.4% of fibrillating binder
wherein, the conductive carbon is coated over 70 to 100 % of the exposed surface of the active material and has a coating thickness of around 10 to 1000 nm over the surface of the active material.
2. The dry manufactured cathode as claimed in claim 1, wherein the active material is selected from oxides of lithium, nickel, manganese, cobalt, or combinations thereof.
3. The dry manufactured cathode as claimed in claim 1, wherein the conducting carbon is selected from graphene, super p, ketjen black, graphite, or combinations thereof.
4. The dry manufactured cathode as claimed in claim 1, wherein the fibrillating binder is selected from poly tetrafluoro ethylene (PTFE), fluorinated ethylene propylene (FEP) polyethylene oxide (PEO), polyvinylidene difluoride (PVDF), or combinations thereof.
5. The dry manufactured cathode as claimed in claim 1, wherein the coated cathode active material has a particle size in a range of 8 to 12 microns.
6. A dry process of preparation of a composite electrode material as claimed in claim 1 for an electrochemical cell, said process comprising:
a) mixing an active material with a conducting carbon to obtain a first mixture at a speed in a range of 1500 to 3000 rpm and for a time period in a range of 30 to 120 minutes;
b) adding a fibrillating binder to the first mixture to obtain a second mixture under stirring speed in a range of 1000 to 2000 rpm for a time period in a range of 10 to 30 minutes; and
c) high shear mixing of the second mixture at a speed in a range of 2000 to 3500 rpm for a time period in a range of 5 to 15 minutes followed by cooling to obtain the composite electrode material,
wherein the conducting carbon forms a uniform coating over the active material.
7. The process as claimed in claim 6, wherein high shear mixing the second mixture is carried out to attain a temperature in a range of 60 to 80°C.
8. The process as claimed in claim 6, wherein cooling the second mixture is carried out at a temperature in a range of 15 to 25°C at a speed in a range of 300 to 700 rpm for a time period in a range of 5 to 20 minutes.
9. The process as claimed in claim 6, wherein composite electrode material is calendared at a shear force in the range of 1 to 250% to obtain a free standing electrode film.
10. The process as claimed in claim 9, wherein the free standing film has a thickness in the range of 100 to 200µm