A dry cathode composite and preparation thereof

Abstract

The present disclosure provides a dry cathode composite comprising: 95.6 to 97% by weight of an active material; 1.2 to 1.5% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.35 to 0.5% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.8 to 1.2% by weight of a fibrillating binder; and 0.7 to 1.2% by weight of an adhesive binder selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide, vinylidene fluoride, polyacrylic acid (PAA), high molecular weight polyethylene (HMWPE), polyvinylidene fluoride-vinylidene difluoride copolymers (PVDF-VF2), or combinations thereof. The present disclosure also provides a process for preparation of the dry cathode composite and a cathode comprising the dry cathode composite as disclosed herein.

Description

A DRY CATHODE COMPOSITE AND PREPARATION THEREOFFIELD OF INVENTION

[0001] The present disclosure broadly relates to the field of battery. Particularly, the present disclosure relates to a dry cathode composite and its preparation.BACKGROUND OF THE INVENTION

[0002] Lithium-ion batteries (LIBs) are the most suitable energy storage device for powering electric vehicles (EVs) owing to their high energy efficiency, lack of memory effect, long cycle life, high energy density and high-power density. These advantages allow them to be smaller and lighter than other conventional rechargeable batteries such as lead-acid batteries, nickel-cadmium batteries (Ni- Cd) and nickel-metal hydride batteries (Ni-MH).

[0003] As a classic feature, Li-ion battery (LIBs) ages with time, losing its capacity to store charge and deliver it efficiently. The life expectancy of LIBs for electrically powered vehicles is closely linked to the adhesion strength between the electrode coating and the substrate. One of the most common modes of battery failure is caused by cracking and / or delamination of the electrode coating material from the current collector. This cracking or delaminating is typically caused by the constant charging and discharging of the battery as well as mechanical loading of the battery in use. It is critical for the active materials to possess better adhesion strength and thereby longevity to ensure that a battery does not fail before the end of its predicted life cycle. Adhesion strength of electrodes are conventionally measured using peel strength test.

[0004] A lithium-ion battery electrode is a composite of active material, polymeric binder, and conductive carbon additive(s), the proportion of which is crucial in determining the overall battery performance. It has been observed that the peel strength increases as the content of the binder increases. However, an increase in the proportion of the binder can significantly affect the electronic as well as ionic conductivity of the electrode, whereas an increased proportion of conductive carboncan reduce the adhesive strength of the electrode; thus, can be detrimental to the longevity of the battery.

[0005] Tuning the percentage of conductive carbon and binder on cathode active material (CAM) surface could result in high conductivity of dry electrode along with high peel strength and tensile strength of free-standing film, ensuing a better electrochemical performance and improved life cycle efficiency.

[0006] Thus, there is a dire need in the art to develop an improved cathode composition with high conductivity and yet maintaining peel strength.SUMMARY OF THE INVENTION

[0007] In an aspect of the present disclosure, there is provided a dry cathode composite comprising: 95.6 to 97% by weight of an active material; 1.2 to 1.5% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.35 to 0.5% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.8 to 1.2% by weight of a fibrillating binder; and 0.7 to 1.2% by weight of an adhesive binder selected from poly vinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide, vinylidene fluoride, poly aery lie acid (PAA), high molecular weight polyethylene (HMWPE), polyvinylidene fluoride-vinylidene difluoride copolymers (PVDF-VF2), or combinations thereof.

[0008] In another aspect of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, said process comprising the steps of: i) mixing an active material, a first conductive carbon, and a second conductive carbon to obtain a first mixture; ii) blending the first mixture with an adhesive binder and a fibrillating binder followed by high shear mixing at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 60 to 80 °C to obtain a second mixture; and iii) cooling the second mixture to a temperature in a range of 10 to 19 °C to obtain the dry cathode composite.

[0009] In yet another aspect of the present disclosure, there is provided a cathode comprising the dry cathode composite as disclosed herein, coated on a current collector.

[0010] In still another aspect of the present disclosure, there is provided a lithium- ion battery comprising: (a) a cathode comprising the dry cathode composite as disclosed herein; (b) an anode; and (c) an electrolyte.

[0011] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. 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 claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE FIGURES

[0012] 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.

[0013] Figure 1 depicts the scanning electron microscopic (SEM) images of (i) first mixtures, (ii) cathode surface and (iii) cathode cross-section, for (A) Cathode- 1 (baseline), (B) Cathode-2 and (C) Cathode-3, in accordance with an embodiment of the present disclosure.

[0014] Figure 2 depicts the charge / discharge capacity of Cathode- 1 (baseline), Cathode-2 and Cathode-3, in accordance with an embodiment of the present disclosure.

[0015] Figure 3 depicts the life cycle performance of Cathode- 1 (baseline), Cathode-2 and Cathode-3, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0016] 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

[0017] 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.

[0018] 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.

[0019] 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”.

[0020] 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 elements or steps but not the exclusion of any other element or step or group of elements or steps.

[0021] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0022] The term “w / w” means the percentage by weight, relative to the weight of the composition or composite, unless otherwise specified.

[0023] The term “current collector” refers to the electric bridging component, which collects electrical current generated at the electrodes of electrochemical cell and connect with external circuits. For the purpose of the present disclosure, the current collector for a cathode include but not limited to aluminium foil, glossy aluminium foils, carbon or polymer pre-coated aluminium foil or combinations thereof. For the purpose of the present disclosure, the current collector for an anodeinclude but not limited to copper foil, polymer pre-coated copper foil or combinations thereof.

[0024] The term “binder” refers to the polymeric substance that provides adhesion and mechanical integrity to some extent, to the active material when loaded on a current collector to obtain an electrode. The term “fibrillating binder” refers to the polymeric substance that forms a fibril matrix or network that adheres the active material particles and conductive carbon particles. The term “adhesive binder” refers to the polymeric substance that provides adhesion between the electrode composite and the current collector upon which it is coated. For the purpose of the present disclosure, fibrillating binder includes but not limited to polytetrafluoroethylene (PTFE), fluoroethylene vinyl ether (FEVE), or combinations thereof; and adhesive binder includes but not limited to poly vinylidene fluoride (PVDF), poly vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide, vinylidene fluoride, polyacrylic acid (PAA), high molecular weight polyethylene (HMWPE), polyvinylidene fluoridevinylidene difluoride copolymers (PVDF-VF2), or combinations thereof.

[0025] The term “BET surface area”, as used herein refers to the Brunauer-Emmett- Teller measurement of an analyte’s specific surface area (m2 / g) through gas adsorption analysis, wherein an inert gas is continuously flowed over a solid sample, to analyze the total volume of gas adsorbed over the surface of the sample. For the purpose of the present disclosure, the first conductive carbon has a BET surface area ranging from 250 m2 / g to 1800 m2; and the second conductive carbon has a BET surface area ranging from 10 m2 / g to 50 m2 / g.

[0026] The term “cathode” refers to a positive electrode which is a dry battery electrode comprising: (a) at least one active material; (b) at least one primary conductive carbon having a BET surface area ranging from 250 m2 / g to 1800 m2 / g; (c) at least one secondary conductive carbon having a BET surface area ranging from 10 m2 / g to 50 m2 / g; and (d) at least one binder.

[0027] The term “conductive carbon” refers to the carbon-based additive added to an electrode composite to enhance the conductivity of the electrode. For the purpose of the present disclosure, the conductive carbon comprises a first conductive carbonand a second conductive carbon. Additionally, conductive carbon of the present disclosure includes but is not limited to carbon black (CB; such as Ketjen black), graphite (KS6L), graphene, carbon nanotubes, acetylene black, or combinations thereof.

[0028] The term “c-rate” refers to the rate at which an electrochemical cell is charged or discharged to a specific potential. 1C means that the battery is fully charged and discharged within one hour, 2C is 30 minutes, 10C is 6 mins, 100C is 6 seconds.

[0029] The term “tensile strength” refers to the largest force in weight per unit area tugging in the direction of length that a given substance can sustain without rupturing. Tensile strength is also described as the "resistance to lengthwise stress." A tensile test (or tension test) applies force to a material in order to measure the material's response to tensile (or pulling) stress. A material either fully or partially cannot be reverted to its former shape and size once the stress approaches the tensile strength value. Force per unit area is a measure of tensile strength. In an aspect of the present disclosure, the cathode exhibits a tensile strength in a range of 30 to 40 MPa.

[0030] 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, temperature in the range of 60 to 80 °C should be interpreted to include not only the explicitly recited limits of 60 to 80 °C but also to include sub-ranges, such as 65 to 70 °C, 69 to 79°C and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 69.5 °C, 70 °C and 70.9 °C.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of thedisclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0032] 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.

[0033] As discussed in the background, there is a dire need in the art to develop an efficient dry cathode composite, which exhibits high conductivity, better electrochemical performance in aspects of improved discharge capacity, initial coulombic efficiency, capacity retention, without compromising the peel strength and tensile strength. The conductivity of electrodes can be enhanced by increasing the weight percentage of conductive carbon and reducing the amount of binder, owing to the insulating behavior of the binder. However, reducing binder content adversely affects the film stability and mechanical integrity of the electrode with respect to adhesion with current collector. To achieve the objective of higher conductivity and better mechanical stability, the present disclosure provides an improved cathode composition containing balanced combinations of conductive carbons and binders, coated on the electrode surface, which enhances conductivity and retains peel strength. The present disclosure provides Ketjen black, as a first conductive carbon and KS6L, as a second conductive carbon in a weight ratio in a range of 10: 1 to 2: 1, an adhesive binder polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) as the fibrillating binder in a weight ratio in a range of 1:0.5 to 1:2.

[0034] Accordingly, in an embodiment of the present disclosure, there is provided a dry cathode composite comprising: 95.6 to 97% by weight of an active material; 1.2 to 1.5% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.35 to 0.5% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.8 to 1.2% by weight of a fibrillating binder; and 0.7 to 1.2% by weight of an adhesive binder selected from poly vinylidene fluoride (PVDF), poly vinylidene fluoride-co-hexafluoropropylene(PVDF-HFP), polyethylene oxide, vinylidene fluoride, polyacrylic acid (PAA), high molecular weight polyethylene (HMWPE), polyvinylidene fluoridevinylidene difluoride copolymers (PVDF-VF2) or combinations thereof.

[0035] In another embodiment of the present disclosure, there is provided a dry cathode composite comprising: 95.8 to 97% by weight of an active material; 1.25 to 1.45% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.35 to 0.48% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.85 to 1.15% by weight of a fibrillating binder; and 0.75 to 1.15% by weight of an adhesive binder selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co- hexafluoropropylene (PVDF-HFP) or combinations thereof.

[0036] In yet another embodiment of the present disclosure, there is provided a dry cathode composite comprising: 96 to 97% by weight of an active material; 1.32 to 1.39% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.36 to 0.45% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.88 to 1.12% by weight of a fibrillating binder; and 0.8 to 1.1% by weight of an adhesive binder selected from polyvinylidene fluoride (PVDF), or polyvinylidene fluoride-co- hexafluoropropylene (PVDF-HFP).

[0037] In still an embodiment of the present disclosure, there is provided a dry cathode composite comprising: 96.5 to 97% by weight of an active material; 1.34 to 1.39% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; 0.38 to 0.48% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.9 to 1.1 % by weight of a fibrillating binder; and 0.85 to 1.05% by weight of an adhesive binder selected as polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP).

[0038] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the first conductive carbon and the second conductive carbon are in combined weight in a range of 1.6 to 2% (w / w) with respect to total weight of the composite. In another embodiment of the present disclosure, the first conductive carbon and the second conductive carbon are incombined weight in a range of 1.65 to 1.9% (w / w) with respect to total weight of the composite. In yet another embodiment of the present disclosure, the first conductive carbon and the second conductive carbon are in combined weight in a range of 1.75 to 1.85% (w / w) with respect to total weight of the composite.

[0039] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the active material is selected from layered lithium nickel manganese cobalt oxide (LiaNixMnyCozMbCh), spinel lithium nickel manganese oxide (LiNiMnMbCU), olivine lithium iron phosphate (LiFeMbPO4) or combinations thereof, wherein M is selected from Fe, Mn, Ni, Co, Cr, Al, Ti, Zr, W, Mo, Ru, V, Y, or Nb, a=0.9 to 1.3, b=0 to 0.5, x=0.1 to 0.9, y=0.01 to 0.7, and z= 0.01 to 0.5; and the active material has a particle size in a range of 2 to 20 micron. In another embodiment of the present disclosure, the active material is layered lithium nickel manganese cobalt oxide (LiaNixMnyCozMbO2), wherein a=0.9 to 1.3, b=0, x=0.1 to 0.9, y=0.01 to 0.7, and z= 0.01 to 0.5; and the active material has a particle size in a range of 5 to 15 micron.

[0040] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the first conductive carbon is selected from carbon black (CB), acetylene black or combinations thereof. In another embodiment of the present disclosure, the first conductive carbon is carbon black (CB) selected from Ketjen Black, Super P or combinations thereof. In another embodiment of the present disclosure, the first conductive carbon is carbon black (CB) (Ketjen Black).

[0041] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the second conductive carbon is selected from graphite, graphene, carbon nanotubes, or combinations thereof. In another embodiment of the present disclosure, the second conductive carbon is graphite selected from KS6L, KS15L, or combinations thereof. In another embodiment of the present disclosure, the second conductive carbon is graphite (KS6L).

[0042] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the fibrillating binder is selected from polytetrafluoroethylene (PTFE), ethylene vinyl acetate (EVA), fluoroethylene vinylether (FEVE), or combinations thereof. In another embodiment of the present disclosure, the fibrillating binder is polytetrafluoroethylene (PTFE).

[0043] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the first conductive carbon and the second conductive carbon are in a weight ratio range of 10 : 1 to 2 : 1. In another embodiment of the present disclosure, the first conductive carbon and the second conductive carbon are in a weight ratio in a range of 8 : 1 or 2.2: 1. In yet another embodiment of the present disclosure, the first conductive carbon and the second conductive carbon are in a weight ratio in a range of 5 : 1 or 2.4 : 1. In still another embodiment of the present disclosure, the first conductive carbon and the second conductive carbon are in a weight ratio range of 4 : 1 or 3 : 1.

[0044] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the first conductive carbon and second conductive carbon are in a surface area ratio in a range of 20 : 1 to 180 : 1. In another embodiment of the present disclosure, the first conductive carbon and second conductive carbon are in a surface area ratio in a range of 22 : 1 to 100 : 1. In yet another embodiment of the present disclosure, the first conductive carbon and second conductive carbon are in a surface area ratio in a range of 25 : 1 to 45 : 1.

[0045] In an embodiment of the present disclosure, there is provided a dry cathode composite as disclosed herein, wherein the first conductive carbon has a particle size in a range of 0.1 to 2.5 pm; and the second conductive carbon has a particle size in a range of 3 to 5 pm. In another embodiment of the present disclosure, the first conductive carbon has a particle size in a range of 0.2 to 2 pm; and the second conductive carbon has a particle size in a range of 3.5 to 4.5 pm. In yet another embodiment of the present disclosure, the first conductive carbon has a particle size in a range of 0.4 to 1 pm; and the second conductive carbon has a particle size in a range of 3.8 to 4.2 pm.

[0046] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, said process comprising the steps of: i) mixing an active material, a first conductive carbon, and a second conductive carbon to obtain a first mixture; ii) blending the first mixture with afibrillating binder and an adhesive binder followed by high shear mixing at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 60 to 80 °C to obtain a second mixture; and iii) cooling the second mixture to a temperature in a range of 10 to 19 °C to obtain the dry cathode composite.

[0047] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the mixing is performed at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 10 to 25 °C for a period in a range of 100 to 150 minutes. In another embodiment of the present disclosure, the mixing is performed at a tip speed in a range of 25 to 35 m / s, at a temperature in a range of 10 to 25 °C for a period in a range of 110 to 140 minutes. In yet another embodiment of the present disclosure, the mixing is performed at a tip speed in a range of 28 to 32 m / s, at a temperature range of 10 to 25 °C for a period in a range of 115 to 130 minutes.

[0048] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, wherein the blending is performed at a temperature range of 10 to 19 °C, for a period in a range of 15 to 40 minutes. In another embodiment of the present disclosure, the blending is performed at a temperature range of 10 to 19 °C, for a period in a range of 15 to 35 minutes.

[0049] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, said process comprising the steps of: i) mixing an active material, a first conductive carbon, and a second conductive carbon at a tip speed in a range of 20 to 40 m / s, at a temperature range of 10 to 25 °C for a period in a range of 100 to 150 minutes to obtain a first mixture; ii) blending the first mixture with a fibrillating binder at a temperature range of 10 to 19 °C, for a period in a range of 15 to 20 minutes and then blending with an adhesive binder for a period in a range of 15 to 20 minutes followed by high shear mixing at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 60 to 80 °C to obtain a second mixture; and iii) cooling the second mixture to a temperature less than 19 °C to obtain the dry cathode composite.

[0050] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, wherein cooling is carried out at a tip speed in a range of 3 to 10 m / s. In another embodiment of the present disclosure, cooling is carried out at a tip speed in a range of 4 to 9 m / s. In yet another embodiment of the present disclosure, cooling is carried out at a tip speed in a range of 5 to 7 m / s.

[0051] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, said process comprising the steps of: i) mixing an active material, a first conductive carbon, and a second conductive carbon at a tip speed in a range of 20 to 40 m / s, at a temperature range of 10 to 25 °C for a period in a range of 100 to 150 minutes to obtain a first mixture; ii) blending the first mixture with a fibrillating binder at a temperature range of 10 to 19 °C, for a period in a range of 15 to 20 minutes and then blending with an adhesive binder for a period in a range of 15 to 20 minutes followed by high shear mixing at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 60 to 80 °C to obtain a second mixture; and iii) cooling the second mixture by mixing at a tip speed in a range of 3 to 10 m / s, to a temperature less than 19 °C to obtain the dry cathode composite.

[0052] In an embodiment of the present disclosure, there is provided a process for preparation of a dry cathode composite as disclosed herein, wherein the dry cathode composite is calendered and optionally laminated on a current collector at a temperature in a range of 60 to 150 °C. In yet another embodiment of the present disclosure, the dry cathode composite is calendered at a temperature in a range of 60 to 150 °C and laminated on a current collector at a temperature in a range of 60 to 150 °C. In another embodiment of the present disclosure, the dry cathode composite is calendered at a temperature in a range of 70 to 140 °C.

[0053] In an embodiment of the present disclosure, there is provided a cathode comprising the dry cathode composite as disclosed herein, coated on a current collector.

[0054] In an embodiment of the present disclosure, there is provided a cathode comprising the dry cathode composite as disclosed herein, coated on a currentcollector selected from aluminium foil, glossy aluminium foils, carbon or polymer pre-coated aluminium foil, copper foil, or polymer pre-coated copper foil. In another embodiment of the present disclosure, the current collector is selected from aluminium foil, glossy aluminium foils, carbon or polymer pre-coated aluminium foil.

[0055] In an embodiment of the present disclosure, there is provided a cathode as disclosed herein, wherein the cathode exhibits a through plane conductivity in a range of 3 to 5 mS / cm at 25 °C; a peel strength in a range of 2 to 3 N / 25mm; and a tensile strength in a range of 30 to 40 MPa. In another embodiment of the present disclosure, the cathode exhibits a through plane conductivity in a range of 3 to 4 mS / cm at 25 °C; a peel strength in a range of 2.2 to 2.8 N / 25mm; and a tensile strength in a range of 33 to 36 MPa.

[0056] In an embodiment of the present disclosure, there is provided a cathode as disclosed herein, wherein the cathode exhibits a discharge capacity of 209 mAh / g to 212 mAh / g. In another embodiment of the present disclosure, the cathode exhibits a discharge capacity of 210 mAh / g to 212 mAh / g.

[0057] In an embodiment of the present disclosure, there is provided a cathode as disclosed herein, wherein the cathode exhibits a capacity retention in a range of 98.6 to 99.5%, for up to 50 cycles. In another embodiment of the present disclosure, the electrode exhibits a capacity retention in a range of 98.6 to 99%, for up to 50 cycles.

[0058] In an embodiment of the present disclosure, there is provided a lithium-ion battery comprising: a) the cathode as disclosed herein; b) an anode; and c) an electrolyte.

[0059] In an embodiment of the present disclosure, there is provided a lithium-ion battery comprising: a) the cathode comprising the dry cathode composite as disclosed herein; b) an anode; and c) an electrolyte.

[0060] In an embodiment of the present disclosure, there is provided a lithium-ion battery comprising: a) the cathode comprising the dry cathode composite comprising: 95.6 to 97% by weight of an active material; 1.2 to 1.5% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g;0.35 to 0.5% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; 0.8 to 1.2% by weight of a fibrillating binder; and 0.7 to 1.2% by weight of an adhesive binder selected from poly vinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyethylene oxide, vinylidene fluoride, poly aery lie acid (PAA), high molecular weight polyethylene (HMWPE), polyvinylidene fluoride-vinylidene difluoride copolymers (PVDF-VF2) or combinations thereof.; b) an anode; and c) an electrolyte.

[0061] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.EXAMPLES

[0062] The disclosure will now be illustrated with following 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

[0063] The procurement details of various chemicals and solvents used in the present disclosure are as follows:1. Cathode active material NMC811 having particle size of 5 to 15 micron was procured from BASF.2. First conductive carbon- Ketjen black (Carbon black; BET surface area: 600 m2 / g; particle size of 0.5 pm) was procured from Noury on.3. Second conductive carbon KS6L (BET surface area: 20 m2 / g; particle size of 4 pm) was procured from Imerys.4. Adhesive binder: polyvinylidene fluoride-co-hexafluoropropylene (PVDF- HFP) was procured from Arkema5. Binder: polytetrafluoroethylene (PTFE) was procured from Daikin.6. Pre-coated aluminium Current collector was procured from BlueGlow Nano.EXAMPLE 1

[0064] For preparing a baseline cathode (Cathode- 1), 96.2% by weight of layered lithium nickel manganese cobalt oxide NMC811 (active material, AM, having an average particle size of 10 micron), was mixed with 1% by weight of ketjen black (first conductive carbon; CC1) and 0.3% by weight of KS6L (second conductive carbon; CC2), were mixed at 30.6 m / s tip speed for 120 minutes in a Zeppelin mixture at a temperature of 15°C, to obtain a first mixture. 1% by weight of polyvinylidene fluoride-co-hexafluoropropylene (adhesive binder (B l); PVDF- HFP) was added to the first mixture and blended at a tip speed of 15.3 m / s, at a temperature of 15°C for 15 min. A polytetrafluoroethylene (fibrillating binder (B2); PTFE) of weight of 1.5% was added to the resulting blend and blended at a tip speed of 15.3 m / s for 15 min at a temperature of 15 °C to obtain a second mixture. The homogenously blended second mixture was then high shear mixed using a Zeppelin high intensity mixer at a tip speed of 30.6m / s until the temperature reached 70°C. The resulting mixture was then cooled to a temperature of 15 °C at a tip speed of 6.1 m / s to obtain a dry cathode composite DCC-1.

[0065] Further, the dry cathode composite DCC-1 was calendered at 120 °C to obtain a free-standing film and was laminated upon a carbon pre-coated aluminium current collector at a temperature of 150 °C to obtain a cathode (Cathode-1). Similarly, various dry cathode composites (DCC-2 and DCC-3) and corresponding cathodes (Cathode 2 and Cathode 3) were prepared by appropriately changing theweight percentages of first conductive carbon, second conductive carbon and fibrillating binders as listed in Table 1.Table 1EXAMPLE 2Analysis of physical properties of the cathodeScanning electron microscopy (SEM):

[0066] The surface morphology of first mixtures obtained during the preparation of dry cathode composites (DCC-1, DCC-2 and DCC-3; as depicted in Figure 1(A- C)(i), Cathode- 1 (baseline), Cathode-2 and Cathode-3 were analyzed (both surface Figure 1(A-C)(ii) and cross section Figure 1(A-C)(iii)) using SEM analysis.

[0067] In Figure l(A)(i), it was found that the first mixture obtained by mixing 1.3% by weight of conductive carbons (KB and KS6L) showed non-uniform coating of carbon upon the active material NMC surface. Therefore, the cathode- 1 formed by calendering DCC-1 resulted in less compactness and dense fibrillation (as shown in Figure 1(A) (ii) and (iii)) due to non-homogenous carbon distribution and high binder content.

[0068] Further, in Figure l(B)(i), the first mixture obtained by mixing 1.8% by weight of conductive carbons (KB and KS6L), showed uniform coating of conductive carbons upon active material NMC surface. In addition, the cathode-2 obtained by calendering DCC-2 showed better compactness of active materials and appropriate fibrillation of fibrillating binder PTFE (as shown in Figure 1(B) (ii) and (iii)).

[0069] Furthermore, the Figure l(C)(i) showed that the conductive carbons when used in a weight percentage above 2% resulted in a dry cathode composite DCC-3 with high conductive carbon agglomeration and non-uniform carbon coating upon NMC surface. Therefore, the cathode-3 obtained by calendering DCC-3 showed higher carbon agglomeration and reduced binder fibrillation (as shown in Figure 1(C) (ii) and (iii)).

[0070] The SEM images showed that cathode-2 exhibited adequate fibrillation and coverage as compared to cathode- 1 which showed lower compactness and cathode 3 which had poor fibril formation.Tensile Strength:

[0071] Tensile strength analysis was performed for the different cathodes prepared by the process as explained in Example 1. The samples of cathodes 1, 2, and 3 having required length (200mm), width (25mm) and thickness (60 pm) were prepared for the tensile strength measurement. The prepared dry electrode was fixed in the fixtures and the load was applied with cross-section speed of 12.5mm / min. Load versus displacement curve was plotted to obtain the yield strength, and tensile strength values are of the dry electrode.

[0072] The tensile strength for the Cathode-2 was found to be 35.99 MPa, Cathode- 3 showed a tensile strength of 39.74 MPa, and that of the baseline Cathode-1 was found to be 36.05 MPa. Cathode-2 employing about 1.8% by weight of conductive carbon and 2% by weight of binder showed comparable tensile strength properties. Peel strength:

[0073] Peel strength analysis is a conventional method in battery industry for ranking the adhesion strength of electrodes. For the test, a double-sided adhesive tape was first stuck onto the movable pull-off table. The composite to be tested was then glued to the adhesive tape. Subsequently, one of the two connected (glued) components was attached to the load cell using a tension clamp, which was integrated in the movable measuring arm of the testing device. During the test, the measuring arm moved upwards, separating the two materials adhering to each other at an angle of 90°. The congruent movement of the table maintained the 90° angleduring the measurement. The pull-off speed was varied. The pull-off force standardized to the width of the test strip is called peel strength and is usually given in N / mm. After measuring and averaging the load required to peel the specimen, the peel strength is derived by dividing the average load by the bond line's unit width.

[0074] The dry cathode composite coating was separated from the current collector using bond tapes at a speed of about 0.01 mm / s to 40 mm / s. It was found that the Cathode-2 had a peel strength of 2.45 N / 25mm, which was in close proximity to the baseline Cathode- 1 (2.44 N / 25mm) as compared to the cathode-3 with a peel strength of 1.93 N / 25mm.

[0075] The peel strength and tensile strength results achieved for the cathodes 1, 2 and 3 are provided in Table 2 along with their electrode densities.Table 2EXAMPLE 3Preparation of an electrochemical cell comprising the cathode

[0076] The electrochemical cell setup was obtained by sequentially assembling cathode prepared by the process as explained in Example 1, and an anode on either side of an electrolyte.

[0077] An electrochemical cell specifically a battery, and more specifically, a lithium-ion battery was prepared. The lithium-ion battery included a cathode as explained in Example 1, a graphite anode disposed to face the cathode, and an electrolyte (LiPFe dispersed in a solvent mixture of ethylene carbonate (EC),vinylene carbonate (VC) and dimethyl carbonate (DMC)) placed between cathode and anode. The electrochemical cell obtained from the process explained above was analysed for its electrochemical performance, C-rate performance, and chargedischarge capacity.

[0078] For the purpose of electrochemical analysis of the cathode as explained in example 1, a half-cell was prepared using Li metal as anode.Characterization of the electrochemical properties of the cathode

[0079] Various electrochemical properties of the different cathodes (Cathode 1 to Cathode 3) were assessed in a half-cell, and the results are provided in Table 3.Conductivity / Resistivity:

[0080] The through plane conductivity was analysed by studying conductivity in the direction perpendicular to the plane of the electrode fdm with two probe electrode system. The various cathodes (Cathode 1 to Cathode 3) exhibited a through plane conductivity around 0.5 to 5 mS / cm at 25 °C. Specifically, the Cathode-2 exhibited a through plane conductivity of 3.36 mS / cm with corresponding resistivity of 297.62 Ohm-cm and Cathode-3 exhibited a through plane conductivity of 4.66 mS / cm with corresponding resistivity of 214.59 Ohm- cm, which was better in comparison to the Cathode-1 (0.753 mS / cm and 1328.02 Ohm-cm).

[0081] The resistance of the cathodes having (Cathode-1 to Cathode-3) 20 mm thickness was also measured and provided in Table 3.Charge-Discharge capacity:

[0082] Galvanostatic charge-discharge cycles at a potential window of 2.5 V to 4.3 V was recorded for a half-cell comprising the cathodes (Cathode-1 to Cathode-3) at a current rate (c-rate) of 0.1 C. The cycling was performed at temperatures of 25°C and 45°C. The discharge capacity of the cell comprising cathode 2 at 0.1C rate was 211.23 mAh / g at 25°C, whereas that of cathode 3 was 208.70 mAh / g as shown in Table 3 and Figure 2. For the cell comprising cathode 1, the discharge capacity was found to be 185.08 mAh / g, at 1C rate which was lower than that ofthe cathode 2 (188.77 mAh / g) and the cathode 3 (187.2 mAh / g). Therefore, the cathode 2 showed better discharge capacity at lower and higher c-rates.Electrochemical performance:

[0083] The C-rate represents the rate at which level the battery provides energy. The half-cells comprising the cathodes (Cathode-1 to Cathode-3) were analysed for their electrochemical performance. The capacity of the Cathode-2 at a c-rate of 1C (1C capacity) was found to be 188.77 mAh / g and 187.2 mAh / g for Cathode-3, which was higher in comparison to the Cathode-1 (185.08 mAh / g).

[0084] Furthermore, the Cathode-2 resulted in an initial coulombic efficiency (ICE) value of 91.9%, and a capacity retention of 98.7%, whereas Cathode-3 showed an ICE value of 92.2% and a capacity retention of 99.12% as evident in Table 3 and Figure 3, indicative of the capacity retention of the cell.

[0085] Hence, the Cathode-2 showed the best 1C capacity in comparison to Cathodes 2 and 3. This higher performance was attributed towards a highly compacted structure and reduced amount of binder used in the cathode system.State of health:

[0086] The capacity retention of the cathode was also analyzed up to 50 cycles at 1C, to find out if appreciable cycle stability was exhibited by the cathodes in the disclosed ratios. The state of health (SoH) was calculated using the formula: SoH = (maximum available capacity of the current cycle / maximum available capacity of the initial cycle) x 100.Table 3: Electrochemical properties of dry cathodes

[0087] The results indicated that although Cathode-3 showed better tensile strength conductivity and state of health in comparison to Cathode-2, the peel strength and the discharge capacity of Cathode-3 were significantly lower than the baseline Cathode- 1, thereby affecting the longevity of the battery.

[0088] As PVDF is an insulative binder when the amount of PVDF was reduced further, it increased the conductivity in the cathode 2. Yet the effective binding of active material particles was reduced which led to reduction in the peel strength of the cathode 2. Hence, a balance between the conductivity and peel strength was considered to be crucial in determining the overall electrochemical performance and the life cycle of the battery, as evident from the results of cathode 2.

[0089] Meanwhile, when the PTFE content was reduced and conductive carbon amount was increased instead from the baseline Cathode- 1, the Cathode-2 showed reduction in sufficient fibril network formation and hence there was a reduction in the peel strength. However, increase in conductive carbon content in the Cathode- 2 enhanced its conductivity, improved tensile strength and still achieved better peel strength value. Therefore, Cathode-2 was considered to be desirable to achieve a better electrochemical performance with high capacity and better capacity retention.ADVANTAGES OF THE PRESENT DISCLOSURE

[0090] The present disclosure provides a dry cathode composite comprising two conductive carbons and two binders in an effective weight ratio.1. The dry cathode composite of the present disclosure contains an increased proportion of conducting carbon additives up to 2% by weight, with reduced binder content, which increased the cathode’s conductivity, while maintaining all the physical and electrochemical properties of the cathode.2. The cathode shows a conductivity in a range of 3 to 5 mS / cm at 25 °C; a peel strength in a range of 2 to 3 N / 25mm; a tensile strength in a range of 30 to 40 MPa; and a capacity retention in a range of 98.6 to 99.5%.3. The cathode also delivers a discharge capacity of 211.23 mAh / g with 91.9% initial coulombic efficiency.4. The properties of the said cathode render it with enhanced life cycle and higher electrochemical performance.

Claims

I / We Claim:

1. A dry cathode composite comprising: a. 95.6 to 97% by weight of an active material; b. 1.2 to 1.5% by weight of a first conductive carbon having a surface area in a range of 250 m2 / g to 1800 m2 / g; c. 0.35 to 0.5% by weight of a second conductive carbon having a surface area in a range of 10 m2 / g to 50 m2 / g; d. 0.8 to 1.2% by weight of a fibrillating binder; and e. 0.7 to 1.2% by weight of an adhesive binder selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co- hexafluoropropylene (PVDF-HFP), polyethylene oxide, vinylidene fluoride, poly aery lie acid (PAA), high molecular weight polyethylene (HMWPE), poly vinylidene fluoride-vinylidene difluoride copolymers (PVDF-VF2), or combinations thereof.

2. The dry cathode composite as claimed in claim 1, wherein the first conductive carbon and the second conductive carbon are in a combined weight in a range of 1.6 to 2% (w / w), with respect to total weight of the composite.

3. The dry cathode composite as claimed in claim 1, wherein the active material is selected from layered lithium nickel manganese cobalt oxide (LiaNixMnyCozMbOi), spinel lithium nickel manganese oxide (LiNiMnMbCU), olivine lithium iron phosphate (LiFeMbPCU) or combinations thereof, wherein M is selected from Fe, Mn, Ni, Co, Cr, Al, Ti, Zr, W, Mo, Ru, V, Y, or Nb, a=0.9 to 1.3, b=0.01 to 0.5, x=0.1 to 0.9, y=0.01 to 0.7, and z= 0.01 to 0.5; and the active material has a particle size in a range of 2 to 20 micron.

4. The dry cathode composite as claimed in claim 1, wherein first conductive carbon is selected from carbon black (CB), acetylene black, or combinations thereof.

5. The dry cathode composite as claimed in claim 1, wherein the second conductive carbon is selected from graphite, graphene, carbon nanotubes, or combinations thereof.

6. The dry cathode as claimed in claim 1, wherein the fibrillating binder is selected from polytetrafluoroethylene (PTFE), ethylene vinyl acetate (EVA), fluoroethylene vinyl ether (FEVE), or combinations thereof.

7. The dry cathode composite as claimed in claim 1, wherein the first conductive carbon and the second conductive carbon are in a weight ratio in a range of 10: 1 to 2: 1.

8. The dry cathode composite as claimed in claim 1, wherein the first conductive carbon and second conductive carbon are in a surface area ratio in a range of 20: 1 to 180: 1.

9. The dry cathode composite as claimed in claim 1, wherein the first conductive carbon has a particle size in a range of 0.1 to 2.5 pm; and the second conductive carbon has a particle size in a range of 3 to 5 pm.

10. A process for preparation of the dry cathode composite as claimed in claim 1, said process comprising: i) mixing an active material, a first conductive carbon, and a second conductive carbon to obtain a first mixture; ii) blending the first mixture with a fibrillating binder and an adhesive binder followed by high shear mixing at a tip speed in a range of 20 to 40 m / s, at a temperature in a range of 60 to 80 °C to obtain a second mixture; and iii) cooling the second mixture to a temperature in a range of 10 to 19 °C to obtain the dry cathode composite.

11. The process as claimed in claim 10, wherein the mixing is performed at a tip speed in a range of 20 to 40 m / s, at a temperature range of 10 to 25 °C for a period in a range of 100 to 150 minutes.

12. The process as claimed in claim 10, wherein the blending is performed at a temperature range of 10 to 19 °C for a period in a range of 15 to 40 minutes.

13. The process as claimed in claim 10, wherein the cooling is carried out at a tip speed in a range of 3 to 10 m / s.

14. The process as claimed in claim 10, wherein the dry cathode composite is calendered and optionally laminated on a current collector at a temperature in a range of 60 to 150 °C.

15. A cathode comprising the dry cathode composite as claimed in claim 1 coated on a current collector.

16. The cathode as claimed in claim 15, wherein the cathode exhibits a through plane conductivity in a range of 3 to 5 mS / cm at 25 °C; a peel strength in a range of 2 to 3 N / 25mm; and a tensile strength in a range of 30 to 40 MPa.

17. The cathode as claimed in claim 15, wherein the electrode exhibits a capacity retention in a range of 98.6 to 99.5%.

18. A lithium-ion battery comprising: a. the cathode as claimed in claim 15; b. an anode; and c. an electrolyte.

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