A dry battery electrode, a lithium-ion battery and processes thereof

Abstract

The present disclosure provides a dry battery electrode comprising a. at least one active material; b. at least one conductive carbon; and c. at least one fluorinated binder; wherein the active material is selected from natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof. The present disclosure further provides a lithium-ion battery comprising the dry battery electrode as disclosed herein. Furthermore, the present disclosure provides a process for preparing the electrode.

Description

A DRY BATTERY ELECTRODE, A LITHIUM-ION BATTERY AND PROCESSES THEREOFFIELD OF INVENTION

[0001] The present disclosure broadly relates to the field of battery. Particularly, the present disclosure relates to dry battery electrode composition, especially anode composition for all lithium-ion battery and a process for fabricating the electrode.BACKGROUND OF INVENTION

[0002] With increasing global demand for batteries, developing more efficient processes for preparation of electrode composition is a growing focus of the industry. The conventional electrode preparation for lithium-ion batteries often involves a wet slurry coating process. This process typically includes the steps of slurry preparation comprising active materials, conducting additives and solvent; coating of slurry on current collector; evaporating the solvent, calendering, electrode assembly and many more sub-processes in between.

[0003] One of the crucial steps in the battery fabrication process is the coating of active material on top of the current collector to form the electrode. After the coating, the electrodes are dried and pressed. The drying process is costly and both energy and time consuming. Moreover, use of certain organic solvents in the slurry is hazardous and involves energy intensive measures for recovering the solvents. Alternatively, as an environment friendly approach, dry electrode processes do not employ solvents and instead use polymeric binders along with the active material to address the issue of drying.

[0004] Dry electrode process has gained popularity in recent years owing to its solvent-free approach, which eliminates the need for organic solvents in the electrode preparation process. This approach offers several other advantages, including cost savings associated with solvent procurement as well as the elimination of solvent evaporation, recovery, and drying process. By removing the solvent-related steps, the dry coating methodology reduces both the time and energy consumption in the manufacturing process. This increased efficiency holds a positive impact on the battery production rates and overall productivity. Additionally, the absence of solvent related processes can contribute to a saferworking environment by minimizing exposure to volatile organic compounds and reducing the risk of solvent related hazards.

[0005] Thus, the dry electrode process holds great promise for commercialization in industrial applications, as it offers a more streamlined and sustainable approach to battery manufacturing. The elimination of solvents not only simplifies the production process but also aligns with environmental and regulatory considerations regarding solvent usage and disposal. However, challenges still exist in such dry electrode compositions. Issues with uniform dispersion of the active material, and associated electrochemical degradation of the polymeric binder, poor adhesion of the electrode film on the collector etc., results in decreased capacity of the battery.

[0006] Dry battery electrode (DBE) process for an anode includes dry mixing of anode active materials with conductive carbon and fluorinated binders such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF). At present, about 1 wt% of PTFE content is used in the dry electrode process, which provides good fibrillation and better flexibility for free-standing film manufacturing. However, it has been observed that PTFE reacts with Lithium ions at lower potential due to the energy of lowest unoccupied molecular orbital (LUMO) of PTFE being less. It is well known that the lithiation process takes place at low voltage (0.2V) on the anode side. Hence, the PTFE reactivity leads to poor initial coulombic efficiency (ICE) and cycle instability of the anode dry electrode.

[0007] Therefore, there exists a need for an effective electrode composition for overcoming the existing challenges of high reactivity of binder with Lithium electrode environment for dry electrode compositions.SUMMARY OF THE INVENTION

[0008] In an aspect of the present disclosure, there is provided a dry battery electrode comprising: (a) at least one active material; (b) at least one conductive carbon; (c) at least one fluorinated binder; wherein the at least one active material is selected from natural graphite, synthetic graphite, silicon, expanded graphite, or combinations thereof.

[0009] In another aspect of the present disclosure, there is provided a process to prepare the dry battery electrode as disclosed herein, said process comprising the steps of: (a) mixing at least one active material, at least one conductive carbon, and at least one fluorinated binder to obtain a powder mixture; (b) shear mixing the powder mixture at a speed in a range of 1000 to 5000 rpm, at a temperature in a range of 50 to 100°C to obtain a dough; and (c) cooling the dough to a temperature in a range of 15-30°C to obtain the electrode, wherein the electrode exhibits a peel strength in a range of 0.008 kgf to 0.5 kgf; a through plane conductivity in a range of 1.45 to 5.8 mS / cm; a tensile strength in a range of 220 to 400 kgf / cm2; and a capacity in a range of 350 to 364 mAh / g.

[0010] In more aspect of the present disclosure, there is provided a lithium-ion battery comprising: (a) the dry battery electrode as disclosed herein as anode; (b) a cathode; 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. 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 x-ray diffraction (XRD) pattern of (a) synthetic graphite; and (b) natural graphite powder materials, in accordance with an embodiment of the present disclosure.

[0014] Figure 2 depicts the scanning electron microscopy (SEM) images of (a), (b)- synthetic graphite and (c), (d) -natural graphite dry battery electrodes, in accordance with an embodiment of the present disclosure.

[0015] Figure 3 depicts the electrochemical impedance (EIS) spectra of synthetic graphite and natural graphite dry battery electrode, in accordance with an embodiment of the present disclosure.

[0016] Figure 4 depicts the X-ray photoelectron spectroscopic (XPS) analysis for natural graphite dry battery electrode NGE-1 after 3 cycles (a) FIs spectrum and (b) Cis spectrum, in accordance with an embodiment of the present disclosure.

[0017] Figure 5 depicts the X-ray photoelectron spectroscopic (XPS) analysis for synthetic graphite dry battery electrode SGE-1 after 3 cycles (a) FIs spectrum and (b) Cis spectrum, in accordance with an embodiment of the present disclosure.

[0018] Figure 6 depicts the comparison of electrochemical analysis for synthetic and natural graphite in dry battery electrode process, in accordance with an embodiment of the present disclosure.

[0019] Figure 7 depicts the graphical representation of initial coulombic efficiency (ICE) comparison of synthetic (SGE-1) and natural graphite (NGE-1) dry battery electrodes, in accordance with an embodiment of the present disclosure.

[0020] Figure 8 depicts the electrochemical performance of the dry battery electrode (a) NS-80 (electrode comprising an active material which is a blend of 80% NG and 20% SG) and (b) NS-50 (electrode comprising an active material which is a blend of 50% NG and 50% SG) comprising a combination of natural graphite and synthetic graphite as active material, in accordance with an embodiment of the present disclosure.

[0021] Figure 9 depicts electrochemical cycle life performance comparison for natural and synthetic graphite, in accordance with an embodiment of the present disclosure.

[0022] Figure 10 depicts electrochemical cycle life performance comparison for the electrodes (a) NS- 10 (blend of 10% NG and 90% SG), NS-20 (blend of 20% NG and 80% SG), NS-30 (blend of 30% NG and 70% SG), and NS-40 (blend of 40% NG and 60% SG); and (b) synthetic graphite, natural graphite, NS- 10 (blend of 10% NG and 90% SG) and NS-30 (blend of 30% NG and 70% SG) materials.DETAILED DESCRIPTION OF THE INVENTION

[0023] 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

[0024] 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.

[0025] 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.

[0026] 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”.

[0027] 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.

[0028] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0029] The term “w / w” means the percentage by weight, relative to the weight of the total composition, unless otherwise specified.

[0030] The term "at least one" is used to mean one or more and thus includes individual components as well as mixtures / combinations.

[0031] The term “active material” refers to the active constituent of an electrode, which comprises the particles that undergo oxidation or reduction, resulting in electroconductivity. Examples of active material in the present disclosure includes but not limited to natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof. In the instant case, synthetic graphite is denoted as “SG” and natural graphite is denoted as “NG”. Further the electrode comprising natural graphite as active material is denoted as “NGE” and the electrode comprising synthetic graphite as active material is denoted as “SGE”. Lastly, the electrodes comprising a combination of natural graphite and synthetic graphite in specific weight ratio as active material are denoted as “NS”. For the purpose of the present disclosure, a denotation “NS-90” simply refers to an electrode comprising the combination of natural graphite and synthetic graphite in 90: 10 weight ratio as active material. Similarly, a denotation “NS-10” simply refers to an electrode comprising the combination of natural graphite and synthetic graphite in 10:90 weight ratio as active material.

[0032] The term “conductive carbon” refers to the carbon-based additives added to an electrode composition to facilitate the charge conduction. In an aspect of the present disclosure, the conductive carbon is selected from super P, ketjen black, amorphous carbon, KS6L, graphene, graphene oxide, carbon black, or combinations thereof.

[0033] The term “fluorinated binder” refers to a type of the binder constituent of an electrode, which comprises fluorine. The fluorinated binder of the present disclosure optionally exhibits fibrillation into thin fibrils upon external force to hold the active material particles within the electrode of a battery together and maintain a strong connection between the electrode and other components. The binder also 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 fluorinated binder of the present disclosure includes but not limited to polytetrafluoroethylene (PTFE), fluoroethylene vinyl ether (FEVE), fluorinated ethylene propylene (FEP), poly vinylidene fluoride (PVDF), or combinations thereof.

[0034] The term “pore volume” refers to the volume of the pore characteristic of the substance which is obtained through a specific synthetic route. In an aspect of the present disclosure, the pore volume of the active material is determined from the amount (cm3 / g) of Nitrogen gas (volume) required to fill the pores of the active material at equilibrium pressure (P / P°), measured using Microtrack MRB Bellsorb, wherein P is liquid nitrogen pressure; P° is sample pressure.

[0035] The term “peel strength” refers to the measurement of the adhesion of a freestanding fdm with a current collector which is optionally primer coated.

[0036] 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 2.5% (w / w) should be interpreted to include not only the explicitly recited limits of 0.1% to 2.5% (w / w) but also to include subranges, such as 1% to 2% (w / w), 1.5% to 2.5% (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 0.8% (w / w).

[0037] 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 the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0038] 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.

[0039] As discussed in the background, there are many challenges in developing an efficient electrode for lithium-ion batteries. One of the major challenges in obtaining an efficient electrode is the undesired high reactivity of the fluoropolymer binder with the lithium ions. A commonly employed binder is polytetrafluoroethylene (PTFE), which reacts with the anodic environment to produce highly reactive carbyne species and leading to diminished electrochemical performance of the electrode through progressive cycles. In order to mitigate the reactivity of PTFE with lithium ion, alternate strategies of using other binders or protective coating over the active material could be used. However, due to uneconomical disadvantages, there is a need in the art to develop an efficient active material for anode material. One technical strategy in this direction is the usage of natural graphite as anode active materials, which decreases the PTFE reactivity in IM electrolyte solution. The objective is to reduce the PTFE reactive sites to Li ion by changing the active materials and the electrode manufacturing process. A substantial amount of reactivity could be reduced by introducing the natural graphite in the anode dry battery electrode.

[0040] The present disclosure provides a dry battery electrode comprising at least one active material with high surface area, at least one conductive carbon, and at least one fluorinated binder that are mixed to enable the uniform coating of the mixture on the current collector, thereby resulting in an electrode with high- capacity post coating. The present disclosure also provides a process for preparing the dry battery electrode and a lithium-ion battery comprising the electrode.

[0041] Accordingly, the present disclosure provides a dry battery electrode comprising: (a) at least one active material; (b) at least one conductive carbon; and (c) at least one fluorinated binder; wherein the active material is selected from natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof.

[0042] In an embodiment of the present disclosure, there is provided a dry battery electrode comprising: (a) at least one active material; (b) at least one conductive carbon; and (c) at least one fluorinated binder; wherein the active material has aBET surface area ranging from 0.78 m2 / g to 4.2 m2 / g; tap density in a range of 1 to 1.3 g / cm3; particle size (D50) in a range of 14.0pm to 20 pm; pore volume in a range of 2.2e-3 to 3.7 e-2 cm3 / g; and the active material is selected from natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof.

[0043] In another embodiment of the present disclosure, the active material has a BET surface area ranging from 0.79 to 4.2 m2 / g; tap density in a range of 1 to 1.3 g / cm3; particle size (D50) in a range of 14.0 pm to 20 pm; and pore volume in a range of 2.4 to 3.7 e'W / g. In yet another embodiment of the present disclosure, the active material has a BET surface area ranging from 1 m2 / g to 4.2 m2 / g; tap density in a range of 1.05 to 1.3 g / cm3; particle size (D50) in a range of 14.5pm to 20 pm; pore volume in a range of 2.4 e-2 to 3.7 e-2 cm3 / g.

[0044] In an embodiment of the present disclosure, there is provided a dry battery electrode comprising: (a) at least one active material; (b) at least one conductive carbon; and (c) at least one fluorinated binder; wherein the active material is preferably natural graphite or a combination of natural graphite and synthetic graphite. In yet another embodiment of the present disclosure, the active material is natural graphite. In still another embodiment of the present disclosure, the active material is a combination of natural graphite and synthetic graphite.

[0045] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the active material is selected from natural graphite or a combination of natural graphite and synthetic graphite, wherein the combination of natural graphite and synthetic graphite has at least 30% (w / w) of natural graphite with respect to the total weight of the active material.

[0046] In an embodiment of the present disclosure, there is provided a dry battery electrode comprising: (a) at least one active material; (b) at least one conductive carbon; and (c) at least one fluorinated binder; wherein the active material is preferably natural graphite or a combination of natural graphite and synthetic graphite, wherein the combination of natural graphite and synthetic graphite has at least 30% (w / w) of natural graphite with respect to the total weight of the active material.

[0047] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the electrode is anode.

[0048] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the conductive carbon is selected from super P, ketjen black, amorphous carbon, KS6L, graphene, graphene oxide, carbon black, or combinations thereof. In another embodiment of the present disclosure, the conductive carbon is preferably super P.

[0049] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the fluorinated binder is selected from of polytetrafluoroethylene (PTFE), fluoroethylene vinyl ether (FEVE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), or combinations thereof.

[0050] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the binder is selected from polytetrafluoroethylene (PTFE), poly vinylidene fluoride (PVDF), or combinations thereof. In another embodiment of the present disclosure, the binder is preferably polytetrafluoroethylene (PTFE). In yet another embodiment of the present disclosure, the binder is preferably polyvinylidene fluoride (PVDF). In still another embodiment of the present disclosure, the binder is preferably a combination of polytetrafluoroethylene (PTFE) and poly vinylidene fluoride (PVDF).

[0051] In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the active material is in a weight range of 97 to 98% with respect to total weight of the electrode; the conductive carbon is in a weight range of 0.5 to 1% with respect to total weight of the electrode; and the fluorinated binder is in a weight range of 0.5 to 2% with respect to total weight of the electrode.

[0052] In an embodiment of the present disclosure, there is provided a dry battery electrode comprising: (a) 97 to 98% (w / w) of at least one active material; (b) 0.5 to 1% (w / w) at least one conductive carbon; (c) 0.5 to 2% (w / w) at least one fluorinated binder; wherein is selected from natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof.In an embodiment of the present disclosure, there is provided a dry battery electrode as disclosed herein, wherein the electrode exhibits a peel strength in a range of 0.008 kgf to 0.5 kgf; a through plane conductivity in a range of 1.45 to 5.8 mS / cm; a tensile strength in a range of 220 to 400 kgf / cm2; and a capacity in a range of 350 to 364 mAh / g.

[0053] In an embodiment of the present disclosure, there is provided a process to prepare the dry battery electrode as disclosed herein, said process comprising the steps of: (a) mixing at least one active material selected from natural graphite, or a combination of natural graphite and synthetic graphite, at least one conductive carbon as super P, and at least one binder selected from polytetrafluoroethylene (PTFE), poly vinylidene fluoride (PVDF), or combinations thereof to obtain a powder mixture; (b) shear mixing the powder mixture at a speed in a range of 1000 to 5000 rpm, at a temperature in a range of 50 to 100°C to obtain a dough; and (c) cooling the dough to a temperature in a range of 15-30°C to obtain the electrode, wherein the electrode exhibits a peel strength in a range of 0.008 kgf to 0.5 kgf; a through plane conductivity in a range of 1.45 to 5.8 mS / cm; a tensile strength in a range of 220 to 400 kgf / cm2; and a capacity in a range of 350 to 364 mAh / g.

[0054] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein mixing is carried out at a stirring speed in a range of 1000 to 3000 rpm for a time period in a range of 10 minutes to 3 hours.

[0055] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein cooling the dough to a temperature in a range of 15-30°C is carried out at a stirring speed in a range of 400 to 800 rpm.

[0056] In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the electrode is calendered to obtain a film of the electrode.

[0057] In an embodiment of the present disclosure, there is provided a lithium-ion battery comprising: (a) the dry battery electrode as disclosed herein as anode; (b) a cathode; and (c) an electrolyte.

[0058] In an embodiment of the present disclosure, there is provided a lithium-ion battery comprising: (a) the dry battery electrode comprising: (i) at least one activematerial selected from natural graphite or combination of natural graphite and synthetic graphite, (ii) at least one conductive carbon Super P, and (iii) at least one fluorinated binder polytetrafluoroethylene (PTFE), wherein the active material is selected from natural graphite, silicon, synthetic graphite, expanded graphite, or combinations thereof; (b) a cathode; and (c) an electrolyte.

[0059] In an embodiment of the present disclosure, there is provided a lithium-ion battery as disclosed herein, wherein the cathode is selected from layered metal oxides.Examples

[0060] 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

[0061] The various chemicals and solvents used in the present disclosure are as follows:Active Component- Natural Graphite (N or NG), Synthetic Graphite (S or SG) Conductive material-Super PFluorinated binder- polytetrafluoroethylene (PTFE)EXAMPLE 1Characterization of the active material:

[0062] The present example provides the structural analysis and characterization of the active material to be used in the dry battery electrode.(A) X-ray diffraction (XRD) analysis

[0063] The active materials, natural graphite (NG) and synthetic graphite (SG) were analyzed for the crystalline structural identification using x-ray diffraction technique. Figure 1 shows the XRD pattern of (a) synthetic and (b) natural graphite powder samples. All the diffraction lines were found to be well indexed. In Figure 1 (a) synthetic graphite shows hexagonal close packing (HCP) structure. But in the case of natural graphite, Figure 1 (b) shows both hexagonal & rhombohedral phases [3R (101)]. There were no other impurity peaks observed in either of the XRD patterns. The rhombohedral phase present in the NG was observed to prevent exfoliation during electrochemical cycling of layered compounds such as graphite. The beneficial effect of the rhombohedral phase in the NG, the presence of defect sites and strains along the grain boundaries prevented the electrolyte cointercalation, thus reducing the irreversible capacity loss in the initial cycles.

[0064] The physical properties of the natural graphite compared with synthetic graphite were analyzed using Microtrack MRB for Particle size analysis, Microtrack MRB Bellsorb for surface area measurement, AutoTap for tap density analysis. The results have been provided in the following Table 1.Table 1(a) Particle shape and mechanical properties:

[0065] In general, natural graphite (NG) was understood to have soft and spherical particle shape (potato shape), whereas synthetic graphite (SG) was found to be random in shape and have rough surface which detrimentally affected in providing good adherence in the anode dry battery electrode. The spherical shape and smooth surface of the natural graphite was found to provide better electrode compaction and adherence in the dry battery electrode. Spherical geometry of NG was found favorable to the diffusion of Li ions from the electrolyte surrounding the natural graphite active material in the dry battery electrode.(B) Tap density:

[0066] The tap density of natural graphite and synthetic graphite is tabulated in Table 1. It was very clearly understood that the natural graphite (NG) showed a higher tap density than the synthetic graphite because of the spherical shape of NG, though it was almost similar in particle size.(C) Surface area and Porosity:

[0067] Natural Graphite was found to have high porosity and surface area as compared to synthetic graphite as shown in table 1. Hence, electrolyte percolation and decomposition were found to be more in the natural graphite thereby high Li ion intercalation / deintercalation took place in the natural graphite. Higher intercalation and deintercalation leads to high capacity and initial coulombic efficiency (ICE).

[0068] Table 2 shows the comparison of physical properties and electrochemical performance of various commercially available synthetic graphite samples S-l to S-5 in comparison with a conventionally employed high surface area Si-C / Graphite composite (silicon / carbon-graphite composite).Table 2

[0069] The physical properties and electrochemical performance for various natural graphite samples N-l to N-7 are tabulated below in Table 3.Table 3

[0070] N-l, N-2, N-3, and N-4 are commercially available natural graphite samples

[0071] In an example, Si-C / Graphite composite (SiGE, comparative example) was used as the active material which possessed a higher surface area. The PTFE reaction was noticed to be less. However, Si-C / Graphite composite showed poor initial coulombic efficiency (ICE%) because of volume expansion of Silicon particles.

[0072] Therefore, natural graphite NG was concluded to have the desired shape, size, porosity, surface area, tap density and mechanical interlocking properties to result in high discharge capacity and ICE% so as to provide a dry battery electrode which has lower reactivity towards Li environment and also high mechanical and electrochemical stability.EXAMPLE 2:Preparation of the electrode composition

[0073] Ninety-seven percentage (97%) (w / w) of natural graphite (N-l, active material), 1% (w / w) of Super P (conductive carbon), and 1% (w / w) of polytetrafluoroethylene (PTFE, fluorinated binder) were mixed at a speed of 1800 rpm and at room temperature for 33 minutes to obtain a powder mixture. The powder mixture was shear-mixed at a speed in a range of 3000 rpm, at a temperature in a range of 70°C to obtain a dough. The dough was then cooled to a temperature in a range of 15-30°C to obtain the electrode NGE-1. Similarly, using 97% (w / w) of natural graphite samples N-2, N-3, and N-4 as active materials, along with Super P, and polytetrafluoroethylene (PTFE) were processed by the method as explained above, to obtain dry battery electrodes NGE-2, NGE-3, and NGE-4 respectively.

[0074] In still another example 97% by weight of synthetic graphite (active material), 1% by weight of Super P (conductive carbon), and 1% by weight of polytetrafluoroethylene (PTFE, binder) were mixed at 1800 rpm at room temperature, to obtain a powder mixture. The powder mixture was shear-mixed at a speed of 3000 rpm, at a temperature in of 70°C to obtain a dough. The dough was then cooled to a temperature of 19 °C to obtain the electrode SGE-1.

[0075] In yet another example, for comparative purpose, 97% by weight of Si- C / Graphite composite (active material), 1% by weight of Super P (conductive carbon), and 1% by weight of polytetrafluoroethylene (PTFE, binder) were mixed at 1800 rpm at room temperature, to obtain a powder mixture. The powder mixture was shear mixed at a speed of 3000 rpm, at a temperature of 70°C to obtain a dough. The dough was then cooled to a temperature of 15-30°C to obtain the electrode SiGE.Preparation of the dry battery electrode comprising a combination of NG and SG as active material

[0076] In an example, natural graphite sample N-l (Surface area-3.9 m2 / g) and synthetic graphite sample S-l (Surface area-0.78 m2 / g) were used as active materials for the preparation of dry battery electrodes for which electrochemical analysis was carried out.

[0077] The blend of NG and SG was obtained by the below procedure:

[0078] The required quantity of natural graphite and synthetic graphite powders are mixed using a high energy blending machine. The synthetic and natural graphite were poured one by one into a high energy mixing chamber and blended at a speed of 200 rpm for 30 mins. The blending speed was found to affect the graphite particle surface by creating new subsurface defects and disorder in the graphite. Therefore, optimum low speed of 400 rpm was required to ensure the homogeneous mixture of the two different graphite. The mixture may be mixed in reverse and forward rotation in the high energy mixer, better mixing may be achieved.

[0079] In an example, a dry battery electrode was prepared using (a) 98% (w / w) of an active material comprising: 80% (w / w) of natural graphite N-l and 20% (w / w) of synthetic graphite S-l with respect to the total weight of the active material, (b) 1% (w / w) of super P; and (c) 1% (w / w) of polytetrafluoroethylene (PTFE) were mixed to obtain a powder mixture. The powder mixture was shear-mixed at a speed of 2500 rpm, at a temperature of 70 °C to obtain a dough. The dough was then cooled to a temperature of 15-30°C to obtain the electrode NS-80.

[0080] Similarly, dry battery electrodes with varying amount of natural graphite and synthetic graphite were prepared having following compositions in Table 4.Table 4Example 3Characterization of the dry battery electrodes(A)SEM analysis:

[0081] Figure 2 (a) and (b) show the scanning electron microscopic (SEM) images of the dry battery electrode NGE-1 and Figure 2 (c) and (d) depict the SEM images of the dry battery electrode SGE-1. The uniform distribution of conductive carbon was observed over the natural graphite particles in the dry battery electrode NGE- 1 (Figure 2b) whereas agglomerated and no carbon coating was noticed on synthetic graphite particles in the dry battery electrode SGE-l(Figure 2d). The high tap density of natural graphite reflected in the electrode compaction and quality of the dry battery electrode NGE-1 (Figure 2b). Figure 2b shows better compaction of the natural graphite in NGE-1 as compared to the synthetic graphite in SGE-1 as shown in Figure 2d. (B) Conductivity measurement:

[0082] The conductivity measurements of the dry battery electrodes NGE-1 and SGE-1 were carried out through electrochemical impedance spectra (EIS) analysisand direct current internal resistance (DCIR) analysis. As shown in Figure 3, a low electrode contact resistance and direct current resistance (after the first cycle) was observed for natural graphite but in synthetic graphite high contact resistance was observed due to poor electrode compactness. The electrochemical impedance spectroscopy (EIS) and direct current internal resistance (DCIR) study confirmed the better compaction in natural graphite than synthetic dry battery electrode, as tabulated in Table 5. The dry battery electrodes exhibited a through plane conductivity in a range of 1.15 to 5.8 mS / cm. Therefore, the dry battery electrode NGE-1 exhibited a lower electrode contact resistance which was found favorable for the electrode application.Table 5Rs: Contact Resistance or Solution ResistanceDCIR: Direct contact internal resistance(C)XPS analysis:

[0083] To understand the electrode composition as well as polytetrafluoroethylene (PTFE) reactivity with Li ion for anode (SGE-1 and NGE-1) dry battery electrodes were characterized further using XPS analysis.

[0084] Figure 4 (a) shows the XPS FIs spectrum for NGE-1 electrode after 3 cycles which revealed LiF formation with binding energy of 684.86 eV. However, as shown in Figure 5 (a), LiF formation was observed in SGE-1 electrode after 3 cycles, with an intensity double that of the NGE-1. It was confirmed that in the SGE-1 dry battery electrode, more defluorination of PTFE (i.e., PTFE reactivity with Li) with Li, resulted in the formation of double the amount of Li-F. But in caseof NGE-1 electrode, the Li-F formation was found less (as shown in Figured (a)) and it led to high Li-intercalation / deintercalation. Figure 4 (b) and 5 (b) reveals the Cis spectrum of natural graphite and synthetic graphite wherein almost similar C- C binding energy was observed for both the dry electrodes which confirms the composition of both synthetic and natural graphite.(D) Mechanical properties.

[0085] The dry battery electrode NGE-1 and SGE-1 were analyzed for their mechanical properties.Peel Strength:

[0086] The peel strength of the various electrodes was measured using scotch tape method where a scotch tape was pasted over the dry battery electrode in the dimension of (25mm length and 25mm width). The prepared electrode was fixed with fixtures at top and bottom. Then a load was applied. The amount of load required to peel out the electrode was measured and tabulated in Table 6.Table 6Tensile Strength Analysis:

[0087] Dry electrode having a length (200-250mm), width (25-30mm) and thickness (100-120 pm) was used to determine the tensile strength by fixing the dry electrode in the fixtures. Then a load was applied with a cross-sectional speed of12.5mm / min. Yield strength, and Tensile strength were determined from the Load versus displacement curve. The measured tensile strength values are tabulated in Table 7.Table 7

[0088] The dry battery electrode NGE-1 exhibited a peel strength in a range of 0.008 kgf to 0.5 kgf and a tensile strength in a range of 220 to 400 kgf / cm2.

[0089] The physical properties of the anode dry electrodes were carried out for the prepared and depicted in Table 8. Table 8(E) Electrochemical performance

[0090] Electrochemical performance was evaluated for both NGE-1 and SGE-1 dry battery electrodes at 0.1 C rate with voltage between 10 mV to 2 V as shown in Figure 6. An inclined line (in the curve at 0.6 - 0.2V) was observed in voltage graph for synthetic graphite. This is due to the defluorination of PTFE fluorine with lithium ions (Li+) to form lithium fluoride and amorphous carbyne as shown in the following reaction.(CF2)n + 2n Li — > n C(amorphous) + 2n LiF - (1)

[0091] From Figure 6, a linear decrease in the voltage plot of up to 0.2V was observed. There was no voltage shift in the plot of NGE-1 dry battery electrode due to low PTFE reactivity with Li ion. An adverse PTFE reactivity (0.5V to 0.2V) was observed in the case of SGE-1, as shown in Figure 6. However, in the case of natural graphite dry battery electrode (NGE-1), PTFE reactivity was exceptionally low due to the high surface area of NG having more active sites to absorb Li ions at the surface of the natural graphite. These Li ions absorbed on the active sites participated in the intercalation and deintercalation. Figure 6 showed that synthetic (SGE-1) and natural graphite (NGE-1) dry battery electrodes delivered an initial discharge capacity of 340.5 and 360.1 mAh / g respectively, with an initial coulombic efficiency (ICE) of 81.3% for SGE-1 and 90.7% for NGE-1 (Bar chart as shown in Figure 7).

[0092] PTFE reactivity was found to be very less in natural graphite (NG) dry battery electrode NGE-1 which could be attributed to one of the following reasons:(a) increased surface area of NG associated with the rounded edges;(b) absence of exfoliation due to the presence of the dual phase crystal structure of the NG (rhombohedral phase) with defects in the grain boundaries;(c) the swelling nature of NG which prevented the breakage of PTFE fibrils during the cycling;(d) better particle to particle contacts in the NG dry battery electrode;(e) surface defects of NG which supported the high reversibility of Li ions; and(f) reduced pore volume of NG.

[0093] In synthetic graphite dry battery electrode (SGE-1), poor electrode compaction and low surface area was observed leading to higher delithiation.

[0094] The enhanced capacity and coulombic efficiency of natural graphite dry battery electrode NGE-1 was attributed to the high Li ion transport kinetics during lithiation and delithiation. These results were in alignment with the cycle performance studies of natural and synthetic graphite. Figure 9 depicts electrochemical cycle life performance comparison for natural and synthetic graphite. From the cycle life performance data, it was understood that the natural graphite had an improved capacity retention over that of the synthetic graphite.Electrochemical performance of the dry battery electrode comprising a combination of NG and SG as active material

[0095] The capacity and initial coulombic efficiency (ICE) of the electrode samples is tabulated in Table 9. The capacity and ICE were higher for the dry battery electrode NS-80 having 20% of synthetic graphite with 80% of natural graphite due to high reversible capacity. On the other hand, the dry battery electrode NS-50 comprising 50% synthetic graphite and 50% natural graphite showed comparatively decreased capacity and ICE due to high irreversible capacity loss. NS-80 electrode was expected to have a much higher surface area and higher ICE with enhanced capacity than NS-50 electrode. However, the dry battery electrode NS-80 showed only a small enhancement compared to that of the dry battery electrode NS-50 due to better SEI layer formation in the NS-80 cells. Figure 8 depicts the electrochemical performance of the dry battery electrodes NS-80 and NS-50.Table 9

[0096] Therefore, from the electrochemical data of the dry battery electrodes provided above, it can be concluded that the active material comprising a combination of NG and SG, where the NG is at least 50%(w / w) by weight of the total active material can overcome the limitations caused by the SG in the dry battery electrodes.Electrochemical cycle life study of anode dry electrode:

[0097] The electrochemical cycle stability of the dry electrode mainly depends on parameters such as porosity, pore volume, adhesion strength and materials loading of the active materials used in dry electrode. The cycle stability analysis of natural graphite, synthetic graphite and their combination of blends were investigated at 0.5C / 1C rate for 50 cycles as shown in Figure 10. The capacity retention versus number of cycles for blend materials as shown in Figure 10 (a). After 50 cycles, the capacity retention was found to be slightly more than 80% for NS- 10 electrode. However, lower capacity retention of 60% was observed after 50 cycles for NS-20 electrode. At the same time, the improved capacity retention of 92% was observed for NS-30. The random fluctuation of capacity retention and poor cycle stability (64% for 40 cycles) performance was noticed for NS-40 due to uneven SEI layer formation and poor cohesion as well as adhesion of the free-standing film. The blend NS-20 showed poor cycle life because of lower pore volume and peel strength of the dry electrode.

[0098] The pore volume of the blend materials was investigated for dry electrodes and shown in table 8. The electrochemical cycle life analysis of natural and synthetic graphite-based anode dry electrodes and their combination of blends (NS- 10 and NS-30) materials is shown in Figure 10 (b). Natural graphite, syntheticgraphite, and combinations of SG and NG showed almost similar capacity retention (78%, 80% and 80%) after 50 cycles. The NS-10 showed 80% of capacity retention due to the better adhesion of free-standing film with primer coated current collector and uniform SEI layer formation. On the other hand, the NS-30 exhibited better capacity retention of 92% after 50 cycles. The reason for this better performance was attributed to the higher pore volume (1.22 E-2 (cm2 / gm)) and better adhesion property (0.03 kgf) of the free-standing film with primer coated current collector. The high pore volume having more active sites for electrolyte decomposition led to participation of more Li+ions in the intercalation-deintercalation process. Further, the adhesion of free-standing film with primer coated current collector was very important in the electronic conductivity of the dry electrode during cycle tests. The optimum pore volume of the dry electrode provided better electrochemical cycle stability.

[0099] Therefore, it was concluded that the active material comprising a combination of NG and SG, wherein the NG is at least 30% by weight of the total active material can overcome the limitations caused by the SG in the dry battery electrodes.ADVANTAGES OF THE PRESENT DISCLOSURE

[0100] The present disclosure provides a dry battery electrode comprising an active material with higher surface area and reduced reactive sites of PTFE and Li ions.

[0101] The present disclosure provides a dry battery electrode that enables high Li- intercalation / deintercalation.

[0102] The present disclosure provides a dry battery electrode with increased surface area associated with the rounded edges and without exfoliation leading to better particle to particle contact in the dry battery electrode.

[0103] The present disclosure provides a dry battery electrode wherein natural graphite (NG) as the active material possesses a dual phase crystal structure (rhombohedral phase) with defects in the grain boundaries.

[0104] The present disclosure provides a dry battery electrode wherein the swelling nature of NG is employed to prevent the breakage of PTFE fibrils during the electrochemical cycling.

[0105] The present disclosure provides a dry battery electrode comprising an active material preferably NG with surface defects, which supported the high reversibility of Li ions. Further, the present disclosure provides a combination of NG and synthetic graphite (SG) as an active material wherein NG is at least 80% (w / w) of the total weight of the active material.

[0106] The present disclosure also provides a convenient, economical, and environment-friendly dry process for preparation of the dry battery electrode as disclosed herein.

Claims

I / We Claim:

1. A dry battery electrode comprising: a. at least one active material; b. at least one conductive carbon; and c. at least one fluorinated binder; wherein the active material is selected from natural graphite or a combination of natural graphite and synthetic graphite, wherein the combination of natural graphite and synthetic graphite has at least 30% (w / w) of natural graphite with respect to the total weight of the active material.

2. The dry battery electrode as claimed in claim 1, wherein the electrode is an anode.

3. The dry battery electrode as claimed in claim 1, wherein the conductive carbon is selected from super P, ketjen black, amorphous carbon, KS6L, graphene, graphene oxide, carbon black, or combinations thereof.

4. The dry battery electrode as claimed in claim 1, wherein the fluorinated binder is a fibrillating binder or non-fibrillating binder.

5. The dry battery electrode as claimed in claim 1, wherein the fluorinated binder is selected from of polytetrafluoroethylene (PTFE), fluoroethylene vinyl ether (FEVE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), or combinations thereof.

6. The dry battery electrode as claimed in claim 1, wherein the fluorinated binder is selected from polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or combinations thereof.

7. The dry battery electrode as claimed in claim 1, wherein the active material is in a weight range of 97 to 98% with respect to total weight of the electrode; the conductive carbon is in a weight range of 0.5 to 1% with respect to total weight of the electrode; and the binder is in a weight range of 0.5 to 2% with respect to total weight of the electrode.

8. The dry battery electrode as claimed in claim 1, wherein the electrode exhibits a peel strength in a range of 0.008 kgf to 0.5 kgf; a through plane conductivityin a range of 1.45 to 5.8 mS / cm; a tensile strength in a range of 220 to 400 kgf / cm2; and a capacity in a range of 350 to 364 mAh / g.

9. A process to prepare the dry battery electrode as claimed in claim 1, said process comprising the steps of: i) mixing at least one active material, at least one conductive carbon, and at least one fluorinated binder to obtain a powder mixture; ii) shear mixing the powder mixture at a speed in a range of 1000 to 5000 rpm, at a temperature in a range of 50 to 100°C to obtain a dough; and iii) cooling the dough to a temperature in a range of 15-30°C to obtain the electrode; wherein the electrode exhibits a peel strength in a range of 0.008 kgf to 0.5 kgf; a through plane conductivity in a range of 1.45 to 5.8 mS / cm; a tensile strength in a range of 220 to 400 kgf / cm2; and a capacity in a range of 350 to 364 mAh / g.

10. The process as claimed in claim 8, wherein mixing is carried out at a stirring speed in a range of 1000 to 3000 rpm for a time period in a range of 10 minutes to 3 hours.

11. The process as claimed in claim 8, wherein cooling the dough to a temperature in a range of 15-30°C is carried out at a stirring speed in a range of 400 to 800 rpm.

12. The process as claimed in claim 8, wherein the electrode is calendered to obtain a film of the electrode.

13. A lithium-ion battery comprising: a. the dry battery electrode as claimed in claim 1 as anode; b. a cathode; and c. an electrolyte.

14. The battery as claimed in claim 12, wherein the cathode is selected from layered metal oxides.

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