Description:FIELD OF THE INVENTION
The present invention pertains to a composite electrode material for battery applications. More specifically, the present invention pertains to a composite electrode material comprising sodium vanadium fluorophosphates and a modified carbon black and a process for the preparation of the composite electrode material.

BACKGROUND OF THE INVENTION
Sodium-ion batteries (SIBs) have been intensively explored as one of the most promising power sources for electrical energy storage as an alternate for lithium-ion batteries. Lithium is in hot demand due to rapidly growing production of electric vehicles that use lithium-ion batteries, but there is a global supply shortage of Li metal. Compared to the Li cost, availability and supply chains, Na availability and the cost of mining is lesser.

Developing sodium-ion battery technology is still immature because of the inherent size of Na (1.02 Å), which is bigger than Li (0.72 Å). The components of the sodium-ion battery include the cathode, anode, current collectors, electrolyte, and separator. Each component contributes to the overall working of the SIBs. Although all the components contributes to the overall cell performance, cathode is very important, and it is highly desirable to possess high voltage, capacity and cyclic stability. In this line, materials such as layered transition metal oxides, tunnel type oxide materials, sulphates, polyanion compounds, phosphates, pyrophosphates, Prussian blue analogues, etc. have been reported. Polyanion compounds especially phosphates with P-O bonds which are stronger are known to have very robust structure which will not undergo any structural change during charging and discharging. Sodium vanadium fluorophosphates possess high voltage as well as capacity. Sodium (Na) Super Ionic Conductor (NASICON) structured Sodium vanadium fluorophosphates has poor electronic conductivity.

WO2020174487A1 discloses a microwave assisted sol-gel method for preparing in-situ carbon coated electrode material comprising an alkali ion transition metal phosphate or alkali ion transition metal fluorophosphate of the general formula: [A3M2(PO4)3] and [A3M2(PO4)2F3] wherein ‘A’ is an alkali ion selected from Li, Na and K; M is a transition metal selected from Fe, Ni, Co, V, Mn, Ti, and Cr. The process however involves high temperature calcination at 600-800 ? which is energy and time consuming.

Therefore, there is a room for exploration of NASICON structured Sodium vanadium fluorophosphate materials in electrode applications if the electronic conductivity of the material could be improved. Further, a less energy and time consuming process is required for the preparation of these materials.

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SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention.

The present invention provides a composite electrode material comprising:
i. 80 to 98 weight % of sodium vanadium fluorophosphates; and
ii. 2 to 20 weight % of a modified carbon black,
wherein the modified carbon black is an acid treated carbon black.

The present invention also provides a process for the preparation of a composite electrode material comprises:
i. adding a precursor of sodium, a precursor of fluorine, a precursor of vanadium, a precursor of phosphate,oxalic acid and NaCl in deionized water to obtain a solution;
ii. adding a modified carbon black to the solution of step i), followed by stirring and transferring the solution to a quarts/PTFE vial;
iii. heating the quarts/PTFE vial containing the solution to obtain a product; and
iv. washing the product with a solvent, followed by drying the product to obtain the composite electrode material of sodium vanadium fluorophosphate-modified carbon black (NVPOF-MCB).

OBJECTIVES OF THE PRESENT INVENTION:
The main objective of the present invention is to provide a composite electrode material.

Another objective of the present invention is to provide a process for the preparation of the composite electrode material.

Another objective of the present invention is to evaluate the cyclic performance of the composite electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 depicts the scanning electron microscopy images of NVPOF-MCB composite electrode material.
Figure 2 depicts the charge-discharge graphs of NVPOF-MCB composite electrode material.
Figure 3 shows the rate capability graph of NVPOF-MCB composite electrode material prepared through microwave synthesis.
Figure 4 shows the cycling ability of NVPOF-MCB composite electrode material prepared through microwave synthesis up to 1100 cycles at 1C rate.
Figure 5 depicts the galvanostatic charge-discharge curves of NVPOF-MCB composite electrode material prepared through hydrothermal synthesis in different C-rates.
Figure 6 depicts the rate capability graph for NVPOF-MCB composite electrode material prepared through hydrothermal synthesis.
Figure 7 depicts (a) Charge-discharge profile of NVPOF-Bare same at different rates 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C (b) Rate performance of NVPOF-Bare same at rates 0.2C, 0.5C, 1C, 2C, 3C, 5C, 10C.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, process, and examples provided herein are illustrative only and not intended to be limiting.

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.

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”.

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.

The term “optionally,” as used in the present invention, means that a feature or element described as ‘optional’ within the context of the invention is not required for the invention to function as claimed. It indicates that the presence or absence of the described feature or element does not alter the fundamental operation or scope of the invention, and its inclusion or exclusion may be determined based on the specific requirements or preferences of a practitioner skilled in the art or the application in question.

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 process and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred process and materials are now described. All publications mentioned herein are incorporated herein by reference.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The present invention provides a composite electrode material comprising:
i. 80 to 98 weight % of sodium vanadium fluorophosphate; and
ii. 2 -20 weight % of a modified carbon black,
wherein the modified carbon black is an acid treated carbon black.

In an embodiment of present invention, the sodium vanadium fluorophosphates is defined by a formula Na3V2(PO4)2O3-xFx, wherein x is in a range between 0 and 3.

In an embodiment of present invention, the sodium vanadium fluorophosphates is Na3V2(PO4)2OF2.

In an embodiment of the present invention, the carbon black is selected from a group comprising super P or acetylene black; the acid is selected from a group comprising H2SO4, HCl, and HNO3 and a mixture thereof.

The present invention provides a process for the preparation of a composite electrode material comprises:
i. adding a precursor of sodium, a precursor of fluorine, a precursor of vanadium, a precursor of phosphate, oxalic acid and NaCl in deionized water to obtain a solution;
ii. adding a modified carbon black to the solution of step i), followed by stirring and transferring the solution to a quarts/PTFE vial;
iii. heating the quarts/PTFE vial containing the solution to obtain a product; and
iv. washing the product with a solvent, followed by drying the product to obtain the composite electrode material of sodium vanadium fluorophosphate-modified carbon black (NVPOF-MCB).
In an embodiment of the present invention, the precursor of sodium and fluorine is selected from a group comprising sodium carbonate, sodium hydroxide, sodium dihydrogen phosphate, sodium oxalate, sodium fluoride, sodium citrate, sodium phosphate, disodium hydrogen phosphate, sodium chloride, sodium dodecylbenzene sulfonate, sodium sulfate, sodium nitrate preferably sodium fluoride.

The precursor of vanadium is selected from a group comprising ammonium metavanadate, vanadium pentoxide, vanadyl acetylacetonate, vanadyl sulfate, vanadium dioxide, and vanadium trioxide. Preferably, the precursor of vanadium (V) is vanadium pentoxide.

The precursor of phosphate is selected from a group comprising monoammonium phosphate, diammonium phosphate, phosphoric acid, monosodium phosphate, ammonium phosphate, disodium phosphate and ammonium dihydrogen phosphate. Preferably, the precursor of phosphate is ammonium dihydrogen phosphate (NH4H2PO4).

In an embodiment of the present invention, the precursor of sodium and fluorine is sodium fluoride, the precursor of vanadium is vanadium pentoxide, and the precursor of phosphate is ammonium dihydrogen phosphate (NH4H2PO4).

In an embodiment of the present invention, the precursor of sodium, the precursor of fluorine, the precursor of vanadium, the precursor of phosphate, oxalic acid and NaCl are added in stoichiometric amount according to the predetermined formula sodium vanadium fluorophosphate.

In an embodiment of the present invention, NaCl is used in the process for the preparation of a composite electrode material as morphology control agent and surface directing agent for crystal facet engineering of sodium vanadium fluorophosphate. The prominent facet is along [110] direction. The Na ion diffusion along [110] or [1-10] is higher compared to other directions.

In an embodiment of the present invention, the modified carbon black is added in a range of 1 to 20 weight %.

In an embodiment of the present invention, the modified carbon black is added in 10 weight %.

In an embodiment of the present invention, the stirring is performed for 15 to 120 minutes.

In a preferred embodiment of the present invention, the stirring is performed for 60 minutes.

In an embodiment of the present invention, the solution is heated at a temperature in a range of 180 to 200 ? for 1 to 24 hrs either by subjecting the solution to microwave radiation or in a hydrothermal set up in a furnace.

In an embodiment of the present invention, the solution is heated at a temperature of 200 ? for 1 h by subjecting the solution to microwave radiation.

In an embodiment of the present invention, the solution is heated at a temperature of 180 ? for 24 h in a furnace.

In an embodiment of the present invention, the solvent is selected from a group comprising water, ethanol, dimethyl sulfoxide, dimethyl formamide ethylene glycol and a mixture thereof.

In an embodiment of the present invention, the product is dried at temperature of 80 to 150?, preferably at 120 ?.

In an embodiment of the present invention, the modified carbon black is prepared by heating a carbon black in an acid selected from a group comprising H2SO4, HCl, and HNO3; followed by washing with a solvent.

In an embodiment of the present invention, the modified carbon black prepared has improved dispersibility in the water.

In an embodiment of the present invention, the carbon black is heated with the acid at a temperature in a range of 70 to 130? for 15 mins to 2h.

In an embodiment of the present invention, the carbon black is heated with concentrated HNO3 at a temperature of 120 ? for 1 h.

In an embodiment of the present invention, the solvent is selected from a group comprising deionized water, ethanol, dimethyl sulfoxide, dimethyl formamide, ethylene glycol, and a mixture thereof.

In an embodiment of the present invention, the composite electrode material shows a cycling ability up to 1100 cycles at 1C rate.

In an embodiment of the present invention, the composite electrode material shows an excellent cycling performance of 97% retention at 1C rate after 1100 cycles.

EXAMPLES:
The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

EXAMPLE 1: Preparation of modified carbon black
Modified carbon black (MCB) was prepared by heating certain amount of carbon black (1 to 10gm) with concentrated HNO3 (5 to 200ml) at 120 ? for 1h. It was washed repeatedly with deionized water and finally washed with ethanol.

EXAMPLE 2: Microwave method for the preparation of NVPOF-MCB composite electrode material
1mM V2O5, 4mM NaF and 2mM NH4H2PO4 and 3mM C2H2O4 and 0.2mM NaCl was added in to 60ml of DI H2O and was completely dissolved. When the solution became dark blue in color, 10% of modified carbon black was added and the solution was kept stirring for 15 mins. The solution was then transferred into quartz/PTFE vial and sealed. The sealed quarts/PTFE vial was kept in a multi wave microwave synthesizer and subjected to microwave synthesis at 200 ? for 1 hour. The obtained sample was washed with water and dried at 120 ? overnight. The SEM images of NVPOF-MCB composite electrode material prepared are shown in Figure 1

Ingredient Amount (in g) Percentage in final product
Oxalic Acid 22.68 Nil
V2O5 10.91 2M
NH4H2PO4 13.8 2M
NaF 10.10 3M of Na and 2M of Fluorine
NaCl 1.40 Nil
MCB 1.2 1 to 1.2gm

Half-cell fabrication using NVPOF-MCB composite electrode material prepared using microwave method
The synthesized NVPOF-MCB is subjected to half-cell fabrication with 1M NaPF6 in Diglyme electrolyte. (Half-cell is fabricated with NVPOF-MCB coated Al foil as cathode, Na foil served as anode, glass microfiber paper as separator in 1M NaPF6 in diglyme as electrolyte) Figure 2. depicts the charge-discharge graphs of NVPOF-MCB composite electrode material. The profile has two plateaus at 4V and 3.6 V corresponding to sodium de-intercalation from Na(1) and Na(2) position in the NVPOF crystal. A capacity close to 120 mAh/g was obtained at 0.1C rate which is close to the theoretical capacity of 128 mAh/g. Figure 3 shows the rate capability graph of NVPOF-MCB composite electrode material, the discharge capacity of 119, 118, 117, 116, 114, 112, 108 and 102 mAh/g was obtained at 0.1, 0.2, 0.5, 1, 2, 3, 5 and 10 C rate. From the above results the rate capability is found to be good and the change in polarization voltage between the charge and discharge curves is found to be minimal.

Figure 4 shows the cycling ability up to 1100 cycles at 1C rate for NVPOF-MCB composite electrode material. It showed an excellent cycling performance of 97% retention at 1C rate after 1100 cycles.

EXAMPLE 3: Hydrothermal method for the preparation of NVPOF-MCB composite electrode material
NVPOF-MCB composite electrode material was prepared by same process as given in Example 2 except the heating is carried out by hydrothermal method at 180 ? for 24hrs to check it is commercially viability.

Half-cell fabrication using NVPOF-MCB composite electrode material prepared using hydrothermal method
Figure 5 depicts the galvanostatic charge-discharge (GCD) curves of NVPOF-MCB composite electrode material in different C-rates, Figure 6 shows its rate capability graph. The GCD profile matches well with the samples prepared by microwave method. The discharge capacity of 114, 113, 112, 109 and 107mAh/g was obtained at 0.2, 0.5, 1, 2 and 3C rates. Which is slightly lesser than the samples prepared by microwave method. Nevertheless, the capacity is good. Cyclability is also comparably good. From the charge-discharge profile of NVPOF-Bare (Figure 7a) and the rate performance of NVPOF-Bare at different rates 0.2C, 0.5C, 1C, 2C, 3C, 5C,10C (figure 7b) it can be inferred that the composite electrode material consisting of NVPOF and MCB shows improved capacity and cyclability in comparison to NVPOF-Bare. , Claims:1. A composite electrode material comprising:
i. 80 to 98 weight % of sodium vanadium fluorophosphate; and
ii. 2 to 20 weight % of a modified carbon black,
wherein the modified carbon black is an acid treated carbon black.

2. The composite electrode material as claimed in claim 1, wherein the sodium vanadium fluorophosphate is defined by a formula Na3V2(PO4)2O3-xFx, wherein x has a value in a range between 0 and 3.

3. The composite electrode material as claimed in claim 1, wherein the sodium vanadium fluorophosphate is Na3V2(PO4)2OF2.

4. The composite electrode material as claimed in claim 1, wherein the carbon black is selected from a group comprising super P or acetylene black; the acid is selected from a group comprising H2SO4, HCl, HNO3 and a mixture thereof.

5. A process for the preparation of a composite electrode material comprises:
i. adding a precursor of sodium, a precursor of fluorine, a precursor of vanadium, a precursor of phosphate, oxalic acid and NaCl in deionized water to obtain a solution;
ii. adding a modified carbon black to the solution of step i), followed by stirring and transferring the solution to a quarts/PTFE vial;
iii. heating the quarts/PTFE vial containing the solution to obtain a product; and
iv. washing the product with a solvent, followed by drying the product to obtain the composite electrode material of sodium vanadium fluorophosphate-modified carbon black (NVPOF-MCB).

6. The process as claimed in claim 5, wherein the precursor of sodium and fluorine is selected from a group comprising sodium carbonate, sodium hydroxide, sodium dihydrogen phosphate, sodium oxalate, sodium fluoride, sodium citrate, sodium phosphate, disodium hydrogen phosphate, sodium chloride, sodium dodecylbenzene sulfonate, sodium sulfate, sodium nitrate preferably sodium fluoride; the precursor of vanadium is selected from a group comprising ammonium metavanadate, vanadium pentoxide, vanadyl acetylacetonate, vanadyl sulfate, vanadium dioxide, and vanadium trioxide; the precursor of phosphate is selected from a group comprising monoammonium phosphate, diammonium phosphate, phosphoric acid, monosodium phosphate, ammonium phosphate, disodium phosphate and ammonium dihydrogen phosphate.

7. The process as claimed in claim 5, wherein the solution is heated at a temperature in a range of 180 to 200 ? for 1 to 24 hrs either by subjecting the solution to microwave radiation or in a furnace.

8. The process as claimed in claim 7, wherein the solution is heated at a temperature of 200 ? for 1 h by subjecting the solution to microwave radiation.

9. The process as claimed in claim 7, wherein the solution is heated at a temperature of 180 to 200 ? for 1 to 24 hrs in a furnace.

10. The process as claimed in claim 5, wherein the modified carbon black is added in a range of 1 to 20 weight %; the stirring is performed for 15 to 120 minutes; the solvent is selected from a group comprising water, ethanol dimethyl sulfoxide, dimethyl formamide ethylene glycol and a mixture thereof; the sample is dried at temperature of 80 to 150 ?.

11. The process as claimed in claim 5, wherein the modified carbon black is prepared by heating a carbon black in an acid selected from a group comprising H2SO4, HCl, and HNO3; followed by washing with a solvent.

12. The process as claimed in claim 11, wherein the carbon black is selected from a group comprising super P and acetylene black; the solvent is selected from a group comprising, water, ethanol dimethyl sulfoxide, dimethyl formamide ethylene glycol and a mixture thereof; the carbon black is heated with the acid at a temperature in a range of 70 to 130 ? for 15 mins to 2 h.

13. The process as claimed in claim 11, wherein the carbon black is heated with concentrated HNO3 at a temperature of 120 ? for 1 h.