Description:FIELD OF THE INVENTION
The present invention relates to a sodium ion battery. More specifically, the present invention relates to an Al-doped cathode and a method of preparation of the Al-doped cathode material. The invention also relates to a process for organic surfactant-based carbon coating of anode. The Al-doped cathode and the organic surfactant-based carbon composite coated anode are utilized in a sodium ion battery for improved electrochemical performance and cyclic stability and hence improved life of the sodium ion battery.

BACKGROUND OF THE INVENTION
Sodium manganese hexa cyano ferrate based cathode material commonly used in sodium-ion batteries due to its high voltage and energy density. However, its cycling stability is limited due to its multiple phase transitions between sodium intercalation and de-intercalation. Further lattice distortion caused by the Jhon teller effects of Mn3+ resulted in less cycling stability of sodium manganese hexa cyano ferrate.

US9546097 discloses synthesis of iron hexa cyano ferrate by first solution containing ferrocyanide source and second solution containing Fe (II) source in the inert atmosphere. US9531003 discloses synthesis of sodium iron (II) hexa cyano ferrate (II) as a battery electrode. US11056689 disclosed the method of synthesis of transition metal cyanide coordination compounds having enhanced reaction potential with methanol and without water. US20140220392 discloses Prussian blue based anode for aqueous electrolyte based batteries. CN114262351A discloses methane sulfonic acid (ligand) based Prussian blue positive electrode material for battery. CN111943228A discloses the synthesis method for transition metal based Prussian blue type sodium ion battery anode material. CN106784696A discloses the method of carbon coating twice over the active material with the use of ball mill of sodium titanium phosphate and carbon black. CN106981641A discloses the kind of carbon coating sodium titanium manganese phosphate using ball mill.

Yun Tang et al. [Yun Tang et al. “High-Performance Manganese Hexacyanoferrate with Cubic Structure as Superior Cathode Material for Sodium-Ion Batteries” Advanced Functional Materials, 2020, 30,1908754] discloses a synthesis method of sodium manganese hexa cyano ferrate with cubic structure. Jinke Li et al. [Jinke Li et al. “Tin modification of sodium manganese hexacyanoferrate as a superior cathode material for sodium ion batteries” Electrochimica Acta, 2020, 342,135928] used tin as a dopant for modification of sodium manganese hexa cyano ferrate to improve the cycling stability of the electrode. Dong-Wook Han et al. [Dong-Wook Han et al. “Aluminum Manganese Oxides with Mixed Crystal Structure: High-Energy-Density Cathodes for Rechargeable Sodium Batteries” ChemSusChem, 2014, 7, 1870 - 1875] discloses the incorporation of aluminium in sodium manganese oxide improved the discharge capacity as well as stability of the electrode and further revealed that the stability improvement due to formation of Al-O bond.

However, there is still a requirement of efficient cathode and anode to improve the electrochemical performance and cyclic stability of sodium ion batteries.

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. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a sodium ion battery comprising:
i. an aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni and wherein the aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6] exhibit cubic phase;
ii. a carbon composite coated anode of sodium titanium phosphate; and
iii. an electrolyte selected from water in salt electrolyte or organic electrolyte.
The present invention also provides an Al-doped cathode of general formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni, and wherein the Al is in 0.07 to 7 weight percentage. Further present invention provides preparation of cubic phase Al-doped cathode of general formula NaxMy[Fe(CN)6].

The present invention also provides a process for preparing a sodium ion battery, said process comprising steps of:
i. preparing an Al-doped cathode of general formula NaxMy[Fe(CN)6] using aluminium sulphate feed precursor;
ii. preparing a carbon composite coated anode of sodium titanium phosphate using sodium based organic surfactant followed by its decomposition process;
iii. arranging the Al-doped cathode of general formula NaxMy[Fe(CN)6] and the carbon composite coated anode of sodium titanium phosphate in a manner suitable to the structural layout of sodium ion battery; and
iv. adding a suitable electrolyte.

OBJECTIVES OF THE PRESENT INVENTION
Primary objective of the present invention is to provide a sodium ion battery with improved electrochemical performance and cyclic stability.

Another main objective of the present invention is to provide improvement in electrochemical performance and life cycle of sodium ion battery using aluminium doped sodium manganese hexa cyano ferrate (Al-SMHCF) cathode and carbon composite coated sodium titanium phosphate.

Another objective of the present invention is to provide an Al-doped cathode of formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni, for sodium ion battery.

Another objective of the present invention is to synthesize cubic phase sodium manganese hexa cyano ferrate by doping of aluminium and prevent the monoclinic phase formation.

Another main objective of the present invention is to provide a process for coating carbon composite over sodium titanium phosphate anode material using organic surfactant (Sodium Ligno Sulphonate) and organic binder and again converting the surfactant and binder into one type of carbon by carbonization.

Another objective of the present invention is to provide sodium ion battery using aluminium doped sodium manganese hexa cyano ferrate (Al-SMHCF) as cathode and carbon composite coated sodium titanium phosphate as an anode and in aqueous or organic based sodium I bis(fluoro sufonyl imide)[NaFSI] salt electrolyte by changing of solvent.

Another objective of the present invention is to provide sodium ion battery using aluminium doped sodium iron hexa cyano ferrate (Al-SFHCF) as cathode and carbon composite coated sodium titanium phosphate as an anode in an organic based electrolyte which contains sodium trifluoro methane sulfonate (NaOTF) salt in organic solvent (tetra ethylene glycol dimethyl ether)

BRIEF DESCRIPTION OF THE DRAWINGS:
The features, aspects, and advantages of the present invention will become better understood when the detailed description is read with reference to the accompanying drawings, wherein:

Figure 1 depicts the Energy Dispersive X-Ray Analysis (EDEX) spectrum from the selected area of sodium manganese hexa cyano ferrate sample.
Figure 2 depicts the Energy Dispersive X-Ray Analysis (EDEX) spectrum from the selected area of aluminium (Al) doped sodium manganese hexa cyano ferrate.
Figure 3 depicts the morphology of sodium manganese hexa cyano ferrate (SMHCF).
Figure 4 depicts the morphology of Al doped sodium manganese hexa cyano ferrate.
Figure 5 depicts the X-Ray Diffraction (XRD) peaks of sodium manganese hexa cyano ferrate and aluminium (Al) doped sodium manganese hexa cyano ferrate prepared using 0.05 M aluminium feed precursor.
Figure 6 depicts the XRD peaks for Al-SMHCF prepared using 0.025 M and 0.05 M aluminium feed precursor.
Figure 7 depicts the XRD peaks for Al-SMHCF prepared using 0.1 M aluminium feed precursor.
Figure 8 depicts the XRD peaks for Al-SMHCF prepared using 0.2 M aluminium feed precursor.
Figure 9 depicts the XPS Carbon (C) peaks for Al doped sodium manganese hexa cyano ferrate.
Figure 10 depicts the XPS aluminium (Al) peaks for Al doped sodium manganese hexa cyano ferrate.
Figure11 depicts the half-cell electro chemical performance evaluation of with or without Al doped sodium manganese hexa cyano ferrate.
Figure12 depicts the half-cell charge - discharge performance evaluation of with or without Al doped sodium manganese hexa cyano ferrate.
Figure13 depicts the scanning electron microscopy (SEM) Image and EDEX of with or without carbon composite coated sodium titanium phosphate.
Figure14 depicts the aluminium concentration optimization in Al doped sodium manganese hexa cyano ferrate vs sodium titanium phosphate anode (Full Cell) – 50 mV scan rate.
Figure 15 depicts the full cell cycle life evaluation at various discharge rates.
Figure 16 depicts the cyclic volta metric evaluation of full cell (Al doped sodium manganese hexa cyano ferrate cathode vs carbon composite coated sodium titanium phosphate anode and 35M NaFSI/water as solvent with different scan rate as 50mV, 30mV, 20mV, 10mV, 15mV, 1mV.
Figure 17 depicts the XRD peaks of aluminium doped sodium iron hexa cyano ferrate (Al-SFHCF) and aluminium doped sodium iron manganese hexa cyano ferrate.
Figure 18 depicts the cyclic voltametric evaluation of full cell (Al doped sodium iron hexa cyano ferrate (Al-SFHCF) cathode vs carbon composite coated sodium titanium phosphate anode and 1M NaOTF salt in tetraethylene glycol dimethyl ether solvent with different scan rate of 5mV, 4mV, 3mV, 2mV, 1mV and 0.1mV.
Figure 19 depicts the capacity vs voltage plot for Al-SFHCF Vs Na/Na+ at various discharge current rates.
Figure 20 depicts the XPS peaks of aluminium doped sodium manganese hexa cyano ferrate cathode after 500 cycling.

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, methods, 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.

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.

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.

According to the present invention cathode comprises aluminium doped sodium manganese hexa cyanoferrate with conductive carbon black, PVDF binder and N-methyl pyrrolidone (NMP) solvent. The cathode is coated with aluminium foil current collector.

According to the present invention anode comprises carbon composite coated sodium titanium phosphate, mixed with conductive carbon black, PVDF binder and N-methyl pyrrolidone (NMP) solvent. The anode is coated with aluminium foil current collector.

According to an aspect, the present invention discloses a process for doping of sodium based Prussian blue analogy which is termed in general formula of NaxMy[M*(CN)6] in which M is a transition metal element selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn, and M* is selected from Fe, Mn, Cr, or Cu. The Al-doped sodium based Prussian blue analogy is prepared from aluminium sulphate precursor.

According to another aspect, the present invention provides doping of aluminium in sodium based Prussian blue analogy selected from one of sodium manganese hexa cyano ferrate, sodium iron hexa cyano ferrate, sodium cobalt hexa cyano ferrate, sodium copper hexa cyano ferrate, sodium chromate hexa cyano ferrate or sodium nickel hexa cyano ferrate.

According to an aspect, the present invention provides a sodium ion battery comprises:
i. an aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni, and wherein the aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6] exhibit cubic phase;
ii. a carbon composite coated anode of sodium titanium phosphate; and
iii. an electrolyte selected from water in salt electrolyte or organic electrolyte.

According to another aspect of the present invention, the cathode is selected from the group consisting of Al-doped sodium manganese hexa cyano ferrate (Al-SMHCF), Al-doped sodium ferrate hexa cyano ferrate (Al-SFHCF), Al-doped sodium cobalt hexa cyano ferrate, Al-doped sodium copper hexa cyano ferrate, Al-doped sodium chromate hexa cyano ferrate, and Al-doped sodium nickel hexa cyano ferrate.

According to another aspect of the present invention, the Al-doped cathode is Al-doped sodium manganese hexa cyano ferrate.

According to another aspect of the present invention, the Al-doped sodium manganese hexa cyano ferrate exists in cubic phase.

According to another aspect of the present invention, aluminium content in the Al-doped sodium manganese hexa cyano ferrate is in a range of 0.07 to 7 weight %.

According to an aspect of the present invention, the cathode is prepared from a cathode slurry comprising Al-doped sodium manganese hexa cyanoferrate, conductive carbon black, PVDF binder and N-methyl pyrrolidone (NMP) solvent.

According to another aspect of the present invention, the carbon composite coated anode is prepared from an anode slurry comprising carbon composite coated sodium titanium phosphate, conductive carbon black, PVDF binder and N-methyl pyrrolidone (NMP) solvent.

According to another aspect of the present invention, the electrolyte is selected from the group comprising 35 molar sodium bis(fluorosulfonyl) imide (NaFSI) as water in salt electrolyte and 1 molar NaFSI in tetra ethylene glycol dimethyl ether solvent, and 1 molar sodium trifluoromethane sulfonate in tetraethylene glycol dimethyl ether solvent (1M NaOTF/TEGDME).

According to an aspect, the present invention provides an Al-doped cathode of general formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni, and the Al is in 0.07 to 7 weight percentage.

According to another aspect of the present invention, the cathode is Al-doped sodium manganese hexa cyano ferrate or Al-doped sodium iron hexa cyano ferrate.

According to another aspect of the present invention, the aluminum doped sodium manganese hexa cyano ferrate is cubic phase structure. The sodium manganese hexa cyano ferrate exists in monoclinic, cubic, and tetragonal structure. According to the present invention, doping of aluminium in sodium manganese hexa cyano ferrate allow it to retain its cubic phase and prevents multiple phase formation thereby improves the stability of the cathode by minimizing structural deformation

According to an aspect, the present invention provides a process for preparing a sodium ion battery, said process comprising steps of:
i. preparing an Al-doped cathode of general formula NaxMy[Fe(CN)6] using aluminium sulphate feed precursor;
ii. preparing a carbon composite coated anode of sodium titanium phosphate using sodium based organic surfactant followed by its decomposition process;
iii. arranging the Al-doped cathode of general formula NaxMy[Fe(CN)6] and the carbon composite coated anode of sodium titanium phosphate in a manner suitable to the structural layout of sodium ion battery; and
iv. adding a suitable electrolyte.

According to another aspect of the present invention, the process for preparing Al-doped cathode of general formula NaxMy[Fe(CN)6] is a co-precipitation method, and wherein said co-precipitation method comprises:
i. dissolving a sulphate metal precursor, aluminium sulphate, and sodium citrate in water to form a solution A wherein molar ratio of the metal precursor to aluminium sulphate is in the range of 0.25 to 2 and molar ratio of sodium citrate to aluminium sulphate is in the range of 0.3 to 2.4;
ii. dissolving sodium ferro cyanide in water to form a solution B;
iii. dissolving sodium nitrate in water to form a solution C;
iv. adding the solution A and the solution B with the volumetric flow rate ratio of 1:1 to the solution C to form a solution D, followed by stirring for 8 to16 hours;
v. filtering the solution D to separate a precipitate using vacuum filtration;
vi. washing the precipitate with distilled water and ethanol; and
vii. drying the precipitate to obtain Al-doped cathode of general formula NaxMy[Fe(CN)6].

According to another aspect of the present invention, the sulphate based metal precursor is selected from a group comprising manganese sulphate, copper sulphate, ferrous sulphate, cobalt sulphate, nickel sulphate, or mixture thereof.

According to another aspect of the present invention, the aluminium sulphate in water is in a concentration of 0.025 M to 0.2 M.

According to another aspect of the present invention, the stirring in step iv) of the process for preparing Al-doped cathode of general formula NaxMy[Fe(CN)6] is carried out for 12 hours.

According to another aspect of the present invention, the aluminium content in the Al-doped sodium manganese hexa cyano ferrate is in a range of 0.07 to 7 weight percent (wt. %).

According to an aspect, the present invention provides a process for preparing carbon composite coated sodium titanium phosphate comprises:
i. mixing an organic binder and an organic surfactant in distilled water to form a mixture;
ii. adding a conductive carbon to the mixture and sonicating the mixture for 15 to 30 minutes;
iii. adding sodium titanium phosphate to the mixture and sonicating the mixture for 15 to 30 minutes;
iv. drying the mixture in vacuum at 100 to 150 ºC at 0.3 atm pressure for 24
hours to obtain a dried mixture;
v. carbonizing the dried mixture in inert atmosphere at 600 ºC to 800 ºC for 4 hours; and
vi. cooling to room temperature to obtain the carbon composite coated sodium titanium phosphate.

According to another aspect of the present invention, the organic binder is selected from the group of carbohydrates, sugar, monosaccharide, disaccharides, polysaccharides or mixture thereof; wherein monosaccharide is selected from glucose, fructose, ribose or mixture thereof; wherein disaccharide is selected from sucrose, maltose, lactose or mixture thereof; wherein polysaccharides selected from starch, cellulose, glycogen or mixture thereof.

According to another aspect of the present invention, the organic surfactant is selected from ligno sulphonate, sodium lingo sulphonate (Vanisperse), calcium lingo sulphonate or mixture thereof.

According to another aspect of the present invention, the conductive carbon is selected from one dimensional carbon comprises carbon nanotube, two dimensional carbon, three dimensional carbon, zero dimensional carbon comprises carbon black, amorphous carbon or mixture thereof.

According to another aspect of the present invention, the carbon nanotube is a multiwalled carbon nanotube having outer diameter in a range of 10 nm to 30 nm.

According to another aspect of the present invention, the organic binder is glucose; wherein the organic surfactant is sodium lingo sulphonate (Vanisperse); and wherein the conductive carbon is a mixture of carbon black and a multiwalled carbon nanotube having outer diameter in a range of 10 nm to 30 nm.

According to another aspect of the present invention, the organic surfactant is used for dispersion of carbon composite in solution. But it hinders the electrochemical performance of anode and affects the sodium ion battery performance. Therefore, the organic surfactant and the organic binder are converted into carbon again. Carbon coating strategy using organic surfactant improves the anode stability by reducing anode interfacial degradation.

According to another aspect of the present invention, carbonizing in step v) is performed at temperatures in a range of 600 ºC to 800 ºC for 4 hours in the presence of an inert gas selected from nitrogen or argon.

According to another aspect of the present invention, the carbonization of the organic surfactant and the organic binder to be heated up to the temperature of 800 ºC at maintained atmospheric pressure conditions in the presence of inert gas selected from nitrogen or argon.

According to one of the aspects of the present invention, the sodium ion battery comprises Al-doped sodium manganese hexa cyano ferrate cathode material, a zinc metal anode material and 35 molar sodium bis(fluorosulfonyl) imide (NaFSI) as water in salt electrolyte.

According to another aspect of the present invention, the sodium ion battery comprises various composition of aluminium doped sodium manganese hexa cyano ferrate cathode, carbon composite coated sodium titanium phosphate anode, 35 molar NaFSI as water in salt electrolyte and aluminium as a current collector used for coin cells fabrication. These coin cells are subjected for cyclic voltammeter scanning for determining performance and operating voltage window and peak current intensity of sodium ion battery and it subjected for various rate of charge discharge cycle.

According to another aspect of the present invention, the sodium ion battery comprises aluminium doped sodium manganese hexa cyano ferrate cathode, carbon composite coated sodium titanium phosphate anode material, 1 molar NaFSI in tetra ethylene glycol dimethyl ether solvent as organic electrolyte.

According to another aspect of the present invention, the Al-doped sodium manganese hexa cyano ferrate cathode performs 150 % more life than non-Al-doped sodium manganese hexa cyano ferrate cathode.

According to another aspect of the present invention, the sodium ion battery comprises aluminium doped sodium iron hexa cyano ferrate cathode, carbon composite coated sodium titanium phosphate anode material, 1 molar NaOTF in tetra ethylene glycol dimethyl ether solvent as organic electrolyte.

According to another aspect of the present invention, in-situ formation of aluminium oxy fluoride (AlOFx) in cathode during charge and discharge cycling, which minimize further cathode active species dissolution in electrolyte and hence improve the cyclic stability.

According to another aspect of the present invention infer face layer distance (d-spacing) increased for aluminium doped sodium manganese hexa cyano ferrate cathode material as compared to without doping of aluminium (1.86 Å Vs 1.80 Å).

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 Sodium manganese hexa cyano ferrate synthesis (Prior Art)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as Solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. A further 60 g of sodium nitrate measured and dissolved in 200 ml of distilled water. It was considered as solution C. Solution A is taken in Burette 1 and solution B is taken in Burette 2. Solution C is taken in Beaker. Solution A flow rate and solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hrs. After 12 hrs the stirrer was stopped, and the resultant solution subjected for vacuum filtration with using of Wattman filter paper. After filtering, the material was washed using distilled water five times. After water washing the material was washed with ethanol. After washing the material was collected and subjected for vacuum drying in oven for 24 hrs. After drying 1.9 g of material collected and the sample was analyzed in EDEX and Morphology using SEM and the results are shown in Figure1 and Figure 3.

Example: 2 Aluminium doped sodium manganese hexa cyano ferrate synthesis with 0.05 M aluminium sulfate feed precursor) (Present invention)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O),3.150 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further, 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as solution C. Solution A is taken in Burette 1 and solution B is taken in Burette 2. Solution C is taken in beaker. Solution A flow rate and solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hrs. After 12 hrs the stirrer was stopped, and the resultant solution subjected for vacuum filtration with using of Wattman filter paper. After filtering, the material was washed using distilled water five times. After water washing the material was washed with ethanol. After washing the material was collected and subjected for vacuum drying in oven for 24 hrs. After drying 1.97 g material collected and the sample was analyzed in EDEX & Morphology using SEM, Phase identification using XRD, and the results are shown in Figure 2, Figure 4, and Figure 5. XPS spectra showing carbon and aluminium peaks in the Al-doped SMHCF samples have been depicted in Figure 9 and Figure 10 respectively. From XRD, it is observed that Al-doping eliminated the multiphase and results in cubic phase formation. Further Monoclinic characteristic peak (111) that is observed in undoped sodium manganese hexa cyano ferrate has been vanished. Al doping results in cubic phase peak shift observed at lower 2 Theta indicates increased d-spacing (1.86 Å Vs 1.8 Å).

Example: 3 Aluminium doped sodium manganese hexa cyano ferrate synthesis with 0.025 M aluminium sulfate feed precursor) (Present invention)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O),1.57 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further, 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as solution C. Solution A is taken in Burette 1 and solution B is taken in Burette 2. Solution C is taken in beaker. Solution A flow rate and solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hrs. After 12 hrs the stirrer was stopped, and the resultant solution subjected for vacuum filtration with using of Wattman filter paper. After filtering, the material was washed using distilled water five times. After water washing the material was washed with ethanol. After washing the material was collected and subjected for vacuum drying in oven for 24 hrs. After drying the collected material was analyzed by using XRD and the results are shown in Figure 6. XPS spectra showing carbon and aluminium peaks in the Al-doped SMHCF samples have been depicted in Figure 9 and Figure 10 respectively.

Example: 4 Aluminium doped sodium manganese hexa cyano ferrate synthesis with 0.1 M aluminium sulfate feed precursor) (Present invention)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O), 6.3 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further, 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as solution C. Solution A is taken in Burette 1 and solution B is taken in Burette 2. Solution C is taken in beaker. Solution A flow rate and solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hours. After 12 hours the stirrer was stopped, and the resultant solution was subjected to vacuum filtration using Wattman filter paper. After filtering, the material was washed using distilled water five times. After water washing the material was washed with ethanol. After washing the material was collected and subjected to vacuum drying in oven for 24 hours. After drying the collected material was analyzed by using XRD and the results are shown in Figure 7. XPS spectra showing carbon and aluminium peaks in the Al-doped SMHCF samples have been depicted in Figure 9 and Figure 10 respectively.

Example: 5 Aluminium doped sodium managnese hexa cyano ferrate synthesis with 0.2 M aluminium sulfate feed precursor) (Present invention)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O),12.6 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further, 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as solution C. Solution A is taken in Burette 1 and solution B is taken in Burette 2. Solution C is taken in beaker. Solution A flow rate and solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hours. After 12 hours the stirrer was stopped, and the resultant solution subjected to vacuum filtration using Wattman filter paper. After filtering, the material was washed using distilled water five times. After water washing the material was washed with ethanol. After washing the material was collected and subjected to vacuum drying in oven for 24 hours. After drying the collected material was analyzed by using XRD and the results have been shown in Figure 8. XPS spectra showing carbon and aluminium peaks in the Al-doped SMHCF is depicted in Figure 9 and Figure 10 respectively.

Example: 6 Metal analysis through ICP (Inductive coupled plasma) analysis
SMHCF prepared by the method of Example: 2, Example: 3, Example: 4 and Example: 5 were subjected to analysis of metal content by ICAP. The metal content results have been shown in Table: 1.

Table :1 Metal content analysis of Aluminium doped SMHCF
S.No Aluminium Sulphate Feed Precursor Concentration in precursor (M) Metal content in Sodium Manganese hexa cyano ferrate
(ppm by mass)
Metal (M) content Mass % M/Al ratio M/Na ratio
1 0.025 Fe 13.44 192 1.47
Mn 14.19 202.71 1.55
Na 9.12 130.28
Al 0.07 0.0007
2 0.05 Fe 12.46 17.8 1.16
Mn 11.57 16.52 1.07
Na 10.72 15.31
Al 0.7 0.07
3 0.1 Fe 13.42 11 1.84
Mn 13.26 10.86 1.81
Na 7.29 5.97
Al 1.22 0.16
4 0.2 Fe 5.70 0.81 0.55
Mn 5.10 0.72 0.49
Na 10.37 1.48
Al 7 0.67

Example: 7 Coin Cell Fabrication-Half cell-water in salt electrolyte
The cathode slurry was prepared by using of 400 mg aluminium doped sodium manganese hexa cyanoferrate which contains 7000 ppm (wt/wt) aluminium as per Example: 2 mixed with 50 mg conductive carbon black, 50 mg PVDF binder and 2.7 g N-methyl pyrrolidone (NMP) solvent. The slurry was coated with aluminium foil with the thickness of 150 Micrometer with the help of doctor blade. Thus, the prepared cathode was kept in vacuum oven for 24 hours to remove the solvent. After drying, 2.8 mg of cathode active material was taken for coin cell fabrication along with zinc foil along with separator. 100 micro litre 35 M NaFSI electrolytes were used for coin cell fabrication.

The above method was used for reference sodium manganese hexa cyano ferrate (without aluminium) cathode and coin cell fabrication.

Example: 8 (Present invention: Half-cell electrochemical performance comparative evaluation on Al doped NMHCF cathode and without Al Vs Zinc - 35M NaFSI water in salt electrolyte)
Coin cells fabricated with Al and without Al as per Example: 7 were subjected for 50 milli volts scan in cyclic voltammetry for 500 cycles with the range of 0 Volts to 2.5 Volts. The cyclic voltameter performance has been shown in Figure 11. From Figure 11, Al doping improves the oxidation and redox reaction as well as reducing the polarity of SMHCF cathode.

Example: 9 (Present invention: Half-cell charge discharge cycle performance)
Coin cell fabricated as per Example: 7 was subjected for charge discharge cycle. The charging and discharging current were 2.24 milli Ampere used. The above same method was used for without aluminium doped (Reference) SMHCF was subjected for charge discharge cycle. The results are shown in Figure 12. From the figure it is observed that aluminium doped sodium manganese hexa cyano ferrate cathode provide 150 cycles (upto 20mAh/g) as compared to 60 cycles for without aluminium doped sodium manganese hexa cyano ferrate. Aluminium doping enhances the cycle life of the sodium manganese hexa cyano ferrate cathode.

Example: 10 (Present invention: Carbon composite coating of sodium titanium phosphate anode)
0.1 g glucose and 0.01 g of sodium ligno sulphonate (Vanisperse) dissolved in 15 ml of distilled water in the beaker with the use of stirrer. Then 0.75 g of carbon black, 0.25 g of multiwalled carbon nanotube with the outer diameter in the range of 10 nm to 30 nm taken in the solution. Then the above solution was subjected for sonification using ultra sonicator for 15 minutes for dispersion of carbon. Then 4 g of sodium titanium phosphate material taken with the above mixture and subjected for 30 minutes sonification Then the mixture was dried using vacuum oven at 120 ? for 24 hours. After drying the material was subjected to heat treatment in the presence of nitrogen atmosphere in a furnace at 800 ? with the heat rate of 3 ?/min for 4 hours. After 4 hours the furnace was cooled, and the material was taken out and subjected to morphology analysis using a scanning electron microscope. The SEM results are given in Figure 13.

Example: 11 (Present invention: Carbon composite coating of sodium titanium phosphate anode)
0.1 g glucose and 0.02 g of sodium lingo sulphonate (Vanisperse) dissolved in 15 ml of distilled water in the beaker with the use of stirrer. Then 0.5 g of carbon black, 0.5 g of multiwalled carbon nanotube with the outer diameter in the range of 10 nm to 30 nm taken in the solution. Then the above solution was subjected for sonification using ultra sonicator for 15 minutes for dispersion of carbon. Then 4 g of sodium titanium phosphate material taken with the above mixture and subjected for 30 minutes sonification. Then the mixture was dried using vacuum oven at 120 ? for 24 hours. After drying the material was subjected to heat treatment in the presence of nitrogen atmosphere with the nitrogen flow rate of 100 standard cubic centimeter (SCCM) in a furnace at 600 ? for 4 hours. After 4 hours the furnace was cooled, and the material was taken out.

Example: 12 Full cell fabrication
The anode slurry was prepared by using 400 milligrams of carbon composite coated sodium titanium phosphate as per Example 10 mixed with 50 mg conductive carbon black, 50 mg PVDF binder and 2.7 g of N-methyl pyrrolidone (NMP) solvent. The slurry was coated with aluminium foil with the help of doctor blade. Thus, the prepared anode was kept in vacuum oven for 24 hours to remove the solvent. After drying, 2.24 mg of anode active material was taken for coin cell fabrication along with 2.8 mg of cathode active material along with glass fibre separator. 100 micro litre 35 M NaFSI electrolytes were used for coin cell fabrication.

Full cell was fabricated with the above procedure for different dosages of with or without aluminium doped sodium manganese hexa cyano ferrate cathode material as mentioned in example1, 2, 3, 4 and 5.

Example: 13 Aluminium doping optimizations in sodium manganese hexa cyano ferrate using carbon composite coated sodium titanium phosphate
Full cells fabricated as per Example: 12 was subjected for 50 milli volts (mV) scan in cyclic voltammetry for 500 Cycles with the range of 0 Volts to 2.5 Volts. The cyclic voltameter performance is given in Figure 14. From Figure 14, doped aluminium concentration is in the range of 7000 ppm to 12200 ppm (0.05M to 0.1M aluminium sulphate feed precursor cases) has shown the highest current intensity peak and polarization less and hence improves the electrochemical performance.

Example:14 Full cell charge and discharge life cycle evaluation
Full cells were fabricated as per Example:12 was subjected to charge discharge life cycle evaluation at different charge and discharge current of 2.24 milli Ampere (mA), 5.4 mA and 14 mA. The results are given in Figure15. From the results it was observed that the degradation rate is lesser for higher discharge rate as compared to lower discharge rate for water in salt electrolyte. The full cell is stable at high discharge rate and high rate capable.

Example: 15 Full cell fabrication with organic electrolyte
Full cells were fabricated as per Example: 12 and all the assembly held in glove box and 100 microliters of 1molar NaFSI salt dissolved in tetra ethylene glycol dimethyl ether solvent was used.

Example: 16 Full cell cyclic voltammetry evaluation with 35M NaFSI Water In Salt (WIS) electrolyte with different scan rates
Full cells were fabricated as per Example: 12 and 100 microliters of 35 molar NaFSI salt dissolved in water as a solvent was used. Then these cells were subjected to cyclic voltametric evaluation at different scan rates such as 50mV, 30mV, 20mV, 10mV, 5mV, and 1mV. The results are given in Figure 16. From the results it is observed that oxidation peaks observed at 1.4V-1.75 V and reduction peaks observed at 0.9 V-1.3V at different scan rates.

Example: 17 Aluminium doped sodium iron hexa cyano ferrate (SFHCF) synthesis with 0.05 M aluminium sulfate feed precursor) (Present invention)
1.390 g of ferrous sulphate, 3.150 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as Solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as Solution C. Solution A is taken in Burette 1 and Solution B is taken in Burette 2. Solution C is taken in Beaker. Solution A flow rate and Solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hrs. After 12 hrs the stirrer was stopped, and the resultant solution subjected for vacuum filtration with using of Wattman filter paper. After filtering, the material was washed using distilled water five times followed by washing the material with ethanol. After washing the material was collected and subjected for vacuum drying in oven for 24 hrs. After drying the material collected and the sample was analyzed in XRD for Phase identification. The XRD results are shown in Figure17. The aluminium content was analyzed using Inductive Coupled Plasma (ICP) analysis. The Aluminium content was observed as 0.5 weight %.

Example: 18 Aluminium doped sodium manganese iron hexa cyano ferrate (SMFHCF) synthesis with 0.05 M aluminium sulfate feed precursor) (Present invention)
0.96 g of manganese sulphate monohydrate (MnSO4.H2O), 1.390 g of ferrous sulphate, 3.150 g of aluminium sulfate (Al2(SO4)3.16 H2O) and 1.67 g of tri sodium citrate di-hydrate weighed using of weighing balance and dissolved in 100 ml of distilled water. It was considered as Solution A. 3.36 g of sodium ferro cyanide weighed and dissolved in 100 ml of distilled water. It was considered as solution B. Further 60 g of sodium nitrate was measured and dissolved in 200 ml of distilled water. It was considered as Solution C. Solution A is taken in Burette 1 and Solution B is taken in Burette 2. Solution C is taken in Beaker. Solution A flow rate and Solution B flow rate was kept 1ml /min each and simultaneously fed into solution C in a beaker. The stirrer was operated at a speed of 500 rpm and kept it for 12 hrs. After 12 hrs the stirrer was stopped, and the resultant solution subjected for vacuum filtration with using of Wattman filter paper. After filtering, the material was washed using distilled water five times followed by washing the material with ethanol. After washing the material was collected and subjected for vacuum drying in oven for 24 hrs. After drying the material collected and the sample was analyzed in XRD. The comparative results of XRD between Al doped SFHCF and SMFHCF are shown in Figure 17.

Example: 19 Full cell cyclic voltammetry evaluation with organic electrolyte
Full cells were fabricated as Al doped SFHCF as cathode and carbon coated sodium titanium phosphate as an anode with use of glove box and 100 microliters of 1 molar NaOTF salt dissolved in tetra ethylene glycol dimethyl ether solvent as an organic electrolyte was used. Then these cells were subjected to cyclic voltametric evaluation at different scan rates such as 5mV, 4mV, 3mV, 2mV, 1mV, and 0.1mV. The results are given in Figure 18. From the results it is observed that oxidation peaks observed at 1.35V-1.45 V and 2.25 V and reduction peaks observed at 1.15V-1.25V at different scan rates.

Example: 20 Half-cell capacity evaluation of Al doped sodium iron hexa cyano ferrate cathode in organic electrolyte (1M NaOTF/TEGDME)
Half cells were fabricated as Al doped SFHCF as cathode and Sodium metal foil as an anode with the use of glove box and 100 microlitres of 1 molar NaOTF salt dissolved in tetra ethylene glycol dimethyl ether solvent as an organic electrolyte was used. The capacity of Al doped SFHCF evaluated at various discharge rate against Na/Na+. The capacity results are shown in Figure 19. The capacity varies from 93 mAh/g for 0.1 A/g discharge rate to 35 mAh/g for 0.9 A/g discharge rate. ,
Claims:1. A sodium ion battery comprising:
i. an aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni and wherein the aluminium (Al) doped cathode of formula NaxMy[Fe(CN)6] exhibit cubic phase;
ii. a carbon composite coated anode of sodium titanium phosphate; and
iii. an electrolyte selected from water in salt electrolyte or organic electrolyte.

2. The sodium ion battery as claimed in claim 1,wherein the Al-doped cathode is selected from the group consisting of Al-doped sodium manganese hexa cyano ferrate (Al-SMHCF), Al-doped sodium ferrate hexa cyano ferrate (Al-SFHCF), Al-doped sodium cobalt hexa cyano ferrate, Al-doped sodium copper hexa cyano ferrate, Al-doped sodium chromate hexa cyano ferrate, and Al-doped sodium nickel hexa cyano ferrate.

3. The sodium ion battery as claimed in claim 1,wherein the Al-doped cathode is Al-doped sodium manganese hexa cyano ferrate in which Al-doped sodium manganese hexa cyano ferrate exists in cubic phase.

4. The sodium ion battery as claimed in claim 1, wherein the aluminium content in the Al-doped sodium manganese hexa cyano ferrate is in a range of 0.07 to 7 weight percent.

5. The sodium ion battery as claimed in claim 1, wherein the electrolyte is selected from the group comprising 35 molar sodium bis(fluorosulfonyl) imide (NaFSI) as water in salt electrolyte, 1 molar NaFSI in tetra ethylene glycol dimethyl ether solvent, and 1 molar sodium trifluoromethane sulfonate in tetraethylene glycol dimethyl ether solvent (1M NaOTF/TEGDME).
6. The sodium ion battery as claimed in claim 1, wherein the Al-doped cathode is in-situ overlaid with aluminium-oxy-fluoride (AlOFx).

7. An Al-doped cathode of general formula NaxMy[Fe(CN)6], wherein M is selected from Mn, Fe, Co, Cu, Cr, or Ni, and wherein the Al is in 0.07 to 7 weight percentage.

8. The Al-doped cathode as claimed in claim 7, wherein the Al-doped cathode is selected from the group consisting of Al-doped sodium manganese hexa cyano ferrate cathode and Al-doped sodium iron hexa cyano ferrate.

9. A process for preparing a sodium ion battery, said process comprising steps of:
i. preparing an Al-doped cathode of general formula NaxMy[Fe(CN)6] using aluminium sulphate feed precursor;
ii. preparing a carbon composite coated anode of sodium titanium phosphate using sodium based organic surfactant followed by its decomposition process;
iii. arranging the Al-doped cathode of general formula NaxMy[Fe(CN)6] and the carbon composite coated anode of sodium titanium phosphate in a manner suitable to the structural layout of sodium ion battery; and
iv. adding a suitable electrolyte.

10. The process as claimed in claim 9, wherein the process for preparing Al-doped cathode of general formula NaxMy[Fe(CN)6] is a co-precipitation method, and wherein said co-precipitation method comprises:
i. dissolving a sulphate based metal precursor, aluminium sulphate, and sodium citrate in water to form a solution A, wherein molar ratio of the metal precursor to aluminium sulphate is in the range of 0.25 to 2 and molar ratio of sodium citrate to aluminium sulphate is in the range of 0.3 to 2.4;
ii. adding sodium ferro cyanide in water to form a solution B;
iii. adding sodium nitrate in water to form a solution C;
iv. adding the solution A and the solution B with the volumetric flow rate ratio of 1:1 to the solution C to form a solution D, followed by stirring for 8 to 16 hours;
v. filtering the solution D to separate precipitates obtained using vacuum filtration;
vi. washing the precipitates with distilled water and ethanol; and
vii. drying the precipitates to obtain Al-doped cathode of general formula NaxMy[Fe(CN)6].

11. The process as claimed in claim 10, wherein the sulphate based metal precursor is selected from a group comprising manganese sulphate, copper sulphate, ferrous sulphate, cobalt sulphate, nickel sulphate or mixture thereof.

12. The process as claimed in claim 10, wherein the aluminium sulphate in water is in a concentration of 0.025 M to 0.2 M, wherein the stirring in step iv) is carried out for 12 hours.

13. The process as claimed in claim 9, wherein the process for preparing the carbon composite coated anode of sodium titanium phosphate comprises:
i. mixing an organic binder and an organic surfactant in distilled water to form a mixture;
ii. adding a conductive carbon to the mixture and sonicating the mixture;
iii. adding sodium titanium phosphate to the mixture and sonicating the mixture for 15 to 30 minutes;
iv. drying the mixture to obtain a dried mixture;
v. carbonizing the dried mixture in inert atmosphere; and
vi. cooling to room temperature to obtain the carbon composite coated sodium titanium phosphate.

14. The process as claimed in claim 13, wherein the organic binder is selected from the group comprising carbohydrates, sugar, monosaccharide, disaccharides, polysaccharides or mixture thereof; wherein monosaccharide is selected from glucose, fructose, ribose or mixture thereof; wherein disaccharide is selected from sucrose, maltose, lactose or mixture thereof; wherein polysaccharides selected from starch, cellulose, glycogen or mixture thereof; wherein the organic surfactant is selected from ligno sulphonate, sodium lingo sulphonate (Vanisperse), calcium lingo sulphonate or mixture thereof; wherein the conductive carbon is selected from one dimensional carbon comprises a carbon nanotube, two dimensional carbon, three dimensional carbon, zero dimensional carbon comprises carbon black, amorphous carbon or mixture thereof; and wherein the carbon nanotube is a multiwalled carbon nanotube having outer diameter in a range of 10 nm to 30 nm.

15. The process as claimed in claim 13, wherein the organic binder is glucose; wherein the organic surfactant is sodium lingo sulphonate (Vanisperse); and wherein the conductive carbon is a mixture of carbon black and a multiwalled carbon nanotube having outer diameter in a range of 10 nm to 30 nm.

16. The process as claimed in claim 13, wherein carbonizing in step v) is carried out at a temperature of 600 to 800 ? for 4 hours in an inert environment.

17. The process as claimed in claim 9, wherein the Al-doped cathode is in-situ overlaid with aluminium-oxy-fluoride (AlOFx).