Claims:1. A sodium-ion electrochemical full-cell comprises of:
-first layer made of the cathode current collector;
-second layer made of cathode active material;
-a separator layer with electrolyte sandwiched between the cathode active material and anode active material;
-third layer made of anode active material;
-fourth layer made of anode current collector;
Plurality of layers that form the sodium-ion full-cell is overall enclosed inside a casing;
Characterized in that the combination of the cathode active material and anode active material which provides a high potential of around 2.0V with an average energy density of 414 W h kg-1 due to layered electrode material with high interlayer spacing.

2. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the current collector are made of metal foil.

3. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the cathode current collector is made of aluminium metal foil.

4. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the anode current collector is made of copper metal foil.

5. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the cathode active material consists of sodium vanadium phosphate (Na3V2(PO4)3) as an active material.

6. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the cathode active material consists of conducting carbon (Super C65).

7. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein Polyvinylidene fluoride (PVDF) acts as binder.

8. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the separator layer sandwiched between the cathode and anode active material is made of borosilicate glass fiber separator soaked in an organic electrolyte.

9. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the organic electrolyte is made of carbonate-based solvent and sodium salt.

10. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the anode active material consists of molybdenum ditelluride MoTe2 as the active material.

11. The sodium-ion electrochemical full-cell as claimed in claim 1, wherein the anode active material consists of conducting additive (Super C65) and an aqueous-based binder, sodium salt of carboxymethylcellulose (CMC).

12. The sodium-ion electrochemical full-cell as claimed in claim 1, where the fabrication of casing has been done inside the glove box filled with argon.

13. The process of synthesis of cathode active material as claimed in claim 1 comprises of obtaining a phase-pure Na3V2(PO4)3 by a simple two-step process comprised of solid-state reaction followed by carbothermal reduction route.

14. The process of synthesis of cathode active material as claimed in claim 13, comprises of:

-Mixing the stoichiometric amount of NH4VO3 (Sigma Aldrich, = 99%) and NaH2PO4.2H2O (Sigma Aldrich, = 99%) with 20% of sucrose in 20 ml of ethanol medium in the first step;
-Subjecting the said mixture to ball mill for 24 h at 300 rpm rotation speed;
-Drying the obtained mixture at 100 °C in air;
-Crushing the air-dried mixture to get powder;
-Heating the powder obtained in the first step by initially keeping the powder at 350 °C for a period of 3 h; and
- Calcining the powder at 800 °C in N2/H2 (95:5) atmosphere for 8 h with the ramp rate of 5°C/min to get desired pure-phase Na3V2(PO4)3 material.

15. The process of synthesizing anode active material as claimed in claim 1, comprises of obtaining MoTe2 by simple solid-state reaction procedure.

16. The process of synthesizing anode active material as claimed in claim 15, comprises of:
-Mixing the appropriate ratio of molybdenum (Sigma-Aldrich, 99.999%) and tellurium (Sigma-Aldrich, 99.999%) in powder form inside the quartz ampoule;
-Heating the powder mix at 800 °C for 20 h;
-preparing a slurry by ball-milling and mixing 70:20:10 (MoTe2: Carbon (Super C-65): CMC Binder;
And
-Fabricating the anode by coating aqueous slurry on thin copper foil followed by vacuum drying at 80 °C for overnight.

17. The sodium-ion electrochemical full-cell mechanism as claimed in claim 1, wherein the intercalation mechanism for sodium-ion full cell is shown in the below equation (1a) and (1b)
Cathode:
Na3V23+(PO4)3? Na3-xV2-x3+Vx4+(PO4)3 + xNa+ + xe- (1a)

Anode:
MoTe2+ xNa++ xe- ? NaxV2-x3+Vx2+(PO4)3 (1b)

, Description:RECHARGEABLE SODIUM-ION BATTERIES BASED ON LAYERED ELECTRODE MATERIALS AND METHOD OF FABRICATING THE SAME

FIELD OF THE INVENTION

[0001] The present disclosure relates to sodium-ion batteries and more particularly relates to an improved structure and fabrication of sodium-ion batteries having low cost, high performance with high energy density.

BACKGROUND OF THE INVENTION

[0002] The sodium-ion batteries generally, use hard carbon as an anode material; however, material limitation makes it inefficient for high current rates and high-power applications.

[0003] Few references disclose MoTe2 as a potential anode material for sodium-ion battery. However, the references have the following limitation, they require sophisticated technique to synthesize the material, and utilization of intermediated precursors (C–MoOx) to synthesize the MoTe2 and only half-cell configuration are disclosed. Further, surface modification of the synthesized material is needed to get better electrochemical performances, despite the higher electronic conductivity of MoTe2.

[0004] Therefore, there is a need to develop an alternative sodium-ion batteries with the full-cell configuration as large-scale energy storage devices with all the functionalities similar to the lithium-ion batteries.

SUMMARY OF THE INVENTION
[0005] An aspect of the present disclosure relates to sodium-ion battery and fabrication of a full-cell based on the same.

[0006] In an implementation of the present disclosure, a metal-free sodium-ion full-cell was constructed using the NASICON-structure Na3V2(PO4)3as cathode and layered MoTe2 as anode.

[0007] The second aspect of the present invention relates to fabricate the components used for the construction of sodium-ion battery full-cell.

OBJECT OF THE INVENTION

[0008] The primary object of the present invention is to demonstrate low cost and high-performance rechargeable sodium-ion full-cells which can store more energy in comparison to conventional lithium-ion batteries.

[0009] Another object of the present invention is to overcome the limitation relating to the use of the sodium-ion battery for high power application by using the advantages of layered electrode materials with high interlayer spacing.

[0010] Yet another object of the present invention is to demonstrate the use of MoTe2 that acts as anode allowing the use of its high specific capacity, which may be reflected in overall high energy density of our sodium-ion battery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The detailed description is described with reference to the accompanying figures.

[0012] Figure 1: Schematics representation of the cross-view design of the electrochemical cell.

[0013] Figure 2: Schematic representation of the preparation of MoTe2 anode material inside the quartz ampoule.

[0014] Figure 3: (a) X-ray diffraction (XRD) study of the MoTe2 material, (b) Scanning Electron Micrograph (SEM) image of MoTe2, (c) High resolution-transmission electron micrograph (HR-TEM) of MoTe2 material.

[0015] Figure 4: Graphical representation of MoTe2//NVP full-cell performances, (a) charge-discharge profile of MoTe2 against NVP cathode, (b) cycling performance of MoTe2 against NVP cathode, (c) Ragone plot for MoTe2//NVP sodium-ion full-cell (Specific values are calculated based on anode mass), (d) cycling rate performance of full-cell at various current rates.

[0016] Figure 5: Demonstration of a prototype using a LED study table lamp powered by a single coin cell.

[0017] Figure 6: Illustrates a comparison of the electrochemical performance of the present cell.

DETAILED DESCRIPTION OF INVENTION

[0018] The present invention discloses a novel layered MoTe2 anode and sodium containing NASICON-structured NVP (Na3V2(PO4)3) cathode electrode materials-based cell or battery, wherein the said battery disclosed herein are of high industrial importance and open up a new approach to developing high-performance batteries with competitive cost. Thus the main aim of the present invention is to demonstrate a low cost and high-performance rechargeable sodium-ion full-cell.
[0019] NASICON is an abbreviation for sodium superionic conductor, which usually refers to a family of solids with the chemical formula Na1+xZr2SixP3-xO12, 0 < x < 3. It can be used for related compounds where Na, Zr, and Si are substituted by isovalent elements. Due to their high ionic conductivities (~ 10-3 S cm-1) which originates from the hopping of sodium-ions among interstitial sites of the NASICON crystal lattice, these materials have the potential application in the sodium-ion battery. Sodium vanadium phosphateNa3V2(PO4)3 is among the class of phosphates electrode materials, having NASICON structure are attractive by considering their stable crystallographic structure which could enable long-term cycling and improved safety

[0020] Till date, there is no standard, commercialized sodium-ion battery technology that has been developed. The present invention discloses one of the promising anode (MoTe2) and NVP (Na3V2(PO4)3) cathode based full-cell.

[0021] In the present invention, the limitations relating to the use of the sodium-ion battery for high power application is conquered using the advantages of layered electrode materials with high interlayer spacing. The use of MoTe2 as anode allows the use of its high specific capacity, which may be reflected in overall high energy density of our sodium-ion battery.

[0022] The novel MoTe2 anode and sodium containing cathode material based battery cell inventions disclosed herein are therefore of high industrial importance and open up a new approach to develop high-performance batteries without compromising the cost. Thus the main objective of the present invention is to demonstrate low cost and high-performance rechargeable sodium-ion full-cells which can store more energy in comparison to conventional lithium-ion batteries.

[0023] The significance of the present invention is to disclose the utilization of the transition metal dichalcogenides based anode materials for sodium-ion full-cell with organic solvent-based electrolytes that support the stable cycling of MoTe2 against Na3V2(PO4)3 (NVP) cathode, without involving any further surface modifications steps. In a still further aspect, the invention demonstrates the sodium-ion electrochemical cell, preferably electrochemical secondary cells.

[0024] The term "cell" refers in this disclosure to an electrochemical cell as a smallest, packed form of a battery. The term "battery" refers to a group of more than one cell.

[0025] Figure 1.shows the schematics of the cross-view design of the electrochemical cell. The sodium-ion electrochemical cell, as described by the present invention comprises of the following:

Casing: Sodium-ion full-cell is enclosed in an overall casing.
Sodium-ion full-cell: wherein the sodium-ion battery in the present invention consists of a NASICON-structured cathode active material, Borosilicate glass fiber soaked with carbonate-based electrolyte used as the separator and a layered anode active material.
Cathode current collector: wherein the cathode current collector is preferably selected as aluminium.
Cathode: consisting of sodium vanadium phosphate (Na3V2(PO4)3) as active material, conducting carbon (Super C65) and Polyvinylidene fluoride (PVDF) as binder.
Separator: borosilicate glass fiber separator soaked in an electrolyte (1M NaClO4+FEC (3.5 wt%))
Anode: containing molybdenum ditelluride, MoTe2 as active material, conducting additive (Super C65) and an aqueous-based binder i.e., sodium salt of carboxymethylcellulose (CMC).
Anode current collector: wherein the anode current collector is preferably selected as copper.

[0026] Figure 2. illustrates the schematic representation of the preparations of MoTe2 anode material inside the quartz ampoule, wherein synthesis of cathode active material is carried out by a simple two-step process comprising of solid-state reaction followed by carbothermal reduction route that has been followed to obtain nearly phase-pure Na3V2(PO4)3. In the first step, the stoichiometric amount of NH4VO3 (Sigma Aldrich, = 99%) and NaH2PO4.2H2O (Sigma Aldrich, = 99%) were mixed with 20% of sucrose in 20 ml of ethanol medium. This mixture was subjected to ball mill for 24 h at300 rpm rotation speed. After the ball milling, the obtained mixture was dried at 100 °C in air and then crushed to get the powder. In the second step, during two-step heating process, the powder was initially kept at 350°C for a period of 3 h and followed by the final calcinations at 800°C in N2/H2 (95:5) atmosphere for 8 h with the ramp rate of 5 °C/min to get desired pure-phase Na3V2(PO4)3 material.

[0027] Synthesis of anode active material is carried out wherein the material MoTe2 has been prepared by simple solid-state reaction procedure by taking the appropriate ratio of molybdenum (Sigma-Aldrich, 99.999%) and tellurium (Sigma-Aldrich, 99.999%) in powder form inside the quartz ampoule and followed by the heating at 800 °C for 20h. The as-synthesized MoTe2 powder sample is used for the fabrication of electrodes for the anode of sodium-ion batteries. A slurry was prepared by ball-milling and mixing 70:20:10 (MoTe2: Carbon (Super C-65): CMC Binder). The anode was fabricated by coating aqueous slurry on thin copper foil followed by vacuum drying at 80°C for overnight.

[0028] Figure 3. illustrates the X-ray diffraction (XRD) study of the MoTe2 material were in Fig. 3(a), Fig. 3 (b) illustrates scanning electron micrograph (SEM) image of MoTe2. Fig. 3 (c) discloses high resolution-transmission electron micrograph (HR-TEM) of MoTe2material. The as-synthesized sample shows a high crystallinity and layered morphology having an interlayer spacing of 0.7 nm as shown in Figure 3.

[0029] Fabrication of MoTe2 based full-cell was constructed against the present invention synthesized Sodium vanadium phosphate (NVP) cathode in the following configuration, (MoTe2 anode ? borosilicate glass separator soaked in an electrolyte (1M NaClO4 in 1:1 ethylene carbonate + propylene carbonate with 3.5 wt% fluoroethylene carbonate additive) ? sodium vanadium phosphate (NVP) cathode) in Argon filled glove box.

[0030] MoTe2//NVP Full-cell Electrochemical Mechanism was studied, wherein it was observed that MoTe2 anode can be better with sodium-containing cathode such as ammonium vanadium phosphate (NVP) for full-cell construction.
The proposed intercalation mechanism for sodium-ion full cell is shown in the below equation (1a) and (1b)

Cathode:
Na3V23+(PO4)3? Na3-xV2-x3+Vx4+(PO4)3 + xNa+ + xe- (1a)
Anode:
MoTe2+ xNa++ xe- ? NaxV2-x3+Vx2+(PO4)3(1b)

[0031] Figure 4.illustrates graphical representation of MoTe2//NVP full-cell performances, (a) charge-discharge profile of MoTe2 against NVP cathode, (b) cycling performance of MoTe2 against NVP cathode, (c) Ragone plot for MoTe2//NVP sodium-ion full-cell (Specific values are calculated based on anode mass), (d) cycling rate performance of full-cell at various current rates. The electrochemical performance of the full-cell comprised of MoTe2 anode and sodium vanadium phosphate cathode is shown in Figure 4. Figure 4a shows the charge-discharge profiles of the sodium-ion full-cell at 0.5 A g-1. The as-fabricated full-cell showed a very stable specific discharge capacity ~178.66 mA h g-1 (~88% capacity retention) after 150 cycles, as shown in Figure 4b. Figure 4d shows the versatile behavior of the full-cell, rate performance study carried at different rates. The cell could deliver back its original output capacity when the current rate is reduced back to low, which shows a good electrochemical performance with respect to the active anode. Further to gain a better overview of the total energy available at various power densities, a Ragone plot was drawn from the obtained results, which elucidates the suitability of the present sodium-ion full-cell prototype to a variety of the applications, shown in Figure 4c.

[0032] Figure 5 demonstrates a prototype using a LED study table lamp powered by a single coin cell. Presently the invention is being carried out in the lab, wherein its practical application through glowing LED-based lantern (2.5W) with a single coin cell of 2Vhas been found out.

[0033] Figure 6 illustrates a comparison of the electrochemical performance of the present cell. When compared with other reported literature, the present electrochemical cell disclosed shows the highest cell capacity which must have arisen due to the high practical specific capacity of MoTe2 anode. The individual and full-cell performance of MoTe2 shows its potential as an anode material for sodium-ion electrochemical cell or battery by delivering higher performance.

[0034] The advantage of improvements of the invention over existing devices are that the working potential of MoTe2 anode lies above the sodium plating potential, that significantly increases the safety of the battery when used as anode material in the sodium-ion electrochemical cell. The present material shows exceptionally high-power performance at higher current rates, without doing any further modifications to the base material. The electrode preparation using MoTe2activematerial disclosed in the present invention uses an aqueous binder, which significantly reduces the toxicity during electrode processing and also improves its eco-friendly nature. Surface modification step during material synthesis and incorporation of expensive conducting additives during the electrode processing has been eliminated, which could reduce the cost of present battery technology.

[0035] Overall, a full-cell is fabricated combining MoTe2 anode and Na3V2(PO4)3 (NVP) cathode. The (MoTe2//NVP) full-cell shows high energy density (414 W h kg-1 at a high current rate of 0.5 A g-1) and outstanding cycling stability (i.e., 88% reversible capacity retention after 150 cycles), implying a great potential of our sodium-ion full-cell to be used for practical application. The technology disclosed in the present invention can be used in grid storage, small-scale stationary and as well as consumer electronics applications.

[0036] The present invention will help the future realization of low-cost energy storage technology due to the following reasons:
1. The present anode MoTe2 does not require further steps in the modification, unlike some other contemporary anodes.
2. Also, the sodium sources are abundant in the earth which will substantially reduce the cost of raw material and hence the battery cost.

[0037] The above-mentioned material will be safer than carbonaceous anodes due to their electrochemical potential that lies quite above the sodium plating potential, which greatly inhibits the safety issues of the battery when used as anode material for sodium-ion electrochemical cell or battery.

[0038] The above description along with the accompanying drawings is intended to describe the preferred embodiments of the invention in sufficient detail to enable those skilled in the art to practice the invention. The above description is intended to be illustrative and should not be interpreted as limiting the scope of the invention. Those skilled in the art to which the invention relates will appreciate that many variations of the described example implementations and other implementations exist within the scope of the claimed invention.