DESC:TECHNICAL FIELD
[0001] The present disclosure relates to lithium-sulfur (Li–S) batteries, and more specifically, to a Lithium–sulfur (Li–S) battery with a Lithium metal anode having a protective coating of Li3N passivating layer.

BACKGROUND
[0002] Recently, the Lithium-sulfur batteries are considered as promising alternatives to commercial lithium-ion batteries due to their high energy density. Success of the lithium-sulfur batteries largely relies on direct utilization of metallic lithium as anode. Unprotected lithium anodes suffer from uncontrollable Li dendrite growth upon repeated Li plating/stripping as well as participate into parasitic reactions with the electrolytes. Moreover, the electrolyte-soluble polysulfides react with bare lithium metal anode to chemically form insoluble/insulating end-discharged products, and thus deteriorates both the dynamic and static stability of the batteries.

[0003] The protection of Li anode in the lithium-sulfur batteries requires a facile and scalable method. It should be observed that during the fabrication, at the time of applying a protective passivation layer on the surface of Li metal anode, the thickness of the protective layer should be as much as less to facilitate Li+ ion transport from electrolyte to Li anode during charge/discharge of the batteries. Various strategies have been explored to protect or stabilize the lithium anode surface so far. One such method uses a solid electrolyte sandwiched between the sulfur cathode and the Li anode. But the use of solid electrolytes in batteries causes a serious issue of poor electrode/electrolyte interfaces.

[0004] Another method to mitigate the effects of dendrites involves with the application of a thin protective coating of a Li+ ion conducting material on the anode. For example, solid electrolytes, polymer, carbon nanospheres, atomic layer Al2O3 deposition, atomic layers of two-dimensional MoS2 nanosheets or hexagonal boron nitride (h-BN) are all found to be promising to prevent the dendrite. However, these thin coating methods also limited due to their large interfacial resistance between the lithium and the coating layer, manufacturing complexity and expensive fabrication.

[0005] Among several strategies to suppress the issues associated with polysulfide-shuttling, the use of additive salts (5-10 wt%) in the electrolyte is considered as one of the most effective, feasible, and economical approaches. Till date, lithium nitrate (LiNO3) has been extensively used as state-of-the-art additive in the ether-based liquid electrolytes for the lithium-sulfur batteries, since the first proposal in 2008. It is further observed that LiNO3 reacts with Li to form a surface passivation layer, which protects Li anode from reacting with the diffused/migrated polysulfides. However, side effects, such as uncontrollable thickness of the passivation layer, side reactions are the limitations of LiNO3 additive, leading the researchers to develop more robust alternative protective materials for Li anode. Thus, there is a need to develop protective Li anodes for lithium-sulfur (Li–S) batteries with alternative protective materials to overcome all of the above limitations.

OBJECT OF THE INVENTION
[0006] It is the primary object of the present disclosure to provide a method of fabricating a novel Lithium Nitride (Li3N) passivated anode electrode for Lithium–sulfur (Li–S) batteries.

[0007] It is another object of the present disclosure to provide a method of fabricating a Lithium–sulfur (Li–S) battery with a novel Lithium Nitride (Li3N) passivated anode electrode.

SUMMARY
[0008] In an aspect of the present disclosure, a method of fabricating Lithium metal anode electrode with a protective coating layer for Lithium–sulfur (Li–S) batteries is disclosed. The method comprises the steps of preparing a Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) solvent, by dissolving ultra-high purity grade Nitrogen in the 1,2-dimethoxy ethane solvent and forming a protective Lithium Nitride (Li3N) passivated layer on a Lithium (Li) metal anode by growing pure phase Lithium nitride (Li3N) nanosheets on a surface of the Lithium (Li) metal anode. The ultra-high purity grade Nitrogen (99.999%, Grade 5.0, BOC) is dissolved in the 1,2-dimethoxy ethane solvent by pressurizing the 1,2-dimethoxy ethane solvent with ultra-high purity grade Nitrogen (N2) gas, at a high pressure, ranging from 14-16 bar, preferably up to 15 bar, using a custom-made barrel cell made of polyether ether ketone (PEEK) equipped with gas in/outlets.

[0009] A protective Lithium Nitride (Li3N) passivated layer on a Lithium (Li) metal anode is formed by roll-pressing a Lithium (Li) metal disc onto at least one side of a current collector material for a reaction of Nitrogen with Lithium on a side of the current collector material, immersing the current collector material containing roll-pressed Lithium Metal foil into Nitrogen (N2) saturated 1,2-dimethoxy ethane solvent and drying the immersed stainless steel disc thereby forming a Lithium nitride (Li3N) passivated layer on the Lithium anode electrode. The immersion of the current collector material into the solvent results in reaction of Lithium with Nitrogen on the side of current collector material containing Lithium metal within the solvent environment, provides to complete the reaction between Lithium and dissolved N2, leading to a formation of pure crystal phase Lithium nitride (Li3N) nanosheets on the exposed surface of Lithium metal anode. The thickness of Lithium nitride (Li3N) nanosheets ranges from 4 nm to 8 nm. The current collector material is selected from a group comprising stainless-steel, Nickel, Alumium foil and Copper foil. The thickness of Li3N passivation layer ranges from 450 to 500 nm. The thickness of pressed Lithium metal foil ranges from 150 µm to 180 µm.

[0010] In another aspect of the present disclosure, a method of fabricating a Lithium–Sulfur (Li–S) battery comprising an anode electrode with a novel protective coating is disclosed. The method comprises the steps of fabricating an anode electrode with a protective coating for Lithium–sulfur (Li–S) batteries by using the method steps as discussed in the previous embodiment. The method of fabricating a Lithium–Sulfur (Li–S) battery further comprises the steps of pasting the fabricated anode electrode on a current collector material, preparing a cathode electrode casted on another current collector, preparing an electrolyte for the battery by dissolving 1M lithium bis(trifluoro methane)-sulfonamide in 1:1 (v/v) ratio of mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents, placing the fabricated anode electrode against a cathode electrode, which is a Sulfur/Lithium Aluminate composite cathode electrode, placed in an electrolyte and placing a polypropylene membrane between the anode electrode and the cathode electrode. The method comprises the steps of air-sealing the fabricated anode electrode, the cathode electrode, and the electrolyte.

[0011] In yet another aspect of the present disclosure, a Lithium–Sulfur (Li–S) battery comprising a Lithium metal anode electrode with a novel protective coating layer is disclosed. The anode electrode is fabricated with a protective coating layer using the method steps as discussed in the first embodiment. The Lithium–Sulfur (Li–S) battery further comprises a cathode electrode, an electrolyte comprising 1M lithium bis(trifluoro methane)-sulfonamide in 1:1 (v/v) mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents and a polypropylene membrane placed between the anode electrode and the cathode electrode. The anode electrode is placed against the cathode electrode placed. The cathode electrode comprises a Sulfur/Lithium Aluminate composite cathode electrode.

BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The detailed description is described with reference to the accompanying figures.
[0013] Figure 1 illustrates a flow chart for a method of fabricating an anode electrode with a protective coating for Lithium–Sulfur (Li–S) batteries in accordance with an exemplary embodiment of the present disclosure.
[0014] Figure 2 illustrates a flow chart depicting the method of fabricating a Lithium–Sulfur (Li–S) battery with a novel Lithium Nitride (Li3N) passivated anode electrode in accordance with another embodiment of the present disclosure.
[0015] Figure 3 illustrates low-resolution SEM images of pristine Li disk and Li3N-passivated Li disk in accordance with the present disclosure.
[0016] Figure 5 illustrates a symmetric cell performance of Lithium anodes in accordance with the present disclosure.
[0017] Figure 6 illustrates a post cycling morphology analysis of pristine Lithium electrode in accordance with the present disclosure.
[0018] Figure 7 illustrates a Lithium-Sulfur battery performance in accordance with the present disclosure.
[0019] Figure 8 illustrates a schematic illustration of the hypothesized role of the passivation layer of Li3N nanosheets grown on the surface of Li anode to control the dendrite growth compared to bare Li anode.
[0020] Figure 9 illustrates a custom-made barrel cell made of polyether ether ketone (PEEK) equipped with the gas in/outlets in accordance with the examples of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION
[0021] In the present invention, a method of fabricating a novel lithium nitride (Li3N) passivated anode electrode for Lithium–sulfur (Li–S) batteries and a method of fabricating a Lithium–sulfur (Li–S) battery employing the anode electrode are disclosed. In the present disclosure, pure phase Lithium Nitride (Li3N) nanosheets are grown on a surface of Lithium (Li) metal anode by immersing a Li metal foil into a molecular nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) solvent. Due to the low concentration and the intermolecular interactions with DME solvent, the dissolved N2 reacts slowly with metallic lithium to form a thin and homogenous layer of Li3N nanosheets. These in-situ grown, homogenous layer of Li3N nanosheets act as Li+ ion conducting protective coating over Li anode and thus suppress the dendrite formation as well as parasitic reaction with the electrolyte.

[0022] Generally, Lithium metal is vigorously reactive, not otherwise highly reactive towards Nitrogen (N2) gas. For commercial usage, the Lithium metal could not be simply exposed to the Nitrogen gas atmosphere due to high reactive nature with Lithium metal. With the vigorous reaction between Lithium (Li) metal and gaseous N2, the passivation layer of Lithium Nitride (Li3N) has a non-uniform layer structure and uncontrollable thickness of the passivation layer, i.e., the reactions between Lithium (Li) metal and gaseous N2 increases the thickness of the Lithium Nitride (Li3N) passivation layer that ultimately increases the impedance and so the resistance of the cell/battery. High impedance and resistance of the cell is always a concern for batteries and impacts the life, efficiency, and durability of the batteries. To reduce the reaction rate, or reaction kinetics between the Lithium (Li) metal and Nitrogen (N2), In the present invention, dissolved N2 is used. The gaseous N2 is dissolved into solvents, for example, 1,2-dimethoxy ethane (DME) solvent. The dissolved N2 is less reactive than its gaseous form with Lithium (Li) metal. When a Lithium metal anode is immersed into the dissolved N2, the dissolved N2 reacts with Lithium metal at low reaction or kinetic rate forming uniform thickness of Lithium Nitride (Li3N) passivation layer and growing Lithium Nitride (Li3N) nanosheets on a surface of the Lithium metal anode.

[0023] In an embodiment of the present disclosure, a method of fabricating an anode electrode for Lithium–sulfur (Li–S) batteries is disclosed. The anode electrode comprises a lithium nitride (Li3N) passivated layer as a protective coating. The method (300) comprises the step of preparing Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) (100), preparing a lithium nitride (Li3N) passivated layer on a lithium metal anode (200) and fabricating the lithium nitride (Li3N) passivated anode electrode for a Lithium–sulfur (Li–S) battery. The protective Lithium Nitride (Li3N) passivated layer on a Lithium (Li) metal anode is formed by growing pure phase Lithium nitride (Li3N) nanosheets on a surface of the Lithium (Li) metal anode electrode. Referring to Figure 1, illustrated is a flow chart for a method of fabricating an anode electrode with a protective coating for Lithium–sulfur (Li–S) batteries in accordance with an exemplary embodiment of the present disclosure.

[0024] The Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) is prepared by pressurizing 1,2-dimethoxy ethane with ultra-high purity grade Nitrogen (110). By pressurizing ultra-high purity grade Nitrogen (N2) into the 1,2-dimethoxy ethane solvent in a custom-made barrel cell made of polyether ether ketone (PEEK), the ultra-high purity grade Nitrogen gets dissolved in the 1,2-dimethoxy ethane solvent. In an implementation of the embodiments, the ultra-high purity grade Nitrogen (N2) pressurized 1,2-dimethoxy ethane in the custom-made barrel cell is statically kept for a period ranging from 70 to 90 hours. The advantage of keeping the PEEK cell statically is to ensure formation of uniform layer of homogeneously grown Li3N nanosheets on the surface of immersed Li metal disc. Further, a Lithium metal anode is pressed onto a current collector material for a reaction between Lithium and Nitrogen on at least one side of the current collector material (210). The current collector material is selected from a group comprising stainless-steel, Nickel, Alumium and Copper. In an exemplary embodiment, a stainless-steel disc is used. The pressing of Lithium metal with stainless-steel disc is performed on only one side to ensure that reactions happen on only one side, i.e., the other side of the Lithium metal anode. In one example of the present invention, the Lithium metal foil is roll pressed onto a side of a stainless-steel disc so that a lower surface of the Lithium metal foil is attached on the stainless-steel and an upper surface of the Lithium metal foil is unprotected and kept for reaction with the Nitrogen. The unprotected Lithium metal anode is highly reactive in nature with Nitrogen.

[0025] The stainless-steel disc is then immersed into Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) (220) forming a Lithium Nitride (Li3N) passivation layer on the Lithium anode electrode. When the stainless-steel disc containing Lithium metal foil is dipped or immersed into the Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) (220), the one side of the Lithium metal foil, i.e., unprotected surface, exposed and reacts completely with the dissolved Nitrogen, and in a result, pure crystal phase Lithium nitride (Li3N) nanosheets are grown on the exposed surface or the unprotected side of Lithium (Li) metal foil of the stainless-steel disc (230). The stainless-steel containing roll-pressed Lithium metal foil with grown nanosheets is further dried (240). thereby forming a Lithium anode electrode with a protective coating layer, i.e., a Lithium Nitride (Li3N) passivated anode electrode for a Lithium–sulfur (Li–S) battery. In an implementation of the embodiments, the stainless-steel disc with Lithium metal foil is immersed into Nitrogen (N2) saturated 1,2-dimethoxy ethane for a period ranging from 24 Hours to 36 Hours to give sufficient time to react the entire amount of dissolved N2 molecules with immersed Li metal. Then, the immersed stainless-steel disc is dried inside argon-filled glove box at room temperature for a period ranging from 24-30 hours. The grown Lithium nitride (Li3N) nanosheets are ionically conductive and electrically insulative in nature, nanosheets allows ions pass through them while not allowing electrons pass through the same.

[0026] In one example of the present of invention, a 10 ml of 1,2-dimethoxy ethane (DME) solvent was taken in a 15 ml vial. The vial was placed into a custom-made barrel cell made of polyether ether ketone (PEEK) equipped with gas in/outlets and sealed. This part of the procedure was performed in Ar filled glove box. The sealed barrel cell containing DME filled glass vial was then taken out of the glove box and was then pressurized with ultra-high purity grade Nitrogen (99.999 %), at a pressure level up to 15 bar. The pressurized (PEEK) cell was kept statically for at least 72 hours. Further, a 12 mm diameter of Lithium metal film was first roll pressed onto a side of a stainless-steel disc to ensure a reaction between Lithium and Nitrogen only happens on one side of the stainless steel disc. The thickness of pressed Lithium metal foil ranges from 150 µm to 180 µm. The stainless-steel disc containing Lithium metal foil was immersed/dipped into Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) solvent and was kept for at least 24 Hours. Post the immersion process, it was observed that complete the reaction between Lithium and dissolved N2 was occurred and pure crystal phase lithium nitride (Li3N) nanosheets were grown on the exposed surface of Lithium (Li) metal anode. The stainless-steel disc containing Lithium metal foil was then taken out and dried at room temperature for at least 24 hours thereby forming a lithium nitride (Li3N) passivated anode electrode for Lithium–sulfur (Li–S) batteries. The thickness of Li3N passivation layer ranges from 450 to 500 nm. The thickness of the pure phase Lithium nitride (Li3N) nanosheets ranges from 4 nm to 8 nm.

[0027] In exemplary implementation of the present invention, a Sulfur/Lithium Aluminate composite cathode is used as a cathode electrode for Lithium–sulfur (Li–S) batteries. The Sulfur/Lithium Aluminate composite cathode is fabricated by using steps comprising synthesizing ultrathin Lithium Aluminate (LiAlO2) nanoflakes, preparing a Lithium Aluminate (LiAlO2)/Sulfur composite by mixing ultrathin Lithium Aluminate (LiAlO2) nanoflakes and commercial sulfur powder, and milling the resultant mixture, heating the Lithium Aluminate (LiAlO2)/Sulfur composite to embed and uniformly distribute the LiAlO2 nanoflakes into the sulfur particles and fabricating the Sulfur/Lithium Aluminate composite cathode electrode for the Lithium–sulfur (Li–S) battery.

[0028] The ultrathin lithium aluminate (LiAlO2) nanoflakes are synthesized by preparing a first mixture of Lithium Hydroxide, aluminium iso-propoxide and cetyltrimethylammonium bromide, dissolving the prepared first mixture into deionized water and performing a hydrothermal synthesis of the dissolved first mixture. The cathode electrode for a Lithium–sulfur (Li–S) battery is fabricated by preparing a second mixture of lithium aluminate (LiAlO2)/sulfur composite, carbon black and polyethylene oxide, dispersing the second mixture in acetonitrile and casting the second mixture on aluminium foil followed by a vacuum drying process.

[0029] In one example of the present invention, the ultrathin lithium aluminate (LiAlO2) nanoflakes are synthesized by using the following steps: a first mixture of lithium hydroxide, aluminium iso-propoxide and cetyltrimethylammonium bromide at a mole ratio of 42:42:16 is prepared and the prepared first mixture is dissolved into deionized water. In an example, 0.25 mmol lithium hydroxide, 0.25 mmol aluminium iso-propoxide and 0.1 mmol cetyltrimethylammonium bromide is used for preparing the first mixture. A hydrothermal synthesis of the dissolved first mixture is performed at a temperature of 150 ? ± 1 ? for a period of 10 hours ± 15 minutes. 20 wt% of ultrathin lithium aluminate (LiAlO2) nanoflakes and 80 wt% of commercial sulfur powder are mixed and ball-milled for 1 hour to prepare the lithium aluminate (LiAlO2)/sulfur composite. The ball-milling process may be performed for a period in a range of 1 hour ± 5 minutes. Then, the lithium aluminate (LiAlO2)/sulfur composite is the heated at a temperature of 150 ? ± 2 ? for a period of 2 hours ± 5 minutes. A second mixture of 75 wt% of lithium aluminate (LiAlO2)/sulfur composite, 10 wt% of carbon black and 15 wt% of polyethylene oxide is dispersed in acetonitrile. Further, the second mixture is casted on aluminium foil followed by vacuum drying at a temperature of 60 ? for 48 hours to fabricate the cathode electrode for Lithium–sulfur (Li–S) batteries. The vacuum drying is performed at a temperature in a range of 60 ? ± 5 ? and for a period of 48 hours ± 15 minutes.

[0030] As disclosed above, the commercial sulfur powder is mixed with high surface area, ionically conductive lithium aluminate (LiAlO2) nanoflakes for preparing the composite, followed by a heat treatment for the fabrication. After heat treatment, the LiAlO2 nanoflakes are uniformly distributed as well as embedded on/into the sulfur particles. The uniform distribution of LiAlO2 nanoflakes on sulfur particles act as a barrier against gradual dissolution of active material and thus could effectively enhance the longevity of Li-S batteries. Due to high Li+ ion conductivity, the embedded LiAlO2 nanoflakes, on other hand, improve the overall reaction kinetics in lithium-sulfur batteries. The enhancement in reaction kinetics results in higher utilization of active material, leading to higher practical cell capacity.

[0031] In another embodiment of the present disclosure, a method of fabricating a Lithium–sulfur (Li–S) battery with a novel Lithium Nitride (Li3N) passivated anode electrode is disclosed. The method comprises the steps of fabricating a novel Lithium Nitride (Li3N) passivated anode electrode pasted on a stainless steel current collector by using the method as discussed in the previous embodiments (300) and fabricating a Sulfur/Lithium Aluminate composite cathode electrode casted on an aluminium foil current collector using various steps as discussed in the previous embodiments (400). The method of fabricating a Lithium–sulfur (Li–S) battery further comprises the steps of preparing a liquid electrolyte for the Lithium–sulfur (Li–S) battery, placing the fabricated Li3N passivated Lithium anode electrode against a Sulfur/Lithium Aluminate composite cathode electrode placed in an electrolyte (500) and placing a polypropylene membrane between the anode electrode and the cathode electrode (600).

[0032] In one example of the present invention, the electrolyte is prepared by dissolving 1M Lithium bis(trifluoro methane)-sulfonamide salt in 1:1 (v/v) ration of mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents. The polypropylene membrane is used as a separator between the anode electrode and the cathode electrode. The lithium bis(trifluoro methane)-sulfonamide solution is used a main salt. A polyproylene membrane separator is soaked with 40 µL of liquid electrolyte in between L3N modified Li anode and LiAlO2/S cathode. Further, the fabricated cathode electrode, passivated anode electrode and the liquid electrolyte soaked separator are air-sealed in 2032 type coin cells. Referring to figure 2, illustrated is a flow chart depicting the method of fabricating a Lithium–sulfur (Li–S) battery with a novel Lithium Nitride (Li3N) passivated anode electrode in accordance with another embodiment of the present disclosure.

[0033] In yet another embodiment of the present disclosure, a Lithium–sulfur (Li–S) battery with a novel Lithium Nitride (Li3N) passivated anode electrode is disclosed. The Lithium–sulfur (Li–S) battery comprises a Lithium Nitride (Li3N) passivated anode electrode, a Sulfur/Lithium aluminate composite cathode electrode, and an electrolyte. As said above, the electrolyte comprises of 1M lithium bis(trifluoro methane)-sulfonamide in 1:1 (v/v) mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents. The Lithium Nitride (Li3N) passivated anode electrode is prepared by growing pure phase Lithium nitride (Li3N) nanosheets on a surface of Lithium (Li) metal anode as discussed in the above method disclosed in the first embodiment. Further, the Sulfur/Lithium aluminate composite cathode is prepared by the method as discussed in the above embodiments. The Lithium–sulfur (Li–S) battery further comprises a polypropylene membrane placed between the anode electrode and the cathode electrode.

[0034] Referring to figure 3, illustrated is low-resolution SEM images of pristine Li disk and Li3N-passivated Li disk in accordance with the present disclosure. Figure 3 (a-c) show low-resolution SEM images of (a-c) pristine Li disk whereas Figure 3 (d-f) show low-resolution SEM images of Li3N-passivated Li disk. Referring to figure 4, illustrated is high-resolution SEM images of vertically oriented Li3N nanosheets formed on the surface of Li anode. The thickness of each nanosheet is estimated to be ˜ 4 nm roughly.

[0035] Referring to figure 5, illustrated is a symmetric cell performance of Lithium anodes in accordance with the present disclosure. Figure 5 - (a) shows Lithium plating/stripping behaviour of pristine Li anode and Li3N-passivated Li anode at a current density of 2 mA cm–2 with 2 mA h cm–2 charge passed. In figure 5 (a), insets show the enlarged views of the voltage profiles at specific times. The figure 5 – (b) shows galvanostatic lithium plating and stripping cycling of symmetric cell containing Li3N-passivated Li electrodes at the various current densities of 1 mA cm–2 and 2 mA cm–2 maintaining 1 h of total charge passed. IN the figure 5 –(b), inset shows the enlarged view of the voltage profiles at specific time.

[0036] Referring to figure 6, illustrated is a post cycling morphology analysis of pristine Lithium electrode in accordance with the present disclosure. Figure 6 (a) and (b) show Cross-sectional and Figure 6 (c) shows top-view SEM images of pristine Li electrode after 120 cycles of plating/stripping at 2 mA cm–2 with 2 mA h cm–2 charge passed. Figure 6 (d) shows cross-sectional and Figure 6 (e, f) show top-view SEM images of Li3N-passivated Li electrode after 300 cycles of plating/stripping at 2 mA cm–2 with 2 mA h cm–2 charge passed. The SEM images for both pristine Li and Li3N-passivated Li electrodes were acquired after the plating step at the end of cycling test.

[0037] Referring to figure 7, illustrated is a Lithium-sulfur battery performance in accordance with the present disclosure. Figure 7 - (a, b) show voltage profiles of S@LiAlO2 cathodes coupled with pristine Li anode and Li3N-passivated Li anode at the current rate of 2C. Figure 7 - (c, d) show cycling performance of the S@LiAlO2 cathode against bare Li anode and Li3N-passivated Li anode at the current rate of 2C. Referring to figure 8, illustrated is a schematic illustration of the hypothesized role of the passivation layer of Li3N nanosheets grown on the surface of Li anode to control the dendrite growth compared to bare Li anode.

[0038] Referring to figure 9, illustrated is a custom-made barrel cell made of polyether ether ketone (PEEK) equipped with the gas in/outlets in accordance with the examples of the present disclosure. The sealed PEEK cell containing DME filled glass vial is being pressurized with ultra-high purity grade nitrogen, (99.999%) up to 15 bar.

[0039] The present invention discloses a lithium-sulfur battery comprised of a Li3N passivated Li anode and a sulfur/lithium aluminate (S/LiAlO2) composite cathode. The lithium-sulfur battery can operate for more than 1000 cycles with an average coulombic efficiency of 99.6%. The key advantage of the present invention is that with utilization of low-cost but effective technique to passivate the lithium metal anode, for achieving long-term Li/S batteries. Moreover, the thickness of Li3N passivating layer on lithium anode can be controlled and optimized (based on the requirements) using the present invention. Thus, the present invention passivates the lithium metal anode surface with desired thickness in such a cost-effective way.

[0040] The present invention discloses novel methods of fabrications that control the reaction kinetics between Lithium metal and gaseous hydrogen by dissolving N2 in the 1,2-dimethoxy ethane (DME) solvent and using the same for reaction with Lithium anode thereby growing Li3N nanostructures on the surface of Lithium anode. The Lithium Nitride (Li3N) passivation layer acts as a protective layer for Li and with the results, provides a robust alternative from conventional protective materials for Li anodes.

[0041] Further, the present invention is advantageous over existing methods as the present invention discloses a cost-effective strategy to protect the lithium anode for rechargeable lithium-sulfur batteries. The present invention also encourages the direct utilization of sulfur powder in lithium-sulfur batteries. Considering the facile, cost-effective approach adopted to prepare the cathode material and its stable cycling performance with adequate practical cell capacity, it is believed that the present invention can be easily scalable to the industrial requirements of bulk production of lithium-sulfur batteries. The present invention is most suited to the electric appliances requiring high energy density, for example drones. The Li-S batteries are also suitable for battery powered “Auto” applications.

[0042] The above description along with the accompanying drawings is intended to disclose and describe the preferred embodiments of the invention in sufficient detail to enable those skilled in the art to practice the invention. It 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 exemplary implementations and other implementations exist within the scope of the claimed invention. Various changes in the form and detail may be made therein without departing from its spirit and scope. Similarly, various aspects of the present invention may be advantageously practiced by incorporating all features or certain sub-combinations of the features.
,CLAIMS:We claim:

1. A method of fabricating a Lithium metal anode electrode with a protective coating layer for Lithium–sulfur (Li–S) batteries, the method comprising the steps of:
preparing a Nitrogen (N2) saturated 1,2-dimethoxy ethane (DME) solvent, by dissolving ultra-high purity grade Nitrogen (99.999%, Grade 5.0, BOC) in the 1,2-dimethoxy ethane solvent; and
forming a protective Lithium Nitride (Li3N) passivated layer on a Lithium (Li) metal anode by growing pure phase Lithium nitride (Li3N) nanosheets on a surface of the Lithium (Li) metal anode.

2. The method as claimed in claim 1, wherein dissolving ultra-high purity grade Nitrogen in the 1,2-dimethoxy ethane solvent comprises pressurizing the 1,2-dimethoxy ethane solvent with ultra-high purity grade Nitrogen (N2) gas, at a high pressure ranging from 14-16 bar using a custom-made barrel cell made of polyether ether ketone (PEEK) equipped with gas in/outlets.

3. The method as claimed in claim 2, wherein the ultra-high purity grade Nitrogen (N2) pressurized 1,2-dimethoxy ethane is statically kept for a period ranging from 70 to 90 hours.

4. The method as claimed in claim 1, wherein the thickness of the pure phase Lithium nitride (Li3N) nanosheets ranges from 4 nm to 8 nm.

5. The method as claimed in claim 1, the thickness of Li3N passivation layer ranges from 450 to 500 nm.

6. The method as claimed in claim 1, wherein forming a protective Lithium Nitride (Li3N) passivated layer on a Lithium (Li) metal anode comprises the steps of:
pressing a Lithium (Li) metal foil onto at least one side of a current collector material for a reaction of Nitrogen with Lithium on a side of the current collector material, wherein the current collector material is selected from a group comprising stainless-steel, Nickel, Alumium foil and Copper foil;
immersing the current collector material containing pressed Lithium Metal foil into Nitrogen (N2) saturated 1,2-dimethoxy ethane solvent to complete the reaction between Lithium and dissolved N2, leading to a formation of pure crystal phase Lithium nitride (Li3N) nanosheets on the exposed surface of Lithium metal anode.

7. The method as claimed in claim 6, wherein thickness of pressed Lithium metal foil ranges from 150 µm to 180 µm.

8. The method as claimed in claim 6, wherein the Lithium (Li) metal foil is roll pressed onto a current collector material on one side.

9. The method as claimed in claim 6, wherein the current collector material containing pressed Lithium metal foil is immersed into Nitrogen (N2) saturated 1,2-dimethoxy ethane for a period ranging from 24 Hours to 36 Hours .

10. A method of fabricating a Lithium–Sulfur (Li–S) battery, the Lithium–Sulfur (Li–S) battery comprises a Lithium metal anode electrode with a protective coating layer fabricated using the steps as claimed in claim 1, the method comprising the steps of:
pasting the fabricated anode electrode on a current collector material;
preparing a cathode electrode casted on another current collector;
preparing an electrolyte for the battery by dissolving 1M lithium bis(trifluoro methane)-sulfonamide in 1:1 (v/v) ratio of mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents;
placing the fabricated anode electrode against a cathode electrode placed in an electrolyte; and
placing a polypropylene membrane between the anode electrode and the cathode electrode.

11. The method as claimed in claim 10, wherein the method comprises the steps of air-sealing the fabricated anode electrode, the cathode electrode, and the electrolyte.

12. The method as claimed in claim 10, wherein the cathode electrode is a Sulfur/Lithium Aluminate composite cathode electrode.

13. A Lithium–Sulfur (Li–S) battery, the Lithium–Sulfur (Li–S) battery comprises a Lithium metal anode electrode with a protective coating layer fabricated using the steps as claimed in claim 1, the Lithium–Sulfur (Li–S) battery further comprising:
a cathode electrode;
an electrolyte comprising 1M lithium bis(trifluoro methane)-sulfonamide in 1:1 (v/v) ratio of mixture of 1,2-dimethoxy ethane and 1,3-dioxolane solvents;
a polypropylene membrane placed between the anode electrode and the cathode electrode;
wherein the anode electrode is placed against the cathode electrode.

14. The Lithium–Sulfur (Li–S) battery as claimed in claim 13, wherein the cathode electrode is a Sulfur/Lithium Aluminate composite cathode electrode.