WO2023238163A1 - MAGNESIUM ION BATTERY EMPLOYING Mg-ENRICHED ELECTROLYTE-CUM-MEMBRANE AND METHOD OF FABRICATION THEREOF - Google Patents

Abstract

The present disclosure provides a Mg-ion-battery, wherein the positive electrode (cathode) comprises a Magnesium (Mg) rich or Iron (Fe) rich phyllosilicate as Cathode active material, and the negative electrode (anode) comprises a carbonaceous material such as carbon black, graphite or graphene, or the negative electrode (anode) material is of metallic-Mg, and a separator membrane coated with a phyllosilicate that is Mg-enriched, wherein the Mg-enriched phyllosilicate in an aspect of the disclosure is in a quasi-solid-state. The Mg-ion-battery exhibits a specific capacity of up to 700 mAh/g, and a cycle stability of up to 10,000 cycles at 0.1 C to 1C.

Description

TITLE

MAGNESIUM ION BATTERY EMPLOYING Mg-ENRICHED ELECTROLYTE-CUM-MEMBRANE AND METHOD OF FABRICATION THEREOF

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims priority to India complete patent application number 202241033599 filed on May 19, 2023, which claims priority to India provisional patent application number 202241033599 filed on June 11, 2022. The entire contents of all are herein incorporated by reference.

FIELD

The present disclosure relates to a Mg-ion-battery, more particularly relates to a Mg-ion-battery employing an Mg-enriched Electrolyte coated on the membrane.

DEFINITION

As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.

As used herein, the terms “Magnesium-enriched”, “Mg-enriched”, “Mg²⁺ enriched”, “Mg²⁺ ion enriched” “enriched with Mg”, “enriched with Mg²⁺”, “enriched with Mg²⁺ ions” and the like may have been used interchangeably in the present disclosure, all of which are to mean strengthening of a natural phyllosilicates with Mg²⁺ ions by artificially adding Mg²⁺ ions into the phyllosilicate lattice.

As used herein, the term “phyllosilicate” is to mean the silicates, the lattice of which are naturally rich in several metal ions (generally present as metal oxides). As used herein, the term “bentonite” and “bentonite clay” may have been used interchangeably, all of which are to mean the phyllosilicate used in the present disclosure for various structural and electrochemical studies.

As used herein, the term “quasi-solid-state” is to mean “moderately solid state” or “partially solid state” or “partly solid state”, which in the context of the present disclosure, is indicative of the membrane-cum-electrolyte, more specifically the coated matter (phyllosilicate) on the membrane that acts as electrolyte is not 100% dried to enable the membrane-cum-electrolyte to remain flexible, as well as the coated electrolytic matter (phyllosilicate) does not crack during handling of the membrane-cum-electrolyte for fabrication of the battery, or during prolonged use of the membrane-cum-electrolyte throughout the battery life.

As used herein, the terms “natural”, or “native” may have been used interchangeably in the context of the clay, phyllosilicates, or especially bentonite clay, which indicates the as procured clay, or phyllosilicates, or especially bentonite clay that are in their natural form, without any artificial alteration in their natural form.

As used herein, the terms “membrane-cum-electrolyte”, or “separator-membrane- cum-electrolyte” may have been used interchangeably, in line with the known electrochemical concepts of a “membrane” or a “separator membrane” are generally used interchangeably.

BACKGROUND

For the past twenty years, the dominance of Lithium-ion batteries (LiBs) in the portable electronics market as energy storage devices is attributed to their high energy density. Nevertheless, LiBs gradually are becoming economically non- feasible due to factors primarily including:

- exponentially increasing requirement of stationary energy storage sector, and

- the high cost of raw materials such as Ni and Co. Lately, other earth abundant material-based batteries such as Sodium ion, Potassium ion, Calcium ion, Magnesium ion, Aluminium and Zinc batteries have been extensively studied in the literature to replace LiBs. In spite of the humongous efforts by the researchers, it is still a challenge to develop earth abundant metal-based batteries possessing good cycle ability and cost effective and identical energy density like LiBs.

CN107645013A discloses a composite quasi-solid-state electrolyte comprises a solid electrolyte, a lithium salt-containing liquid electrolyte, inorganic nanoparticles and a binder, wherein the static electricity or functional groups on the surface of the inorganic nanoparticles can adsorb the electrolyte so as to make the composite quasi-solid-state electrolyte have strong adsorption capacity and strong liquid retention ability, and the inorganic nanoparticles can adsorb the lithium salt so as to change the lithium ion conduction mechanism, reduce the interfacial resistance between the liquid electrolyte and the solid-state electrolyte, change the deposition morphology of lithium, hinder the formation of lithium dendrite, and reduce the pulverization of lithium.

CN115241529A discloses a quasi-solid-state battery that comprises a polymer gel electrolyte comprising the steps: Step 1. dissolving 100 mg of trimethylolpropane ethyloxyl triacrylate and 5-10 g of polyethylene oxide in 20 mL of an organic solvent, and stirring for 12 h to obtain a first mixture; Step 2. adding 2-5g of lithium salt into the first mixture, and stirring for 30 minutes to obtain a second mixture; and Step 3. adding a photoinitiator 2-hydroxy-2-methyl-l -phenyl- 1- propane into the second mixture, and carrying out stirring for 30 min so as to obtain the gel electrolyte precursor.

As discussed in the following literature:

— F.F. Liu, T.T. Wang, X.B. Liu, L.-Z. Fan, Adv. Energy Mater. 10 (2020) 2000787, - P. Saha, M.K. Datta, 0.1. Velikokhatnyi, A. Manivannan, D. Alman, P.N. Kumta, Prog. Mater Sci., 66 (2014) 1-86,

- Y. Liang, H. Dong, D. Aurbach, Y. Yao, Nat. Energy, 5 (2020) 646-656,

- F.F. Liu, Y.C. Liu, X.D. Zhao, K. Y. Liu, H.Q. Yin, L.-Z. Fan, Small, 16 (2020) 1906076, on account of the inherent advantages of Mg anode in Mg- ion batteries (MBs) such as high theoretical specific capacity and abundance, it has gained great attention amongst researchers as an alternative to lithium (Li) metal anode.

The major advantages of Mg over Li come from the fact that:

- Mg metal anodes possesses higher volumetric capacity of 3833 mAh cm'³ in comparison to 2036 mAh cm'³ for Li,

- the low susceptibility towards dendrite formation by Mg²⁺ which is very high in Li metal anodes, as discussed in J. Muldoon, C.B. Bucur, T. Gregory, Angew. Chem. Int. Ed., 56 (2017) 12064-12084.

- lesser reactivity and higher mechanical strength of Mg metal anode allows it to be prepared in room temperature and in atmospheric conditions when compared to high reactivity of Li metal in air, moisture and environment, and hence Mg is easy to produce on a large scale. In the cost perspectives, Mg is approximately 30 times cheaper than Li and 5^th abundant metal in the earth’s crust, as discussed in F.F. Liu, T.T. Wang, L.Z. Fan, J. Chinese Ceram. Soc., 48 (2020) 947-962.

Thus, due to the above advantages, MBs are considered as the most favourable candidate for next-generation battery technologies.

As discussed in Z. Lu, A. Schechter, M. Moshkovich, D. Aurbach, J. Electroanal. Chem., 466 (1999) 203-217, the major bottleneck in commercialization of MBs are the electrolytes including magnesium salts in polar aprotic solvents that react with Mg metal anode leading to the formation of insulating passivation films on Mg anode surface. As the passivation layer is insulating in nature, it hinders the diffusion of Mg²⁺ ions during charge-discharge cycle and subsequent solid state electrodic reactions. Hence, to mitigate the loss of the electroactive species Mg²⁺ ions, it becomes inevitable to identify an electrolyte that does not form a passivation layer on the surface of Mg anode.

In this aspect, as discussed in the following literature:

— D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature, 407 (2000) 724-727,

— D. Aurbach, I. Weissman, Y Gofer, E. Levi, Chem. Rec., 3 (2003) 61-73,

— N. Pour, Y Gofer, D.T. Major, D. Aurbach, J. Am. Chem. Soc., 133 (2011) 6270-6278,

— O. Tutusaus, R. Mohtadi, T.S. Arthur, F. Mizuno, E.G. Nelson, Y.V. Sevryugina, Angew, Chem. Int. Ed., 54 (2015) 7900-7904,

— R.E. Doe, R. Han, J. Hwang, A. J. Gmitter, I. Shterenberg, H.D. Yoo, N. Pour, D. Aurbach, Chem. Comm., 50 (2014) 243-245,

— I. Shterenberg, M. Salama, H.D. Yoo, Y. Gofer, J.-B. Park, Y.-K. Sun, D. Aurbach, J. Electrochem. Soc., 162 (2015) A7118-A7128, in the past few decades, several liquid electrolytes that possess reversible plating/stripping of Mg²⁺ ions were developed. The liquid electrolytes include Grignard reagents such as dichloro, all phenyl complex, Boron-centric magnesium monocarborane, magnesium aluminium chloride complex electrolyte, magnesium- bis (trifluoromethanesulfonyl) imide-based electrolyte, so on and so forth.

Unfortunately, the solvents used for all the above-mentioned magnesium electrolytes are ether-based solvents such as 4-Tetrahydrofuran (THF), 1,2- Dimethoxy ethane (DME), that does not react with Mg anode to form passivation layer. In addition, polymer electrolytes are also of importance in MBs due to its safety, broad potential window and outstanding flexibility. When Gel polymer electrolyte is combined with liquid electrolyte, it resulted in advantageous Quasi Solid State Electrolyte (QSSE) having exceptional Mg²⁺ conductivity and safety. Several gel polymer electrolytes are reported in the following literature:

— G.P. Pandey, S.A. Hashmi, J. Power Sources, 187 (2009) 627-634.

— = R. Manjuladevi, M. Thamilselvan, S. Selvasekarapandian, R. Mangalam, M. Premalatha, S. Monisha, Solid State Ion., 308 (2017) 90-100.

— M.A.K.L. Dissanayake, L.R.A.K. Bandara, L.H. Karaliyadda, P.A.R.D. Jayathilaka, R.S.P. Bokalawala, Solid State Ion., 177 (2006) 343-346.

— G.P. Pandey, R.C. Agrawal, S.A. Hashmi, J. Power Sources, 190 (2009) 563- 572. that include PVDF (Polyvinylidene fluoride), PEO (polyethylene oxide), PVDF- HFP, PAN (Polyacrylonitrile) as polymer substrates, Mg(Tf)2, Mg(C104)2 as magnesium salts, and EMITf, EMIMFSI, EC/PC, Pyri4-TFSI, as disclosed in the following literature as plasticizers:

— G.P. Pandey, S.A. Hashmi, J. Power Sources, 187 (2009) 627-634,

— J.-S. Oh, J.-M. Ko, D.-W. Kim, Electrochim. Acta, 50 (2004) 903-906,

— S. Song, M. Kotobuki, F. Zheng, Q. Li, C. Xu, Y. Wang, W.D.Z. Li, N. Hu, L. Lu, J. Electrochem. Soc., 164 (2017) A741-A743,

— R. Deivanayagam, M. Cheng, M. Wang, V. Vasudevan, T. Foroozan, N.V. Medhekar, R. Shahbazian-Yassar, ACS Appl. Energy Mater., 2 (2019) 7980- 7990.

But these gel polymer electrolytes, when fabricated as full cell with cathode and anode displayed very low cycle stability of less than 15 cycles as disclosed in the following literature:

— J.-S. Oh, J.-M. Ko, D.-W. Kim, Electrochim. Acta, 50 (2004) 903-906,

— O. Chusid, Y. Gofer, H. Gizbar, Y. Vestfrid, E. Levi, D. Aurbach, I. Riech, Adv. Mater., 15 (2003) 627-630,

— [22] G.P. Pandey, R.C. Agrawal, S.A. Hashmi, J. Solid State Electrochem., 15 (2010) 2253-2264. These facts indicate that a stable electrolyte that does not react with Mg electrode surface is the need of the hour to achieve high stability and extended performance in MBs as discussed in the following literature:

— M. Jia, Z. Bi, C. Shi, N. Zhao, X. Guo, ACS Appl Mater Interf., 12 (2020) 46231-46238,

— [24] C. Yan, H. Yuan, H.S. Park, J.-Q. Huang, J. Energy Chem., 47 (2020) 217-220.

Recently published literature A. Du, H. Zhang, Z. Zhang, J. Zhao, Z. Cui, Y. Zhao, S. Dong, L. Wang, X. Zhou, G. Cui, Adv. Mater., 31 (2019) el 805930, discloses that PTB@GF-GPE (polytetrahydrofuran (PTHF)-borate based gel polymer electrolyte coupled with glass fiber is found to be stable for long at room temperature, while usage of THF resulted in volatility and toxicity risks as disclosed in literature Kamland. O, Olsson. S, Nilsson. U, Clay Technology AB, December 2006.

In 2020, researchers have developed porous PVDF-HFP based PPE by immersing porous PVDF-HFP based PPE in MgCh-AlCh/TEGDME electrolyte. This QSSE exhibited high Mg²⁺ conductivity of the order of 4.72x10-4 Scm ¹, at 25°C and reversible Mg²⁺ plating/stripping vs Mg anode. The quasi-solid-state Magnesium ion Batteries (QSSMgBs) with this electrolyte, M0S2/C cathode, and Mg anode showed specific capacity of 91.5 mAhg ¹ at 20 mAg^-1, 48.7 mAhg ¹ at 200 mAg^-1 with cycling stability up to 1700 cycles as discussed in literature A. Du, H. Zhang, Z. Zhang, J. Zhao, Z. Cui, Y. Zhao, S. Dong, L. Wang, X. Zhou, G. Cui, Adv. Mater., 31 (2019) H805930, without forming passivation layer on Mg anode and other solvent based side reactions.

Owing to the above-mentioned bottlenecks, and organic solvent-based solutions for QSSE, there is a need to develop an environmentally friendly quasi-solid-state magnesium ion battery (QSSMgB) that exhibits higher specific capacity, and higher cycle stability, which the present inventors envisaged by providing a membrane cum electrolyte with high ionic conductivity, enabling high electrolyte uptake, and empowering its operation in a wide voltage window.

SUMMARY

The present disclosure provides a Mg-ion-battery, wherein the positive electrode (cathode) comprises a Magnesium (Mg) rich or Iron (Fe) rich material as Cathode active material, and the negative electrode (anode) comprises a carbonaceous material such as carbon black, graphite or graphene, or the negative electrode (anode) material is of metallic-Mg, and a separator membrane coated with a material that is Mg-enriched, wherein the Mg-enriched material in an aspect of the present disclosure is in a quasi-solid-state.

Cathode: The Magnesium (Mg) rich or Iron (Fe) rich material is coated on a cathode current collector.

Anode: Carbonaceous material is coated on an anode current collector, or alternately, Mg-metal is used as anode.

Membrane-cum-Electrolyte: Separator membrane coated with a Mg-enriched material that acts as membrane-cum-electrolyte, which is sandwiched between the cathode and the anode.

In an aspect of the disclosure, the separator membrane is a polymer membrane, preferably a Polypropylene (PP) membrane.

In an aspect of the disclosure, the Mg-enriched material coated on the separator membrane is in quasi-solid-state.

In an aspect of the disclosure, the Mg-enriched material coated on the separator membrane is a Mg-enriched clay. In an aspect of the disclosure, the Mg-enriched material coated on the separator membrane is a Mg-enriched phyllosilicate.

In an aspect of the disclosure, the Magnesium (Mg) or Iron (Fe) rich material of the cathode is a natural clay that is naturally rich in Magnesium (Mg) or Iron (Fe).

In an aspect of the disclosure, the Magnesium (Mg) or Iron (Fe) rich material of the cathode is a natural phyllosilicate that is naturally rich in Magnesium (Mg) or Iron (Fe).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 illustrates structural analysis of natural phyllosilicates RSW(O) and Fe-rich RSW(N) and Mg-rich (B ENGEL RSI) Phyllosilicates by XRD.

Fig. 2 illustrates HR-SEM of the phyllosilicates at 60x magnification and 500nm.

Fig. 3A and 3B illustrates Energy dispersive X-ray analysis (ED AX) and chemical composition analysis of the BENGEL RSI tagged phyllosilicates.

Fig. 3C and 3D illustrates Energy dispersive X-ray analysis (ED AX) and chemical composition analysis of the RSW(N) tagged phyllosilicates.

Fig. 3E and 3F illustrates Energy dispersive X-ray analysis (ED AX) and chemical composition analysis of the RSW(O) tagged phyllosilicates.

Fig. 4 illustrates UV-Visible spectra of phyllosilicates used in the Mg-ion-battery of the present disclosure.

Fig. 5 illustrates FTIR spectra of phyllosilicates used in the Mg-ion-battery of the present disclosure.

Fig. 6 illustrates Cyclic voltammetry (CV) of BENGEL RSI tagged phyllosilicate coated on Pt disc electrode as working electrode, Ag/AgCl reference electrode and Pt wire as counter electrode in the potential window of -1.2 to 1.2 V at different scan rates such as 10, 25, 50, 75 and 100 mV/s in aqueous IM MgCh electrolyte.

Fig. 7 illustrates Cyclic voltammetry (CV) of RSW(N) tagged phyllosilicate coated on Pt disc electrode as working electrode, Ag/AgCl reference electrode and Pt wire as counter electrode in the potential window of -1.2 to 1.2 V at different scan rates such as 10, 25, 50, 75 and 100 mV/s in aqueous IM MgCh electrolyte.

Fig. 8 illustrates Cyclic voltammetry (CV) of RSW(O) tagged phyllosilicate coated on Pt disc electrode as working electrode, Ag/AgCl reference electrode and Pt wire as counter electrode in the potential window of -1.2 to 1.2 V at different scan rates such as 10, 25, 50, 75 and 100 mV/s in aqueous IM MgCh electrolyte.

Fig. 9 illustrates Electrochemical Impedance Spectroscopy (EIS) of BENGEL RSI, RSW(N) and RSW(O) coated on Pt disc electrode as working electrode, Ag/AgCl reference electrode and Pt wire as counter electrode in the frequency window of ImHz to 1MHz at an AC amplitude of 50mV in aqueous IM MgC12 electrolyte.

Fig. 10 illustrates electrochemical behaviour of the phyllosilicate cathodes and quasi-solid-state-electrolyte (QSSE) (((Ca)_x(Al,Mg)2-x(SuOio)(OH)_y- nF O)), 0<x,y<l, corresponding to a maximal charge capacity of 280 mAhg ¹. The electrolyte is IM MgCh in water. A chrono-potentiogram (voltage versus capacity) at constant current of 1 mA cm'² of steady state Mg insertion-de- insertion cycles vs metallic Mg anode.

Fig. 11 (Prior Art) Octahedral, tetrahedral sites and the exchangeable ions (cations) in the phyllosilicates as demonstrated in the literature Abdelfattah. M.M, Geber. R, Abdel-Kader. N. A, Kocserha. I, Arabian Journal of Geosciences ( 2022 ) 15: 205.

Fig. 12 illustrates the discharge profile of the coin cell with Fe-rich RSW(N) cathode, Mg-enriched RSW(O) coated on PP as QSSE, graphite anode at 0.1C, 0.5C and 1 C rate.

Fig. 13 illustrates the discharge profile of the coin cell with Fe-rich RSW(N) cathode, Mg-enriched RSW(O) coated on PP as QSSE, Carbon Black anode at 0.1C, 0.5C and 1 C rate.

Fig. 14 illustrates the discharge profile of the coin cell with Fe-rich RSW(N) cathode, Mg-enriched RSW(O) coated on PP as QSSE, graphite anode at 0.1C, 0.5C and 1 C rate, in acetone-water binary solvent at 1:1 ratio. Fig. 15 illustrates the discharge profile of the coin cell with Mg-rich BENGEL RSI cathode, Mg-enriched RSW(O) coated on PP as QSSE, graphite anode at 0.1C, 0.5C and 1 C rate.

Fig. 16 illustrates the discharge profile of the coin cell with Mg-rich BENGEL RSI cathode, Mg-enriched RSW(O) coated on PP as QSSE, CB anode at 0.1C, 0.5C and 1 C rate.

Fig. 17 illustrates the discharge profile of the coin cell with Mg-rich BENGEL RSI cathode, Mg-enriched RSW(O) coated on PP as QSSE, Mg anode at 0.1C, 0.5C and 1 C rate.

DETAILED DESCRIPTION

The preferred embodiments of the present disclosure will be described in detail with the following disclosure and examples. The foregoing general description and the following detailed description are provided to illustrate only some embodiments of the present disclosure and not to limit the scope of the present disclosure. The disclosure is capable of other embodiments and can be carried out or practiced in various other ways.

Unless otherwise specified, all the technical and scientific terms used herein have the same meaning as is generally understood by a person skilled in the art pertaining to the present disclosure.

Headings are used solely for organizational purposes, and are not intended to limit the disclosure in any way.

The use of the singular includes the plural unless specifically stated otherwise. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well. The use of “or” means “and/or” unless stated otherwise.

As used herein, the terms “comprises” and/or “comprising” specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, to the extent that the terms “includes,” “having,” “has,” “with,” “composed,” “comprised” or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.”

As used herein, ranges and amounts can be expressed as “about” a particular value or range. “About” is intended to also include the exact amount. Hence “about 5 percent” means “about 5 percent” and also “5 percent.” “About” means within typical experimental error for the application or purpose intended.

It is to be understood that wherein a numerical range is recited, it includes all values within that range, and all narrower ranges within that range, whether specifically recited or not.

Reference throughout this specification to “one embodiment,” “an embodiment,” “one example,” or “an example” means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “one example,” or “an example” in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and/or sub -combinations in one or more embodiments or examples. In addition, it should be appreciated that if any figures are provided herewith, they are for explanation purposes to persons ordinarily skilled in the art and that the drawings of them are not necessarily drawn to scale.

In this specification, certain aspects of one embodiment include process steps and/or operations and/or instructions described herein for illustrative purposes in a particular order and/or grouping. However, the particular order and/or grouping shown and discussed herein are illustrative only and not limiting. Those of skill in the art will recognise that other orders and/or grouping of the process steps and/or operations and/or instructions are possible and, in some embodiments, one or more of the process steps and/or operations and/or instructions discussed above can be combined and/or deleted. In addition, portions of one or more of the process steps and/or operations and/or instructions can be re-grouped as portions of one or more other of the process steps and/or operations and/or instructions discussed herein. Consequently, the particular order and/or grouping of the process steps and/or operations and/or instructions discussed herein do not limit the scope of the disclosure.

The present disclosure provides a Mg-ion-battery, wherein the positive electrode (cathode) comprises a Magnesium (Mg) rich or Iron (Fe) rich material as Cathode active material, and the negative electrode (anode) comprises a carbonaceous material such as carbon black, graphite or graphene, or the negative electrode (anode) material is of metallic-Mg, and a separator membrane coated with a material that is Mg-enriched, wherein the Mg-enriched material in an aspect of the present disclosure is in a quasi-solid-state.

Cathode: The Magnesium (Mg) rich or Iron (Fe) rich material is coated on a cathode current collector.

Anode: Carbonaceous material is coated on an anode current collector, or alternately, Mg-metal is used as anode.

Membrane-cum-Electrolyte: Separator membrane coated with a Mg-enriched material that acts as membrane-cum-electrolyte, which is sandwiched between the cathode and the anode.

While a person skilled in the art can select a suitable polymer for the separator membrane that can withstand the ionic diffusivity, conductivity, and resistance due to diffusion of ions, in an aspect of the disclosure, the polymer for the separator membrane is Polypropylene (PP).

In an aspect of the disclosure, the Mg-enriched material coated on the separator membrane is a Mg-enriched clay, more preferably a Mg-enriched phyllosilicate, and most preferably a Mg-enriched phyllosilicate that is also naturally rich in Mg.

Fabrication of Electrolyte-cum-Membrane

In an embodiment of the invention, the Electrolyte-cum-Membrane is prepared in the following manner:

- making a slurry of natural phyllosilicate in an organic solvent such as acetone or isopropanol,

- coating the slurry on both sides of a flexible membrane, preferably a polymeric membrane,

- drying the coated membrane in vacuum at 60°C to remove the organic solvent,

- Treating the dried coated membrane in aqueous solution of a Mg Salt for 2 hours, to allow sufficient amount of Mg²⁺ ions migration into the phyllosilicate, thereby forming ‘Mg-enriched phyllosilicate’, wherein this ‘Mg-enriched phyllosilicate’ acts as the electrolyte,

- drying the Mg-enriched phyllosilicate coated membrane at 80°C for 3 hrs to remove water content.

In a preferred embodiment of the disclosure, the Mg-enriched phyllosilicate electrolyte is not completely dried in order to avoid mud-cracks on the coating, thereby having the electrolyte in a quasi-solid-state (QSS), wherein thus formed quasi-solid-state electrolyte may be for the purpose of the present disclosure may be abbreviated as QSSE, and the battery fabricated using such QSSE in the present disclosure is quasi-solid-state Magnesium ion Battery (QSSMgB). Fabrication of the Cathode:

In an aspect of the disclosure, the Magnesium (Mg) or Iron (Fe) rich material of the cathode is a natural clay that is naturally rich in Magnesium (Mg) or Iron (Fe).

In an aspect of the disclosure, the Magnesium (Mg) or Iron (Fe) rich material of the cathode is a natural phyllosilicate that is naturally rich in Magnesium (Mg) or Iron (Fe).

- The Fe-rich or Mg-rich material is made into a slurry in a suitable solvent such as acetone or isopropanol,

- A stainless Steel (SS) current collector sheet of an appropriate size is cut and washed with Cone. HNO3 to remove surface grease and other impurities. It is then washed thoroughly several times with deionized water and dried in an oven at 100°C for 2 hrs,

- The Fe-rich or Mg-rich material slurry is coated on the dried SS sheets,

- The coated SS sheet is dried in vacuum at 60°C to remove the solvent,

- The dried coated SS sheet is used as cathode for the Mg-ion-Battery.

Fabrication of the Anode:

Anode of Carbonaceous material:

- Carbonaceous material such as carbon black, graphite or graphene is mixed with 2% by weight of PVDF as binder and ground well in a mortar and pestel to form a mixture.

- The ground mixture is mixed with a suitable medium such as acetone, isopropanol or ethanol that does not react with carbon to form a slurry,

- An Aluminium (Al) current collector sheet of an appropriate size is cut and washed with Cone. HNO3 to remove surface grease and other impurities. It is then washed thoroughly several times with deionized water and dried in an oven at 100°C for 2 hrs,

- The Carbonaceous material slurry is coated on the Al current collector, - The coated Al current collector is dried in vacuum at 60°C to remove the solvent,

- The dried coated Al sheet is used as anode for the Mg-ion-Battery.

Metallic Mg Anode:

- Mg-metal powder is mixed with 2% by weight of PVDF as binder to form a mixture,

- The mixture is mixed with a suitable medium such as acetone, isopropanol or ethanol to form a slurry,

- An Aluminium (Al) current collector sheet of an appropriate size is cut and washed with Cone. HNO3 to remove surface grease and other impurities. It is then washed thoroughly several times with deionized water and dried in an oven at 100°C for 2 hrs,

- The Mg-metal powder slurry is coated on the Al current collector,

- The coated Al current collector is dried in vacuum at 60°C to remove the solvent,

- The dried coated Al sheet is used as anode for the Mg-ion-Battery.

It is to be noted that, as known in the art, natural phyllosilicates such as Bentonite clay that belongs to the montmorillonite group of phyllosilicates, are generally rich in metal oxides such as oxides of Mg, Fe, Na, Ca. Natural phyllosilicates (“phyllo” meaning sheet), or sheet silicates, are an important group of minerals that includes the micas, chlorite, serpentine, talc, and the clay minerals. Phyllosilicates such as montmorillonite with a chemical structure of (Na, Ca)o.33(Al, Mg)2(Si40io)(OH)2._nH20 is a 2:1 type layered silicate construction consisting of packets of two tetrahedral silicate layers and an octahedral with adjacent margins.

In order to estimate the suitability of the phyllosilicates to be used in the Mg-ion- battery of the present disclosure, several characterising studies were conducted. For the sake of clarity, and scientific inclusivity, it is to be noted that, while in the present disclosure, bentonite clay and its Mg-enriched form were considered for carrying out the experimentation of the present disclosure, a person skilled in the art may use other phyllosilicates such as smectites, Liquid Crystals of bentonite, the lattice of which are naturally rich in Fe ions or Mg ions (generally present in the form of Magnesium oxides) in comparison to the fraction of other metal ions (generally present as metal oxides), or a person skilled in the art can be selective in choosing those phyllosilicates, or other silicates that are known to be Fe-rich or Mg-rich in order to meet the desired requirements of the present disclosure, or tested and characterised to be found as Fe-rich Mg-rich through targeted experimentation, or hit and trial in order to meet the desired requirements of the present disclosure, i.e. the need as a cathode material or the need as a electrolyte coating material on the membrane.

Characterisation of Bentonite clay samples:

Natural bentonite clay was chosen as the natural phyllosilicate for experimental purpose, which was procured from Cutch Oil and Allied Industries Pvt Ltd, Gujarat, India, and was used as such without any further purification.

After characterisation of several bentonite clay samples, three of them were identified to be used for the purpose of the present disclosure, which have been identified with the following three names for the sake of reference and clarity.

- RSW(O)

- RSW(N)

- BENGEL RSI

Physicochemical characterization :

Physiochemical characterizations of different natural bentonite clay samples were carried out via FTIR, UV-Vis, and XRD, and High Resolution Scanning Electron Microscopy (HR-SEM). The surface morphologies were observed by Scanning Electron Microscopy (SEM), Jeol, USA. The electronic spectroscopy characterization was conducted via UV-Vis and FTIR by Brucker, USA. The structural studies were done using Brucker p-XRD, USA. The chemical compositions were obtained by Energy Dispersive X-Ray Fluorescence (ED-XRF) technique.

Structural Analysis of the phyllosilicates for use as cathode material and as electrolyte

Fig. 1 illustrates structural analysis of natural phyllosilicates (RSW(O)), Fe-rich RSW(N) and Mg-rich (B ENGEL RSI) Phyllosilicates by XRD.

As inferred from Fig. 1:

- The mineral composition for the natural Bentonite clay sample “BENGEL RSI” being gy - Gypsum; g - goethite; f - feldspar; a - Anatase; Bun - Bunsite; Wur - Wurtzite; Cup - cuprite; m - mica; h - hematite, which indicates that the sample “BENGEL RSI” is a Mg-rich Bentonite clay).

- The mineral composition of the natural Bentonite clay sample “RSW(N)” is montmorilonite, feldspar, goethite, anatase, magnelite, wurtzite and cuprite, which indicates that the sample “RSW(N)” is a Fe-rich Bentonite clay.

- The mineral composition of the natural Bentonite clay sample “RSW(O)” being montmorilonite and illite.

Surface morphology of the phyllosilicates by High Resolution Scanning Electron Microscopy (HR-SEM)

The surface morphology of the phyllosilicates was carried out employing HR- SEM as provided in Fig. 2. As shown in Fig 2, it is explicitly observed that the phyllosilicates labelled BENGEL RSI and RSW(N) possess needle like surface morphology with high aspect ratio. This high aspect ratio of the phyllosilicates renders high Mg²⁺ ion conductivity and hence act as a better cathode material resulting in fast electrode kinetics of Mg²⁺ ions solid phase diffusion between cathode and cathode/electrolyte interface.

The RSW(O) possess bulk agglomerated surface morphology making them unsuitable for the electrocatalysis purpose, but suitable as electrolyte to hold the electroactive Mg²⁺ ions in it, which the present inventors made it possible by enriching it with Mg²⁺ ions.

ED AX analysis of the phyllosilicates

Fig. 3A and 3B illustrates Energy dispersive X-ray analysis (EDAX) and chemical composition analysis of the BENGEL RSI tagged phyllosilicates.

Fig. 3C and 3D illustrates Energy dispersive X-ray analysis (EDAX) and chemical composition analysis of the RSW(N) tagged phyllosilicates.

Fig. 3E and 3F illustrates Energy dispersive X-ray analysis (EDAX) and chemical composition analysis of the RSW(O) tagged phyllosilicates.

The EDAX chemical composition analysis of the phyllosilicates indicate that BENGEL RSI and RSW(N) are the ones with appropriate Mg-rich and Fe-rich composition to act as electrocatalyst or cathode material for the Mg-ion-Battery of the present disclosure, whereas RSW(O) possess replaceable Na⁺ sites that can be enriched with Mg²⁺ ions (as excess resource of Mg²⁺ ions) in order to act as electroactive species. Thus, the phyllosilicates utilized as cathode in the present invention are Mg-rich BENGEL RSI and Fe-rich RSW(N), whereas RSW(O) as the electrolyte.

Electronic spectra analysis of the phyllosilicates

Fig. 4 illustrates UV-Visible spectra of phyllosilicates used in the Mg-ion-Battery of the present disclosure. From Fig. 4, it is explicitly clear that the bentonite sample BENGEL RSI, showed a sharp peak at 261 nm indicating the Ca, Mg smectite composition corresponding to the presence of Ca²⁺, Mg²⁺, Al³⁺ in BENGEL RSI.

The bentonite sample RSW(N) shows broad peak from 260 to 302nm indicating tetrahedrally coordinated Fe³⁺ composition in the clay, which accounts for Fe³⁺, Al³⁺ and Si⁴⁺ presence in the Fe-rich bentonite clay.

The bentonite sample RSW(O), depicts broad peak from 261 nm to 304 nm, 370 nm, 513 nm and 659 nm. Broad peak from 261nm to 304 nm corresponds to tetrahedrally coordinated Fe³⁺ in the compound. 370 nm accounts for Ti⁴⁺ and Zn²⁺ whereas 513 & 659 nm represents Ni²⁺ and Cu²⁺ composition respectively in the clay. These results are in satisfactory agreement with the XRD and EDAX analysis conducted in the present disclosure.

FTIR studies of phyllosilicates

Fig. 5 illustrates FTIR spectra of phyllosilicates used in the Mg-ion-Battery of the present disclosure.

FTIR peaks of BENGEL RSI as shown in Fig. 5

The high intensity 476.3313 cm'¹ peak corresponds to ferroelectric absorptions.

Very high intensity peak at 982.5539 cm'¹ represents Ca-Al-Si-0 and Mg-Al-Si-0 stretching and bending vibrations.

A normal intensity peak at 1436.7079 cm'¹ denotes Mg-OH stretching and bending vibrations.

The intense peak at 1664.267 cm'¹ depicts Ca-OH stretching and bending modes. Small and sharp peaks at 2361.4077 and 2531.1178 cm'¹ accounts for the Fe(III)2- OH, Mg-OH, Si-O, Metal ion-hydroxyl group (M-OH), Fe(II)2-OH and H2O stretching as well as bending vibrations.

A small peak around 3088.4397cm ¹ is caused by the stretching vibrational mode of water molecules adsorbed on the phyllosilicate.

The intense overtone peak of water is noticed at 3246.574 cm ¹.

A small visible peak at 3397.9587 cm'¹ denotes Al-OH stretching vibrations.

Intense Mg-OH stretching peak is seen at 3585.02 cm ¹.

Thus, from FTIR analysis, it can be concluded that BENGEL RSI possess Mg²⁺, Al³⁺, Ca²⁺, Fe²⁺, Fe³⁺, Si⁴⁺ in its composition and is in concurrence with the XRD, ED AX and UV-Vis analysis conducted in the present disclosure.

FTIR peaks of RSW(N) as shown in Fig. 5

The high intensity peaks at 4550.297, 468.6175, 532.2569 cm-1 corresponds to the ferroelectric absorptions of the RSW(N) phyllosilicates.

A small sharp peak at 700.0335 cm-1 is accounted for Fe(III)2-OH stretching mode.

Very small but sharp peak at 791.6357 cm-1 denotes Al-Fe(III)-OH bending vibrations.

A very high intense at 1040.408 cm'¹ indicates Si-OH stretching frequency.

A shoulder peak to 1040.408 cm ¹, which is intense at 913.1291 cm ¹, again indicates ferroelectric absorptions. Metal ion-hydroxyl group (M-OH) stretching vibrations are seen at 1637.2684 cm^-1.

A lump kind of peak with good intensity at 3252.3594 cm'¹ is related to the overtone vibrations of water molecules.

The stretching vibration modes of water molecules adsorbed on the surface of phyllosilicates is noticed at 3414.3506cm ¹.

Intense peak at 3620.6965 cm'¹ depicts the Fe(III)-OH stretching vibration mode.

Al-OH stretching modes are observed at 3694.9426 cm-1.

Thus, the FTIR analysis of RSW(N) indicates that the phyllosilicate is rich in Fe and is in concurrence with the XRD, ED AX and UV-Vis studies conducted in the present disclosure.

FTIR peaks of RSW(O) as shown in Fig. 5

Three peaks of high intensity at 453.1897, 465.7248, 540.935 cm'¹ corresponds to Si-0 bending vibrations, Fe(III)-Si-0 bending mode and Fe(II) - OH bending vibrations respectively.

A small sharp peak at 699.0335 cm'¹ indicates Mg-OH bending vibration mode.

A very small and sharp peak at 785.8503 cm'¹ denotes the bending vibrations of Fe(III)2-OH functional group.

A sharp shoulder peak at 916.0218 cm-1 depicts the bending vibrations of Al-Fe- OH bond. Si-0 stretching mode is observed at 1035.5868 cm ¹. Bumpy shoulder peak after Al-Fe-OH peak is noticed at 1110.797cm ¹ and is also accounted for Si-0 bond stretching frequency.

Sharp intense peak at 1642.0896 cm'¹ is attributed to the M-OH stretching mode, where M may be Al³⁺, Fe²⁺, Fe³⁺, Ti⁴⁺, Cu²⁺ etc.

A very weak and small peak at 2368.1575 cm'¹ amounts to stretching and bending modes of water molecules adsorbed on the phyllosilicates.

Further, at 2921.6274 cm'¹ also water stretching mode is noticed.

A bumpy shoulder peak at 3224.3967 cm'¹ is seen due to the overtone by water molecules.

Less sharp and less intense peak at 3420.136 cm'¹ is due to the presence of Fe(III) - OH bond stretching mode.

Analogously, a less intense but sharp peak at 3619.7324 cm'¹ is caused by Fe(III)- OH bond stretching.

A very sharp and less intense peaks at 3694.9426 and 3747.9753 cm'¹ is contributed by the stretching vibrations of Al-OH bond in the phyllosilicate.

Thus, the FTIR analysis of RSW(O) supports the observations by XRD, EDAX and UV-Vis studies conducted in the present disclosure.

Chemical composition analysis of phyllosilicates by ED-XRF studies

The chemical composition of the phyllosilicates labelled as BENGEL RSI, RSW(N) and RSW(O) are deduced by subjecting to Energy Dispersive - X Ray Fluorescence (ED-XRF) and the composition of them are as depicted in Tables 1, 2 and 3. The general chemical composition of the phyllosilicate is represented as ((Ca)_x(Al,Mg)_2.xFe_y(Si₄Oio)(OH)_z-nH₂0).

Table 1 represents the ED-XRF based chemical composition analysis of the bentonite clay sample BENGEL RSI.

Table 1

Table 2 represents the ED-XRF based chemical composition analysis of the bentonite clay sample RSW(O).

Table 2

Table 3 represents the ED-XRF based chemical composition analysis of the bentonite clay sample RSW(N). Table 3

Thus the results of ED-XRF confirms and supports the characterization of the phyllosilicates by other studies such as XRD, SEM, UV-Vis and FTIR conducted in the present disclosure.

Electrochemical characterization of phyllosilicates

The three phyllosilicate (bentonite) samples i.e., BENGEL RSI, RSW(N) and RSW(O) were subjected to electrochemical characterization employing techniques such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic studies to understand the redox behaviour, ionic conductivity and the voltage retention of the materials upon electrochemical perturbations.

Zahner Zennium E4 electrochemical workstation (Germany) is used to perform electrochemical studies of materials to device.

Cyclic Voltametric (CV) Analysis:

The CV analysis of the phyllosilicates were carried out in a three-electrode assembly.

- Phyllosilicate coated Pt disc of 5mm diameter is used as working electrode,

- Ag/AgCl is used as the reference electrode,

- and Pt wire being the counter electrode,

- IM MgCh as electrolyte.

The potential window is in the range of -1.2 to 1.2 V. CV is recorded in different scan rates from 10 mV/s to 100 mV/s. CV studies of BENGEL RSI

Fig. 6 illustrates the plating and stripping behaviour of Mg²⁺ ions on the Mg-rich phyllosilicate (BENGEL RSI) in IM MgCh solution.

The reversible anodic and cathodic peaks indicate the deposition of Mg from electrolyte on BENGEL RSI and dissolution of the same by reduction process from the phyllosilicate at BENGEL RSI/MgCL interface.

In the forward scan, reduction of Mg²⁺ ions occur on BENGELRSI/electrolyte interface and deposition on the surface takes place. The deposition of Mg on BENGEL RSI leads to shift in the reduction potential as the surface of BENGEL RSI is covered with metallic Mg.

As the scan rate increases, the reduction potential shifts towards right from -0.1 to 0.25 V. This positive shift in the reduction potential is attributed to the change in the electric double layer or electrode/electrolyte interface from BENGEL RSI/MgCh to BENGEL RSI-Mg/MgCh. As more and more Mg gets deposited more positive shift is seen in at the electrochemical interface.

In the reverse scan, oxidation of deposited Mg on BENGEL RSI occurs leading to dissolution of Mg²⁺ ions into the electrolyte solution. The dissolution peaks of Mg²⁺ is seen as (i) hump at -0.4 V and (ii) a peak at -0.6V. Since the oxidation of Mg into Mg²⁺ is a two-step process as depicted below in equation 1 and equation 2, the characteristics of the two-step oxidation is seen as a hump and peak respectively.

Mg <-> Mg⁺ + e E = -0.4 V — Equation 1

Mg+ <-> Mg²⁺ + e E = -0.6 V — Equation 2

The oxidation peaks also shift with increase in scan rate from -0.35, -0.5 V to -0.4, -0.6V. The rationale behind the negative shift in the oxidation potential is due to the change in the electrode/electrolyte interface from BENGELRSI-Mg/MgCh to BENGELRSI/MgCh.

Hence, in the forward scan, approximately 350mV shift and in the reverse scan 200mV shift respectively with scan rate increase is noticed.

This reversible plating and stripping mechanism of Mg²⁺ ions on BENGEL RS I/clcctrolytc interface demonstrates the stability of the phyllosilicate on Mg deposition and dissolution, thereby indicating the ability of the phyllosilicate to act as cathode material for the Mg-ion-Battery of the present disclosure.

CV studies of RSW(N)

Fig. 7 depicts the platting and stripping process of Mg²⁺ ions on the Fe-rich RSW(N) phyllosilicate in IM MgCh solution.

In comparison with Mg-rich BENGEL RSI (as shown in Fig. 6), as RSW(N) possesses exchangeable Fe²⁺ sites in its lattice with Mg²⁺ ions, in the forward scan, Mg²⁺ reduction occurs leading to deposition of Mg on RSW(N). The shift in potential with increase in scan rate is from 0.05 to 0.5 V.

In the reverse scan, stripping or dissolution of the Mg into electrolyte as Mg²⁺ ions take place at -0.49 to -0.6 V. The potential shift with scan rate increase is approximately 50 mV, indicating the reversibility of the process. Thus RSW(N) can act as cathode material for Mg-ion-Battery of the present disclosure. The major advantage of using phyllosilicates such as Mg-rich BENGEL RSI and Fe- rich RSW(N) as cathode material is the fact that in the former due to the Mg-rich nature of the material (common ion effect), the plating process is thermodynamically favourable with negative AG, whereas in the case of RSW(N), it is due to the replacement of Fe²⁺ or Fe³⁺ sites in the octahedral lattice by Mg²⁺ ions. As the ionic radii of Fe²⁺ or Fe³⁺ in the octahedral geometry is close to about 0.89 and 0.92 pm, replacing either of the one by similar sized Mg²⁺ ions (approx. 0.82 pm) becomes facile. Thus, plating and stripping of Mg²⁺ ions in both Mg-rich B ENGEL RSI and Fe-Rich RSW(N) requires almost same Gibbs free energy due to similar ionic radii of the species involved and hence redox peaks show up at almost identical potential window.

CV studies of RSW(O)

Fig. 8 represents the plating and stripping process of Mg²⁺ ions in the phyllosilicate (bentonite) sample RSW(O) enriched with Mg²⁺ ions via soaking the phyllosilicate in IM MgCh, wherein the Mg-enriched RSW(O) is used as electrolyte in the Mg-ion-Battery of the present disclosure. This Mg-enrichment makes further diffusion of Mg²⁺ ions from bulk of the electrolyte on plating process more feasible, thereby allowing more solid phase diffusion of Mg²⁺ ions across the Mg-enriched RSW(O) electrolyte. Thus, the plating voltage is around - 0.1 to 0.4 V (from scan rate 10 to 100 mV/s respectively). This 500mV difference in reduction potential with increase in scan rate indicates that as the scan rate increases, Mg²⁺ insertion becomes more facile and thermodynamically feasible allowing fast solid phase diffusion in the Mg-enriched RSW(O) electrolyte. In the reverse scan, during the stripping process where oxidation of deposited Mg occurs in the system and dissolution of Mg²⁺ ions into bulk electrolyte is noticed. The two-step, two electron transfer process starts at much more negative potential from -0.6 to -0.9 V in comparison with the cathode active materials (BENGEL RSI and RSW(N)).

This clearly implies that, the solid phase deposition on Fe³⁺ or Fe²⁺ and Al³⁺ octahedral sites are highly feasible, whereas stripping the same from those sites become less facile.

The CV behaviour of the Mg-enriched RSW(O) electrolyte is superior in comparison to the state of the Art Polymer gel electrolyte so far demonstrated in the literature in terms of ionic conductivity and the solid phase diffusivity of Mg²⁺ ions as discussed under Electrochemical Impedance spectroscopy studies of the phyllosilicates in the present disclosure.

Thus, from the CV analysis of the phyllosilicates, Mg-rich BENGEL RSI, Fe-rich RSW(N) and Mg-enriched RSW(O), it is clearly demonstrated that Mg-rich BENGEL RSI and Fe-rich RSW(N) are good cathode active materials, whereas Mg-enriched RSW(O) is a good electrolyte material to be coated on the membrane (to form a membrane-cum-electrolyte) for the Mg-ion-Battery of the present disclosure.

Electrochemical Impedance spectroscopy (EIS) of the phyllosilicates

The EIS studies of the phyllosilicate samples i.e., Mg-rich BENGEL RSI, Fe-rich RSW(N) and Mg-enriched RSW(O) are carried out in three electrode assembly in the frequency range of 1 mHz (Milli hertz) to 1 kHz (Kilo hertz) at an AC amplitude of 50mV. The working electrode is the phyllosilicate coated Pt disc, Ag/AgCl reference electrode and Pt wire counter electrode.

Fig. 9, illustrates the Nyquist plot of the phyllosilicate samples Mg-rich BENGEL RSI, Fe-rich RSW(N) and Mg-enriched RSW(O). The x-axis intercept of the Nyquist plot indicates the solution resistance (Rs) of the appropriate system.

For Mg-rich BENGEL RSI, Rs is obtained as 400 Q, Fe-rich RSW(N) accounts to 600 Q (Rs) and that of Mg-enriched RSW(O) possess 350 Q (Rs).

The solution resistance (Rs) of the materials indicates the ionic conductivity of the system. The corresponding ionic conductivity of the phyllosilicates per unit area of the electrode surface is calculated as 2.5 mS/cm; 1.67mS/cm and 2.86 mS/cm for Mg-rich BENGEL RSI, Fe-rich RSW(N) and Mg-enriched RSW(O) respectively.

The ionic conductivity is of the order OMg-enriched RSW(O) > OMg-rich BENGEL RSI > OFe-rich RSW(N)

The ionic conductivity trend as obtained above demonstrates the fact that Mg- enriched RSW(O) has high Mg²⁺ conductivity of the order of 1.144 times that of Mg-rich BENGEL RSI and 1.713 times that of Fe-rich RSW(N). Thus, Mg- enriched RSW(O) can act as a good electrolyte as well as membrane for the Mg- ion-Battery of the present disclosure. The ionic conductivity of Mg-enriched RSW(O) electrolyte is 2.87 mS/cm, which is 2.87 times higher than the polymer gel electrolytes (approx. ImS/cm) so far used in Mg-ion-Battery.

The Nyquist plot of the phyllosilicates explicitly indicates that diffusion process is predominant in the phyllosilicates. The charge transfer is completely absent and demonstrates the plating and stripping of Mg²⁺ ions after its solid phase diffusion to the available octahedral sites previously occupied by Fe³⁺, Fe²⁺, Al³⁺, Ca²⁺ etc.

Thus, EIS studies also support the structural, morphological, optical, chemical composition and CV analysis of the phyllosilicates conducted in the present disclosure.

Potentiodynamic studies of the phyllosilicates

Fig. 10 illustrates the potentiodynamic behavior of the phyllosilicates.

From the chronopotentiogram, it can be seen that two voltage plateaus are possible for all the three phyllosilicates.

The nominal voltage for Mg-rich BENGEL RSI is 3.3 V, and for Fe-rich RSW(N) and Mg-enriched RSW(O) is 3.2 V.

In Fig. 10, SITE A represents the exchangeable sites available for the incoming Mg²⁺ ions from the electrolyte. As the free energetics of the exchangeable sites are very low, feasible insertion of Mg²⁺ ions occur, and the plateau is short due to limited exchangeable cation sites per lattice of the phyllosilicates. Thus, for (i) Mg-rich BENGEL RSI, a constant plateau at 3.3 V upto 110 mAh/g is noticed. As the lattice is already rich in Mg²⁺, the exchangeable sites are less and the plateau is short.

For (ii) Fe-rich RSW(N), a constant plateau at 3.2 V upto 125 mAh/g corresponds to the fact that more exchangeable cation sites are available for Mg²⁺ ions as the source phyllosilicate has less or negligible Mg²⁺ in the composition, and

For (iii) Mg-enriched RSW(O) shows a constant plateau up to 130 mAh/g indicating facile Mg²⁺ insertion in the exchangeable cation sites of the lattice.

SITE B represents the other octahedral sites in the phyllosilicates that are occupied by ions similar or identical in ionic radius that of Mg²⁺ including Mg²⁺ ions. Since the number of octahedral sites are identical in all the three phyllosilicates, the second plateau extends up to 280 mAh/g. Once all the available sites are filled by Mg²⁺ ions, total discharge of the phyllosilicate material happens leading to sudden drop in the voltage to -2.7 V (as shown in Fig. 10).

As shown in Fig. 11 (Prior Art), the structure of phyllosilicate involves octahedral sites occupied by Al³⁺, Mg²⁺, Fe³⁺, Fe²⁺, Ti⁴⁺, Ca²⁺ based oxides or hydroxides, tetrahedral Si20s sheets and exchangeable cations sandwiched between the tetrahedral Si20s sheets. The general formula of the phyllosilicates are usually written as ((Ca)_x(Al,Mg)2-_x(Si40io)(OH)_y-nH20), where x and y are between 0 to 1, depending on the Mg²⁺ ion insertion and de-insertion.

Examples:

The present disclosure will now be explained in further detail by the following examples. These examples are illustrative of certain embodiments of the disclosure without limiting the scope of the present disclosure. Fabrication of coin cells:

Mg-ion-Battery coin-cells were prepared according to the teachings of the present invention.

- Cathode: Mg-rich BENGEL RSI bentonite clay or Fe-rich RSW(N) bentonite clay coated on a Stainless steel (SS) current collector of 5*5 cm dimension.

- Anode: Carbonaceous material or metallic-Mg coated on an Aluminium (Al) current collector of 5*5 cm dimension.

Electrolyte-cum membrane: RSW(O) bentonite clay coated Polypropylene (PP) membrane was soaked in IM MgCh to form Mg-enriched RSW(O) bentonite clay and the coated and dried membrane is cut into 5*5 cm dimension.

In an embodiment, the Mg-enriched RSW(O) bentonite clay electrolyte is not completely dried in order to avoid mud-cracks on the coating, thereby having the electrolyte in a quasi-solid-state (QSS), wherein thus formed quasi-solid-state electrolyte may be for the purpose of the present disclosure may be abbreviated as QSSE, and the battery fabricated using such QSSE in the present disclosure is quasi-solid-state Magnesium ion Battery (QSSMgB)..

Mg-ion-Battery Fabrication: The electrolyte-coated PP membrane was sandwiched between the cathode and the anode and crimped to obtain the Mg-ion- Battery coin cell. The coin-cell was closed with the casings and pressed tight at a pressure of 3 bar in a sealing machine.

Seven such Mg-ion-Battery Coin cells was prepared with the following architecture:

Evaluation of the coin-cells:

The sealed cells were subjected to Galvanostatic Charge Discharge (GCD) profile evaluation employing Zahner Zennium E4 electrochemical workstation, Germany at different C-rates such as 0.1C, 0.5 C and 1C.

The theoretical specific capacity of Mg-rich BENGEL RSI, Fe-Rich RSW(N) and RSW(O) bentonite clay is obtained as follows:

Theoretical Specific Capacity of a material = zF/M where z is the charge, F is Faraday’s constant in C/mol and M is the molecular weight of the material in g/mol.

In the present scenario, charge associate with the Mg²⁺ ions is 2, F is given as 96500 C/mol and the molecular weight of the bentonite clay under investigation is 422 + 10 g/mol.

Thus, the theoretical Specific Capacity of Bentonite clay is 1271 mAh/g. This high theoretical Specific capacity of the phyllosilicate explicitly implies the capability of these materials as cathode active material and electrolyte in Mg-ion- Batteries. GCD analysis of Coin cell of Example 1

SS/Fe-rich RSW(N)//RSW(O)-1M MgCl₂ on PP//graphite/Al

As shown in Fig. 12, the coin cell of Example 1 is stable up to 1000 cycles at lower C-rates such as 0.1 C, up to 880 cycles at 0.5 C and the cell capacity falls immediately within 100 cycles at 1C.

Fig. 12 exhibited three plateau regions at all C-rates. Region I contributes to the occupancy of exchangeable cation sites in the phyllosilicates, Region II attributes to the vacant octahedral sites occupancy by Mg²⁺ ions, whereas Region III depicts the replacement of other ions of identical or similar ionic radii in the octahedral sites (such as Ca²⁺, Fe³⁺, Fe²⁺ etc).

Example 1 - Case I: At very low discharge rate of 0.1 C rate

Region-I starts at higher specific capacity of 194.4 mAh/g and stays at 165 mAh/g till 25 cycles, this is due to the occupancy of exchangeable cation sites (as the number of exchangeable sites are less, the plateau is also short).

Region-II: The specific capacity rapidly falls to 140 mAh/g, as more Mg²⁺ ions are inserted into the octahedral sites of the phyllosilicates. The plateau length depends on the number of vacant octahedral sites and the rate at which the Mg²⁺ ions are inserted into the sites. At 0.1 C rate, the octahedral sites are occupied within 250 cycles of the GCD. After 250 cycles, again a sudden fall in the specific capacity to 140 mAh/g occurs.

Region-Ill starts at 140 mAh/g where, the ions of similar or identical ionic radii are replaced by Mg²⁺ ions, thereby completely discharging the cell upto 1000 cycles and drastically falls to 82 mAh/g. So for Cell (i), QSSMgBs, the specific capacity of the cell is 194.4 mAh/g, after 25 cycles, 84.88% capacity retention is noticed. After, 250 cycles, 72% capacity retention is observed. After 1000 cycles, 42.4% capacity retention is observed. Thus, at slower C-rate of 0.1 C, the cell performed with high capacity retention for higher number of cycles.

Example 1 - Case II: At moderate discharge rate of 0.5 C rate

Region-I starts at higher specific capacity of 194.4 mAh/g and stays at 170mAh/g till 75 cycles, the occupancy of exchangeable cation sites (as the number of exchangeable sites are less, the plateau is also short) is highly feasible due to higher diffusion of the Mg²⁺ ions in solid phase from quasi-solid state.

Region-II: The specific capacity rapidly falls to 136 mAh/g, as more Mg²⁺ ions are inserted into the octahedral sites of the phyllosilicates. At 0.5 C rate, the octahedral sites are occupied within 600 cycles of the GCD. After 600 cycles, again a sudden fall in the specific capacity to 104 mAh/g occurs.

Region III starts at 104 mAh/g where, the ions of similar or identical ionic radii are replaced by Mg²⁺ ions, thereby completely discharging the cell upto 880 cycles and drastically falls to 93 mAh/g. So, for Cell (i), QSSMgBs, the specific capacity of the cell is 194.4 mAh/g, after 75 cycles, 87.45% capacity retention is noticed. After, 600 cycles, 53.50% capacity retention is observed. After 880 cycles, 47.84% capacity retention is observed. Thus, at moderate C-rate of 0.5 C, the cell performed with high capacity retention but the cycle life and longevity is reduced to 880 cycles.

Example 1 - Case III: At high discharge rate of 1 C rate

Initial fall in capacity occurs within first 10 cycles from 194.4 mAh/g to 170 mAh/g. Region I is observed for only 10 cycles of GCD and at 170 mAh/g.

Region II starts at 11^th cycle with rapid fall in specific capacity to 137 mAh/g. The plateau is very short upto 125 cycles and the specific capacity falls to 111.11 mAh/g. Region III is not noticed in high discharge rate of 1C. Thus, the cell performs very poorly at 1C rate with 87.45% capacity retention upto 10 cycles, 70.47% capacity retention upto 125 cycles and the performance falls to 57.51% capacity retention. At 1C rate, although the cell performed with very high capacity retention, the longevity is very low upto 125 cycles.

As observed, the cell of Example 1 with configuration of the coin-cell SS/Fe-rich RSW(N)//RSW(0) - IM MgCh on PP//graphite/Al possess specific capacity of 194.4 mAh/g and nominal voltage of 1.1 V, therefore the gravimetric energy density of the cell (i) would be 349.53 Wh/kg (discharge current is 0.1271 A, At=90s).

GCD analysis of Coin cell of Example 2

SS/Fe-rich RSW(N)//RSW(0) - IM MgCl₂ on PP//CB/A1

Fig. 13 shows the discharge profile of the coin cell of Example 2.

The discharge profile of the coin cell with anode graphite replaced by Carbon black appeared totally different from the cell of Example 1.

Trend of the specific capacity with C-rate is almost identical, but at all C-rates, the cell of Example 2 performed up to 10000 cycles indicating at least 10 times more cycle stability than cell of Example 1.

As observed from Fig. 13, at 0.1 C, the specific capacity maintained a plateau up to 2650 cycles with an initial fall to 132 mAh/g from 200 mAh/g. Till 2650 cycles, the specific capacity is maintained at 132 mAh/g. After 2650 cycles, there is a drastic fall in specific capacity up to 3575 cycles to 62 mAh/g and then remained at 40 mAh/g till 10000 cycles. Thus, the cell of Example 2 maintained 66% capacity retention up to 2650 cycles (Region I), 31% capacity retention up to 3575 cycles (Region II) and 20% capacity retention up to 10000 cycles (Region III). At 0.5 C, Region I starts at 60 mAh/g and stays up to 1750 cycles, Region II commences at 40 mAh/g and remains up to 3000 cycles, Region III indicates a sudden increase in the specific capacity from 40 to 60 mAh/g and remains stable till 10000 cycles. Thus, at moderate C-rate, although three regions of insertion of Mg²⁺ occurs in the system, the performance is very low but with reasonable cycle stability.

At 1C rate, the specific capacity is very low of the order of 15 mAh/g and falls to almost 5 mAh/g till 10000 cycles.

Thus, the cell of Example 2 although possess high longevity does not have performance stability, the rationale behind this behaviour could be attributed to the electroactive Mg²⁺ ions loss in the system via utilization by the anode to form passive layer of insoluble salts in the presence of aqueous media. Therefore, the specific capacity of the cell of Example 2 rapidly falls below 50% within 2000 cycles.

GCD analysis of Coin cell of Example 3

SS/Fe-rich RSW(N)//RSW(O)-1M MgCE-acctonc on PP//graphite/Al

In order to avoid the reactivity of aqueous electrolyte on anode and loss of electroactive Mg²⁺ ions, acetone is tried as solvent and cell (iii) fabricated. The specific capacity of the cell (iii) is obtained as 4 mAh/g and did not perform well at any C-rate.

GCD analysis of Coin cell of Example 4

SS/Fe-rich RSW(N)//RSW(O)-1M MgCh -H2O-acetone on PP//graphite/Al

The solvent employed is binary solvent of acctonc-PEO in the ratio 1:1. The GCD profile of the cell (iv) is provided in Fig .14. Fig. 14 depicts that when solvent in the QSSE is replaced by acetone-water binary mixture in the ratio of 1:1, the specific capacity of the cell is obtained as 98 mAh/g. At 0.1 C, the performance of the cell remained constant up to 100 cycles at 80-90 mAh/g, whereas at 0.5 C, the initial capacity lowered to 40 mAh/g and remained stable between 20-40 mAh/g up to 100 cycles.

At high C-rate of 1C, the initial specific capacity of the cell is much lower than 20 mAh/g and hence the performance is not good even though cycle stability up to 100 cycles is noticed.

Thus, the cell of example 4 possess specific capacity of 98 mAh/g and nominal voltage of 0.85 V, therefore the gravimetric energy density of the cell would be 270 Wh/kg (discharge current is 0.1271 A, At=90s).

GCD analysis of Coin cell of Example 5

SS/Mg-rich BENGEL RSI//RSW(O)-1M MgCh on PP//graphite/Al

The GCD analysis of cell of Example 5 as provided in Fig. 15.

Fig. 15 exhibits the discharge profile of the coin cell of Example 5.

The cell of Example 5 behaved with Mg²⁺ insertion/de-insertion mechanism analogous to any metal-batteries. The initial specific capacity of the cell is obtained as 250 mAh/g. At 0.1 C rate, the specific capacity falls rapidly to 150 mAh/g and stabilize up to 100 cycles. With continuous insertion of Mg²⁺ ions from QSSE, the capacity fell to 35 mAh/g and remained stable up to 1000 cycles. The cell maintained 60% capacity retention up to 100 cycles and then 14% capacity retention till 10000 cycles. At 0.5C, the cell started with 200 mAh/g and continuously fall to 40 mAh/g and stabilized up to 10000 cycles. At 1C, the cell did not perform well and remained steady at 5 mAh/g from 1 to 10000 cycles. Thus, the cell of Example 5 is stable and operable up to 100 cycles at lower C- rates (ca. 0.1 and 0.5 C). The gravimetric energy density of cell of Example 5 is obtained as 247.85 Wh/kg at a discharge current of 0.1271 A, At=90s, nominal voltage of 0.78 V and active material mass of 10 mg.

GCD analysis of Coin cell of Example 6

SS/Mg-rich BENGEL RSU/RSW(O)-1M MgCl₂ on PP//CB/A1

The GCD profile of the same is discussed below with Fig. 16.

From Fig. 16, it can be observed that the initial specific capacity of the cell of Example 6 is obtained as 262.24 mAh/g. At 0.1 C -rate, the Mg2+ insertion into the phyllosilicates occurred at two different steps. The first step is stable at 250 mAh/g up to 4052 cycles and then a sudden fall in specific capacity to 198 mAh/g is noticed. Upon further insertion of Mg²⁺ ions from QSSE, the specific capacity again increases to 220 mAh/g and remained stable up to 10000 cycles. Thus, at lower C-rate, the cell behaved well with almost constant specific capacity in the range of 220 to 250 mAh/g up to 10000 cycles. The first step is attributed to the occupancy of Mg²⁺ ions in exchangeable cation sites and the second step is due to the insertion of Mg²⁺ ions in the octahedral sites of the phyllosilicates. At moderate C-rate of 0.5 C, the cell performed stably with specific capacity of 178 mAh/g up to 8000 cycles and then a small fall to 170 mAh/g up to 10000 cycles. Thus, at moderate C-rate of 0.5 C, the cell performed stably with 170-178 mAh/g up to 10000 cycles. At high C-rates of 1C, the cell performed stably at a specific capacity of 100 mAh/g up to 1000 cycles. Thus, the capacity retention is 88% at 0.1 C, 68% at 0.5 C and 40% at 1C after 10000 cycles. The cycle stability and longevity of the cell of Example 6 is very high. The gravimetric energy density of the cell (vi) is calculated as 349.53 Wh/kg at nominal voltage of 1.1 V, At = 90 s and discharge current of 0.1271 A.

GCD analysis of Coin cell of Example 7

SS/Mg-rich BENGEL RSI//RSW(O)-1M MgCl₂ on PP//Mg/Al Fig. 17 depicts the GCD profile of the cell of Example 7.

From Fig. 17, it can be observed that the cell of Example 7 at 0.1 C possess initial specific capacity of 700 mAh/g and falls to 400 mAh/g at 1028 cycles, after which it stabilizes at 375 mAh/g up to 10000 cycles. At 0.5 C, the specific capacity is stable at 250 mAh/g throughout 10000 cycles. At 1C, the performance of the cell is stable at 110 mAh/g up to 10000 cycles. The high specific capacity of the cell and its consistent performance is attributed to the Mg anode (theoretical capacity of 2150 mAh/g). The gravimetric energy density of the cell is obtained as 889.7Wh/kg (Discharge current is 127.1 mA, At = 90 s, nominal voltage = 2.8 V and active mass of the material is lOmg). The performance profile of cell of Example 5 is stable unlike other cells due to the excess presence of Mg²⁺ ions in the system. The cathode, QSSE and anode are Mg-rich or Mg-enriched and hence the supply of Mg²⁺ ions and its sold phase diffusion is accelerated in the system. The gravimetric energy density of the cell of Example 7 is the highest amongst all cells studied in the present investigation and is close to 0.9 kWh/kg. This value is three times higher than the reported literature value and is close to the value for organic pyrene-2-one based cathode, Magnesium carborane based organic electrolyte for the cell developed and studied at Swagelok method recently by Toyota Research Institute as disclosed in literature [Liang, Y. et al. Universal quinone electrodes for long cycle life aqueous rechargeable batteries. Nat. Mater. 16, 841-848 (2017)].

Advantages:

The Mg-ion-battery of the present disclosure has the following non-limiting advantages.

- utilization of earth abundant and naturally available phyllosilicates makes the battery environmentally friendly, - avoids formation of complex chloride ions such as [MgCL]²’ that hinders the solid phase diffusion of Mg²⁺ ions in the cathode and hence increases the electrode kinetics on the cathodic surface,

- enhanced gravimetric energy density of the order of three times the value reported so far in the state-of-the-art in the literature,

- Excellent cyclability of about 10,000 cycles,

- Mg²⁺ being the common ion, enhances the specific capacity of the system,

- The bentonite clay acts as a good Mg²⁺ storage material at the electrical double layer.

Applications:

The Mg-ion-battery of the present disclosure has the following non-limiting industrial applications.

- Low power electronics,

- Stationary storage,

- E-mobility.

Although the present disclosure is described in terms of certain preferred embodiments, it is to be understood that they have been presented by way of example, and not limitation. Thus, the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A Mg-ion-battery comprising:

- a cathode electrically coupled to a Magnesium (Mg)-rich cathode material, or electrically coupled to an Iron (Fe)-rich cathode material;

- an anode electrically coupled to a carbonaceous material, or the anode is electrically coupled to metallic Mg; and

- a membrane-cum-electrolyte including a coating of a Magnesium (Mg)- enriched electrolyte material on a membrane, wherein the membrane-cum- electrolyte is positioned between the cathode and the anode, wherein the cathode, the anode, and the membrane-cum-electrolyte are retained within a casing in a compact configuration.

2. The Mg-ion-battery as claimed in claim 1, wherein the Mg-rich cathode material is a Mg-rich phyllosilicate, and the Fe-rich cathode material is a Fe- rich phyllosilicate.

3. The Mg-ion-battery as claimed in claim 1, wherein the carbonaceous material is selected from carbon black, graphite or graphene.

4. The Mg-ion-battery as claimed in claim 1, wherein the Mg-enriched material is an electrolyte material that is capable of retaining excess Mg²⁺ ions.

5. The Mg-ion-battery as claimed in claim 1, wherein the Mg-enriched material coated on the membrane is a phyllosilicate artificially enriched with Mg²⁺ ions.

6. The Mg-ion-battery as claimed in claim 1, wherein the Mg-enriched material is in quasi-solid-state.

7. The Mg-ion-battery as claimed in claim 1, wherein the Magnesium (Mg)- enriched electrolyte material coated on the membrane is obtained by treating an electrolyte material with a Mg-salt.

8. The Mg-ion-battery as claimed in claim 1, wherein the Magnesium (Mg)- enriched electrolyte material coated on the membrane is obtained by treating an electrolyte material with IM MgCh-

9. The Mg-ion-battery as claimed in claim 1, wherein the membrane is a polymer membrane, preferably a polypropylene (PP) membrane.

10. The Mg-ion-battery as claimed in claim 1 exhibits a specific capacity of up to 700 mAh/g.

11. The Mg-ion-battery as claimed in claim 1 exhibits a cycle stability of up to 10,000 cycles at 0.1 C to 1C.

12. A method of fabricating a Mg-ion-battery comprising positioning a membrane-cum-electrolyte between a cathode and an anode, wherein the cathode includes a cathode current collector electrically coupled to a Magnesium (Mg)-rich phyllosilicate or an Iron (Fe)-rich phyllosilicate, and the anode includes an anode current collector electrically coupled to a carbonaceous material, or the anode current collector is electrically coupled to metallic Mg; wherein the membrane-cum-electrolyte is fabricated by a method comprising the steps of:

- making a slurry of a natural phyllosilicate in an organic solvent;

- coating the slurry on both sides of a flexible membrane;

- drying the coated membrane in vacuum at 60°C to remove the organic solvent;

- treating the dried coated membrane in aqueous solution of a Mg Salt for 2 hours, to allow sufficient amount of Mg²⁺ ions migration into the phyllosilicate, thereby forming Mg-enriched phyllosilicate, wherein this Mg-enriched phyllosilicate acts as the electrolyte; and

- drying the Mg-enriched phyllosilicate electrolyte coated membrane at 80°C for 3 hrs to remove water content. The method of fabricating the Mg-ion-battery as claimed in claim 12, wherein the drying step of the Mg-enriched phyllosilicate electrolyte coated membrane is modulated in order to have the Mg-enriched phyllosilicate electrolyte in a quasi-solid-state (QSS). The method of fabricating the Mg-ion-battery as claimed in claim 12, wherein the Mg-enriched phyllosilicate electrolyte coated on the membrane is obtained by treating a natural phyllosilicate with IM MgCh-