Surface-functionalized, fluoride-free mxene as an electrode, and a method of synthesizing the same

Abstract

The present invention relates to a process for preparation of a fluoride-free, surface functionalized MXene, the process comprising etching MAX phase with sulfuric acid to obtain a partially oxidized MAX phase, treating the partially oxidized MAX phase with hydrogen iodide (HI) to obtain a charge transfer complex, etching the charge transfer complex with vinegar to obtain the fluoride-free, surface functionalized MXene and optionally treating the fluoride-free, surface-functionalized MXene with oxygen to obtain an oxygenated MXene. The process invention also relates to a fluoride-free, surface functionalized MXene as electrode and a process for preparation of the same. The present invention further relates to a full cell for electrochemical device comprising the fluoride-free, surface functionalized MXene electrode.

Description

[0001]PT / 2025 / 14696 SURFACE-FUNCTIONALIZED, FLUORIDE-FREE MXENE AS AN ELECTRODE, AND A METHOD OF SYNTHESIZING THE SAME TECHNICAL FIELD OF THE INVENTION The present invention relates to a process for preparation of a fluoride-free, surface functionalized two-dimensional MXene. The present invention also relates to a fluoride-free, surface functionalized MXene electrode for electrochemical devices and a process for preparation of the same. The present invention also relates to an electrochemical energy storage device comprising the fluoride free, surface-functionalized MXene as an electrode. BACKGROUND AND PRIOR ART OF THE INVENTION Layered transition-metal carbides and carbonitrides, also referred to as MXene, offer a combination of excellent mechanical properties as well as high electrical conductivity which are seen in other 2D crystals such as element-enes (such as phosphene), transition metal dichalcogenides (TMDs). MXenes, titanium carbide (Ti3C2Tx) has a long range of applications, including energy storage and conversion, electromagnetic interference shielding, water purification gas and bio-sensors, lubricants, and catalysts, due to its metallic conductivity and tunable surface functionalities (P. Yu, G. Cao, S. Yi, X. Zhang, C. Li, X. Sun, K. Wang, Y. Ma, Nanoscale 2018, 10, 5906–591; and L. Huang, T. Li, Q. Liu, J. Gu, Electrochemistry Communications 2019, 104, 106472). Further, delaminated MXene layers incorporated into composites, different inks and films have attracted considerable attention in conductive coatings, catalysis, and energy storage. MXenes are described by a general chemical formula of Mn+1XnTx(n = 1−3), where M represents an early transition metal, X is carbon and / or nitrogen, and Tx represents the surface terminations. They are synthesized by the selective etching of the A interlayer from their main three-dimensional (3D) MAX phase (Mn+1AXn). The etching is usually carried out by hydrofluoric (HF)-containing media such as in situ generation of HF via salts or acids (LiF / HCl, NaHF2, NH4HF2, KHF2,). However, HF is highly corrosive and further the waste generated during the process is toxic. Additionally, MXenes, such as Ti3C2Tx, are hydrolytically unstable, and thus the quality and yield vary significantly. Furthermore, the MXene surface contains various elements like fluoro, PT / 2025 / 14696 oxo, and hydroxyl terminations. Properties, such as electronic and chemical performance, are highly sensitive to the surface structure comprising such various elements. Solid-state methods such as molten salt etching have been developed as an attempt to mitigate aqueous HF approaches. however, they need higher temperatures which limits many usages. Further, CN111943207 reports a process for preparation of fluoride free MXene surface functionalized with -I atoms by etching the ‘A’ layer of MAX phase by eutectic iodine agent vapor under high temperatures and sealed conditions to obtain the said MXene. CN114657599 disclose a process for preparation of MXene catalyst by etching the ‘A’ layer from MAX phase using hydrochloric acid (HCl) followed by iodine doping with the cathode polarization method. However, the process disclosed in CN114657599 is complex and involves multiple steps. Thus, safe, simple and efficient formation of MXenes with a long range of homogeneous surfaces remains an experimental challenge. Accordingly, the inventors have developed an efficient and green etching method to remove the A-layer to produce exfoliated / surface-functionalized fluoride-free MXenes by using simple hydrothermal method and less hazardous reagent. OBJECTS OF THE INVENTION An object of the present invention is to provide a green method of synthesizing fluoride-free, surface-functionalized MXene having formula Mn+1XnTx. Another object of the present invention is to develop and fabricate high-performance anode materials comprising fluoride-free, surface-functionalized MXene prepared by the process of the present invention. Another object of the present invention is to provide a surface-functionalized MXene as electrode for advanced energy storage systems. Yet another object of the present invention is to provide electrochemical components comprising the surface-functionalized MXene of the present invention. PT / 2025 / 14696 Another objective of the present disclosure is to provide an advanced energy storage systems comprising the fluoride-free, surface-functionalized MXene of the present invention with higher energy and power density with long cycle life. SUMMARY OF THE INVENTION Aspects of the present invention relate to a process for preparation of a fluoride-free, surface functionalized MXene. The present invention also relates to a fluoride-free, surface functionalized MXene electrode for electrochemical devices and a process for preparation of the same. The present invention also relates to an electrochemical energy storage device comprising the fluoride-free, surface-functionalized MXene as an electrode. In an aspect, the present invention provides a process for preparation of a fluoride-free, surface-functionalized MXene, the process comprising:a) etching MAX phase with sulfuric acid to obtain a partially oxidized MAX phase; b) treating the partially oxidized MAX phase with hydrogen iodide (HI) to obtain a charge transfer complex; c) etching the charge transfer complex with vinegar to obtain the fluoride-free,surfacefunctionalized MXene; and d) optionally treating thefluoride-freesurface-functionalized MXene with oxygen to obtain an oxygenated MXene. In another aspect, the present invention relates to a process for preparation of an electrode, the process comprising preparing a slurry by mixing the fluoride free, surface functionalized MXene prepared by the process of the present invention, binder and carbon and depositing the slurry on a current collector. In another aspect, the present invention relates to a fluoride free, surface functionalized MXene having formula: Mn+1XnTxwherein, PT / 2025 / 14696 M is a transition metal selected from scandium (Sc), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), zirconium (Zr), hafnium (Hf) and combination thereof; X is selected from carbon or nitrogen; Tx is selected from hydroxyl (OH), oxygen (=O) and iodine (I); and n is selected from 1 to 3. In another aspect, the present invention relates to an electrode comprising the fluoride free, surface functionalized MXene of the present invention. In another aspect, the present invention provides a full cell for electrochemical device comprising: (a)fluoride-free, surface-functionalized MXeneelectrode prepared by the process of thepresent invention as anode (2); (b) a cathode (4); (c) cell components such as positive (7) and negative (1) stainless steel cell cases along with spacer (5) and spring (6) for coin cell fabrication purpose; (d) an organic electrolyte for back-and-forth movement of ions; and (e) a separator (3) to prevent the physical contact between cathode and anode. DETAILED DESCRIPTION OF THE DRAWINGS The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which: Figure 1(a) and (b): depicts the reaction scheme illustrating the synthesis scheme of fluoride- free, surface-functionalized Ti3C2Tx MXene (F-free MXene) prepared according to Example 1. Figure 2: depicts the a) PXRD data of MXene prepared according to Example 1 and of Comparative Example A; b) Comparative Raman spectra of HFM and HVM electrode materials; and c) UV visible spectra of MXene prepared according to Example 1 and of Comparative Example A. PT / 2025 / 14696 Figure 3: (a) and (b) depicts N2adsorption-desorption BET analysis and Pore size distribution (PSD) analysis of HFM and HVM respectively. Figure 4: (a) depicts the environmental Scanning Electron Microscope (ESEM), and (b) selected area electron diffraction (SAED) analysis of HVM prepared according to Example 1. Figure 5: depicts XPS of (a) MXene prepared according to Example 1, and (b), depicts the deconvoluted peaks of Ti2p, C1s, and O1s respectively. Figure 6: depicts the electrical conductivity of HVM of Example 1, MAX, in comparison to fluoride based MXenes.Figure 7 depicts the stability of MXeneprepared according to Example 1 in comparison toHFM of Comparative Example A after two weeks. Figure 8: a) Comparative CV curves of MAX, HFM, and HVM at 0.2 mV s-1; b) Comparative rate capability at various current densities and c) Comparative cycling stability at 1 A g-1. Figure 9: Cycling stability of HVM after 500 cycles Figure 10 depicts the coin cell assembly ofthehalf-cell LIB comprising fluoride-free, surface functionalize MXene electrode of the present invention. Figure 11 depicts the schematic representation in half-cell LIBcomprisingfluoride-free, surface functionalize MXene electrode of the present invention. Figure 12 depicts the coin cell assembly of full-cell comprising F-free MXene / / NSC devicecomprisingfluoride-free (F-free), surface functionalized MXene electrode as anode and N doped porous sucrose carbon as cathode. Figure 13 depicts the schematic representation ofthefull-cell comprising F-free MXene / / NSC devicecomprisingfluoride-free, surface functionalized MXene electrode of the present invention as anode. SOURCE OF BIOLOGICAL MATERIAL: Not applicable DETAILED DESCRIPTION OF THE INVENTION: PT / 2025 / 14696 While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope. Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein. The tables, figures and protocols have been represented where appropriate by conventional representations in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein. In an embodiment, the present invention provides a process for preparation of a fluoride-free, surface functionalized MXene, the processcomprising:a) etching MAX phase with sulfuric acid to obtain a partially oxidized MAX phase; b) treating the partially oxidized MAX phase with hydrogen iodide (HI) to obtain a charge transfer complex; c) etching the charge transfer complex with vinegar to obtain thefluoride-free, surfacefunctionalized MXene; and d) optionally treating the fluoride-free, surface-functionalized MXene with oxygen to obtain an oxygenated MXene.Preferably, the fluoride-free MXene obtained in step c)has surface functionalized iodide (-I)ions. PT / 2025 / 14696 Preferably, the MAX phase has the formula Ti3AlC2. In step a), the MAX phase is present in an amount ranging from 4% wt / vol to 13% wt / vol. The sulfuric acid is present in a concentration ranging from 0.1 M to 1.0 M. Preferably, the concentration of sulfuric acid is 1.0 M. Step a) is carried out by hydrothermal method at a temperature in a range from 100℃ to 200℃ for 20 hours to 24 hours. Preferably, step a) is carried out at 1500Cfor 24 hrs. In step b), the partially oxidised MAX phase in an amount ranging from 8% wt / vol to 12% wt / vol. is treated with HI present in an amount ranging from 3 % wt / vol to 12 % wt / vol. Preferably, the HI is used in an amount ranging from 5 ml to 7 ml. Preferably, the partially oxidised MAX phase and the HI has a molar ratio ranging from 1:5 to 1:7. The step b) is carried out at a temperature in a range from 700C to 900C for 2 hours to 24 hours. The charge transfer complex formed in step b) is an aluminium iodide charge transfer complex (Al(I)x). Then, in step c) the vinegar is present in an amount ranging from 5 ml to 10 ml. The step c) is carried out at a temperature in a range from 700C to 900C for 2 hours to 5 hours. The process of the present invention by formation of a strained or partially oxidized MAX phase (step a)) enables the easy penetration of iodine atoms when treated with HI (step b)).Due to the high reactivity of elemental hydrogen halides with Al, the HI is introduced into to Al-containing MAX phase thereby, producing aluminium iodide charge transfer complex Al(I)x, where the x-mer (charge transfer complex) dissociates readily into monomeric AlI3, and AII5. The high solubility of AlI3 and AII5 in nonpolar solvents provides strong driving force for selective removal of etched Al from the MAX phase. The vinegar as etchant removes the A layer from the MAX phase resulting in a fluoride-free MXene surface functionalized with iodide ions. Optionally, treating the obtained fluoride-free, iodide functionalized MXene with oxygen results in an oxygenated MXene with removal of iodide ions. Unlike traditional fluoride-based etching methods, which suffer from limited penetration in the MAX phase, due to the large ionic radius of fluoride and generate hazardous, highly corrosive by-products, the process of the present invention employs less toxic, easily handled reagents such as hydrogen iodide and vinegar for etching of A layer. Thus, the process of the present invention is simple, provides a green method of synthesis of MXene and significantly improves operational safety, eliminates environmental concerns, and enhances scalability. In an embodiment of the present invention, the fluoride-free, surface-functionalized MXene obtained by the process of the present invention has the formula Ti3C2Tx,wherein the Txrefers PT / 2025 / 14696 to I.The process for preparation of fluoride-free, surface functionalized Ti3C2TxMXene is represented by Scheme 1 below: Scheme 1: In a preferred embodiment, the present invention provides a process for preparation of fluoride- free MXene surface functionalized with iodide, the processcomprising:a) addingTi3AlC2MAX toH2SO4followed by stirring for 1h at room temperature to obtain a uniform dispersion of MAX / H2SO4 solution; b) treating the MAX / H2SO4 solution by hydrothermal method for 20 h to 24 h at 1000C to 2000C to obtain a mixture; c) filtering the mixture with water, followed by removal of acidic content of sulfuric acid, and vacuum drying in an oven to obtain a dried powder ofpartially oxidized Ti3AlC2 MAXphase;d) effecting HI treatment, by mixing thepartially oxidized Ti3AlC2MAX phase with HI,followed bystirring under heating to obtain an aluminium iodidecharge transfer complex(Al(I)x); e) cleaning the aluminium iodidecharge transfer complexby vacuum filtration, followed by drying; and f) etching thecharge transfer complexby adding vinegar and heating the same, followed by vacuum filtration, washing and drying in vacuum oven to obtain the fluoride-free Ti3C2TxMXene surface functionalized with iodide. Preferably, thedrying in step c), e) and f) is carried outat a temperature in a range from 800Cto 1000C for 12 hours to 24 hours.In an embodiment of the present invention, the fluoride-free, surface-functionalized Ti3C2TxMXeneprepared by the process of the present inventioncomprises titanium (Ti) in an amountranging from 5% to 10%, aluminum (Al) in an amount ranging from 2% to 4%, carbon (C) in PT / 2025 / 14696 an amount ranging from 76% to 78%, oxygen (O) in an amount ranging from 10% to 12%, and iodide (I) in an amount ranging from 0.5% to 2%. Preferably, the fluoride-free, surface-functionalized Ti3C2TxMXeneprepared by the processof the present inventioncomprises titanium (Ti) in an amount of 7.01%, aluminum (Al) in an amount of 3.2%, carbon (C) in an amount of 78%, oxygen (O) in an amount of 11%, and iodide (I) in an amount of 0.79%. The surface functionalized Ti3C2TxMXene prepared by the present invention has longer stability, higher surface area and exhibits good porosity and wettability properties. The fluoride-free, surface functionalized MXene prepared by the process of the present invention is stable even after two weeks and exhibits a BET surface area in a range from 1-20 m2g-1. For example 1 m2g-1, 2 m2g-1, 3 m2g-1, 4 m2g-1, 5 m2g-1, 6 m2g-1, 7 m2g-1, 8 m2g-1, 9 m2g-1, 10 m2g-1, 11 m2g-1, 12 m2g-1, 13 m2g-1, 14 m2g-1, 15 m2g-1, 16 m2g-1, 17 m2g-1, 18 m2g-1, 19 m2g-1, 20 m2g-1. Further, the fluoride-free, surface functionalized Ti3C2TxMXene of the present invention exhibits a Non-local Density Functional Theory (NLDFT) pore size distribution in a range from 1 nm-100 nm. For example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 nm. Preferably 2-10 nm. The enhanced porous structure of MXene prepared by the process of the present invention provides more active sites to accommodate electrolyte ions and diffusion paths, thereby demonstrating an improved electrochemical performance. Furthermore, the fluoride-free, surface functionalized Ti3C2Tx MXene prepared by the process of the present invention has a total amount of porosity of at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or higher based on the total volume. In many cases, the total porosity is within the range of from 5 to 10%; from 10 to 15%; from 15 to 20%; from 20 to 25%; from 25 to 30%; from 30 to 35%; from 35 to 40%; from 40 to 40%; from 40 to 45%; from 45 to 50%; from 50 to 55% based on the total volume. In some embodiments, the total porosity can be 30 to 45% or from 35 to 50% based on the total volume. Higher or lower levels of total porosity can also be obtained. PT / 2025 / 14696 In an embodiment, the present invention provides a fluoride free, surface functionalized MXene having formula: Mn+1XnTx wherein, M is a transition metal selected from scandium (Sc), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), zirconium (Zr), hafnium (Hf) and combination thereof; X is selected from carbon or nitrogen; Tx is selected from hydroxyl (OH), oxygen (=O) and iodine (I); and n is selected from 1 to 3. Preferably, the MXene is Ti3C2Tx, wherein the Txrefers to iodide (I). In yet another embodiment of the present invention, the surface functionalized MXene is employed in electrochemical devices. In another embodiment, the present invention provides advanced cell electrodes and their assembly components, metal-ion battery electrodes, supercapacitors, electromagnetic interference (EMI) shielding, fabricated using the fluoride- free, surface functionalized MXene of the present invention. For example, electrodes and current collectors employ said fluoride-free, surface-functionalized MXene, and those embodiments of these electrodes and current collectors are considered within the scope of this disclosure, as are electrochemical storage devices that comprise fluoride-free, surface-functionalized MXene. Preferably, the MXene employed in electrochemical devices has the formula Ti3C2Txwherein Txrefers to iodide (-I) ions. In an embodiment, the present invention discloses a process for preparation of electrode, the process comprising: (a) preparing a slurry by mixing the fluoride free, surface functionalized MXene prepared by the present invention, carbon and a binder in a solvent; and (b) depositing the slurry on a current collector. PT / 2025 / 14696 The binder is selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber- carboxymethyl cellulose) (SBR / CMC), or combination thereof. Preferably, the MXene, carbon and binder are mixed in a weight ratio of 60 to 80: 10 to 20: 10 to 20. Preferably, the MXene, carbon and binder are in a ratio of 80:10:10. The solvent is selected from N-methyl-2- pyrrolidone (NMP), dimethyl formamide (DMF) or mixtures thereof. In step (b), the current collector is selected from copper, aluminium or combination thereof. In an embodiment, the present invention provides an electrode comprising the fluoride free, surface functionalized MXene. In another embodiment, the present invention provides anelectrochemical device comprisingthe fluoride-free surface functionalized MXene electrodeas an anode.Theelectrochemicaldevice is selected from group consisting of batteries, which may be configured as a half-cell or full cell device selected from lithium-ion batteries (LIB), sodium-ion capacitor (SIC), lithium- ion capacitor (LIC), other hybrid-ion capacitors (HICs) or combination thereof.When used inlithium or sodium ion batteries, it may exhibit a low power density than supercapacitors, primarily due to intercalation-related kinetic limitations. Specific embodiments further consider the use of fluoride-free, surface-functionalized MXene in ion storage devices, for example sodium or lithium-ion capacitors. In case of lithium-ion capacitor, the surface functionalized MXene of the present invention may exhibit higher power density than that of electric double layer capacitor / supercapacitors due to the high electrical conductivity and surface area of the MXene of the present invention. The electrode comprising the fluoride-free, surface functionalized MXene of the present invention due to its high surface area and porosity enables the rapid transport network of ions and electrons throughout the electrode thereby reducing polarization in the electrode. Thus, the electrode of the present invention demonstrates good electrochemical performance, attributed to the good conductive network of the fluoride-free, surface functionalized MXene of the present invention. Further, the electrode comprising the fluoride-free, surface functionalized MXene of the present invention provides multidimensional metal ion diffusion system during the charge-discharge process of batteries resulting in efficient performance in metal ion batteries (MIB). In an embodiment, the present invention provides a half-cell for electrochemical device as depicted in (Figure 10), comprising: PT / 2025 / 14696 (a) fluoride free, surface functionalized MXene deposited on a current collector as a working electrode(4); (b) a counter or reference electrode (2); (c) cell components such as positive (7) and negative (1) stainless steel cell cases along with spacer (5) and spring (6) for coin cell fabrication purpose; (d) an organic electrolyte for back-and-forth movement of ions; and (e) a separator (3) to prevent the physical contact between the electrodes. The current collector is as described above. Preferably, the current collector is copper foil when employed in lithium-ion capacitor (LIC) applications and the current collector is aluminum foil when employed in sodium-ion capacitor (SIC) applications. The counter or reference electrode is selected from lithium, sodium, or combination thereof. Preferably, the counter or reference electrode is lithium. The electrolyte is selected from lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), or a mixture thereof. Preferably, the electrolyte is lithium hexafluorophosphate (LiPF6, 1M) in ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) solventin the ratio of 1:1:1 v / v / v.The separator is selected from Whatman glass fibre, Celgard 2325 and the like. Preferably the separator is Celgard 2325. In half-cell, the MXene deposited on copper or aluminium current collector, is electrochemically tested within a lower voltage window relative to Li / Li⁺ and / or Na / Na⁺ reference electrodes. Additionally, the MXene may also be utilized for electrochemical evaluation of cathode materials, such as coating of nitrogen doped sucrose carbon (NSC) for LIC applications and / or sulphur doped sucrose carbon (SSC) for SIC applications, wherein such testing is performed within a higher voltage window relative to Li / Li⁺ and / or Na / Na⁺ reference electrodes. In an embodiment, the present invention provides a schematic representation of half-cell for LIB (Figure 11) comprising surface functionalized MXene as working electrode, Li foil as counter / reference electrode, separator and an organic electrolyte. PT / 2025 / 14696In another embodiment, the present invention provides afull cell for electrochemical device asdepicted in Figure 12,comprising:(a)fluoride-free, surface-functionalized MXeneelectrode prepared by the process of thepresent invention as anode (2); (b) a cathode (4); (c) cell components such as positive (7) and negative (1) stainless steel cell cases along with spacer (5) and spring (6) for coin cell fabrication purpose; (d) an organic electrolyte for back-and-forth movement of ions; and (e)a separator (3) to prevent the physical contact between cathode and anode. In an embodiment, the present invention provides schematic representation of a full cell electrochemical device as depicted in Figure 13 comprising fluoride-free, surface functionalized Ti3C2Tx MXeneelectrode asanode, nitrogen or sulphur doped porous carbon as a cathode, wherein the anode-to-cathode mass ratio is 1:4, an organic electrolyte and separator. The electrolyte and the separator are as described above. The electrode of the present invention comprising fluoride free, surface functionalized Ti3C2Tx MXene as anode shows a specific capacity in a range from 30-50 mAh g-1at 0.2 A g-1and 20- 30 mAh g-1at 1 A g-1in lithium-ion batteries, sodium ion batteries or capacitors. Further, the electrode of the present invention demonstrates a power density in a range from 100 W kg1to 10000 W kg1. For example, 100 W kg−1to 1000 W kg−1, from 1000 W kg−1to 9000 W kg−1, from 2000 W kg−1to 8000 W kg−1, from 3000 W kg−1to 7000 W kg−1, from 4000 W kg−1to 5000 W kg−1or any combination of two or more of these ranges when tested at 1 A g−1after 5000 cycles.Furthermore, the electrode of the present inventioncomprising fluoride-free, surfacefunctionalized Ti3C2TxMXene demonstrates a capacitance retention in a range from 20 to 30%, from 30 to 40%, from 40 to 50%, from 50 to 60%, from 60 to 70%, from 70 to 80%, from 80 to 90%, or any combination of two or more of these ranges when tested at 1 A g−1after 5000 cycles. Capacitance retention ranges preferably 80%-90% at 1 A g−1after 5000 cycles. EXAMPLES PT / 2025 / 14696 The following examples, which include preferred embodiments, illustrate the invention and is non-limiting. Materials: Chemicals: Titanium Aluminium carbide (Ti3AlC2, particle size of 45 µm, >99 %) was procured from Intelligent Materials Pvt. Ltd. Hydrochloric acid (HCl, 36.0-38.0%) and Lithium fluoride (LiF). Hydroiodic acid (HI 57%) was purchased from Sigma Aldrich. Vinegar with 95 to 98 % acetic acid was purchased from local store. N-methyl-2- Pyrrolidinone (NMP) and polyvinylidene fluoride (PVDF) were used from Sigma Aldrich for electrode slurry preparation. Super- p conducting carbon for slurry preparation. N doped porous carbon (NSC) was prepared by using urea and sucrose purchased from sigma Aldrich and global nanotech respectively. The electrolyte used was 1 M LiPF6 in ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). Whatman glass fiber as a separator, and Li discs as counter and reference electrode were purchased from Global Nanotech. Example 1: Process for preparation of fluoride-free MXene surface functionalized with iodide ions The synthesis of fluoride free, Ti3C2MXene comprising iodide ions as surface groups (HVM) is prepared by using HI and vinegar. Since iodide ion is larger than the fluoride ion it will not penetrate or will not react directly with Ti3AlC2 MAX, the MAX is treated with 1M sulfuric acid to form a partially oxidized MAX named as OM or (M1)ox.and then treated with HI in 1:5 molar ratio to convert it as charge transfer complex (HIM) & then with Vinegar as etchant called as HVM. The process for preparation is shown in figure 1(a) and 1(b). In particular, 1g of Ti3AlC2 (MAX precursor) was added in 25 ml 1 M H2SO4 and kept for 1h under stirring at room temperature (rt) to obtain a uniform dispersion of MAX / H2SO4solution. In the next step, hydrothermal reaction was carried out for 24 h at 1500C using MAX / H2SO4 solution. The resultant reaction mixture after hydrothermal treatment was filtered by washings with DI water, and by removal of acidic content of sulfuric acid which was confirmed by measuring the pH, which was measured to be 5. The product was dried in vacuum oven at 800C for 12 h. The dried powder was named as OM & weighed 780 mg. In the subsequent step, HI treatment was carried out using 400 mg of the OM in 5 ml of HI (57% in water). The solution was stirred for 2 h at room temperature & 700C. (Before doing the reaction, solution was pale PT / 2025 / 14696 black in colour & after 2h it turned to pale green in colour). Sample cleaning was performed by vacuum filtration using 0.2µm polytetrafluoroethylene (PTFE) membrane & was kept for drying at 800C for 12 h to obtain an AlI3 complex. The product was named as ‘HI treated OM1’(HIM1 or HIM). Last step was carried out to etch (AlI3) complex using vinegar treatment. 50 mg HI treated OM1 was added in 5 ml of vinegar & kept for heating for 2 h at 700C. After 2 h, the product was filtered by vacuum filtration & washed using DI water. The product was dried for 12 h in vacuum oven at 800C to obtain the fluoride-free MXene surface functionalized with iodide (-I) ions as nanosheets. It was named as ‘vinegar treated HVM’ or ‘HVM’. Comparative Example A: Process for preparation of HF treated MXene 0.5 g of MAX was mixed and stirred in 20 mL of HF solution at room temperature for 24 hours. The resulting suspension was then centrifuged at 5000 rpm for the separation of powder from the supernatant, followed by washing multiple times with DI water till the pH became neutral. The obtained multilayered MXene powder was mixed and sonicated in 10 mL of dimethyl sulphoxide (DMSO) for 30 minutes. The suspension was centrifuged at 3000 rpm for 1 hour and then washed with DI water. The obtained product was added to 50 mL of DI water and was again centrifuged for 30 minutes to get delaminated supernatant. This sample is labelled as HFM. Example 2:- Characterization of compounds of Example 1 and Comparative Example A PXRD data: Figure 2a shows the PXRD data of MAX precursor, HF treated MXene (Comparative Example A) & vinegar treated MXene (Example 1) before etching and after etching respectively. In PXRD analysis of the HFM sample, comparison of the PXRD patterns with the standard Ti3AlC2 MAX (JCPDS file: 52-0875) revealed the disappearance of the characteristic peak at 39° corresponding to the (104) plane of the aluminium layers, indicating successful Al removal. Additionally, a noticeable shift of the (002) peak from 9.4° to 8.9° was observed, suggesting an increase in the interlayer d-spacing (9.9 Å) of the HFM nanosheets compared to the original MAX phase, as shown in Figure 2a. However, in the case of HVM prepared according to the present invention, the (104) peak was still present but significantly weakened, indicating that trace amounts of Al remaining in the HVM structure. Furthermore, the (002) peak was further shifted to a lower angle at 6.1°, suggesting a substantial increase in interlayer d spacing by 14.4 PT / 2025 / 14696 Å due to iodide doping. A weak (002) peak corresponding to the unreacted MAX phase was also observed, further confirming the partial retention of the original structure and the presence of residual aluminium in HVM. These results demonstrate that the process of the present invention for preparation of fluoride-free MXene surface functionalized with iodide effectively expands the interlayer spacing in a relatively short time. In contrast, the HF-assisted method is more hazardous and typically yields HFM nanosheets with a comparatively smaller interlayer spacing. In order to study the surface terminations onto the nanosheet structure, comparative Raman spectra of HF-etched MXene (HFM) and HI / vinegar etched MXene (HVM) samples were examined, as shown in Figure 2b. The weak peak at around 147 cm-1in HVM shows the fundamental vibration because of the iodide species. HFM shows a dominant peak at 151 cm-1can be assigned to the O-Ti-O bond, which may be due to the surface oxidation in the presence of air.4The representative bands at 715 cm-1are assigned to Ti and C atoms with A1g out-of-plane vibration modes in both cases. The Eg vibrations of in-plane modes are seen at 253 and 260 cm-1for Ti atoms and the terminal -OH group; 438 and 408 cm-1for C modes, and 604 cm-1related to some of the functional groups in HFM and HVM, respectively. The result was further verified by using a UV-visible spectroscopy test of iodine and HVM- containing solutions in ethanol solvent to capture the capability of iodide species, as shown in Figure 2c. HVM absorbance illustrates the intense peaks of iodide ions at a lower shift at 281 and 360 nm when compared with iodine, indicating the iodide ions' absorption in the form of I-, I3-,and the formation of a bond between -OH and iodide ion may also take place. Surface area and Pore size distribution: The N2 adsorption-desorption BET specific surface area (SSA) of HVM was measured to be 49 m2g-1, significantly higher than that of HFM, which showed SSA to be 13 m² g-1as illustrated in Figure 3a. The improved surface area of HVM is primarily attributed to the surface modification of nanosheets following iodide ion incorporation. The iodine doping effectively expands the interlayer spacing, exposing more active sites and thereby enhancing the SSA. The porous structure of HVM features an interconnected network of dense micro and meso pores, which can facilitate faster Li-ion transport and accommodate structural expansion during lithiation and delithiation. The adsorption isotherm is the combination of characteristics of type PT / 2025 / 14696 IV and VI isotherms with an H3 hysteresis loop, suggesting the coexistence of micro- and mesopores ranging from 0 to 10 nm, as depicted in Figure 3b. The enhanced SSA, high porosity, and appropriate pore size indicate that the HVM effectively serves as a carrier for iodide species. Environmental Scanning Electron Microscope (ESEM), and Selected Area Electron Diffraction (SAED) analysis Figure 4a shows the sheet-like, porous morphology of HVM, synthesized through a novel and effective etching process. HVM with structural features resembling those of fluoride-etched MXene. HVM exhibits a significantly wider interlayer spacing than both MAX and HFM, consistent with the observed PXRD and high SSA analysis. The presence of gaps formed by slightly curved MXene flakes in HVM may offer additional adsorption sites for iodine doping and facilitate improved Li-ion transport. The corresponding selected area electron diffraction (SAED) pattern in Figure 4b displays a hexagonal symmetry with high crystallinity. Example 3:- Analysis of chemical composition of MXene prepared according to Example 1. X-ray Photoelectron (XPS): To confirm the interaction of iodine with MXene as surface functionality, XPS was examined to understand the surface electronic state and chemical composition. Figure 5a and Figure 5b illustrate the XPS survey scan along with the I 3d peak in the inset and its deconvoluted I 3d spectra of HVM, which exhibits peaks at 618.9 and 630.5 eV binding energies of I 3d3 / 2and I 3d5 / 2, respectively. This indicates that the iodide ion exists in the form Ti-I. Iodine doping may enhance the conductivity of 2D materials. Example 4:- Electrical conductivity performance: The electrical conductivity of the MXene surface functionalized with iodide (HVM), prepared by the process of the present invention was compared with different conventionally known MXenes surface functionalized with fluoride ions (Samples 1 and 2) by using four probe conductivity measurement. Samples 1 was HFM (DMSO / HF MXene) prepared according to Comparative Example A and Sample 2 was prepared according to the process. Further, the conductivity was also measured for MAX precursor (Sample 3). The electrical conductivity of PT / 2025 / 14696 these MXenes was compared with standard HF treated MXene as depicted in Figure 6. The results are mentioned in Table 2 below: Table 2: Conductivity Data using four probe measurements Sample σ (S / cm) DMSO / HF MXene (HFM) 1 19.5 LiF / HCl MXene (LiFHM) 2 232 MAX 3 139.2 HVM 4 388 HVM prepared by the process of the present invention showed an electrical conductivity of 388 s / cm which is highest in comparison to the Comparative samples as mentioned in Table 2 and depicted in Figure 6. This superior conductivity is attributed to the effective doping of iodide, which acts as a counter ion in the charge transfer complex formed during the process of the present invention, thereby resulting in MXene with iodide ions as surface groups. The enhanced conductivity of HVM MXene prepared by the process of the present invention makes it highly suitable for applications in energy storage devices, such as batteries and capacitors, where high electrical conductivity is essential for efficient charge transport. Example 5: Stability test An ambient stability study of HFM and HVM dispersions in DI water was conducted, considering the hydrophilic nature of Ti3C2Tx-based MXenes. As shown in the real-time digital images in Figure 4, both HFM and HVM appeared as black coloured dispersions on day 1. After 15 days, HVM retained its colour and structural integrity, indicating excellent stability. The results are demonstrated in Figure 7 and Table 3 below. Table 3: MXene Electrical Stability Specific Conductivity (S / cm) surface area (m2 / g) HF / DMSO treated MXene 0.78 Upto 1 week 13 PT / 2025 / 14696 Surface functionalized 388 after 2 weeks 49 MXene of Example 1 As observed from Table 3, the HI treated MXene is stable after two weeks compared to HF / DMSO treated MXene (comparative Example A) which becomes unstable after a week in aqueous dispersion. Example 6:- Process for preparation of electrode comprising the MXene of Example 1 The prepared HI treated Ti3C2(HIM) sample was tested for the proof of concept as anode in half-cell of Lithium-ion battery (LIB). The coin cells were fabricated using 1M LiPF6in EC: EMC: DMC as the electrolyte, lithium as counter or reference electrode and Celgard 2500 as the separator. The anodes were prepared by making slurry of HIM with conducting carbon and PVDF in the ratio of 80:10:10 in NMP solvent and was coated on Cu foil. The coated electrodes were dried in a vacuum oven at 80 ⁰C for 12h. The cells were assembled in an argon gas filled glove box with O2 and H2O levels below 0.1 ppm. Example 7: Electrochemical performance tests of anode of Example 6 The electrochemical performance of the HVM was evaluated using galvanostatic charge– discharge measurements in a half-cell configuration, within the potential range of 0.01 to 3V vs. Li / Li+. The relatively low potential observed around 0.9 V is likely due to the formation of a Li-Al alloy in HVM, which is evident from the CV curves of Ti3AlC2 MAX, HFM, and HVM, as shown in Figure 8a. In contrast, the CV profile of HFM shows no distinct redox peaks, as illustrated in Figure 8a. This highlights the active participation of Li+ions in the redox reactions of HVM, contributing to its pseudocapacitive behaviour. Furthermore, the larger area under the CV curve for HVM, compared to HFM and MAX, reflects its superior charge storage capability. The comparative rate performance of MAX, HFM, and HVM, ranging from 0.05 A g-1to 1 A g-1, was evaluated as shown in Figure 8b. HVM delivers high average specific capacities of 500, 475, 444, 388, and 328 mAh g-1at current densities of 0.05, 0.1,0.2, 0.5, and 1 A g-1, respectively, significantly exceeding the performance of both pristine MAX and HFM. The significantly improved rate capability suggests that HVM effectively overcomes ion storage kinetic limitation, even at higher current densities, due to the presence of rapid ion PT / 2025 / 14696 diffusion channels. The recovered capacity of 478 mAh g-1at 0.1 A g-1demonstrates the excellent reversibility of the HVM electrode. Figure 8c presents the cycling performance of the comparative electrode materials at a higher current density of 1 A g-1. HFM and MAX exhibit relatively low specific capacities of 70 and 37 mAh g-1, with capacity retentions of 84 % and 69 % after 150 cycles, respectively. Whereas HVM demonstrates excellent long-term stability, maintaining a specific capacity of about 300 mAh g⁻¹ after 150 cycles at 1 A g⁻¹ (Figure 8c) with 90 % capacity retention. Figure 9 demonstrates the cyclic stability of the anode of the present invention at a current density of 1 A g⁻¹. Even after 500 cycles, HVM retains a high capacity of 295 mAh g-1with a coulombic efficiency (C.E.) of 99.7 % as illustrated in Figure 9. ADVANTAGES OF THE INVENTION 1. Development of novel iodide / vinegar assisted etching strategy towards synthesis of fluoride free, iodide-doped MXene using hydroiodic acid (HI) leads to the environmentally safe pathway. 2. Two-dimensional surface functionalized Ti3C2Tx MXene are designed with a green approach, where acids are used for doping the halides. 3. The surface functionalized Ti3C2TxMXene possess higher surface area and good wettability properties. 4. By using hydrogen iodide and vinegar, hazardous side products are eliminated, preventing any unwanted exposures and greatly improving process safety through safe handling. 5. The surface functionalized Ti3C2TxMXene prepared by present invention have a superior electrical conductivity compared with different fluoride treated MXenes. 6. The surface functionalized Ti3C2Tx MXene electrode exhibits outstanding performance as anode with electrical conductivity of 388 s / cm. 7. Because of the higher electrical conductivity, the surface functionalized Ti3C2TxMXene results in the remarkable electrochemical performance in the energy storage applications, especially LIB and LICs. PT / 2025 / 14696 8. Surface functionalized Ti3C2TxMXene exhibits superior performance as anode with a discharge capacity of around 86 mAh g-1at 0.1 A g-1input current and at 1 A g-1it is 27 mAh g-1. 9. The surface functionalized Ti3C2TxMXene is stable in water after 2 weeks, superior to fluoride-assisted MXenes prepared from traditional etching techniques.

Claims

AMENDED CLAIMS received by the International Bureau on 23 January 2026 (23.01.2026)WE CLAIM:

1. A process for preparation of a fluoride-free, surface functionalized MXene, the process comprising: a) etching MAX phase with sulfuric acid to obtain a partially oxidized MAX phase; b) treating the partially oxidized MAX phase with hydrogen iodide (HI) to obtain a charge transfer complex; c) etching the charge transfer complex with vinegar to obtain the fluoride-free, surface functionalized MXene; and d) optionally treating the fluoride-free, surface-functionalized MXene with oxygen to obtain an oxygenated MXene.

2. The process as claimed in claim 1, wherein the MAX phase is present in an amount ranging from 4% wt / vol to 13% wt / vol and the sulfuric acid is present in a concentration ranging from0.1 M to 1.0 M and wherein, step a) is carried out by hydrothermal method at a temperature in a range from 100°C to 200°C.

3. The process as claimed in claim 1, wherein the partially oxidised MAX phase in an amount ranging from 8% wt / vol to 12% wt / vol is treated with HI present in an amount ranging from 3 % wt / vol to 12 % wt / vol.

4. The process as claimed in claim 1, wherein the vinegar is present in an amount ranging from 5 ml to 10 ml and wherein the step c) is carried out at a temperature in a range from 70 °C to 90°C.

5. The process as claimed in claim 1, wherein the fluoride-free MXene has surface functionalized iodide (-1) ions.

6. The process as claimed in claim 1, wherein the fluoride-free, surface functionalized MXene has a surface area in a range from 1 m2g-1to 20 m2g-1, and pore size distribution in a range from 1 nm to 100 nm.

7. A process for preparation of an electrode, the process comprising:(a) preparing a slurry by mixing the fluoride free, surface functionalized MXene prepared by the process as claimed in claim 1, carbon and a binder in a solvent; and(b) depositing the slurry on a current collector.

8. A fluoride free, surface functionalized MXene prepared by the process as claimed in claim 1 having formula:Mn+1XnTx wherein,M is a transition metal selected from scandium (Sc), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), zirconium (Zr), hafnium (Hf) and combination thereof;X is selected from carbon or nitrogen;Txis selected from hydroxyl (OH), oxygen (=0) and iodine (I); and n is selected from 1 to 3.

9. An electrode comprising the fluoride free, surface functionalized MXene as claimed in claim 8.

10. A full cell comprising for electrochemical device, comprising:(a) fluoride-free, surface-functionalized MXene electrode prepared by the process as claimed in claim 7 as anode (2);(b) a cathode (4);(c) cell components such as positive (7) and negative (1) stainless steel cell cases along with spacer (5) and spring (6) for coin cell fabrication purpose;(d) an organic electrolyte for back-and-forth movement of ions; and(e) a separator (3) to prevent the physical contact between cathode and anode.

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