Porous aromatic framework host material for lithium-sulfur batteries, its process of preparation, and use thereof

Abstract

The present invention generally relates to porous aromatic framework host material for batteries. Particularly, the present invention relates to a porous aromatic framework host material for lithium sulfur battery, comprising carbon porous 3D polymers (3DPs) that do not contain heteroatoms or functional groups and do not require post-functionalization, and a process of preparation thereof. The present invention also relates to a lithium sulfur battery comprising said porous aromatic framework host material as cathode / working electrode.

Description

[0001] P_IN105499

[0002] POROUS AROMATIC FRAMEWORK HOST MATERIAL FOR LITHIUM- SULFUR BATTERIES, ITS PROCESS OF PREPARATION, AND USE THEREOF

[0003] FIELD OF THE INVENTION

[0004] The present invention generally relates to porous aromatic framework host material for batteries. Particularly, the present invention relates to a porous aromatic framework host material for lithium sulfur battery, comprising carbon porous 3D polymers (3DPs) that do not contain heteroatoms or functional groups and do not require post-functionalization, and a process of preparation thereof. The present invention also relates to a lithium sulfur battery comprising said porous aromatic framework host material as cathode / working electrode.

[0005] BACKGROUND OF THE INVENTION

[0006] Lithium-sulfur batteries (LSBs) have garnered significant attention in the field of energy storage due to their high theoretical energy density, cost-effectiveness, and environmental friendliness. With a theoretical specific energy of ~2600 Wh / kg, LSBs far surpass the energy density of conventional lithium-ion batteries, positioning them as a promising candidate for next-generation energy storage systems. However, despite their potential, LSBs face several challenges such as poor electrical conductivity of sulfur, the dissolution and diffusion of lithium polysulfides between the electrodes, low coulombic efficiency, and quick capacity fade that hinder their commercialization. Further, the high-volume expansion of sulfur during cycling leads to the detachment of active materials from the current collector, ultimately leading to cell failure. To address these issues, various host materials such as carbon-based materials, conducting polymers, organic small molecules, transition metal oxides, and their composites have been explored. Out of all, organic LSBs have emerged as a promising alternative to overcome these challenges. Organic materials offer flexibility in molecular design, tunable porosity, and redox properties which enable high sulfur loading and suppress polysulfide shuttle thus extending the cycle life of LSBs.

[0007] Porous organic polymers with optimized and uniform pore size distribution are considered an effective strategy to prevent the migration of polysulfides through physical confinement, thereby improving the performance of LSBs. Additionally, the flexibility in molecular design allows porous organic polymers to be customized for specific functions, such as polysulfide trapping and enhanced conductivity, while their lightweight nature and thermal stability contribute to improving energy density and operational safety. In general, the pore size below 0.5 nm hinders the migration of ions and will affect the kinetics of redox reactions and large pore size may intensify the shuttling of polysulfides resulting in weak performance. In fact, it is easier to design host materials that consist of positive charges, Lewis bases, or heteroatoms to interact complementarily with lithiumP_IN105499

[0008] polysulfides, or to allow post-functionalization for the grafting of polysulfides. On the other hand, the neutral cyclic sulfur doesn’t comprise a specific interaction motif. However, there is no specific report or alternative known in the art covering a host material that can interact with neutral sulfur and anionic polysulfides.

[0009] In the work “Guo, Ben et al. Chem. Commun., 2013, 49, 4905”, there is a detailed explanation on the use of a porous aromatic framework (PAF) as a host material to disperse sulfur and reduce the polysulfide shuttle effect in Li-S batteries. However, the reported PAF, does not provide anion-7t interaction with polysulfides and no mechanism for stabilization. In yet another work by Yan, Ren, Ma et.al:, Volume 173, June 2013, Pages 92-98, the construction of pyrene-based porous aromatic frameworks (PAF- 19 and PAF -20) prepared via Sonogashira-Hagihara coupling reactions are described. This however represents an early stage lithium sulfur cathode design based on simple carbon / sulfur composite structures with limited control over porosity and sulfur distribution. In an article by Pathak, Neem et. al.; Journal of Energy Storage Volume 117, 1 May 2025, 116176 the development of a composite material made from a diamondoid covalent organic framework (COF) is taught, which serves as a sulfur cathode host in lithium-sulfur batteries. However, the document requires multi-component composite (COF + MXene) to achieve conductivity and polysulfide trapping which increases the complexity. In Lin, Ding et.al, J. Mater. Chem. A, 2018,6, 17186-17191, the loading (impregnation) of sulfur into a two-dimensional pyrene-based covalent organic framework (Py-COF) to be used as a cathode host in lithium-sulfur batteries, achieving high reversible capacity and excellent rate performance due to fast lithium-ion transport within the COF’s pores is disclosed. The material still suffers from limited conductivity and dependence on functionalized building blocks.

[0010] There is a need in the art to provide novel carbon only, non-functionalized host material for lithium sulfur battery which can interact with neutral sulfur and anionic polysulfides, and provide overall effective battery life with enhanced working, thus addressing said problems of the art.

[0011] OBJECTIVES OF THE INVENTION

[0012] It is an object of the present invention to provide scalable all-carbon porous 3D polymers (3DPs) that do not contain heteroatoms or functional groups and do not require post-functionalization as hosts in lithium-sulfur batteries.

[0013] Another object of the present invention is to provide porous host materials for lithium sulfur batteries which can interact with neutral sulfur and anionic polysulfides and provide overall effective battery life.

[0014] Another object of the present invention is to provide a process of preparation of said porous host material.P_IN105499

[0015] Yet another object of the present invention is to provide a cathode or working electrode based on said porous host material in lithium sulfur batteries.

[0016] Still another embodiment of the present invention is to provide a lithium sulfur battery comprising cathodes having porous host materials that can interact with polysulfides as well as neutral sulphur with enhanced cycling stability and improved overall battery performance.

[0017] SUMMARY OF THE INVENTION

[0018] In an aspect, the present invention provides a porous host material of formula I,

[0019]

[0020] [Formula (I)]

[0021] wherein:

[0022] - R is phenyl or pyrene ring, and

[0023] - 1 bond represents connection of repeating units of R and tetrakis(4-phenyl) methane.

[0024] In an embodiment, tetrakis (4-phenyl) methane and R are the repeating units in Formula (I) and are in the range of 10-1000.

[0025] In a specific embodiment, the porous host material of formula (I) is selected from,

[0026]

[0027] [Formula (TA)]; orP_IN105499

[0028]

[0029] [Formula (IB)];

[0030] wherein the repeating units of R and tetrakis (4-phenyl) methane is in the range of 10-1000.

[0031] In an embodiment, the porous host material of formula (I) is hydrophobic with a porosity in the range of 1.2 to 1.7 nm. The porous host material of formula (I) is a diamondoid framework in shape.

[0032] In another aspect, the present invention relates to a process of preparing a porous host material having structure of formula (I), comprising reacting Pd catalyzed Suzuki coupling reaction of tetrakis(4-bromophenyl) methane with a monomer to obtain the porous aromatic framework host material having structure of formula (I).

[0033] In an embodiment, the process of preparing a porous host material having structure of formula (I), comprising the steps of:

[0034] (a) preparing a mixture comprising tetrakis(4-bromophenyl) methane with monomer in presence of a base, a catalyst;

[0035] (b) degassing the mixture of step a) under freeze-pump-thaw followed by heating to obtain crude product; and

[0036] (c) cooling the crude product of step b) followed by precipitating, washing, purifying and drying to obtain the host material having structure of formula (I).

[0037] In a further aspect, the present invention provides a lithium sulfur battery (LSB) comprising:

[0038] (i) cathode,

[0039] (ii) anode,

[0040] (iii) electrolyte, and

[0041] (iv) additive(s);

[0042] wherein the cathode comprises the porous host material having structure of formula (I) or a composite of the porous host material having structure of formula I.P_IN105499

[0043] BRIEF DESCRIPTION OF THE DRAWINGS:

[0044] FIG. 1 shows (a and b) solid-state CP -MAS 13C NMR spectra, asterisks denote spinning sidebands; (c and d) FT-IR spectra (3DPs and their precursors); (e and f) N2 adsorption curves; and (g and h) corresponding pore-size distribution of Ph3DP and Py3DP, respectively.

[0045] FIG. 2 shows PXRD data of a) Ph3DP and b) Py3DP, respectively.

[0046] FIG. 3 shows (a & b) FESEM images, and (c & d) HRTEM images of Ph3DP and Py3DP, respectively.

[0047] FIG. 4 shows TGA data of Ph3DP and Py3DP, respectively.

[0048] FIG. 5A shows (a-c) SEM images of Py3DP / S before cycling.

[0049] FIG. 5B shows (a-c) SEM images of Ph3DP / S before cycling.

[0050] FIG. 6 shows (a) polysulfide adsorption, (b) TGA of Ph3DP / S and Py3DP / S, and CV profiles of (c) Ph3DP and (d) Py3DP at 0.2 mV / s.

[0051] FIG. 7 shows (a) rate performance of Ph3DP and Py3DP; galvanostatic discharge-charge profiles at different C rates of (b) Ph3DP and (c) Py3DP; and (d) comparison of the charge-discharge profile of Ph3DP and Py3DP at 0.2 C with an inset showing the polarization potential (AE).

[0052] FIG. 8 shows (a) cycling performance of Py3DP and Ph3DP at 0.2 C; charge-discharge profiles of (b) Ph3DP and (c) Py3DP at 0.2 C; and (d) cycling performance of Py3DP and Ph3DP at 4.1 mg / cm2 sulfur loading.

[0053] FIG. 9 shows cycling performance of Li-S batteries with (a) Py3DP / S and (b) Ph3DP / S; and chargedischarge profiles of Li-S cells with (c) Py3DP / S (d) Ph3DP / S electrodes at 1C.

[0054] FIG.10 shows the representative coin cell of the LSB of the present invention.

[0055] DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention relates to porous aromatic framework host materials particularly for lithium sulphur batteries which are carbon only scaffolds capable of confining sulphur polysuplfides and neutral sulphur in the aromatic framework.

[0057] The term “diamondoid” used herein means a cage-like, saturated hydrocarbon molecules that resemble a diamond lattice structure, where the main building block has sp3hybridisation and that resembles diamond lattice structure.

[0058] The term “host material” is used herein for cathode host materials in batteries, particularly lithiumsulfur (Li-S) that are structures designed to hold active materials, facilitate electron / ion transport, and manage volume changes and act as conductivity-enhancing scaffolds, metallic structures, acting as conductivity-enhancing scaffolds.P_IN105499

[0059] The term “COF” used herein relates to Covalent Organic Frameworks ae high-performance, sustainable cathode materials for rechargeable batteries (Li, Na, Zn, K) due to their customizable porous structures, crystalline nature, and tunable redox-active sites. They offer high capacity, long cycle life, and fast ion transport. They are also ideal as host materials as they also reflect high reactivity due to their well-defined porosity, structural tunability, and the ability to incorporate specific functional groups.

[0060] The phrase “3DP” as per the present invention refers to all-carbon 3-dimensional polymers that do not contain heteroatoms or functional groups and do not require post-functionalization as host in lithium-sulfur batteries, demonstrating enhanced cycling stability and overall battery performance.

[0061] In an aspect, the present invention relates to a porous host material of formula I,

[0062]

[0063] [Formula (I)]

[0064] wherein:

[0065] - R is phenyl or pyrene ring;

[0066] - 1 bond represents connection of repeating units of R and tetrakis(4-phenyl) methane.

[0067] In an embodiment, the repeating units of R and tetrakis(4-phenyl) methane in the formula I are in the range of 10-1000. In a preferred embodiment, the repeating units of R and tetrakis(4-phenyl) methane in the formula I are in the range of 20-1000.

[0068] In an embodiment, the porous aromatic framework host material having structure of formula I is selected from:P INl 05499

[0069] [Formula (IA)]

[0070]

[0071] [Formula (IB)]

[0072] wherein the repeating units of R and tetrakis (4-phenyl) methane is in the range of 10-1000.

[0073] In a specific embodiment, the porous aromatic framework host material having structure of formula I is:

[0074]

[0075] [Formula (IA)]

[0076] wherein the dashed bond means connected with repeating units of phenyl ring and tetrakis(4-phenyl) methane, and and 1.02 nm is a pore diameter of the material; orP_IN105499

[0077]

[0078] [Formula (IB)]

[0079] wherein the dashed bond means connected with repeating units of pyrene ring and tetrakis(4-phenyl) methane, and 1.68 nm is a pore diameter of the material. The dashed and wedged bonds in tetrakis(4-phenyl) methane unit of formula I, Formula (IA) and Formula (IB) represents its 3D nature (sp3hybridization), and the dashed bond in the periphery means connected with repeating units of pyrene / phenyl ring and tetrakis(4-phenyl) methane.

[0080] In an embodiment, the porous aromatic framework host material having structure of formula (I) is in a diamondoid shape. These interconnected, sponge-like or diamondoid framework morphologies with isotropic porosity, provide a more open structure that facilitate rapid ion transport and electrolyte infiltration. 3DPs typically exhibit hierarchical porosity to improve electrolyte accessibility and reaction kinetics.

[0081] The pore structure of the compounds of Formula I of the present invention (inventive 3DPs) ar critical in preventing the migration of polysulfides through physical confinement wherein the large II-clouds of 3DPs interact with the negative charge-bearing polysulfides generated in charge-discharge cycles through anion II-interaction. By containing the migration of the polysulfides as well as neutral sulphur, the inventive 3DPs are able to prevent the high volume expansion of sulfur during cycling. The expansion and migration of sulphur leads to the detachment of active materials from the current collector, ultimately leading to cell failure. This is successfully prevented by the porous host material as per the invention. In an embodiment, the pore diameter of the porous host material having structure of formula I is in the range of 1 to 1.7 nm. In a preferred embodiment, the pore diameter of the porous aromatic framework host material having structure of formula (I) is in the range of 1.02 to 1.68 nm.

[0082] In another embodiment the porous host material having structure of formula I enables the physical confinement of the polysulfides through the micropores of size in the range of 1-1.7 nm, which can trap Li2Sx (4<x<8) having size of 1.2-1.7 nm.P_IN105499

[0083] In another embodiment, the porous aromatic framework host material having structure of formula I is polycrystalline in nature as evidenced in Fig. 2. In an embodiment, the porous aromatic framework host material having structure of formula I is having uniform nanosphere shape.

[0084] In an embodiment, the porous aromatic framework host material having structure of formula I comprises 7t-surface, which facilitates stronger interactions with lithium polysulfides through anion-Ti interactions.

[0085] The porous aromatic framework host material having structure of formula I does not contain heteroatoms or functional groups and hence does not require post-functionalization. In an embodiment, the porous aromatic framework host material having structure of formula I is composed solely of carbon and hydrogen. It is a unique and surprising feature of the present invention that leads to high cycling stability and strong polysulfide suppression due to structural design, through a rigid 3D framework with well-defined pores and large 7t-electron systems that physically confine and interact with polysulfides.

[0086] The porous host material having the structure of formula I comprises hydrophobic pores which effectively confine the sulfur and interact efficiently with lithium polysulfides due to anion-7t-interaction. The hydrophobic host material is designed to comprise it cloud and hence it can also attract negative charge-bearing polysulfides due to anion-7t-interaction. Surprisingly it was observed that the porous host material compound of formula (I) composed solely of carbon and hydrogen having hydrophobic pores of the compound of formula (I) of the present invention effectively confine the sulfur and interact efficiently with lithium. In an embodiment, the Brunauer-Emmett-Teller (BET) surface area of the porous aromatic framework host material having structure of formula I is in the range of 450 to 470 m2 / g. In another embodiment, the BET surface area of the porous aromatic framework host material having structure of formula I is in the range of 458.06 to 467.51 m2 / g.

[0087] In another aspect, the present invention relates to a process of preparation of the porous host material having structure of formula I, comprising reacting Pd catalyzed Suzuki coupling reaction of tetrakis(4-bromophenyl) methane (1) with a monomer to obtain the porous aromatic framework host material having structure of formula I.

[0088] In an embodiment, the process comprising the steps of:P_IN105499

[0089] a) preparing a mixture comprising tetrakis(4-bromophenyl) methane with monomer in presence of a base, a catalyst;

[0090] b) degassing the mixture of step a) under freeze-pump-thaw to obtain crude product; and c) cooling the crude product of step b) followed by precipitating, washing, purifying and drying to obtain the host material having structure of formula I.

[0091] In an embodiment, the freeze-pump-thaw comprises freezing a reaction flask containing the mixture of step a) in a liquid nitrogen at temperature of around -196 °C, followed by thaw at temperature in the range of 40-60 °C.

[0092] In an embodiment, the freeze-pump-thaw is done at least two times.

[0093] In another embodiment, the freeze-pump-thaw takes around 10-20 minutes time period.

[0094] In an embodiment, the monomer is selected from the group comprising 1,4-phenylenediboronic acid, 2,7-bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl) pyrene and bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl) hexabenzocoronene.

[0095] In an embodiment, the base in step (a) is selected from the group comprising potassium carbonate (K2CO3) and cesium carbonate (CS2CO3).

[0096] In an embodiment, the catalyst employed in step (a) is selected from a group comprising Palladium-tetrakis(triphenylphosphine) [Pd (PPh3)4] and Bis(triphenylphosphine)palladium (II) dichloride [Pd (PPh3)2Cl2].

[0097] In an embodiment, a solvent is employed in step (a) and is selected from N, N-dimethylformamide, water, toluene, dimethoxyethane (DME), tetrahydrofuran (THF), and any two combination thereof. In a specific embodiment, the solvent comprises N, N-dimethylformamide and water in av / v ratio of 3:0.5 to 5:1.

[0098] The crude product of step b) is poured into water after cooling to obtain the precipitate crude product. In an embodiment, the washing of the precipitated crude product is done by using solvent selected from but not limited to H2O, THF, methanol, and acetone or mixture thereof.

[0099] Optionally, the purification of the washed crude host material of formula I is done by using Soxhlet extraction with solvent selected from but not limited to dichloromethane, THF, acetone, and methanol or mixture thereof for time period in the range of 70-74h to obtain pure polymer / host material of formula I.

[0100] In another aspect, the present invention provides a lithium sulfur battery (LSB) comprising:

[0101] (i) cathode;

[0102] (ii) anode;

[0103] (iii) electrolyte; and

[0104] (iv) additive(s);P_IN105499

[0105] wherein the cathode comprises the porous aromatic framework host material having structure of formula I or a composite of the porous aromatic framework host material having structure of formula I.

[0106] In an embodiment, the lithium sulfur battery is in the form of a coin cell.

[0107] In an embodiment, the coil cell further comprises: i) said cathode coated onto an aluminium foil, b) separator, c) cell cap, d) cell can, e) spacer, f) spring, and g) gasket.

[0108] In an embodiment, the spacer is selected from but not limited to polyethylene (PE) and stainless steel (SS) and the gasket is selected from but not limited to stainless steel (SS), plastic and glass.

[0109] In an embodiment, the separator is made of material selected from polypropylene (PP), silicone and fluorinated ethylene-propylene (Tefzel) to create a seal and prevent leakage.

[0110] In an embodiment, the anode is selected from but not limited to lithium foil and sodium foil. In an embodiment, the electrolyte is selected from bis(trifluoromethane)sulfonimide (LiTFSI) and / or lithium nitrate (LiNOy) in dioxolane, dimethoxyethane, mixture of dioxolane and dimethoxyethane with weight ratio in the range of 0.5:1 to 1 :0.5, lithium difluoro(oxalato)borate (LiDFOB), lithium triflate (LiOTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiCICh).

[0111] In another embodiment, the additive is selected from super P carbon, PVDF binder or combination thereof.

[0112] In an embodiment the composite of the porous aromatic framework host material having structure of formula (I) is prepared by melt-diffusion technique, wherein it comprises treating the porous aromatic framework host material having structure of formula (I) with a sulfur in a weight ratio of 20:80 to 50:50 for time period in the range of 20-45 minutes, followed by heating at temperature in the range of 140-170 °C for time period in the range of 10-14 h to obtain the composite.

[0113] The cathode is prepared by a process comprising: a) casting homogeneous slurry of the porous aromatic framework host material having structure of formula (I) or a composite of the porous aromatic framework host material having structure of formula (I), a carbon black, and PVDF binder in a ratio in the range of 7:1.5:1.5 to 9:0.5:0.5 in a solvent onto a current collector to obtain a cathode film; and b) drying the film of step a) in a vacuum oven at temperature in the range of 100-140 °C for time period in the range of 6-10h followed by hot roll pressing to obtain the cathode material for LSB. In an embodiment, the solvent is selected from but not limited to NMP, DME.

[0114] In an embodiment, the current collector is selected from but not limited to carbon-coated aluminium. In another embodiment, the sulfur loading in the cathode or working electrode is maintained at 30-80 wt. %, preferably the sulfur loading in the cathode or working electrode is maintained in the range of 75-81 weight %, more preferably, the sulfur loading in the cathode or working electrode isP_IN105499

[0115] maintained in the range of 75.8-80.4 weight %. In yet another preferred embodiment, the sulfur loading in the cathode or working electrode is maintained at 1.0-4.0 mg / cm2. In another specific embodiment, the electrolyte-to-sulfur ratio is maintained between 10-25 pL / mg, preferably the electrolyte-to-sulfur ratio is maintained at 20 pL / mg.

[0116] In another embodiment, the coating thickness of sulfur onto the cathode is in the range of 50-80 micrometre.

[0117] In another embodiment, the higher Csp and superior cyclic stability of the host material of formula (I) is attributed to the high polysulfide interaction energy, which results in a faster conversion rate of polysulfides, and improved sulfur utilization.

[0118] In another embodiment, the host material of formula I is stable at least 600 cycles with retaining around 65-75% of its initial capacity (refer, Fig. 9a-b).

[0119] The host material of formula I contained in cathode or working electrode causes stable and reversible electrochemical conversion of sulfur to polysulfides. The present invention provides a scalable all-carbon porous 3D polymer (3DPs) that do not contain heteroatoms or functional groups and do not require post-functionalization or doping as host in lithium-sulfur batteries, demonstrating enhanced cycling stability and overall battery performance. The pyrene containing 3DP exhibits 75 % capacity retention after 600 cycles at 1 C and 52% capacity retention after 1300 cycles at 0.2 C. Furthermore, even at higher sulfur loading (4.1 mg / cm2) with an electrolyte / sulfur ratio of 5 pL / mg, pyrene 3DP displayed a high capacity of 600 mA h / g and stable performance over 250 cycles with negligible capacity fade. The defined pore structure of 3DPs prevents the migration of polysulfides through physical confinement and the large K-clouds of 3DPs interact with the negative chargebearing polysulfides generated in charge-discharge cycles through anion-K interaction. Additionally, unlike composite systems (e.g., COF / MXene or MOFs) that rely on multiple components to achieve conductivity and stability, the present inveniton provides intrinsic conductivity and stability, making it simpler, scalable, and more durable.

[0120] EXAMPLES

[0121] Examples are set forth below and are illustrative of varying reactants and reaction conditions that can be utilized in practicing the invention. The following examples are given to describe further the details of the instant invention and therefore should not be construed to limit the scope of the invention. DETAILS OF MATERIALS AND EQUIPMENT USED:

[0122] All reagents and solvents were of commercial reagent grade procured from Vendors named as Finar, BLD, TCI, ALFA ACER, Sigma Aldrich (in India), and were used without further purification unless otherwise noted. The solvents such as di chloromethane were purified before use according to theP_IN105499

[0123] reported procedure and stored under an inert atmosphere. All the reactions were carried out in oven-dried round-bottomed flasks under an atmosphere of argon unless otherwise mentioned.

[0124] The NMR spectra were recorded on a Bruker NMR spectrometers have 400 MHz and 500 MHz operational frequencies. The chemical shift values of 1H NMR are reported to Me4Si (1H) residual solvent as internal standards. Infrared spectra were recorded as KBr pellets, on a Bruker Alpha-E Infrared spectrophotometer, and the wavenumbers of recorded IR signals are quoted in cm-1. FEI Tecnai G2 F20 XTWIN TEM with an accelerating voltage of 200 kV was used for the TEM imaging on a carbon-coated copper grid (200 meshes, TED PELLA, INC). The scanning electron microscope images were obtained using FEI, QUANTA 2003D SEM instrument operating at 10, 15, and 20 kV, using tungsten filament as an electron source, and before imaging, the samples were sputtered with gold by using SCD 040 Balzers Union sputtered. X-ray photoelectron spectroscopy (XPS) analyses were performed on a Thermo Fisher Scientific Instruments UK, Sr.No.-KAS2020 with an Aluminium Ka+. Raman spectroscopy studies were carried out using LabRAM HR with Ar laser (1500 nm) in the backscattering geometry. The detector was a Synapse CCD detector with thermoelectric cooling to -70 °C. A 50 X (long distance) objective was used to focus the laser beam and to collect the Raman signal. The laser power on the sample was ~2 mW (DI filter), to avoid the possible heating effect by the laser on the material surface.

[0125] GENERAL PROCEDURE FOR THE PREPARATION OF POROUS AROMATIC FRAMEWORK HOST MATERIAL (3D-POLYMER MATERIAL)

[0126] Two 3D polymer materials were exemplified based on formula I disclosed in the present specification i.e., Ph3DP (Phenyl three-dimensional polymer) and Py3DP (Pyrene three-dimensional polymer). Both compound of formula (I) of the present invention were synthesized by palladium (0) catalysed Suzuki -Miyaura cross-coupling reaction. For that a 30 mL Schlenk tube was charged with Tetrakis(4-bromophenyl) methane, another corresponding monomer, N, N-dimethylformamide and water (4:1) as solvent, K2CO3 and Pd (PPhs the mixture was degassed with three cycles of freeze-pump-thaw and heated to 150 °C for 72 h. The resulting reaction crude was cooled to room temperature and then poured into water and precipitates were collected and washed with H2O, THF, methanol, and acetone, respectively. Further purification of the polymers was carried out by Soxhlet extraction with dichloromethane, THF, acetone, and methanol for 72h, respectively. The product was dried and used for further experiments.

[0127] EXAMPLE 1A: SYNTHESIS OF Ph3DP HOST MATERIAL

[0128] To a mixture of tetrakis(4-bromophenyl)methane (159 mg, 0.25 mmol), 1,4-phenylenediboronic acid (82.87 mg, 0.50 mmol), K2CO3 (276.40 mg, 2 mmol), and Pd(PPh3)4 (34.67 mg, 0.03 mmol), in Schlenk tube a degassed mixture of N, N-dimethylformamide and water 10 ml (4: 1) was added. After that, the mixture was degassed with three cycles of freeze-pump-thaw and heated to 150 °C for 72 h.P_IN105499

[0129] After cooling to room temperature precipitates were filtered and washed with water and further purification of the polymer was carried out by Soxhlet extraction with dichloromethane, THF, acetone, and methanol for 72h, respectively to afford a light gray powder of Ph3DP host material of compound of formula (IA) (108.4 mg, 92.5%).

[0130] EXAMPLE IB: SYNTHESIS OF Py3DP HOST MATERIAL

[0131] To a mixture of tetrakis(4-bromophenyl)methane (150 mg, 0.23 mmol), 2,7-bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)pyrene (215.18 mg, 0.47 mmol), K2CO3 (260.76 mg, 1.89 mmol), and Pd(PPh3)4 (32.70 mg, 0.028 mmol), in Schlenk tube a degassed mixture of N, N-dimethylformamide and water 10 ml (4:1) was added. After that, the mixture was degassed with three cycles of freeze-pump-thaw and heated to 150 °C for 72 h. After cooling to room temperature precipitates were filtered and washed with water and further purification of the polymers was carried out by Soxhlet extraction with dichloromethane, THF, acetone, and methanol for 72h, respectively to afford a gray powder of Py3DP host material of compound of formula (IB) (153.4 mg, 90.6%).

[0132] EXAMPLE 1C: SCALABLE (GRAM SCALE) SYNTHESIS OF PY3DP HOST MATERIAL To a mixture of tetrakis(4-bromophenyl)methane (1 g, 1.57 mmol), 2,7-bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl)pyrene (1.43 g, 3.14 mmol), K2CO3 (1.74 g, 12.58 mmol), and Pd(PPh3)4 (218.03 mg, 0.18 mmol), in Schlenk tube a degassed mixture of N, N-dimethylformamide and water 60 ml (4:1) was added. After that, the mixture was degassed with three cycles of freeze-pump-thaw and heated to 150 °C for 72 h. After cooling to room temperature precipitates were filtered and washed with water and further purification of the polymers was carried out by Soxhlet extraction with di chloromethane, THF, acetone, and methanol for 72h, respectively to afford a gray powder of Py3DP host material of compound of formula (IB) (1.01g, 88.9%).

[0133] EXAMPLE 2: CHARACTERIZATION OF THE SYNTHESIZED HOST MATERIALS EXAMPLE 2A: NMR ANALYSIS

[0134] The chemical structure of compound of formula (I) was investigated by solid-state cross-polarization magic angle spinning carbon- 13 nuclear magnetic resonance (CP -MAS 13C-NMR) spectroscopy showed the different carbon atoms in compound of formula (I). As illustrated in Fig. la and lb, the peaks at 118-150 ppm correspond to aromatic carbons. Besides, the peaks at 64.44 and 64.51 ppm correspond to the Sp3 carbons of tetraphenyl methane units in Ph3DP and Py3DP, respectively.

[0135] EXAMPLE 2B: FTIR ANALYSISP_IN105499

[0136] Fourier transform infrared spectroscopy (FT-IR) analysis of formula (IA) and (IB) were compared to their corresponding precursors, showed the disappearance of bands corresponding to O-H, B-O, C-B, C-O, and C-Br stretching, confirming the formation of C-C bonds (Fig. 1c and Id). Specifically, FTIR spectra of Ph3DP showed characteristic absorption bands at 3027, 2954, and 2921 cm'1for the stretching C-H aromatic groups, in addition to absorption bands at 1600, 1487, and 1393 cm'1for C=C bonds and disappearance of the bands at 1335 cm'1for the B-0 asymmetric stretching, 1257 cm'1for C-B stretching, 3200-3500 cm'1broad absorption for O-H stretching, and a diminished band at 1007 cm'1corresponding to C-Br stretching altogether confirmed C-C bond formation. Further, FTIR spectra of Py3DP showed characteristic absorption bands at 3039, 2953, and 2922 cm'1for the stretching C-H aromatic groups, in addition to absorption bands at 1604, 1507, and 1445 for C=C bonds. The disappearance of the bands at 1235 cm'1for the C-B and 1350 cm'1for B-0 1139 cm'1for C-0 stretching vibration of boronic acid pinacol ester groups, and a diminished band at 1007 cm'1corresponding to C-Br stretching altogether confirmed C-C bond formation.

[0137] EXAMPLE 2C: XRD ANALYSIS

[0138] Powder X-ray diffraction (PXRD) patterns confirmed the amorphous nature of 3DPs (Fig. 2a and 2b)

[0139] EXAMPLE 2D: FESEM AND HRTEM ANALYSIS

[0140] The samples for Scanning Electron Microscope (SEM) analysis were prepared by drop-casting (10 pL) of Py3DP and Ph3DP dispersions in MeOH on a carbon tape and drying in air. After complete evaporation of the solvent, the samples were coated with Au in an ion coater for 5 min before SEM analysis. Further, the samples for TEM were prepared by drop-casting Py3DP and Ph3DP dispersions in MeOH on carbon-coated Cu grid and allowed to dry overnight in desiccators. The morphology of the 3DPs was analyzed using scanning electron microscope (SEM) and high-resolution transmission electron microscope (HR-TEM), revealing uniform nanospheres for both 3DPs, of which Py3DP nanospheres are smaller and denser (Fig. 3a to 3d).

[0141] EXAMPLE 2E: XPS ANALYSIS

[0142] The sample was prepared by drop-casting of Py3DP and Ph3DP dispersions in MeOH (10 pL) on a silicon wafer substrate (freshly cleaned with pure isopropanol; dried) and dried under Ar in a desiccator. After complete evaporation of the solvent, the sample was directly used for XPS analysis. Samples after long-term cycling are similarly prepared for analysis. The Cis X-ray photoelectron spectroscopy (XPS) results show the presence of C-C bonds at -285 eV for both Py3DP and Ph3DP.P_IN105499

[0143] EXAMPLE 3: POLYSULFIDE ADSORPTION TEST

[0144] 0.625 M Li2Se solution was prepared by mixing sulfur and Li2S in a molar ratio 5:1 in a 1,2-dimethoxyethane (DOL): 1,2-dimethoxy ethane anhydrous (DME), (1:1) solvent mixture inside an Ar-filled glovebox. The mixture was stirred for 24 hours at 60 °C, which resulted in a homogeneous dark brown solution. This solution was diluted to 0.0005 M, and the Py3DP and Ph3DP were added into the solution and left overnight undisturbed for 12 hours. Polysulfide adsorption capabilities of both Ph3DP and Py3DP were tested by dispersing them in a Li2Se solution (Fig. 6a). Further, the supernatant solution was analyzed using UV -visible absorption spectroscopy. The Li2Se solution showed characteristic peaks at 260, 280, and 300 nm respectively corresponding to the Se. The absorbance intensity peaks at 260, 280, and 300 nm of Li2Se solution comprising Py3DP and Ph3DP was found to be reduced, indicating the strong adsorption of Li2Se on these 3DPs (Fig. 6a).

[0145] EXAMPLE 4: PREPARATION OF POLYMER / S COMPOSITE

[0146] The compound of formula (I) (three-dimensional polymers and sulphur composite) was prepared by melt-diffusion strategy. For this, Ph3DP and Py3DP and sulfur with a weight ratio of 30:70 was grounded for 30 minutes, followed by heating at 155 °C for 12 h under Argon atmosphere. Finally, the resulting mixture was cooled to room temperature. The sulfur content in the polymers was quantified by TGA. Thermogravimetric analysis (TGA) reveals that compound of formula (I) were thermally stable (Fig. 4).

[0147] EXAMPLE 5: BET SURFACE AREA ANALYSIS

[0148] BET adsorption BET adsorption experiment (up to 1 bar) of Py3DP and Ph3DP was performed on a Quantachrome Quadrasorb automatic volumetric instrument. Prior to surface area analysis, the samples were activated at 125 °C for 24 hours. The porosity of Py3DP and Ph3DP was measured by N2 adsorption of an activated sample at 77 K. The average pore diameter of Py3DP and Ph3DP was calculated by nonlocal density functional theory (NLDFT). The Brunauer-Emmet-Teller (BET) surface area of Py3DP and Ph3DP was determined by Multipoint BET analysis. P and P0 are the equilibrium and the saturation pressure of N2. The Brunauer-Emmett-Teller (BET) surface area was determined to be 458.06 and 467.51 m2 / g for Ph3DP and Py3DP, respectively (Fig. le and If). The increased porosity of Py3DP is primarily due to the C2 building block of pyrene, while the phenyl unit is smaller and more flexible, resulting in a lower range surface area. Moreover, the pore size distribution plots indicate a narrow / lower range pore size centered at 1.03 nm for Ph3DP and higher range of 1.69 nm for Py3DP (Fig. 1g and Ih). This pore size can effectively capture most polysulfide intermediates, as their sizes range from 1.2 to 1.7 nm.P_IN105499

[0149] EXAMPLE 6: LITHIUM SULFUR BATTERY AND ITS ELECTROCHEMICAL ANALYSIS EXAMPLE 6A: PREPARATION OF ELECTRODE CONTAINING POLYMER COMPOSITE OF EXAMPLE 1

[0150] The cathodes were prepared by casting homogeneous slurry of Ph3DP / S or Py3DP / S composite, carbon black, and PVDF binder in an 8: 1 : 1 ratio in the NMP solvent onto a carbon-coated aluminum current collector. The casted film was dried in a vacuum oven for 8h at 120 °C and hot roll pressed. The sulfur loading in the electrodes was maintained at 1.0-2.0 mg / cm2, and the electrolyte-to-sulfur ratio was maintained at 20 pL / mg. High sulfur loading (3-4 mg / cm2) electrodes were prepared by increasing the coating thickness. The cells were assembled inside an argon-filled glovebox (02 <0.1 ppm and H2O <0.1 ppm) using Ph3DP / S or Py3DP / S, Li foil as counter and reference electrode, and 1.0 M LiTFSI electrolyte with 2 wt. % LiNO3 additive in the DOL: DME (1 : 1) mixture. Galvanostatic charge-discharge experiments were done using NEW ARE battery testers with a potential window of 1.7 to 2.8 V against Li / Li+. Cyclic voltammetry tests were carried out using BioLogic VSP-300 potentiostat within the potential window of 1.7 V to 2.8 V. The Electrochemical Impedance Spectroscopic (EIS) analysis was carried out in the frequency range of 10 mHZ to 1 MHz with an amplitude of 10 mV.

[0151] EXAMPLE 6B: ANALYSIS OF LSBS CONTAINING SAID CATHODE PREPARED IN 6A) (REFER, FIG. 10)

[0152] A series of electrochemical measurements were carried out on LSBs fabricated using Ph3DP and Py3DP hosts. SEM images of the Ph3DP / S and Py3DP / S electrodes indicate that the 3DPs / S composites were evenly blended with carbon and binder (Fig.5A and 5B). The sulfur loading in the polymers was analyzed using TGA and was found to be 75.8 and 80.4% for Ph3DP and Py3DP, respectively (Fig. 6b). The observed variation in sulfur loading was due to differences in structural features such as surface area, 7t-surface, and pore size distribution.

[0153] LSBs comprising host material of formula (I) were then cycled between 1.7 and 2.8 V. The cyclic voltammogram (CV) of LSB with host material of formula (I) possesses two reduction peaks at 2.3 and 2.05 V corresponding to the conversion of Ss to Li2Sx (4<x<8) and Li2S2 / Li2S, respectively (Fig.

[0154] 6c and 6d). During the anodic scan, these polysulfides get oxidized back to Ss at 2.4 V. Notably, the CV profile of Py3DP exhibits highly reversible redox peaks with consistent peak currents, indicating the stable and reversible electrochemical conversion of sulfur to polysulfides (Fig.6d). The CVs were recorded for both formulae (IA, IB) at different scan rates to understand the Li-ion diffusion kinetics. The peak currents increased with an increase in the scan rates as per the Randles Sevcik equation. The peak currents were fitted with scan rates and showed a linear increase with (scan rate). Next, theP_IN105499

[0155] cells were subjected to rate performance at various C rates ranging from 0.2 to 3 (Fig. 7a). The initial specific capacity (Csp) values for the cell comprising Py3DP are 1090, 865, 750, 670, and 620 mA h / g at 0.2, 0.5, 1.0, 2.0, and 3.0 C, respectively. When the C rate was switched back to 0.2, the cell retained -950 mA h / g, indicating good rate performance of Py3DP. The cell comprising Ph3DP displayed Csp 1020, 830, 710, 615, and 585 mA h / g at0.2, 0.5, 1.0, 2.0 and 3.0 C, respectively. When the C rate was switched back to 0.2, the cell retained -880 mA h / g. Fig. 7b and 7c represent the charge-discharge profiles for LSBs comprising Ph3DP and Py3DP, respectively, at various C rates. Even at 3 C, the polarization potential for the cell with Py3DP is 338 mV, and 410 mV for the cell with Ph3DP. Furthermore, the Py3DP cell has a polarization potential of 161 mV, whereas the Ph3DP cell has a polarization voltage of 190 mV at a rate of 0.2 C (Fig. 7d).

[0156] The cells were then cycled at 0.2 C, where the Py3DP cell displayed a higher Csp of 961 mA h / g, and 904 mA h / g for the cell with Ph3DP (Fig. 8a). At the end of the 200th cycle, the Py3DP cell could still retain a capacity of 846 mA h / g (-89%), and 648 mA h / g (71%) for the Ph3DP cell. The higher Csp and superior cyclic stability of Py3DP and Ph3DP were attributed to the high polysulfide interaction energy, which resulted in a faster conversion rate of polysulfides, and improved sulfur utilization. Specifically, considering the Csp retention of Py3DP, the cycling was extended and the cell could retain 491 mA h / g at the 1300th cycle. Fig. 7b and 7c depict the corresponding chargedischarge profiles at 0.2 C for batteries with Ph3DP and Py3DP, respectively.

[0157] Further, the long-term cycling of the cells was tested at 1.0 C. The Py3DP cell delivered an initial Csp of 776 mA h / g while the Ph3DP cell had an initial Csp of 769 mA h / g. After 600 cycles, the Py3DP cell could retain 75% of its initial capacity (Fig. 9a), whereas the Ph3DP cell retained 67% of its initial capacity after 600 cycles (Fig. 9b). The corresponding charge-discharge profiles for Py3DP / S and Ph3DP / S were depicted in Fig. 9c and 9d. The superior long-term stability of Py3DP and Ph3DP was due to the strong polysulfide confining capability, the high surface area, and distinct pore size distribution which alleviates the polysulfide shuttle and simultaneously promotes their redox conversion.

[0158] The stable performance of 3DPs of formula (I) of the present invention in LSBs were significantly higher than many reported 3DPs or POPs (Table 1). These two 3DPs have a pore size distribution ranging from 1.0 to 1.7 nm, which helps suppress the polysulfide shuttle and improves conversion kinetics. Additionally, the large 7t-surface area of Py3DP supports strong anion-7t interactions with polysulfide intermediates, which in turn enhance their capacity retention over several hundreds of charge-discharge cycles.

[0159] Table 1:P_IN105499

[0160] Materials Sulfur Specific Cycle numbers Ref.

[0161] loading capacity (mA h and capacity

[0162] (wt.%) g'1) (mA h g1)

[0163] COF-l / S 40 620@1.0 C 200th, 770@0.5 Adv. Energy Mater.

[0164] C 2016, 6, 1601250 COF- 53 583@0.5C 500th, Chin. J. Polym. Sci.

[0165] 300 / S 62 690@0.5C 290@0.5C 2020, 38, 550-557.

[0166] COF- 500th,

[0167] 301 / S 412@0.5C

[0168] FMCTF-S 77 681@1.0 C 400th, 426@1.0 ChemElectroChem

[0169] C 2019, 6, 2777-2781.

[0170] Ph3DP 75.8 1020@0.2C 700th, 526@0.2 Present invention 75.8 749@1.0 C C

[0171] 600th, 520@1.0

[0172] C

[0173] Py3DP 80.4 1090@0.2C 1300th, Present invention 80.4 777@1.0 C 569@0.2C

[0174] 600th, 585@1.0

[0175] C

[0176]

[0177] Furthermore, the cells were tested at higher sulfur loading under lean electrolyte conditions (E / S:5 pL / mg). The cell comprising Py3DP / S with 3.05 mg / cm2showed initial capacity of 900 mA h / g at 0.2 C, which retained capacity of -70% after 100 cycles. The Ph3DP / S retained nearly 60% of its initial capacity (850 mA h / g) after 100 cycles under identical experimental conditions. The cells were also tested at sulfur loading of 4.1 mg / cm2and Py3DP / S cell delivered initial capacity of 600 mA h / g at a rate of 0.1 C, retaining approximately 80% of its initial capacity after 250 cycles (Fig. 9d). The Ph3DP / S cell exhibited capacity of 500 mA h / g, with nearly 72% capacity retention after 250 cycles. This is attributed to better polysulfide adsorption and immobilizing capabilities of Py3DP & Ph3DP. To better understand the interaction mechanism between polysulfides and compounds of formula (I) of the present invention, post-cycling XPS analysis was conducted. The cells comprising Py3DP / S and Ph3DP / S cells were dismantled, and the electrode was subjected to XPS analysis. The XPS spectra of Py3DP / S revealed the presence of Cis, S2p, and Lils peaks. The deconvoluted Cis spectrum showed the presence of C-Li interactions at 286.2 eV. Similarly, the Lils spectrum also showed the presence of Li-S and Li-C at 55.6 and 56.1 eV, respectively. The S2p XPS spectrum showed the presence of different sulfur-containing species formed during the charge-dischargeP INl 05499

[0178] process. Similar findings were observed for the Ph3DP / S cells. Post-analysis of the electrodes using SEM showed that the material remains intact, along with the Li2S layer deposited during the chargedischarge cycles.

[0179] ADVANTAGES OF THE INVENTION

[0180] • The porous host material of Formula lis a carbon only PAF (porous aromatic framework) with long-term stability due to its strong polysulfide confinement capability, high surface area, and distinct pore size distribution, which alleviate the polysulfide shuttle and simultaneously promote redox conversion.

[0181] • The porous host material of Formula I has a pore size distribution ranging from 1.0 to 1.7 nm, which helps suppress the polysulfide shuttle and improves conversion kinetics. • The porous host material of Formula I also has a large 7t-surface area that supports strong anion-7t interactions with polysulfide intermediates, which, in turn, enhances capacity retention over several hundred charge-discharge cycles.

Claims

P_IN105499We Claim:

1. A porous host material of formula (I):[Formula (I)]wherein:- R is a phenyl or a pyrene ring; and- bond represents connection of repeating units of R and tetrakis(4-phenyl) methane.

2. The porous host material as claimed in claim 1, wherein Brunauer-Emmett-Teller (BET) surface area of the porous host material is in the range of 450 to 470 m2 / g.

3. The porous host material as claimed in claim 1, wherein the Formula (I) is selected from,[Formula (IA)]; orP_IN105499[Formula (lb)].

4. The porous host material as claimed in claim 1, wherein the host material of formula I is hydrophobic with a porosity in the range of 1.2 to 1.7 nm.

5. The porous host material as claimed in claim 1, wherein the host material of formula I is in a diamondoid framework.

6. A process of preparing a porous host material as claimed in claim 1 comprising the steps of:(i) preparing a mixture comprising tetrakis(4-bromophenyl) methane with a monomer in the presence of a base and a catalyst;(ii) degassing the mixture of step a) under freeze-pump-thaw followed by heating to obtain crude product; and(iii) cooling the crude product of step b) followed by precipitating, washing, purifying and drying to obtain the host material having structure of formula (I).

7. The process as claimed in claim 6, wherein the monomer is selected from a group comprising 1,4- phenylenediboronic acid, 2,7-bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl) pyrene and bis(4,4,5,5-tetramethyl-l,3,2-dioxaborolan-2-yl) hexabenzocoronene.

8. The process as claimed in claim 6, wherein the base in step (a) is selected from a group comprising Potassium carbonate and cesium carbonate.

9. The process as claimed in claim 6, wherein the catalyst employed in step (a) is selected from Palladium-tetrakis(triphenylphosphine) [Pd(PPh3)4] and Bis(triphenylphosphine)palladium(II) di chloride [Pd(PPh3)2Ch].P_IN10549910. A Lithium sulfur battery comprising:(i) cathode;(ii) anode;(iii) electrolyte; and(iv) additive;wherein:the cathode comprises the porous host material having structure of formula (I) as claimed in claim 1.

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