Hybrid polymer network enabled soluble-polysulfide-free lithium-sulfur battery

Abstract

Embodiments relate to a sulfur-based cathode including a sulfurized hybrid polymer network configured to avoid soluble polysulfide formation, and to lithium-sulfur batteries include the sulfur-based cathode. The sulfurized hybrid polymer network includes a sulfurized inorganic polymer hybridized with a sulfurized organic polymer, specifically configured to interactively re-bond and / or adsorb dissociative sulfur species, thereby preventing soluble polysulfide formation.

Description

HYBRID POLYMER NETWORK ENABLED SOLUBLE-POLYSULFIDE-FREE LITHIUMSULFUR BATTERYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority of U.S. Provisional Application 63 / 709,634, filed on October 21, 2024, the entire contents of which is incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH DEVELOPMENT

[0002] This invention was made with government support under Grant No. DE-EE0009650 awarded by the Department of Energy. The Government has certain rights in the invention.FIELD

[0003] Embodiments relate to a sulfur-based cathode including a sulfurized hybrid polymer network configured to avoid soluble polysulfide formation, and to lithium-sulfur batteries that include the sulfur-based cathodeBACKGROUND

[0004] In the quest for sustainable energy solutions without carbon emissions, redox chemistries based on earth-abundant sulfur (S) are gaining prominence because they diminish reliance on potentially limited transition metal elements and promise high energy density at low cost when paired with lithium (Li) anode. Typical Li-S battery chemistry fully utilizes the high theoretical capacity of elemental sulfur (Sg) through a multistep conversion between insulating Sx and lithium sulfide (Li2S), wherein sluggish kinetics and drastic volume changes occur, involving the formation of soluble poly sulfide (Li2Sx, x>4) intermediates. The dissolution of polysulfidesinevitably causes capacity degradation from the continuous loss of active sulfur and poor cycling efficiency due to the shuttling phenomena, especially under practical conditions.SUMMARY

[0005] One can mediate a soluble-polysulfide-free, solid-to-solid sulfur conversion with enhanced electronic transport by covalently bonding small sulfur species onto conductive carbon backbones derived from organic polymers as sulfur cathodes. Despite the cost-effectiveness and sustainability of these sulfurized organic polymer-based cathodes, the corresponding conversion between small sulfur molecules and IUS, generally exhibits limited capacities, caused by the short length of bonded sulfur chains (e.g., -S1-2-) and sparse C-S bonding sites in typical organic polymers. Moreover, the C-S bonds in these cathodes undergo irreversible cleavage during electrochemical lithiation and delithiation, further diminishing the already limited capacity and impeding cycling stability.

[0006] Therefore, the realization of high-energy, long-cycle-life sulfur cathodes necessities a high-capacity sulfur conversion being free from soluble polysulfides, but typical sulfur speciation pathways suffer from either polysulfide dissolution (conversion between Ss / lUS) or limited capacity (conversion between -Sw / IUS).

[0007] We have found that sustainable, sulfurized inorganic-organic hybrid polymer (S-HYB) networks as sulfur cathodes can invoke a unique inserting conversion reaction to enable high-capacity, soluble-polysulfide-free Li-S batteries. In particular, we have discovered that the hybrid polymer network functions as a volume-stable framework, to reversibly accommodate sulfur conversions between extensive bonded sulfur chains (involving -S3-4-) and nano-crystallized LUS network. It interactively re-bonds / adsorbs dissociative sulfur species, and thus circumvents soluble polysulfide formation, by proceeding through a unique, reversible inserting conversionreaction. This approach not only advances the Li-S chemistry by minimizing the dissolution of soluble-polysulfide but also promotes sustainability through reducing the environmental impact associated with the non-renewable materials.

[0008] These characteristics form the foundation for soluble poly sulfide-free sulfur cathodes of both high capacity, capacity retention, and cycling stability.

[0009] In an exemplary embodiment, a sulfur-based cathode includes a sulfurized hybrid polymer network, wherein the sulfurized hybrid polymer network includes a sulfurized inorganic polymer hybridized with a sulfurized organic polymer, wherein the sulfurized hybrid polymer network is configured to prevent soluble polysulfide formation during cycling.

[0010] In some embodiments, a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 1 : 1 to 5 : 1.

[0011] In some embodiments, a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 2:1 to 4: 1.

[0012] In some embodiments, the sulfurized inorganic polymer is selected from the group consisting of sulfurized polyphosphazene, sulfurized polythiophosphine, sulfurized polythiazyl, sulfurized polydithiophosphate, sulfurized polyphosphonates, sulfurized poly(thio)phosphoramidates, sulfurized polyphosphonitrile oxides, sulfurized polyphosphonitrile, and mixtures thereof.

[0013] In some embodiments, the sulfurized inorganic polymer is a sulfurized polyphosphazene.

[0014] In some embodiments the sulfurized inorganic polymer has a sulfur content of at least 60 wt%.

[0015] In some embodiments, the sulfurized organic polymer is a sulfurized polymer of a sp2carbon material.

[0016] In some embodiments, the sp2carbon material is selected from the group consisting of polyacrylonitrile, pitch, nitrile rubber, and mixtures thereof.

[0017] In some embodiments, the sulfurized organic polymer is selected from the group consisting of sulfurized phenolic resin, sulfurized polyimide, and mixtures thereof.

[0018] In an exemplary embodiment, a sulfur-based cathode includes a sulfurized hybrid polymer network, wherein the sulfurized hybrid polymer network includes a sulfurized polyphosphazene hybridized with a sulfurized polymer of a sp2carbon material selected from the group consisting of polyacrylonitrile, pitch, nitrile rubber, and mixtures thereof, wherein the sulfurized hybrid polymer network is configured to prevent soluble polysulfide formation during cycling.

[0019] In some embodiments, the ratio of an amount of sulfurized inorganic polymer to an amount of sulfurized organic polymer is from 1 : 1 to 5 : 1.

[0020] In some embodiments, a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 2:1 to 4: 1.

[0021] In an exemplary embodiment, a lithium-sulfur battery includes the cathode described above; an anode comprising a lithium-based material; and an electrolyte composition disposed between the cathode and the anode.

[0022] In some embodiments, the sulfurized hybrid polymer network includes covalent phosphorus-sulfur and carbon-sulfur bonds that facilitate reversible sulfur conversion between sulfur chains and lithium sulfide.

[0023] In some embodiments, the battery is configured in a coin cell format.

[0024] In some embodiments, the battery is configured in a pouch cell format.

[0025] In an exemplary embodiment, a method of operating the lithium-sulfur battery described above includes discharging the battery; and charging the battery.

[0026] In some embodiments, during discharging the battery, lithium ions convert sulfur chains into lithium sulfide nanocrystals within the sulfurized hybrid polymer network, and during charging the battery, the lithium sulfide nanocrystals are converted back into sulfur chains.

[0027] These and other embodiments shall be described in more detail herein and in the drawings that show exemplary embodiments. Therefore, other details, objects, and advantages will become apparent as the following description of certain present preferred embodiments thereof and certain present preferred methods of practicing the same proceeds.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, aspects, features, advantages, and possible applications of embodiments of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0029] FIG. 1 shows a schematic representation of an exemplary sulfurized inorganic-organic hybrid polymer (S-HYB) networks, where sulfur chains are immobilized by multiple covalent tethers, and the Li2S discharge products are regulated by on-site atomic adsorption and gathered within the inorganic-organic hybrid polymer network

[0030] FIG. 2 shows a schematic representation of a conversion process of an exemplary S-HYB.

[0031] FIG. 3 shows a synthetic process of sulfurized polyphosphazene (SPZ) polymeric network. The as-synthesized SPZ consists of the typical inorganic polyphosphazene backbonemade of alternating phosphorus and nitrogen atoms grafted with sulfur side chains (-Sx-, 2s=x 8, controlled by the molar ratio of NPCh and Na2Sx).

[0032] FIG. 4 is a graph showing a comparison of specific capacity and capacity retention (after 50 cycles) of a series S-HYB cathode materials based on varying ratio between organic and inorganic components during synthesis.

[0033] FIG. 5 is a graph showing a comparison of specific capacity and capacity retention (after 50 cycles) of a series S-HYB cathode materials synthesized at varying temperatures. Error bars show standard deviations for the results from three samples.

[0034] FIG. 6 is a thermogravimetric analysis (TGA) showing the increased sulfur content of S-HYB compared to the control sulfurized homo-polymer (S-HOM) material.

[0035] FIG. 7 is a graph showing calculations of computed free energy revealing that it is more thermodynamically favorable to form prolonged sulfur chains in S-HYBs than the control S-HOMs.

[0036] FIG. 8 shows S 2p XPS spectra of S-HYB indicating the covalent tethers of P-S and C-S bonds.

[0037] FIG. 9 shows schematic and low-magnification transmission electron microscopy (TEM) image showing the in situ bias set-up TEM measurement for S-HYB (de)-lithiation. Scale bar is 10 nm.

[0038] FIG. 10 shows scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) mapping showing the homogeneous distribution of elemental S, P, N, and C at nanoscale in S-HYB materials. Scale bar is 200 nm.

[0039] FIG. 11 shows a typical high-resolution TEM image and corresponding inverse Fast Fourier Transform (FFT) pattern showing the amorphous structure of pristine S-HYB. Scale bar is 5 nm.

[0040] FIG. 12 shows time-series TEM images demonstrating the formation of nano-cry stallized Li2S in S-HYB upon the first in situ lithiation. The arrows in the second panel indicate the observed amorphous aggregation during lithiation, and the arrows in the third and fourth panels indicate the gradual formation of nano-crystalline LisS, as evidenced by the rightmost inverse FFT pattern of S-HYB after lithiation. Scale bar is 10 nm.

[0041] FIG. 13 shows an inverse FFT pattern of lithiated S-HYB, demonstrating that the nanocrystallized Li2S is highly gathered within the interpenetrating hybrid polymer network. Scale bar is 5 nm.

[0042] FIG. 14 shows time-series TEM images demonstrating the conversion of nanocrystallized Li2S to amorphous species in S-HYB upon the first in situ delithiation. The arrows indicate the thorough conversion of nano-crystalline Li2S to amorphous species, as evidenced by the rightmost inverse FFT pattern of S-HYB after delithiation. Scale bar is 10 nm.

[0043] FIG. 15 shows a TEM image and a corresponding inverse FFT pattern of S-HYB after the second in situ lithiation, suggesting the formation of nano-crystalline Li2S is reversible. Scale bar is 10 nm.

[0044] FIG. 16 is a graph showing galvanostatic charge and discharge curves of S-HYB based cells using carbonate-based electrolyte at 200 mA g '. The primary motivation for these coin cells was to explore the electrochemical performance limitations of the S-HYB cathode, which required minimizing the influence of other components. Therefore, a relatively low S-HYBloading of 2 mg cm2, excessive Li in the anode, and a high electrolyte to sulfur (E / S) ratio (10 |iL mg1) were used for these coin cells.

[0045] FIG. 17 is a graph showing corresponding evolution of discharge capacity and CE versus cycle number in FIG. 16.

[0046] FIG. 18 is a graph showing the dQ / dV curves of the S-HYB cathode during the first 200 cycles at 200 mA g '. Inset, proposed conversion processes of S-HYB cathode corresponding to the dQ / dV curves.

[0047] FIG. 19 is a graph showing the dQ / dV curves of the S-HOM cathode during the first 200 cycles at 200 mA g1. Inset, proposed conversion processes of S-HOM cathode corresponding to the dQ / dV curves.

[0048] FIG. 20 is a Randles-Sevcik plot of peak current versus square root of scan rate derived Dij values of S-HYB and S-HOM. Linear fits of data are indicated by the dashed line.

[0049] FIG. 21 is a graph showing potential response and equilibrium potential of S-HYB and the control S-HOM electrodes during GITT measurements.

[0050] FIG. 22 is a graph showing specific capacities at different current densities showing the outperformed rate capability of S-HYB compared to the control S-HOM cathodes.

[0051] FIG. 23 is a graph showing normalized P K-edge spectra of the S-HYB-based cathode during the first discharge-charge process in the carbonate-based electrolyte.

[0052] FIG. 24 is a graph showing normalized S K-edge spectra of the S-HYB-based cathode during the first discharge-charge process in the carbonate-based electrolyte.

[0053] FIG. 25 is a graph showing synchrotron-based PDF results of S-HYB cathode during the first discharge-charge process using the carbonate-based electrolyte. The inset dash lines indicatethat: 1. the irreversibly decreased abundance of C-S bonds; 2. the slight shortening of S-S bond; and 3. the formation of S-S-S after the first charge.

[0054] FIG. 26 is a graph showing a PDF comparison of S-S bonded on P sites (from the control SPZ sample) and on C sites (from the control S-HOM sample), suggesting that the slightly shortened S-S bond can be attributed to the translocation of S-S from C sites to P sites during the first discharge-charge process.

[0055] FIG. 27 is a graph showing a comparison of PDF results from the 1stand 50thdischarged / charged S-HYB cathodes showing that the sulfur conversion based on S-S-S and S-S is reversible in the carbonate-based electrolyte.

[0056] FIG. 28 is a schematic illustration of the structural evolution of S-HYB upon cell operation using the carbonate-based electrolyte, according to the combined PDF results in FIGS.25-27.

[0057] FIG. 29 shows high-angle annular dark-field (HADDF) images and the corresponding elemental mapping of S, P, N, C by scanning transmission electron microscopy (STEM) and Li mapping by energy-filtered transmission electron microscopy (EF-TEM) from the 1stdischarged, 1stcharged, and recharged S-HYB cathodes, suggesting the (de)lithiation of bonded sulfur species in S-HYB are homogeneous and reversible at nanoscale. Scale bars are 20 nm.

[0058] FIG. 30 is a graph showing the cycling performance of the S-HYB-based pouch cell comprising limited Li metal anode, lean electrolyte, and high areal cathode loading. Inset, a photograph of the as-fabricated S-HYB-based pouch cell.

[0059] FIG. 31 is a graph showing a comparison of specific capacity and capacity retention (after 100 cycles) of a series of sulfur cathodes based on the inorganic-organic hybrid polymer network (denoted as ‘hybrid’, fabricated from inorganic SPZ and organic polymers ofpolyacrylonitrile, pitch, or nitrile rubber) and the sulfurized homo-polymer (denoted as ‘homo’, fabricated without inorganic SPZ), showing that the hybrid polymer network strategy is extendable and effective upon synthesizing various sulfur cathodes with improved electrochemical properties. Error bars show standard deviations for the results from three samples.DETAILED DESCRIPTION

[0060] The following description is of exemplary embodiments and methods of use that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of various aspects of the present invention. The scope of the present invention is not limited by this description.

[0061] A lithium-sulfur battery refers to a rechargeable electrochemical cell in which lithium ions move between a lithium-based anode and a sulfur-based cathode. The battery stores and releases energy through the flow of lithium ions via an electrolyte composition. For example, lithium ions may migrate from the anode to the cathode during discharging, and then move back from the cathode to the anode during charging.

[0062] However, one challenge that lithium-sulfur batteries face is the “shuttle effect,” which relates to the migration of soluble lithium polysulfides. Lithium polysulfides are formed during discharge as sulfur molecules at the cathode react with lithium ions to produce polysulfides, some of which are soluble in the electrolyte composition. The soluble poly sulfides may diffuse away from the cathode toward the anode during discharge (and vice versa during charge), causing unintended side reactions. The shuttle effect can lead to issues such as capacity loss,self-discharge (which reduces the efficiency of the battery), electrode degradation, and other related problems.

[0063] Accordingly, embodiments generally relate to a cathode comprising a sulfurized hybrid polymer network (S-HYB) designed to mitigate soluble polysulfide formation. As illustrated in FIG. 1, the S-HYB includes a sulfurized inorganic polymer hybridized with a sulfurized organic polymer, specifically configured to interactively re-bond and / or adsorb dissociative sulfur species, thereby preventing soluble polysulfide formation.

[0064] The S-HYB may include any relative amount of sulfurized inorganic polymer. In some embodiments, the S-HYB may include at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt %, at least 30 wt %, at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, at least 95 wt %, at least 99 wt %, and / or the like, of the sulfurized inorganic polymer. In other embodiments, the S-HYB may include no greater than 99 wt%, no greater than 95 wt%, no greater than 90 wt%, no greater than 80 wt%, no greater than 70 wt%, no greater than 60 wt%, no greater than 50 wt%, no greater than 40 wt%, no greater than 30 wt%, no greater than 20 wt%, no greater than 10 wt%, no greater than 5 wt%, no greater than 1 wt%, and / or the like, of the sulfurized inorganic polymer.

[0065] The S-HYB may also include any relative amount of sulfurized organic polymer. In some embodiments, the S-HYB may include at least 1 wt%, at least 5 wt%, at least 10 wt%, at least 20 wt %, at least 30 wt %, at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, at least 95 wt %, at least 99 wt %, and / or the like, of the sulfurized organic polymer. In other embodiments, the S-HYB may include no greater than 99 wt%, no greater than 95 wt%, no greater than 90 wt%, no greater than 80 wt%, no greater than 70 wt%, no greater than 60 wt%, no greater than 50 wt%, no greater than 40 wt%, no greaterthan 30 wt%, no greater than 20 wt%, no greater than 10 wt%, no greater than 5 wt%, no greater than 1 wt%, and / or the like, of the sulfurized organic polymer.

[0066] In some embodiments, the ratio of the amount of sulfurized inorganic polymer to the amount of sulfurized organic polymer is from 1 : 1 to 5: 1, preferably from 2: 1 to 4:1, more preferably about 3:1.

[0067] The sulfurized inorganic polymer may have a high sulfur content. For example, the sulfurized inorganic polymer may have a sulfur content of at least 60 wt%, at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, and / or the like.

[0068] The sulfurized inorganic polymer may be selected from the group consisting of sulfurized polyphosphazene, sulfurized polythiophosphine, sulfurized polythiazyl, sulfurized polydithiophosphate, sulfurized polyphosphonates, sulfurized poly(thio)phosphoramidates, sulfurized polyphosphonitrile oxides, sulfurized polyphosphonitrile, and mixtures thereof.

[0069] In one embodiment, the sulfurized inorganic polymer is a sulfurized polyphosphazene (SPZ). The SPZ advantageously exhibits a high sulfur content with a backbone of alternating phosphorus and nitrogen atoms, which provides abundant phosphorus-sulfur sites for grafting sulfur chains and adjacent nitrogen sites for on-site absorption of lithium polysulfides.

[0070] In one embodiment, the sulfurized organic polymer is a sulfurized polymer of a sp2carbon material. The term “sp2carbon” refers to a carbon atom that has undergone sp2hybridization, where one s orbital and two p orbitals combine to form three equivalent sp2hybrid orbitals. This results in a trigonal planar geometry with advantageous bonding characteristics. Specifically, the sp2carbon material provides sites for grafting sulfur, thereby forming sulfur chains with the inorganic polymer.

[0071] The sp2carbon material may be selected from the group consisting of polyacrylonitrile (PAN) (e.g., carbonized PAN), pitch, nitrile rubber (NBR), or any other suitable material containing sp2carbons.

[0072] In other embodiments, the sulfurized organic polymer may be selected from the group consisting of sulfurized phenolic resin, sulfurized polyimide, and mixtures thereof.

[0073] In one particular embodiment, the sulfurized inorganic polymer is SPZ and the sulfurized organic polymer is a material selected from the group consisting of PNA, pitch, NBR, and / or mixtures thereof.

[0074] The inventors have found that the S-HYB functions as a volume-stable framework that may reversibly accommodate sulfur conversions between sulfur chains and a nano-crystallized Li2S network. Referring to FIGS. 1 and 2, the S-HYB includes extensive sulfur chains (Sn) bonded within the inorganic-organic polymer network, for example by covalent phosphorussulfur and carbon-sulfur tethers. During lithiation (e.g., insertion of lithium ions into the cathode material), the sulfur chains react with lithium ions to form Li2S nano-crystals within the S-HYB framework. Importantly, during delithiation (e.g., extraction of lithium ions), the nanocrystallized IJ2S is fully converted back into an amorphous species, namely the sulfur chains, thereby avoiding soluble polysulfide formation.

[0075] The S-HYB thus proceeds through a reversible, inserting conversion reaction designed to prevent polysulfide formation. In this reaction, lithium ions may be uniformly inserted along the electronically and ionically conductive framework backbones to complete the conversion without significant volume change or microstructural collapse during charge and discharge.

[0076] Embodiments further relate to methods of utilizing the cathode comprising the S-HYB, as described above, for practical applications in lithium-sulfur batteries. These methods mayinclude assembling the cathode within various cell configurations, applying specific electrochemical protocols to optimize performance, and / or employing the S-HYB to effectively suppress the shuttle effect during cycling.

[0077] The S-HYB ’s ability to prevent soluble polysulfide formation may enhance the battery’s cycle life, capacity retention, and / or overall stability, making it suitable for use in portable electronic devices , electric vehicles, grid storage systems, etc.

[0078] In some embodiments, the lithium-sulfur battery incorporating the S-HYB cathode may be configured into a coin cell format. A coin cell design may offer advantages such as ease of assembly, standardized dimensions, and compatibility with existing testing protocols. An exemplary coin cell configuration may include a metallic lithium anode, a separator soaked in electrolyte composition, and the S-HYB cathode, all enclosed within a sealed, compact casing.

[0079] The S-HYB cathode may exhibit both high capacity (e g., up to 900 mAh g'1) and excellent cycling stability (e.g., up to 2,000 cycles at 2.0 A g'1) in lithium-sulfur coin cells.

[0080] In other embodiments, the S-HYB cathode may be employed within a pouch cell configuration. A pouch cell configuration can provide a flexible, lightweight, and scalable platform that may be more suitable for commercial applications. The pouch cell design may allow for larger active material loading, enhanced thermal management, and customizable form factors. The pouch cell may include a metallic lithium or lithium-alloy anode, a separator soaked in electrolyte composition, and the S-HYB cathode, all contained within a flexible, sealed pouch made of a laminated polymer film.

[0081] The S-HYB cathode may exhibit a projected energy density of up to 300 Wh kg1and greater than 80% capacity retention after 150 cycles in lithium-sulfur pouch cells.EXAMPLES

[0082] Methods

[0083] Chemicals and materials

[0084] All reagents and solvents were purchased from Sigma-Aldrich and Alfa Aesar and used without further purification unless otherwise stated. Battery grade lithium hexafluorophosphate (LiPFe), lithium difluoro(oxalate)borate (LiDFOB), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and 1,2-dimethoxy ethane (DME) were purchased from Gotion and used as received. Lithium bis(fluorosulfonyl)imide (LiFSI), bis(2,2,2-trifluoroethyl)ethe (BTFE), and 1, 1,2,2-tetrafluoroethyl-2',2',2'-trifluoroethyl ether (TTE) were purchased from SynQuest Labs Inc and purified using standard procedures before use. Li chips with a thickness of 600 pm and Li foil with a thickness of 50 pm supported by a copper substrate (thickness of 5 pm) were purchased from MTI Corporation.

[0085] Preparation of SPZ

[0086] As the inorganic polymer in S-HYB materials, sulfurized polyphosphazene (SPZ) of high sulfur content was designed and synthesized through the sulfurization of poly(dichlorophosphazene) by sodium polysulfide (Na2Sx) (FIG. 3). Poly(dichlorophosphazene) was obtained by a molten phase thermal polymerization method. In a typical preparation, hexachlorocyclotriphosphazene (3 g) and the initiator BCh PO(OPh)3 (3 mg) were first ground for thorough mixing and then sealed in an evacuated glass tube. The as-sealed glass tube was heated at 250 °C for 10 h to form poly(di chlorophosphazene) (weight-average molecular weight of -15,000). The concentration of initiator BCh PO(OPh)3 was optimized to 0.1 wt% for the control of chain length, avoid terminal cross-linking, and thus yield sufficient chloride (Cl) side atoms in the obtained poly(di chlorophosphazene) for sulfurization. For the preparation of Na2Sx,sodium sulfide nonahydrate (Na2S 9H2O, 25.0 g) and elemental sulfur (Ss, 13.4 g) powders were first dissolved in the water-ethanol mixed solvent (75 mL, volume ratio of 1 : 1). The as-obtained mixture was reacted at 30 °C for 2 h, and then allowed to be dried in vacuum overnight to remove the solvent for obtaining Na2Sxpowders. Following that, for the synthesis of SPZ, poly(dichlorophosphazene) (0.60 g) and Na2Sx(1.52 g) were dissolved into tetrahydrofuran (30 mL). The mixture was first reacted at room temperature for 10 h and then at an elevated temperature of 66 °C for another 10 h for thorough sulfurization. The obtained SPZ was rinsed with deionized water and dried in a vacuum overnight before use.

[0087] Preparation of S-HYIi and control samples

[0088] To fabricate sulfurized inorganic-organic hybrid polymer (S-HYB) as sulfur cathode materials, SPZ was fused into elemental sulfur (Ss) and the organic polymer (polyacrylonitrile, pitch, or nitrile rubber)-based conducting matrix. We first prepared S-HYB by reacting the SPZ with Ss as the sulfur source and polyacrylonitrile to form the conducting matrix. Pyrolyzed polyacrylonitrile was first adopted for S-HYB preparation due to its facile dehydrogenation and cyclization into conjugated backbones at elevated temperatures. The synthesis parameters of S-HYB cathode materials were optimized to give both desirable specific capacity and capacity retention. Different S-HYB materials based on other organic polymers (pitch or nitrile rubber) as conducting matrices were prepared in the same procedures. In a typical process, for the synthesis of S-HYB sulfur cathode materials, SPZ, polyacrylonitrile (Sigma-Aldrich, weight-average molecular weight of -150,000), and elemental sulfur (Ss, Sigma-Aldrich) were ball milled in a 1 : 3: 14 weight ratio for 10 h. The powdered mixture was heated in a nitrogen (N2) filled tube furnace at 300 °C for 2.5 h with a ramp rate of 2 °C min-1, followed by a post-heating treatment at 250 °C for 4 h to vaporize the residual sulfur. S-HYB powders were collected after a naturalcooling process to room temperature. For the synthesis of control samples, namely, sulfurized homo-polymer (S-HOM) without SPZ, polyacrylonitrile (or pitch / nitrile rubber), and Ss were ball milled in a weight ratio of 1 :5 for 10 h, followed by the identical synthetic procedures with that of the S-HYB described above.

[0089] Material characterization

[0090] The morphological and structural information of pristine and cycled sulfur cathode materials were characterized by scanning electron microscope (SEM, Thermo Scientific Apreo and ESEM Q250), transmission electron microscope (TEM), high-resolution TEM (HR-TEM, dual spherical aberration-corrected FE1 Titan2G260-300 STEM), energy filtering-TEM (EF-TEM), and high-resolution electron energy loss spectroscopy (EELS). The TEM samples were prepared by loading dry powders onto the Cu grids in an argon-filled glovebox (H2O <0.1 ppm, O2 <0.1 ppm). X-ray photoelectron spectroscopy (XPS) experiments were carried out on a PHI VersaProbe II Scanning XPS Microprobe. The involved air- and moisture-sensitive samples, e.g., S-HYB cathodes and Li anodes disassembled from cycled Li-S cells, were loaded in a glovebox and transferred into the XPS instrument through a vacuum transfer vessel. XPS data analysis was processed using CasaXPS 2.3.23. Fourier transform infrared spectroscopy (FTIR) spectra were obtained on a Bruker Vertex V70 spectrometer. Raman spectra of pristine S-HYB and S-HOM powders were collected on a Horiba Lab Ram HR Evolution v / s-NIR optimized & AIST-NT Scanning Probe using the 532 nm laser. A Rigaku Mini-flex II spectrometer with Cu Ka radiation was used to collect the X-ray diffraction (XRD) patterns of the pristine sulfur cathode materials. Thermogravimetric analysis (TGA) was conducted on a Netzsch STA 449 F3 Jupiter with a heating rate of 5 °C min-1. Samples were loaded inside an alumina pan at room temperature and then to 900 °C with N2 flows. Element analysis for sulfur content determinationwas performed on a Perkin Elmer 2400 Series II CHN elemental analyzer. The sorption analysis of surface area using the Brunauer-Emmett-Teller (BET) theory of pristine S-HYB and S-HOM powders was measured by a Micrometrics ASAP 2020 physisorption analyzer.

[0091] In situ TEM measurement of (de)-lithiation processes

[0092] In situ measuring the (de)-lithiation processes of S-HYB particles was conducted inside TEM using a nano-factory STM- TEM holder. The TEM holder features a dual-probe design, comprising two distinct components. One probe utilizes a tungsten (W) wire to scratch Li metal inside an Ar-fdled glove box, while the other probe consists of a Cu wire attached to S-HYB nanoparticles. The W wire probe with loaded Li is movable within the TEM column and is driven by a piezo motor with a 1-nm-step size. The bias voltage of ±2.5 V versus Li was applied to the two probes for (de)-lithiation of the S-HYB particles. The dose rate for high resolution videos was around 22 e A-2s-1and the frame rate of recorded videos was 10 frames per second.

[0093] Electrochemical characterizations

[0094] For the electrochemical measurements, S-HYB-based electrodes were fabricated. In a typical process, S-HYB powders were mixed with conducting carbon C45 and a water-based composite binder (carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), CMC / SBR = 1) by an 80: 10: 10 weight ratio. The mixture was then cast on a carbon-coated aluminum foil current collector. After drying in a vacuum oven at 60 °C for 12 h, the S-HYB-based composite film was punched into 12 mm discs for coin cell fabrication. Electrodes for other sulfur cathode materials, including S-HOM control samples, were fabricated using the same procedures as those applied to the S-HYB as above described.

[0095] The electrochemical properties were first investigated in coin cells (CR2016), which were assembled in an argon-filled glovebox (H2O<0.1 ppm, O2 <0.1 ppm) with S-HYB or controlsample-based cathodes, the lithium foil anode, the Celgard polypropylene separator, and the electrolyte (E / S ratio from 5 to 10 pL mg-1, specified in different cases in the example). Both carbonated-based electrolyte (1 M LiPFe dissolved in EC / DEC by a 1:1 volume ratio, with 15 wt% FEC and 1 wt% LiDFOB as additive) and ether-based electrolyte (2 M LiFSI dissolved in DME-BTFE by a 1 :4 weight ratio) were used for the electrochemical measurements of coin cells.

[0096] The pouch cell fabrication process was carried out in an Ar-filled glovebox by assembling the S-HYB-based cathode (3 cm x 4 cm in dimension) on a carbon-coated Al current collector (MTI Corporation), the anode of lithium foil (thickness of 50 pm, MTI Corporation), and the Celgard polypropylene separator into Al-laminated films (MTI Corporation), followed by the injection of the localized high-concentration carbonate-based (1 M LiPFe dissolved in FEC / EMC / DMC / TTE by a 2: 1:2:5 volume ratio, with 1 wt% LiDFOB as additive) electrolyte (E / S ratio = 2.5 pL mg-1) and final encapsulation. Al and Ni tabs (MTI Corporation) were welded to the cathodes and anodes, respectively, and utilized for external connections of pouch cells. The energy densities of pouch cells provided in the main text were calculated based on the total weight of cathode, anode, current collectors, electrolyte, and separator. The as-fabricated pouch cells demonstrated projected energy densities of -349 Wh kg-1for the first cycle of activation (at 50 mA g-1s-HYB), -319 Wh kg-1for the second cycle (at 200 mA g-1s-HYB), and then -305 Wh kg-1for the following cycles (at 200 mA g-1s-HYB). Based on the weight of every component (including cathode, anode, current collectors, electrolyte, separator, casing, and Al / Ni tabs), the energy density of the pouch cell was -274 Wh kg-1.

[0097] Galvanostatic charge-discharge (GCD) measurements of coin and pouch cells were performed in the voltage range of 3.0 to 1.0 V at various current densities from 100 to 5,000 mA g-1cathode using Landt battery testers and Arbin electrochemical station (MSTATS-5V / 10mA / 32Ch). During the formation process, all the coin and pouch cells were first discharged and charged at 50 mA g-1Cathode for 1 cycle before GCD tests. The cycling stability was recorded during continuous GCD cycles after the formation process, without rest between charge and discharge. CV curves were collected at various scan rates using a CHI 660D electrochemical workstation, where the peak currents were used for lithium diffusion coefficient ( / V i) calculation by following the Randles-Sevcik equation. EIS tests were operated on a Nuvant EZStat Pro instrument with a frequency range from 10 to 105Hz and an amplitude of 5 mV. The equilibrium (open-circuit) potential of the cells is obtained by GITT measurements that are comprised of a series of current pulses for 30 min, followed by a 6-h relaxation process. The open-circuit voltage at the end of relaxation is the thermodynamic equilibrium potential. Data analysis was processed using LAND V7.4, ZView 3.1, and Origin V8.5 software.

[0098] Density functional theory calculation

[0099] The calculations were performed using density functional theory (DFT) implemented in Gaussian 16 software package. For geometry optimization and vibrational frequency calculations, B3LYP functional with 6-31G* basis set was used, with energy convergence set to KT6Hartree and force convergence set to ICT4Hartree / Bohr. Three different reaction schemes (denoted as S-HYB, S-HOM type 1, and S-HOM type-2, in Supplementary Fig.3) were considered, and their changes in Gibbs free energy of reactions ( Greac[lon) were computed using the formula given in Equation (1).AGreaction— ^products ~ X ^reactants (1)

[0100] For the S-HYB scheme, the AGreaction for the formation of various S-HYB structures by varying the length of sulfur atom chains (i.e., from n=l to 6) from sulfurized polyphosphazene and polyacrylonitrile was calculated. The resultant formation energy showed avery slight decrease with an increase in the length of the sulfur chains. For the two S-HOM schemes, the Greaction for the formation of various S-HYB structures by varying the length of sulfur atom chains (i.e., from n =1 to 6) from sulfur and polyacrylonitrile was calculated. As a result, for both types of S-HOM, the obtained formation energy rapidly decreases with an increase in the length of the sulfur chains.

[0101] Synchrotron-based, sXAS and PDF analysis

[0102] Sulfur K-edge and phosphorus XAS experiments were carried out at beamline 8-BM (TES) of the National Synchrotron Light Source II (NSLS II) at Brookhaven National Laboratory. The samples were prepared in an Ar-filled glove box (H2O <1 ppm, O2 <5 ppm). The cycled electrodes collected from the coin cells were rinsed with DEC solvent and then dried. The dried electrodes were affixed to Kapton tape, with the tape facing the current collector side of the electrode. A Mylar film was then applied to cover the electrode surface, serving to prevent exposure to air. The sXAS measurements were carried out in a helium-filled chamber at the TES beamline with reduced air exposure of the sample. The sXAS measurements were conducted using a micro-beam with a size of 16 pm (horizontal) x 5 pm (vertical). The acquired data were analyzed using the Demeter software package.

[0103] PDF experiments were carried out at the X-ray Powder Diffraction beamline (28-ID-2) at the National Synchrotron Light Source II, Brookhaven National Laboratory. Given the air-sensitive nature of the ex situ samples, they were loaded into capillaries within an Ar-filled glovebox. These samples were then transferred to the beamline and subjected to high-energy X-ray with a photon wavelength of 0.1855 A. Due to the predominance of low-scattering elements in these samples, a long-time exposure (30 min) was employed to guarantee reliable statistical data. Besides the electrode materials, an empty capillary was also measured for backgroundsubtraction. For data collection to high values of momentum transfer (Qmax = 22 A-1), a large-area amorphous-silicon-based detector was utilized.

[0104] Results

[0105] Design and characterization of S-HYB

[0106] We synthesized low-cost and eco-friendly S-HYBs by hybridizing the inorganic sulfurized polyphosphazene (SPZ) that has high sulfur content and organic polymers (such as polyacrylonitrile, pitch, or nitrile rubber) that allow the facile formation of conjugated, sp2-carbon frameworks for electron transporting. We chose the SPZ of a backbone consisting of alternating phosphorus (P) and nitrogen (N) atoms, as the inorganic component, because it has abundant P-S sites to graft sulfur chains, and adjacentN sites for on-site adsorption of lithiated sulfur species (FIG. 3). We anticipate this designed S-HYB structure, wherein the extensive sulfur chains are bonded within the interpenetrating inorganic-organic polymer network by covalent P-S / C-S tethers and atomic adsorption from N sites, to unlock high-capacity sulfur conversions without soluble polysulfides (FIG. 1). The S-HYB based on inorganic SPZ and organic polyacrylonitrile polymers, and its control sample of sulfurized homo-polymer without SPZ (S-HOM, i.e., sulfurized polyacrylonitrile), were first prepared and optimized (FIGS. 4 and 5).

[0107] By introducing the inorganic SPZ, the S-HYB exhibited a higher sulfur content (~62 wt%) than the control S-HOM (~51 wt%), as determined by elemental analysis, which aligns with the thermogravimetric analysis (TGA) showing increased weight loss below 300 °C in S-HYB (FIG. 6). We ascribe this enhanced sulfur content to the facilitated immobilization of prolonged sulfur chains (-S-Sx-S-, x>l) in S-HYB with lower formation energy (AGreaction) due to the introduction of P-S bonding sites, in contrast to the control S-HOM (FIG. 7). The sulfurspecies bonded within S-HYBs were indicated by the absence of crystalline sulfur diffraction peaks in X-ray diffraction (XRD). The X-ray photoelectron spectroscopy (XPS) further suggested that the sulfur chains were covalently immobilized by S-P and S-C bonds in S-HYBs (FIG. 8).

[0108] Lithiation and delithiation of S-HY

[0109] To directly observe the lithiation and delithiation behaviors of S-HYBs, we used in situ bias TEM technique (FIG. 9). The pristine S-HYB particle showed homogeneous distribution of S, P, N, and C (FIG. 10) with an amorphous feature (FIG. 11). Both S-HYB and S-HOM materials demonstrated structural stability under in situ electron beam irradiation during characterizations. Time-series in situ TEM images and their corresponding inverse fast Fourier transform (FFT) patterns revealed a clear trend of Li2S nano-crystalline formation upon lithiation (FIGS. 12 and 15) and its reversible conversion to amorphous species upon delithiation (FIG. 14) in S-HYBs. During the 1stlithiation, amorphous domains in dark contrast were first observed (8.37 s), attributed to the 1stcycle formation. Following that, dispersed nano-crystallization of Li2S gradually formed (from 38.34 s, FIG. 12), wherein the presence of irregular and continuously changing domains suggested that the sulfur species were not entirely nucleated or crystallized but highly gathered within the interpenetrating inorganic-organic polymer network. At the end of lithiation (FIG. 13), we observed a homogeneous, nano-crystallized Li2S network, composed of interconnected elongated Li2S domains.

[0110] We found this thorough conversion from bonded sulfur chains to Li2S network was driven by the rapid Li ion inserting process in S-HYB, in contrast to S-HOM without observed formation of Li2S networks under the same condition. Importantly, upon the subsequent delithiation, the nano-crystallized Li2S in S-HYBs fully converted back to amorphousspecies (FIG. 14). And during recurring lithiation and delithiation processes, neither notable volume expansion (around ±1% during lithiation and delithiation) nor microstructural collapse was detected. The above results indicated that our designed S-HYB initiated a unique inserting conversion reaction, distinguished from conventional sulfur conversions in the fast Li-ion inserting / volume-stable feature as opposed to sluggish kinetics / drastic volume change during Ss / i2S conversions, and in the high yield of longer sulfur chain-based redox to achieve high capacity as opposed to conversions between -Si-2- / Li2S of low capacities.

[0111] Electrochemical properties

[0112] To evaluate the soluble-polysulfide-free feature of S-HYBs, we tested the S-HYB-based Li-S batteries in the carbonate-based liquid electrolyte. Given the fact that the carbonate solvent reacts with soluble lithium polysulfides, resulting in the expedited capacity fading, these measurements can exclude the contribution of soluble polysulfides to specific capacity or cycling stability and thus determine the soluble polysulfide-free feature. The S-HYB-based cell exhibited a single discharge plateau after the first cycle of activation, delivering both higher specific capacity (903.2 mAh g-1, FIG. 16) and improved capacity retention (87.8% after 300 cycles, FIG. 17) than the control S-HOM-based cells. The observed high sulfur utilization of 87% in this case (FIG. 16) indicated that the S-HYB could unlock the high capacity of the high sulfur content without forming soluble polysulfides, in good agreement with the absence of shuttled sulfur species in the cycled Li anodes.

[0113] We then conducted differential capacity (dQ / dV) analysis to show the electrochemical origin of S-HYBs. The sulfur conversion was highly reversible in S-HYBs since its dQ / dV curves were nearly overlapped for over 200 cycles (FIG. 18). In comparison, in the control S-HOMs, a newly emerged oxidation peak at ~2.3 V was observed within 50 cycles(FIG. 19). This oxidation reaction was primarily attributed to the oxidation of unbonded sulfur species like soluble polysulfides (inset, FIG. 19). As increasing unbonded sulfur species generated and evolved into soluble polysulfide in S-HOMs, the increased voltage fading and reduced capacity due to side reactions between the carbonate solvent were then observed (FIG.19). Collectively, the sulfur inventory was exclusively maintained in a bonded manner within S-HYBs (inset, FIG. 18), in contrast to the S-HOMs (inset, FIG. 19) and conventional sulfur cathodes, where dispersion of unbonded sulfur species occurred during cycling.

[0114] Upon the incorporation of the inorganic polyphosphazene, the S-HYB exhibited enhanced Li+transport kinetics during sulfur conversion. A Li+diffusion coefficient (DH, derived by Randles-Sevcik equation) of 4.0 x 10-8cm2s-1was determined for S-HYBs (FIG. 20), 48% higher than that of S-HOMs (2.7 x 10-8cm2s-1). The S-HYB also showed constantly lower overpotential than the control S-HOM at varying states of discharge measured by the galvanostatic intermittent titration (GITT) technique (FIG. 27), further manifesting its enhanced Li+migration and rate capability (FIG. 22). In addition to using carbonate electrolytes, Li-S cells with ether electrolytes also demonstrated accelerated sulfur redox transformation in S-HYBs, resulting in a high capacity (908 mAh g-1at 200 mA g1), excellent cycling stability (91.6% capacity retention over 200 cycles), and impressive rate capability.

[0115] S-HYB in Li-S chemistry

[0116] To correlate the electrochemical performances of S-HYB with its atomic local structure and electronic states, we conducted soft X-ray absorption spectroscopy (sXAS, FIGS.23 and 24). Besides the CEI formation (2,157 eV) after the 1stdischarge observed in P K-edge spectra, the peaks at 2,152 eV representing P Is transition to P-S t2* state from the P-S sites in S-HYB, were nearly overlapped among pristine, discharged and charged S-HYBs during the 1stcycling (FIG. 23). This pointed to the stable presence of P-S covalent tethers during electrochemical lithiation and delithiation. In contrast, S=C u* (2,468.5 eV) and S-C o* (2,472.5 eV) peaks exhibited irreversibly decreased abundance after the first discharge-charge processes (FIG. 24), indicating the release of unbonded sulfur species from C-S sites during the first discharge, probably correlated with their chemical environments. Further, the observed change in the ratio of pyrrolic N (C-N-C / N-P, 399.9 eV) to pyridinicN (C-N=C / N=P, 397.8 eV) in XPS analysis suggested the participation of N sites with atomic adsorption capabilities in S-HYBs during cycling.[00117J Given the predominantly amorphous nature of S-HYB, we further used synchrotron-based pair distribution function (PDF, FIGS. 25-27), which is not constrained by crystallinity, to specify the sulfur conversion pathway. A clear trend of sulfur dimer (S-S, at -2.10 A) consumption on discharge and re-formation on charge existed in S-HYB, wherein the re-formed S-S showed a slightly reduced bond length after the first charge (FIG. 25). We attribute this reduction in bond length (from -2.09 to 2.07 A) to the translocation of S-S from C-S to P-S sites within S-HYBs, based on the observation that S-S bonds have a length of -2.10 A when bonded at C-S sites, as compared to -2.06 A at P-S sites (FIG. 26). It is noteworthy that the translocation of S-S from C-S to P-S sites upon the first charge, was also coincident with the irreversible loss of C-S bonds and formation of sulfur trimer (-S-S-S-, -3.25 A, FIG. 25). Based on above results, we deduce that the P-S sites can dynamically re-bond the irreversibly released sulfur species from C-S sites to form P-Sx-S (x>2) containing S-S-S (FGI. 28) during cell cycling, thus accounting for the soluble-poly sulfide-free nature of S-HYBs. Notably, the sulfur conversion involving prolonged sulfur chains (P-Sx-S, x>2) bridged between SPZ and organic polymers in S-HYBs exhibited high reversibility over 50 cycles (FIG. 27), and the morphologyof S-HYBs remained nearly unchanged after cycling. The homogeneous sulfur conversions at nanoscale were evidenced by TEM (FIG. 29), in line with the stable cycling performance of high-capacity S-HYB-based cells.

[0118] Practical and extended applicability

[0119] Benefiting from the high capacity, enhanced Li -ion / electron transport kinetics, and soluble-polysulfide-free features, the S-HYB-based Li-S cells exhibited equally desirable performances under practical conditions, surpassing that of the control S-HOM-based cells. In particular, the S-HYB-based pouch cell of high cathode areal loading (>5 mAh cm2), limited Li anode (~2* excess of Li metal), and lean carbonate electrolyte (E / S ratio of 2.5), showed capacity retention of 84.9% after 150 cycles (FIG. 30) with projected energy density approaching 300 Wh kg-1(based on the total weight of cathode, anode, current collectors, electrolyte, and separator), which outperformed reported Li-S pouch cell batteries under similar conditions.

[0120] Considering the extensive recycling opportunities of pitch from waste paving materials and nitrile rubber from scrap tires, we assessed the applicability of our renewable hybrid polymer network strategy by synthesizing S-HYBs based on inorganic SPZ and organic polymers of pitch or nitrile rubber. As a result, each type of S-HYB exhibited both improved specific capacity and capacity retention through cycling compared to their control S-HOM samples (FIG. 31). This highlights the broad applicability of our strategy: hybridizing inorganic and organic polymers into an interpenetrating network to form a dynamically and covalently (re)-bonded framework that invokes a reversible inserting conversion reaction. In this inserting conversion reaction, Li ions are uniformly inserted along the electronically and ionically conductive framework backbones to complete the conversion without significant volume change,paving the way for developing various cost-effective and sustainable high-performance sulfur cathode materials.

[0121] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. For instance, the number of components or parameters can be varied to meet a particular objective. As another example, component configurations may be varied to meet a particular set of design criteria.

[0122] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternative embodiments may include some or all of the features of the various embodiments disclosed herein. For instance, it is contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. The elements and acts of the various embodiments described herein can therefore be combined to provide further embodiments.

[0123] It is the intent to cover all such modifications and alternative embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. Thus, while certain exemplary embodiments of the apparatus and process and / or utilization and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

What is claimed is:

1. A sulfur-based cathode comprising:a sulfurized hybrid polymer network, wherein the sulfurized hybrid polymer network includes a sulfurized inorganic polymer hybridized with a sulfurized organic polymer, wherein the sulfurized hybrid polymer network is configured to prevent soluble polysulfide formation during cycling.

2. The sulfur-based cathode of claim 1, wherein a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 1 : 1 to 5 : 1.

3. The sulfur-based cathode of claim 1, wherein a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 2:1 to 4: 1.

4. The sulfur-based cathode of claim 1, wherein the sulfurized inorganic polymer is selected from the group consisting of sulfurized polyphosphazene, sulfurized polythiophosphine, sulfurized polythiazyl, sulfurized polydithiophosphate, sulfurized polyphosphonates, sulfurized poly(thio)phosphoramidates, sulfurized polyphosphonitrile oxides, sulfurized polyphosphonitrile, and mixtures thereof.

5. The sulfur-based cathode of claim 1, wherein the sulfurized inorganic polymer is a sulfurized polyphosphazene.

6. The sulfur-based cathode of claim 1, wherein the sulfurized inorganic polymer has a sulfur content of at least 60 wt%.

7. The sulfur-based cathode of claim 1, wherein the sulfurized organic polymer is a sulfurized polymer of a sp2carbon material.

8. The sulfur-based cathode of claim 7, wherein the sp2carbon material is selected from the group consisting of polyacrylonitrile, pitch, nitrile rubber, and mixtures thereof.

9. The sulfur-based cathode of claim 1, wherein the sulfurized organic polymer is selected from the group consisting of sulfurized phenolic resin, sulfurized polyimide, and mixtures thereof.

10. A sulfur-based cathode comprising:a sulfurized hybrid polymer network, wherein the sulfurized hybrid polymer network includes a sulfurized polyphosphazene hybridized with a sulfurized polymer of a sp2carbon material selected from the group consisting of polyacrylonitrile, pitch, nitrile rubber, and mixtures thereof,wherein the sulfurized hybrid polymer network is configured to prevent soluble polysulfide formation during cycling.

11. The sulfur-based cathode of claim 10, wherein a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 1 : 1 to 5: 1.

12. The sulfur-based cathode of claim 10, wherein a ratio of an amount of the sulfurized inorganic polymer to an amount of the sulfurized organic polymer is from 2:1 to 4: 1.

13. A lithium-sulfur battery comprising:the cathode of claim 1;an anode comprising a lithium-based material; andan electrolyte composition disposed between the cathode and the anode.

14. The lithium-sulfur battery of claim 13, wherein the sulfurized hybrid polymer network includes covalent phosphorus-sulfur and carbon-sulfur bonds that facilitate reversible sulfur conversion between sulfur chains and lithium sulfide.

15. The lithium-sulfur battery of claim 13, wherein the battery is configured in a coin cell format.

16. The lithium-sulfur battery of claim 13, wherein the battery is configured in a pouch cell format.

17. A method of operating the lithium-sulfur battery of claim 13, the method comprising:discharging the battery; andcharging the battery.

18. The method of claim 17, wherein:during discharging the battery, lithium ions convert sulfur chains into lithium sulfide nanocrystals within the sulfurized hybrid polymer network, andduring charging the battery, the lithium sulfide nanocrystals are converted back into sulfur chains.

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