Ferroelectric-doped holey graphene / sulfur composite cathodes for lithium-sulfur batteries

Abstract

The present technology relates generally to a cathode for a lithium-sulfur battery and lithium-sulfur batteries including the cathode. The cathode includes about 25 wt.% to about 75 wt.% sulfur, about 1% to about 60% holey graphene, and about 2 wt.% to about 10 wt.% ferroelectric nanoparticles.

Description

FERROELECTRIC-DOPED HOLEY GRAPHENE / SULFUR COMPOSITECATHODES FOR LITHIUM-SULFUR BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Appl. No. 63 / 569,925, filed March 26, 2024, which is incorporated herein by reference in its entirety for any and all purposes.GOVERNMENT RIGHTS

[0002] This invention was made with government support under OIA- 1849243 awarded by The National Science Foundation, and 80NSSC22M0025 and 80NSSC19M0236 awarded by The National Aeronautics and Space Administration. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present technology relates generally to lithium-sulfur batteries, cathodes for lithium-sulfur batteries, and methods of making thereof.SUMMARY

[0004] In an aspect, a cathode for a lithium-sulfur battery is disclosed. The cathode includes about 25 wt.% to about 75 wt.% sulfur, about 1 wt.% to about 60 wt.% holey graphene, and about 2 wt.% to about 10 wt.% ferroelectric nanoparticles.

[0005] In any embodiment, the ferroelectric nanoparticles may include BiFeCh, BaTiCh, Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of two or more thereof. The ferroelectric nanoparticles may include Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination thereof. The cathode may include about 5 wt.% of the ferroelectric nanoparticles. The cathode may include about 25 wt.% to about 50 wt.% sulfur. The cathode may include about 5 wt.% to about 20 wt.% polyvinylidene fluoride. The cathode may further include about 20 wt.% to about 70 wt.% carbon black. The cathode may include holey graphene and carbon black in a weight ratio of about 1 : 99 to about 5:95.

[0006] In another aspect, an electrochemical cell is disclosed. The electrochemical cell includes the cathode described herein, an anode including lithium metal, a separator between the cathode and the anode, and an electrolyte including a solvent and a lithium salt.

[0007] The solvent may include dioxolane and dimethoxyethane. The lithium salt may include bis(trifluoromethylsulfonyl)imide lithium (LiTFSI) and LiNCh dissolved in the solvent. The electrolyte may include 0.5 M to 1.5 M LiTFSI and 0.05 M to 0.5 M LiNCh. The electrolyte may include 1.0 M LiTFSI and 0.2 M LiNCh.

[0008] In another aspect, a process for forming a cathode for a lithium-sulfur battery is disclosed. The process includes forming a mixture of sulfur, holey graphene, and ferroelectric nanoparticles; and compressing the mixture to form the cathode.

[0009] Forming the mixture may include ball milling the sulfur, the holey graphene, and the ferroelectric nanoparticles. The ball milling may be conducted for about 5 seconds to about 20 seconds. The mixture may include about 5 wt.% of the ferroelectric nanoparticles. The mixture may include about 25 wt.% to about 50 wt.% sulfur. The ferroelectric nanoparticles may include BiFeCh, BaTiCh, Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of two or more thereof.

[0010] Further aspects and embodiments of the present technology are described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 A is a schematic illustration of the synthesis process of ferroelectric nanoparticles.

[0012] FIG. IB is a schematic illustration of the preparation of S / hG (left) and S / FNPs / hG composite cathodes (right).

[0013] FIG. 1C is an illustration of a Li-S battery having the S / FNPs / hG composite cathode from FIG. IB.

[0014] FIG. 2 is a graph of X-ray diffraction (XRD) spectra of the materials used to prepare the composite cathode materials and the composite cathode materials.

[0015] FIG. 3 is a graph of Raman spectra of composite cathode materials.

[0016] FIGS. 4A-4D are graphs of hysteresis loops of different FNPs. FIG. 4A is a graph of the hysteresis loop of BiFeCh. FIG. 4B is a graph of the hysteresis loop of BaTiCh. FIG. 4C is a graph of the hysteresis loop of Bi4NdTi3Feo.7Nio.3O15, and Bi4NdTi3Feo.5Coo.5O15.

[0017] FIGS. 5A-5E are SEM images. FIG. 5A is an image of SsohGso. FIG. 5B is an image of S47.s(BFO)5hG47.5. FIG. 5C is an image of S47.s(BTO)5hG47.5. FIG. 5D is an image of S47.5(BNTFN)5hG47.5. FIG. 5E is an image of S47.5(BNTFC)5hG47.5.

[0018] FIGS. 6A-6E are energy-dispersive spectrometry (EDS) spectra of composite cathode materials. FIG. 6A is a spectra of SsohGso. FIG. 6B is a spectra of S47.5(BFO)shG47.5. FIG. 6C is a spectra of S47.5(BTO)shG47.5. FIG. 6D is a spectra of S47.5(BNTFN)shG47.5. FIG. 6E is a spectra of S47.5(BNTFC)shG47.5.

[0019] FIGS. 7A-7J are discharge-charge profiles, specific capacity, and coulombic efficiency of different Li-S batteries. FIGS. 7A and 7B characterize a Li-S battery with a SsohGso composite cathode. FIGS. 7C and 7D characterize a Li-S battery with a S47.s(BFO)hG47.5 composite cathode. FIGS. 7E and 7F characterize a Li-S battery with a S47.s(BTO)hG47.5 composite cathode. FIGS. 7G and 7H characterize a Li-S battery with a S47.s(BNTFN)hG47.5 composite cathode. FIGS. 71 and 7J characterize a Li-S battery with a S47.s(BNTFC)hG47.5 composite cathode. All batteries were cycled at 0.3 mA / cm2for the first three cycles followed by 0.2 mA / cm2.

[0020] FIG. 8 is a comparison of discharge-charge profiles of two cycles for Li-S batteries with SsohGso, S47.s(BFO)hG47.s, S47.s(BTO)hG47.s, S47.s(BNTFN)hG47.s, or S47.s(BNTFC)hG47.5 composite cathodes. All batteries were evaluated at a current density of 0.2 mA / cm2.

[0021] FIG. 9 is a comparison of areal capacity for batteries evaluated at current densities of 0.2 mA / cm2, 0.3 mA / cm2, and 0.5 mA / cm2.

[0022] FIG. 10 is a graph of XRD spectra of composite cathode materials.

[0023] FIG. 11 is a graph of Raman spectra of composite cathode materials.

[0024] FIGS. 12A-12E are SEM images of composite cathode materials. FIG. 12A is S2s(CBhG)6sPVDFio. FIG. 12B is S2sBTOs(CBhG)6oPVDFio. FIG. 12C isS25BF05(CBhG)6oPVDFio. FIG. 12D is S25BNTFN5(CBhG)6oPVDFio. FIG. 12E is S25BNTFC5(CBhG)6oPVDFio.

[0025] FIG. 13A-13E are graphs of EDS spectra of composite cathode materials. FIG. 13 A is a graph of the EDS spectrum of S25(CBhG)6sPVDFio. FIG. 13B is a graph of the EDS spectrum of S25BT05(CBhG)6oPVDFio. FIG. 13C is a graph of the EDS spectrum of S25BFOs(CBhG)6oPVDFio. FIG. 13D is a graph of the EDS spectrum of S25BNTFN5(CBhG)6oPVDFio. FIG. 13E is a graph of the EDS spectrum of S25BNTFC5(CBhG)6oPVDFio.

[0026] FIG. 14 is a Nyquist plot comparing electrochemical impedance spectra before charge-discharge of battery cells with different composite cathodes from 1 MHz to 0.1 Hz at room temperature with a circuit model.

[0027] FIGS. 15A-15J are graphs of charge-discharge profiles, specific capacity, and Coulombic efficiency of batteries with different composite cathodes. FIGS. 15A and 15B show cycling data for batteries with S25(CBhG)6sPVDFio. FIGS. 15C and 15D show cycling data for batteries with S25BT05(CBhG)6oPVDFio. FIGS. 15E and 15F show cycling data batteries with S25BFOs(CBhG)6oPVDFio. FIGS. 15G and 15H show cycling data for batteries with S25BNTFN5(CBhG)eoPVDFio. FIGS. 151 and 15J show cycling data for batteries with S25BNTFC5(CBhG)eoPVDFio. All batteries were run at 0.2 mA / cm2after the first three cycles run at 0.3 mA / cm2.

[0028] FIGS. 16A and 16B compare electrochemical performance of S25(CBhG)6sPVDFio and S25FNPs5(CBhG)6oPVDF io cathode materials. FIG. 16A is a graph of charge-discharge profiles of two cycles evaluated at a current density of 0.2 mA / cm2. FIG. 16B is a graph of specific capacity at current densities of 0.2 mA / cm2and 0.3 mA / cm2.

[0029] FIG. 17 is graph of areal capacity of batteries evaluated at a current density of 0.2 mA / cm2and 0.3 mA / cm2. The composite cathodes are represented by circles for S25(CBhG)6sPVDFio, triangles for S25BT05(CBhG)6oPVDFio, hexagons for S25BF05(CBhG)6oPVDFio, grey circles for S25BNTFN5(CBhG)6oPVDFio, and stars for S25BNTFC5(CBhG)6oPVDFio.DETAILED DESCRIPTION

[0030] It is to be appreciated that certain aspects, modes, embodiments, variations, and features of the present methods are described below in various levels of detail in order to provide a substantial understanding of the present technology.Definitions

[0031] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this technology belongs.

[0032] As used herein and in the appended claims, singular articles such as “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential. For example, reference to “a cell” includes a combination of two or more cells, and the like. Generally, the nomenclature used herein and the laboratory procedures in cell culture, molecular genetics, organic chemistry, analytical chemistry and nucleic acid chemistry and hybridization described below are those well- known and commonly employed in the art.

[0033] As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term - for example, “about 10 wt.%” would be understood to mean “9 wt.% to 11 wt.%.” It is to be understood that when “about” precedes a term, the term is to be construed as disclosing“about” the term as well as the term without modification by “about” — for example, “about 10 wt.%” discloses “9 wt.% to 11 wt.%” as well as disclosing “10 wt.%.”

[0034] The phrase “and / or” as used in the present disclosure will be understood to mean any one of the recited members individually or a combination of any two or more thereof - for example, “A, B, and / or C” would mean “A, B, C, A and B, A and C, B and C, or the combination of A, B, and C.”

[0035] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 atoms refers to groups having 1, 2, or 3 atoms. Similarly, a group having 1-5 atoms refers to groups having 1, 2, 3, 4, or 5 atoms, and so forth.

[0036] Throughout this disclosure, various publications, patents, and published patent specifications are referenced by an identifying citation. Also within this disclosure are Arabic numerals referring to referenced citations, the full bibliographic details of which are provided immediately preceding the claims. The disclosures of these publications, patents, and published patent specifications are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.The Present Technology

[0037] Disclosed herein are cathodes for lithium-sulfur (Li-S) batteries that include a composite of sulfur, holey graphene, and ferroelectric nanoparticles. Also disclosed herein are electrochemical cells including these cathodes, and methods of forming these composite cathodes and electrochemical cells.

[0038] In one aspect, the composite cathode material includes elemental sulfur that acts as an electroactive material in the Li-S battery. In any embodiment, the sulfur may be evenly dispersed in the composite cathode. Sulfur may be present in the composite cathode material as a particles having a particle size of about 50 nm to about 5 pm (e.g., about 100 nm to about 2 pm, or about 500 nm to about 1 pm), and the particles may be supported by a conductive carbon. The sulfur may be present in an amount of about 25 wt.% to about 85 wt.% (e.g., about 25 wt.% to about 75 wt.% sulfur, about 25 wt.% to about 50 wt.%, about 15 wt.% to about 30 wt.%, about 40 wt.% to about 60 wt.%, about 25 wt.%, or about 50 wt.%).

[0039] The composite cathode material also includes holey graphene. The hole graphene is a form of conductive carbon that may act as an electrically conductive and lightweight scaffold for the sulfur and ferroelectric nanoparticles in the composite material. Holey graphene is graphene with in-plane holes formed therein. In any embodiment, the holes may be formed in the graphene using a gas-phase etching process, which uses controlled partial air oxidation of the graphene at a temperature greater than room temperature (e.g., greater than 200 °C) to form holes at defect sites in the graphene. In any embodiment, the gas-phase etching process may be that described in Lin, Y. et al., Holey Graphene Nanomanufacturing: Structure, Composition, and Electrochemical Properties, Adv. Funct. Mater., 2015, 25, 2920- 2927, which is incorporated by reference in its entirety. The average pore diameter may be about 1 nm to about 100 nm (e.g., about 2 nm to about 50 nm). The holey graphene may be present in the composite cathode material in an amount of about 0.5 wt.% to about 80 wt.% (e.g., about 25 wt.% to about 75 wt.%, about 40 wt.% to about 60 wt.%, about 45 wt.% to about 50 wt.%, about 50 wt.%, about 48 wt.%, about 0.5 wt.% to about 10 wt.%, about 0.5 wt.% to about 5 wt.%, about 0.5 wt.% to about 2 wt.%, or about 0.5 wt.% to about 1.5 wt.%).

[0040] In any embodiment, the holey graphene may not be the only conductive carbon present in the composite cathode material. The composite cathode material may further include carbon black (e.g., Ketjen black, acetylene carbon black, or Super P), graphite, graphite, hard carbon, amorphous carbon, soft carbon, mesocarbon microbeads (MCMB), mesoporous carbon, carbon nanotubes, carbon nanofibers, graphene, or a mixture of any two or more thereof. Where the composite cathode material includes two different conductive carbons, the ratio of conductive carbons may be about 99: 1 to 1 :99 (e.g., about 1.5:98.5 to about 98.5: 1.5, about 1 :99 to about 2:98). For example, the composite cathode material may include holey graphene and a second conductive carbon, where the ratio of holey graphene tosecond conductive carbon is about 1 :99 to about 10:90, about 1 :99 to about 5:95, or about 1 : 99 to about 2:98. The second conductive carbon may be present in the composite cathode material in an amount of about 2 wt.% to about 80 wt.% (e.g., about 10 wt.% to about 75 wt.%, about 20 wt.% to about 70 wt.%, or about 50 wt.% to about 60 wt.%).

[0041] The composite cathode material also includes ferroelectric nanoparticles (FNPs). In any embodiment, the FNPs may be evenly dispersed in the composite cathode. Without being bound by any theory, FNPs ferroelectric polarization within the composite cathode may induce an internal electric field, which effectively reduces the undesired polysulfide shuttling effect that can cause irreversible sulfur loss, rapid capacity fading and poor Coulombic efficiency in Li-S batteries. The FNPs may include BiFeCh (BFO), BaTiCh (BTO), Bi4NdTi3Feo.7Nio.3O15 (BNTFN), Bi4NdTi3Feo.5Coo.5O15 (BNTFC), or a combination of two or more thereof. The FNPs may be present in an amount of about 1 wt.% to about 20 wt.% (e.g., about 2 wt.% to about 10 wt.%, about 3 wt.% to about 7 wt.%, or about 5 wt.%).

[0042] In any embodiment, the composite cathode material may further include a binder. The binder may support volume changes in the cathode during battery cycling. The binder may be poly(vinylidene fluoride) (PVDF), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), poly(tetrafluoroethylene) (PTFE), styrene-butadiene rubber (SBR), or a mixture of two or more thereof. For example, the binder may be PVDF. The binder may be present in an amount of about 0 wt.% to about 20 wt.% (e.g., about 5 wt.% to about 20 wt.%, about 5 wt.% to about 15 wt.%, or about 10 wt.%).

[0043] In another aspect, an electrochemical cell including the composite cathode material is disclosed. The electrochemical cell also includes an anode, a separator between the cathode and the anode, and an electrolyte including a solvent and a lithium salt. The electrochemical cell may be a Li-S battery with a lithium metal anode.

[0044] The anode material may be metallic lithium, and may further include conductive carbon. The conductive carbon may include carbon black (e.g., Ketjen black, acetylene carbon black, or Super P), graphite, graphite, hard carbon, amorphous carbon, soft carbon, mesocarbon microbeads (MCMB), mesoporous carbon, carbon nanotubes, carbon nanofibers, graphene, or a mixture of any two or more thereof. The metallic lithium may be lithium foil, metallic lithium mixed with a conductive carbon, or metallic lithium intercalated in a conductive carbon.

[0045] The separator is disposed between the anode and the cathode to prevent an electrical short in the cell. The separator may be a microporous polymer film, glass fiber, paper fiber, and ceramic material. Illustrative microporous polymer films include, but are not limited, nylon, cellulose, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene, or a blend or copolymer thereof. The separator may be a commercially available separator. Commercially available separators include those such as, but not limited to, Celgard® 2400, 2025, 3501, and 2325. Separators of a wide range of thickness may be used. For example, the separator may be from about 5 pm to about 50 pm thick.

[0046] The electrochemical cell includes an electrolyte. The electrolyte includes a solvent and a lithium salt dissolved therein. The solvent may include 1,2-dimethoxy ethane (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), ethylene carbonate (EC), propylene carbonate (PC), ethylmethylcarbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or mixtures of two or more thereof. For example, the solvent may be a mixture of two solvents in a volume ratio of about 1 :99 to about 99: 1 (e.g., about 10:90 to 90: 10, about 20:80 to 80:20, about 30:70 to 70:30, about 40:60 to 60:40, or about 50:50). For example, the solvent may be DOL and DME in about 1 : 1 volume ratio.

[0047] The lithium salt may include lithium trifluoromethanesulfonamide (LiTFSI), LiPFe, LiSBFe, LiClO4, LiAlCL, Lil, LiBr, LiCl, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiODFB), LiSCN, LiBF4, LiB(C6Hs)4, LiAsFe, LiCFsSOs, LIFSI, LiNOs, and mixtures of two or more thereof. The electrolyte may include lithium salt in a concentration of about 0.1 M to about 2 M (e.g., about 0.5 M to about 1.5 M, about 0.8 M to about 1.5 M, about 1 M to about 1.3 M, about 0.5 M, about 1 M, or about 1.5 M). For example, the electrolyte may include about 0.5 M to about 1.5 M LiTFSI and about 0.05 M to about 0.5 M LiNCh, or about 1 M LiTFSI and about 0.2 M LiNCh.

[0048] In any embodiment, the electrochemical cell may further include current collectors for the anode and the cathode. The current collectors may include copper, stainless steel, titanium, platinum, gold, aluminum, nickel, or a mixture or alloy of two or more thereof. The current collectors may be in the form of a foil, mesh, or screen.

[0049] In another aspect, a method of forming the composite cathode material is provided.The method includes forming a mixture of sulfur, holey graphene, and FNPs and thencompressing the mixture to form the cathode in a monolithic form. The mixture may further include a binder and / or an additional conductive carbon, as described herein.

[0050] Forming the mixture may include mechanically mixing the components together until they are dispersed. The components may be present in the mixture in the desired weight ratios in the composite cathode material. Mechanical mixing may include ball milling. Ball milling may be performed for a time period of about 5 seconds to about 1 hour (e.g., about 5 seconds to about 30 minutes, about 5 seconds to about 10 minutes, about 5 seconds to about 5 minutes, about 5 seconds to about 1 minute, about 5 seconds to about 30 seconds, about 5 seconds to about 20 seconds, or about 10 seconds to about 15 seconds). The ball milling may be conducted in a variety of containers. An illustrative container is an agate container having agate balls, a stainless steel container having stainless steel balls, or a zirconium container containing zirconium balls.

[0051] In another aspect, a method of forming a Li-S battery including the composite cathode is disclosed. The method includes assembling the cell to include the composite cathode, the anode including metallic lithium, the separator between the cathode and the anode, and the electrolyte, as these components are described herein.EXAMPLES

[0052] The present technology is further illustrated by the following Examples, which should not be construed as limiting in any way. The examples herein are provided to illustrate advantages of the present technology and to further assist a person of ordinary skill in the art with preparing or using the compositions and systems of the present technology. The examples should in no way be construed as limiting the scope of the present technology, as defined by the appended claims. The examples can include or incorporate any of the variations, aspects, or embodiments of the present technology described above. The variations, aspects, or embodiments described above may also further each include or incorporate the variations of any or all other variations, aspects, or embodiments of the present technology. The following Examples demonstrate the preparation, characterization, and use of illustrative composite cathodes for Li-S batteries.Example 1: Binder- and Solvent-Free Holey Graphene / Ferroelectric / Sulfur Composite Cathodes for High-Capacity Lithium-Sulfur Batteries

[0053] Lithium-sulfur (Li-S) batteries have attracted interest as next-generation high- density energy storage devices. However, their practical application has been limited by rapid capacity fading when cycling cells with high mass loading levels. This may be related to lower electron / ion conduction and the shuttling effect of soluble polysulfide species. To address these issues, composite cathodes including sulfur, ferroelectric nanoparticles, and holey graphene (S / FNPs / hG) were fabricated for high-mass-loading S cathodes. The solvent- free and binder-free procedure used holey graphene as a dry -pressable electrode material for Li-S batteries. The structure of the holey graphene framework may provide faster electron and ion transport within the electrode and sufficient mechanical properties to mitigate the electrode’s volume expansion during cycling than some other forms of conductive carbon. Moreover, without being limited by any theory, ferroelectric polarization due to the FNPs within the composite cathode may induce an internal electric field, which may effectively reduce the undesired polysulfide shuttling effect. The S / FNPs / hG composite cathodes exhibited stable cycling and a specific capacity up to 1409 mAh / g for the S / BTO / hG cathode. A capacity retention value of 90% was obtained for the S / BNTFN / hG battery up to cycle 18. The mass loading of sulfur of about 5.72 mg / cm2to about 7.01 mg / cm2provided an areal capacity of up to about 10 mAh / cm2for the S / BaTiCh / hG battery and a rate capability of about 0.2 mA / cm2and 0.5 mA / cm2.

[0054] Materials and Methods

[0055] Materials. The hG was prepared from graphene (Vorbeck materials) using a one- step air oxidation procedure as described in Lin, Y. et al., Holey Graphene Nanomanufacturing: Structure, Composition, and Electrochemical Properties, Adv. Funct. Mater., 2015, 25, 2920-2927, which is incorporated by reference in its entirety. Bis(trifluoromethylsulfonyl)imide lithium salt (LiTFSI; 98+%), lithium nitrate (LiNCh; 99.99%), 1,2-dimethoxy ethane (DME; 99+%), and 1,3-dioxolane (DOL; 99.5%) were purchased from Thermo Fisher. Sulfur (S; 99.998%), barium carbonate (BaCCh; 99.8%), neodymium (III) oxide (TSkhCh; 99.9%), lithium foil 0.75 mm thick x 19 mm wide (Li;99.9%), cobalt (II, III) oxide (CO3O4; 99.998%), polyvinylidene fluoride (PVDF), and carbon back (CB) were purchased from Alfa Aesar. Iron oxide (Fe20s; 99.998%), nickel (III) oxide nanopowder (Ni2Ch; 99%), and Celgard membrane (25 pm) thickness and 85 mm width was purchased from Sigma-Aldrich. Bismuth oxide (Bi2Ch; 99.9%) was purchased from Fluka, and titanium dioxide (TiCh; 97%) was purchased from Fisher Scientific. All precursors andelements for the battery assembly were used inside the glove box with argon filled, water (H2O) and oxygen (O2) contents <0.5 ppm.

[0056] Synthesis of ferroelectric nanoparticles. The FNPs were synthesized via mechanical activation followed by thermal treatment. Stoichiometric amounts of 15 wt.% excess of Bi2Ch were used to compensate volatilization loss during the thermal treatment. The oxides were mixed with isopropanol using a high-energy ball-milling planetary machine with zirconia balls (Across International, PQ-N04 planetary ball mill, USA) operating at 45 Hz (2700 rpm) for 8 hrs. The synthesized material was dried on a hot plate at 100 °C for 8 hrs. A furnace (Carbolite, HTF1700, USA) was used at a heating and cooling rate of 5 °C / min in which the powders were calcined. FIG. 1 A provides a schematic illustration of the synthesis process for ferroelectric nanoparticles. The calcination parameters time and temperature are provided in Table 1.Table 1: Summary of the cell parameters with sulfur mass loading of 47.5%.

[0057] Sulfur / FNPs / holey graphene composite cathode preparation and characterizations.

[0058] The hG was used as a dry-pressable, solvent-free, and binder-free process to prepare five component powders. The sulfur, hG, and ferroelectric nanoparticles were mixed in a particular ratio by ball-milling for aboutlO seconds. The composite powders were mixed as follows: SsohGso and S47.5(FNPs)5hG47.5 (subscripts indicate the relative weight percentages of the components). Then the electrodes were fabricated by dry pressing the powders on a stainless-steel die (13 mm diameter) and a hydraulic press at 200 mbar sandwiched between aluminum foil. The product was a dense electrode that may be directly used as the composite cathode when assembling the coin cells (CR2032). This technique facilitated preparation and was less time consuming than conventional solvent-based methods. FIG. IB is a schematic of this cathode preparation process, with or without FNPs.

[0059] Coin Cell Fabrication. The coin cells CR2032 were assembled in an Ar-filled glovebox (MBraun) with H2O and O2 contents < 0.5 ppm using a composite cathode SsohGso and a composite cathode S47.5(FNPs)shG47.5 (13 mm), a polypropylene membrane (16 mm; Celgard-2400) as the separator, and a lithium foil (12 mm) as the anode. The salt mixture of 1 M lithium bis(trifluoromethane)sulfonimide (LiTFSI)and 0.2 M LiNCh was dissolved in di oxolane (DOL) and dimethoxy ethane (DME) in an equal volume ratio (1 : 1 v / v) and used as an electrolyte. FIG. 1C is an illustration of a Li-S electrochemical cell including a composite cathode.

[0060] Characterization. Powder X-ray diffractometer was used to characterize structure, scanning electron microscopy was used to characterize surface morphology of the electrodes, Raman spectroscopy was used to characterize electronic structure, and Galvanostatic discharge-charge curves were collected using a battery tester.

[0061] Results and Discussion

[0062] FIG. 2 is a graph of X-ray diffraction (XRD) spectra of the pristine and modified composites. The composites were fabricated using hG, sulfur, and FNPs, namely, bismuth ferrite (BTO), barium titanate (BTO), Bi4NdTi3Feo.7Nio.3O15 (BNTFN), and Bi4NdTi3Feo.5Coo.5O15 (BNTFC). The pristine S diffraction peaks were consistent with the Fddd orthorhombic phase of sulfur data of JCPDS no. 08-024726. The diffraction peak at 20° to 30° may be assigned to the overlapping of the graphene characteristic peak at about 26° and the Miller index (002) corresponding to graphitic carbon regions (PDF 00-001-0640) present within the hG powder. XRD patterns of BFO, BTO, BNTFN, and BNTFC confirmed the formation of the perovskite structure. The BFO was verified against the powder data of JCPDS no. 86-1518.27. These peaks revealed that BFO crystallites had the perovskite structure with the rhombohedral space group R3c (no. 161). The BTO sample exhibited (002) / (200) peak splitting of diffraction lines around 45°, indicating a tetragonal phase. The intensity ratios of the modeled peaks were compared to the values given in JCPDS file no. 05-062628. The compounds of BNTFN and BNTFC exhibited a layered Aurivillius phase with four perovskite layers; both having an orthorhombic phase. The XRD patterns of composite electrodes showed characteristic peaks of mixed materials. Table 2 provides crystallite sizes calculated from the XRD spectra using the Sherrer equation.Table 2. Crystallite size calculated from XRD spectra.

[0063] FIG. 3 is a graph of the Raman spectra of S / hG and S / FNPs / hG composites. As shown in the spectra, there are two major peaks at 1430 cm1and 1590 cm1corresponding to the D band (disorder-induced phonon mode) and the G band (graphitic band), suggesting a disordered graphene-like framework. The Raman peaks for 2D and D + G are also visible around 2700 cm1and may be attributed to the layered structure of graphene. The intensity as well as the ratio of IDIIG phonon peaks remained similar across samples, indicating the presence of FNPs in the composites.FIGS. 4A-4D are graphs of the measured ferroelectric polarization (P-E) hysteresis loops for BFO, BTO, BNTFN, and BNTFC FNPs. All of these systems showed ferroelectric polarization characteristics. The remnant polarization (Pr) values for BFO at 3 kV / cm were approximately 8.5 pC / cm2and 8.0 pC / cm2for BTO, while BNTFN and BNTFC compounds had smaller Prvalues, although a less leaky hysteresis loop than BFO. BTO is a displacive ferroelectric with a well-behaved hysteresis loop.

[0064] FIGS. 5A-5E show scanning electron microscopy (SEM) images of composite cathode materials. FNPs were attached to the hG-S composite surface, which is relatively smooth. hG and FNPs may be uniformly distributed within the surface of composites.

[0065] FIGS. 6A-6E are graphs of energy-dispersive spectrometry (EDS) spectra of S / hG and S / FNPs / hG composites. In each spectrum, the S-peak was dominant due to its higher concentration relative to the hG, BFO, BTO, BNTFN, and BNTFC peaks.

[0066] FIGS. 7A-7J are graphs of the electrochemical performance, along with the cyclic behavior of assembled cells with various composite cathodes. To determine the electrochemical performance of the assembled cells, galvanostatic discharge-charge performances were measured at different current densities: 0.5 mA / cm2, 0.3 mA / cm2, and 0.2 mA / cm2(corresponding to C-rates of C / 10, 3C / 50, and C / 25). In FIGS. 7A, 7C, 7E, 7G, 71,the initial discharge capacities of S / hG and the various S / FNPs / hG composites cycled at 0.2 mA / cm2were 1390, 1316, 1409, 1062, and 1330 mAh / g for S / hG, S / BFO / hG, S / BTO / hG, S / BNTFN / hG, and S / BNTFC / hG, respectively. The Li-S battery with the S / BTO / hG cathode had a higher discharge capacity of 1409 mAh / g over 58 cycles. The capacity of cells coupled with FNPs improved compared with S / hG cells. Without being bound by any theory, this result was consistent with the hypothesis that there is an extra internal field induced by the ferroelectric nanoparticles that may reduce polysulfide formation during cycling and improve the efficiency of ion transport since the induced macroscopic charges on the surface of ferroelectrics act as trapping centers for the polysulfides that are heteropolar in nature. The polarization of ferroelectric particles also influenced the distribution of Li ions, yielding diffusion pathways in the electrolyte / active material, which accelerated the transfer speed of Li ions, thus decreasing or preventing the formation of a concentration gradient of Li+ions near the deposition surface.

[0067] As the C-rate varied, capacity retention and discharge profiles of Li-S cells became differentiated. For 0.2 mA / cm2and 0.3 mA / cm2cycling, the discharge-charge capacity displayed a higher retention during the cycling test up to 90% for the S / BNTFN / hG cathode over 18 cycles. The capacity fading may be related to the ability of Li-S insertion-extraction within the electrodes.

[0068] As shown in FIGS. 7E and 7F, the S47.5(BTO)5hG47.5 electrode with the 7.01 mg / cm2mass loading also exhibited a higher capacity in the 1st cycle of 1409 mAh / g, 5thcycle of 1095 mAh / g, 20th cycle of 959 mAh / g, and 58th cycle of 477 mAh / g (or 9.9 mA / cm2, 7.6 mA / cm2, 6.7 mA / cm2, and 3.3 mA / cm2, respectively) at current densities of 0.2 mA / cm2and 0.3 mA / cm2, with an overpotential of 0.20 V. The results for the S47.5(BFO)5hG47.5 electrode with 6.87 mg / cm2mass loading capacity were 1316 mAh / g, 1216 mAh / g, 875 mAh / g, and 342 mAh / g and the areal capacity values were 9.0 mA / cm2, 8.3 mA / cm2, 6.0 mA / cm2, and 3.3 mA / cm2with a lower overpotential of 0.16 V at 0.2 mA / cm2as shown in FIGS. 7C and 7D. The specific capacity values of S / BNTFN / hG for the 1st, 2nd, 5th, 10th, and 18th cycles were 1062 mAh / g, 1337 mAh / g, 1215 mAh / g, 1113 mAh / g, and 960 mAh / g, respectively, while the current density was 0.2 mA / cm2for the first three cycles and 0.3 mA / cm2for the rest of the cycles as shown in FIGS. 7G and 7H. The specific capacity values of the S / BNTFC / hG cathode for the 1st, 2nd, 5th, 10th, 20th, and 37th cycles were 1330 mAh / g, 1061 mAh / g, 1048 mAh / g, 978 mAh / g, 917 mAh / g, and 708 mAh / g,respectively, while the current density was 0.2 mA / cm2for the first three cycles and 0.3 mA / cm2for the rest of the cycles as shown in FIGS. 71 and 7 J. Incorporating FNPs in Li-S battery cathodes increased cyclability of the batteries, which may indicate that FNP incorporation decreased the rapid formation of polysulfides. The higher specific capacity was for the cathode containing BFO, with a value of 1409 mAh / g. The second higher was the electrode containing BNTFC with a value of 1330 mAh / g. A capacity retention value of 90% was obtained for the S / BNTFN / hG battery up to cycle 18. The average Coulombic efficiency for S / hG batteries not containing FNPs was 78.57%, while the average Coulombic efficiencies for batteries incorporating FNPs ranged from 62.70% to 94.71%. The FNPs increased the cyclability in the batteries (i.e., 18 cycles for S / BNTFN, 37 cycles for S / BNTFC / hG, 57 cycles for S / BFO / hG, and 58 cycles for S / BTO / hG). The batteries that did not contain FNPs presented lower cyclability values, not surpassing the 6-cycle mark.

[0069] The discharge-charge profiles of the five batteries are shown in FIG. 8. A characteristic of Li-S batteries is that the discharge curve shows two plateau regions. The formation of a valley at the end of the first discharge plateau and a peak at the beginning of the charging process can be seen in the curves as shown in FIG. 8. The presence of the valley may be due to the formation of soluble long-chain polysulfides by the reduction of elemental sulfur, which was produced during discharge, increasing the viscosity, and decreasing the ion conductivity. However, when the medium-chain polysulfides were reduced to the insoluble species (Li2S2 / Li2S) in the second plateau, the viscosity of the electrolyte was reduced and reduction of the soluble poly sulfides was followed by formation of a solid reduction. The peak at the beginning of the charge curve was attributed to the formation of soluble lithium poly sulfides from the insulating layers of the insoluble species.

[0070] The use of ferroelectric nanoparticles and hG significantly improved the performance of high-mass-loading cathodes, as shown in FIG. 9. In comparison to S / hG, S / FNPs / hG cathodes exhibited improved S utilization in terms of specific capacity (1316 mAh / g vs 1049 mAh / g for the first cycle) and areal capacity (6.09 mAh / cm2vs 9.89 mAh / cm2for the first cycle). In addition, the S / FNPs / hG electrodes exhibited a reduced overpotential (AE ~ 0.15 V vs 0.28 V in the second cycle) in comparison to the S / hG cathode. To achieve high areal capacity, high mass loading of sulfur ranging from 5.72 mg / cm2to 7.01 mg / cm2was procured, and the obtained value of high areal capacity was on the order of about 10 mAh / cm2. FNPs may be useful in avoiding the loss of solublepolysulfides in electrolytes as well as reducing polysulfide formation due to their higher internal field of polarization.Example 2: Holey Graphene / Carbon Black / Ferroelectric Nanoparticles / PYDF / Sulfur Composite Cathodes for High-Capacity Lithium-Sulfur BatteriesIn this study, the impact of the incorporation of ferroelectric nanoparticles (FNPs), including BaTiCh (BTO), BiFeCh (BFO), Bi4NdTi3Feo.7Nio.3O15 (BNTFN), and Bi4NdTi3Feo.5Coo.5O15 (BNTFC), as well as the mass loading of sulfur to fabricated solvent-free sulfur / holey graphene-carbon black / polyvinylidene fluoride (S / FNPs / CBhG / PVDF) composite electrodes to achieve higher areal capacity for lithium-sulfur (Li-S) batteries. A dry-press method was used to fabricate composite cathodes. The hG, a conductive and lightweight scaffold derived from graphene, served as a matrix to host sulfur and FNPs for the fabrication of solvent-free composites. Raman spectra indicated a dominant hG framework for all the composites, with strong D, G, and 2D bands. The surface morphology of the fabricated cathode system showed a homogeneous distribution of FNPs throughout the composites, indicated by the EDS spectra. The observed Li+ion diffusion coefficient for the composite cathode was about 2.17 x 10'16cm2 / s for S25(CBhG)6sPVDFio and about 4.15 x 10'15cm2 / s for S25BNTFC5(CBhG)eoPVDFio. The higher discharge capacity values for the S25(CBhG)65PVDFio and S25BNTFC5(CBhG)eoPVDFio composites started at 1123 mAh / g and 1509 mAh / g and dropped to 612 mAh / g and 572 mAh / g, respectively, after 100 cycles. The areal capacity for the S25(CBhG)6sPVDFio composites was 4.84 mAh / cm2with a mass loading of 4.31 mg / cm2, while that for the S25BNTFC5(CBhG)eoPVDFio composites was 6.74 mAh / cm2with a mass loading of 4.46 mg / cm2. Effective FNP incorporation within the S cathode improved the cycling response and stability of cathodes, providing higher performance Li-S batteries.

[0071] Materials and Methods

[0072] Materials. The hG was prepared from graphene (Vorbeck materials) using the established one-step air oxidation procedure as described in Lin, Y. etal., Holey Graphene Nanomanufacturing: Structure, Composition, and Electrochemical Properties, Adv. Funct. Mater., 2015, 25, 2920-2927, which is incorporated by reference in its entirety. Bis(trifluoromethylsulfonyl)imide lithium salt (LiTFSI; 98+%), lithium nitrate (LiNCh; 99.99%), 1,2-dimethoxy ethane (DME; 99+%), and 1,3-dioxolane (DOL; 99.5%) werepurchased from ThermoFisher. Sulfur (S; 99.998%), barium carbonate (BaCCh; 99.8%), neodymium (III) oxide QSkhCh; 99.9%), lithium foil (0.75 mm thick x 19 mm wide) (Li; 99.9%), cobalt (II, III) oxide (CO3O4; 99.998%), polyvinylidene fluoride (PVDF), and carbon back (CB) were purchased from Alfa Aesar. Iron oxide (Fe20s; 99.998%), nickel (III) oxide nanopowder (N12O3; 99%), and Celgard membrane (25 pm thickness and 85 mm width) were purchased from Sigma-Aldrich. Bismuth oxide (Bi2Ch; 99.9%) was purchased from Fluka and titanium dioxide (TiCh; 97%) was purchased from Fisher Scientific. All precursors and elements for the battery assembly were used inside the glove box with argon-filled water (H2O) and oxygen (O2) contents < 0.5 ppm.

[0073] Synthesis of ferroelectric nanoparticles. The FNPs were synthesized via mechanical activation followed by thermal treatment. Stoichiometric amounts of 15 wt.% excess of Bi2Ch were used to compensate for volatilization loss during the thermal treatment. The oxides were mixed with isopropanol using a high-energy ball-milling planetary machine with zirconia balls operating at 45 Hz (2700 rpm) for 8 hrs. The synthesized material was dried on a hot plate at 100 °C for 8 hrs. A furnace was used at a heating and cooling rate of 5 °C / min in which the powders were calcined.

[0074] Sulfur-FNPs-holey sraphene / carbon black-PVDF composite cathode preparation and characterizations. S25(CBhG)6sPVDFio and S25FNPs5(CB98.5%hGi.5%)6oPVDFio composite cathodes were prepared. Each of the composite cathodes was prepared by mixing powders in a particular ratio by using ball milling to fabricate composite electrodes of S25(CB98.5%hGi.5%)6sPVDFio and S25FNPs5(CB98.5%hGi.5%)eoPVDFio. For each sample, 100 mg of cathode composite was prepared in the desirable amount of S, CBhG, FNP, and PVDF powders (weight ratios of 2.5:0.0:6.5: 1.0 and 2.5:0.5:6.0: 1.0 for a total of five different samples) and loaded in a 50 mL zirconia vial. After placing two zirconia balls in the vial, the set was secured in PQ-N04 series planetary ball mills and milled for 10-15 seconds to yield the S25(CBhG)65PVDFio and S25FNPs5(CB98.5%hGi.5%)6oPVDFio composites. PVDF was used as binder and CB as conductor to improve the electrical conductivity and cycle life of the active material. The PVDF binder may counter volumetric changes occurring in the insertion electrodes during intercalation / deintercalation and provide adhesion to the current collectors, which is useful for the stability of the electrodes. The fabrication of composite cathodes using the dry -press method does not require the use of solvent. The hG can be compressed from its dry powder form into solid architectures of various shapes. For thefabrication of the electrode disc, 20 mg of the material was added to the 13 mm diameter stainless-steel pressing die. The pressed powders were directly used as the composite cathode S25(CBhG)6sPVDFio and S25FNPss(CBhG)6oPVDFio, with a polypropylene membrane as separator and lithium foil as anode for assembling the coin cells (CR2032). To prepare the electrolyte, 1 M LiTFSI and 0.2 M LiNCh were dissolved in DOL / DME (1 : 1, v / v). To calculate the amount of electrolyte (40 pL), 5.72 mg of the active mass was used with cathode loadings as 7 mL / g. This technique facilitated preparation, and it was less time consuming than conventional solvent-based methods. Table 3 summarizes the cell parameters sulfur content, sulfur loading, and electrolyte to sulfur ratios.Table 3. Summary of the cell parameters with sulfur mass loading of 25%.

[0075] Results and Discussion

[0076] FIG. 10 shows the X-ray diffraction (XRD) spectra of the S25(CBhG)6sPVDFio and S25FNPss(CBhG)6oPVDFio composites. The XRD analysis was performed to investigate structural changes due to the incorporation of FNP materials, including BTO, BFO, BNTFN, or BNTFC, and their possible reactions with S, CB, hG, and PVDF. As shown in FIG. 10, the prominent peak of hkl (222) at 23° corresponded to the Fddd orthorhombic structure of S (JCPDS no. 08-0247). The peak planes of (002) and (101) were at 25° and 43° (attributed to carbon materials CB or hG), respectively; however, the (110) plane at 27° corresponded to PVDF. These peaks were detected in all cathode compounds demonstrating the presence of all the aforementioned materials. Furthermore, the rest of the identified peaks were indexed with their respective miller indices in the XRD spectra corresponding to the FNPs.

[0077] FIG. 11 shows the Raman spectra for the S25(CBhG)6sPVDFio and S25FNPss(CBhG)6oPVDFio composites. The pronounced D band (disorder-induced phonon mode) at approximately 1336 cm’1and G band (associated with in-plane vibration of the graphite lattice) at approximately 1575 cm’1suggested a graphite-like carbon framework. The intensity ratios (IDIIG) shown in FIG. 11 were 1.06 for S25(CBhG)6sPVDFio, 1.10 forS25BT05(CBhG)6oPVDFio, 1.01 for S25BF05(CBhG)6oPVDFio, 1.00 for S25BNTFC5(CBhG)6oPVDFio, and 0.97 for S25BNTFC5(CBhG)6oPVDFio. These ratios were slightly reduced, which may be due to defect removal through the combined effects of ferroelectric nanoparticles doping. The Raman peaks for 2D and D + G were also visible at approximately 2700 cm’1, which was attributed to the layered structure of the graphene.

[0078] FIGS. 12A-12E show SEM images of the S25(CBhG)65PVDFio and S25FNPs5(CBhG)6oPVDFio composites. The images indicate that the FNPs, CB, hG, and S were well mixed in the composites. The composite surface was smooth, which indicated that the S had dispersed in the hG framework. The hG and CB may act as efficient electron transport carriers for electrical contact within the composites. The layered structures may absorb electrolyte between layers, and buffer volume expansion of the S, to provide improved cycling performance.

[0079] FIGS. 13A-13E are graphs of EDS spectra of S25(CBhG)65PVDFio and S25FNPs5(CBhG)6oPVDFio composites. In each spectrum, the S-peak was dominant due to its higher concentration relative to the CB, hG, PVDF, BFO, BTO, BNTFN, and BNTFC, although the observed peaks clearly indicated their presence.

[0080] FIG. 14 is a Nyquist plot of S25(CBhG)65PVDFio, S25BT05(CBhG)6oPVDFio, S25BNTFN5(CBhG)6oPVDFio, and S25BNTFC5(CBhG)6oPVDFio composites. The inset shows S25BF05(CBhG)eoPVDFio. The electrical impedance spectroscopy (EIS) spectra showed depressed semicircles in the high-frequency region, corresponding to the chargetransfer process, and a sloping straight line in the low-frequency region consistent with the semi-infinite Warburg diffusion process.

[0081] The EIS spectra before charge-discharge for batteries were fitted with an R(CR)W model and the results are shown in Table 4. The charge-transfer resistance (RCT) values for S25BNTFN5(CBhG)eoPVDFio composites were higher than for the S25(CBhG)6sPVDFio composite. The diffusion coefficients for samples with various FNPs were similar except for the BFO nanoparticles, which exhibited slightly higher values favoring higher ionic conduction for lithium ions. The values of solution resistances (Rs) for FNP-doped composite cathodes varied between 11.08 W and 5.32 W. In comparison, the S25(CBhG)65PVDFio composite exhibited a low Rs of about 4.92 W and a low RCT of about7.63 W. Rs reflected not only the electrolytic solution resistance but also a penetration or affinity of the solution within the cathode, anode, and separator.Table 4. Interfacial characteristics calculated using EIS with R(CR)W model.

[0082] FIGS. 15A-15J show the charge-discharge profiles for the S25(CBhG)6sPVDFio and S25FNPss(CBhG)6oPVDFio composite cathodes with varying fractions of FNPs. The S25(CBhG)65PVDFio cathode without FNPs provided an initial specific capacity of 1123 mAh / g at a current density of 0.2 mA / cm2and a reversible capacity of 541 mAh / g after 134 cycles at 0.3 mA / cm2, as shown in FIGS. 15A and 15B. The specific capacity values of the S25BTOs(CBhG)6oPVDFio cathode for the 1st, 2nd, and 110th cycles were 1402 mAh / g, 1287 mAh / g, and 625 mAh / g, respectively, as shown in FIGS. 15C and 15D. The specific capacity values of the S25BFOs(CBhG)6oPVDFio cathode for the 1st, 2nd, and 116th cycles were 1430 mAh / g, 1325 mAh / g, and 564 mAh / g, respectively, as shown in FIGS. 15E and 15F. The specific capacity values of S25BNTFNs(CBhG)6oPVDFio for the 1st, 2nd, and 158th cycles were 1486 mAh / g, 1287 mAh / g, and 676 mAh / g, respectively, as shown in FIGS. 15G and 15H. The specific capacity values of the S25BNTFCs(CBhG)6oPVDFio cathode for the 1st, 2nd, and 107th cycles were 1509 mAh / g, 1350 mAh / g, and 505 mAh / g, respectively, as shown in FIGS. 151 and 15 J. For all batteries, the current density was 0.2 mA / cm2for the first three cycles and 0.3 mA / cm2for the rest of the cycles. The Coulombic efficiency values of the S25FNPss(CBhG)6oPVDFio composite cathodes were in the range of 80-90%, as shown in FIGS. 15D, 15F, 15H, and 15 J, an improvement upon 67% for the composite cathodes without FNPs. This indicated that the composite cathodes with FNPs had a higher reversible capacity. In FIGS. 15 A, 15C, 15E, 15G, and 151, the initial discharge capacities of various S25FNPss(CBhG)6oPVDFio composites increased to 1400 mAh / g to 1500 mAh / g, in comparison to 1123 mAh / g for the S25(CBhG)6sPVDFio. The comparison of specific capacity, areal capacity, and capacity retention for the Li-S batteries is shown in Table 5.Table 5. Comparison of cycling performance at first and 1001cycle.

[0083] FIG. 16A is a graph of specific capacity with cycle number. There are three plateau regions in the charge-discharge profiles, which are typical characteristics of Li-S batteries. The formation of a valley at the end of the first discharge plateau and a peak at the beginning of the charging process may be observed in the curves during the transition of ions from solid to liquid. In comparison to S25(CBhG)6sPVDFio, S25BNTFCs(CBhG)6oPVDFio cathodes exhibited improved S utilization in terms of specific capacity (1123 mAh / g versus 1509 mAh / g), with mass loading (4.84 mgs / cm2versus 6.74 mgs / cm2) and overpotential (AE-0.16 V versus 0.17 V at the 2nd cycle), as shown in FIGS. 16A and 16B. Cycle performance testing (FIG. 16B) was conducted to quantify the population of the battery. With varying current densities, the discharge performance resulted in a two-way acceleration by means of increasing the battery degradation (capacity fade) rate and reducing the time to complete one full charge-discharge cycle. To achieve high areal capacity, high mass loadings of 4.31 mg / cm2, 3.625 mg / cm2, 3.92 mg / cm2, 3.45 mg / cm2, and 4.46 mg / cm2were used. The higher initial discharge areal capacity reached > 6 mAh / cm2.EQUIVALENTS

[0084] While certain embodiments have been illustrated and described, a person with ordinary skill in the art, after reading the foregoing specification, can effect changes, substitutions of equivalents and other types of alterations to the compounds of the present technology or salts, compositions, derivatives, and mixtures as set forth herein. Each aspect and embodiment described above can also have included or incorporated therewith such variations or aspects as disclosed in regard to any or all of the other aspects and embodiments.

[0085] The present technology is also not to be limited in terms of the particular aspects described herein, which are intended as single illustrations of individual aspects of the presenttechnology. Many modifications and variations of this present technology can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods within the scope of the present technology, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. It is to be understood that this present technology is not limited to particular methods, reagents, compounds, compositions, labeled compounds or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. Thus, it is intended that the specification be considered as exemplary only with the breadth, scope and spirit of the present technology indicated only by the appended claims, definitions therein and any equivalents thereof.

[0086] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.

[0087] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0088] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass anyand all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0089] All publications, patent applications, issued patents, and other documents (for examplejournals, articles and / or textbooks) referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0090] The present technology may include, but is not limited to, the features and combinations of features recited in the following lettered paragraphs, it being understood that the following paragraphs should not be interpreted as limiting the scope of the claims as appended hereto or mandating that all such features must necessarily be included in such claims:A. A cathode for a lithium-sulfur battery comprising: about 25 wt.% to about 75 wt.% sulfur; about 1 wt.% to about 60 wt.% holey graphene; and about 2 wt.% to about 10 wt.% ferroelectric nanoparticles.B. The cathode of Paragraph A, wherein the ferroelectric nanoparticles comprise BiFeCh,BaTiCh, Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of any two or more thereof.C. The cathode of Paragraph A or Paragraph B, wherein the ferroelectric nanoparticles comprise Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination thereof.D. The cathode of any one of Paragraphs A-C, wherein the cathode comprises about 5 wt.% of the ferroelectric nanoparticles.E. The cathode of any one of Paragraphs A-D, wherein the cathode comprises about 25 wt.% to about 50 wt.% sulfur.F. The cathode of any one of Paragraphs A-E, further comprising about 2 wt.% to about 20 wt.% polyvinylidene fluoride.G. The cathode of any one of Paragraphs A-F, further comprising about 20 wt.% to about 70 wt.% carbon black.H. The cathode of Paragraph G, wherein a weight ratio of the holey graphene to the carbon black is about 1 :99 to about 5:95.I. An electrochemical cell comprising: a cathode of any one of Paragraphs A-H; an anode comprising lithium metal; a separator between the cathode and the anode; and an electrolyte comprising a solvent and a lithium salt.J. The electrochemical cell of Paragraph I, wherein the solvent comprises di oxolane and dimethoxy ethane.K. The electrochemical cell of Paragraph I or Paragraph J, wherein the lithium salt comprises bis(trifluoromethylsulfonyl)imide lithium (LiTFSI) and LiNCh dissolved in the solvent.L. The electrochemical cell of Paragraph K, wherein the electrolyte comprises 0.5 M to 1.5M LiTFSI and 0.05 M to 0.5 M LiNCh.M. The electrochemical cell of Paragraph L, wherein the electrolyte comprises 1.0 M LiTFSI and 0.2 M LiNCh.N. A process for forming a cathode for a lithium-sulfur battery comprising: forming a mixture of sulfur, holey graphene, and ferroelectric nanoparticles; and compressing the mixture to form the cathode.O. The process of Paragraph N, wherein forming the mixture comprises ball milling the sulfur, the holey graphene, and the ferroelectric nanoparticles.P. The process of Paragraph O, wherein the ball milling is conducted for about 5 seconds to about 20 seconds.Q. The process of any one of Paragraphs N-P, wherein the mixture comprises about 5 wt.% of the ferroelectric nanoparticles.R. The process of any one of Paragraphs N-Q, wherein the mixture comprises about 25 wt.% to about 50 wt.% sulfur.S. The process of any one of Paragraphs N-R, wherein the ferroelectric nanoparticles comprise BiFeCh, BaTiCh, Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of any two or more thereof.

[0091] Other embodiments are set forth in the following claims, along with the full scope of equivalents to which such claims are entitled.

Claims

WHAT IS CLAIMED IS:

1. A cathode for a lithium-sulfur battery comprising: about 25 wt.% to about 75 wt.% sulfur; about 1 wt.% to about 60 wt.% holey graphene; and about 2 wt.% to about 10 wt.% ferroelectric nanoparticles.

2. The cathode of claim 1, wherein the ferroelectric nanoparticles comprise BiFeCh, BaTiCh,Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of any two or more thereof.

3. The cathode of claim 1, wherein the ferroelectric nanoparticles compriseBi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination thereof.

4. The cathode of claim 1, wherein the cathode comprises about 5 wt.% of the ferroelectric nanoparticles.

5. The cathode of claim 1, wherein the cathode comprises about 25 wt.% to about 50 wt.% sulfur.

6. The cathode of claim 1, further comprising about 2 wt.% to about 20 wt.% polyvinylidene fluoride.

7. The cathode of claim 1, further comprising about 20 wt.% to about 70 wt.% carbon black.

8. The cathode of claim 7, wherein a weight ratio of the holey graphene to the carbon black is about 1 :99 to about 5:95.

9. An electrochemical cell comprising: a cathode of any one of claims 1-8; an anode comprising lithium metal; a separator between the cathode and the anode; and an electrolyte comprising a solvent and a lithium salt.

10. The electrochemical cell of claim 9, wherein the solvent comprises di oxolane and dimethoxy ethane.

11. The electrochemical cell of claim 9, wherein the lithium salt comprises bis(trifluoromethylsulfonyl)imide lithium (LiTFSI) and LiNCh dissolved in the solvent.

12. The electrochemical cell of claim 11, wherein the electrolyte comprises 0.5 M to 1.5 MLiTFSI and 0.05 M to 0.5 M LiNCh.

13. The electrochemical cell of claim 11, wherein the electrolyte comprises 1.0 M LiTFSI and 0.2 M LiNCh.

14. A process for forming a cathode for a lithium-sulfur battery comprising: forming a mixture of sulfur, holey graphene, and ferroelectric nanoparticles; and compressing the mixture to form the cathode.

15. The process of claim 14, wherein forming the mixture comprises ball milling the sulfur, the holey graphene, and the ferroelectric nanoparticles.

16. The process of claim 15, wherein the ball milling is conducted for about 5 seconds to about 20 seconds.

17. The process of claim 14, wherein the mixture comprises about 5 wt.% of the ferroelectric nanoparticles.

18. The process of claim 14, wherein the mixture comprises about 25 wt.% to about 50 wt.% sulfur.

19. The process of claim 14, wherein the ferroelectric nanoparticles comprise BiFeCh,BaTiCh, Bi4NdTi3Feo.7Nio.3O15, Bi4NdTi3Feo.5Coo.5O15, or a combination of any two or more thereof.

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