Patent Application
20220376246
The presently disclosed subject matter relates to lamellar transition metal sulfides, such as lamellar iron sulfides, comprising layers of transition metal sulfides with cations (e.g., solvated cations or organic cations) between the layers. The presently disclosed subject matter further relates to methods of synthesizing the lamellar transition metal sulfides and to the use of the lamellar transition metal sulfides in electrodes, e.g., for metal-ion batteries, metal-ion/sulfur batteries, and capacitors.
There is an enormous projected need for inexpensive and long-lived energy storage devices over the coming decades.1 This energy storage will be employed in many different capacities, such as aiding in the utilization of intermittent renewable energy sources, improving the reliability of electricity in grid-scale deployment, as well as in mobile forms such as electric vehicles.2 The broad application and scale of batteries therefore provides incentive into developing new and improved technology.3
The existing state-of-the-art technology for batteries involves lithium ion batteries (LIBs).4 The three main materials which can be modified to improve performance of batteries are the anode, the cathode, and the solvent/electrolyte. The anode and the cathode are the materials that actually undergo redox changes under charge/discharge cycling.5 Graphite and related carbon-based anodes have emerged as inexpensive and relatively robust anode materials, although titanate and silicon based electrodes have also attracted attention.6 Cathode materials are typically based on cobalt oxide with various other metal dopants such as Mn, Ni, and Al, although iron phosphate cathodes are also employed in some applications.7,8
These materials, particularly the cathode materials, represent a significant fraction of the cost of battery cells and thus represent an important target for new materials science.9 However, while there has been significant interest in modifying these materials to lower cost and increase performance,7 virtually all large-scale battery production is still limited to the materials mentioned above.
Accordingly, there is an ongoing need to provide new materials suitable for cathode applications, particularly for less expensive materials prepared from more abundant sources. There is also a need for materials that can provide improved storage density and service lifetimes.
In some embodiments, the presently disclosed subject matter provides a lamellar transition metal sulfide composition comprising layers of an amorphous transition metal sulfide and further comprising cations between layers of the amorphous transition metal sulfide. In some embodiments, the cation is a solvated cation.
In some embodiments, the transition metal sulfide comprises one or more transition metal selected from the group comprising scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). In some embodiments, the transition metal sulfide is an iron sulfide. In some embodiments, the ratio of iron (Fe) to sulfur (S) in the iron sulfide is about 0.75 to 1.
In some embodiments, the cations comprise monocations, dications, or combinations thereof. In some embodiments, the cations are alkali metal cations, alkaline earth metal cations, or organic cations. In some embodiments, the cations comprise one or more cations selected from Li+, Na+, K+, Mg2+, Ca2+, and tetraalkylammonium cations.
In some embodiments, the cations are solvated by a polar aprotic solvent. In some embodiments, the polar aprotic solvent comprises a carbonate solvent, an ether solvent, dimethyl formamide (DMF), or acetonitrile. In some embodiments, the cation and/or a solvent for solvation of the cation is selected to obtain a desired interlayer spacing between consecutive layers.
In some embodiments, the presently disclosed subject matter provides a method of preparing a lamellar transition metal sulfide composition comprising layers of an amorphous transition metal sulfide and further comprising cations between layers of the amorphous transition metal sulfide, wherein the method comprises contacting a transition metal complex selected from the group consisting of a bis- or tris(dialkyldithiocarbamato)transition metal complex and a bis- or tris(alkylxanthato)transition metal complex with a polar aprotic solvent for a period of time in the presence of an alkali metal salt, an alkaline earth metal salt, or an organic salt. In some embodiments, the cations between layers of the amorphous transition metal sulfide are solvated cations.
In some embodiments, the contacting is performed at a temperature of at least about 25° C. In some embodiments, the contacting is performed at a temperature of between about 25° C. and about 140° C.
In some embodiments, the transition metal complex is selected from tris(diethyldithiocarbamato)iron(III) (Fe(DEDTC)3) and tris(ethylxanthato)iron(III) (Fe(EX)3). In some embodiments, the alkali metal salt, the alkaline earth metal salt, or the organic salt comprises a lithium, sodium, potassium, magnesium, calcium, or tetraalkylammonium salt and/or wherein the salt comprises an anion selected from a triflate, a chloride, and a hexafluorophosphate. In some embodiments, the polar aprotic solvent comprises a carbonate, an ether, DMF, or acetonitrile. In some embodiments, the polar aprotic solvent is selected from the group consisting of DMF and tetrahydrofuran (THF).
In some embodiments, the contacting is performed in the presence of a soluble sulfide source. In some embodiments, the soluble sulfide source comprises an alkali metal sulfide, S8, a thiourea, or 1,2,4,5-tetrazinane-3,6-dithione.
In some embodiments, interlayer spacing between consecutive layers of the lamellar transition metal sulfide is tuned based on selection of the salt and/or solvent. In some embodiments, the presently disclosed subject matter provides a lamellar transition metal sulfide prepared by contacting a transition metal complex selected from the group consisting of a bis- or tris(dialkyldithiocarbamato)transition metal complex and a bis- or tris(alkylxanthato)transition metal complex with a polar aprotic solvent for a period of time in the presence of an alkali metal salt, an alkaline earth metal salt, or an organic salt
In some embodiments, the presently disclosed subject matter provides a method of preparing a lamellar transition metal sulfide composition comprising layers of an amorphous transition metal sulfide and further comprising cations between layers of the amorphous transition metal sulfide, wherein the method comprises contacting a synthetic transition metal-sulfide cluster with an oxidizing agent in the presence of a polar aprotic solvent and an alkali metal salt, an alkaline earth metal salt, or an organic salt. In some embodiments, the cations between layers of the amorphous transition metal sulfide are solvated cations.
In some embodiments, the synthetic transition metal-sulfide cluster is a 4Fe-4S cluster. In some embodiments, the 4Fe-4S cluster is [Fe4S4(SC6H5)4](C16H36N)2. In some embodiments, the oxidizing agent is selected from the group comprising tetracyanoethylene (TCNE), iodine, ferrocenium tetrafluoroborate (FeCp2BF4), tetracyanoquinodimethane (TCNQ), and lithium chloroanilate (Li2C6Cl2O4).
In some embodiments, the polar aprotic solvent is DMF and/or the contacting is performed at a temperature between about 25° C. and about 140° C. In some embodiments, interlayer spacing between consecutive layers is tuned based on selection of the salt and/or solvent. In some embodiments, the presently disclosed subject matter provides a lamellar transition metal sulfide composition prepared by contacting a synthetic transition metal-sulfide cluster with an oxidizing agent in the presence of a polar aprotic solvent and an alkali metal salt, an alkaline earth metal salt, or an organic salt.
In some embodiments, the presently disclosed subject matter provides a composite comprising (i) a conductive substrate and (ii) a polymeric binder combined with a lamellar transition metal sulfide composition further comprising cations between layers of the amorphous transition metal sulfide. In some embodiments, the conductive substrate is carbon fiber paper or carbon black. In some embodiments, the polymeric binder is poly(vinylidene fluoride) (PVDF), natural rubber, or synthetic rubber.
In some embodiments, the presently disclosed subject matter provides an electrode comprising a lamellar transition metal sulfide composition, wherein the lamellar transition metal sulfide composition further comprises cations between layers of the amorphous transition metal sulfide, or a composite of said lamellar transition metal sulfide composition. In some embodiments, the presently disclosed subject matter provides a metal-ion battery comprising said electrode.
In some embodiments, the battery is a lithium-, sodium-, or magnesium-ion battery. In some embodiments, the battery is a lithium-ion battery and the electrode has a discharge capacity of at least about 450 mAh/g or more for at least a first 17 cycles. In some embodiments, said electrode exhibits a cycling stability of at least 90% for at least 17 cycles when cycled between 1.0 volts (V) and 3.0 V.
In some embodiments, the presently disclosed subject matter provides a capacitor comprising an electrode comprising a lamellar transition metal sulfide composition, wherein the lamellar transition metal sulfide composition further comprises cations between layers of the amorphous transition metal sulfide, or a composite of said lamellar transition metal sulfide composition. In some embodiments, the electrode has a specific capacitance of about 100 F/g.
In some embodiments, the presently disclosed subject matter provides a metal-ion/sulfur battery comprising an electrode comprising a lamellar transition metal sulfide composition, wherein the lamellar transition metal sulfide composition further comprises cations between layers of the amorphous transition metal sulfide, or a composite of said lamellar transition metal sulfide composition. In some embodiments, the metal is lithium, sodium, or magnesium.
Accordingly, it is an object of the presently disclosed subject matter to provide lamellar transition metal sulfide compositions that comprise interlayer cations, methods of synthesizing such compositions, and composites, electrodes, batteries, and capacitors comprising such compositions.
An object of the presently disclosed subject matter having been stated hereinabove, and which is achieved in whole or in part by the presently disclosed subject matter, other objects will become evident as the description proceeds hereinbelow.
The presently disclosed subject matter will now be described more fully. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein below and in the accompanying Examples. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art.
All references listed herein, including but not limited to all patents, patent applications and publications thereof, and scientific journal articles, are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, or teach methodology, techniques, and/or compositions employed herein.
Throughout the specification and claims, a given chemical formula or name shall encompass all optical and stereoisomers, as well as racemic mixtures where such isomers and mixtures exist.
While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs.
Following long-standing patent law convention, the terms “a,” “an,” and “the” refer to “one or more” when used in this application, including the claims.
The term “and/or” when used in describing two or more items or conditions, refers to situations where all named items or conditions are present or applicable, or to situations wherein only one (or less than all) of the items or conditions is present or applicable.
The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” As used herein “another” can mean at least a second or more.
The term “comprising,” which is synonymous with “including,” “containing,” or “characterized by” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. “Comprising” is a term of art used in claim language which means that the named elements are essential, but other elements can be added and still form a construct within the scope of the claim.
As used herein, the phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
As used herein, the phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
With respect to the terms “comprising,” “consisting of,” and “consisting essentially of,” where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.
Unless otherwise indicated, all numbers expressing quantities of size, temperature, time, weight, volume, concentration, capacitance, specific capacity, discharge capacity, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.
As used herein, the term “about,” when referring to a value is meant to encompass variations of in one example ±20% or ±10%, in another example ±5%, in another example ±1%, and in still another example ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods.
Numerical ranges recited herein by endpoints include all numbers and fractions subsumed within that range (e.g. 1 to 5 includes, but is not limited to, 1, 1.5, 2, 2.75, 3, 3.90, 4, and 5).
Transition metals feature prominently in cathode materials due to their facile redox chemistry which facilitates charging and discharging. In particular, Co has formed the basis of the most successful commercial cathodes, but the cost and abundance of Co are major drivers of the expense of cathode materials.9 Fe is the most abundant transition metal, and, therefore, could be useful in reducing cost. However, the charge density of materials such as LiFePO4 has been a drawback to their use.8
Iron sulfides are a potentially attractive class of materials due to a higher potential charge density as well as favorable charge and ion transport properties imbued by sulfur (S). Indeed, pyrite-based electrodes were some of the earliest materials studied in LIBs and similar iron sulfide-based materials have attracted a great deal of recent attention.10,11 Despite this, significant challenges remain, notably cycling life, volume expansion, and charge density. One way to address these issues is the use of layered iron sulfides. A prime example of these materials is Li2FeS2, although other layered materials have also been reported more recently.10,12 The layered nature of these materials should enable better ion transport and facilitate volume changes more readily. Nevertheless, there have only been limited investigations into the applicability of layered sulfides as battery components.13 Furthermore, while Li2FeS2 is nominally layered, it is a close packed structure with potentially poor ion transport characteristics.
As described hereinbelow, the presently disclosed subject matter provides, in some embodiments, lamellar transition metal sulfide compositions (i.e., synthetic lamellar transition metal sulfide compositions) further comprising cations. The cations can be present between layers of the transition metal sulfide. In some embodiments, the cations are solvated. In some embodiments, the lamellar transition metal sulfide further comprises solvated metal cations (e.g., solvated alkali metal cations or solvated alkaline metal cations) or organic cations (e.g., tetraalkylammonium cations) between layers of the transition metal sulfide. The lamellar transition metal sulfide compositions can have tunable layer spacing and composition. In particular, the lamellar structure and flexible redox characteristics make these materials ideal candidates for anode or cathode applications. See
In some embodiments, the presently disclosed transition metal sulfide materials have a lamellar structure comprising transition metal sulfide layers (e.g., amorphous transition metal sulfide layers) with cations positioned between the layers. The distance between consecutive layers can be varied depending upon factors such as the identity of the cation and/or the solvation of the cation. The ability to vary the spacing between layers can, for example, provide flexible lattice parameters that can facilitate the large volume changes associated with sulfur cathodes.
In some embodiments, the transition metal is a first-row transition metal or a combination thereof, i.e., scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), or a combination thereof. In some embodiments, the transition metal sulfide is an iron sulfide. In some embodiments, the transition metal sulfide can comprise metal centers of more than one oxidation state and/or more than one type of coordination geometry. In some embodiments, the stoichiometric ratio of transition metal to sulfur is less than 1. In some embodiments, the ratio of transition metal to sulfur can be adjusted to increase the sulfur content, e.g., by the inclusion of additional sulfide ions (such as by exposure of the transition metal sulfide to a solution of S2− ions). In some embodiments, as further described hereinbelow, the inclusion of additional sulfide ions can add additional negative charge to the transition metal sulfide layers, which can, for example, increase the charge storage density of the layers.
In some embodiments, the transition metal sulfide can comprise iron sulfide comprising both Fe(II) and Fe(III). In some embodiments, the ratio of Fe(II) and Fe(III) can be varied to include relatively more Fe(III), for example, to provide higher charge storage density via reduction to Fe(II) during discharge from electrodes prepared from the materials. In some embodiments, the iron sulfide comprises both tetrahedral and octahedral coordination sites. In some embodiments, the iron sulfide has a stoichiometric ratio of iron (Fe) to sulfur (S) that is less than 1. In some embodiments, the ratio of Fe to S in the presently disclosed synthetic lamellar iron sulfides is between that for the naturally occurring iron sulfides Tochilinite or Mackinawite (i.e., about 1) and Greigite (i.e., about 0.75). In some embodiments, the ratio of Fe to S is about 0.75.
In some embodiments, the cations can include, but are not limited to, monocations or dications. In some embodiments, the monocations or dications are cations (e.g., solvated cations) of an alkali metal or an alkaline earth metal (e.g., lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba)). In some embodiments, the cations are selected from Li+, Na+. K+, Mg2+, and Ca2+. However, in some embodiments, the lamellar transition metal sulfides can also comprise or consist of organic cations (e.g., tetraalkylammonium cations, etc.) located between the layers. The inclusion of organic cations, for instance, can keep the layers of the lamellar transition metal sulfide separate under cycling conditions.
In some embodiments, the cations are solvated by a polar aprotic solvent. As used herein, the term “polar aprotic solvent” refers to a solvent having a high dielectric constant and high dipole movement and that lacks an acidic hydrogen. Suitable polar aprotic solvents include, but are not limited to, carbonate solvents, such as, but not limited to, cyclic and noncyclic alkyl carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC); alkyl esters (e.g., methyl formate, ethyl formate, methyl acetate, and ethyl acetate); ethers, including cyclic ethers (e.g., 1,3-dioxolane (DN), tetrahydrofuran (THF), 2-methyl tetrahydrofuran (Me-THF), and 2,5-dimethyl tetrahydrofuran) and noncyclic aliphatic ethers (e.g., diethyl ether and 1,2-dimethoxyether (DME)); lactones (e.g., valerolactone and γ-butyrolactone), dimethyl formamide (DMF), dimethylacetamide (DMAc), acetone, acetonitrile (MeCN), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). In some embodiments, the polar aprotic solvent is selected from a carbonate, an ether, DMF, and MeCN.
As indicated above, the particular cation or solvent can be selected to obtain a desired interlayer spacing between the layers of transition metal sulfide (i.e., the sheets of transition metal sulfide). For example, for a lamellar iron sulfide of the presently disclose subject matter, inclusion of solvated Li+ ions where the solvent is DMF can provide an interlayer spacing of about 16 angstroms (Å). Upon drying, the interlayer spacing of the same material is reduced to about 10 Å.
In some embodiments, the presently disclosed subject matter provides a method of preparing a lamellar transition metal sulfide composition comprising layers of a transition metal sulfide (e.g., an amorphous transition metal sulfide) and further comprising cations (e.g., solvated cations) between layers of the transition metal sulfide via solvothermal decomposition. In some embodiments, the method comprises contacting a transition metal complex with a polar aprotic solvent in the presence of salt. In some embodiments, the transition metal complex is a bis- or tris(dialkyldithiocarbamato)transition metal complex or a bis- or tris(alkylxanthato)transition metal complex. In some embodiments, the salt is an alkali metal salt or an alkaline earth metal salt. In some embodiments, the salt is an organic salt (e.g., a tetraalkylammonium salt). In some embodiments, an excess of salt is present compared to the transition metal complex. In some embodiments, 2, 3, 4, 5 or more molar equivalents of the salt are present compared to the transition metal complex.
The contacting can be performed at any suitable temperature. In some embodiments, the contacting is performed at a temperature between ambient temperature and the boiling point of the solvent or just below (e.g., about 5° C. or about 10° C. lower than the boiling point of the solvent). In some embodiments, the contacting is performed at a temperature of at least about 25° C. In some embodiments, the contacting is performed at a temperature of between about 25° C. and about 140° C. Typically, increasing the temperature can result in a faster conversion of the starting material to the product. In some embodiments, changing the temperature can alter the ordering or crystallinity of the resulting transition metal sulfide layers.
In some embodiments, the transition metal complex is a bis- or tris (diethyldithiocarbamato) metal complex or a bis- or tris(ethylxanthato) transition metal complex. In some embodiments, the transition metal complex is selected from tris(diethyldithiocarbamato)iron(III) (Fe(DEDTC)3) and tris(ethylxanthato)iron(III) (Fe(EX)3).
In some embodiments, the alkali metal salt or the alkaline earth metal salt comprises a lithium, sodium, potassium, magnesium, or calcium salt. In some embodiments, the organic salt comprises a tetraalkylammonium salt (e.g., a tetramethylammonium (TMA) salt or a tetraethylammonium salt). Suitable anions for the salts include, but are not limited to triflate (OTf), a halide (e.g., chloride), and hexafluorophosphate. In some embodiments, the polar aprotic solvent is a carbonate, an ether, DMF, or acetonitrile. In some embodiments, the polar aprotic solvent is selected from DMF and THF. As noted above, interlayer spacing between consecutive layers of the transition metal sulfide can be dependent upon the identity of the cation and/or solvent present. Thus, in some embodiments, the interlayer spacing is tuned based on selection of a particular alkali metal salt, alkaline earth salt, or organic salt and/or based on the selection of a particular solvent.
In some embodiments, an additional sulfur source is added. For instance, in some embodiments, the contacting is performed in the presence of a soluble sulfide source (i.e., a sulfide source that is soluble in the polar aprotic solvent). In some embodiments, the soluble sulfide source is an alkali metal sulfide, S8, a thiourea, or 1,2,4,5-tetrazinane-3,6-dithione. The inclusion of additional sulfide can result in the net adjustment of the transition metal:S ratio. This can be used, for example, to alter the morphology of the layers of the transition metal sulfide. See
In some embodiments, the presently disclosed subject matter provides a lamellar transition metal sulfide composition prepared by solvothermal decomposition of a transition metal complex in the presence of a salt.
In some embodiments, the presently disclosed subject matter provides a method of preparing a lamellar transition metal sulfide composition comprising layers of a transition metal sulfide (e.g., an amorphous transition metal sulfide) and further comprising cations (e.g., solvated cations) between layers of the transition metal sulfide, wherein the method comprises contacting a synthetic transition metal-sulfide cluster with an oxidizing agent in the presence of a polar aprotic solvent and a salt. In some embodiments, the salt is an alkali metal salt, an alkaline earth metal salt or an organic salt. In some embodiments, the transition metal sulfide cluster is a Fe4S4 cluster. In some embodiments, the transition metal sulfide cluster is [Fe4S4(SC6H5)4](C16H36N)2 (i.e., [Fe4S4(SPh)4](TBA)2). Suitable oxidizing agents include, but are not limited to, tetracyanoethylene (TCNE), iodine, ferrocenium tetrafluoroborate (FeCp2BF4), tetracyanoquinodimethane (TCNQ), and lithium chloroanilate (Li2C6Cl2O4).
As with the solvothermal decomposition method, in some embodiments, the alkali metal salt or the alkaline earth metal salt comprises a lithium, sodium, potassium, magnesium, or calcium salt. In some embodiments, the organic salt comprises a tetraalkylammonium salt (e.g., a TMA salt). Suitable anions for the salts include, but are not limited to triflate (OTf), a halide (e.g., chloride), and hexafluorophosphate. In some embodiments, the polar aprotic solvent is a carbonate, an ether, DMF, or acetonitrile. In some embodiments, the polar aprotic solvent is selected from DMF and THF. In some embodiments, the polar aprotic solvent is DMF. In some embodiments, the contacting is performed at a temperature between about 25° C. and about 140° C. As also noted above with regard to the compositions and solvothermal decomposition-based methods, interlayer spacing between consecutive layers of the transition metal sulfide can be dependent upon the identity of the cation and/or solvent present. Thus, in some embodiments, the interlayer spacing is tuned based on selection of a particular alkali metal salt, alkaline earth salt, or organic salt and/or based on the selection of a particular solvent.
In some embodiments, the presently disclosed subject matter provides a lamellar transition metal sulfide composition prepared by oxidizing a synthetic transition metal-sulfide cluster with an oxidizing agent in the presence of a polar aprotic solvent and a salt.
In some embodiments, the presently disclosed subject matter provides composites comprising the lamellar transition metal sulfide compositions of the presently disclosed subject matter. For example, the lamellar transition metal sulfides can be used to coat a conductive substrate, such as, a carbon-based substrate, such as a carbon fiber paper or carbon black. To facilitate the coating, the lamellar transition metal sulfide can be mixed with a polymeric binder (e.g., poly(vinylidene fluoride) (PVDF), natural rubber, or synthetic rubber). Thus, in some embodiments, the composite can comprise a conductive substrate coated with a mixture comprising a polymeric binder and a lamellar transition metal sulfide of the presently disclosed subject matter. The composites can be prepared, for instance, by dip-coating the substrate or painting the substrate with a slurry of the binder and the lamellar transition metal sulfide prepared in a polar aprotic solvent. In some embodiments, the resulting coating can comprise about 10% by weight of the binder.
In some embodiments, the presently disclosed subject matter provides an electrode comprising a lamellar transition metal sulfide composition of the presently disclosed subject matter. For example, in some embodiments, the electrode can comprise a composite of a presently disclosed lamellar transition metal sulfide as described hereinabove. In some embodiments, the presently disclosed subject matter provides a battery comprising an electrode comprising a lamellar transition metal sulfide composition of the presently disclosed subject matter or a composite thereof. The use of the material for battery electrodes allows it to be used to store electrical energy. Lithium- and sodium-ion battery materials with high capacity and stability have significant commercial potential, as lithium-ion batteries in particular are widely used in portable electronics, grid storage, and electric vehicles.
In some embodiments, the battery is a lithium-ion battery, a sodium-ion battery, or a magnesium-ion battery. In some embodiments, the battery is a lithium-ion battery having a discharge capacity of at least about 450 mAh/g for at least the first 17 cycles. In some embodiments, the battery exhibits cycling stability (e.g., of at least about 90%) for at least about 17 cycles when cycled between about 1.0 volts (V) and about 3.0 V. In some embodiments, the presently disclosed subject matter provides a metal-ion/sulfur battery comprising an electrode comprising a lamellar transition metal sulfide composition of the presently disclosed subject matter or a composite thereof. In some embodiments, the metal is lithium, sodium or magnesium.
The pseudocapacitance of electrodes made from the presently disclosed materials allow them to be used to store charge, for example, in a capacitor or supercapacitor device. The electrical conductivity of the material allows efficient charging/discharging of the electrode. Current and emerging applications for supercapacitors include computers, electric and fossil fuel vehicles, and storage of intermittent renewable energy. The simple synthesis of the material from low-cost materials could allow the presently disclosed materials to compete with existing supercapacitor technologies. Accordingly, in some embodiments, the presently disclosed subject matter provides a capacitor comprising an electrode comprising a lamellar transition metal sulfide composition of the presently disclosed subject matter or a composite thereof. In some embodiments, the electrode has a specific capacitance of about 100 F/g.
The presently disclosed lamellar transition metal sulfides are described further hereinbelow with regard to various exemplary iron sulfide embodiments. Approaches for the synthesis of the lamellar iron sulfides are shown in
The material is obtained as a bulk powder or as a thin film on a substrate. The powder can be mixed with a polymeric binder and solvent to form a slurry and coated onto a conductive substrate (such as carbon fiber paper). Both the slurry- and thin film-coated substrates display pseudocapacitive electrochemical behavior over a potential window of about 1 V with specific capacitance of about 100 F/g (for material synthesized with Li). The bulk powder displays moderate electrical conductivity of about 0.5 S/cm at room temperature.
The exemplary lamellar iron sulfides comprise highly Earth-abundant elements (Fe and S) and can be prepared, as described above, from inexpensive commodity chemicals (e.g., potassium or sodium ethyl xanthate, iron (III) chloride, and a metal triflate salt). In contrast to previously reported iron sulfides, the lamellar structure of the material is expected to allow for easy/fast ion intercalation, which can increase the ability of the material to store charge in a capacitor. The specific capacitance of the material in preliminary measurements is comparable to other supercapacitor materials.
Pyrite has been tested extensively in lithium-ion batteries but suffers from degradation with cycling. The presently disclosed materials have a layered structure that can allow more reversible addition and removal of lithium ions, potentially improving stability on cycling. The initial capacity of the material is also higher than materials currently used in commercial lithium-ion batteries.
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter.
To synthesize the iron sulfides, precursor Fe(DEDTC)3 was heated in dimethyl formamide with excess LiOTf (LiOTf=LiCF3SO3; DEDTC=diethyl dithio carbonate).14 X-ray powder diffraction (XRPD) analysis of the resulting deposit includes a specific peak position indicative of a lamellar structure. See
Similarly, precursor Fe(EX)3 was contacted with excess (e.g., 5 equivalents) LiOTf in DMF. At ambient temperature, the reaction was slow (72 h), but lead to uniform coatings due to a lack of thermal gradient. At 50° C., the reaction was faster (16 h) and led to a bulk powder. Compared to the reaction with Fe(EX)3 as the precursor, solvothermal decomposition using Fe(DEDTC)3 involved higher temperatures (e.g. 140° C.) and longer reaction times. In either case, the resulting material is air sensitive. XRPD analysis of the resulting wet material from solvothermal decomposition of Fe(EX)3 is shown in
Lamellar iron sulfide was also prepared from oxidation of Fe4S4(SPh)4](TBA)2 with TCNE in DMF. XRPD analysis of the resulting material is shown in
To investigate the effects of salt addition during synthesis, solvothermal decomposition was performed in the absence of added salt, with 5 equivalents of LiOTf (compared to the metal complex), 40 equivalents of LiOTf or with 5 equivalents of LiCl. It can be noted that the sample prepared without added salt can contain Me2NH2+ from the DMF solvent used in the synthesis. Preparation in the presence of the LiCl salt showed low yield. However, the XRPD spectra of the samples prepared in the presence of both lithium salts were very similar. See
The effect of changing the cation in the salt was also investigated. Lamellar iron sulfides were prepared in the presence of triflate salts of Li, Na, and K, as well as in the presence of a salt of an organic cation, tetramethylammonium (TMA+). XRPD spectra of the resulting lamellar iron sulfides are shown in
In addition to monocations, the inclusion of dications, including Mg2+ and Ca2+, was investigated. Similar solids were obtained in these cases, although the materials were less crystalline. Lamellar peaks were still observed however, and the materials are still conductive. These observations support that a similar lamellar structure is being formed with dications.
The present synthetic lamellar iron sulfides were next compared to a naturally occurring iron sulfide with ordered lamellar structure, i.e., Smythite. The calculated XRPD spectrum of Smythite is shown in
To further verify the structure of the material, X-ray absorption (XAS) measurements including extended X-ray absorbance fine structure analysis (EXAFS) was conducted. See
In summary, the data suggests that the synthetic iron sulfides comprise poorly ordered FeS lamellae with mostly tetrahedral, but also octahedral coordination, with solvated ions (but probably just cations) between lamellae. For material synthesized with a lithium salt in DMF, the distance between lamellae in a wet state was about 16 Å, and about 10 Å after drying.
An initial electronic analysis was carried out on a synthetic lamellar iron sulfide material to determine its bulk conductivity. A crude pressed pellet conductivity of 0.4(2) S/cm was estimated, which suggests either a metallic or highly doped semi-conductor band structure. Initial experiments were performed to estimate the band gap of the material via a Tauc direct band gap from UV-visible absorption data. See
XAS analysis was performed to help determine the oxidation state(s) of the Fe centers in the lamellar material. While XAS analysis was generally consistent with an Fe(II) or Fe(III) oxidation state, the compositional analysis suggests the presence of Fe(III) states. Alternatively, there could also be incorporation of additional organic cations as mentioned. XAS only gives an average estimate of oxidation state, so Mössbauer spectroscopy was also performed to better understand the distribution of oxidation states in these materials. See
In addition to the characterization of the electronic structure of this material, its electrochemical properties were also characterized. The high conductivity and lamellar structure of this material make it a target for capacitor and battery applications. These properties were initially studied by cyclic voltammetry (CV). See
It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.
The presently disclosed subject matter claims the benefit of U.S. Provisional Patent Application Ser. No. 62/907,979 filed Sep. 30, 2019, the disclosure of which is incorporated herein by reference in its entirety.
This invention was made with government support under grant number DESC0019215 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/053252 | 9/29/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62907979 | Sep 2019 | US |
