WO2013003836A9 - Hybrid materials and nanocomposite materials, methods of making same, and uses thereof - Google Patents

Abstract

Hybrid materials and nanocomposite materials, methods of making and using such materials. The nanoparticles of the nanocomposite are formed in situ during pyrolysis of a hybrid material comprising metal precursor compounds. The nanoparticles are uniformly distributed in the carbon matrix of the nanocomposite. The nanocomposite materials can be used in devices such as, for example, electrodes and on-chip inductors.

Description

HYBRID MATERIALS AND NANOCOMPOSITE MATERIALS, METHODS OF MAKING SAME, AND USES THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional patent application nos.

61/503,085, filed June 30, 2011, and 61/578,464, filed December 21, 2011, the disclosures of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under contract no. DE- SC0001086 awarded by the Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] The present invention generally relates to composite materials and methods of making such composite materials. More particularly, the present invention relates to in situ formation of nanoparticles embedded in a carbon matrix.

BACKGROUND OF THE INVENTION

[0004] Rising energy prices and unmet demand for secondary batteries with higher energy & power densities, higher operating voltages, improved cycling stability, enhanced safety, and lower initial and life cycle costs has increased interest in lithium ion batteries (LIB). LIBs demonstrate higher energy density, higher operating voltage and lower self- discharge rates compared to conventional rechargeable batteries. They have consequently received intense scientific and commercial interest for portable electronics applications since the early 1990s. In recent years, the demand for secondary (rechargeable) batteries with better performance, higher charge -rate capability, improved cycling stability, and enhanced safety has steadily increased to meet new needs for smaller, lighter, more powerful electronic devices, as well as to accommodate growing interests in hybrid electric and plug-in hybrid electric vehicles.

[0005] A crucial performance criterion is the cyclability of the electrode materials and a key issue in capacity retention lies in the large structural and morphological changes many electrode materials undergo during cyclic insertion and deinsertion of lithium. Significantly, these changes occur in materials following rather different lithiation mechanisms, including alloying, conversion, and intercalation; implying that general solutions are required. Despite the sustained efforts of research groups worldwide, the performance achieved with the current LIB platforms based on a graphite anode and a lithium metal oxide (e.g., L1C0O₂) cathode is believed to be close to its limits due to the limited gravimetric capacity and rate capability of graphitic carbon as the anode material. BRIEF SUMMARY OF THE INVENTION

[0006] The present invention provides hybrid materials, nanocomposite materials, methods of making such materials. Also provided are uses of such materials. The hybrid/m situ approach of the instant invention provides homogeneous dispersion of the metal precursor in the polymer matrix (e.g., a cross-linked polymer matrix).

[0007] In an aspect, the present invention provides a hybrid material. The hybrid material is a polymer comprising a metal precursor. The metal precursor is chemically bonded to the polymer. During pyrolysis of the hybrid material, nanoparticles are formed from the metal precursors. In an embodiment, the step of pyrolysing the hybrid material is carried out such that a nanocomposite material comprising a plurality of nanoparticles, the nanoparticles being formed from the metal component of the one or more metal precursor compounds, embedded in a carbon matrix is formed.

[0008] In an aspect, the present invention provides a nanocomposite material. The nanocomposite material has nanoparticles (e.g., metal nanoparticles, metal oxide

nanoparticles, metal halide (e.g., metal fluoride) nanoparticles, metal boride nanoparticles, metal phosphate nanoparticles) embedded in a continuous phase of carbon (i.e., a carbon matrix).

[0009] In an aspect, the present invention provides methods of forming a material.

The material can be a hybrid material or nanocomposite material as described herein.

[0010] In an embodiment, the method for forming a material comprises the steps of: contacting one or more monomers, one or more metal precursor compounds, optionally, an initiator, and, optionally, one or more solvents to form a reaction mixture, heating the reaction mixture such that a hybrid material comprising a plurality of metal precursor compounds chemically bonded to the polymer matrix is formed and, optionally, isolating the hybrid material. In an embodiment, the method further comprises the step of pyrolysing the hybrid material, such that a nanocomposite material comprising a plurality of metal oxide nanoparticles (or metal nanoparticles) embedded in a carbon matrix is formed.

[0011] In various embodiments, the nanocomposite material is subjected to various ex situ treatments such that nanoparticles of the resulting nanocomposite have different chemical compositions than the starting nanoparticles. For example, metal oxide nanoparticles are reacted such that metal, metal halide, metal sulfide, and metal phosphate nanoparticles are formed or metal sulfide nanoparticles are reacted such that metal oxides, metal halide, metal, or metal phosphate nanoparticles are formed.

[0012] In an aspect, the present invention provides devices comprising the hybrid material or nanocomposite materials described herein. Examples of such devices include batteries (e.g., secondary batteries), on-chip inductors.

BRIEF DESCRIPTION OF THE FIGURES

[0013] Figure 1. An example of an in situ synthesis scheme for Fe₃0₄-C

nanocomposite.

[0014] Figure 2. Representative XRD pattern for the Fe₃0₄-C composite created by pyrolysing the as-prepared PAN-Fe(undec)₃ complex.

[0015] Figure 3. Examples of (a) Morphology of polymer-iron complex; (b) morphology of Fe₃0₄-C composite; (c) EDS spectrum for the polymer-iron complex; and (d) TGA data for the Fe₃0₄-C composite.

[0016] Figure 4. Representative Raman spectrum for the Fe₃0₄-C composite, deconvoluted into peaks for graphitic carbon, disordered graphite lattices and amorphous carbon.

[0017] Figure 5. Representative cyclic voltammograms and voltage-capacity profiles for Fe₃0₄-C nanocomposites.

[0018] Figure 6. Representative cycling performance for (a) Fe₃0₄-C composites run at 1 C (924 mA h g^_1); (b) composite run at 0.2 C; (c) composite run at charging rates; (d) bare Fe₃0₄ nanoparticles run at 1 C; and (e) bare carbon made from pyrolysis of PAN-DVB run at 1 C.

[0019] Figure 7. Representative nitrogen adsorption isotherms and pore size distribution for the Fe₃0₄-C composite.

[0020] Figure 8. Representative (a) X-Ray diffractogram and (b) TEM image for

MnO-C composite.

[0021] Figure 9. Representative (a) cyclic voltammograms, (b) voltage-capacity profiles of MnO-C composite and (c) cycling performance of MnO-C composite at 1 C (755 mA h g^_1), 0.2 C and at varied charging rates, and cycling performance of pure MnO. [0022] Figure 10. Representative XRD patterns of nanocomposites embedding the nanoparticles of the following phases: Fe, Fe₃0₄, Fe₂C>3, MnO, M^C , Sn, Co, C0₃O4, Cu, CuO; an example of a TEM image of Cu@C composite.

[0023] Figure 11. Representative XRD patterns of nanocomposites embedding the nanoparticles of the following phases: Ti0₂(anatase), V2O5, ZnO, Zr0₂; an example of a TEM image of Ti0₂@C composite.

[0024] Figure 12. Scheme for synthesizing Co@C and CoS@C nanocomposites; representative XRD patterns of Co@C and CoS@C nanocomposites.

[0025] Figure 13. Representative XRD pattern for Fe₃0₄@C and LiFeP0₄@C nanocomposites.

[0026] Figure 14. Representative TEM image for LiFeP0₄@C nanocomposites.

[0027] Figure 15. Representative XRD pattern for Mn_{0 75}Fe_{0 25}0 @ C and

LiMn_{0 75}Fe_{0 25}P0₄@C nanocomposites.

[0028] Figure 16. Representative TEM image for Mn_{0 75}Fe_{0 25}O@C nanocomposite.

[0029] Figure 17. Representative TEM image for LiMn_{0 75}Fe_{0 25}PO₄@C

nanocomposite.

[0030] Figure 18. Representative scanning electron micrographs of (a) MS-22, (d)

MS-0; transmission electron micrographs of (b and c) MS-22, (e and f) MS-0; insets of (b) shows MoS₂ nanosheet; SAED patterns of MS-22 and MS-0 in the insets of (c) and (f) respectively.

[0031] Figure 19. An example of a schematic of the synthesis of (A) MoS₂-carbon nanostructure and (B) pure MoS₂.

[0032] Figure 20. Representative galvanostatic charge-discharge curves of (a) MS-0 and (b) MS-22 at a current density of 100 mA g^_1; cyclic voltammetry (CV) curves of (c) MS-0 and (d) MS-22 at a scan rate of 0.2 mV s^"1 ; (e) cycling stability of pure MoS₂ and various MoS₂-carbon composites; (f) variation of discharge capacity as a function of carbon weight fraction.

[0033] Figure 21. Representative Ex situ X-ray diffraction patterns of (a) MoS₂- carbon (22 wt ) composite and (b) pure MoS₂ after 1^st discharge cycle. Peaks marked by * corresponds to Cu current collector; scanning electron micrographs of 1^st cycle discharged product of (c) MS-22 and (d) MS-0. [0034] Figure 22. Representative cycling stability of MS-22 with 0%, 10%, 25% and

50% carbon black in the electrode composition at various current rates in the range of 0.4-4 A g^"1.

[0035] Figure 23. Representative X-ray diffraction patterns of pure MoS₂ and MoS₂- carbon (22 wt %) composite.

[0036] Figure 24. Representative thermogravimetry analysis of pure MoS₂, MS-11,

MS-22, MS32 and MS-41.

[0037] Figure 25. Representative (a) N₂ adsorption/desorption isotherms and (b) pore size distribution of pure MoS₂, MS-22 and MS-41.

[0038] Figure 26. Representative transmission electron micrographs of (a) MS-11 and

(b) MS-32.

[0039] Figure 27. (a) Representative cycling stability of pure MS-22 with 0%, 10%,

25% and 50% carbon black in the electrode at a current rate of (a) 100 mAg^"1; (b) at various current rates in the range of 0.4-4 Ag^"1.

[0040] Figure 28. Representative cycling stability of 550 °C and 700 °C calcined

MoS₂-carbon (22 wt %) composite at a current rate of (a) 100 mAg^"1 ; (b) at various current rates in the range of 0.4-4 Ag^"1.

[0041] Figure 29. Representative SAED patterns of (a) pure MoS₂ and (b) MoS₂- carbon (22 wt %) composite.

[0042] Figure 30. An example of a schematic of synthesis process for creating organic-inorganic copolymer hybrids.

[0043] Figure 31. Representative TEM images of Fe₃C>4@C nanocomposite (A) before cycling and (B) after 100 charge-discharge cycles.

[0044] Figure 32. An example of an overview of the platform for synthesizing nanocomposites with embedded structures involving different classes of materials.

[0045] Figure 33. Representative powder XRD patterns (A), TEM images for Fe@C

(B) and FeS₂@C (C) composites and size distribution histograms for Fe@C (D) and FeS₂@C (E).

[0046] Figure 34. Representative (A) Cyclic voltammograms of FeS₂@C; (B) cycling performance of FeS₂@C and pristine FeS₂. Red cross indicates result from reference 28 (0.58C).

[0047] Figure 35. Representative (A) XRD pattern, (B) TEM image, (C) STEM image and (D) EDX spectrum for FeSn₂@C nanocomposite. [0048] Figure 36. Representative (A) Cyclic voltammograms of FeSn₂@C; (B) cycling performance of FeSn₂@C and pristine FeSn₂ at 0.1C.

[0049] Figure 37. Representative (A) XRD patterns of the embedded carbon composites involving iron/iron oxides; (B) TEM image of γ -Fe₂0₃@C composite; (C) and (D) XRD pattern and TEM image of V₂0₅@C composite; (E) and (F) XRD pattern and TEM image of Ti0₂@C composite.

[0050] Figure 38. Representative (A) Cyclic voltammograms of γ -Fe₂0₃@C; (B) cycling performance of γ -Fe₂0₃@C at 0.5C, 1C and 2C and pristine Fe₂0₃ at 0.5C.

[0051] Figure 39. Representative infrared spectra of crosslinked PAN-DVB, Fe(CioHi₉COO)3 and PAN-iron composite. Inset: close-up of 1600-1700 cm^"1, normalized using peak at 2930 cm^"1.

[0052] Figure 40. Representative oxidative TGA curves for FeS₂@C, FeSn₂@C and

7 -Fe₂0₃@C

[0053] Figure 41. Representative voltage-capacity profiles for FeS₂@C composite run at 0.2C and 1C.

[0054] Figure 42. Representative voltage-capacity profiles for FeSn₂@C composite run at O. lC.

[0055] Figure 43. Representative voltage-capacity profiles for γ -Fe₂C>3@C composite run at 0.5C, 1C and 2C. DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention provides hybrid materials, nanocomposite materials, methods of making such materials. Also provided are uses of such materials.

[0057] The hybrid/m situ approach of the instant invention provides homogeneous dispersion of the metal precursor in the polymer matrix (e.g., a cross-linked polymer matrix) and thus the pyrolysis of the hybrid is able to yield composites with particles uniformly dispersed in the matrix. Additionally, the synthesis of the composite via simultaneous creation of the active material and the carbon matrix reduces the complexity of synthesis procedure and lends itself to the development of low-cost/scalable production processes.

[0058] In an aspect, the present invention provides a hybrid material. The hybrid material is a polymer comprising a metal precursor. The metal precursor is chemically bonded to the polymer. During pyrolysis of the hybrid material, nanoparticles are formed from the metal precursors. In an embodiment, the hybrid material comprises a plurality of metal precursor compounds embedded in a polymer.

[0059] By chemically bonded it is meant that the metal precursor (i.e., a chemical moiety of or metal center of the metal precursor) is chemically bonded via a chemical bond (e.g., covalent bond, coordinate covalent bond, or ionic bond) to the polymer.

[0060] A variety of polymers can be used. Suitable polymers can be thermally degraded (i.e., pyrolysed) to provide a graphitic material or partially graphitic material. The resulting material is electrically conducting. The polymer can be a homopolymer or a copolymer. Examples of suitable polymers include poly (aery lonitrile), polyvinylpyrroilidone, polypyrrole, polyacetylene, polythiophene, polyphenylene vinylene, polyphenylene sulfide, polysaccharides (e.g., galactose, maltose, and glucose), acrylonitrile-divinylbenzene copolymer, phenol resin, and resorcinol-formaldehyde copolymer.

[0061] The metal precursor is a compound with a metal center and one or more ligands. The metal precursor compounds are chemically bonded to the polymer. The metal precursor is uniformly distributed throughout the polymer. The metal precursors form nanoparticles in situ during pyrolysis of the polymer. Depending on the components of the reaction mixture, it may be desirable the metal precursor be water soluble. The metal precursors are present in the hybrid material at from 10 % by weight to 90% by weight, including all integer % by weight values and ranges therebetween. Examples of suitable metal precursor compounds include metal carboxylates, metal coordination compounds (e.g., metal thiolates), amino acid metal salts, and other metal-organic compounds.

[0062] By uniformly distributed it is meant there is a homogeneous distribution of a preponderance of the metal precursors in the polymer-based hybrid materials, or a homogeneous distribution of a preponderance of the nanoparticles in the nanocomposite materials. For the hybrid materials, there is a substantial absence of phase separation (e.g., no observed phase separation) between the polymer and metal precursors and/or a substantial absence of metal precursor aggregates (e.g., no metal precursor aggregates are observed). For the nanocomposite materials, there is a substantial absence of phase separation between the carbon matrix and nanoparticles (e.g., no observed phase separation) and/or a substantial absence of particle-particle aggregates (e.g., no particle-particle aggregates are observed).

[0063] The metal precursor can be a metal carboxylate. In an embodiment, the metal carboxylate comprises an alkyl moiety. The alkyl moiety can be a C₆ to C30 alkyl moiety, including all integer number of carbons and ranges therebetween. The moiety can be branched or linear. The moiety can be substituted. For example, the alkyl moiety can be substituted with a reactive chemical moiety (e.g., a carbon-carbon double bond, and amine, hydroxyl, carboxylate groups and combinations of such groups (which can hydrogen bond with moieties in the polymer/monomer)) that can be incorporated in the polymer by a polymerization reaction. Examples of suitable metal carboxylates include alkyl metal carboxylates (e.g., iron undecylenate, manganese undecylenate, tin undecylenate, or vanadium undecylenate), metal citrates (e.g., iron citrate, manganese citrate, tin citrate, and vanadium citrate), amino acid metal salts (e.g., iron aspartate), and other metal-organic compounds (e.g., iron gluconate).

[0064] In an embodiment, the metal precursor has a chemical moiety that reacts with the polymer or monomer to form a covalent bond. For example, the metal precursor is a metal carboxylate (e.g., iron undecylenate, manganese undecylenate, tin undecylenate, or vanadium undecylenate) having a carbon-carbon double bond that is copolymerized with a monomer or monomers.

[0065] The metal precursor can be a metal coordination compound. In an

embodiment, the metal center (e.g., Mo) of the metal precursor (e.g., ammonium

molybdenum tertrathiolate) is chemically bound to the polymer via a coordinate covalent bond.

[0066] In an aspect, the present invention provides a nanocomposite material. The nanocomposite material has nanoparticles embedded (e.g., encapsulated) in a continuous phase of carbon (i.e., a carbon matrix). In an embodiment, the nanocomposite material comprises a plurality of nanoparticles embedded in a carbon matrix.

[0067] The nanocomposite materials can include a variety of nanoparticles. For example, the nanoparticles can be metal nanoparticles, metal oxide nanoparticles, metal halide (e.g., metal fluoride) nanoparticles, metal boride nanoparticles, metal phosphate nanoparticles, or combinations of such nanoparticles. The nanoparticles can include a variety of metals. The nanoparticles can have multiple metals (e.g., metal alloys and mixed metal oxides). In the case of multiple metals in the nanoparticles, depending on the composition the individual nanoparticles can have mixed composition (alloyed nanoparticles) or a mixture of nanoparticles with different composition. For example, Feo.75Mno.25O can provide alloyed nanoparticles and Sn/FeSn2 can provide a mixture of nanoparticles with different

compositions. The nanoparticles can be crystalline or amorphous.

[0068] Examples of suitable metal nanoparticles include Fe, Mn, and FeSn₂, FeNi₃,

Al, Sn, Ge, and Si. Examples of suitable metal oxides include Fe₂C>3 (e.g., γ- Fe₂C>3), Fe₃0₄, M₂Fe0₄ (M=Li, Na, K, Ag), CuO, Cu₂0, NiO, M-Ni0₂ (M = Li, Na, K), MnO, Mn₂0₄, Mn₂0₃, M-Mn₂0₄ (M = Li, Na, K), M0O₃, V₂0₅, Ti0₂, M₄Ti₅0i₂ (M = Li, Na, K, Ag), Sn0₂, SnO, (¾0₄, and MCo0₂ (M = Li, Na, K). Examples of suitable metal sulfides include MoS₂, M0S₃ FeS₂, FeS, Fe_!__xS(x=0-0.2), CoS, CuS, Cu₂S, TiS₂, and M₂S (M = Li, Na, K). Examples of suitable metal borides include TiB₂, VB₂, and LiBio- Examples of a suitable metals fluoride are CuF₂, FeF₂, and FeF₃. Examples of suitable metal phosphates include MFeP0₄ (M=Li, Na, K) and LiMn_xFe₁„_xP0₄.

[0069] The nanoparticles are present at 10 % by weight to 90 % by weight, including all integer % by weight values and ranges therebetween. In an example, the nanoparticles are present at 40 % by weight to 90 % by weight.

[0070] Based on the composition of the nanoparticles and the methods used to form the nanoparticles, the nanoparticles can have a variety of shapes and sizes. In various examples, the nanoparticles have a spherical shape (e.g., Fe₂C>3 nanoparticles) or a rectangular shape (e.g., MoS₂ nanoparticles). In the case of spherical nanoparticles, the diameter of the nanoparticles is from 5 nm to 500 nm, including all integer nanometer values and ranges therebetween, in size. In the case of rectangular nanoparticles, the nanoparticles have a length of 20 to 100 nm, including all integer nanometer values and ranges

therebetween, and a thickness of 5 to 20 nm, including all integer nanometer values and ranges therebetween. The size can be an average size. For example, the size of individual nanoparticles and the average nanoparticle size can be measured by transmission electron microscopy.

[0071] The nanoparticles have a narrow size distribution. For example, the nanoparticles have a polydispersity index of 1.001 to 1.05, including all values to 0.001 and ranges therebetween. In an embodiment, the nanoparticles are monodisperse (i.e., the fraction of nanoparticles within one standard deviation from the number average size is greater than or equal to 75%). In another embodiment, the fraction of nanoparticles within one standard deviation from the number average size is greater than or equal to 90%.

[0072] The nanoparticles are embedded in a carbon matrix. The carbon matrix is a partially graphitic or graphitic material. The graphitic material is a material consisting of graphite. The partially graphitic material is a material comprising graphite that may also contain disordered graphitic lattices and/or amorphous carbon. The presence of graphite, disordered graphitic lattices and/or amorphous carbon can be determined by techniques such as, for example, XRD and Raman spectroscopy. The carbon matrix is porous and amorphous. Aggregation of the nanoparticles in the carbon matrix is not observed (e.g., by TEM, SEM, or light microscopy). For example, the carbon matrix is formed by pyrolysing a hybrid material as described herein.

[0073] The carbon matrix can have a range of porosity based the materials and conditions used to form the matrix. In various examples, the pores of the carbon matrix are less than lOOnm, less than 20nm, or less than 5nm.

[0074] The nanocomposite materials exhibit desirable properties. The nanocomposite material is conductive. The material can have a conductivity of 10^~5 to 100 S/cm. The material can have a Vickers Hardness of the composite is 1 to 40 GPa. The material can have

1/2

a fracture toughness of the composite is 5 to 25 MPa m . In various examples, the capacity retentions of the composites in lithium-ion batteries is greater than 90%, greater than 95%, greater than 98% in 100 cycles at a 1C charge/discharge rate.

[0075] In an aspect, the present invention provides methods of forming a material.

The material can be a hybrid material or nanocomposite material as described herein. In an embodiment, the hybrid material is made by a method described herein. In an embodiment, the nanocomposite material is made by a method described herein.

[0076] In an embodiment, the method for forming a material comprises the steps of: contacting one or more monomers, one or more metal precursor compounds, optionally, an initiator, and, optionally, one or more solvents to form a reaction mixture, heating the reaction mixture such that a hybrid material comprising a plurality of metal precursor compounds chemically bonded to the polymer matrix is formed and, optionally, isolating the hybrid material.

[0077] In an embodiment, the reaction mixture comprises: a first (e.g., bulk) monomer (e.g., acrylonitrile), optionally, a second (vinyl or cross-linking) monomer (e.g., divinyl benzene), a metal precursor compound (metal carboxylate) (e.g., iron undecylenate), an initiator (e.g., AIBN), a (anionic) surfactant (e.g., sodium dodecyl sulfate), water, and one or more organic solvents such that a reaction mixture that is an aqueous emulsion is formed. In this embodiment, the reaction mixture is, optionally, subjected to high-shear mixing such that a miniemulsion having oil-in-water droplets with an average size of 0.01 microns to 0.5 microns if formed. For example, high shear mixing (for bench-top scale synthesis) can be provided by a sonication horn operated at 500W and at 20kHz with 50% amplitude. A larger scale reaction may require higher power to achieve the desired shear.

[0078] In another embodiment, the reaction mixture comprises: a first (e.g., bulk) monomer (e.g., resorcinol), and, optionally, a second (bulk) monomer (e.g., formaldehyde), a metal precursor compound (e.g., ammonium tetrathiomolybdate), and water. [0079] In an embodiment, the reaction mixture comprises a plurality (e.g., two, three, or four) of metal precursors, where the metal precursors each comprise a different metal.

[0080] The hybrid material can be pyrolysed to form a nanocomposite material.

Nanoparticles are formed in situ from the metal precursor compounds as a result of the pyrolysis process. The pyrolysis process can be carried out in a single step or can have multiple steps. For example, carbonization can comprise consecutive, stabilization, carbonization, and graphitization steps. The determination of pyrolysis conditions is material dependent and is within the purview of one having skill in the art. For example, a single step pyrolysis step can be from 500 to 900 °C, including all values to the degree Celsius and ranges therebetween. For example, a multiple step pyrolysis can be 320°C for lhour for stabilization and 500°C for 2hrs for carbonization. Higher temperatures may be required for complete graphitization.

[0081] The pyrolysis step (or one of the steps of a multiple step pyrolysis) can be carried out in an atmosphere comprising a variety of gases. A mixture of gases can be used. For example, the pyrolysis step can be carried out in air (or an oxygen containing atmosphere) or an inert atmosphere (e.g., a nitrogen atmosphere, an argon atmosphere, or a mixture thereof). For example, a reactive gas such as carbon dioxide (an oxidizing gas) can be used to provide increased mesopore and micropore content of the carbon matrix relative to pyrolysis in the absence of such gas.

[0082] In an embodiment, the method further comprises the step of pyrolysing the hybrid material, such that a nanocomposite material comprising a plurality of metal oxide nanoparticles (or metal nanoparticles) embedded in a carbon matrix is formed.

[0083] In an embodiment, the resorcinol-formaldehyde hybrid polymers are pyrolysed in an atmosphere comprising carbon dioxide or in a carbon dioxide gas

atmosphere. The carbon dioxide is present at atmospheric pressure or substantially atmospheric pressure. The use of carbon dioxide in the pyrolysis step can provide a carbon matrix having a desirable morphology. For example, the carbon matrix can have an interconnected pore structure and higher surface area than materials obtained without using carbon dioxide in the pyrolysis step. For example, pyrolysis of a resorcinol-formaldehyde hybrid polymer at 800°C in a C0₂(g) atmosphere provides carbon with broad pore size distribution (including mesopores and micropores) with graphene-like sheet textures. Using carbon dioxide in the pyrolysis step can result in a loss of mass in the resulting composite material and increases the interconnectivity of the pores of the carbon matrix. [0084] The nanocomposite material can be subjected to various ex situ treatments.

The nanoparticles of the starting nanocomposite are subjected to reaction conditions that result in formation of a portion of or all nanoparticles having a different chemical composition than the starting nanoparticles. For example, metal oxide nanoparticles are reacted such that metal, metal halide, metal sulfide, and metal phosphate nanoparticles are formed or metal sulfide nanoparticles are reacted such that metal oxides, metal halide, metal, or metal phosphate nanoparticles are formed.

[0085] In an embodiment, the method further comprises reducing the metal oxide nanoparticles of the nanocomposite material comprising a plurality of metal oxide nanoparticles embedded in a carbon matrix by contacting the nanocomposite material with a reductant (e.g., hydrogen gas) or heating the nanocomposite material under inert conditions (to a temperature higher than the carbonization temperature (carbon serves as the reductant)), such that a nanocomposite material comprising a plurality of metal nanoparticles embedded in a carbon matrix is formed.

[0086] In an embodiment, the method further comprises contacting the

nanocomposite material comprising a plurality of metal oxide nanoparticles embedded in a carbon matrix with a sulfur compound (e.g., sulfur), halide compound (e.g., fluoride compound), or phosphate compound, such that a nanocomposite material comprising a plurality of metal sulfide, metal halide, or metal phosphate nanoparticles embedded in a carbon matrix is formed.

[0087] In an embodiment, the method further comprises reducing the metal sulfide nanoparticles of the nanocomposite material comprising a plurality of metal sulfide nanoparticles embedded in a carbon matrix by contacting the nanocomposite material with a reductant (e.g., hydrogen gas) or heating the nanocomposite material under inert conditions (to a temperature higher than the carbonization temperature (carbon serves as the reductant)), such that a nanocomposite material comprising a plurality of metal nanoparticles embedded in a carbon matrix is formed.

[0088] In an embodiment, the method further comprises contacting the

nanocomposite material comprising a plurality of metal sulfide nanoparticles embedded in a carbon matrix with an oxygen compound, halide compound, or phosphate compound, such that a nanocomposite material comprising a plurality of metal oxide, metal halide, or metal phosphate nanoparticles embedded in a carbon matrix is formed. [0089] The bulk monomer or monomers form the majority of the polymer in the hybrid material. Examples of suitable bulk monomers include acrylonitrile, resorcinol, formaldehyde, vinylpyrrolidone, vinyl alcohol, acrylic acid, and phenol.

[0090] The cross-linking monomer forms cross links in the polymer. Examples of suitable cross-linking monomers include divinylbenzene, 1 ,4-butadiene, isoprene, vinylsilane, and sulfur.

[0091] Any initiator that initiates the polymerization of the monomers can be used.

For example radical polymerization initiators can be used. Examples of suitable initiators include 2,2'-azobisbutyronitrile (AIBN), benzoyl peroxide, dicumyl peroxide, potassium persulfate, and 4,4'-azobis(4-cyanovaleric acid).

[0092] Any surfactant that forms a suitable aqueous emulsion can be used. For example anionic surfactants can be used. Examples of suitable surfactants include sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and polysorbates.

[0093] A single solvent or mixture of solvents can be used. For example, the solvent can be water. In the case where water is a solvent, depending on, for example, the

components of the reaction mixture, it may be desirable to have the pH of the reaction mixture be greater than 7. Examples of suitable solvents include water, toluene, and cyclohexane.

[0094] The selection of reaction conditions that result in formation of the desired nanoparticle composition is within the purview of one having skill in the art. The

polymerization temperature for acrylonitrile is typically 60-80°C.

[0095] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to produce hybrid materials and/or nanocomposite materials of the present invention. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps.

[0096] In an aspect, the present invention provides devices comprising the hybrid material or nanocomposite materials described herein. Examples of such devices include batteries (e.g., secondary batteries), on-chip inductors. Such device structures and methods of making such structures are known in the art.

[0097] In an embodiment, the present invention provides an electrode comprising a nanocomposite material. In an embodiment, a device comprises an electrode (e.g., an anode) comprising the nanocomposite material. In an embodiment, the present invention provides an on-chip inductor comprising the nanocomposite material. In an embodiment, a device comprises an on-chip inductor. The on-chip inductors can be constructed using, for example, nanocomposites containing iron or iron/nickel alloy nanoparticles.

[0098] The following examples are presented to illustrate the present invention. They are not intended to limiting in any manner.

EXAMPLE 1

[0099] This example describes the synthesis and characterization of examples of hybrid materials and nanocomposite materials of the present invention.

[0100] An in situ, scalable method for creating a variety of transition metal oxide- carbon nanocomposites was developed based on free-radical polymerization and cross- linking of poly(acrylonitrile) in the presence of the metal oxide precursor containing vinyl groups. The approach yields a cross-linked polymer network, which uniformly incorporates nanometer-sized transition metal oxide particles. Thermal treatment of the organic-inorganic hybrid material produces nearly monodisperse metal oxide nanoparticles uniformly embedded in a porous carbon matrix. Cyclic voltammetry and galvanostatic cycling electrochemical measurements in a lithium half-cell are used to evaluate the electrochemical properties of a Fe₃0₄-carbon composite created using this approach. These measurements reveal that when used as the anode in a lithium battery, the material exhibits stable cycling performance at both low and high current densities. The polymer/nanoparticle

copolymerization approach can be readily adapted to synthesize metal oxide/carbon nanocomposites based on different particle chemistries for applications in both the anode and cathode of LIBs.

[0101] A facile, scalable emulsion polymerization technique for synthesizing transition metal oxide nanoparticles embedded in a porous carbon matrix has been reported. The method (illustrated in Figure 1) relies upon co-polymerization and cross-linking of the carbon precursor (acrylonitrile) and the nanoparticle precursor in a single-step; it yields polymer-nanoparticle hybrids with uniform particle distributions at high nanoparticle loadings. The procedure is also applicable for large-scale production of metal oxide-carbon composites required for commercial-scale LIB manufacturing processes. The procedure was demonstrated by using a high-capacity (924 mA h g^_1) transition metal oxide (Fe₃0₄) and show that it is adaptable to other oxides.

[0102] A nanocomposite of metal oxide/metal and carbon has been synthesized via a polymerization-carbonization process. A metal precursor (a carboxylic acid salt of the metal), soluble in nonpolar solvents, is mixed with a monomer, a cross-linking agent and a surfactant to form an oil-in- water emulsion. For example, emulsion polymerization is performed to yield a composite of polymer nanoparticles encapsulating the iron precursor. The material is then separated from the liquid phase and carbonized to give a composite material of metal oxide/metal-carbon nanoparticles, which may be used as the active electrode material for lithium-ion batteries. Fe₃0₄ was demonstrated as an example compound but the method is applicable to various metal oxides/metals. The method can also be extended to synthesize nanocomposites consisting of nanoparticles of other materials (e.g., other compounds which contain the metal such as CoS or a metal fluoride such as CuF₂) embedded in a carbon matrix, through ex situ treatment of metal/carbon composites with sulfur, fluorine, and other materials (see, e.g., Example 2).

[0103] Reagents used in the study were purchased from Sigma- Aldrich unless otherwise specified and used without purification. Iron undecylenate was synthesized by the following procedure. 10.8 g (40 mmol) of FeCl₃- 6H₂0, 4.8 g (0.12 mol) of NaOH and 22.1 g (0.12 mol) of undecylenic acid were added to a mixture of 80 ml of ethanol, 60 ml of water and 140 ml of hexane under vigorous stirring. The mixture was heated at 70 °C for 3 hours and then the organic phase was collected using a separation funnel. After washing with water for 3 times, hexane was driven off from the mixture using a rotary evaporator to obtain iron undecylenate, a waxy solid.

[0104] In a typical reaction, 2 ml acrylonitrile (AN), 2 ml divinylbenzene (DVB) and 1.8 g of iron undecylenate were mixed to form a homogeneous solution. 3 mg of

azobisisobutyronitrile (AIBN) and 100 mg sodium dodecyl sulfate (SDS) were added to 25 ml of water and the former solution introduced into the aqueous phase under sonication with a Sonics VCX500 horn (500 W, 20 kHz, amplitude 50%). The mixture was sonicated for 3 minutes and after a stable emulsion was formed, heated at 70 °C for 12 h. Sodium chloride was added to induce aggregation of the resultant polymer-inorganic hybrid particles, which were collected by centrifugation. The material obtained was heated in a nitrogen atmosphere, first to 320 °C, held at this temperature for 1 h, then to 500 °C and held for 2 h to obtain the final metal-oxide/carbon nanocomposite product.

[0105] The crystal structures of the particles were characterized using a Scintag Theta-theta PAD-X X-ray Diffractometer (Cu Κα, λ = 1.5406 A) and their morphologies were studied using an FEI Tecnai G2 T12 Spirit Transmission Electron Microscope (120 kV). Raman spectra were taken using a Renishaw In Via Confocal Raman Microscope.

Thermogravimetric analysis was performed using a TA Instruments Q5000 IR

Thermogravimetric Analyzer. Electrical conductivity measurement was made using a Lucas Signatone SP4 four-point probe station and the pellets were made using a pressure of 7 tons cm^-2. Gas adsorption analysis for porous materials was performed using a Micromeritics ASAP 2020 Accelerated Surface Area and Porosimetry System.

[0106] Electrochemical characterization of the composites as anode materials in rechargeable lithium-ion batteries was performed at room temperature in homemade

Swagelok-type cells. The working electrode consists of 80 wt of the active material, 10 wt of carbon black (Super-P Li from TIMCAL) as a conductivity aid, and 10 wt of polymer binder (PVDF, polyvinylidene fluoride, Aldrich). Lithium foil was used as the counter and reference electrodes. A I M solution of LiPF₆ in a 50 : 50, w/w mixture of ethylene carbonate and diethyl carbonate was used as the electrolyte. Celgard 2500 polypropylene membranes are used as the separator. Assembly of cell was performed in a glove box with moisture and oxygen concentrations below 1 ppm. The room-temperature electrode capacities were measured using Neware CT-3008 battery testers.

[0107] Powder X-ray diffraction was performed to determine the crystalline phase of the transition metal oxide. The XRD results, shown in Figure 2(a), match well with those of magnetite (JCPDS card no. 19-629). The broad signal in the range of 20-30° may be due to the presence of non-crystalline carbon in the composite, because the most intense reflection for graphitic carbon (002 layer) should appear at 26.8°. From the Scherrer's formula, the average crystallite size of the Fe₃0₄ phase is found to be 21 nm.

[0108] Transmission Electron Micrographs (TEM) for the polymer-particle complex are shown in Figure 3(a). The material generally consists of particles with sizes in the range 200-400 nm aggregated together. Energy Dispersive X-Ray Spectroscopy (EDX) was performed on the complex, as shown in Figure 3(c), which confirms that iron has been successfully incorporated in the complex. The morphology of the material after calcination is shown in Figure 3(b). It consists of uniformly sized Fe₃0₄ nanoparticles embedded in a carbon matrix and the size is consistent with the average crystallite size calculated from the X-Ray diffractograms (21 nm). Oxidative thermal gravimetric analysis (TGA) may be used to measure the weight fraction of active material Fe₃0₄ in the composite and the data are shown in Figure 3(d). The material is heated to 700 °C under air so that Fe₃0₄ is oxidized to Fe₂0₃ and carbon is oxidized to C0₂. From the remaining weight (of Fe₂0₃), the original weight fraction of Fe₃0₄ is calculated to be 66%.

[0109] Other carboxylic acid salts of iron have been used as the precursor, for example iron oleate, but the amount of Fe₃0₄ eventually encapsulated in the product can be substantially lower (e.g., 33%) than for iron undecylenate. The higher molecular weight of oleic acid compared to undecylenic acid and the bulkier molecule of iron oleate results in less efficient incorporation in the polymer complex. In addition, the fractional weight loss of conversion of Fe(ole)₃ to Fe₃0₄ (91%) is larger than conversion of Fe(ole)₃ to Fe₃0₄ (87%), because of the larger molecular weight of Fe(ole)₃. Iron(III) acetylacetonate (Fe(acac)₃), which has a lower molecular weight than Fe(undec)₃ was also investigated. In this case, the higher water solubility of the particle precursor does not allow formation of stable micelles required for emulsion polymerization.

[0110] Polyacrylonitrile is frequently used to synthesize graphitic materials through calcination at high temperatures. To obtain highly graphitic carbon, PAN should be subjected to three consecutive processes, namely, stabilization, carbonization and graphitization. In the stabilization step, PAN is heated to 200-300 °C in air and converted to a cyclic or a ladder compound, followed by treatment in nitrogen atmosphere to about 1000 °C to achieve carbonization of the material. The third step, known as graphitization, is to heat the material to 1500-3000 °C under argon atmosphere to improve the ordering and orientation of the crystallites. Because the present system contains metal oxides, if the material is heated to temperatures above - 700 °C for the sake of increasing the graphite content in the product, there is the possibility of carbon reducing the metal oxide to pure metal. As a compromise, a carbonization protocol requiring heating the material at 500 °C in dry N₂ was used.

[0111] The Raman spectrum of the Fe₃0₄-C composite is shown in Figure 4. It is immediately noticeable that the spectrum contains two prominent peaks at around 1350 and 1590 wavenumbers. Raman spectra for carbon materials usually contain several peaks. In particular, the spectrum can be deconvoluted to five bands, corresponding to ideal graphite (G 1580 cm^"1), a disordered graphitic lattice (Dl 1350 cm^"1, D2 1620 cm^"1 and D4 1200 cm^"1), or amorphous carbon (D3 1500 cm^"1). G and D2 both come from sp² carbon vibrations, which can be difficult to distinguish, and in some works have been treated as one single component in the fitting procedure. Lorentzian functions were used in the fitting and the calculated positions for the peaks are: G 1596 cm^"1, Dl 1349 cm^"1, D3 1471 cm^"1, and D4 1230 cm^"1. This analysis indicates the carbon obtained in the composite is partially graphitic.

[0112] Magnetite has the formula Fe²⁺[Fe³⁺ ₂]0₄ and adopts an inverse spinel structure. In each unit cell (containing 8 multiples of Fe₃0₄), 8 out of 16 Fe³⁺ ions occupy 8 out of the 64 tetrahedral sites and all the Fe²⁺ ions and the remaining 8 Fe³⁺ ions are distributed in 16 out of 32 octahedral sites. Lithiation of Fe₃0₄ follows the following pathway: l i s ! f Phase 2}

[0113] Here parentheses denote ions in tetrahedral sites and square brackets denote ions in octahedral sites. During the insertion of up to 1.0 Li, the Li⁺ ions fill up octahedral vacancies, with Fe³⁺ in the tetrahedral sites displaced to octahedral sites, leading to the formation of a rock-salt-like structure of Lii.oFe₃C>4 at the end of this step. Further insertion of lithium involves the filling of the tetrahedral sites by Li⁺ ions. Metallic iron is extruded from the rock-salt structure to accommodate the incoming Li⁺ ions.

[0114] Cyclic voltammograms for Fe₃C>4-C composites are shown in Figure 5(a)

(scan rate = 0.2 mV s^_1). The patterns are consistent with the CV results from other reports on Fe₃C>4-C composites. In the anodic process, starting from the second cycle, the lithium intercalation occurs mainly at around 0.7 V and in the cathodic process the oxidation of Fe° occurs at around 1.8 V. In the first cycle, the intercalation occurred at a lower voltage of around 0.4 V, probably because of an overpotential arising from the crystal structure changes from the inverse spinel structure to the rock salt type structure. The voltage-capacity profiles for the complex cycled at different charging rates (1 C or 0.5 C) are shown in Figure 5(b).

The lithium intercalation plateaus are not as flat for the Fe₃C>4 in carbon composites compared to the pure oxide, probably because of reduction in crystallinity and/or change in surface site energetics during the process of the carbon formation for the composite.

[0115] Cycling performance data for the Fe₃C>4-C composites are shown in Figure 6. The material was cycled at 1 C and 0.2 C, respectively for 100 cycles and the performance under different charging rates ranging from 0.5 °C to 5 °C was also studied. The capacities are calculated based on the metal oxide mass because the capacity-voltage profiles do not indicate significant contribution from lithium intercalation into the carbon host. It is apparent from Figure 6 that the composites show very stable performance and little fading for 100 cycles, even at 1 C charging rate. The performance is also stable for higher charging rates (20 cycles are shown as examples). The performance of bare Fe₃C>4 nanoparticles (50 nm in size, commercially available from Alfa Aesar) as the anode material is also shown in Figure 6(d) for comparison purposes; the clear improvements provided by the composite materials are visible from this plot. The performance of pure carbon made from pyrolysis of PAN-DVB at 500 °C is also shown. It is seen that this material does not make any significant contribution to the lithium storage capacity.

[0116] The stable electrochemical performance of the Fe₃0₄-C nanocomposites can be attributed to different features of the materials. Considering the relatively low electronic conductivity of the carbon component, it is not a consequence of enhanced electronic transport afforded by the carbon. The uniformly sized Fe₃0₄ nanoparticles are embedded in the carbon matrix, which might serve to alleviate the volume change incurred during the repeated cycling. A porous, mechanically flexible reinforcement that allows good penetration by the electrolyte into the active material is therefore considered advantageous. Nitrogen adsorption analysis was performed on the composite and the surface area measured by the

BET method is 122 m² g^_1, with the isotherms and the pore size distribution for the composite (calculated using BJH method) shown in Figure 7. The BET surface area of pure carbon obtained from pyrolysis of the PAN-DVB polymer (without Fe₃0₄ nanoparticles) is about three times higher, 369 m² g^"1. The pore size distribution results show that most of the pores are less than 10 nm in size.

[0117] The size of the Fe₃0₄ nanoparticles also seems to be an important factor in determining the electrochemical performance. Average diameters of Fe₃0₄ particles synthesized using hydrothermal/solvothermal methods are usually greater than 150 nm because the particles are typically aggregates of smaller primary crystallites. In the current method, the size of the Fe₃0₄ nanoparticles is relatively small and the greater surface area and shorter diffusion length may allow easier access of the active material by the lithium ions.

[0118] The method developed for creating Fe₃0₄-C composites can be applied to synthesize nanocomposites of various other metal oxides (or other related materials such as pure metal) embedded in carbon matrices. Another interesting material is MnO, which has a theoretical lithium storage capacity of 755 mA h g^"1. MnO undergoes conversion reaction in lithium- ion batteries: 2Li + MnO→ Mn + Li₂0 and upon lithium insertion, Mn grains <5 nm in size are formed. MnO-C composites can be synthesized using manganese(II) undecylenate as the precursor. Figure 8(a) shows the X-ray diffractogram for the MnO-C composite, which matches well with MnO (JCPDS card no. 07-230). Again a broad band is observed in the range of 20-30°, but no sharp peak could be found at 26.8°, indicating that the carbon component is largely amorphous. TGA is used to determine the fraction of MnO in the composite. Upon heating to 700 °C in air, MnO is oxidized to Mn₂0₃ and the weight fraction of MnO in the composite is calculated to be 58% assuming all the remaining material is carbon. The morphology of the MnO-C composite is shown in Figure 8(b) and similar to the case of Fe₃0₄, MnO nanoparticles embedded in a carbon matrix are obtained.

[0119] A typical cyclic voltammogram for the MnO-C composite is shown in Figure

9(a) and lithium insertion/Mn²⁺ reduction seems to occur at around 0.5 V against Li/Li⁺, which is consistent with previous reports on MnO anode materials. Voltage-capacity curves at 0.5 C and 1 C charging rates are shown in Figure 9(b) and cycling data for the composite run at 1 C and 0.2 C, and at varied charging rates are shown in Figure 9(c). Similar to what was observed for the Fe₃0₄-C composite, little capacity fade is observed even when the material is subject to 1 C charging rate for over >100 cycles. Cycling at higher charging rates is also seen to give stable performance. Therefore a prominent feature of the current protocol is the ability to yield materials with stable performance at moderately high charging rates.

[0120] In conclusion, a one-step free-radical polymerization method is used to synthesize cross-linked metal-oxide/poly(acrylonitrile) nanocomposites. Pyrolysis of the composite at moderate temperatures in an inert atmosphere yields metal-oxide/carbon particles comprised of uniformly distributed metal oxide nanoparticles in a partially graphitic, but poorly conducting carbon host. The versatility of the approach has been demonstrated using two different metal oxides, Fe₃0₄ and MnO. When evaluated as anode materials in lithium-ion batteries, composites of both materials display stable performance at low and high current densities.

EXAMPLE 2

[0121] This example describes the synthesis and characterization of examples of hybrid materials and nanocomposite materials of the present invention.

[0122] Synthesis of LiFeP0₄@C nanocomposite. 108mg LiOH, 221mg H₃P0₄ and

660mg L-ascorbic acid are dissolved in 10ml DI water, to which 116mg Fe₃0₄@C nanocomposite powder is added. The solution is loaded into a pressurized container and heated at 270°C for 12hr. The powder obtained is centrifuged and washed with water.

[0123] Synthesis of Mn₀₇₅Fe₀₂₅0@C nanocomposite. Manganese (II) undecylenate is synthesized using the same method as iron (III) undecylenate, with MnCl₂ as the Mn precursor. 1.58g manganese (II) undecylenate and 0.75g iron (III) undecylenate are mixed to form a homogeneous mixture, and polymerization with acrylonitrile and divinylbenzene is performed using the same method as used for iron (III) undecylenate alone. The

polymerization product is collected ant heat treated in the same way to obtain

Mn₀₇₅Fe₀₂₅O@C nanocomposite. [0124] Synthesis of LiMn_{0 75}Fe_{0 25}P0₄@C nanocomposite. 90mg LiOH, 162mg

H₃P0₄ and 49mg H₃PO₃ are dissolved in 10ml DI water, to which 142mg Mn₀.75Fe₀.25O@C nanocomposite powder is added. The solution is loaded into a pressurized container and heated at 270°C for 12hr. The powder obtained is centrifuged and washed with water.

EXAMPLE 3

[0125] The synthesis, structural characterization and electrochemical performance of

MoS₂-carbon nanostructures is described in this example.

[0126] Composites of M0S₂ and amorphous carbon were grown and self-assembled into hierarchical nanostructures via a hydrothermal method. Application of the composites as high-energy electrodes for rechargeable lithium-ion batteries was investigated. The critical roles of nanostructuring of MoS₂ and carbon composition on lithium-ion battery performance are described. Pure M0S₂ and 22 wt carbon containing M0S₂ materials are designated as MS-0 and MS-22 respectively.

[0127] Morphological investigations using SEM (Figure 18a) reveal that the product obtained via the hydrothermal treatment of the molybdenum sol in presence of carbon precursors (resorcinol and formaldehyde) takes the form of open structure of M0S₂ and carbon. The TEM images of MS-22 (22 wt carbon), as shown in Figures 18b and c, indicate that M0S₂ in the composites are in the form of stacked nanosheets homogeneously embedded in a very thin matrix of amorphous carbon. The length and thickness of M0S₂ nanosheets are about 40 and 10 nm respectively (inset of Figure 18b). It can be observed that the M0S₂ sheets are composed of few M0S₂ layers (~6 to 10 layers). A schematic of the in situ synthesis of MoS₂-carbon composites is shown in Figure 19 A. In absence of resorcinol and formaldehyde, the M0S₂ particles aggregate to form large M0S₂ lumps (Figure 19B) as verified by the SEM and TEM images (Figures 18d and f). On the other hand,

polycondensation of resorcinol with formaldehyde takes place during the hydrothermal process forming low density carbon gels. The M0S₂ particles in the form of layers simultaneously crystallize during the hydrothermal process and are eventually uniformly dispersed in the carbon gel. The successive restacking of M0S₂ layers is significantly inhibited by the carbon gel resulting in few layers of M0S₂ nanosheet and consequently self- assembled in interconnected flakes resulting in three dimensional MoS₂-carbon

nanostructures.

[0128] The X-ray diffraction patterns (XRD) of the MS-0 and MS-22 shows broad diffraction peaks which can be indexed to 2H polytype of M0S₂ crystal structure with space group P6Jmmc (194) (ICDD no. 071-809) (see ESI, Figure 23). In the case of MoS₂-carbon composites, no peak shifts are observed suggesting that the MoS₂ crystallites are

unconstrained by chemical bonding to the carbon framework. Furthermore, no characteristic peak from graphitic carbon was detected in the XRD, indicating the formation of amorphous carbon. It can be observed that the intensity of (002) peak for MS-22 is relatively lower compared to pure MoS₂ particles (see ESI, Figure 23). The peak at (002) is typically observed in bulk analogue. It suggests that the carbon inhibits the growth of (002) planes of MoS₂ crystallites, which confines its growth in the plane favoring formation of few-layer nanosheets in the amorphous carbon matrix. The carbon content is estimated using thermogravimetric analysis; the results are depicted in (see ESI, Figure 24). It is seen that there is successful incorporation of 11, 22, 32 and 41 wt of carbon in MoS₂-carbon nanostructures. The BET surface areas of MS-0, MS-22 and MS-41 are 3, 35 and 157 m² g^"1 respectively (see ESI, Figure 25). The increase in surface area with increasing carbon content is attributed to the porous nature of amorphous carbon.

[0129] The electrochemical properties and lithium battery performance of all MoS₂- carbon composites using galvanostatic discharge and cyclic voltammetry measurements was investigated. Electrodes were prepared from the MoS₂-carbon composites and a PVDf binder, i. e. , no carbon black or other conductivity aid was added. Figure 20 shows the galvanostatic charge (Li removal)/discharge (Li insertion) profiles obtained from pure and carbon-composited MoS₂ at room temperature (25 °C) and at a constant current density of 100 mA g^_1 in the voltage range of 0.05-3 V. In the present study, pure MoS₂ particle exhibited a discharge capacity of 2362 mA h g^_1 in the 1^st discharge cycle (Figure 20a). Two potential plateaus at 1.1 V and 0.61 V corresponding to the formation of LLMoS₂ and conversion of MoS₂ to Mo respectively are also readily apparent from Figure 20. The pure MoS₂ shows very poor 1^st charge and 2^nd discharge capacities of 247 and 53 mA h g^_1, respectively without any noticeable potential plateaus.

[0130] The MoS₂-carbon nanocomposite structures all exhibit significantly improved capacity retention (Figures 20b and e). All MoS₂-carbon composites manifest the prominent characteristic discharge potential plateaus at 1.1 V and 0.6 V in the 1^st discharge cycle and charge potential plateau at 2.3 V in all charge cycles (Figure 20b). During subsequent discharge cycles, the potential plateau observed at 0.6 V disappeared with emergence of two new inconspicuous potential plateaus at -1.9 V and 1.2 V (Figure 20b) which is in agreement with previous observations. The first discharge capacities of MS-11, MS-22, MS-32 and MS- 41 are 2108, 1462, 1130, and 1078 mA h g^"1 with coulombic efficiencies of 79%, 62%, 63%, and 61% respectively. Among all the carbon-MoS₂ composites, MS-22 exhibits the best battery performance in terms of showing higher capacity and long-term stability. MS-22 shows a discharge capacity of 755 mA h g^_1 with coulombic efficiencies of 98% after 100^th cycle at constant current density of 100 mA g^"1. In contrast, MS-11, MS-32 and MS-41 show capacities of 10, 517 and 354 mA h g^"1 after 100^th cycle. Although MS-32 and MS-41 show good long-term capacity retention, the lower capacity possessed by both of them is due to higher amount of inactive carbon in the electrode compositions. It ascertains the importance of optimization of inactive carbon in electrode materials.

[0131] The improved cycling stability of MoS₂-carbon composites can be attributed to the inhibition of the side reaction of Li₂S with the electrolyte that forms a thick, gel-like polymeric layer and manifests particle aggregation. The evidence in support of this explanation is provided by cyclic voltammetry (CV) (Figures 20c and d), ex situ XRD (Figure 21) and SEM of the 1^st cycle discharged product (Figure 21). The CV plot of MS-22 (Figures 20d) shows two distinct reduction peaks at 0.93 V and 0.37 V in the 1^st cycle, which is indicative of the respective formation of LyVloS₂ and decomposition of MoS₂ to Mo and Li₂S. In the subsequent oxidation cycles shown until the 15^th cycle, small but sharp intensity peaks at 1.67 V and 2.34 V can be observed. These peaks are attributed to partial and complete oxidation of Mo to MoS₂, respectively. In the subsequent reduction cycles, peaks at 0.93 V and 0.37 V disappear and two new small intensity peaks at 1.83 V and 1.01 V can be observed. The peaks are in agreement with the potential plateaus observed in charge- discharge curves of MS-22 (Figure 20b). It is also evident from the CV data that even after 15^th cycle, the MoS₂-carbon composite material shows excellent electroactivity, with negligible decrease in peak intensities. On contrary, pure MoS₂ shows a distinct reduction peak at 0.93 V and a broad reduction peak in the voltage range of 0.05-0.5 V in the 1^st reduction cycle. Two minor intensity oxidation peaks at 1.8 V and 2.3 V can also be observed in the 1^st oxidation cycle followed by little noticeable electrochemical activity after the 1^st cycle. The ex situ XRD of MS-0 and MS-22 both shows the signature of Mo (ICDD no. 071- 3771) and Li₂S (ICDD no. 071-4841) after 1^st discharge cycle (Figure 21). However, the peak intensity of Li₂S for MS-0 (Figure 21b) is significantly lower than MS-22 (Figure 21a). The breadth of the CV peak at 0.05-0.5 V and decrease in Li₂S XRD peak intensity in case of pure MoS₂ particle can be explained in terms of the side reaction of Li₂S with the electrolyte. Further evidence is provided by the ex situ SEM images of the 1^st cycle discharge products of MS-0 (Fig. 21d) and MS-22 (Figure 21c). MS-22 maintains its original structure whereas pure MoS₂ particles aggregated due to electrolyte degradation with Li₂S. As a consequence of electrolyte degradation with the first cycle discharge product Li₂S, the pure MoS₂ particle show higher capacity (2362 mA h g^_1) but with extremely poor coulombic efficiency of 10% compared to all carbon-MoS₂ composites. In addition, particle agglomeration is also a serious cause for the poor cyclability of pure MoS₂.

[0132] Another important result, as shown in Figure 20f, is that lithium storage capacity of MoS₂-carbon composites is a strong function of carbon concentration. A significant jump in stability can be observed in increasing the carbon concentration from 11% to 22% (Figure 20e). Figures 20e and f reflects two important implications. First, although the 1^st and 2^nd discharge cycle capacities of MS-11 are higher than MS-22, MS-32 and MS- 41, MS- 11 exhibits less stable storage capacity over extended cycling. Evidently, carbon does have a stabilizing effect on the cycling stability of MoS₂ and the composition of the composites can be used to influence their stability. Second, there is a critical concentration of carbon at which the capacity and cyclability are optimized. 22% carbon containing MoS₂- carbon composite exhibits the best stability. It suggests that the optimum value of carbon in rendering stable cycle life is around 22%. At carbon concentrations less than 22%, the MoS₂ particles are not effectively coated with carbon (ESI, Figure 26a) that promotes possible electrochemical reaction of Li₂S and electrolyte during the first discharge process. It is important for lithium-ion battery purposes to ensure good buffering for active material.

Therefore, similar to MS-0, MS- 11 shows higher first cycle discharge capacity (2108 mA h g^_1) compared to other carbon-MoS₂ compositions. On the other hand, increasing carbon concentrations more than 22% results in thicker carbon coating (ESI, Figure 26b) and increase in inactive mass in the electrode. Since resorcinol-formaldehyde synthesized carbon is porous, the electrolyte can wet the MoS₂ particle. Therefore, MS-32 and MS-41 show stable electrochemical activity. However, the lithium storage capacities are lower than MS-22 due to increased proportion of inactive mass in the electrode.

[0133] The cycling stability and rate capability of MS-22 with additional carbon black in the electrode is shown in Figures 22 and 23 (ESI). It is observed that incorporation of higher amount (50%) of carbon black facilitates higher rate capability. To further testify the carbon quality present in the MoS₂-carbon composites, the material is calcined at 700 °C. The lithium battery performance is shown in (see ESI, Figure 28). Heat treatment of 700 °C is found to have deteriorating effect on the cyclability due to possible temperature induced crystallite growth.

[0134] A facile one-pot hydrothermal method for the synthesis of MoS₂-carbon nanostructures with various carbon compositions was demonstrated. The procedure utilizes water as the only solvent and creates stacked nanosheets of MoS₂ in a carbon matrix. It is demonstrated that incorporation of carbon provides significantly improved cycling stability when the material is used as a lithium battery electrode. It is also found that an optimum level of carbon is required to produce materials with both high lithium storage capacity and good electrochemical cycling stability. The improved performance is attributed to following three main factors. First, the porous structure of the composites allows for facile Li⁺ insertion- deinsertion into MoS₂ nanosheets and for structural stresses induced by Li⁺ insertion- deinsertion to be properly accommodated since the dimension of MoS₂ nanosheets are small (thickness -10 nm) and composed of few layers (~6 to 10 layers). Second, incorporation of MoS₂ in the carbon matrix inhibits the side reaction of Li₂S with electrolyte at the interface of Mo and carbon and finally, the carbon framework limits particle agglomeration. The synthesis approach reported in the present invention will be beneficial for designing new organic-solvent free synthesis methods for creating composite electrode materials for lithium batteries.

[0135] Synthesis of MoS₂-carbon: The MoS₂-carbon composites with varying carbon weight fractions were synthesized by a hydrothermal method. Resorcinol/formaldehyde (Sigma- Aldrich) and ammonium tetrathiomolybdate (Sigma- Aldrich) were used respectively as carbon and MoS₂ precursors. A desired concentration (0.076 M) of aqueous solution of ammonium tetrathiomolybdate was added to another aqueous solution containing resorcinol, formaldehyde and sodium carbonate under continuous stirring. The ratios of resorcinol to formaldehyde and to sodium carbonate were kept at 0.185 g ml-1 and 251 respectively calculated on a molar basis for all MoS₂-carbon composites. However, the concentrations of resorcinol, formaldehyde and sodium carbonate were varied to obtain various carbon loadings in the final product. The intense violet color sol was transferred to a Teflon-lined stainless steel autoclave of capacity 100 ml (70% filling) and heated at 180 °C for 12 hours and then cooled to room temperature. The resultant black product was recovered by centrifugation and washed with deionized water and freeze dried. The dried product was further calcined at 550 °C for 4 hours in an atmosphere of 5% H₂ balanced with Ar at a heating rate of 5 ⁰Cmin^_1. Pure MoS₂ was synthesized by hydrothermal treatment of ammonium tetrathiomolybdate (180 °C for 12 h, calcination at 550 °C for 4 hours under H₂/Ar), but without any addition of resorcinol and formaldehyde. The materials were designated as MS-0, MS- 11, MS-22, MS- 32 and MS-41corresponding to 0, 11, 22, 32 and 41 wt % of carbon in the MoS₂-carbon composites. [0136] The crystallographic phase identification was performed using powder x-ray diffraction (Scintag theta-theta PAD-X-ray Diffractometer; Cu-Κα radiation, λ = 1.5406 A). The morphology was observed by scanning electron microscopy (SEM, LEO 1550 FESEM) and transmission electron microscopy (TEM, FEI Tecnai G2 T12). Specific surface area (BET) was obtained from nitrogen adsorption-desorption isotherms (Micromeritics ASAP 2020). Estimation of carbon content in MoS₂-carbon composites was done using

thermogravimetric analysis (TGA, TA Instruments Q5000). TGA experiments were performed by heating the sample in air from room temperature to 700 °C at a heating rate of 10 ⁰Cmin^_1. For the working electrode, slurry of the active material and carbon black (Super P Timacal) was prepared with PVdF (Sigma) in a weight ratio of MoS₂:CB:PVDf = 90:0: 10, 80: 10: 10, 65: 10: 10, 40:50: 10 in N-methyl-pyrrolidone (ΝΜΡ). The slurry was cast on a copper foil and dried in vacuum at 120 °C for 12 h. Room temperature cyclic voltammetry (CV, CH608 CH Instruments) and galvanostatic charge/discharge cycling (Maccor) were done in 2032 coin-type cells with pure metal Li (Aldrich) as anode, Whatman glass fibre as separator and 1M LiPF6 in ethylene carbonate (EC, Aldrich) and dimethyl carbonate (DMC, Aldrich) (1: 1 w/w) as an electrolyte.

EXAMPLE 4

[0137] This example describes the synthesis and characterization of examples of hybrid materials and nanocomposite materials of the present invention.

[0138] A method is reported for creating functional organic-inorganic hybrid materials by copolymerization of organic molecules and inorganic compounds. The approach is based on miniemulsion polymerization technique followed by a thermal pyrolysis step, and yields nanostructured composites in which nanoparticles are uniformly embedded in a porous, partially graphitic carbon matrix. Depending upon the chemistry of the starting materials, nanoscale organic-inorganic hybrid materials created using the approach are attractive as anodes and cathodes for next-generation lithium and other rechargeable battery systems. Additionally, the platform is very versatile and through ex situ conversion or utilization of multiple precursors, can be applied to various classes of materials including metal oxides, metals, metal sulfides and alloys. The approach also lends itself to the development of scalable processes for production of nanostructured battery materials.

[0139] This general approach for synthesizing metal oxide-, metal sulfide-, and metal alloy-carbon nanocomposites ameliorates the physical and chemical stresses associated with repeated insertion and de-insertion of lithium present a fundamental challenge to further development of next-generation lithium ion battery (LIB) technologies. Remarkably, in every case investigated the nanocomposites manifest improved electrochemical stability whether they are applied as anodes or cathodes in a secondary battery.

[0140] An approach for the in situ synthesis of nanoparticles embedded in a carbon matrix through a miniemulsion polymerization technique was shown. The as prepared carbon-nanoparticle hybrid materials can be facilely modified ex situ to significantly increase the range of materials chemistries that can be achieved by the method. The approach is based on the in situ synthesis of inorganic nanoparticles and organic polymers from precursors capable of forming chemical cross-links with each other. After pyrolysis of the organic phase, the process yields a well-defined nanostructured material comprised of discrete inorganic nanoparticles embedded in a porous carbon matrix. Post treatment of the embedded particles creates carbon-nanoparticle hybrids based on metals, metal alloys, and a variety of other particles attractive for lithium battery applications.

[0141] Emulsion polymerization is a widely used method for synthesizing polymer latexes for applications such as adhesives and coatings. The method typically uses monomers with low water solubility, stabilized by surfactant in an aqueous media. The polymerization rate is limited by the diffusion of reactive monomer, through the aqueous phase, from monomer droplets to monomer-swollen polymer particles where polymerization takes place. Application of high shear force to the emulsion yields a so-called miniemulsion, comprised of droplets with small sizes, usually 0.01-0.5 μιη, compared to 1-10 μιη in conventional emulsion polymerization. Because of the high surface area of monomer droplets in a miniemulsion, nucleation takes place mainly via radical entry into the emulsified monomer droplets and reaction proceeds through polymerization of the monomers in these small droplets. If more than one monomer chemistry is employed simultaneously or sequentially, the approach can be used to create copolymers with different architectures. If the

polymerization reaction is performed in the presence of guest species miscible with the monomer (e.g. dyes, metal complexes, etc.), the guest species can be embedded in the polymer particle host. However, a common drawback is that only relatively low loadings (a few percent by weight) of the guest can be achieved. A new method to overcome this drawback and demonstrate the applicability of the method to synthesize composites involving various types of LIB electrode materials was demonstrated.

[0142] Chemicals and materials synthesis. Chemical reagents were purchased from

Sigma- Aldrich and used without purification. Fe₃0₄@C nanocomposite was synthesized according to a previously reported procedure. 2ml acrylonitrile (AN), 2ml divinylbenzene (DVB) and 2g of iron undecylenate were mixed to form a homogeneous solution. 3mg of azobisisobutyronitrile (AIBN) and lOOmg sodium dodecyl sulfate (SDS) were added to 25ml of water and the former solution added dropwise to the aqueous phase under sonication with a Sonics VCX500 horn (500W, 20kHz, amplitude 50%). The mixture was sonicated for 3 minutes and after a stable emulsion was formed, heated at 70°C for 12 hrs. Sodium chloride was added to induce aggregation of the resultant polymer-inorganic hybrid particles, which were collected by centrifugation. The material obtained was heated in an argon atmosphere, first to 320°C, held at this temperature for lhr, then to 500°C and held for 2hrs to obtain the Fe₃0₄@C nanocomposite product. Fe₃0₄@C was then ground into powder and heated at 650°C in a tube furnace under a 7% H₂ (balance Ar) gas environment for 2hrs to obtain

Fe@C powders. The latter is mixed with 2x mass of sulfur, loaded into a Pyrex tube, sealed and heated at 500°C for 4hrs to obtain FeS₂@C nanocomposite. The product is washed with CS₂ to remove any residual elemental sulfur. To synthesize y-Fe₂C>3@C and a-Fe₂C>3@C composites, Fe₃0₄@C powder is heated in air at 350°C for 5hrs and 390°C for lhr, respectively, to obtain the products. To synthesize V₂Os@C, VCI₃ is used as the starting material to synthesize V(CioHi9COO)3. After polymerizing with acrylonitrile, the material is pyrolysed at 500°C in argon for 2hrs and then heated in air at 390°C for lhourto obtain V₂C>5@C. To synthesize FeSn₂@C nanocomposite, tin undecylenate (Sn(CioHi9COO)₂) was synthesized in a similar fashion as iron undecylenate, except with SnCl₂ as the starting material. 2.2g Fe(Ci₀H₁₉COO)₃ and 1.8g Sn(Ci₀H₁₉COO)₂ were mixed first, 2ml AN and 2ml DVB were added, and then the rest of the procedure was carried out as above.

[0143] The crystal structures of the particles were characterized using Scintag Theta- theta PAD-X X-Ray Diffractometer (Cu Κα, λ= 1.5406 A) and their morphologies were studied using FEI Tecnai G2 T12 Spirit Transmission Electron Microscope (120kV).

Thermogravimetric analysis was performed using TA Instruments Q5000 IR

Thermogravimetric Analyzer.

[0144] Cell assembly and testing. Electrochemical characterization of the composites as anode materials in rechargeable lithium-ion batteries was performed at room temperature in 2032 coin-type cells. The working electrode consisted of 80 wt% of the active material, 10 wt% of carbon black (Super-P Li from TIMCAL) as a conductivity aid, and 10 wt% of polymer binder (PVDF, polyvinylidene fluoride, Aldrich). Copper foil was used as the current collector for nanocomposites targeted for application as the LIB anode and aluminum for those targeted as cathodes. Lithium foil was used as the counter and reference electrode for evaluating both that anode and cathode materials. A I M solution of LiPF₆ in a 50:50 w/w mixture of ethylene carbonate and dimethyl carbonate was used as the electrolyte. Celgard 2500 polypropylene membranes are used as the separator. Assembly of cell was performed in a glove box with moisture and oxygen concentrations below 1 ppm. The room-temperature electrode capacities were measured using Neware CT-3008 battery testers. Cyclic voltammetry was performed with a CHI600D potentiostat.

[0145] Figure 30 illustrates the chemistry of a miniemulsion polymerization methodology that could be used to create organic-inorganic hybrid copolymers with high inorganic loadings. Using an organic monomer (e.g. acrylonitrile, or AN) and the metal salt of an unsaturated carboxylic acid (e.g. iron (III) undecylenate) and divinylbenzene as crosslinker the method yields well-defined iron oxide nanoparticles uniformly embedded in a polyacrylonitrile host (Figure 31 A). FTIR spectra of iron (III) undecylenate and the AN-iron copolymer composite are compared in Figure 39. Significant decrease in the intensity of the C=C stretch peak at around 1640 cm^"1 (normalized with respect to C-H stretch at around 2910 cm^"1) is observed, showing that as expected many of the double bonds in iron (III) undecylenate have been eliminated during polymerization.

[0146] Upon thermal treatment, the as prepared polyacrylonitrile (PAN) - nanoparticle hybrids are transformed into carbon-Fe₃0₄ nanocomposites characterized by the uniform distribution of Fe₃0₄ in a partially graphitic carbon host was demonstrated. When evaluated as the anode in a lithium ion battery, the material showed significantly improved cycling stability and capacity retention relative to anodes based on pristine Fe₃0₄

nanoparticles. The performance enhancement brought about by the in situ synthesis approach was argued to largely originate from the uniform separation of the embedded nanoparticles achieved in the composites, which simultaneously minimizes aggregation of the active nanostructures, facilitates electron transport, and maximizes the degree to which the carbon framework is able to absorb and isolate mechanical stresses produced by structural changes. Figure 3 IB shows the TEM image of the nanocomposite after 100 charge-discharge cycles. It indicates that with the mechanical support provided by the carbon matrix, the pulverization of the active material nanoparticles is mitigated, which is the source of the observed

improvement in cyclability.

[0147] A goal of the present work is to illustrate the versatility of the synthesis method and to evaluate the generality of the hybrids produced. Figure 32 shows an abbreviated list that identifies the variety of hybrid materials relevant for application in lithium battery electrodes that can be synthesized using the approach. Because of the large number of Fe-based compounds and alloys that are of interest for LIB applications, demonstrated is the simplicity and versatility of the method using nanoparticles based on Fe compounds; the enhancements were subsequently evaluated in their properties by using the composites as anodes or cathodes for LIBs. Results on other examples (e.g. materials based on vanadium and titanium) will also be discussed.

[0148] As illustrated in Figure 32, carbon-Fe₃0₄ nanocomposites (Fe₃0₄@C) synthesized using the procedures outlined earlier can be reduced to Fe@C composites either by heating the material in an H₂ environment or simply by heating the composite in an inert gas to a temperature somewhat higher than the carbonization temperature (whereby carbon serves as the reducing agent). The XRD pattern of the material obtained after heating Fe₃0₄@C to 650~700°C under H₂ is shown in Figure 33A, which is unambiguously assigned to the a-Fe (JCPDS card #06-0696). Figure 33B is a transmission electron micrograph of the material showing that the materials are comprised of well-dispersed ca. 30 nm Fe nanoparticles, which is consistent with the average crystallite size of 29nm deduced from XRD.

[0149] Because the carbon matrix is porous, it allows the infusion of other chemical agents, which can react with the embedded Fe nanoparticles. FeS₂ is a promising cathode material for lithium batteries because of its high reversible capacity (625 mAh/g), low cost and low toxicity. It is well-known in primary lithium battery applications and high temperature thermal batteries, but its use in room-temperature rechargeable cells has been hindered by the material's limited cyclability. A vapor infusion procedure was used to react the Fe@C composites with sulfur at 500°C. Figures 33 A and C are the corresponding XRD and TEM patterns for this material. The XRD pattern is unambiguously assigned to FeS₂ (JCPDS card # 42-1340) and reveals that reaction with sulfur has nearly doubled the crystallite size to 54nm; again consistent with results from TEM, which show uniformly distributed ca. 55nm FeS₂ particles in the carbon host. Particle size histograms obtained from TEM images for Fe@C and FeS₂@C composites are shown in Figures 33(D) and (E), with average sizes of 29.7+3.8nm and 53.8+9.9nm, respectively. Through oxidative TGA (Figure 40) the weight fraction of FeS₂ in the product is found to be 75%.

[0150] Figure 34 report results from cyclic voltammetry and galvanostatic cycling measurements performed using the as prepared FeS₂@C composites. In the cathodic scan of the first cycle, FeS₂ follows a two-step lithiation: FeS₂ + 2Li⁺ + 2e -> Li₂FeS₂ (~2V) and Li₂FeS₂ + 2Li⁺ + 2e -> Fe + 2Li₂S (-1.4V). In the anodic scans, the material is converted to Li₂FeS₂ at around 1.8V and then to Li₂__xFeS₂ (0<x<0.8) at around 2.5V. At room temperature if the material is driven to high potentials (above 2.45V), instead of regenerating the FeS₂ (cubic structure), FeS_x and elemental sulfur may be formed because of the relative ease of transformation from Li₂-_xFeS₂ (hexagonal) to FeS_x (hexagonal). Subsequent cycling occurs between Li₂-_xFeS₂ and Fe/Li₂S. Voltage-capacity profiles at different charging rates are shown in Figure 41. Plateaus at ~2V and 1.4- 1.5V in the discharge curve correspond to lithiation peaks in the anodic scan. The gravimetric capacity is calculated with respect to active material mass (the same for the materials to follow in this work). The cyclability is compared with commercially available pristine FeS₂, showing the enhancement of cycling performance brought about by forming nanocomposites with carbon.

[0151] When more than one metal precursor is used, the approach yielded nanocomposites with alloy nanoparticles embedded in the carbon matrix. An example of this is the iron-tin alloy, which is being actively investigated as an anode material in LIBs. Alloys of tin with another metal (e.g. Sb, Co, Fe, Ni) are able to provide some alleviation effect for the pulverization of tin through the mechanical protection offered by the other metal which gets extruded during lithiation. The incorporation of such alloy nanoparticles in a carbon matrix provides a means of additional mechanical support so that the cycling stability of the material may be further enhanced.

[0152] FeSn₂@C nanocomposites can be synthesized using a combination of iron and tin precursors, as confirmed by XRD (Figure 35A). EDX indicates the presence of iron and tin in the composite (Figures 35C and 35D) and yields an atomic ratio of Fe/Sn=0.59. The weight fraction of FeS¾ in the composite is determined using oxidative TGA to be 68% (Figure 40). The TEM images are shown in Figure 35B. There appears to be a broader distribution of nanoparticle size compared to other materials (e.g. metal oxides, sulfides) synthesized using the same approach. The reason may be that tin has a relatively low melting point and liquid tin likely formed droplets with broad size distribution before reacting with iron. Cyclic voltammograms of the material are shown in Figure 36A. The electrochemical reaction of FeS¾ in LIB can be expressed as follows: FeS¾ + 8.8Li⁺ + 8.8e -> 2Li_{4 4}Sn + Fe and Li_{4 4}Sn -> Sn + 4.4 Li⁺ + 4.4e. The reversible capacity of the material results from the repeated alloying and dealloying of lithium with tin. Multiple lithiation peaks occur in the CV indicating the multi-step reaction associated with Li-Sn alloying. Some of the important intermediate phases include Li₇Sn₃ (formed at -0.45V vs. Li/Li⁺) and Li₇Sn₂(~0.28V).

Overlapping with the SEI formation peak may have caused some broadening of these lithiation peaks. The cycling performance of the composite at different rates is compared with pristine FeSn₂ synthesized from heating a mixture of iron and tin powders at 500⁰ C and enhancement over the bare material is clearly seen.

[0153] Ex situ treatment may also be performed on metal oxides themselves to yield the oxides with different valences of the metal. This brings about a method to overcome the limitations on the types of metal oxides that can be synthesized using the current approach. There are two main reasons for this limitation. One is that in general metal salts with higher valences has a higher tendency to hydrolyze and the corresponding carboxylic acid salt may be more difficult to synthesize. For example, only Mn(CioHi9COO)₂ can be synthesized using the current approach and not Mn(CioHi9COO)3. The other is that with a given precursor, usually only one type of metal oxide can be obtained from the direct pyrolysis of the precursor. For example, the pyrolysis of the Fe(CioHi9COO)3 precursor only yields magnetite and does not directly give maghemite or hematite. With ex situ oxidation, the composites involving lower- valence metal oxides may be transformed into composites containing metal oxides with higher valences, which cannot be directly made. For example, Fe₃0₄ (magnetite) may be oxidized to maghemite or hematite and MnO may be oxidized to form Mn₃0₄. The XRD patterns of a-Fe@C (JCPDS card #06-0696), Fe₃0₄@C (#19-0629), a-Fe₂0₃@C (#33- 0664) and y-Fe₂0₃@C (#25-1402) are shown in Figure 37 A and TEM image for y-Fe₂0₃@C in 6B.

[0154] Another example is vanadium. V(V) salt is not stable in water and V₂Os cannot be directly synthesized using this approach. However, V(III) salt may be used to synthesize V(CioHi9COO)3 precursor which can be pyrolysed to form V0₂@C which is then oxidized in air to give V₂Os@C composite. The XRD patterns and TEM images of V₂Os@C (JCPDS card #41-1426) and Ti0₂@C (anatase, JCPDS card #21-1272) are shown in Figures 37C-F.

[0155] The electrochemical performance of y-Fe₂C>3@C was tested. a-Fe₂C>3 has been extensively investigated as LIB electrode materials undergoing either intercalation mechanism at low levels of lithiation or conversion reaction at high levels of lithiation and there have also been some reports on y-Fe₂C>3. Cyclic voltammograms of they-Fe₂0₃@C composite synthesized using the current method are shown in Figure 38A. Fe₂C>3

nanoparticles follow the reversible conversion reaction Fe₂C>3 + 6Li⁺ +6e 2Fe +3Li₂0 when fully lithiated. The large peak in the first cathodic scan at -0.5V vs. Li/Li⁺ is usually attributed to SEI formation and in the subsequent cycles lithiation of Fe₂C>3 takes place at -0.8V corresponding to the reduction of Fe³⁺ to Fe°. The broad peak centered at -1.7V in the anodic scan corresponds to the reoxidation of Fe to Fe . The overlapping of the traces of cyclic voltammograms indicates stable cycling performance, which is shown in Figure 38B at 1C, 0.5C and 2C charging rates.

[0156] Since the active material is incorporated in an amorphous carbon matrix, which does not make a significant contribution to the lithiation capacity, it is useful to determine the effect of the carbon. Using as an example the Fe₃0₄-carbon nanocomposite containing 66% by weight Fe₃0₄ (924mAh/g) and the balance carbon (40mAh/g), the gravimetric theoretical capacity of the composite is 620 mAh/g. From mercury porosimetry, the pore volume of carbon is found to be 0.5516 ml/g and assuming the bulk densities of magnetite and amorphous carbon to be 5.2 and 2.1 g/cm³, respectively, the volumetric theoretical capacities of magnetite and the composite are 4.81 and 1.30 Ah/cm³. Therefore the employment of the porous carbon matrix comes at the cost of a reduced volumetric capacity, which can be limited in an actual battery design by engineering the porosity and weight fraction of the carbon matrix to achieve desired gravimetric and volumetric capacity goals while preserving the improving cyclability imparted by the porous carbon support.

[0157] In conclusion, a platform has been developed whereby through the

copolymerization of organic and inorganic starting materials and formation of a hybrid followed by calcination, embedded nanostructures consisting of uniformly sized

nanoparticles incorporated in a porous carbon matrix may be synthesized in situ. Either by mere in situ reaction, or combined with ex situ engineering of the embedded material, a wide variety of embedded nanostructures may be synthesized which show enhanced lithium storage performance over the bare material. The method obviates the relatively stringent experimental control required in many other methods of creating carbon composites and provides a convenient way to prevent the aggregation of particles. Therefore the process lends itself to cheap and facile scale-up. Besides the materials, which have been demonstrated, additional categories of materials can be made using the current approach (e.g. silicon and phosphates), which is part of the ongoing work.

[0158] While the invention has been particularly shown and described with reference to specific embodiments (some of which are preferred embodiments), it should be understood by those having skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as disclosed herein.

Claims

WHAT IS CLAIMED IS:

1) A method for forming a material comprising the steps of:

contacting one or more monomers,

one or more metal precursor compounds,

optionally, an initiator, and

optionally, one or more solvents,

to form a reaction mixture,

heating the reaction mixture such that a hybrid material comprising a plurality of metal precursor compounds chemically bonded to the polymer matrix is formed and, optionally, isolating the hybrid material.

2) The method of claim 1, further comprising the step of pyrolysing the hybrid material, such that a nanocomposite material comprising a plurality of nanoparticles embedded in a carbon matrix is formed, the nanoparticles being formed from the metal component of the one or more metal precursor compounds.

3) The method of claim 1, wherein the reaction mixture comprises:

a first monomer,

optionally, a second monomer, wherein the second monomer is a cross-linking monomer,

a metal precursor compound,

an initiator,

an anionic surfactant,

water, and

one or more organic solvents,

such that a reaction mixture that is an aqueous emulsion is formed.

4) The method of claim 1, wherein the reaction mixture comprises:

a first monomer,

optionally, a second monomer,

a metal precursor compound, and water.

5) The method of claim 1, wherein the reaction mixture comprises a plurality of metal precursors, wherein the metal precursors have a different metal.

6) The method of claim 1, wherein the one or more monomers are selected from the group consisting of acrylonitrile, divinyl benzene, resorcinol, formaldehyde, vinylpyrrolidone, vinyl alcohol, acrylic acid, phenol, 1,4-butadiene, isoprene, vinylsilane, sulfur, and combinations thereof.

7) The method of claim 1, wherein the one or more metal precursor compounds are selected from the group consisting of metal carboxylates, metal coordination compounds, and combinations thereof.

8) The method of claim 2, further comprising reducing the metal oxide nanoparticles of the nanocomposite material comprising a plurality of metal oxide nanoparticles embedded in a carbon matrix by contacting the nanocomposite material with a reductant or heating the nanocomposite material under inert conditions,

such that a nanocomposite material comprising a plurality of metal nanoparticles embedded in a carbon matrix is formed.

9) The method of claim 2, further comprising contacting the nanocomposite material comprising a plurality of metal oxide nanoparticles embedded in a carbon matrix with a sulfur compound, halide compound, or phosphate compound,

such that a nanocomposite material comprising a plurality of metal sulfide, metal halide, or metal phosphate nanoparticles embedded in a carbon matrix is formed.

10) The method of claim 2, further comprising reducing the metal sulfide nanoparticles of the nanocomposite material comprising a plurality of metal sulfide nanoparticles embedded in a carbon matrix by contacting the nanocomposite material with a reductant or heating the nanocomposite material under inert conditions,

such that a nanocomposite material comprising a plurality of metal nanoparticles embedded in a carbon matrix is formed.

11) The method of claim 2, further comprising contacting the nanocomposite material comprising a plurality of metal sulfide nanoparticles embedded in a carbon matrix with an oxygen compound, halide compound, or phosphate compound,

such that a nanocomposite material comprising a plurality of metal oxide, metal halide, or metal phosphate nanoparticles embedded in a carbon matrix is formed.

12) A hybrid material comprising a plurality of metal precursor compounds embedded in a polymer,

wherein the metal precursor compounds are chemically bonded to the polymer and uniformly distributed in the polymer.

13) The hybrid material of claim 12, wherein the metal precursor compounds are selected from the group consisting of metal carboxylates, metal coordination compounds, and combinations thereof.

14) The hybrid material of claim 12, wherein the polymer is poly(acrylonitrile), polyvinylpyrroilidone, polysaccharide, acrylonitrile-divinylbenzene copolymer, phenol resin, or resorcinol-formaldehyde copolymer.

15) A nanocomposite material comprising a plurality of nanoparticles embedded in a carbon matrix,

wherein the nanoparticles are present at 40 % by weight to 90 % by weight, are from 5 nm to 500 nm in diameter, and

no phase separation between the carbon matrix and nanoparticles is observed. 16) The nanocomposite material of claim 14, wherein the nanocomposite material is Fe@C, Mn@C, FeSn₂@C, Fe₂0₃@C (e.g., a-Fe₂0₃@C, γ- Fe₂0₃@C), Fe₃0₄@C, CuO@C, Cu₂0@C, MnO@C, Mn₃0₄@C, Mn₂0₃@C, V0₂@C, V₂0₅@C, Ti0₂@C, MoS₂@C, FeS₂@C, CuF₂@C, LiFeP0₄@C and nMn_xFei_-xP0₄@C, ZnO@C, Zr0₂@C, Ti0₂@C, Co@C, CoS@C, Mno.75Feo.₂₅0@C, LiMn₀.75Feo.₂₅P0₄@C, Sn@C, Co₃0₄@C, or Cu@C.

17) A device comprising the nanocomposite material of claim 11.

The device of claim 17, wherein the device is a battery or an on-chip inductor.