WO2014066299A1

WO2014066299A1 - Lithium nanocomposite nanofibers

Info

Publication number: WO2014066299A1
Application number: PCT/US2013/066033
Authority: WO
Inventors: Yong Lak Joo; Nathaniel S. HANSEN; Kyoung Woo KIM; Yong Seok KIM
Original assignee: Cornell University
Priority date: 2012-10-23
Filing date: 2013-10-22
Publication date: 2014-05-01

Abstract

Provided herein are lithium-containing nanofibers (e.g., nanocomposite nanofibers) and processes for preparing the same. In specific examples, provided herein are nanocomposite nanofibers comprising continuous lithium matrices and nanocomposite nanofibers comprising non-aggregated lithium domains.

Description

LITHIUM NANOCOMPOSITE NANOFIBERS

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. Provisional Application No. 61/717,230, filed on October 23, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] Batteries comprise one or more electrochemical cell, such cells generally comprising a cathode, an anode and an electrolyte. Lithium ion batteries are high energy density batteries that are fairly commonly used in consumer electronics and electric vehicles. In lithium ion batteries, lithium ions generally move from the negative electrode to the positive electrode during discharge and vice versa when charging. In the as-fabricated and discharged state, lithium ion batteries often comprise a lithium alloy (such as a lithium metal oxide) at the cathode (positive electrode) and another material, generally carbon, at the anode (negative electrode).

SUMMARY OF THE INVENTION

[0003] Provided herein is an efficient lithium nanomaterials platform suitable for providing improved lithium containing electrodes. In some embodiments, provided herein are nanofibers comprising a lithium material (e.g., a lithium metal oxide, or a lithium material of any one of the formulas described herein). For example, in some instances, provided herein are nanocomposite nanofibers comprising lithium distributed along the length of a nanofiber (e.g., in a non-aggregated manner), which, in some instances, facilitates high lithium loading, and improved lithium migration in and out of the nanofiber/electrode. In other embodiments, provided herein are nanofibers comprising a continuous matrix of at least one lithium material (e.g., a core matrix and/or a sheath matrix of a lithium material - such as any lithium material described herein). Provided herein are lithium nanocomposite nanofibers (including treated and as- spun nanofibers), fluid stocks (e.g., for preparing such nanofibers), and processes for preparing lithium nanocomposite nanofibers (including treated and as-spun nanofibers).

[0004] Provided herein is one or a plurality of nanocomposite nanofibers comprising:

a. (i) a continuous matrix of at least one lithium material; (ii) a plurality of non-aggregated, discrete domains of at least one lithium material; or (iii) a combination thereof; and b. a second material.

[0005] In some embodiments, the nanocomposite nanofibers are coaxially layered nanofibers, the nanofibers comprising a core and a sheath that at least partially surrounds the core. In specific embodiments, the core comprises a lithium material and the sheath comprises a second material. In other specific embodiments, the sheath comprises a lithium material and the core comprises a second material. In some embodiments, the core comprises a first lithium material and the sheath comprises a second lithium material. In certain embodiments, the nanocomposite nanofibers comprise a continuous matrix of at least one lithium material and the continuous matrix of each nanocomposite nanofiber has an average length of at least 1 micron. In some embodiments, the nanocomposite nanofibers comprise a continuous matrix of at least one lithium material and the continuous matrix of each nanocomposite nanofiber has an average length of at least 10% (e.g., at least 50%, at least 80%, or the like) of the average length of the nanofibers.

[0006] In some embodiments, the nanocomposite nanofibers comprise non-aggregated, discrete domains of at least one lithium material and a continuous matrix of a second material. In certain embodiments, the non-aggregated discrete domains comprise non-aggregated nanoparticles comprising at least one lithium material. In some embodiments, the discrete domains comprise crystalline lithium material. In some embodiments, the nanofibers comprising non-aggregated domains do not comprise a concentration of domains 20 times higher along a 500 nm long segment along the length of the nanofiber than an adjacent 500 nm length of the nanofiber.

[0007] Generally, the lithium material comprises lithium, such as in the form of a lithium alloy. In some embodiments, the nanofibers comprising at least 30% by weight (e.g., on average) of the lithium containing material. In specific embodiments, the nanofibers comprising at least 50% by weight (e.g., on average) of the lithium containing material. In more specific embodiments, the nanofibers comprising at least 70% (e.g., on average) by weight of the lithium containing material. In still more specific embodiments, the nanofibers comprising at least 80% by weight (e.g., on average) of the lithium containing material. In yet more specific embodiments, the nanofibers comprising at least 90% by weight (e.g., on average) of the lithium containing material. In certain embodiments, the nanofibers comprising at least 0.25% by weight (e.g., on average) of the lithium (e.g., on an elemental basis). In specific embodiments, the nanofibers comprising at least 0.5% by weight (e.g., on average) of the lithium. In more specific embodiments, the nanofibers comprising at least 1% by weight (e.g., on average) of the lithium. In still more specific embodiments, the nanofibers comprising at least 2.5% by weight (e.g., on average) of the lithium. In yet more specific embodiments, the nanofibers comprising at least 5% by weight (e.g., on average) of the lithium. In some embodiments, at least 2.5% of the atoms of the nanofiber are lithium atoms (including +0 and/or +1 oxidation states). In specific embodiments, at least 5% of the atoms of the nanofiber are lithium atoms. In more specific embodiments, at least 10% of the atoms of the nanofiber are lithium atoms. In still more specific embodiments, at least 15% of the atoms of the nanofiber are lithium atoms. In yet more specific embodiments, at least 2% of the atoms of the nanofiber are lithium atoms. In specific embodiments, at least 25% of the atoms of the nanofiber are lithium atoms.

[0008] In some embodiments, the lithium containing material comprises one or more material represented by formula (I):

Li_aM_bX_c (I)

[0009] In some embodiments, M is one or more metal, X is one or more non-metal, a is 1-5 (e.g., 1-2), b is 0-5 (e.g., 0-2), and c is 0- 10 (e.g., 1-3). In specific embodiments, M is Fe, Ni, Co, Mn, V, or a combination thereof. In further or alternative specific embodiments, X is O, S, P0₄, or C. In specific embodiments, the lithium material is LiMn₂0₄,

LiNio.₄Mno.₄Coo.2O2, LiCo0₂, L1C0PO₄, LiNi0₂, Li₂Mn0₃, Li₂S, or a combination thereof. In alternative embodiments, a nanofiber provided herein comprises a material of formula (I), e.g., as a continuous matrix thereof, regardless of whether or not the nanofiber is a nanocomposite. [0010] In some embodiments, the second material comprises ceramic, metal, organic polymer, or carbon. In other specific embodiments, the second material comprises an organic polymer, e.g., water-soluble organic polymer.

[0011] In certain embodiments, the nanofiber(s) has an average diameter of less than 1 micron (e.g., less than 800 nm). In some embodiments, the nanofiber(s) has an average aspect ratio of at least 100 (e.g., at least 1000 or at least 10,000). In some embodiments, the nanofibers are cross-linked.

[0012] Also provided herein is an electrode comprising a non-woven mat of a plurality of nanocomposite nanofibers described herein. Further, provided herein is a battery (e.g., lithium ion battery) comprising such an electrode. In more specific embodiments, the lithium ion battery comprises, such as in an initial or discharged state, a negative electrode, a separator, and a positive electrode, the positive electrode comprising any nanocomposite nanofiber as described herein, or a woven mat comprising one or a plurality of such nanocomposite nanofibers.

[0013] Provided in certain embodiments herein is a process of producing a nanocomposite nanofiber (e.g., of any nanocomposite nanofiber described above), the process comprising electrospinning a fluid stock, the fluid stock comprising or prepared by combining, in any order, a lithium metal component, an organic polymer, and a fluid. In specific embodiments, the fluid comprises water or is aqueous. In some embodiments, the organic polymer is a water-soluble polymer. In some embodiments, the fluid stock is prepared by combining lithium precursor and additional (non-lithium) metal precursor (in any order). In some of such embodiments, the weight-to-weight ratio of the metal precursor (including both the lithium and non-lithium precursor) to organic polymer is at least 1 :2 (e.g., at least 1 : 1). In some embodiments, the weight-to-weight ratio of the lithium component (e.g., lithium material nanoparticles) to organic polymer is at least 1:5 (e.g., at least 1:2). In some embodiments, the process further comprises thermally treating the electrospun (e.g., as-spun) nanofiber. In some embodiments, the thermal treatment occurs under inert conditions (e.g., to carbonize the polymer). In further or alternative embodiments, the process comprises oxidizing the electrospun (e.g., as-spun) nanofiber (e.g., concurrently with thermal treatment) (e.g., to remove the polymer). In further or alternative embodiments, the process further comprises reducing the electrospun (e.g., as-spun) (or a previously treated, e.g., thermally treated) nanofiber (e.g., concurrently with thermal treatment) (e.g., to minimize oxidation of metal components).

[0014] In some embodiments, the lithium metal component is a lithium containing nanoparticle. In specific embodiments, the lithium containing nanoparticle comprises a lithium material represented by formula (I). In some embodiments, the lithium metal component is a lithium precursor (e.g., lithium salt). In specific embodiments, the lithium precursor is lithium carboxylate, lithium nitrate, lithium halide, lithium diketone, lithium halide, lithium alkoxide, or a combination theroef. In certain embodiments, the polymer is nucleophilic. In some embodiments, the polymer is polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyvinyl ether, polyvinyl pyrrolidone, polygly colic acid, hydroxyethylcellulose (HEC), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, or a combination thereof.

[0015] In some embodiments, preparation fluid stock further comprises combining, in any order, at least one non-lithium metal precursor. In certain embodiments, the non-lithium metal precursor optionally includes, by way of non-limiting example, iron precursor, nickel precursor, cobalt precursor, manganese precursor, vanadium precursor, or a combination thereof. In some embodiments, the metal concentration (including lithium and non-lithium metal) in the fluid stock is at least 200 mM (e.g., at least 250 mM, or at least 300 mM), wherein the molarity is based on moles of metal atoms, irrespective of what form the metal (including silicon) may take.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

[0017] FIG. 1 illustrates a multiaxial electro spinning (multiple fluids about a substantially common axis) system for preparing a coaxially layered nanocomposite nanofiber, and a coaxially layered nanocomposite nanofiber.

[0018] FIG. 2 illustrates a nanocomposite nanofiber comprising (i) discrete domains of a first material, and (ii) a continuous matrix (e.g., core matrix) of a second material.

[0019] FIG. 3 illustrates SEM images of both gas assisted and non-gas assisted electrospun fibers.

[0020] FIG. 4 illustrates SEM images of various lithium-containing nanofibers.

[0021] FIG. 5 illustrates XRD patterns of various lithium-containing nanofibers.

[0022] FIG. 6 illustrates SEM images of as-spun lithium- and polymer-containing (precursor) nanofiber (top) and lithium-containing nanofiber (middle). Also illustrated is a TEM image of the lithium- containing (lithium matrix) nanofiber.

[0023] FIG. 7 illustrates an XRD pattern of lithium-containing nanofibers after calcinating precursor nanofibers.

[0024] FIG. 8 illustrates the trace of a half cell test using a lithium-containing nanofiber cathode. Top: Charge-discharge curve of the first cycle at C/5 rate. Bottom: Cyclic performance, which demonstrates the initial energy density around 200 mAh/g, and around 175 mAh/g after 25 cycles.

[0025] FIG. 9 illustrates the charge/discharge curves for the first three cycles of the Li-ion full cell with lithium containing nanofiber cathode (top); and the full cell cyclic performance with lithium-containing nanofiber cathode.

[0026] FIG. 10 illustrates a cross section of lithium-containing core/ shell hybrid nanofiber (and that a precursor of such a nanofiber is optionally prepared with gas assisted electrospinning).

[0027] FIG. 11 illustrates a TEM image of a lithium-containing core/shell hybrid nanofiber.

[0028] FIG. 12 illustrates an EDX profile of a lithium-containing core/ shell hybrid nanofiber.

[0029] FIG. 13 illustrates cyclic performance of a lithium-containing core/shell hybrid nanofiber compared to a non-layered nanofiber cathode with the uniform, but same average composition,

LiNio.4COo.2Mno.4O2. DETAILED DESCRIPTION OF THE INVENTION

[0030] Provided herein are lithium containing nanofibers (e.g., nanocomposite nanofibers) and nanofiber mats and processes for preparing lithium containing nanofibers (e.g., nanocomposite nanofibers) and nanofiber mats. In certain embodiments, a nanofiber (e.g., of a plurality of nanofibers, of a nanofiber mat, or of a process described herein) comprise at least one lithium-containing material (e.g., in a nanofiber core and/or sheath). In some embodiments, a nanofiber (e.g., of a plurality of nanofibers, of a nanofiber mat, or of a process described herein) comprise a first material and a second material (e.g., the first and second materials comprising different compositions of matter, chemically - i.e., different chemical formulas), the first material comprising a lithium containing material. In further embodiments, the first material, the second material, or both form a continuous matrix within the nanofiber (e.g., a core and/or sheath material). In specific embodiments, both the first and second materials form continuous matrix materials within the nanofiber (e.g., a core and a sheath). In other specific embodiments, the first material comprises a plurality of discrete domains within the nanofiber. In more specific embodiments, the second material is a continuous matrix material within the nanofiber.

[0031] In some embodiments, nanofibers provide herein are coaxially layered nanofibers, the nanofibers comprising a core and a sheath that at least partially surrounds the core. In some embodiments, the sheath runs along the entire length of the nanofiber. In other embodiments, the sheath runs along at least a portion of the nanofiber. In certain embodiments, the core comprises a lithium material and the sheath comprises a second material. In other embodiments, the sheath comprises a lithium material and the core comprises a second material. In specific embodiments, the second material is a second lithium material (i.e., both the sheath and the core comprise a lithium material, which may be the same or different). In other embodiments, the second material is a non-lithium containing material.

[0032] FIG. 1 illustrates a nanofiber provided herein comprising a first and a second continuous matrix material, wherein the first and second continuous matrix materials are coaxially layered. In specific embodiments, the first (lithium containing) material forms the core 110 of the coaxially layered nanofiber

107 (illustrated in the cross sectional view 111) and the second material forms a layer 109 at least partially surrounding the core 110. In other specific embodiments, the second material forms the core 110 of the coaxially layered nanofiber 107 (illustrated in the cross sectional view 111) and the first (lithium containing) material forms a layer 109 at least partially surrounding the core 110. In some instances, the nanofibers are prepared by coaxially electrospinning the two layers with a third coaxial layer 108. In some embodiments, the third coaxial layer 108 comprises a third matrix material. In other embodiments, the third coaxial layer 108 comprises air, e.g., for gas assisting the electrospinning process. Moreover, in some embodiments, the core 110 is optionally hollow, with one or both of the outer layers 109 and/or 108 comprising a lithium material. FIG. 1 also illustrates an exemplary system or schematic of a process described herein, particularly a system or process for preparing a coaxially layered nanocomposite nanofiber (e.g., by a coaxial gas assisted electrospinning process). In some instances, a first fluid stock

101 (e.g., comprising a lithium component and a polymer) is electrospun with a second fluid stock 102

(e.g., comprising a second metal precursor and a second polymer, the second precursor and polymer independently being either the same or different from the first), and a third fluid (e.g., gas or third fluid stock) 103. The fluid stocks may be provided to an electrospinning apparatus by any device, e.g., by a syringe 105. And a gas may be provided from any source 106 (e.g., air pump). In some embodiments such a system comprises a plurality of co-axial needles 104. In some embodiments, the electrospun nanofiber 107 is collected on a grounded collector (not shown). Similarly, 111 is representative of an exemplary cross section of coaxial needles/spinnerets. For example, exemplary co-axial needles comprise an outer sheath tube (which would be represented by 108) at least one intermediate tube (which is optionally absent, which would be represented by 109), and a core tube (which would be represented by 110). In specific embodiments, such tubes are aligned along a common axis (e.g., aligned within 5 degrees of one another). In some instances, the tubes are slightly offset, but the angle of the tubes is substantially aligned (e.g., within 5 degrees of one another).

[0033] In some embodiments, a nanocomposite nanofiber provided herein comprises (i) a lithium material (e.g., lithium metal oxide); and (ii) a continuous matrix material (e.g., ceramic, metal, or carbon). In certain embodiments, the continuous matrix is a continuous core matrix (e.g., not a hollow tube). In some embodiments, the lithium material forms discrete isolated domains of the nanocomposite nanofibers. In some specific embodiments, the lithium material domains are non-aggregated.

[0034] FIG. 2 illustrates a lithium nanocomposite nanofiber 200 comprising (i) discrete domains of lithium material 201, and (ii) a continuous core matrix 202. As illustrated in the cross-sectional view 203, the discrete domains of lithium material 204 may penetrate into the core 205 of the nanocomposite nanofiber. In some instances, the nanocomposite nanofibers comprise lithium material on the surface of the nanofiber. And in some instances, the nanofibers comprise or further comprise discrete domains of lithium material completely embedded within the core matrix material.

[0035] In certain embodiments, continuous matrix materials of any nanocomposite nanofiber described herein is continuous over at least a portion of the length of the nanocomposite nanofiber. In some embodiments, the continuous matrix material runs along at least 10% the length of the nanofiber (e.g., on average for a plurality of nanofibers). In more specific embodiments, the continuous matrix material runs along at least 25% the length of the nanofiber (e.g., on average for a plurality of nanofibers). In still more specific embodiments, the continuous matrix runs along at least 50% the length of the nanofiber (e.g., on average for a plurality of nanofibers). In yet more specific embodiments, the continuous matrix runs along at least 75% the length of the nanofiber (e.g., on average for a plurality of nanofibers). In some embodiments, the continuous matrix is found along at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, or at least 99% the length of the nanofiber (e.g., on average for a plurality of nanofibers). In some embodiments, the continuous matrix material runs along at least 1 micron of the length of the nanofiber (e.g., on average for a plurality of nanofibers). In more specific embodiments, the continuous matrix material runs along at least 10 microns of the length of the nanofiber (e.g., on average for a plurality of nanofibers). In still more specific embodiments, the continuous matrix runs along at least 100 microns of the length of the nanofiber (e.g., on average for a plurality of nanofibers). In yet more specific embodiments, the continuous matrix runs along at least 1 mm of the length of the nanofiber (e.g., on average for a plurality of nanofibers). [0036] In some embodiments, a nanocomposite nanofiber provide herein comprises discrete domains within the nanocomposite nanofiber. In specific embodiments, the discrete domains comprise a lithium material. In certain embodiments, the discrete domains are non-aggregated. In some embodiments, the non-aggregated domains are dispersed, e.g., in a substantially uniform manner, along the length of the nanofiber. In certain embodiments, the nanocomposite nanofibers provided herein do not comprise a concentration of domains in one segment (e.g., a 500 nm, 1 micron, 1.5 micron, 2 micron) segment that is over 10 times (e.g., 20 times, 30 times, 50 times, or the like) as concentrated as an immediately adjacent segment. In some embodiments, the segment size for such measurements is a defined length (e.g., 500 nm, 1 micron, 1.5 micron, 2 micron). In other embodiments, the segment size is a function of the average domain (e.g., particle) size (e.g., the segment 5 times, 10 times, 20 times, 100 times the average domain size). In some embodiments, the domains have a (average) size 1 nm to 1000 nm, 1 nm to 500 nm, 1 nm to 200 nm, 1 nm to 100 nm, 20 nm to 30 nm, 1 nm to 20 nm, 30 nm to 90 nm, 40 nm to 70 nm, 15 nm to 40 nm, or the like.

Lithium Material

[0037] In various embodiments, the lithium material in a nanocomposite nanofiber provided herein is any suitable lithium material. In some embodiments, the lithium material is a lithium alloy (e.g., a lithium metal oxide), or a lithium precursor (e.g., a lithium salt). In certain embodiments, the lithium material is a material suitable for use in a lithium ion battery cathode or positive electrode. In some embodiments, the lithium material is a precursor material capable of being converted into a material suitable for use in a lithium ion battery cathode or positive electrode. In various embodiments, the lithium of the lithium material is in a zero oxidation state, a positive oxidation state, or a combination thereof. In specific embodiments, the lithium of the lithium material is generally in a positive oxidation state (e.g., a +1 oxidation state, or having an average oxidation state of at least +0.95, on average).

[0038] In certain embodiments, provided herein are nanocomposite nanofibers comprising a lithium material, the lithium material comprising lithium (and other optional elements - e.g., cations and/or anions). In specific embodiments, the nanocomposite nanofibers comprise at least 25% by weight of the lithium material (e.g., on average for a plurality of nanofibers). In more specific embodiments, the nanocomposite nanofibers comprise at least 50% by weight of the lithium material (e.g., on average for a plurality of nanofibers). In still more specific embodiments, the nanocomposite nanofibers comprise at least 60% by weight of the lithium material (e.g., on average for a plurality of nanofibers). In yet more specific embodiments, the nanocomposite nanofibers comprise at least 70% by weight of the lithium material (e.g., on average for a plurality of nanofibers). In specific embodiments, the nanocomposite nanofibers comprise at least 80% by weight of the lithium material (e.g., on average for a plurality of nanofibers).

[0039] In certain embodiments, the nanocomposite nanofibers comprise at least 0.5% by weight of lithium (e.g., on an elemental basis) (e.g., on average for a plurality of nanofibers). In specific embodiments, the nanocomposite nanofibers comprise at least 1 % by weight of the lithium (e.g., on average for a plurality of nanofibers). In more specific embodiments, the nanocomposite nanofibers comprise at least 2.5% by weight of lithium (e.g., on average for a plurality of nanofibers). In yet more specific embodiments, the nanocomposite nanofibers comprise at least 5% by weight of lithium (e.g., on average for a plurality of nanofibers). In specific embodiments, the nanocomposite nanofibers comprise at least 10% by weight of lithium (e.g., on average for a plurality of nanofibers).

[0040] In some embodiments, the nanocomposite nanofibers comprise at least 2.5% of the atoms of the nanofiber or the lithium material are lithium (e.g., on average for a plurality of nanofibers). In specific embodiments, the nanocomposite nanofibers comprise at least 5% of the atoms of the nanofiber or the lithium material are lithium (e.g., on average for a plurality of nanofibers). In more specific embodiments, the nanocomposite nanofibers comprise at least 10% of the atoms of the nanofiber or the lithium material are lithium (e.g., on average for a plurality of nanofibers). In yet more specific embodiments, the nanocomposite nanofibers comprise at least 15 of the atoms of the nanofiber or the lithium material are lithium (e.g., on average for a plurality of nanofibers). In specific embodiments, the nanocomposite nanofibers comprise at least 25% of the atoms of the nanofiber or the lithium material are lithium (e.g., on average for a plurality of nanofibers).

[0041] In some embodiments, the lithium material is or comprises one or more material represented by formula (I):

Li_aM_bX_c (I)

[0042] In some embodiments, M is one or more metal (e.g., Fe, Ni, Co, Mn, V, Ti, Zr, Ru, Re, Pt, Bi, Pb, Cu, Al, Li, such as cations thereof). In certain embodiments, X is one or more non-metal (e.g., C, N, O, P, S, S0₄, P0₄, Se, halide, F, CF, S0₂, S0₂C1₂, I, Br, or a combination thereof, such as anions thereof). In some embodiments, a is 1-5 (e.g., 1-2). In certain embodiments, b is 0-5 (e.g., 0-2). In some embodiments, c is 0-10 (e.g., 1 -3). In various embodiments, M has any suitable (average) oxidation state, such as +1 to +6, e.g., +3 or +4.

[0043] In certain embodiments, M is Fe, Ni, Co, Mn, V, or a combination thereof. In some embodiments, X is O or C. In certain embodiments, a is 1-2. In some embodiments, b is 0-2. In certain embodiments, c is 1-3.

[0044] In specific embodiments, the lithium material(s) comprises LiMn₂0₄,

LiNio.₄Mn₀.₄Coo.₂0₂, LiCo0₂, L1C0PO₄, LiNi0₂, Li₂Mn0₃, Li₂S,or a combination thereof.

[0045] In more specific embodiments, the lithium material of formula (I) is represented by the lithium material of formula (la):

Li_aM_b0₂ (la)

[0046] In specific embodiments, M, a, and b are as described above. In specific embodiments, a lithium material of formula (la) has the structure LiM0₂ (e.g.,

In some embodiments, a and b are each 1 and the one or more metal of M have an average oxidation state of 3.

[0047] In more specific embodiments, the lithium material of formula (la) is represented by the lithium material of formula (lb):

Li(M'₍₁__g)Mn_g)0₂ (lb) [0048] In certain embodiments, M' represents one or more metal element (e.g., M' represents Fe, Ni, Co, Mn, V, Li, Cu, Zn, or a combination thereof). In some embodiments, g is 0-1 (e.g., 0<g<l). In specific embodiments, M' represents one or more metal having an average oxidation state of +3.

[0049] In more specific embodiments, the lithium material of formula (la) or (lb) is represented by the lithium material of formula (Ic):

Li[Li₍₁._2h)/3)M"_hMn₍₂._ll)/3)0₂ (Ic)

[0050] In certain embodiments, M" represents one or more metal element (e.g., M" represents Fe, Ni, Co, Zn, V, or a combination thereof). In some embodiments, h is 0-0.5 (e.g., 0<A<0.5, such as 0.083<A<0.5). In a specific embodiment, the lithium material of formula (Ic) is Li[Li₍i_₂h_{) 3}Ni_ll'Co(_ll.h'₎Mn(2.h) 3)02, wherein A' is 0-0.5 (e.g., 0<A'<0.5).

[0051] In more specific embodiments, the lithium material of formula (la) is represented by the lithium metal of formula (Id):

LiNi_b.Co_b..M"'_b .0₂ (Id)

[0052] In certain embodiments, M'" represents one or more metal element (e.g., M'" represents Fe, Mn, Zn, V, or a combination thereof). In some embodiments, each of b ', b", and b'" is independently 0-2 (e.g., 0-1, such as 0< b ', b ", and b "'<\). In specific embodiments, the sum of b', b", and b '" is 1. In some embodiments, the one or more metal of M'" when taken together with the Ni and Co have an average oxidation state of +3.

[0053] In some embodiments, the lithium material of formula (I) is represented by the lithium material of formula (Ie):

Li_aM_b0₃ (Ie)

[0054] In specific embodiments, M, a, and b are as described above. In specific embodiments, a lithium material of formula (Ie) has the structure Li₂M0₃ (e.g., Li₂Mn0₃). In some embodiments, a is 2, b is 1 and the one or more metal of M have an average oxidation state of +4.

Second Material

[0055] In some embodiments, a nanocomposite nanofiber provided herein comprises a lithium material and a second material. In certain embodiments, additional materials are optionally present. In some embodiments, the second material is a continuous matrix material, as described herein. In certain embodiments, the second material is a second lithium material, as described herein, such as a lithium material of any one of formulas (I)-(Ie). In some embodiments, the second material is a polymer (e.g., an organic polymer, such as a water soluble organic polymer). In other embodiments, the second material is a metal oxide, a ceramic, a metal (e.g., a single metal material or an alloy), carbon, or the like. In some embodiments, the second material comprises at least 10%, at least 15%, at least 20%, at least 30% or the like of the second material.

[0056] In certain embodiments, the nanocomposite nanofibers provided herein comprise a first lithium material and a second lithium material. In specific embodiments, the first lithium material is a first continuous matrix material and the second lithium material is a second continuous matrix material. In more specific embodiments, the first lithium material forms the core of a coaxially layered nanocomposite nanofiber and the second lithium material forms the sheath at least partially surrounding the core. In certain embodiments, such nanocomposite nanofibers optionally comprise an additional matrix material between the lithium containing core and lithium containing sheath, and/or an additional matrix material at least partially surrounding the lithium containing sheath. In specific embodiments, the lithium containing core material is a lithium material of formula (Ie) and the lithium containing sheath material of formula (la).

Nanofibers

[0057] In certain embodiments, nanocomposite nanofiber provided herein have any suitable characteristic.

[0058] In some embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 2 microns (e.g., an average diameter of a plurality of nanofibers). In specific embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 1.5 microns (e.g., an average diameter of a plurality of nanofibers). In more specific embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 1 micron (e.g., an average diameter of a plurality of nanofibers). In still more specific embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 850 nm (e.g., an average diameter of a plurality of nanofibers). In yet more specific embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 750 nm (e.g., an average diameter of a plurality of nanofibers). In more specific embodiments, a nanocomposite nanofiber provided herein has a diameter of less than 600 nm (e.g., an average diameter of a plurality of nanofibers). In some embodiments, a nanofiber provided herein has a diameter of at least 50 nm. In specific embodiments, a nanofiber provided herein has a diameter of at least 100 nm (e.g., 100 nm to 1 micron). In still more specific embodiments, a nanofiber provided herein has a diameter of at least 200 nm (e.g., 200 nm to 1 micron).

[0059] In some embodiments, nanocomposite nanofibers provided herein have a (e.g., average) length of at least 1 μηι, at least 10 μηι, at least 20 μηι, at least 100 μηι, at least 500 μηι, at least 1,000 μηι, at least 5,000 μηι, at least 10,000 μηι, or the like. In specific embodiments, nanofibers provided herein have a (e.g., average) length of at least 1 mm.

[0060] In some embodiments, a nanocomposite nanofiber provided herein has an aspect ratio of greater than 10 (e.g., an average aspect ratio of a plurality of nanofibers). In specific embodiments, a nanocomposite nanofiber provided herein has an aspect ratio of greater than 100 (e.g., an average aspect ratio of a plurality of nanofibers). In more specific embodiments, a nanocomposite nanofiber provided herein has an aspect ratio of greater than 500 (e.g., an average aspect ratio of a plurality of nanofibers). In still more specific embodiments, a nanocomposite nanofiber provided herein h has an aspect ratio of greater than 1000 (e.g., an average aspect ratio of a plurality of nanofibers). In yet more specific embodiments, a nanocomposite nanofiber provided herein has an aspect ratio of greater than 10⁴ (e.g., an average aspect ratio of a plurality of nanofibers).

[0061] In some embodiments, the nanocomposite nanofiber is crosslinked. In specific instances, the second material (e.g., non-lithium containing second material) of the nanocomposite nanofiber provided herein is crosslinked with the second material of one or more adjacent nanofiber. [0062] In some embodiments, nanofibers provided herein comprise (e.g., on average) at least 99%, at least 98%, at least 97%, at least 96 %, at least 95%, at least 90%, at least 80%, or the like of metal, oxygen and carbon, when taken together, by mass (e.g., elemental mass). In specific embodiments, nanofibers (e.g., on average) provided herein comprise at least 99%, at least 98%, at least 97%, at least 96 %, at least 95%, at least 90%, at least 80%, or the like of metal and oxygen, when taken together, by mass (e.g., elemental mass).

[0063] In some embodiments, the porosity of a nanofiber mat (comprising one or more nanofiber described herein) is at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 50%, or the like. Porosity can be measured in any suitable manner. For example, in some instances, the porosity of a nanofiber mat is determined by measuring the fluid volume present in the nanofiber mat after the nanofiber mat is submerged in or filled with a fluid.

[0064] Described herein are nanofibers and methods for making nanofibers that have a plurality of pores. The pores may be of any suitable size or shape. In some embodiments the pores are "mesopores", having a diameter of less than 100 nm (e.g., between 2 and 50 nm, on average). In some embodiments, the pores are "ordered", such as having a substantially uniform shape, a substantially uniform size and/or are distributed substantially uniformly through the nanofiber. In some embodiments, nanofibers described herein have a high surface area and/or specific surface area (e.g., surface area per mass of nanofiber and/or surface area per volume of nanofiber). In some embodiments, nanofibers described herein comprise ordered pores, e.g., providing substantially flexible and/or non-brittleness.

[0065] In some embodiments, nanofibers provided herein comprise a lithium material that is highly crystalline. In specific embodiments, the lithium material is at least 50% crystalline. In more specific embodiments, the lithium material is at least 75% crystalline. In still more specific embodiments, the lithium material is at least 90% crystalline.

[0066] In one aspect, described herein are nanofibers comprising any one or more of: (a) a surface area of at least 10 π r h, wherein r is the radius of the nanofiber and h is the length of the nanofiber; (b) a specific surface area of at least 10 m²/g (e.g., 100 m²/g); (c) a porosity of at least 20% and a length of at least 1 μηι; (d) a porosity of at least 35%, wherein the nanofiber is substantially contiguous; (e) a porosity of at least 35%, wherein the nanofiber is substantially flexible or non-brittle; (f) a plurality of pores with an average diameter of at least 1 nm; (g) a plurality of pores, wherein the pores have a substantially uniform shape; (h) a plurality of pores, wherein the pores have a substantially uniform size; and (i) a plurality of pores, wherein the pores are distributed substantially uniformly throughout the nanofiber.

[0067] In some embodiments, the pores comprise spheres, cylinders, layers, channels, or any combination thereof. In some embodiments, the pores are helical. In some embodiments, the nanofiber comprises metal, metal alloy, ceramic, polymer, or any combination thereof.

[0068] In one aspect, described herein is a method for producing an ordered mesoporous nanofiber, the method comprising: (a) coaxially electrospinning a first fluid stock with a second fluid stock to produce a first nanofiber, the first fluid stock comprising at least one block co-polymer and a lithium component

(e.g., lithium precursor), the second fluid stock comprising a coating agent, and the first nanofiber comprising a first layer (e.g., core) and a second layer (e.g., coat) that at least partially coats the first layer; (b) annealing the first nanofiber; (c) optionally removing the second layer from the first nanofiber to produce a second nanofiber comprising the block co-polymer; and (d) selectively removing at least part of the block co-polymer from the first nanofiber or the second nanofiber (e.g. thereby producing an ordered mesoporous nanofiber). Additional coaxial layers are optional - e.g., comprising a precursor and block copolymer for an additional mesoporous layer, or a precursor and a polymer as described herein for a non- mesoporous layer.

[0069] In some embodiments, the block co-polymer comprises a polyisoprene (PI) block, a polylactic acid (PLA) block, a polyvinyl alcohol (PVA) block, a polyethylene oxide (PEO) block, a polyvinylpyrrolidone (PVP) block, polyacrylamide (PAA) block or any combination thereof (i.e., thermally or chemically degradable polymers).

[0070] In some embodiments, the block co-polymer further comprises a block that does not degrade under conditions suitable for degrading and/or removing the degradable and/or removable block.

[0071] In some embodiments, the block co-polymer comprises a polystyrene (PS) block, a poly(methyl methacrylate) (PMMA) block, a polyacrylonitrile (PAN) block, or any combination thereof (i.e., thermally or chemically stable polymers).

[0072] In some embodiments, the coating layer and at least part of the block co-polymer (concurrently or sequentially) is selectively removed in any suitable manner, such as, by heating, by ozonolysis, by treating with an acid, by treating with a base, by treating with water, by combined assembly by soft and hard (CASH) chemistries, or any combination thereof.

[0073] Additionally, U.S. Application Ser. No. 61/599,541 is incorporated herein by reference for disclosures related to such techniques.

Batteries and Electrodes

[0074] In some embodiments, provided herein is a battery (e.g., a primary or secondary cell) comprising at least one nanofiber described herein. In specific instances, the battery comprises plurality of such nanofibers, e.g., a non-woven mat thereof. In some embodiments, the battery comprises at least two electrodes (e.g., an anode and a cathode) and a separator, at least one of the electrodes comprising at least one nanofiber described herein. In specific embodiments, the battery is a lithium-ion battery and the cathode comprises at least one nanofiber described herein (e.g., a nanofiber mat thereof). Likewise, provided herein is an electrode comprising any nanocomposite nanofiber described herein (e.g., a nanofiber mat comprising one or more such nanofibers).

[0075] In some embodiments, layered nanofibers described herein have a specific capacity (as a lithium ion battery cathode material) that is at least 1.5 times as great (e.g., initial, or after 5 or 10 cycles) as the a non-layered cathode material having the same average composition. In some embodiments, the specific capacity is at least 2 times as great as the non-layered cathode nanofiber material having the same average composition. In some embodiments, the percentage capacity decay of a layered nanofiber material provided herein is less than 3/4 of a non-layered cathode nanofiber material having the same average composition. In specific embodiments, the percentage capacity decay of a layered nanofiber material provided herein is less than half of a non-layered cathode nanofiber material having the same average composition. For example, FIG. 13 illustrates cyclic performance of coaxial (layered) nanofiber cathode with composition gradient (core: Mn Rich, LiNio.₂Coo.₂Mno.6O₂, shell: Ni-rich, LiNio.6Coo.₂Mno.₂O₂) The cyclic performance of the non-layered nanofiber cathode with the uniform, but same average composition, LiNio.₄COo.₂Mno.₄O₂ is shown for comparison. As demonstrated by the figure, in some instances, layered nanofibers with composition gradient exhibits high capacity and better stability than nanofiber with uniform composition. In certain embodiments, provided herein is an electrode or a lithium ion battery comprising such nanofibers as a cathode or cathode material.

[0076] In some embodiments, nanofibers described herein have an initial energy density (as a lithium ion battery cathode material) that is at least 150 mAh/g. In specific embodiments, nanofibers described herein have an initial energy density (as a lithium ion battery cathode material) that is at least 200 mAh/g. In some embodiments, nanofibers described herein have an energy density (as a lithium ion battery cathode material) after 25 cycles that is at least 125 mAh/g. In some embodiments, nanofibers described herein have an energy density (as a lithium ion battery cathode material) after 25 cycles that is at least 175 mAh/g. In some embodiments, provided herein is a lithium ion battery comprising lithium-containing nanofibers described herein and having an initial energy density of at least 500 Wh/kg. In specific embodiments, provided herein is a lithium ion battery comprising lithium-containing nanofibers described herein and having an initial energy density of at least 650 Wh/kg. In some embodiments, provided herein is a lithium ion battery comprising lithium-containing nanofibers described herein and having an energy density after 25 cycles of at least 400 Wh/kg. In some embodiments, provided herein is a lithium ion battery comprising lithium-containing nanofibers described herein and having an energy density after 25 cycles of at least 500 Wh/kg. FIG. 8 illustrates the trace of a half cell test using a LiMni ₃Nii ₃Coi ₃0₂ nanofiber cathode. Top: Charge-discharge curve of the first cycle at C/5 rate. Bottom: Cyclic performance, which demonstrates the initial energy density around 200 mAh/g, and around 175 mAh/g after 25 cycles. FIG. 9 (top) illustrates the charge/discharge curves for the first three cycles of the Li-ion full cell with Si-C composite nanofiber anode and LiMn_{1 3}Ni_{1 3}Co_{1 3}0₂ nanofiber cathode. FIG. 9 (bottom) illustrates the full cell cyclic performance with Si-C nanofiber anode and LiMni ₃Nii ₃Coi ₃0₂ nanofiber cathode which demonstrates the initial energy density over 650 Wh/kg, and around 500 Wh/kg after 25 cycles.

Process

[0077] In certain embodiments, provided herein is a process for preparing lithium containing nanocomposite nanofibers. In some embodiments, such lithium containing nanocomposite nanofibers comprise high amounts of lithium (e.g., as described herein). Moreover, in some embodiments, provided herein are high quality nanofibers and processes for preparing high quality nanofibers that have good structural integrity, few voids, few structural defects, tunable length, and the like. In certain embodiments, high loading of precursor or other lithium component, relative to polymer loading, in the fluid stock and/or precursor/electrospun nanofibers, facilitates and/or provides such high quality nanofibers. In general, the processes described herein provide the ability to prepare nanostructures with improved performance properties over other nanostructures, such as those prepared by nanowire growth, including deposition, precipitation and growth techniques.

[0078] In some embodiments, the electrospun nanofiber comprising a lithium material and a polymer is prepared by electrospinning a fluid stock, the fluid stock comprising (1) a lithium metal component; and (2) polymer. In specific embodiments, the lithium metal component comprises a metal precursor, a lithium containing nanoparticle (e.g., a nanoparticle comprising a lithium metal oxide or any material of any one of formulas (I)-(Ie)). In more specific embodiments, the lithium metal component is a lithium precursor (e.g., a lithium salt). In other specific embodiments, the lithium metal component is a nanoparticle.

[0079] In certain embodiments, the electrospun nanofiber comprising a metal reagent component and a polymer is prepared by electrospinning a fluid stock, the fluid stock comprising (1) a lithium salt; (2) a non-lithium metal precursor (e.g., a cobalt precursor); and (3) polymer. In some embodiments, the process further comprises coaxially electrospinning the fluid stock with a second fluid stock (along a common longitudinal axis). In some embodiments, the second fluid stock comprises a polymer. In specific embodiments, the second fluid stock further comprises a metal precursor (e.g., a lithium and/or other metal precursor). In certain embodiments, the second fluid stock is electrospun in a surrounding manner to the (first) fluid stock. In other embodiments, the (first) fluid stock is electrospun in a surrounding manner to the second fluid stock.

[0080] In specific embodiments, the process further comprises treating the electrospun (e.g., as-spun, or pre-treated, such as with low temperature annealing or washing) nanocomposite nanofiber (e.g., comprising polymer, lithium salt or ion (which may be in association with an anionic group of the polymer or an another anion), and a metal precursor (which, likewise, may be in association with the polymer or another group or anion). In some embodiments, the electrospun nanocomposite nanofiber provided herein comprises a core matrix and a sheath matrix. In specific embodiments, the core matrix comprises a polymer and a metal precursor (e.g., lithium ions in association with a ligand and/or the polymer and/or other metal precursor optionally in association with a ligand or the polymer), and the sheath matrix comprises a polymer and a metal precursor, which is the same or different from the metal precursor of the core matrix. In more specific embodiments, the core matrix comprises polymer (e.g., PVA), lithium (e.g., lithium ions) and a first non-lithium metal precursor, and the sheath matrix comprises polymer (e.g., PVA), lithium (e.g., lithium ions), and a second non-lithium metal precursor. In still more specific embodiments, the first non-lithium metal precursor and second non-lithium metal precursor are different. In further or alternative embodiments, the ratio of core matrix lithium to first non-lithium metal precursor is different from the ratio of the sheath matrix lithium to second non-lithium metal precursor (e.g., wherein the first and second non-lithium metal precursors are the same). Generally, the ratios utilized or present are at least as great as the ratios of lithium to non-lithium metal found in any of the formulas described herein. For example, if a lithium metal oxide of Formula I is being prepared, the lithium to non-metal precursor is at least as great as a:b. In some embodiments, the ratio is at least 1:2 (e.g., at least 1: 1). In more specific embodiments, the ratio is at least 3:2 (e.g., at least 2: 1). In specific embodiments, the ratio in the core matrix at least 3:2 and the ratio in the sheath matrix is 1 :2 to 3:2. [0081] In other specific embodiments, the electrospun nanofiber comprising a metal reagent component and a polymer is prepared by electrospinning a fluid stock, the fluid stock comprising (1) a plurality of nanoparticles comprising a material of any one of formulas (I)-(Ie) or a lithium metal oxide; and (2) polymer.

[0082] In specific embodiments, the fluid stock comprises an aqueous medium (e.g., water or an aqueous mixture, such as water/alcohol, water/acetic acid, or the like).

[0083] In some embodiments, the treatment process comprises (a) thermal treatment; (b) chemical treatment; or (c) a combination thereof. In specific embodiments, treatment of the electrospun (e.g., as- spun) nanocomposite nanofiber comprises thermally treating the electrospun (e.g., as-spun) nanocomposite nanofiber under oxidative conditions (e.g., air). In other specific embodiments, treatment of the electrospun (e.g., as-spun) nanocomposite nanofiber comprises thermally treating the electrospun (e.g., as-spun) nanocomposite nanofiber under inert conditions (e.g., argon). In still other specific embodiments, treatment of the electrospun (e.g., as-spun) nanocomposite nanofiber comprises thermally treating the electrospun (e.g., as-spun) nanocomposite nanofiber under reducing conditions (e.g., hydrogen, or a hydrogen/argon blend). In certain embodiments, the electrospun (e.g., as-spun) nanofiber is heated to a temperature of about 500 °C to about 2000 °C, at least 900 °C, at least 1000 °C, or the like. In specific embodiments, the electrospun (e.g., as-spun) nanofiber is heated to a temperature of about 1000 °C to about 1800 °C, or about 1000 °C to about 1700 °C.

[0084] In one aspect, the process has a high yield (e.g., which is desirable for embodiments in which the precursor is expensive). In some embodiments, the metal atoms in the nanofiber are about 10%, about 20%, about 30%, about 33%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 98%, or about 100% of the number of (e.g., in moles) metal (i.e., lithium and other metal) molecules in the fluid stock.

[0085] In some embodiments, the fluid stock is uniform or homogenous. In specific embodiments, the process described herein comprises maintaining fluid stock uniformity or homogeneity. In some embodiments, fluid stock uniformity and/or homogeneity is achieved or maintained by any suitable mechanism, e.g., by agitating, heating, or the like. Methods of agitating include, by way of non-limiting example, mixing, stirring, shaking, sonicating, or otherwise inputting energy to prevent or delay the formation of more than one phase in the fluid stock.

[0086] In some embodiments, (e.g., where metal precursors are utilized, such as a lithium salt and one or more additional (non-lithium) metal precursor) the weight ratio of the metal component(s) (including lithium and other metal components, such as lithium and metal precursors) to polymer is at least 1 :2, at least 1 : 1, at least 1.25: 1, at least 1.5: 1, at least 1.75: 1, at least 2: 1, at least 3: 1, or at least 4: 1. In some embodiments, the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 100 mM. In specific embodiments, the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 200 mM. In more specific embodiments, the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 400 mM. In still more specific embodiments, the monomeric residue (i.e., repeat unit) concentration of the polymer in the fluid stock is at least 500 mM. In some embodiments, the fluid stock comprises at least about 0.5 weight %, at least about 1 weight %, at least about 2 weight %, at least about 5 weight %, at least about 10 weight %, or at least about 20 weight polymer.

[0087] In some embodiments, the optional or additional metal precursor comprises an alkali metal salt or complex, an alkaline earth metal salt or complex, a transition metal salt or complex, or the like. In specific embodiments, the optional or additional metal precursor comprises an iron precursor, a nickel precursor, a cobalt precursor, a manganese precursor, a vanadium precursor, a titanium precursor, a ruthenium precursor, a rhenium precursor, a platinum precursor, a bismuth precursor, a lead precursor, a copper precursor, an aluminum precursor, or the like. In specific embodiments, metal (lithium and other metals) precursors include metal salts or complexes, wherein the metal is associated with any suitable anion or other Lewis Base, e.g., a carboxylate (e.g., -OCOCH₃ or another -OCOR group, wherein R is an alkyl, substituted alkyl, aryl, substituted aryl, or the like), an alkoxide (e.g., a methoxide, ethoxide, isopropyl oxide, t-butyl oxide, or the like), a halide (e.g., chloride, bromide, or the like), a diketone (e.g., acetylacetone, hexafluoroacetylacetone, or the like), a nitrates, amines (e.g., NR'₃, wherein each R" is independently R or H or two R", taken together form a heterocycle or heteroaryl), and combinations thereof.

[0088] In some embodiments, a polymer in a process or nanocomposite nanofiber described herein is an organic polymer. In some embodiments, polymers used in the compositions and processes described herein are hydrophilic polymers, including water-soluble and water swellable polymers. In some aspects, the polymer is soluble in water, meaning that it forms a solution in water. In other embodiments, the polymer is swellable in water, meaning that upon addition of water to the polymer the polymer increases its volume up to a limit. Exemplary polymers suitable for the present methods include but are not limited to polyvinyl alcohol ("PVA"), polyvinyl acetate ("PVAc"), polyethylene oxide ("PEO"), polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid, hydroxyethylcellulose ("HEC"), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, and the like. In some embodiments, the polymer is isolated from biological material. In some embodiments, the polymer is starch, chitosan, xanthan, agar, guar gum, and the like.

[0089] In some embodiments, a polymer described herein (e.g., in a process, precursor nanofiber, a fluid stock, or the like) is a polymer (e.g., homopolymer or copolymer) comprising a plurality of reactive sites. In certain embodiments, the reactive sites are nucleophilic (i.e., a nucleophilic polymer) or electrophilic (i.e., an electrophilic polymer). For example, in some embodiments, a nucleophilic polymer described herein comprises a plurality of alcohol groups (such as polyvinyl alcohol - PVA - or a cellulose), ether groups (such as polyethylene oxide - PEO - or polyvinyl ether - PVE), and/or amine groups (such as polyvinyl pyridine, ((di/mono)alkylamino)alkyl alkacrylate, or the like).

[0090] In certain embodiments, the polymer is a nucleophilic polymer (e.g., a polymer comprising alcohol groups, such as PVA). In some embodiments, the polymer is a nucleophilic polymer and a lithium and/or optional metal precursor is an electrophilic precursor (e.g., a metal acetate, metal chloride, or the like). In specific embodiments, the nucleophilic polymer and the lithium and/or metal precursor form a precursor-polymer association in the fluid stock and/or the electrospun (e.g., as-spun) nanocomponsite nanofiber and that association is a reaction product between a nucleophilic polymer and electrophilic precursor(s).

[0091] In other embodiments, the polymer is an electrophilic polymer (e.g., a polymer comprising chloride or bromide groups, such as polyvinyl chloride). In some embodiments, the polymer is an electrophilic polymer and a precursor (e.g., lithium and/or optional metal precursor) is a nucleophilic precursor (e.g., metal-ligand complex comprising "ligands" with nucleophilic groups, such as alcohols or amines). In specific embodiments, the nucleophilic polymer and the lithium and/or metal precursor form a precursor-polymer association in the fluid stock and/or the electrospun (e.g., as-spun) nanocomponsite nanofiber and that association is a reaction product between an electrophilic polymer and a nucleophilic first precursor.

[0092] For the purposes of this disclosure metal precursors include both preformed metal-ligand associations (e.g., salts, metal-complexes, or the like) (e.g., reagent precursors, such as metal acetates, metal halides, or the like) and/or metal-polymer associations (e.g., as formed following combination of reagent precursor with polymer in an aqueous fluid).

Electrospinning

[0093] In some embodiments, the process comprises electrospinning a fluid stock or fluid stocks (e.g., wherein multiple layered (hybrid) nanostructures are prepared). Any suitable method for electrospinning is used.

[0094] In some instances, elevated temperature electrospinning is utilized. Exemplary methods comprise methods for electrospinning at elevated temperatures as disclosed in U.S. 7,326,043 and U.S. 7,901,610, which are incorporated herein for such disclosure. In some embodiments, elevated temperature electrospinning improves the homogeneity of the fluid stock throughout the electrospinning process.

[0095] In some embodiments, gas assisted electrospinning is utilized (e.g., about a common axis with the jet electrospun from a fluid stock described herein). Exemplary methods of gas-assisted electrospinning are described in PCT Patent Application PCT/US2011/024894 ("Electrospinning apparatus and nanofibers produced therefrom"), which is incorporated herein for such disclosure. In gas-assisted embodiments, the gas is optionally air or any other suitable gas (such as an inert gas, oxidizing gas, or reducing gas). In some embodiments, gas assistance increases the throughput of the process and/or reduces the diameter of the nanofibers. In some instances, gas assisted electrospinning accelerates and elongates the jet of fluid stock emanating from the electrospinner. In some embodiments, incorporating a gas stream inside a fluid stock produces hollow nanofibers. In some embodiments, the fluid stock is electrospun using any method known to those skilled in the art.

[0096] In specific embodiments, the process comprises coaxial electrospinning (electrospinning two or more fluids about a common axis). As described herein, coaxial electrospinning a first fluid stock as described herein (e.g., comprising a lithium component and a polymer) with a second fluid is used to add coatings, make hollow nanofibers, make nanofibers comprising more than one material, and the like. In various embodiments, the second fluid is either outside (i.e., at least partially surrounding) or inside (e.g., at least partially surrounded by) the first fluid stock. In some embodiments, the second fluid is a gas (gas- assisted electrospinning). In some embodiments, gas assistance increases the throughput of the process, reduces the diameter of the nanofibers, and/or is used to produce hollow nanofibers. In some embodiments, the method for producing nanofibers comprises coaxially electrospinning the first fluid stock and a gas. In other embodiments, the second fluid is a second fluid stock and comprises a polymer and an optional metal component (e.g., a lithium and/or non-lithium metal component).

EXAMPLES

Example 1 - Preparing a fluid stock of lithium/cobalt acetate and PVA

[0097] 0.5 grams of lithium acetate and 1.5 grams of cobalt acetate, the metal precursor(s), is dissolved in 20 ml of 1 molar acetic acid solution. The solution is stirred for 2 hours to create a solution of lithium acetate and cobalt acetate.

[0098] In a second solution, 1 gram of 99.7% hydrolyzed polyvinyl alcohol (PVA) with an average molecular weight of 79 kDa and polydispersity index of 1.5 is dissolved in 10 ml of de- ionized water. The polymer solution is heated to a temperature of 95°C and stirred for 2 hours to create a homogenous solution.

[0099] The lithium acetate and cobalt acetate solution is then combined with the PVA solution to create a fluid stock. In order to distribute the precursor substantially evenly in the fluid stock, the precursor solution is added gradually to the polymer solution while being continuously vigorously stirred for 2 hours. The mass ratio of precursor to polymer for the fluid feed (based on initial lithium acetate and cobalt acetate mass) was 2: 1.

Example 2 - Preparing a fluid stock of lithium/manganese acetate and PVA

[00100] 0.8 grams of lithium acetate and 1.2 grams of manganese acetate, the metal precursor(s), is dissolved in 20 ml of 1 molar acetic acid solution. The solution is stirred for 2 hours to create a solution of lithium acetate and manganese acetate.

[00101] In a second solution, 1 gram of 99.7% hydrolyzed polyvinyl alcohol (PVA) with an average molecular weight of 79 kDa and polydispersity index of 1.5 is dissolved in 10 ml of de- ionized water. The polymer solution is heated to a temperature of 95°C and stirred for 2 hours to create a homogenous solution.

[00102] The lithium acetate and manganese acetate solution is then combined with the PVA solution to create a fluid stock. In order to distribute the precursor substantially evenly in the fluid stock, the precursor solution is added gradually to the polymer solution while being continuously vigorously stirred for 2 hours. The mass ratio of precursor to polymer for the fluid feed (based on initial lithium acetate and manganese acetate mass) was 2: 1.

[00103] Such a fluid stock is capable of being electrospun with and without gas assistance. FIG. 3 (top panel) illustrates both gas assisted and non-gas assisted electrospun fibers. As can be seen, gas-assisted electrospinning produces fibers with more uniform morphologies and smaller fiber diameter than with non-gas-assisted electrospinning. Moreover, non-gas-assisted electrospinning was incapable of electrospinning solutions above 10 wt. %, while solutions up to 25 wt. % were electrospun using the gas assisted approach.

Example 3- Preparing a fluid stock of lithium/manganese/cobalt acetate and PVA [00104] Similar to the methods described in Examples 1 and 2, a fluid stock is prepared by combining PVA, lithium acetate, manganese acetate, and cobalt acetate, with a precursor:polymer ratio of 2: 1.

[00105] Such a fluid stock is capable of being electrospun with and without gas assistance. FIG. 3 (middle panel) illustrates both gas assisted and non-gas assisted electrospun fibers. As can be seen, gas-assisted electrospinning produces fibers with more uniform morphologies and smaller fiber diameter than with non-gas-assisted electrospinning. Moreover, non-gas-assisted electrospinning was incapable of electrospinning solutions above 10 wt. %, while solutions up to 25 wt. % were electrospun using the gas assisted approach.

Example 4- Preparing a fluid stock of lithium/manganese/nickel/cobalt acetate and PVA

[00106] Similar to the methods described in Examples 1 and 2, a fluid stock is prepared by combining

PVA, lithium acetate, manganese acetate, nickel acetate, and cobalt acetate, with a precursonpolymer ratio of 2: 1.

[00107] Such a fluid stock is capable of being electrospun with and without gas assistance. FIG. 3 (bottom panel) illustrates both gas assisted and non-gas assisted electrospun fibers. As can be seen, gas- assisted electrospinning produces fibers with more uniform morphologies and smaller fiber diameter than with non-gas-assisted electrospinning. Moreover, non-gas-assisted electrospinning was incapable of electrospinning solutions above 10 wt. %, while solutions up to 25 wt. % were electrospun using the gas assisted approach. FIG. 4 illustrates SEM images of various types of LiNi_xMn_yCo_z0₂ nanofibers from water based spinning of PVA/(Li-Ac/Mn-Ac/Ni- Ac/Co-Ac) (1 :2) solution, followed by thermal treatment at 900°C for 6 hours. Top left: x = 0.1, y =0.8, and z = 0.1. Top right: x = 0.4, y =0.4, and z = 0.2. Bottom left: x = 1/3, y =1/3, and z = 1/3. Bottom right: x = 0.8, y =0.1, and z = 0.1. The fiber morphology is well preserved after the calcination. Gas-assisted electrospinning was utilized to electrospin 20 wt% of aqueous PV A/metal acetate solution. FIG. 5 illustrates XRD patterns of various LiNi Mn_j,Co_z0₂ nanofibers (top: x= 0.8, y=0.1, z=0.1; second from top x=0.4, y=0.4, z=0.2; third from top: x=l/3, y=l/3, z=l/3; bottom: x=0.1, y=0.8, z=0.1) from water based spinning of PVA/(Li-Ac/Mn-Ac/Ni-Ac/Co-Ac) (1 :2) solution, followed by thermal treatment at 900°C for 6 hours. The fiber morphology is well preserved after the calcination. Gas-assisted electrospinning was utilized to electrospin 20 wt% of aqueous PV A/metal acetate solution. FIG. 6 illustrates SEM Images of as-spun PVA/(Li-Ac/Mn-Ac/Co- Ac) (1 : 1.5) nanofibers (top) and

nanofibers after calcination at 900°C for 8 hours (middle), and TEM image of LiMni ₃Nii ₃Coi ₃0₂ nanofiber showing purely crystalline structures that, in some instances, enhance conductivity and lifetime. FIG. 7 illustrates an XRD pattern of LiMni ₃Nii ₃Coi ₃0₂ nanofibers after calcinating precursor nanofibers at 900°C for 8 hours. FIG. 8 illustrates the trace of a half cell test using a

nanofiber cathode. Top: Charge- discharge curve of the first cycle at C/5 rate. Bottom: Cyclic performance, which demonstrates the initial energy density around 200 mAh/g, and around 175 mAh/g after 25 cycles. FIG. 9 (top) illustrates the charge/discharge curves for the first three cycles of the Li-ion full cell with Si-C nanofiber anode and LiMni ₃Nii ₃Coi ₃0₂ nanofiber cathode. FIG. 9 (bottom) illustrates the full cell cyclic performance with Si-C nanofiber anode and LiMni ₃Nii ₃Coi ₃0₂ nanofiber cathode which demonstrates the initial energy density over 650 Wh/kg, and around 500 Wh/kg after 25 cycles. Example 5 - Preparing LiCo0₂/Li₂Mn0₃ nanocomposite nanofiber

[00108] Two fluid stocks of Examples 1 and 2 are electrospun in a co-axial manner using a spinneret similar to the one depicted in FIG. 1 (where 111 illustrates the spinneret). The center conduit contains lithium acetate and manganese acetate fluid stock of Example 2 and the outer conduit contains lithium acetate and cobalt acetate fluid stock of Example 1. The electrospinning procedure is optionally gas- assisted, e.g., by flowing high velocity gas through the outer tube depicted in FIG. 1. The electrospun hybrid fluid stock is calcined by heating for 2 hours at 600 °C in an atmosphere of air.

Example 6 - Preparing a fluid stock of aluminum acetate and PVA

[00109] 2 grams of aluminum acetate, the metal precursor, is dissolved in 20 ml of 1 molar acetic acid solution. The solution is stirred for 2 hours to create a solution of aluminum acetate.

[00110] In a second solution, 1 gram of 99.7% hydrolyzed polyvinyl alcohol (PVA) with an average molecular weight of 79 kDa and polydispersity index of 1.5 is dissolved in 10 ml of de- ionized water. The polymer solution is heated to a temperature of 95°C and stirred for 2 hours to create a homogenous solution.

[00111] The aluminum acetate solution is then combined with the PVA solution to create a fluid stock. In order to distribute the precursor substantially evenly in the fluid stock, the precursor solution is added gradually to the polymer solution while being continuously vigorously stirred for 2 hours. The mass ratio of precursor to polymer for the fluid feed (based on initial aluminum acetate mass) was 2: 1.

Example 7 - Preparing LiCo02/A1203 core-shell nanocomposite nanofiber

[00112] Two fluid stocks (e.g., Examples 1 and 6) are electrospun in a co-axial manner using a process similar to that described in Example 5. The center conduit contains aluminum acetate fluid stock of Example 6 and the outer conduit contains lithium acetate and cobalt acetate fluid stock of Example 1. The electrospinning procedure is optionally gas-assisted, e.g., by flowing high velocity gas through the outer tube depicted in FIG. 1. The electrospun hybrid fluid stock is calcined by heating for 2 hours at 600 °C in an atmosphere of air.

Example 8 - Preparing Li(Ni_xCo_yMn_z)OJLi(Ni_xCo_yMn_z)0₂ core-shell nanocomposite nanofiber

[00113] Two fluid stocks (e.g., of Example 4) are electrospun in a co-axial manner using a process similar to that described in Example 5. The center conduit contains a first fluid stock of Example 4 and the outer conduit contains a second fluid stock of Example 4. The electrospinning procedure is optionally gas- assisted, e.g., by flowing high velocity gas through the outer tube depicted in FIG. 1. The electrospun hybrid fluid stock is calcined by heating for 2 hours at 600-800 °C in an atmosphere of air.

[00114] FIG. 10 illustrates a cross section of such a nanofiber. In the figure, the core is manganese rich and the shell is nickel rich. Also, the figure illustrates that the manganese rich fluid stock is electrospun out of a core needle, the nickel rich stock is electrospun out of a shell needle, and the electrospinning is gas assisted with high speed air. FIG. 11 illustrates a TEM image of such a nanofiber (core: Mn Rich, LiNio.₂Coo.₂Mno.6O₂, shell: Ni-rich, LiNio.6Coo.₂Mno.₂O₂). FIG. 12 illustrates an EDX profile of coaxial nanofibers illustrated in FIG. 11 with average composition of LiNio.₄COo.₂Mno.₄O₂. EDX results confirms that the ratio of Mn:Co:Ni = 2: 1 : 1 in the core of the fiber. FIG. 13 illustrates cyclic performance of coaxial (layered) nanofiber cathode with composition gradient (core: Mn Rich, LiNio.₂Coo.₂Mno.6O₂, shell: Ni-rich, LiNio.6Coo.₂Mno.₂O₂) The cyclic performance of the non-layered nanofiber cathode with the uniform, but same average composition, LiNio.₄COo.₂Mno.₄O₂ is shown for comparison. As demonstrated by the figure, in some instances, layered nanofibers with composition gradient exhibits high capacity and better stability than nanofiber with uniform composition.

Claims

CLAIMS What is Claimed is:

1. A plurality of nanocomposite nanofibers comprising:

a. (i) a continuous matrix of at least one lithium material; (ii) a plurality of non-aggregated, discrete domains of at least one lithium material; or (iii) a combination thereof; and b. a second material;

the at least one lithium material(s) comprising lithium.

2. The plurality of nanocomposite nanofibers of claim 1, wherein the nanocomposite nanofibers are coaxially layered nanofibers, the nanofibers comprising a core and a sheath that at least partially surrounds the core.

3. The plurality of nanocomposite nanofibers of claim 2, wherein the core comprises a lithium material and the sheath comprises a second material.

4. The plurality of nanocomposite nanofibers of either of claims 2 or 3, wherein the sheath comprises a lithium material and the core comprises a second material.

5. The plurality of nanocomposite nanofibers of claim 2, wherein the core comprises a first lithium material and the sheath comprises a second lithium material.

6. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the nanocomposite nanofibers comprise a continuous matrix of at least one lithium material and the continuous matrix of each nanocomposite nanofiber has an average length of at least 1 micron.

7. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the nanocomposite nanofibers comprise a continuous matrix of at least one lithium material and the continuous matrix of each nanocomposite nanofiber has an average length of at least 10% of the average length of the nanofibers.

8. The plurality of nanocomposite nanofibers of claim 1, wherein the nanocomposite nanofibers comprise non-aggregated, discrete domains of at least one lithium material and a continuous matrix of a second material.

9. The plurality of nanocomposite nanofibers of claim 9, wherein the non-aggregated discrete domains comprise non-aggregated nanoparticles comprising at least one lithium material.

10. The plurality of nanocomposite nanofibers of either of claims 8 or 9, wherein the discrete domains comprise crystalline lithium material.

11. The plurality of nanocomposite nanofibers of any one of claims 8-10, wherein the nanofibers do not comprise a concentration of domains 20 times higher along a 500 nm long segment along the length of the nanofiber than an adjacent 500 nm length of the nanofiber.

12. The plurality of nanocomposite nanofibers of any one of the preceding claims, the nanofibers comprising at least 50% by weight of the lithium containing material.

13. The plurality of nanocomposite nanofibers of any one of the preceding claims, the nanofibers comprising at least 0.5% by weight of the lithium.

14. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein at least 5% of the atoms of the nanofiber are lithium atoms (including +0 and/or +1 oxidation states).

15. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the lithium containing material comprises one or more material represented by formula (I):

Li_aM_bX_c (I) wherein M is one or more metal, X is one or more non-metal, a is 1-5 (e.g., 1-2), b is 0-5 (e.g., 0- 2), and c is 0-10 (e.g., 1-3).

16. The plurality of nanocomposite nanofibers of claim 15, wherein M is Fe, Ni, Co, Mn, V, or a combination thereof.

17. The plurality of nanocomposite nanofibers of either of claims 15 or 16, wherein X is O, S, P0₄, or C.

18. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the at least one lithium containing material comprises LiMn₂0₄,

LiNio.4Mno.4Coo.2O2, LiCo0₂, LiNi0₂, Li₂Mn0₃, L1C0PO₄, Li₂S or a combination thereof.

19. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the second material comprises ceramic, metal, organic polymer, or carbon.

20. The plurality of nanocomposite nanofibers of claim 19, wherein the second material comprises water-soluble organic polymer.

21. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the nanofibers have an average diameter of less than 1 micron.

22. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the nanofibers have an average aspect ratio of at least 100.

23. The plurality of nanocomposite nanofibers of any one of the preceding claims, wherein the nanofibers are cross-linked.

24. An electrode comprising a non-woven mat of a plurality of nanocomposite nanofibers according to any one of claims 1-23.

25. A lithium ion battery comprising an anode, a cathode, and a separator, the cathode comprising a non-woven mat of a plurality of nanocomposite nanofibers according to any one of claims 1-23.

26. A process of producing a nanocomposite nanofiber (e.g., of any one of claims 1-23), the process comprising electrospinning a fluid stock, the fluid stock comprising or prepared by combining, in any order, a lithium metal component, an organic polymer, and a fluid.

27. The process of claim 25, wherein the fluid is aqueous.

28. The process of either one of claims 25 or 26, wherein the organic polymer is a water-soluble polymer.

29. The process of any one of the preceding claims, wherein the weight-to-weight ratio of the lithium metal component to organic polymer is at least 1 :2 (e.g., at least 1 : 1).

30. The process of any one of the preceding claims, further comprising thermally treating the electrospun (e.g., as-spun) nanofiber.

31. The process of claim 30, wherein the thermal treatment occurs under inert conditions.

32. The process of any one of claims 26-30, further comprising oxidizing the electrospun (e.g., as- spun) nanofiber (e.g., concurrently with thermal treatment).

33. The process of any one of claims 26-30, further comprising reducing the electrospun (e.g., as- spun) nanofiber (e.g., concurrently with thermal treatment).

34. The process of any one of claims 26-33, wherein the lithium metal component is a lithium containing nanoparticle.

35. The process of claim 34, wherein the lithium containing nanoparticle comprises a lithium material represented by formula (I).

36. The process of any one of claims 26-33, wherein the lithium metal component is a lithium precursor (e.g., lithium salt).

37. The process of claim 36, wherein the lithium precursor comprises lithium carboxylate, lithium nitrate, lithium halide, lithium diketone, lithium halide, lithium alkoxide, or a combination theroef.

38. The process of any one of the preceding claims, wherein the polymer is nucleophilic.

39. The process of any one of the preceding claims, wherein the polymer is polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO), polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid, hydroxyethylcellulose (HEC), ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate, or a combination thereof.

40. The process of any one of the preceding claims, wherein preparation fluid stock further comprises combining, in any order, at least one non-lithium metal precursor.

41. The process of claim 40, wherein the at least one non-lithium metal precursor comprises iron precursor, nickel precursor, cobalt precursor, manganese precursor, vanadium precursor, or a combination thereof.

42. The process of either one of claims 40 or 41, wherein the metal concentration (including lithium and non-lithium metal) in the fluid stock is at least 200 mM (e.g., at least 250 mM, or at least 300 mM).