CA2587906A1 - Bismuth flouride based nanocomposites as electrode materials - Google Patents

Abstract

The present invention relates to primary and secondary electrochemical energy storage systems, particularly to such systems as battery cells, which use materials that take up and release ions as a means of storing and supplying electrical energy.

Description

BISMUTH FLUORIDE BASED NANOCOMPOSITES AS
ELECTRODE MATERIALS

CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional application number 60/615,480 filed October 1, 2004, the entire disclosure of which is incorporated by reference.
GOVERNMENT RIGHTS

This invention was made with govei-iunent support. The govei-tunent has cei-tain rights in the invention.

FIELD OF THE INVENTION
The present invention relates to primary and secondary electrochemical energy storage systems, particularly to such systems as battery cells, which use materials that take up and release ions as a iileans of storing and supplying electrical energy.

BACKGROUND OF THE INVENTION
The lithium-ion battery cell is the premiere high-energy rechargeable energy storage technology of the present day. Unfortunately, its high perfonnance still falls short of energy density goals in applications ranging from telecommunications to biomedical.
Although a number of factors witliin the cell contr-ibute to this performance parameter, the most cnicial ones relate to how much energy can be stored in the electrode materials of the cell.
During the course of development of rechargeable electrochemical cells, such as lithium (Li) and lithium-ion battery cells and the like, numerous materials capable of reversibly accommodating lithium ions have been investigated. Among these, occlusion and intercalation materials, such as carbonaceous compounds, layered transition metal oxide, and three dimensional pathway spinels, have proved to be particularly well-suited to such applications. However, even while performing reasonably well in recycling electrical storage systems of significant capacity, many of these materials exhibit detrimental properties, such as marginal environmental compatibility and safety, wliich detract from the ultimate acceptability of the rechargeable cells. In addition, some of the more promising materials are available only at costs that limit widespread use. However, of most importance is the fact that the present state of the art materials only have the capability to store relatively low capacity of charge per weight or volume of material (e.g. specific capacity, (mAh/g);
gravimetric energy density (Wh/kg-1); volumetric energy density, (Wh/1-1)).
Materials of choice in the fabrication of rechargeable battery cells, particularly highly desirable and broadly implemented Li-ion cells, for some considerable time have centered upon graphitic negative electrode compositions, which provide respectable capacity levels in the range of 300 mA.h/g. Unfortunately, complementary positive electrode materials in present cells use less effective layered intercalation compounds, such as LiCoO-2, which generally provide capacities only in the range of 150 mAh/g.
Intercalation compounds are not highly effective because the intercalation process is not an ideal energy storage mechanism. This situation occurs because of the limited number of vacancies available for lithium. An alternative process, reversible conversion, allows for all of the oxidation states of a compound to be utilized. The reversible conversion reaction proceeds as follows:
nLi+ + ne + Me"+X < > 77LiX + Me where Me is a metal and X is 0,2, S2-, N- or F. This reaction can lead to znucli higher capacities than can an intercalation reaction and, therefore, to much higher energy densities.
Badway et al. (Jeu7-17al of The Electroche zical Society, 150(9) A1209-A1218 (2003)), for example, has described electrode materials having liigh specific capacities via a reversible conversion reaction. They reported specific capacities for carbon metal fluoride nanocomposites, such as a carbon FeF3 nanocomposite, active for this reaction, having >
90% recovery of its theoretical capacity (>600 mAli/g) in the 4.5-1.5 V
region. They attained this major improvement in specific capacity by reducing the particle size of FeF3 to the nanodimension level in combination with highly conductive carbon.
Reversible conversion reactions may also be active for other metal fluorides.
Bismuth fluoride, for example, is known to have a thei-modynamic condition favorable for a 3V
electrode material in lithium batteries, a voltage particularly useful for the development of a wide range of products fi=om biomedical to telecommunications. Furthermore, the theoretical specific capacity, gravimetric energy density and volumetric energy density of bismuth fluoride exceed those of LiCoO2. The theoretical gravimetric and volumetric densities for BiF3 are, for example, 905 Wh/lcg"1, and 7170 Wh/1"1, respectively, for the equation:
BiF3 < > 3LiF + Bi whereas such energy densities for the reaction LiCoO2 < > Li,CoOZ + Li are only 560 Wh/kg 1 and 2845 Wh/1"1.
However, to date, bismuth fluoride has not been utilized as a positive electrode material in Li-ion battery cells. Most transition metal fluorides are insulators and possess little or no electrochemical activity as macromaterials. The present invention solves this problem by reducing the particle size of bismuth fluoride composites to the nanodimensional level in combination with a conductive matrix.

SUMMARY OF THE INVENTION
The invention provides a composition including a nanocrystalline bismuth fluoride compound.
In another embodiment, the invention provides a composition including a nanocrystalline bismuth fluoride compound nanocomposite.
In a fiirther embodiment, the invention provides a composition including a bismuth fluoride compound nanocomposite.
Finally, the invention provided herein is an electrochemical cell including a negative electrode; a positive electrode ineluding a bismuth fluoride compound nanocomposite and a separator disposed between the negative and positive electrodes.

BRIEF DESCRIPTION OF THE FIGURES
FIG. 1. XRD patterns of the pristine macro BiF3 and of the macro BiF3 high-energy milled in He for lh, 2h, 3h and 4h in the presence of carbon Super P, showing the phase transfornlation from orthorhombic (SG Pnma) to Tysonite (SG P(-3)cl) FIG. 2. Selected Area Electron Diffi=action (SAED) on the BiF3/C nanocomposite high-energy milled for one hour.
FIG. 3. hi-situ XRD of the tysonite BiF3/C nanocomposite during the first lithiation.
FIG. 4. SAED on the BiF3/C nanocomposite high-energy milled for one hour and lithiated down to 2V vs Li/Li+ at a current density of 7.58mA/g in a LiPF6 EC:PC:DEC:DMC
electrolyte.

FIG. 5. In-situ XRD of the o-BiF3/C nanocomposite during the first lithiation (a) galvanostatic cuive with integrated intensities of the Bi (012) and BiF3 orthorhombic (111) peaks and (b) XRD patterns.
FIG. 6. First cycle of the BiF3/C nanocomposite at different cun=ent densities.
FIG. 7. Schematics of the two different transpoi-t mechanisms suggested for lithiation.
FIG. S. In-situ XRD of the tysonite BiF3/C nanocomposite during the first delithiation (a) galvanostatic curve with integrated intensities of the Bi (012) and Tysonite BiF3 (111) peaks and (b) XRD patterns.
FIG. 9. In-situ XRD of the o-BiF3/C nanocomposite during the first delithiation (a) galvanostatic curve with integrated intensities of the Bi (012) and BiF3 Tysonite (111) peaks and (b) XRD patterns.
FIG. 10. X-ray Absorption Near Edge Spectra (XANES) data collected during the first cycle of charging a discharged BiF3 cathode at 0.25 mA (as a function of state of charge).
FIG. 11. Phase-uncorrected Fourier transfonns of k3-weighted X-ray Absorption Fine Sti-Licture (EXAFS) data collected during the first cycle of charging a fully discharged BiF3 cathode at 0.25 inA (as a fiuiction of state of charge).
FIG. 12. SAED on the BiF3/C nanocomposite high-energy milled for one hour and delithiated to 3.35V vs Li/Li+ after a first lithiation at 2V.
FIG. 13. Schenlatics of the two different transport mechanisms suggested for delithiation.
FIG. 14. Specific discharge capacities versus cycle numbers for the BiF3/C
nanocomposite high-energy milled for 30 min, lh, 2h and 4h.
FIG. 15. The effect of MoO3 on specific capacity in a bismuth fluoride nanocomposite.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides improved materials for battery components, specifically for positive electrodes in primary and rechargeable battery cells.
Provided herein is a composition including a nanocrystalline bismuth fluoride compound. The phrase "bisnnith fluoride compound" includes any compound that comprises the elements of bismuth (Bi) and fluorine (F). Examples of bismuth fluoride compounds include, but are not limited to, BiF3.

As used herein, ""nanocrystalline size" or "nanociystalline" are used interchangeably and refer to particles of about 100 run or less. As is well known in the art, crystallite size niay be deter-inined by conunon methodologies such as peak breadth analysis in X-ray diffraction (XRD) and high resolution transmission electron inicroscopy (HRTEM).
In a preferred embodiment, the bismuth fluoride compound of nanocrystalline size includes a bismuth fluoride compound wherein bismuth lias an ionic charge of Bi5+ . hi another preferred embodiment, the bismuth has an ionic charge of Bi3+.
Preferably, the nanocrystalline bismuth fluoride compound of the inventive composition is BiF3.
Preferably, the bismuth fluoride compound of nanocrystalline size includes a bismuth fluoride compound having the formula BiFZ, wherein 3< z<5. Even more preferably, the Bi cation in BiF, wherein 3< z < 5 has a charge of Bi5+.
In another embodiment, the charge of a bismuth cation may be partially substituted with a metal cation. As used herein "partial substitution" refers to a condition where an alternative cation is placed within the atomic crystal structure of the bismuth compound.
Charge compensation can be made by a change in cllarge of the Bi cation or change in anion content such as loss of F- or gain of O''-.
Suitable metal elements having charges that may be included in the inventive crystalline bismuth fluoride compound that can partially substitute the charge of a bismuth cation include, but are not limited to, non-transition metals and transition metals, preferably transition metals, and more preferably first row transition metals. Specific examples of metals for use in the inventive composition include, but are not limited to, Fe, B, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag, and Zn. Preferably, Mo or Cu are included in the inventive composition. It is desirable, but not required, that such compounds retain both electrical and ionic conductivity.
In a preferred embodiment, when Cu is the metal whose cations may act to partially substitute the Bi cation included in the nanocrystalline bismuth fluoride inventive composition, the compound is of the fonnula Bil_,Cu,;F3_,, where 0< x < 1.
As used herein, metal elements refer to simple substances which cannot be resolved into simpler substances by nonnal chemical means.
In another embodiment, the bismuth fluoride compound fiu-ther includes oxygen.
One of sltill in the art will recognize that oxygen can substitute for fluorine in metal fluorides.
Oxygen may act to significantly improve the electrical conductivity of the nanocrystalline bismuth fluoride compound of the invention. For example, oxygen may replace, partially, the fluorine in, for example, Bi5+F5 resulting in Bi5+OF3. Preferably, when oxygen is included in the bismuth fluoride inventive composition, the compound includes BiOxFz_2,, wherein 3< z <5and 0<x<1.5.
The invention also provides a composition including a nanocrystalline bismuth fluoride compound nanocomposite. The phrase "nanocrystalline bismuth fluoride compound nanocomposite" as used herein means nanociystallites comprising at least a bismuth fluoride compound incorporated within a matrix.
In one embodiment, the matrix is composed of particles or crystallites of a nanocrystalline size.
In another embodiment, the matrix is composed of particles of macrodimensional size. As used herein, "macrodimensional size" or "macrocrystalline size" are used interchangeably and refer to particles greater than 100 nrn.
In a preferred embodiment, the matrix is a conductive matrix. As used herein, a "conductive matrix" refers to a matrix that includes conductive materials, some of which may be ionic and/or electronic conductors. Preferably, the matrix will retain both ionic and electronic conductivity; such materials are conimonly referred to as "mixed conductors."
In one embodiment, the conductive matrix is carbon. Preferably, less than 50 weight % of carbon is used. More preferably, less than 25 weight % carbon is used.
Even more preferably less than 5 weight % carbon is used.
In another embodiment, the conductive matrix is a metal sulfide. In a fiirther embodiment, the conductive matrix is a metal nitride. Preferably, the conductive matrix is a metal oxide. In another preferred embodiment, the conductive matrix is a metal fluoride. In yet, still another preferred embodiment, the conductive matrix is a metal oxyfluoride.
Preferably, the metal from the metal oxide, nietal fluoride or the metal oxyfluoride is Fe, B, Bi, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag or Zn.
Suitable metal sulfides include, but are not limited to, molybdenum sulfides, molybdenum oxysulfides, and titanium sulfide. Suitable metal nitrides include, but are not limited to, copper nitride, molybdenum nitride, and titanium nitride. Suitable metal oxide conductive matrices include, but are not limited to, VO-1, MoO2, NiO, V205, V6013, CuO, Mn02, chromium oxides and MoO3. Suitable metal fluoride conductive niatrices include, but are not limited to MoF3, MoF4, Ag2F. Suitable metal oxyfluoride conductive matrices include, but are not limited to, MoO,;Fz, wherein x is 0<_x <_._i' and z is 0<z <_5 and combined in such a way that the effective charge on the Mo cation is not more than 6+.
Preferably, the conductive matrix is MoO3.
In a prefer-red enibodiment, the conductive matrix is present in an amount that is less than about 50 weight % of the nanocomposite.
In yet another embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite includes carbon. Preferably, less than 50 weight % of carbon is used. More preferably, less than 25 weight % carbon is used. Even more preferably less than weight % carbon is used.
In yet another embodiment, both oxygen and a metal are included in the bismutll fluoride compound of the nanocomposite of the present invention. In a preferred embodiment, the compound is of the foi-nlula Bil_,;MehF3_ZO,,,, wherein Me is a metal and x <
1 and w < z. Preferably, the metal is copper.
In another embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite includes crystallites that are less than about 100 nm in diameter;
preferably, less than about 50 run in diameter; and even more preferably less than about 20 mn in diameter.
The nanocrystalline bismuth fluoride compound of the inventive nanocomposite preferably includes Bi5+ or Bi3+ as described above. Even more preferably, the compound of the inventive nanocomposite is BiFZ wherein 3< z < 5. In this embodiment, Bi is preferably Bi3+. Preferably, BiFZ is BiF3. Furthermore, the bismuth fluoride compound of the nanocomposite can include a Bi cation wherein a metal cation is in partial substitution of the Bi cation as described above.
In another embodiment, the specific capacity of the nanocrystalline bismuth fluoride nanocomposite is reversible. As used herein, "specific capacity" refers to the amount of energy the bismuth fluoride compound nanocomposite contains in millianip hours (mAh) per unit weight. "Reversible specific capacity" means that the nanocomposite of the present invention may be recharged by passing a current through it in a direction opposite to that of discharge.
In another embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposites demonstrates a conversion reaction. As used herein "conversion reactions" are decomposition reactions in which the bismuth fluoride compound of the nanocomposites of the present invention are fully reduced during battery cell discharge to Bi with the concomitant fonnation of a lithium, magnesium or calcium compound.

Preferably, the nanocrystalline bismuth fluoride compound of the nanocomposite of the invention is BiF3 and is capable of a conversion reaction. In this embodiment, the conversion reaction con=esponds to the following chemical equation.

BiF3 + 3Li+ + 3e- > 3LiF +Bi In another embodiment, the conversion reaction of the bismuth fluoride compound nanocomposite of the present invention is reversible. As used herein, "reversible conversion reactions" are reactions in which the nanocrystalline bismuth fluoride compound of the nanocomposite of the present invention is capable of reforming during a batteiy cell charge.
Preferably, the nanocrystalline bismuth fluoride compound of the nanocomposite of the present invention that is capable of a reversible conversion reaction is BiF3. hi this embodiment, the chemical equation is BiF3 + 3Li+ + 3e- E->- 3LiF +Bi In another embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite includes orthorliombic crystallites. As used herein "orthorhombic crystallites" refer to a crystalline structure of three mutually perpendicular axes of different length. In a more preferred embodiment, the orthorhombic crystallites include Pnrna space groups.
As used herein "space group" refers to an arrangement of the crystallites into orderly arrays. Pnma space groups result in a crystal arrangement as described in JCPDS-Intei-national Centre for Diffi=action Datat7, Card 15-0053.
In an even more preferred embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite includes tysonite crystallites. As used herein "tysonite crystallites" refers to crystalline structures of a hexagonal shape.
Yet, even more preferably, the tysonite crystallites have P(-3)cl space groups. P(-3)cl space groups result in a crystal ai-rangement as described in JCPDS-International Centre for Diffraction Datag, Card 35-038.
In another einbodiment, the nanocrystalline bismuth fluoride compound of the inventive nanoconiposite including orthorhombic crystallites is capable of a conversion reaction. Preferably, these crystallites include Piuna space groups. Even more preferably, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite is an orthorhombic BiF3 compound having Piuna space groups and is capable of a conversion reaction. The corresponding chemical reaction is BiF3 Piuna + 3Li+ + 3e- >3LiF + Bi In another embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite, that includes tysonite crystallites, is capable of a conversion reaction. In a more prefeiTed embodiment, the conversion reaction is reversible. Preferably, these crystallites include P(-3)cl space groups. Even more preferably, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite is a tysonite BiF3 compound having P(-3)c1 space groups and is capable of a conversion reaction. Even more preferably, the reaction is reversible. Without being bound by theory, the corresponding chemical reactions are:
conversion Tysonite-BiF3 P(-3)c l+ 3Li+ + 3e- < > 3LiF + Bi conversion reversible conversion In a preferred embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposites is capable of pllase transformation. As used herein "phase transfonnation" refers to a phenomenon where the crystallite structure of the nanocrystalline bismuth fluoride compound of the present invention transfonns into a different crystallite sti-ucture. Transformation can occur during battery cell cycling, or, for example, during high-energy milling of the nanocrystalline bismuth fluoride compound. In a prefeiTed embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite is capable of transfonning from a tysonite crystallite into a orthorliombic crystallite. In a more preferred embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite is capable of transfonning from an orthorhombic crystallite into a tysonite crystallite. In an even more preferred embodiment, the nanocrystalline bismuth fluoride compound of the inventive nanocomposite is an orthorhombic crystallite BiF3 compotmd capable of phase transformation into a tysonite crystallite BiF3 compound according to the equation:

Orthorhombic-BiF3 + 3Li+ + 3e- > 3LiF + Bi > Tysonite-BiF3 + 3Li+ + 3e-The inventive nanocomposites may be prepared by extreme, high impact-energy milling of a mixture that includes a bismuth fluoride compound and, optionally, a second metal such as copper and/or carbon and/or oxygen. Thus, the nanocrystalline bismuth fluoride compound nanocomposite of the present invention can be prepared by using an impact mixer/mill such as the cotnmercially available SPEX 8000 device (SPEX
Industries, Edison N.J., USA). Unlike the shearing action of conventional planetary, roller, or ball mills, wluch at best may allow for size reduction of crystallite particles to the micrometer range, the extremely high-energy impact action impressed upon the component mixture by the impact mill provides, within milling periods as short as about 10 minutes, a particle size reduction of the processed material to the nanodimensional range of less than about 100 nnl. Further milling for as little as 30 minutes, up to about 4 hours, brings about crystallite-particle size reduction to less than about 40 nni.
Other methods may be used to form the nanocoznposites of the present invention. As will be evident to a skilled artisan, solution or gel techniques may be used to fabricate the nanocomposites.
When bisinuth fluoride is milled with another component, the bismuth fluoride undergoes chemical changes such that its X ray diffi=action characteristics takes on the character of a new, highly electrochemically active material, although retaiiiing major aspects of the bismuth fluoride. In addition, the nanocrystallite formation can be easily character-ized by well known methods such as Bragg peak broadening in x-ray diffraction and microscopy by methods such as transmission electron microscopy.
In one embodiment, milling occurs for about three hours to obtain tysonite bismuth fluoride compounds of the nanocomposite. Preferably, the milling results in bismuth fluoride crystallites that are nanostructured in a conductive matrix. In this form, surface area contact with an electrolyte is less than that of typical discrete nanoparticles, which can result in improved cycle life performance. To enllance the size and density of the nanocomposites without affecting nanocrystallinity, brief thermal amiealing maybe utilized or the present of laiown sintering aids such as glass fluxes.
In another embodiment, the orthorhombic nanocrystalline bismuth fluoride compound nanocomposites are formed by milling the inventive tysonite bismuth fluoride compound of the nanocomposite for one hour in the presence of HF.

In another aspect of the present invention, a composition including a bismuth fluoride compound nanocomposite is provided. In one embodiment of this aspect of the invention, the inventive nanocomposite is comprised of a nanocrystalline bismuth fluoride compound in a matrix. In another embodiment, the inventive composite is comprised of a bismuth fluoride compound of nanocrystalline particles in a nanocrystalline matrix. In another embodiment, the inventive nanocomposite comprises a bismuth fluoride compound in a nanocrystalline matrix. \
In another aspect of the present invention, an electrochemical cell, preferably a primary or, more preferably, a rechargeable battery cell, is provided, which employs the inventive bismuth fluoride compound nanocomposites, or the nanocrystalline bismuth fluoride nanocomposites of the present invention, as described herein, as the cathode material. The cell may be prepared by any known method. The inventive nanocomposite electrode (cathode) materials function well with most other known primary or secondary cell composition components, including polymeric matrices and adjunct compounds, as well as with conunonly used separator and electrolyte solvents and solutes.
For exaniple, electrolyte compositions commonly used in known rechargeable electrochemical-cell fabrication seive equally well in the cells of the present invention.
These electrolyte compositions may include one or more metallic salts, such as, but not limited to, lithium, magnesium, calcium and yttrium. Lithium salts, such as LiPF6, LiBF4, LiC1Oa, and the like, dissolved in conunon cyclic and acyclic organic solvents, such as ethylene carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, and mixtures thereof, may be used. As with optimization of the nanocomposites of the present invention, specific combinations of electrolyte components will be a matter of the preference of the cell fabricator and may depend on an intended use of the cell, although consideration may be given to the use of solutes such as LiBF4, which appear less susceptible during cell cycling to hydrolytically forming HF, which could affect the optimum perfoimance of some metal fluorides. For such reason, for instance, a LiBF4:propylene carbonate electrolyte may be preferred over one comprising a long-utilized standard solution of LiPF6 in a mixture of ethylene carbonate:dimethyl carbonate. In addition, such nanocomposites may be incorporated into solid state polymer cells utilizing solid state ionically conducting matrices derived from compounds such as polyethylene oxide (PEO). Nanocomposites also may be fabricated by thin fihn deposition techniques and may be incorporated into solid state thin film lithium batteries utilizing a glassy electrolyte. Finally, such electrode materials may be incorporated into cells utilizing ionic liquid solvents as the electrolytes.
Likewise, the negative electrode members of electrochemical cells may advantageously include any of the widely used known ion sources such as lithium metal and lithium alloys, such as those comprised of lithium tin, lithium silicon, lithium aluminum, lithiated carbons sueh as those based on coke, hard carbon, graphite, nanotubes or C60, and lithiated metal nitrides.
Unless defined otherwise, all teclulical and scientific terms used herein have the same meaning as coinmonly understood by one of ordinary skill in the art to whieh this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, the prefen=ed methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and described the methods and/or materials in coiuiection with which the publications are cited.
It must be noted that as used herein and in the appended claims, the singular foi-nIs "a", "and", and "the" include plural references unless the context clearly dictates otherwise.
All tecluiical and scientific terms used herein have the same meaning.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be consti-ued as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.
Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirnled.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to liinit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed.
Efforts have been made to ensure accuracy with respect to numbers used (e.g.
amounts, temperature, etc.) but some experimental er-rors and deviations should be accounted for.
Unless indicated otherwise, parts are pai-ts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric.

Example 1. Preparation of the tysonite and orthorhombic BiF3 nanocomposites of the invention a. Tysonite onite In order to prepare the tysonite BiF3 nanocomposites of the present invention, a sample of 85 weight % BiF3, (Alfa Aesar) and 15 weight % carbon of carbon black (Super P, 3M), were milled for one to three hours in a Spex 8000 mill. The high-energy milling cell, as well as the balls, were made out of hardened steel. The high-energy milling cell was sealed and reopened after milling inside a He filled glove box at -80 C dew point, thus preventing the powder from moisture or oxygen containination. The resulting inventive tysonite nanocomposites were composed of crystallites of 30 nm or less.
Orthorhombic BiF3 inventive nanocomposites were prepared by treating tysonite BiF3 nanocomposites with 48% concentrated hydrofluoric acid in a Teflon container.
The container then was placed overnight in an oven at 95 C to let the HF
evaporate. The powder thus obtained then was dried a second time overnight at 120 C under vacuum before entering the glove box for one hour of high energy milling. The resulting inventive orthorhombic nanocomposites were composed of crystallites of approximately 30 nm. The size of the orthorhombic crystallites was found to be more uniform than those of the tysonite crystallites.
Example 2. Electrode preparation.
Electrodes were prepared by adding poly-vinylidene fluoride-co-hexafluoropropylene (Kynar 280, Elf Atochem), carbon black (Super P, 3M), and dibutyl phthalate (Aldrich) to the inventive nanocomposites in acetone. The slurry was tape cast, dried for 1 hour at 22 C, and rinsed in 99.8% anhydrous ether (Aldrich) to extract the dibutyl phthalate plasticizer. The electrodes, 1 cm2 disks, or coin cells, typically containing 57 +/-1 %
inventive nanocomposites and 12+/-1% carbon black, were tested electrochemically versus Li metal (Johnson Mattliey). The coin cells were cycled under controlled temperatures.
The batteries were cycled either on an Arbin, a Maccor or a-Mac Pile (Biologic). Tlu=ee different electrolytes were used: 1) LiPF6 salt in a mixture of ethylene carbonate (EC)/propylene carbonate (PC)/diethyl carbonate (DEC)/dimethyl carbonate (DMC) solvents at 1 M, (1:1 ratio by volume) 2) LiPF6 in EC/DMC at 1 M (1: 1 ratio by volume) or 3) LiC1Oa in EC/DMC at 0.4 M(1:1 ratio by volume).

Example 3. Physical characterization of the tysonite and orthorhombic BiF3 nanocomposites of the invention.
a. XRD analysis In order to characterize the stnicture of the inventive BiF3 nanocomposites, XRD
analyses were performed on a Sintag X2 using Cu Ka radiation. The inventive nanocomposites were placed on glass slides and covered with a Kapton film sealed with silicon based vacuum grease inside a glove box to minimize air exposure.
The XRD patterns of the pristine macro BiF3 powder and of the macro BiF3 powder high-energy milled in He in the presence of 15 wt% of carbon Super P for 1h, 2h, 3h and 4h are shown on FIG. 1. It is readily apparent from this figure that BiF3 undergoes a phase transforniation fi=onz the initial orthorhombic phase to a hexagonal Tysonite phase. The calculated lattice parameters of this phase are a=7.100 .004A and c=7.292 .007A.

After one hour of high-energy milling, the ratio of tysoiiite/orthorhombic phases has been evaluated as 70:30, respectively, from the relative intensity of their respective I100 Bragg's reflections. This ratio increases with milling time. The transformation is complete after a milling time between 3h and 4h, as seen froin the disappearance of the ortho BiF3 reflection at 210 degrees 20 and appearance of the tysonite BiF3 reflection at 111 degrees 20.
Another feature clearly apparent on the XRD patterns of FIG. 1 is the broadening of the diffraction peaks between the niacro BiF3 and the BiF3/C nanocomposite high-energy milled for one hour. Peak broadening is consistent with the diminution of the primary crystallite size. (See, eg.,Bewes et al., Electf=onaechafaical and Solid-StateLettefs, 8(4) A 147-A183 (2005), which is hereiTZ iracoiporated by referef7ce.) b. Selected area electron diffi-action analysis Selected area electron diffraction analysis (SAED) was perforined on the BiF3/C
nanocomposite to characterize the patterns of BiF3 phases at one hour of milling time. SAED
picttu=es were taken with a Topcon 002B transmission electron microscope (TEM). Powder samples were first dispersed in dimethyl carbonate, a few drops of which were then disposed on a Lacey carbon grid and allowed to dry overnight inside a glove box. The grids to be analyzed were placed in a bag and sealed inside the glove box. The glove box was re-opened only to put the grid into the TEM colurml.
The electron diffraction patterns resulting fi=om SAED can be seen in FIG. 2 after one hour of high-energy milling. Each pattern collected could be indexed either as the pure tysonite phase (pattei7i a) or the pure orthorhombic phase (pattern b).
Mixtures of both tysonite the tysonite phase and the orthorhombic phase were not observed.

Example 4. In situ XRD reveals that the tysonite and orthorhombic BiF3 nanocomposites are capable of a conversion reaction upon lithiation.
A galvanostatic discllarge cuive and XRD patterns, obtained during in-situ XRD
conducted on the BiF3/C nanocomposite high-energy milled for one hour during a first lithiation down to 2V vs Li/Li+, are presented in FIGS. 3(a) and (b), respectively. The corresponding SAED pattern of this inventive nanocomposite is depicted in FIG.
4. Without being bound by theory, the progressive appearance of the Bi Bragg's reflections, and the disappearance of the BiF3 Bragg's reflections from the XRD patterns when x in "Li,BiF3"
increases, demonstrates that a conversion reaction is taking place in the BiF3/C
nanocomposite during the lithiation (FIG. 3b), according to the equation:
BiF3 + 3 Li+ + 3e" 0 3 LiF + Bi The Bi Bragg's reflections become visible at a very early stage of the lithiation, at an x in "Li,BiF3" smaller than 0.1, while the BiF3 reflections do not exhibit any shift, indicating that the conversion reaction starts from the very begimiing of the lithiation and that there is no concomitant intercalation reaction of the lithiuni in the metal fluoride. The LiF Bragg's reflections cannot be observed on these pattems because (1) they are overlapped by the Bi reflections, and (2) the x-ray scattering factors of Li and F are much smaller than the x-ray scattering factor of Bi . As the intensities in such an in-situ experiment are low, those peaks cannot be resolved.

However, LiF clearly fonns during the lithiation. The presence of LiF was confirmed by SAED, as shown on the pattern of FIG. 4. In addition to the Bi and LiF
rings, this pattern features a ring that can be attributed either to the (002) reflection from the tysonite BiF3 or to the carbon matrix. It is not surprising that some residual BiF3 remains in the nanocomposite at this stage, since the x at 2 V is at about 2.8. X must be equal to 3 to fully reduce the metal fluoride. The evolution of the integrated intensities with x of the Bi (012) Bragg's reflection, Bragg's reflection from the tysonite BiF3 phase (111) Bragg reflection from and from the orthorhombic BiF3 phase (210) were overlaid onto the galvanostatic curve of FIG.
3(a). The integrated intensity of the Bi (012) reflection increased continuously wlien x increased, indicating that the completion of the conversion reaction progressed linearly with x, as expected.
From the evolution of the integrated intensities of the two BiF3 Bragg's reflections, it can be inferred that the conversion reaction occurs preferentially in the tysonite phase rather than in the orthorhombic phase. The integrated intensity of the (111) tysonite BiF3 peak has a greater negative slope and therefore decreased faster with x than the integrated intensity of the (210) peak fi=om the orthorhombic BiF3 phase. At an x in "LiBiF3" of about 1.8, only the peaks from the orthorhombic phase can be seen.
Although the conversion reaction takes place preferentially in the tysonite BiF3 phase, it is clear nonetheless that it also occurs in the orthorhombic phase. This is demonstrated in FIG. 5. This figure depicts an in situ XRD analysis (LiPF6 EC:DMC electrolyte 1:1 ratio by volume) and cui-rent density of 7.58 mA/g conducted on an orthorhombic BiF3/C
nanocomposite. This orthorhombic BiF3/C nanocomposite was prepared by an HF
treatment on the BiF3/C nanocomposite, high-energy milled for one hour.
FIG. 5 is divided into two parts: pai-t (a) describes the variation with x of the output voltage of the integrated intensities of the Bio (012) and the orthorhombic BiF3 (111) Bragg's reflections and part (b) depicts the in-situ XRD patterns. The patterns reveal the progressive increase of the Bi XRD peaks and the progressive decrease of the BiF3 peaks, as expected from a typical conversion reaction. In both FIGS. 3 and 5, the orthorhombic BiF3 Bragg reflections at (210) remain visible until a much more advanced state of completion of the conversion reaction than do the tysonite BiF3 reflections at (111). Although both nanoconiposites have crystallite sizes of about 30 nm, the tysonite BiF3/C
nanocomposite, high energy milled for one hour, has a wider size distribution of particles, 30 nm being the upper linzit of the distribution. Alteniatively, the size of the pai-ticles of the orthorhombic nanocomposite are more homogeneous. Because, on average, the crystallite size is larger in the orthorhombic BiF3/C nanocomposite, the oi-thorhombic phase may remain visible by XRD for a deeper lithiation. (See, eg., M. Bei-ves, Dissertatioia, Rzttgef s, New Jei=sev, 2005, whic7a is herein iizcorporated by reference.) Example 5. Mechanism of Lithium Transport The conversion reaction for tysonite BiF3 nanocomposite is associated with two voltage plateaus FIG. 6 depicts the first cycle of the tysonite BiF3/C nanocomposite (4 hours energy-milled) at different current densities in a LiC1O4 EC: DMC 0.4 M electrolyte (1: 1 by volume). A separation of two pseudo-plateaus occurs on the voltage profile for this nanocomposite (2.9 voltage vs Li/Li+ and 2.75 voltage vs Li/Li+) during discharge.
Because from a thermodynamics standpoint, a conversion reaction is a two-phase reaction, this reaction should have a very flat output voltage. And indeed, the lithiation output voltage after relaxation is perfectly flat as shown on the galvanostatic intei7nittent titration technique (GITT) curves of the tysonite BiF3 and or-thorhombic BiF3 nanocomposites, (FIGS.
7 and S, respectively), thus demonstrating that the occui7=ence of voltage plateaus during lithiation is due to kinetic effects.
If the occurrence of these two plateaus during the lithiation is due to kinetic effects, the kinetics that develop the pseudo-plateaus are most likely associated with different electronic and ionic transport mechanisms of the different phases present at the different stages of the lithiation reaction. Without being limited by theory, one plateau should be associated with the lithiation reactant (BiF3) and the other should be associated with the products (LiF and Bi ).
Without being limited by theory, schematics of the two suggested lithiation transport mechanisins are provided in FIG. 7. At the begizuling of the lithiation, the nanocomposite is composed of BiF3 nanoparticles surrounded by a carbon matrix. Owing to the extremely high porosity of the carbon matrix, the bismuth fluoride particles are in direct contact with the electrolyte, enabling facile ionic transport. At that early stage of the reaction, the electrons are transferred to the BiF3 surface via the carbon matrix and the Li+ ions migrate to the BiF3 surface directly from the electrolyte, inducing the surface conversion into Bi and LiF
(transport mechanism A on FIG. 7). After a certain degree of completion of the conversion reaction, the entire surface of the BiF3 particles will have reacted. The point at which this occurs is dependent on the specific surface area of the bismuth fluoride. The nanocomposite then is composed of BiF3 crystallites of only a few nanometers sui7=ounded by the conversion reaction products, Bi and LiF, and no longer by the carbon matrix. At this point, the transport mechanisms will change dramatically as Li+ ion diffusion will take place through the defect boundaries of the LiF and Bi nanoparticles. Electrons then will be transfeiTed to the core BiF3 via percolation of metal Bi (transport mechanism B on FIG. 7).
Such dramatic differences in transport mechanisms can justify a dramatic polarization change, leading to the occurrence of these two pseudo-plateaus during the lithiation.
Example 6. Galvanostatic curves and in situ XRD reveals that the tysonite BiF3 nanocomposite is capable of a reversible conversion reaction.
A galvanostatic curve and in-situ XRD patterns were collected on the first delitluation of the tysonite BiF3/C nanocomposite to assess whether or not this nanocomposite was capable of a reversible conversion reaction. The voltage curve and XRD
pattei7ls are presented, respectively, in FIGS. 10(a) and (b). These analyses were conducted by first lithiating a disc containing the inventive tysonite nanocomposite (see Example 1 for electrode preparation) to 2V at a cuiTent density of 45.45niA/g in an in-situ cell without an X-ray. The cycling was stopped at the end of the lithiation and one XRD pattern was collected. The same in-situ cell was then delithiated until x in Li,BiF3 was at about 1.55, at a cuiTent density of 45.45 mA/g, without an X-ray, before the start of the actual in-situ XRD.
After two hours, in-situ XRD was initiated using a current density of 7.58mA/g and LiPF6 EC:DMC
(1:1 ratio by volume) as the electrolyte.
FIG. 8(b) shows the XRD patterns obtained. These patterns depict the reforniation of tysonite BiF3 during delithiation, thus revealing that the conversion reaction is reversible.
Without being limited by theory, the overall chemical reaction for this inventive tysonite BiF3 nanocomposite is:

discharge BiF3 +3 Li Bi + 3 LiF
charge In contrast to the reversibility of the conversion reaction seen for tysonite BiF3, galvanostic curves and in-situ XRD patterns shown in FIGS. 11a and 11b, respectively, reveal that the orthorhombic BiF3 is not reversible. As seen in the in-situ XRD of the orthorhombic BiF3 in FIG. 9a, only the tysonite BiF3 forms during the delithiation, even when the starting material is the pure orthorhombic BiF3/C nanocomposite.

Example 7. Proposed MeclZanism of the reversible conversion reaction a. XRD analysis reveals two voltage plateaus FIG. S(b) also reveals that the BiF3 Bragg's reflections begin to be visible only at an advanced state of completion of the delithiation, at an x in "Li,BiF3" on the order of 1.3. As can be seen on FIG. 8(a), this x value is almost precisely the x value at which a first delithiation plateau ends and the voltage increases sharply before reaching a second plateau at 3.7 V. Hence, based on the XRD results, and without being limited by theory, it would seem that the only bismuth compound present in the nanocomposite along this first plateau is Bi and that the actual reconversion reaction begins on the second plateau at higher voltage.
However, as the first delithiation plateati covers approximately two thirds of the delithiation, and the capacity on the second discharge is almost identical to the capacity on the first discharge, there can nevertheless be no doubt that some, if not the majority, of the reversibility comes froni the first plateau. Further-niore, as seen in FIGS.
10(a) and 11(a), the integrated intensity of the (012) Bi Bragg's reflection clearly decreases along the first delithiation plateau, indicating that the amount of Bi in the material decreases continuously along this 3.3V plateau.

The sudden polarization increase leading to the second plateau occurs at an earlier stage of delithiation in the orthorhombic BiF3/C nanocomposite than in the tysonite BiF3 nanocomposite, as evident from comparison of FIGS. 10(a) and 11(a). As mentioned earlier, the average BiF3 crystallite size is larger in the orthorhombic BiF3/C
nanocomposite than in the tysonite BiF3 nanocomposite. This means that (i) the size of the (LiF + Bi ) aggregates at the end of the lithiation will also be larger in the orthorhombic BiF3/C
nanocomposite than in the tysonite BiF3 nanocomposite, and (ii) the surface over volume ratio thus will be smaller in the foi-nier than in the latter. Without being bound by theory, during the delithiation reaction, the surface of (LiF + Bi ) aggregates therefore will become covered by the BiF3 layer at an earlier stage of the conversion reaction and the polarization increase, brought about by the foimation of this layer, and the resulting transition from a first transport mechanism to a second transport mechanism, will happen earlier. (See below for FIG. regarding transport mechanisms).

b. Bi is oxidized to Bi3+ in BiF3 at the first lap teau Without being bound by theory and in order to provide a fundamental understanding of the origin of the redox reaction on the first delithiation plateau, x-ray absorption spectroscopy (XAS) was used to monitor the evolution of the electronic and atomic sttucture of Bi under in situ conditions. The discharge and charge capacities are summarized in Table 1. The cell was discharged and charged within the potential range of 2.0-4.5V
vs. Li/Li+. The x-ray absorption near edge structure (XANES) data, collected during the first cycle of charging, are shown in FIG. 10 as a function of state of charge and versus Bi and Bi3+F3 standards. The data demonstrate the direct oxidation of metallic Bi to Bi3+
in BiF3 during the charging of a discharged BiF3 cathode. Structurally, this conclusion is also suppor-ted by the Fourier transfoi7n X-ray Absorption Fine Structure (EXAFS) data displayed in FIG. 11 as a function of state of charge, along with data shown for metallic Bi and BiF3 as reference standards for Bi and Bi3+

Table 1: Summary of discharge and charge capacities for the Li/BiF3 cell used for the in-situ XAS.

Cycle Current (mA) Time (hr) Capacity (mAh) 1st discharge 0.20 14.083 2.82 1sr char e 0.25 11.639 2.91 2nd discharge 0.25 10.472 2.62 2nd char e 0.25 11.472 2.S7 The Fourier transform of EXAFS data for metallic Bi in FIG. 1ldisplays a doublet at 2.499A and 3.148A, which corresponds to contributions from 3 Bi atoms at a crystallographic distance of 3.073A and 3 Bi atoms at 3.527A, respectively. The Fourier transform of BiF3, on the other hand, displays mainly a single peak at 1.549A, which corresponds to contributions from eight F atoms. For the discharged cathode, as expected, the Fourier transfonn mainly shows the presence of metallic Bi. During charge, the Fourier transforins display both the Bi-F and Bi-Bi contributions: the Bi-F contribution increases and the Bi-Bi contribution decreases with the state of charge in a distinct two phase manner. Finally, the Fourier transform for the charged cathode is consistent with that of BiF3. These analyses, therefore, reveal that there is no intermediate bismuth fluoride compound forming, in which the oxidation state of the bismuth is lower than 3.

c. Tysonite BiF3 is reformed at the first plateau FIG. 12 depicts SAED patterns of the BiF3/C nanocomposite high-energy milled for one hour and then delithiated to 3.35 vs Li/Li+ after a first delithiation at 2 V using a current density of 7.58 mA/g and an LiPF6 EC:PC:DEC:DMC (1: 1 ratio by volume) electrolyte. All the diffraction rings of this pattern were indexed on the basis of the BiF3 tysonite structure.

Hence, this SAED analysis confinns the presence of refonned tysonite BiF3 along the first delithiation plateau. Without being limited by theory, it is possible to reconcile the in-situ XRD data, on which the reconverted BiF3 can be seen only on the second plateau at higher voltage, and the SAED and in-situ XAS data, which shows that BiF3 does indeed refonn on the first plateau as well. It appears that the primary crystallite size of the reconverted BiF3 on the first delithiation plateau is too small to be resolved by XRD. Without being limited by theory, similar to the situation resolved during lithiation, the separation of the delithiation voltage profile in two plateaus at about 3.3 V and 3.7V is a pure kinetic effect and is due to a polarization increase.
Analogous to what we have proposed for the lithiation reaction, the division of the delithiation reaction into two plateaus, atti-ibutable to kinetics effects, can be understood in teinis of transport mechanisms. Without being limited by theory, schematics of the two proposed transpoi-t mechanisms for the delithiation are depicted in FIG. 13.
At the end of the lithiation, what were the BiF3 nanoparticles in the initial nanocomposite are now aggregates of very fine Bi and LiF nanoparticles an=anged in a shell. When the oxidation reaction cominences, Li* ions difftlse from the LiF nanoparticles near the surface of the aggregates directly into the electrolyte, and electrons are transfen=ed fi=om the Bi nanoparticles near the surface of the (LiF + Bi ) aggregates directly to the carbon matrix, inducing the oxidation of the bismuth metal into BiF3 (transport mechanism A in FIG. 13). The kinetic hindrances for those electronic and ionic transport mechanisms are small and, therefore, the polarization is small (less than 0.1 V according to the GITT plot of FIG. 7) resulting in a plateau at 3.3 V vs Li/Li+. After a while, the surface has been fully oxidized and all the (LiF +
Bi ) aggregates are covered with an electron insulative BiF3 product layer. The electronic and ionic transport mechanisms change, going fi=om what we called mechanism A to mechanism B. In the proposed transport mechanism, the electrons have to tunnel from the remaining Bi nanoparticles at the core of the aggregates to the carbon matrix through the BiF3 layer.
Likewise, Li+ions have to diffuse through this BiF3 layer, migrating from the remaining LiF
nanoparticles at the core of the aggregate to the electrolyte. Obviously, the kinetic hindrances are much more severe in mechanisin B than they were in mechanism A, and the polarization increases suddenly and significantly (by about 0.3V according to the GITT
curve of FIG. 7), the output voltage then entering the second plateau at 3.7V. Since this transition is due to the fornzation of a (proportionally) thick BiF3 layer on the surface of the (LiF +
Bi ) aggregates, this also explains why the BiF3 only becomes visible by XRD at the second delithiation plateau.
The specific discharge capacity versus cycle number plot of tysonite BiF3/C
nanocomposite high-energy milled for 30min, lh, 2h and 4h and cycled between 2V and 4V
at a current density of 40 mA/g in a LiPF6 EC:PC: DEC:DMC electrolyte is presented in FIG.
14. This figure shows that cycling stability improves when the milling time is increased.
Although fi=om the XRD patterns shown on FIG. 1 the BiF3 crystallite size does not seem to decrease much when the milling time is increased, the distribution of crystallite size is probably different. Hence, the longer the milling time, the more the nanocomposite will have BiF3 crystallites of extremely small dimensions and the less the nanocomposite will have 30 mn BiF3 crystallites. Without being limited by theory, if the average particle size gets smaller wlien the high-energy milling time is increased, the surface over volume ratio of the BiF3 particles will become larger, and thus the transition from the transport mechanism A to the transport mechanism B during the delithiation will occur later. Without being limited by theory, this would explain why, as can be seen in the inset of the FIG. 14, the tysonite BiF3/C
nanocomposite high-energy milled for 4h does not exhibit the second plateau at 3.7V during the delithiation. The smaller average crystallite size also may justify the improved capacity retention wlien the milling time is increased.

Example S. The Effect Of MoO3 On Specific Capacity In A Bismuth Fluoride Nanocomposite.
An MoO3 bismuth fluoride nanocomposite was fabricated by incorporating 15 weight % MoO3 and 85 weight percent BiF3. The resultant inventive nanocomposite was of the formula Bio.ssMoo.i50o.45F2.55= The nanocominposite was foi-ined by high energy milling the mixture for two hours. The material was tested versus a Li metal counter electrode at 40 mA/g discharge cuiTent. FIG. 15 depicts voltage versus specific capacity. As can be seen from the figure, at 2 Volts the specific capacity is greater than 200 mAh/g.
While the present invention has been described with reference to the specific embodiments thereof it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the ti-ue spirit and scope of the invention. In addition, many modifications may be made to adopt a particular situation, material, composition of matter, process, process step or steps, to the objective spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims (97)

1. ~A composition comprising a nanocrystalline bismuth fluoride compound.

2. ~The composition according to claim 1, wherein the bismuth fluoride compound is BiF2, and wherein 3<=z<=5.

3. ~The composition according to claim 1, wherein the bismuth fluoride compound is comprised of Bi5+.

4. ~The composition according to claim 2, wherein the bismuth fluoride compound is comprised of Bi5+.

5. ~The composition according to claim 1, wherein the bismuth fluoride compound is comprised of Bi3+.

6. ~The composition according to claim 1, wherein the bismuth fluoride compound further comprises a Bi cation, and wherein a metal cation is in partial substitution of the Bi cation.

7. ~The composition according to claim 6, wherein the metal cation is a metal element selected from the group consisting essentially of Fe, B, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

8. ~The composition according to claim 6, wherein the metal cation is a metal element selected from the group consisting of Cu and Mo.

9. ~The composition according to claim 1, wherein the bismuth fluoride compound comprises nanocrystallites that are less than about 100 nm in diameter.

10. ~The composition according to claim 1, wherein the bismuth fluoride compound comprises nanocrystallites that are less than about 50 nm in diameter.

11.~The composition according to claim 1, wherein the bismuth fluoride compound comprises nanocrystallites that are less than about 20 nm in diameter.

12. ~The composition according to claim 1, wherein the bismuth fluoride compound is BiF3.

13. ~The composition according to claim 1, further comprising oxygen.

14. ~The composition according to claim 13, wherein the nanocomposite comprises BiO x F z-2x, wherein 0<x<1.5 and 3<=z<=5.

15. ~A composition comprising a nanocrystalline bismuth fluoride compound nanocomposite.

16. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite is BiF z, and wherein 3<=z<=5.

17.~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+.

18. ~The composition according to claim 16, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+.

19. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi3+.

20. ~The composition according to claim 15, wherein the bismuth fluoride compound further comprises a Bi cation, and wherein a metal cation is in partial substitution of the Bi cation.

21. ~The composition according to claim 20, wherein the metal cation is a metal element selected from the group consisting essentially of Fe, B, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

22. ~The composition according to claim 20, wherein the metal cation is a metal element selected from the group consisting of Cu and Mo.

23. ~The composition according to claim 15, further comprising a conductive matrix.

24. ~The composition according to claim 23, wherein the conductive matrix is a conductive matrix selected from the group consisting of a metal oxide, a metal fluoride and a metal oxyfluoride.

25. ~The composition according to claim 24, wherein a metal from the metal oxide, the metal fluoride and the metal oxyfluoride is a metal selected from the group consisting of Fe, B, Bi, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

26. ~The composition according to claim 23, wherein the conductive matrix is present in an amount that is less than about 50 weight % of the nanocomposite.

27. ~The composition according to claim 23, wherein the conductive matrix is carbon.

28. ~The composition according to claim 27, wherein the carbon is in an amount that is less than about 5 weight percent of the nanocomposite.

29. ~The composition according to claim 15, wherein the bismuth fluoride nanocomposite further comprises carbon.

30. ~The composition according to claim 29, wherein the carbon is in an amount that is less than about 50 weight percent carbon of the nanocomposite.

31. ~The composition according to claim 29, wherein the carbon is in an amount that is less than about 25 weight percent carbon of the nanocomposite.

32. ~The composition according to claim 29, wherein the carbon is in an amount that is less than about 10 weight percent carbon of the nanocomposite.

33. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 100 nm in diameter.

34. ~The composition according to claim 15, wherein the bismuth fluoride compound comprises crystallites that are less than about 50 nm in diameter.

35. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 20 nm in diameter.

36. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite is BiF3.

37. ~The composition according to claim 15, wherein the nanocomposite has a rechargeable specific capacity when a current passes through the nanocomposite in a direction opposite a discharge direction.

38. ~The composition according to claim 15, further comprising oxygen.

39. ~The composition according to claim 38, wherein the nanocomposite comprises BiO x F z-2x, wherein 0<x<1.5 and 3<=z<=5.

40. ~The composition according to claim 15, wherein the composition is utilized in an electrode of a rechargeable battery.

41. ~The composition according to claim 15, wherein the bismuth fluoride compound of the nanocomposite is capable of a conversion reaction.

42. ~The composition according to claim 41, wherein the conversion reaction is reversible.

43. ~A composition comprising a bismuth fluoride compound nanocomposite.

44. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite is BiF z, and wherein 3<=z<=5.

45. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+

46. ~The composition according to claim 44, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+.

47. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi3+.

48. ~The composition according to claim 43, wherein the bismuth fluoride compound further comprises a Bi cation, and wherein a metal cation is in partial substitution of the Bi cation.

49. ~The composition according to claim 48, wherein the metal cation is a metal element selected from the group consisting essentially of Fe, B, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

50. ~The composition according to claim 48 wherein the metal cation is a metal element selected from the group consisting of Cu and Mo.

51. ~The composition according to claim 43, further comprising a conductive matrix.

52. ~The composition according to claim 51, wherein the conductive matrix is a conductive matrix selected from the group consisting of a metal oxide, a metal fluoride and a metal oxyfluoride.

53. ~The composition according to claim 52, wherein a metal from the metal oxide, the metal fluoride and the metal oxyfluoride is a metal selected from the group consisting of Fe, B, Bi, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

54. ~The composition according to claim 51, wherein the conductive matrix is present in an amount that is less than about 50 weight % of the nanocomposite.

55. ~The composition according to claim 51, wherein the conductive matrix is carbon.

56. ~The composition according to claim 55, wherein the carbon is in an amount that is less than about 5 weight percent of the nanocomposite.

57. ~The composition according to claim 43, wherein the bismuth fluoride nanocomposite further comprises carbon.

58. ~The composition according to claim 57, wherein the carbon is in an amount that is less than about 50 weight percent carbon of the nanocomposite.

59. ~The composition according to claim 57, wherein the carbon is in an amount that is less than about 25 weight percent carbon of the nanocomposite.

60. ~The composition according to claim 57, wherein the carbon is in an amount that is less than about 10 weight percent carbon of the nanocomposite.

61. ~The composition according to claim 43, whierein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 100 nm in diameter.

62. ~The composition according to claim 43, wherein the bismuth fluoride compound comprises crystallites that are less than about 50 nm in diameter.

63. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 20 nm in diameter.

64. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite is BiF3.

65. ~The composition according to claim 43, wherein the nanocomposite has a rechargeable specific capacity when a current passes through the nanocomposite in a direction opposite a discharge direction.

66. ~The composition according to claim 43, further comprising oxygen.

67. ~The composition according to claim 66, wherein the nanocomposite comprises BiO x F z-2x, wherein 0<x<1.5 and 3<=z<=5.

68. ~The composition according to claim 43, wherein the composition is utilized in an electrode of a rechargeable battery.

69. ~The composition according to claim 43, wherein the bismuth fluoride compound of the nanocomposite is capable of a conversion reaction.

70. ~The composition according to claim 69, wherein the conversion reaction is reversible.

71. ~An electrochemical cell comprising:
a negative electrode;
a positive electrode comprising a bismuth fluoride compound nanocomposite;
and a separator disposed between the negative and positive electrodes.

72. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite is BiF z, and wherein 3<=z<=5.

73. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+.

74. ~The cell according to claim 72, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi5+.

75. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite is comprised of Bi3+.

76. ~The cell according to claim 71, wherein the bismuth fluoride compound further comprises a Bi cation, and wherein a metal cation is in partial substitution of the Bi cation.

77. ~The cell according to claim 76, wherein the metal cation is a metal element selected from the group consisting essentially of Fe, B, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

78. ~The cell according to claim 76, wherein the metal cation is a metal element selected from the group consisting of Cu and Mo.

79. ~The cell according to claim 71, further comprising a conductive matrix.

80. ~The cell according to claim 79, wherein the conductive matrix is a conductive matrix selected from the group consisting of a metal oxide, a metal fluoride and a metal oxyfluoride.

81.~The composition according to claim 80, wherein a metal from the metal oxide, the metal fluoride and the metal oxyfluoride is a metal selected from the group consisting of Fe, B, Bi, Co, Ni, Mn, V, Mo, Pb, Sb, Cu, Sn, Nb, Cr, Ag and Zn.

82. ~The cell according to claim 79, wherein the conductive matrix is present in an amount that is less than about 50 weight % of the nanocomposite.

83. ~The cell according to claim 79, wherein the conductive matrix is carbon.

84. ~The cell according to claim 83, wherein the carbon is in an amount that is less than about 5 weight percent of the nanocomposite.

85. ~The cell according to claim 71, wherein the bismuth fluoride nanocomposite further comprises carbon.

86. ~The cell according to claim 85, wherein the carbon is in an amount that is less than about 50 weight percent carbon of the nanocomposite.

87. ~The cell according to claim 85, wherein the carbon is in an amount that is less than about 25 weight percent carbon of the nanocomposite.

88. ~The cell according to claim 85, wherein the carbon is in an amount that is less than about 10 weight percent carbon of the nanocomposite.

89. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 100 nm in diameter.

90. ~The cell according to claim 71, wherein the bismuth fluoride compound comprises crystallites that are less than about 50 nm in diameter.

91. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite comprises crystallites that are less than about 20 nm in diameter.

92. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite is BiF3.

93. ~The cell according to claim 71, wherein the nanocomposite has a rechargeable specific capacity when a current passes through the nanocomposite in a direction opposite a discharge direction.

94. ~The cell according to claim 71, wherein the nanocomposite further comprises oxygen.

95.~The cell according to claim 94, wherein the nanocomposite comprises BiO x F z-2x, wherein 0<x<1.5 and 3<=z<=5.

96. ~The cell according to claim 71, wherein the bismuth fluoride compound of the nanocomposite is capable of a conversion reaction.

97. ~The cell according to claim 96, wherein the conversion reaction is reversible.