# Patent

## Title
High energy cathode for a battery

## Abstract

An electrode for an electrochemical cell including a metal fluoride containing active electrode material and an intrinsically conductive coating wherein the coating is applied to the active electrode material by heating the mixture for a time and at a temperature that limits degradation of the cathode active material. The active material can be a hybrid material formed from the reaction of a metal fluoride and a metal complex.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of copending International Application No. PCT/US2014/028271, having an international filing date of Mar. 14, 2014 entitled “Cathode for a Battery,” which in turn claims priority to copending U.S. application Ser. No. 13/831,924 filed Mar. 15, 2013 entitled “Cathode for a Battery,” which is a continuation-in-part of co-pending U.S. application Ser. No. 13/612,800 filed Sep. 12, 2012 entitled “Cathode for a Battery,” which in turn claims priority to and the benefit of U.S. Provisional Application No. 61/533,911 filed Sep. 13, 2011 entitled “Cathode for Metal-Fluoride Battery” and U.S. Provisional Application No. 61/621,205 filed Apr. 6, 2012 entitled “Cathode for a Battery.”
This application is a continuation-in-part of International Application No. PCT/US2014/028506, having an international filing date of Mar. 14, 2014 entitled “High Energy Materials For A Battery And Methods For Making And Use,” which claims priority to U.S. Provisional Application No. 61/786,602 filed Mar. 15, 2013 entitled “High Energy Materials For A Battery And Methods For Making And Use.”
This application claims priority to and the benefit of each of these above applications, and each application is incorporated herein by reference in its entirety.


BACKGROUND OF THE INVENTION
The present invention is in the field of battery technology and, more particularly, in the area of using coatings to enhance electrolyte and electrode performance in batteries including high-energy electrodes metal-fluoride, carbon-fluoride, or oxide-based electrode materials.
One type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing carbon and fluorine. During discharge, lithium ions and electrons are generated from oxidation of the negative electrode while fluoride ions and carbon are produced from reduction of the positive electrode. The generated fluoride ions react with lithium ions near the positive electrode to produce a compound containing lithium and fluorine, which may deposit at the positive electrode surface.
Metal fluoride based batteries are an attractive energy storage technology because of their extremely high theoretical energy densities. For example, certain metal fluoride active materials can have theoretical energy densities greater than about 1600 Wh/kg or greater than about 7500 Wh/L. Further, metal fluorides have a relatively low raw material cost, for example less than about $10/kg. However, a number of technical challenges currently limit their widespread use and realization of their performance potential.
One challenge for certain metal fluoride materials is comparatively poor rate performance. Many metal fluoride active materials have electrochemical potentials greater than about 2.5 V because of their relatively large bandgap produced by the highly ionic bonding between the metal and fluorine, and in particular between a transition metal and fluorine. Unfortunately, one of the drawbacks to wide bandgap materials is the intrinsically low electronic conductivity that results from the wide bandgap. As a result of this low conductivity, discharge rates of less than 0.1 C are required in order to obtain full theoretical capacity. More typically, discharge rates of 0.05 C to 0.02 C are reported in the literature. Such low discharge rates limit the widespread use of metal fluoride active materials.
Another challenge for certain metal fluoride active materials is a significant hysteresis observed between the charge and discharge voltages during cycling. This hysteresis is typically on the order of about 1.0V to about 1.5V. While the origin of this hysteresis is uncertain, current evidence suggests that kinetic limitations imposed by low conductivity play an important role. Further, asymmetry in the reaction paths upon charge and discharge may also play a role. Since the electrochemical potential for many of the metal fluorides is on the order of 3.0V, this hysteresis of about 1.0V to about 1.5V limits the overall energy efficiency to approximately 50%.
Limited cycle life is another challenge for certain metal fluoride active materials. Although rechargeability has been demonstrated for many metal fluoride active materials, their cycle life is typically limited to tens of cycles and is also subject to rapid capacity fade. Two mechanisms are currently believed to limit the cycle life for the metal fluoride active materials: agglomeration of metallic nanoparticles and mechanical stress due to volume expansion. It is believed that metal fluoride active materials can cycle by virtue of the formation during lithiation of a continuous metallic network within a matrix of insulating LiF. As the number of cycles increases, the metal particles tend to accumulate together into larger, discrete particles. The larger agglomerated particles in turn create islands that are electrically disconnected from one another, thus reducing the capacity and ability to cycle the metal fluoride active materials. The second limitation to extended cycle life is the mechanical stress imparted to the binder materials by the metal fluoride particles as a result of the volume expansion that occurs during the conversion reaction. Over time, the binder is pulverized, compromising the integrity of the cathode. Notably, for the metal fluoride CuF2, no demonstrations of rechargeability have been reported.
For CuF2, an additional challenge prevents rechargeability. The potential required to recharge a CuF2 electrode is 3.55V. However, in typical electrolytes for lithium ion batteries, Cu metal oxidizes to Cu2+ at approximately 3.4 V vs. Li/Li+. The oxidized copper can migrate to the anode, where it is irreversibly reduced back to Cu metal. As a result, Cu dissolution competes with the recharge of Cu+2LiF to CuF2, preventing cycling of the cell. The Cu metal accumulating on the anode surface can increase the impedance and/or destroy the solid-electrolyte interphase (SEI) on the anode.
The following papers and patents are among the published literature on metal fluorides that employ mixed conductors that are not electrochemically active within the voltage window of the metal fluoride: Badway, F. et al., Chem. Mater., 2007, 19, 4129; Badway, F. et al., J. Electrochem. Soc, 2007, 150, A1318; “Bismuth fluoride based nanocomposites as electrode materials” U.S. Pat. No. 7,947,392; “Metal Fluoride And Phosphate Nanocomposites As Electrode Materials” US 2008/0199772; “Copper fluoride based nanocomposites as electrode materials” US 2006/0019163; and “Bismuth oxyfluoride based nanocomposites as electrode materials” U.S. Pat. No. 8,039,149.
In some prior batteries, conductive coatings have been applied to electrode materials. In secondary battery applications, some electrodes have been formed from carbon-coated LiFePO4. Also, some research has occurred on coating carbon-fluoride compounds used for electrodes in primary batteries (see Q. Zhang, et al., Journal of Power Sources 195 (2010) 2914-2917). Prior art coatings are typically applied at high temperatures and under inert atmosphere which can degrade cathode active materials. Thus, temperature-sensitive active materials for cathodes have not typically been coated with conductive carbon materials.
Certain embodiments of the present invention address the challenges found in batteries. Certain embodiments of the present invention can be used to form electrochemical cells for batteries that exhibit lower underpotential, higher power, higher capacity at a high discharge rate, less heat generation, or faster heat dissipation when compared to prior batteries.
Certain embodiments of the present invention can be used to form electrochemical cells having metal fluoride active material that exhibit improved rate performance, improved energy efficiency, and improved cycle life when compared to prior batteries.
These and other challenges can be addressed by embodiments of the present invention described below.
BRIEF SUMMARY OF THE INVENTION
Certain embodiments of the invention include an electrode for an electrochemical cell including an active electrode material, a binder material, and an intrinsically conductive coating wherein the coating is applied to the active electrode material. In certain embodiments, the intrinsically conductive coating is formed from an organic coating compound comprising a conjugated core. In certain embodiments, the intrinsically conductive coating is formed from an organic coating compound comprising a conjugated core in which at least 90% of the carbon atoms are sp or sp2 hybridized. In certain embodiments, the intrinsically conductive coating is formed from an organic coating compound in which at least 35% of the carbon atoms are sp or sp2 hybridized.
Certain embodiments of the invention include a method of making an electrode for an electrochemical cell including combining a coating compound characterized by having an intrinsic conductivity and an active electrode material to form a mixture, heating the mixture to form a conductively coated active electrode material, wherein the mixture is heated for a time and at a temperature that limits degradation of the active electrode material, mixing the conductively coated active electrode material with a binder material and a conductive additive to form an electrode-forming mixture, and heating the electrode-forming mixture to form the electrode. In certain embodiments, the coating compound is heated at less than about 450 degrees C. In certain embodiments, the coating compound is heated for a time in a range of from about 0 hours to about 6 hours.
Certain embodiments of the invention include a method of making a composition for use in forming a cathode for a battery. The method includes milling a metal fluoride material with a metal complex and annealing the mixture, wherein at least a portion of the metal fluoride material and at least a portion of the metal complex undergo a phase change. The method can include forming a coating on at least a portion of the metal fluoride material. The metal fluoride material is preferably CuF2. The metal complex can be a metal oxide including, but not limited to, Al2O3, SiO2, MoO3, MoO2, NiO, CuO, VO2, V2O5, TiO2. Preferably, the metal oxide is NiO. The annealing temperature is less than 450 degrees C., less than 400 degrees C., less than 325 degrees C., or less than 200 degrees C. Preferably, the annealing temperature is about 325 degrees C. The temperature is chosen such that it is sufficiently high for the metal complex to react with the metal fluoride, but not high enough to decompose the metal fluoride. Without such heat treatment and the resulting reaction, the material is not rechargeable, as is demonstrated by experiments described herein.
Certain embodiments of the invention include a composition formed by the methods disclosed herein. The composition is characterized by having reversible capacity. The composition can include particles with a grain size greater than 100 nm, 110 nm, 120 nm, or 130 nm. The composition can include a particle having a first phase and a coating on the particle having a second phase. Preferably, the first phase includes the metal fluoride and the second phase includes the metal oxide. The coating can be bonded to the particle, such as by covalent bonding.
Certain embodiments include the method of making an electrochemical cell containing coated cathode materials and methods of use of such electrochemical cells.



BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 illustrates electrochemical characterization of a hybrid cathode formed from a metal fluoride and a reactant material according to certain embodiments. The cathode demonstrates rechargeability.
FIG. 2 illustrates a powder X-ray diffraction pattern of a material used to for a rechargeable metal fluoride cathode.
FIG. 3 illustrates second cycle discharge capacity for a variety of hybrid cathode materials used according to embodiments of the invention.
FIG. 4 illustrates second cycle discharge capacity for a hybrid cathode material used according to embodiments of the invention versus annealing temperature.
FIG. 5 illustrates second cycle the capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF2 with 15 wt % of certain metal oxides (in this case NiO or TiO2) at certain annealing temperatures.
FIG. 6 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF2 with 15 wt % of certain metal oxides (in this case NiO or TiO2) for certain annealing times.
FIG. 7 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, 90 wt %, or 95 wt % CuF2 with 5 wt %, 10 wt %, 15 wt % of NiO.
FIG. 8 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO as a function of milling energy.
FIG. 9 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO as a function of milling time.
FIG. 10 illustrates the second cycle reversible capacity measured for various starting materials used to react with CuF2.
FIG. 11 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting CuF2 with nickel(II) acetylacetonate using various processing conditions.
FIG. 12 illustrates the capacity as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO and for a control material.
FIG. 13 illustrates a galvanostatic intermittent titration technique measurement for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO.
FIG. 14 illustrates the capacity of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO.
FIG. 15 illustrates voltage traces of the full cell and half cells prepared as described in relation to FIG. 14.
FIG. 16 illustrates the capacity retention of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO.
FIG. 17 depicts the results of testing of an electrochemical cell containing metal fluoride active materials coated according to certain embodiments of the invention as compared to control. Certain coated metal fluoride materials demonstrate improved rate capability as compared to control while other coated metal fluoride materials demonstrate diminished rate capability as compared to control.
FIG. 18 depicts the results of testing of an electrochemical cell containing metal fluoride active materials coated according to certain embodiments of the invention as compared to control. A CuF2/MoO3 composite material coated with anthracene demonstrated improved rate performance as compared to an uncoated CuF2/MoO3 composite material.
FIG. 19 depicts the results of testing of an electrochemical cell containing metal fluoride active materials coated according to certain embodiments of the invention. A metal fluoride material coated with anthracene demonstrated a minimal voltage drop from low rate to high rate of discharge.
FIG. 20 depicts the results of testing of an electrochemical cell containing metal fluoride active materials coated according to certain embodiments of the invention, demonstrating a low voltage drop from low rate to high rate of discharge and improved energy density.
FIG. 21 depicts the results of testing of an electrochemical cell containing metal fluoride active materials coated according to certain embodiments of the invention.



DETAILED DESCRIPTION OF THE INVENTION
The following definitions apply to some of the aspects described with respect to some embodiments of the invention. These definitions may likewise be expanded upon herein. Each term is further explained and exemplified throughout the description, figures, and examples. Any interpretation of the terms in this description should take into account the full description, figures, and examples presented herein.
The singular terms “a,” “an,” and “the” include the plural unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.
The terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein.
The term “about” refers to the range of values approximately near the given value in order to account for typical tolerance levels, measurement precision, or other variability of the embodiments described herein.
The terms “coating,” “coat,” “coated,” and the like refer to a relatively thin film of material on the surface of a substrate and the process of making the same. The terms include films that are continuous and films that are discontinuous.
The terms “conductive,” “conductor,” “conductivity,” and the like refer to the intrinsic ability of a material to facilitate electron or ion transport and the process of doing the same. The terms include materials whose ability to conduct electricity may be less than typically suitable for conventional electronics applications but still greater than an electrically-insulating material.
The term “core” and the like refers to the central moiety of a molecule as opposed to pendant groups on the molecule. The core may occupy the entire molecule. The shape of the molecule is not determinative of the presence or lack of a core.
The term “solvent” and the like refers to a materials capable of at least partially dissolving another material. The term includes a single solvent or a mixture containing one or more solvents, and such mixture can include non-solvents.
The term “slurry” and the like refers to a mixture in which at least some amount of one or more components is not dissolved in the solvent, and includes mixtures of two materials where the mixture is formed without a solvent or the mixture that results when the solvent is substantially removed but before the final product or article to be made from the mixture has been formed.
The term “active material” and the like refers to the material in an electrode, particularly in a cathode, that donates, liberates, or otherwise supplies the conductive species during an electrochemical reaction in an electrochemical cell.
The term “transition metal” refers to a chemical element in groups 3 through 12 of the periodic table, including scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), and meitnerium (Mt).
The term “halogen” refers to any of the chemical elements in group 17 of the periodic table, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
The term “chalcogen” refers to any of chemical elements in group 16 of the periodic table, including oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
The term “alkali metal” refers to any of the chemical elements in group 1 of the periodic table, including lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
The term “alkaline earth metals” refers to any of the chemical elements in group 2 of the periodic table, including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
The term “rare earth element” refers to scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
A rate “C” refers to either (depending on context) the discharge current as a fraction or multiple relative to a “1 C” current value under which a battery (in a substantially fully charged state) would substantially fully discharge in one hour, or the charge current as a fraction or multiple relative to a “1 C” current value under which the battery (in a substantially fully discharged state) would substantially fully charge in one hour.
In certain embodiments, a novel active material, which may be referred to as a matrix material or a coated material or a hybrid material, is prepared for use in a cathode with metal fluoride (MeFx) active materials. In some embodiments, the novel active material is prepared by combining a metal fluoride and a metal complex, followed by heat treatment of the mixture under an inert atmosphere according to the formula (I)

MeFx+Me′yXz+heat  (I)

According to certain embodiments, the heat treatment of the metal fluoride and metal complex causes a reaction to form a new phase according to the formula (II)

MeFx+Me′yXz→MeaMe′bXcFd  (II)

where x, y, z, a, b, and c depend on the identity and valence of the Me, Me′, and X. In other embodiments, the heat treatment causes the formation of covalent bonds between the metal fluoride and the metal complex, improving conductivity and passivating the surface. The heat treatment drives the reaction of in formula (II) and is required to the form the desired reaction product.

Suitable metal complexes, which can act as precursors for the reaction described herein, for use in synthesizing the matrix, coating, or active material include, but are not limited to, MoO3, MoO2, NiO, CuO, VO2, V2O5, TiO2, Al2O3, SiO2, LiFePO4, LiMeTPO4 (where Mer is one or more transition metal(s)), metal phosphates, and combinations thereof. According to embodiments of the invention, these oxides can be used in Formula (I).
It is understood that the synthetic route for achieving the matrix, coating, hybrid, or active matrix material may vary, and other such synthetic routes are within the scope of the disclosure. The material can be represented by MeaMe′bXcF and in the examples herein is embodied by a Cu3Mo2O9 matrix. Other matrices and coatings are within the scope of this disclosure. For example, NiCuO2, Ni2CuO3, and Cu3TiO4.
The matrix and coating materials disclosed herein provide rechargeability to otherwise non-rechargeable metal fluoride matrix materials. Without being bound by a particular theory or mechanism of action, the rechargeability may be due to the electrochemical properties of the novel matrix, the coating of the metal fluoride to prevent copper dissolution, or a more intimate interface between the metal fluoride and the matrix material as a result of the heat treatment and reaction. Further, the novel matrix material may provide a kinetic barrier to the Cu dissolution reaction, or to similar dissolution reactions for other metal fluoride materials to the extent such dissolution reactions occur in the cycling of electrochemical cells.
In the case of oxide-based matrices (such matrices include those generated according to Formula II), intimate mixing of the metal fluoride and the metal complex (or other suitable precursor material) and moderate heat treatment can be used to generate rechargeable electrode materials. Other suitable precursors include materials that decompose to form metal oxides (and in particular, transition metal oxides) as opposed to using a metal oxide to directly react with the metal fluoride. Examples of such precursors include, but are not limited to, metal acetates, metal acetylacetonates, metal hydroxides, metal ethoxides, and other similar organo-metallic complexes. In either event, the final rechargeable matrix material is not necessarily a pure oxide or a purely crystalline material. The reaction of Formula II predicts that there would not be a pure oxide or a purely crystalline material. In some instances, the metal oxide precursor or metal oxide material can form a coating, or at least a partial coating, on the metal fluoride active material. Without being bound by a particular theory or mechanism of action, the reaction of the metal oxide precursor or metal oxide material with the surface of the metal fluoride (and in particular copper fluoride) active material is important for generating a rechargeable electrode active material.
Certain embodiments of the invention relate to compounds useful for the formation of conductive coatings on such novel active materials. Preferably, the compounds of embodiments of the invention are used to coat active materials that degrade, decompose, or are otherwise rendered unsuitable or undesirable for use after exposure to high temperatures or high temperature under an inert atmosphere, where high temperatures are those higher than about 500 degrees C. The compounds are capable of forming conductive coatings at temperatures less than about 500 degrees C. on such active materials.
In certain embodiments, conductive coatings are used to improve the electrical conductivity of desirable active materials, including metal-fluoride and carbon-fluoride active materials. In certain embodiments, conductive coatings are used to improve the electrical conductivity of iron-fluoride compounds (such as FeF3), manganese-fluoride compounds (such as MnF3), copper-fluoride compounds (such as CuF2), and carbon-fluoride compounds. In certain embodiments, conductive coatings are used to improve the electrical conductivity of lithium-manganese-nickel-oxygen (LMNO) compounds, lithium-manganese-oxygen (LMO) compounds, and lithium-rich layered oxide compounds. More generally, conductive coatings are used to improve active materials for cathodes including phosphates, fluorophosphates, fluorosulphates, silicates, spinels, and composite layered oxides. In particular, conductive coatings are formed on the novel active materials of Formula (I) and/or Formula (II).
According to certain embodiments, active materials are coated using a precursor material. Suitable precursor materials facilitate the deposition of a conductive coating onto the active material, and in particular onto particles of the active material.
According to certain embodiments, the compounds useful for the formation of conductive carbon coatings on active materials are organic molecules with delocalized electron configurations. According to certain embodiments, the compounds are conductive organic molecules. It is understood that any compound with a high degree of electron delocalization or any compound with high conductivity could be used to form conductive coatings on active materials.
Generally speaking, delocalized electrons are electrons that are not limited to the orbital of a single atom, in the case of ions or metals, or a single covalent bond, in the case of organic materials. In carbon-based materials, bonds including a carbon atom can be a source for delocalized electrons when more than one of the four electrons in the outer energy levels of the carbon atom is in a covalent bond with another atom. Often, electron delocalization occurs in carbon-carbon bonds. These bonds are sometimes referred to as conjugated bonds.
According to hybridization theory, delocalized electrons can be described as mixing among valence orbitals of an atom such as carbon. In carbon, hybridized orbitals can be sp3 hybrids, sp2 hybrids, and sp hybrids. Without being bound by theory or a particular mode of action, it is believed that organic materials with a high degree of sp or sp2 hybridization are preferable for forming conductive carbon coatings on active materials. Compounds, according to embodiments of the invention, contain conjugated cores in which many of the carbon atoms are sp or sp2 hybridized. Compounds, according to embodiments of the invention, may be known for their intrinsic conductivity.
Conductive carbon coatings of the prior art, such as graphitic coatings, are formed from non-conductive carbon molecules with non-hybridized or sp3 hybridized orbital electrons. Such materials are typically heated to high temperatures to decompose and graphitize them, often forming carbon coatings with sp2 hybridized orbitals. In such coatings, it is known that the efficiency of the graphitization increases with temperature and that high temperature heat treatment gives the best performing coatings.
In contrast, compounds of certain embodiments do not require high temperature heat treatment due at least in part to their intrinsic conductivity. Compounds of the embodiments of the present invention do not require graphitization to provide a conductive carbon coating. Further, decomposition of compounds of embodiments of the invention may be undesirable as it would likely reduce or destroy the intrinsic conductivity of the compounds.
According to embodiments of the invention, compounds for coating active materials contain carbon atoms that are sp or sp2 hybridized. Preferably, at least 35% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 40% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 45% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 50% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 55% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 60% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 65% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 70% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 75% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 80% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 85% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 90% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, at least 95% of the carbon atoms in the compound are sp or sp2 hybridized. Preferably, 100% of the carbon atoms in the compound are sp or sp2 hybridized.
According to embodiments of the invention, compounds for coating active materials contain conjugated cores in which many of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 35% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 40% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 45% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 50% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 55% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 60% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 65% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 70% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 75% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 80% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 85% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 90% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in which at least 95% of the carbon atoms are sp or sp2 hybridized. Preferably, the compounds contain conjugated cores in 100% of the carbon atoms are sp or sp2 hybridized.
Examples of compounds containing conjugated cores include but are not limited to: pentacene, anthracene, naphthalene, rubrene, C60, graphene, multi-walled carbon nanotubes (MWCNT), N,N′-dioctyl-3,4,9,10 perylenedicarboximide, perylene, pyrene, tetrathiafulvalene, polyaniline, 6,13-bis(triisopropylsilylethynyl)pentacene, 4-(heptadecafluorooctyl) aniline, poly(3-hexylthiophene-2,5-diyl), 7,7,8,8-tetracyanoquinodimethane, 11-phenoxylundecanoic acid, triphenylene, poly(2,6-naphthalenevinylene), octofluoronapthalene, oligothiophenes, hexabenzocoronene, phthalocyanine, p-quinquephenyl 8, tetra-N-phenylbenzidine, octafluoronaphthalene and N,N′-dioctyl-3,4,9,10-perylenedicarboximide. More than one compound can be combined in a single coating to generate additive or enhanced performance.
Examples of carbon source coating materials according to certain embodiments of the invention include but are not limited to: tris[4-(5-dicyanomethylidenemethyl-2-thienyl)phenyl]amine, triphenylene, tetrathiafulvalene, rubrene, pyrene, polyaniline (emeraldine base), poly(3-hexylthiophene-2,5-diyl), PNV, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene, pentacene/MWCNT, pentacene/anthracene (4:1), pentacene/anthracene (1:4), pentacene-N-sulfinyl-tert-butylcarbamate, pentacene, naphthalene, N,N′-dioctyl-3,4,9,10-perylenedicarboximide, dithieno[3,2-b:2?,3?-d]thiophene, dilithium phthalocyanine, dibenzotetrathiafulvalene, dibenz[a,h]anthracene, coronene, copper(II) phthalocyanine, C60, bis(ethylenedithio)tetrathiafulvalene, benz[b]anthracene, anthracene, 29H,31H-phthalocyanine, 11-phenoxyundecanoic acid, 7,7,8,8-tetracyanoquinodimethane, 6,13-bis(triisopropylsilylethynyl)pentacene, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, 4-(heptadecafluorooctyl)aniline, 2,2′:5′,2′′:5′′,2′′′-quaterthiophene, 1,8-naphthalic anhydride, 1,6-diphenyl-1,3,5-hexatriene, 1,4,5,8-naphthalenetetracarboxylic dianhydridem, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzoimidazole, and combinations thereof.
According to certain embodiments, electrodes for use in electrochemical cells are formed from an active material, a binder material, and a conductive material. The active material is typically in particulate form, but it may take other forms. Prior to forming the electrode, active materials are coated using compounds according to embodiments of the invention. In certain embodiments, the compound “wets” the particles of the active material. The compound can wet the particles due to being in solution or due to melting. According to certain embodiments, preferred compounds for coating active material particles would both wet the particles and form a conductive coating at a temperature below about 500 degrees C. According to certain embodiments, preferred carbon precursors for coating carbon-fluoride or metal-fluoride particles would both wet the particles and form a conductive coating at a temperature below about 600 degrees C. to about 700 degrees C. Preferably, the compounds produce a substantially conductive carbon coating at temperatures below the range of decomposition temperatures for the active materials.
According to certain embodiments of the invention, the compound is mixed with a solvent. In these embodiments, solvents are paired with compounds based on solubility, wettability, viscosity, flashpoint, volatility, and other properties. The compound and the solvent are mixed using any means of mixing, including ball milling. In certain embodiments, active material and compound are ball-milled with acetone as a solvent. Examples of appropriate solvents include acetone, NMP, methanol, hexane, acetonitrile, THF, DMSO, pyridine, benzene, water, ethanol, isopropanol, and combinations thereof. In certain embodiments, the solvent improves the wetting of the compound onto active material particles to produce a more uniform and complete coating prior to the heating step. In other embodiments, the solvent aids the processing of compound particles and active material particles to improve mixing and/or control particle size prior to the heating step. Such improvements in the uniformity and completeness of the coating prior to heating provide more uniform and complete molecular coatings on the active material after heating.
According to certain embodiments, the active material, compound, and solvent are mixed using a method such as ball milling. Preferably, the active material, coating compound, and solvent are mixed using a method that produces a substantially uniform and complete coating of the coating compound on the active material. In some embodiments, the active material, compound, and solvent are agitated to produce a substantially uniform and complete coating of the compound on the active material. In some embodiments, the active material and the coating compound are mixed without a solvent.
According to certain embodiments, the mixture of the active material, compound, and solvent forms a slurry. In certain embodiments, the slurry is heated to produce a conductive carbon coating on the active material. In certain embodiments, it is preferable for the heating to occur under inert atmosphere.
According to certain embodiments, the heating conditions are chosen to produce a thin layer of conducting carbon on the active material while limiting degradation of the active electrode material. In some embodiments, the heating occurs at a range of temperatures from about 300 degrees C. to about 700 degrees C., or preferably from about 400 degrees C. to about 600 degrees C. In some embodiments, the heating occurs at less than about 500 degrees C. Preferably, the heating occurs at less than about 450 degrees C. Preferably, the heating occurs at less than about 400 degrees C. Preferably, the heating occurs at less than about 350 degrees C. Preferably, the heating occurs at less than about 300 degrees C. Preferably, the heating occurs at less than about 250 degrees C. Preferably, the heating occurs at less than about 200 degrees C. Preferably, the heating occurs at less than about 150 degrees C. Preferably, the heating occurs at less than about 100 degrees C.
In certain embodiments, it is preferable to tailor the annealing such that the sp or sp2 hybridized atoms are not decomposed and that the delocalized electrons of the conjugated cores are substantially maintained. However, it is also preferable to provide the system with sufficient energy (e.g., thermal and/or mechanical energy) to yield desirable coverage on the particles of active material. In certain embodiments, lower annealing temperatures increase battery capacity but reduce voltage performance. In certain embodiments, a reaction occurs between the coating precursor and the active materials such that the system undergoes a color change, which may be evidence of covalent bonding between the coating compounds and the active materials.
In some embodiments, the heating occurs for less than about 6 hours. Preferably, the heating occurs for less than about 5 hours. Preferably, the heating occurs for less than about 4 hours. Preferably, the heating occurs for less than about 3 hours. Preferably, the heating occurs for less than about 2 hours. Preferably, the heating occurs for less than about 1 hour.
According to certain embodiments, the coated active materials are further mixed with a binder material and a conductive material. In such embodiments the mixing can be done by suitable methods, such as ball milling, to form an electrode-forming material. The electrode-forming material is typically composed primarily of coated active material, preferably in the range of from about 85% to about 97% of active material. The remainder of the electrode-forming material is composed of the binder material and the conductive material. The binder material is typically present at about 2.5% to about 11%. In certain embodiments, the conductive material is present in a range of from about 0.5% to about 7.5%.
According to certain embodiments, metal fluoride active materials are coated using the methods disclosed herein. Coated metal fluoride active materials may be prepared with or without solvents. Certain embodiments exemplified herein were prepared without solvents. Further, coated metal fluoride active materials may be combined into mixture or composites with ionic conductors to improve ionic conduction. For example, MoO3 may be used to improve ionic conduction with coated CuF2 active materials. Further, the metal fluoride active materials may be formed into cathode materials using conductive matrix materials as disclosed herein. Alternately, the conductive matrix may be formed by combining CuF2 and a matrix material and then applying the conductive coating. Indeed, the components may be combined and applied in any order. These metal fluorides composites may also benefit from the use of an adjunct ionic conductor.
For example, the matrix material LiFePO4 combined with a coated CuF2 active material demonstrates significant improvement in rate performance and also demonstrates a low voltage drop when comparing low discharge rates and high discharge rates. These performance benefits are not limited to CuF2 and are applicable to other metal fluorides as well.
Unexpectedly, as compared to our work with carbon fluoride active materials, certain coating precursors did not perform well with conductive matrix materials for use with metal fluoride materials. For example, certain conductive matrix materials for use with metal fluoride active materials coated with dilithium phthalocyanine, perylene, or PVDF displayed inferior performance as compared to uncoated conductive matrix materials for use with metal fluoride active materials.
As described in the examples below, certain embodiments produce coated electrodes that deliver higher power, increased operating voltage, higher capacity at a high discharge rate, and reduced heat buildup when compared with uncoated electrodes. Without being bound by a particular principle, hypothesis, or method of action, coatings of certain embodiments of the invention provide a low resistance pathway for electron and lithium ion transport, which significantly lowers the electrode resistance. One consequence of this is an electrochemical cell with higher power and lower underpotential. As a result, higher capacity can be obtained when electrochemical cells are run at comparatively high rate.
As illustrated in certain examples herein, the coatings of certain embodiments of the invention address some of the challenges of batteries by enabling higher power, increasing operating voltage, increasing capacity at a high discharge rate, reducing heat generation, and increasing heat dissipation. For example, in high-drain applications certain embodiments improve the energy capacity of batteries such that a higher voltage may be achieved at a high current when compared to prior batteries. Certain embodiments extend the useful life of batteries under moderate to high drain conditions. Unexpectedly, the coatings of certain embodiments of the present invention address these challenges at low concentrations. Coated cathode materials according to certain embodiments of the invention demonstrated improved voltage and power at late depths of discharge.
Coated cathode materials according to certain embodiments of the invention were included in electrochemical cells according to the examples set forth below. In some situations, the electrolyte solution in the electrochemical cell included additives according to using materials and methods disclosed in copending U.S. patent application Ser. No. 13/612,798 filed Sep. 12, 2012 and titled “Electrolyte Materials for Batteries and Methods of Use,” which application is incorporated by reference herein in its entirety. The combination of the coated cathode materials of certain embodiments of the invention and such electrolyte solutions including additives demonstrated improved performance. In many cases, the performance improvements were substantially greater than the performance improvements realized by either the coating or the additive on its own.
The following examples describe specific aspects of some embodiments of the invention to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of the invention.
EXAMPLES
Example 1
Fabrication of Matrix and/or Coated Electrodes for Rechargeable Cells
Materials and Synthetic Methods.
All reactions were prepared in a high purity argon filled glove box (M-Braun, O2 and humidity contents <0.1 ppm). Unless otherwise specified, materials were obtained from commercial sources (e.g., Sigma-Aldrich, Advanced Research Chemicals Inc., Alfa Aesar, Strem) without further purification.
Preparation of CuF2/Matrix.
Milling vessels were loaded with CuF2 at from about 85 wt % to about 95 wt % and reactant (metal oxide or metal oxide precursor) at from about 5 wt % to about 15 wt %, and the vessels were sealed. The mixture was milled. After milling, samples were annealed at from about 200 degrees C. to about 575 degrees C. for 1 to 12 hours under flowing N2. Specific matrix reactants were processed as described below.
Preparation of CuF2/CusMo2O9.
Milling vessels were loaded with CuF2 (85 wt %) and MoO3 (15 wt %), sealed, and then milled. After milling, samples were annealed at 450 degrees C. for 6 hours under flowing N2.
Preparation of CuF2/NiO.
Milling vessels were loaded with CuF2 (85 wt %) and NiO (15 wt %), sealed, and then milled. After milling, samples were annealed at 325 degrees C. for 6 hours under flowing N2.
Preparation of CuF2/Nickel(II) Acetylacetonate.
A fine dispersion of CuF2 was prepared by milling in the presence of THF (40-120 mg CuF2/mL THF). The dispersed sample was then added to a solution of Ni(AcAc)2 in THF such that Nickel(II) acetylacetonate accounted for 15 wt % of the solids in the solution. The solution was then agitated by either shaking, sonication, or low energy milling for from about 1 to about 12 hours. The solution was then dried at room temperature under vacuum and the resulting solid was annealed at 450 degrees C. for 6 hours under dry air.
Electrode Formulation.
In some embodiments, cathodes were prepared using a formulation composition of 80:15:5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 44 mg Super P Li (Timcal) was dissolved in 10 mL NMP (Sigma Aldrich) overnight. 70 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. In other embodiments, cathodes were prepared using a formulation composition of 85:7.5:7.5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 133 mg Super P Li (Timcal) was dissolved in 15 mL NMP (Sigma Aldrich) overnight. 150 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. Films were cast by dropping about 70 μL of slurry onto stainless steel current collectors and drying at 150 degrees C. for about 1 hour. Dried films were allowed to cool, and were then pressed at 1 ton/cm2. Electrodes were further dried at 150 degrees C. under vacuum for 12 hours before being brought into a glove box for battery assembly.
Example 2
Electrochemical Characterization of Electrochemical Cells Containing Rechargeable Electrodes
All batteries were assembled in a high purity argon filled glove box (M-Braun, O2 and humidity contents <0.1 ppm), unless otherwise specified. Cells were made using lithium as an anode, Celgard 2400 separator, and 90 μL of 1M LiPF6 in 1:2 EC:EMC electrolyte. Electrodes and cells were electrochemically characterized at 30 degrees C. with a constant current C/50 charge and discharge rate for the first 2 cycles and C/5 charge and discharge rate for the following cycles between 4.0 V and 2.0 V. A 3 hour constant voltage step was used at the end of each charge. In some instances, cathodes were lithiated pressing lithium foil to the electrode in the presence of electrolyte (1M LiPF6 in 1:2 EC:EMC) for about 15 minutes. The electrode was then rinsed with EMC and built into cells as described above, except graphite was used as the anode rather than lithium.
Example 3
Fabrication of Conductively Coated Metal Fluoride Electrodes
Materials and Synthetic Methods.
All reactions were prepared in a high purity argon filled glove box (M-Braun, O2 and humidity contents <0.1 ppm). Unless otherwise specified, materials were obtained from commercial sources (Sigma-Aldrich, Advanced Research Chemicals Inc, Alfa Aesar, Strem, etc) without further purification.
Preparation of Conductively Coated CuF2/NiO.
Milling vessels were loaded with CuF2, NiO, and conductive coating precursor at the desired ratios, sealed, and then milled for about 20 hours. The milling vessels were opened under argon gas and the conductive coating precursor materials were added. The milling vessels were sealed and milled at low energy. After milling, the powder samples were annealed (for example, at 325 degrees C. for 6 hours).
Electrode Formulation.
In some embodiments, cathodes were prepared using a formulation composition of 80:15:5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 44 mg Super P Li (Timcal) was dissolved in 10 mL NMP (Sigma Aldrich) overnight. 70 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. In other embodiments, cathodes were prepared using a formulation composition of 85:7.5:7.5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 133 mg Super P Li (Timcal) was dissolved in 15 mL NMP (Sigma Aldrich) overnight. 150 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. Films were cast by dropping about 70 μL of slurry onto stainless steel current collectors and drying at 150 degrees C. for about 1 hour. Dried films were allowed to cool, and were then pressed at 1 ton/cm2. Electrodes were further dried at 150 degrees C. under vacuum for 12 hours before being brought into a glove box for battery assembly.
Example 4
Electrochemical Characterization of Conductively Coated Metal Fluoride Electrodes
All batteries were assembled in a high purity argon filled glove box (M-Braun, O2 and humidity contents <0.1 ppm), unless otherwise specified. Cells were made using lithium as an anode, Celgard 2400 separator, and 90 μL of 1M LiPF6 in 1:2 EC: EMC electrolyte. Electrodes and cells were electrochemically characterized at 30 degrees C. using the following protocol: constant current discharge at 1 C, 0.5 C, 0.2 C, 0.1 C, 0.05 C, and 0.02 C rate to 2.0 V cutoff.
FIG. 1 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the first and second cycle voltage traces for a cell containing a cathode formed from a metal fluoride and the new matrix material. In this case, the metal fluoride active material is CuF2 and the matrix material is Cu3Mo2O9. FIG. 1 demonstrates that the cell has about 140 mAh/g of reversible capacity. Previously known cathodes containing CuF2 have not demonstrated such significant reversible capacity.
FIG. 2 illustrates the results of structural characterization of certain embodiments disclosed herein. Specifically, the powder X-ray diffraction pattern of the material forming the cathode tested in FIG. 1 is shown along with the powder X-ray diffraction patterns of CuF2 and Cu3Mo2O9. FIG. 2 demonstrates that the material contains phases rich in CuF2 and phases rich in Cu3Mo2O9. Thus, FIG. 2 demonstrates a new matrix material in combination with a metal fluoride active material. Further, grain size analysis of this powder X-ray diffraction data shows that the CuF2 has a grain size greater than 130 nm. This is a significant finding since such comparatively large particles were thought to be too large to provide good electrochemical performance.
For many of the rechargeable matrices described herein (and in particular for matrices including Mo, Ni, or Ti), the reactions described herein yield a new matrix material at least at the surface of the particles of the metal fluoride active material. The novel material present at least at the surface of the particles of the metal fluoride active material is believed to provide many of the benefits disclosed herein.
FIG. 3 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the second cycle discharge capacity of CuF2 with various matrices and annealing temperatures. FIG. 3 shows many oxide matrices that provide recharge capability, demonstrated by capacities greater than 100 mAh/g.
Table 1 presents the results of further electrochemical characterization of certain embodiments disclosed herein. Table 1 shows that many metal oxide and metal oxide precursor starting materials can be used in the reactions described herein to yield rechargeable metal fluoride electrode materials. The materials in Table 1 include metal oxides, metal phosphates, metal fluorides, and precursors expected to decompose to oxides. In particular, nickel oxide showed excellent performance.







TABLE 1







Electrochemical Characterization of Various Precursor


Materials as a Function of Anneal Temperature













Reversible




Initial Capacity
Capacity


Matrix/Coating
Annealing
(0.02 C, Cy1,
(0.05 C, Cy2,


Precursor
Temp (C.)
mAh/g)
mAh/g)













(NH4)H2PO4
200
307
5


(NH4)H2PO4
325
406
178


(NH4)H2PO4
450
397
0


Al2O3
200
281
70


Al2O3
325
348
107


Al2O3
400
203
78


AlF3
200
397
124


AlF3
325
384
125


AlF3
400
320
98


AlPO4
200
410
115


AlPO4
325
356
136


AlPO4
450
284
74


Bi2O3
200
128
32


Bi2O3
325
89
34


Bi2O3
400
103
36


CaF2
200
301
86


CaF2
325
310
107


CaF2
400
282
125


CaO
200
1
1


CaO
325
138
27


CaO
400
84
29


Co3(PO4)2
200
323
93


Co3(PO4)2
325
373
161


Co3(PO4)2
450
382
126


Co3O4
200
167
112


Co3O4
325
216
132


Co3O4
450
329
151


Co3O4
575
310
134


Cr2O3
200
223
88


Cr2O3
325
234
132


Cr2O3
450
227
102


Cr2O3
575
184
70


Fe(OAc)2
200
407
31


Fe(OAc)2
325
431
11


Fe(OAc)2
450
393
180


Fe2O3
200
197
135


Fe2O3
325
200
142


Fe2O3
450
170
112


Fe2O3
575
308
131


FeF2
200
427
202


FeF2
325
382
220


FeF2
400
370
155


FeF3
200
443
188


FeF3
325
406
218


FeF3
400
359
141


FePO4
200
252
76


FePO4
325
393
147


FePO4
450
429
197


In2O3
200
250
64


In2O3
325
203
106


In2O3
400
347
109


La2O3
200
281
74


La2O3
325
155
39


La2O3
450
68
29


La2O3
575
114
36


Li2O
200
32
11


Li2O
325
49
18


Li2O
400
38
18


Li3PO4
200
318
123


Li3PO4
325
435
136


Li3PO4
450
409
114


LiCoPO4
200
372
97


LiCoPO4
325
408
142


LiCoPO4
450
338
136


LiH2PO4
200
300
111


LiH2PO4
325
423
149


LiH2PO4
450
387
107


LiMnPO4
200
351
77


LiMnPO4
325
368
102


LiMnPO4
450
397
178


LiNiPO4
200
402
116


LiNiPO4
325
396
191


LiNiPO4
450
405
176


MgF2
200
387
135


MgF2
325
378
147


MgF2
400
360
122


MgO
200
313
181


MgO
325
259
155


MgO
400
198
126


MnO
200
117
52


MnO
325
130
65


MnO
450
83
55


MnO
575
59
38


MnO2
200
120
76


MnO2
325
123
57


MnO2
450
242
150


MnO2
575
104
69


Mo(OAc)2
200
396
10


Mo(OAc)2
325
433
17


Mo(OAc)2
450
398
46


Na2O
200
2
1


Na2O
325
26
13


Na2O
400
24
13


Ni
200
345
197


Ni
325
301
178


Ni
400
302
158


Ni
450
300
152


Ni acac
200
425
56


Ni acac
325
306
87


Ni Acac
400
247
30


Ni acac
450
362
172


Ni(OAc)2
200
397
148


Ni(OAc)2
325
376
46


Ni(OAc)2
350
370
191


Ni(OAc)2
400
383
180


Ni(OAc)2
450
371
186


Ni(OAc)2
500
373
171


Ni3(PO4)2
200
410
124


Ni3(PO4)2
325
430
52


Ni3(PO4)2
450
126
44


Ni(C2O2)
200
359
90


Ni(C2O2)
325
395
195


Ni(C2O2)
450
381
175


Ni(CP)2
200
304
27


Ni(CP)2
325
317
14


Ni(CP)2
450
258
148


Ni(OH)2
200
412
186


Ni(OH)2
325
362
196


Ni(OH)2
400
327
181


Ni(OH)2
450
300
169


NiBr2
200
125
0


NiBr2
325
225
78


NiBr2
400
244
113


NiCO3*Ni(OH)2
200
380
17


NiCO3*Ni(OH)2
325
359
215


NiCO3*Ni(OH)2
450
317
184


NiF2
200
367
121


NiF2
325
395
207


NiF2
400
411
170


NiF2
450
396
177


NiO
125
257
131


NiO
200
403
222


NiO
225
384
212


NiO
250
385
221


NiO
275
370
229


NiO
300
335
175


NiO
325
402
252


NiO
350
365
209


NiO
375
260
123


NiO
400
371
200


NiO
425
361
186


NiO
450
386
183


NiO
500
308
150


NiO
575
319
112


None
200
181
30


None
325
394
216


None
450
247
61


Sb2O3
200
111
34


Sb2O3
325
147
37


Sb2O3
400
223
104


Sc2O3
200
359
159


Sc2O3
325
293
159


Sc2O3
400
84
33


Sc2O3
450
150
68


Sc2O3
575
55
17


ScF3
200
400
178


ScF3
325
387
174


ScF3
400
243
100


SiO2
200
1
1


SiO2
325
114
28


SiO2
400
230
92


SnO2
200
210
48


SnO2
325
182
68


SnO2
400
133
65


SrO
200
152
12


SrO
325
66
16


SrO
400
134
48


Ta2O5
200
289
4


Ta2O5
325
269
141


Ta2O5
450
298
121


Ta2O5
575
317
74


Ti(OEt)4
200
438
21


Ti(OEt)4
325
453
12


Ti(OEt)4
450
353
5


TiO2
225
322
150


TiO2
250
309
169


TiO2
275
262
162


TiO2
300
199
127


TiO2
325
322
173


TiO2
350
327
187


TiO2
375
120
77


TiO2
400
359
199


TiO2
425
345
194


TiO2
450
353
169


Y2O3
200
353
130


Y2O3
325
279
104


Y2O3
450
83
37


Y2O3
575
80
30


ZnF2
200
438
206


ZnF2
325
372
191


ZnF2
400
318
134


ZnO
200
210
95


ZnO
325
242
93


ZnO
400
194
44


ZnO
450
205
99


ZnO
575
151
71


ZrO2
200
302
122


ZrO2
325
288
129









FIG. 4 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the second cycle discharge capacity for cells containing a cathode formed from a metal fluoride and the matrix material treated at different temperatures. In this case, the metal fluoride active material is CuF2 and the matrix material is NiO. FIG. 4 shows a peak for cycle 2 capacity at about 325 degrees C. for NiO matrices, with nearly 250 mAh/g discharge capacity.
FIG. 5 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF2 with 15 wt % of certain metal oxides (in this case NiO or TiO2) at certain annealing temperatures. The mixtures were milled at high energy for about 20 hours. The anneal temperatures ranged from about 225 degrees C. to about 450 degrees C. and the anneal time was 6 hours. The 325 degree C. anneal temperature for the NiO starting material generated the best performance. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.
FIG. 6 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF2 with 15 wt % of certain metal oxides (in this case NiO or TiO2) for certain annealing times. The mixtures were milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 1 hour, 6 hours, or 12 hours. The 6 hour anneal time yielded the best results for both the NiO and TiO2 starting materials, and the NiO starting material generated better performance. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.
FIG. 7 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, 90 wt %, or 95 wt % CuF2 with 5 wt %, 10 wt %, 15 wt % of NiO. The mixtures were milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Using 10 wt % or 15 wt % of the NiO starting material generated better performance. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.
FIG. 8 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO. The mixtures were milled at various energies comparable to milling on a Fritch Pulverisette 7 Planatery Mill at 305, 445, 595, and 705 RPM for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Performance improves with increasing milling energy, suggesting that intimate physical interaction of the materials is required. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V.
FIG. 9 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO. The mixtures were milled for various times (3 hours, 20 hours, or 40 hours) at a high energy (comparable to 705 RPM on Fritch Pulverisette 7). The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Performance does not improve after 20 hours of milling. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V.
FIG. 10 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, FIG. 13 shows the second cycle reversible capacity measured for various starting materials used to react with CuF2. The starting materials include NiO, nickel(II) acetylacetonate, nickel acetate, nickel hydroxide, NiCO3*Ni(OH)2, Ni(C2O2), Ni(CP)2, and Ni. In some instances, the starting materials react to form a new phase. The materials react with the surface of the CuF2 particles. Additionally, the anneal atmosphere was either N2 or dry air. The precursor-type starting materials decompose to NiO (although this depends on the atmosphere for some precursors) at or below the annealing temperatures used for the reaction. The precursors that are soluble or have low boiling points can enable solution or vapor deposition processing methods. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V. Several materials show similar performance to the NiO baseline.
FIG. 11 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting CuF2 with nickel(II) acetylacetonate using various processing conditions. In some cases, the CuF2 was dispersed using methods described herein. The coatings were applied using mill coating techniques (that is, agitating the mixture in a milling apparatus) or by solution coating techniques (including solution coating driven by physisorption). All samples were annealed under dry air. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V. Testing demonstrates that solution coating methods can provide similar performance to the mill coating techniques.
FIG. 12 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO and for a control material. The NiO/CuF2 mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a cycle 1 rate of 0.02 C, a cycle 2 rate of 0.05 C, and a cycle 3 through cycle 25 rate of 0.5 C and over a voltage range of 2.0 V to 4.0 V. With the reacted NiO/CuF2 as the active material, the cell cycles reversibly for extended cycling with capacity greater than 100 mAh/g for 25 cycles. Further, the reacted NiO/CuF2 active material demonstrates retention of 80% of cycle 3 capacity as far out as cycle 15. The control material, which was prepared according to the process described in Badway, F. et al., Chem. Mater., 2007, 19, 4129, does not demonstrate any rechargeable capacity. Thus, the material prepared according to embodiments described herein is significantly superior to known materials processed according to known methods.
FIG. 13 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, a galvanostatic intermittent titration technique (GITT) measurement for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO and for a control material. The NiO/CuF2 mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed over a voltage range of 2.0 V to 4.0 V at a rate of 0.1 C and with a 10 hour relaxation time. The GITT measurement relaxation points show low voltage hysteresis (about 100 mV), which indicate that the overpotential and/or underpotential are likely caused by kinetic and not thermodynamic limitations. This is consistent with other properties and characteristics observed for the reacted NiO/CuF2 active material.
FIG. 14 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO. The NiO/CuF2 mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The label “Cu+2LiF” indicated that the NiO/CuF2 electrode was lithiated by pressing Li foil to CuF2 electrode in the presence of electrolyte as described above. The other half cell was lithiated electrochemically in the initial cycles. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed over a voltage range of 2.0 V to 4.0 V. Half cell performance is essentially identical between the two lithiation methods after cycle 2, while full cell shows additional irreversible capacity loss as compared to the half cells but similar capacity retention.
FIG. 15 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the voltage traces of the full cell and half cells prepared as described in relation to FIG. 14. The full cell has similar charge capacity to the half cells, but larger irreversible capacity loss and lower discharge voltage (which can indicate increased cell impedance). FIG. 15 demonstrates that the full cell has about 250 mAh/g of reversible capacity and about 500 mV hysteresis between charge and discharge plateau voltages.
FIG. 16 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity retention of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF2 with 15 wt % of NiO. The results from a control material are also depicted. The full cell and half cells were prepared as described in relation to FIG. 14. The cells used a Li anode and an electrolyte containing 1M LiPF6 in EC:EMC. The testing was performed at a cycle 1 rate of 0.1 C and over a voltage range of 2.0 V to 4.0 V. The capacity retention is essentially identical for the full and half cells of the NiO/CuF2 active material. The control material shows essentially no rechargeable capacity.
As depicted in FIG. 17, CuF2 coated with anthracene and naphthalic anhydride showed an improvement over uncoated CuF2. Anthracene coated CuF2 (annealed at about 250 degrees C.) demonstrated about 94% rate retention and naphthalic anhydride coated CuF2 (annealed at about 300 degrees C.) demonstrated about 92% rate retention at first cycle when comparing 0.1 C rate and 0.02 C rate discharge. Other coatings on CuF2, such as PVDF annealed at about 450 degrees C., demonstrated inferior rate capability as compared to uncoated CuF2.
As depicted in FIG. 18, an anthracene coated CuF2/MoO3 composite material demonstrates improvement in rate performance as compared to a baseline uncoated CuF2/MoO3 composite material for rates from 0.02 C to 10. In particular, the anthracene coated material showed significant improvement in rate performance at higher discharge rates as compared to the uncoated control material.
As depicted in FIG. 19, there is a low voltage drop from 0.1 C to 10 rate for an anthracene coated material. Further, the coated material shows capacity of 285 mAh/g at 10 rate.
FIG. 20 depicts further rate improvements in a CuF2/MoO3 composite material coated according to embodiments of the invention. The capacity at 10 rate is greater than about 375 mAh/g and at lower rates the capacity approaches or exceeds 400 mAh/g. Further, FIG. 20 demonstrates a low voltage drop from 0.01 C to 10 rate due to the conductive coating.
FIG. 21 depicts the capacity retention as compared to the rate for the baseline CuF2/MoO3 composite and the imporved anthracene coated material. The optimized material showed significant improvement in rate performance with about 94% retention at 10 rate.
Notably, certain hybrid metal fluoride active materials disclosed herein can be coated with the conductive coating precursor materials also disclosed herein to yield a comparatively high energy rechargeable cathode material. For example, Table 2 lists the results of testing a NiO/CuF2 active material coated with various intrinsically conductive precursors.







TABLE 2







Electrochemical Characterization of NiO/CuF2 Hybrid Active


Materials Coated with Conductive Precursors










Reversible
Rate Capability



Capacity
(cy 1,


Coating Precursor
(mAh/g)
1/0.02 C, %)












—
214
70


Octafluoronaphthalene
211
78


N,N′-Dioctyl-3,4,9,10-
198
84


perylenedicarboximide


Perylene-3,4,9,10-tetracarboxylic
172
52


dianhydride


PVDF
153
84


Perylene
118
64


29H,31H-Phthalocyanine
56
3


Tri-1-naphthylphosphine
29
43


1,8-Naphthalic anhydride
22
87


5,10,15,20-
21
91


Tetrakis(pentafluorophenyl)porphyrin


Pentacene
18
86


Pyrene
15
44


1,6-Diphenyl-1,3,5-hexatriene
15
89


2-BENZOYLDIBENZO-P-DIOXIN
15
42


7,7,8,8-Tetracyanoquinodimethane
14
86


4-(2,3-Dihydro-1,3-dimethyl-1H-
13
0


benzimidazol-2-yl)-N,N-


dimethylbenzenamine


Dilithium phthalocyanine
13
81


Benz[b]anthracene
11
91


Anthracene
11
87


Copper(II) phthalocyanine
10
72


Rubrene
7
86









Table 2 demonstrates that not all materials are capable of yielding a material that has reversible capacity. The top performing coating precursors include octafluoronaphthalene and N,N′-dioctyl-3,4,9,10-perylenedicarboximide. Without being bound by a particular theory or mechanism of action, the coating precursors that remain comparatively stable at the temperatures required to react CuF2 and NiO perform better than those that completely decompose at that reaction temperature. Generally speaking, balancing the reaction temperature required to form the hybrid metal fluoride active material with the decomposition temperature of the coating material can yield the desired improved high energy cathode material. For example, other hybrid active material precursors (that is, other than NiO) can yield the desired result if they react at a temperature where the conductive coating precursor does not fully decompose.
Various materials disclosed herein demonstrated improved performance as compared to control. In certain testing, naphthalic anhydride demonstrated a 3% capacity improvement, power performance improvement, and improved power stability over control. In certain testing, perylene demonstrated a 9% voltage improvement over control. In certain testing, rubrene demonstrated superior capacity at high voltage as compared to control.
While the 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 true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.

## Claims

1. An electrode for an electrochemical cell, comprising:
a fluorine-containing active electrode material comprising particles having a first phase including a metal fluoride material and a coating on the particle having a second phase including a metal complex material;
a binder material; and
an intrinsically conductive coating covalently attached to the active electrode material wherein the coating is formed from an organic coating compound comprising a conjugated core.

2. The electrode of claim 1 wherein the organic coating compound comprises a conjugated core in which at least 90% of the carbon atoms are sp or sp2 hybridized.

3. The electrode of claim 1 wherein the metal fluoride material comprises copper fluoride.

4. The electrode of claim 1 wherein the metal complex material comprises a metal oxide.

5. The electrode of claim 4 wherein the metal oxide comprises a nickel oxide.

6. The electrode of claim 1 wherein the metal complex material comprises a metal fluoride.

7. The electrode of claim 1 wherein the metal complex material comprises a metal phosphate.

8. The electrode of claim 1 wherein the organic coating compound is octafluoronaphthalene.

9. The electrode of claim 1 wherein the organic coating compound is N,N′-dioctyl-3,4,9,10-perylenedicarboximide.

10. The electrode of claim 1 wherein the intrinsically conductive coating is formed at a temperature below 450 degrees C.

11. The electrode of claim 1 wherein the intrinsically conductive coating is a network of conjugated cores.

12. The electrode of claim 1 wherein the electrode is characterized as having reversible capacity.

13. The electrode of claim 1 wherein the active electrode material comprises particles with a grain size greater than 100 nm.

14. The electrode of claim 1 wherein the active electrode material comprises particles with a grain size greater than 130 nm.

15. The electrode of claim 1 wherein the metal oxide is selected from the group consisting of MoO3, MoO2, NiO, CuO, VO2, V2O5, TiO2, and combinations thereof.

16. A method of making an electrode, comprising:
reacting a metal fluoride material and a metal complex material to form a fluorine-containing active electrode material comprising particles having a first phase including a metal fluoride material and a coating on the particle having a second phase including a metal complex material;
mixing the formed active electrode material and an intrinsic organic conductor comprising a conjugated core; and
heating the mixture to form a conductive coating on the active electrode material at a temperature that limits degradation of the active electrode material.

17. The method of claim 16 wherein the metal fluoride material comprises copper fluoride.

18. The method of claim 16 wherein the metal complex material comprises a metal oxide.

19. The method of claim 18 wherein the metal oxide comprises a nickel oxide.

20. The method of claim 16 wherein the metal complex material comprises a metal fluoride.

21. The method of claim 16 wherein the metal complex material comprises a metal phosphate.

22. The method of claim 16 wherein the organic conductor is octafluoronaphthalene.

23. The method of claim 16 wherein the organic conductor is N,N′-dioctyl-3,4,9,10-perylenedicarboximide.

24. The method of claim 16 wherein the conductive coating is formed at a temperature below 450 degrees C.