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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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  • Y02E60/10—Energy storage using batteries

Definitions

• the field includes ion storage materials, and in particular nanoscale ion storage materials useful in devices such as batteries.
• Ion storage materials are widely employed in storage batteries and other electrochemical devices.
• Various ion storage materials are known, including alkaline transition metal phosphates.
• This class of compounds can crystallize in a number of structure types. Examples include ordered or partially disordered structures of the olivine (A x MXO 4 ), NASICON (A x (M', M") 2 (XO 4 ) 3 ), VOPO 4 , LiVPO 4 F, LiFe(P 2 O 7 ) or Fe 4 (P 2 O 7 ) 3 structure types, wherein A is an alkali ion, and M, M' and M" are metals.
• Amorphous FePO 4 materials prepared in the delithiated state, also have been used as lithium storage materials (Okada et al., Patent Abstracts of Japan Publication No. 06-283207). Amorphous materials including lithium cobalt phosphate also have been described (U.S. Patent No. 5,705,296).
• nanoscale lithium transition metal phosphate storage compounds for example, certain compounds having chemical compositions as disclosed in US2004/0005265 or U.S. Patent Application No. 11/396,557
• processing methods, particle sizes, and/or compositional ranges as described herein can be prepared in amorphous or partially crystalline/partially amorphous form.
• certain such materials can be rendered disordered or amorphous upon electrochemical intercalation or de-intercalation by lithium, thereby conferring certain benefits, for example, when used as lithium storage electrodes.
• disclosed herein are novel amorphous and partially amorphous nanoscale ion storage materials, and methods of preparing the same.
• the nanoscale ion storage materials are useful for producing devices such as high energy and high power storage batteries, battery- capacitor hybrid devices, and high rate electrochromic devices.
• One aspect provides a predominantly crystalline nanoscale lithium transition metal phosphate material having a specific surface area of at least about 10 m 2 /g, for example, at least about 25 m 2 /g, or at least about 50 m 2 /g.
• the amorphous content of the material increases upon delithiation and/or lithiation.
• the material has a primary particle size with an average smallest cross- sectional dimension of about 200 nm or less, in some instances about 100 nm or less.
• the lithium transition metal phosphate material has an overall composition of Li] -3 N b M c (XO 4 ) c j, wherein M is at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni; N is an element from Groups IIA, IIIA, IVA, VA, VIA, IIB, IHB or VIIB of the periodic table; X is one or more of P, Si, Ge, As and S; O ⁇ a ⁇ l ; O ⁇ b ⁇ O.lO; 0.8 ⁇ c ⁇ l .2; and 0.9 ⁇ d ⁇ 2.2.
• M is Fe, or M includes Mn and Fe.
• the lithium transition metal phosphate material has an overall composition of Lii -X MPO 4 , wherein M is at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, and wherein in use x ranges between 0 and 1.
• M is Fe, or M includes Mn and Fe.
• x in the as-prepared material is at least about 0.05, or at least about 0.15.
• N is Nb and 0 ⁇ b ⁇ 0.10.
• the as-prepared composition contains lithium at a concentration of at least about 5% by mole, or at least about 10% by mole, relative to the transition metal concentration.
• the lithium transition metal phosphate material is included in a cathode, which can be used in an electrochemical cell.
• Another aspect provides a method of increasing the amorphous content of a predominantly crystalline nanoscale lithium transition metal phosphate material.
• the method includes lithiating and/or delithiating the material.
• the material has a specific surface area of at least about 10 m 2 /g.
• lithiating and/or delithiating the predominantly crystalline nanoscale lithium transition metal phosphate material is achieved by incorporating the material into the cathode of a storage battery and charging and/or discharging the battery.
• Still another aspect provides a compound having the formula Li a C b M c N d X e O f , wherein M is one or more first-row transition metals; N is an element from Groups HA, IHA, IVA, VA, VIA, HB, IHB or VIIB of the periodic table; X is one or more of P, Si, Ge, As, S; O ⁇ a ⁇ l; 0.001 ⁇ b ⁇ 0.10; 0.8 ⁇ c ⁇ 1.2; O ⁇ d ⁇ O.10; 0.9 ⁇ e ⁇ 2.2; and 3.6 ⁇ f ⁇ 8.8.
• M includes at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni.
• M is Fe, or M includes Mn and Fe.
• N is Nb and 0 ⁇ d ⁇ 0.10.
• X is P.
• the as-prepared composition contains lithium at a concentration of at least about 5%, or at least about 10%, by mole relative to the transition metal concentration. In some embodiments, the as-prepared composition contains lithium at a concentration of no more than about 95%, in some instances no more than about 85%, by mole relative to the transition metal concentration. [0014] In certain embodiments, the compound is at least partially amorphous.
• the compound has a specific surface area of at least about 10 m 2 /g, at least about 25 m 2 /g, or at least about 50 m 2 /g. In certain embodiments, the compound has a primary particle size with an average smallest cross-sectional dimension of about 200 nm or less, or about 100 ran or less. In certain embodiments, the compound is included in a cathode, which can be used in an electrochemical cell.
• Another aspect provides an amorphous nanoscale lithium transition metal phosphate material containing carbon at a concentration between about 0.1 % and about 10% by mole relative to the transition metal concentration, and including an electrochemically active, amorphous Li-M-P-O-C phase, where M is one or more first row transition metals.
• Figure 1 is a plot of discharge capacity at various C-rates for SwagelokTM type lithium half-cells made from powders of nanoscale Lio. 9 FeP0 4 (sample A),
• Figures 2A, B and C are plots showing the capacity on charge and discharge for cycle 1 at C/50 rate for SwagelokTM type lithium half-cells made from samples A, B, and C, respectively.
• Figures 3A-B show scanning transmission electron microscope (“STEM”) dark field and bright field images, respectively, of sample B.
• STEM scanning transmission electron microscope
• Figures 4A-G show spectra at different locations of the sample from Figure
• Figures 5 A, B, C and D show, respectively, C 5 Fe, P and O elemental maps for the sample from Figure 3.
• Figure 6 shows another STEM image of sample B.
• Figures 7A, B, C, D and E show, respectively, C 5 Fe, P, O and S elemental maps for the sample from Figure 6.
• Figure 8 shows a STEM image of sample A.
• Figures 9A, B, C and D show, respectively, C, Fe, P and O elemental maps for the sample from Figure 8.
• Figure 10 shows another image of sample A.
• Figures 1 IA, B, C and D show, respectively, C, Fe, P and O elemental maps for the sample from Figure 10.
• Figures 12A-E show spectra at different locations of the sample from
• Figure 13 shows X-ray diffraction patterns of sample A and commercial highly crystalline LiFePO 4 (labeled as having carbon added), with 50 wt % of a crystalline silicon powder added to each sample.
• Figure 14 shows X-ray diffraction patterns of samples A, B, commercial
• LiFePO 4 LiFePO 4
• samples D and E two different samples of 1% Nb-doped LiFePO 4 (samples D and E), each mixed with 50 wt % crystalline silicon powder.
• Figures 15A-B show X-ray diffraction patterns of samples A, B, D, E and commercial LiFePO 4 , each mixed with 50 wt % crystalline silicon powder.
• 15B shows the Si diffraction peak at 28.5°, which can be used to calibrate the peaks from the sample.
• Figure 16 shows X-ray diffraction patterns of Lio. 5 FeP0 4 (sample F) and
• FePO 4 (sample G), having BET surface areas of 42.86 m /g and 22.96 m Ig, and carbon contents of 4.00% and 4.68%, respectively, each mixed with 50 wt% Si.
• Figure 17 shows X-ray diffraction patterns of samples A, B, D, E, F, G, and commercial LiFePO 4 , each mixed with 50 wt % Si.
• Figure 18 shows X-ray diffraction patterns of a nanoscale LiFePO 4 powder having BET specific surface area of 39.8 m 2 /g, which was formulated into an electrode in a SwagelokTM type lithium half-cell. The cell was charged to 50% state- of-charge (SOC) at a C/10 rate and immediately disassembled. X-ray diffraction patterns were obtained upon cell disassembly, and again 48 hours after disassembly, and 5 days after disassembly. Si powder placed on the surface of the electrode served as a peak calibration standard.
• SOC state- of-charge
• Figure 19 shows X-ray diffraction patterns of a nanoscale LiFePO 4 powder having BET specific surface area of 48.8 m 2 /g, which was formulated into an electrode in a SwagelokTM type lithium half-cell. The cell was charged to 50% state- of-charge (SOC) at a C/10 rate and immediately disassembled. X-ray diffraction patterns were obtained upon cell disassembly, and again 27 hours after disassembly, and 6 days after disassembly. [0036] Figure 20 shows X-ray diffraction patterns of a nanoscale Lio. 99 Nbo.oiMno. 7 oFeo.
• 3 oP0 4 powder having BET specific surface area of 40.2 m 2 /g, which was formulated into an electrode in a SwagelokTM type lithium half-cell.
• the cell was charged to 90% state-of- charge (SOC) and immediately disassembled.
• SOC state-of- charge
• X-ray diffraction patterns were obtained upon cell disassembly, and again 20 hours after disassembly, and 3 days after disassembly.
• Si powder applied to the face of the electrode was used as a diffraction peak reference.
• nanoscale lithium transition metal phosphate storage compounds for example, certain compounds having chemical compositions as disclosed in US2004/0005265 and U.S. Patent Application No. 11/396,557
• processing methods, particle sizes, and/or compositional ranges as described herein can be prepared in amorphous or partially crystalline/partially amorphous form.
• the present disclosure is based on the further unexpected discovery that certain such materials (initially in a crystalline form) can be rendered disordered or amorphous upon electrochemical intercalation or de-intercalation by lithium, thereby conferring certain benefits, for example, when used as lithium storage electrodes.
• certain such materials initially in a crystalline form
• can be rendered disordered or amorphous upon electrochemical intercalation or de-intercalation by lithium thereby conferring certain benefits, for example, when used as lithium storage electrodes.
• nanoscale lithium transition metal phosphates including certain doped phosphates having a composition as disclosed in US2004/0005265, lithium-deficient compositions or undoped phosphates as described in U.S. Patent Application No. 11/396,557
• processing methods, particle sizes, and/or compositional ranges as described herein can be made in a glassy (amorphous) structural state, or a partly amorphous and partly crystalline state.
• “Amorphous” refers to materials that are lacking in long-range atomic periodicity, as is commonly known to those skilled in the art of materials science, chemistry, or solid-state physics.
• the periodicity of solids is measurable using diffraction methods, for example, X-ray or neutron or electron diffraction.
• diffraction methods for example, X-ray or neutron or electron diffraction.
• One measure of whether a material is crystalline or amorphous is the nature of the diffraction pattern. In such spectra, a crystalline material exhibits increased diffracted intensity above background at diffraction angles satisfying Bragg' s law. Thus a crystalline compound exhibits a diffraction pattern, the peak positions and intensities of which can be measured or computed from atomic positions by methods well-known to those skilled in the art.
• Rietveld refinement the determination that a material is crystalline is arrived at when the experimental diffraction pattern can be modeled to an acceptable "goodness of fit" by assuming a particular crystal structure of infinite extent and including additional structural parameters to account for the thermal vibration amplitude, small crystallite size, or differential strain within the crystal.
• an amorphous material does not exhibit the characteristic diffraction peaks corresponding to a long-range periodic arrangement of atoms, and may exhibit broad diffracted intensity over a wide range of diffraction angle, corresponding to a short-range periodicity of the material. It is also possible for crystalline phases to exhibit varying degrees of atomic disorder.
• Such disordered materials may have diffraction spectra with broadened peaks and unexpected integrated peak intensities compared to a substantially perfectly ordered crystal, and are included amongst the "partially amorphous" or “disordered” materials of the invention.
• a “partially amorphous” material may have at least about 5% amorphous phase by mass or volume of the active phase.
• Partially amorphous materials may include at least about 10%, or at least about 20% by mass or volume of the active phase. Higher amorphous loads are also contemplated.
• amorphous or partially amorphous nanoscale ion storage materials having the formula Li] -3 N b M c (XO 4 ) d , where M comprises at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni; N is an element from Groups HA, HIA, IVA, VA, VIA, HB, IHB or VIIB of the periodic table; X is one or more of P, Si, Ge, As, and S; O ⁇ a ⁇ l; O ⁇ b ⁇ O.10; 0.8 ⁇ c ⁇ 1.2; and 0.9 ⁇ d ⁇ 2.2.
• amorphous or partially amorphous materials are provided in which the as-prepared composition contains lithium at a concentration of at least about 5% by mole relative to the transition metal concentration, in some instances at least about 10%, at least about 25%, or at least about 50%.
• the advantageous properties of amorphous nanoscale ion storage materials as described herein may be augmented by doping with foreign ions, such as metals or anions. However, doping is not required for an amorphous nanoscale material to exhibit special properties.
• amorphous or partially amorphous nanoscale ion storage materials are provided- having the formula Lii -X MXO 4 , where M is one or more transition metals, such as, for example, V, Cr, Mn, Fe, Co and Ni; X is one or more of P, Si, Ge, As, S; and O ⁇ x ⁇ l . In some embodiments, x ranges between zero and one during lithium insertion and de-insertion reactions.
• lithium deficiency is used to promote the formation of amorphous or partially amorphous materials. In at least some instances, greater lithium deficiency results in a more amorphous material.
• amorphous or partially amorphous nanoscale lithium transition metal phosphate materials are provided, which in the as-prepared state contain lithium at a concentration of no more than about 95% by mole relative to the transition metal concentration, for example, no more than about 85%, no more than about 75%, or no more than about 50%.
• amorphous or partially amorphous nanoscale ion storage materials having the formula Lii_ x MX ⁇ 4, where M is one or more transition metals, such as, for example, V, Cr, Mn, Fe, Co and Ni; X is one or more of P, Si, Ge, As, S; and x in the as-prepared material is at least about 0.05, in some instances at least about 0.1, at least about 0.15, at least about 0.2, at least about 0.3, or at least about 0.5.
• the amorphous material in some instances comprises more than one specific composition.
• amorphous Lii -x FeP ⁇ 4 can exist over a wide range of x from zero to one.
• an amorphous material or materials co-exist with a crystalline phase or phases.
• the amorphous material or materials have the same, or different, composition compared to the crystalline phase or phases.
• the amorphous phase may have a different dopant solubility than the crystalline material.
• the amorphous material When procedures are taken to produce the undoped materials in the amorphous state, the amorphous material may have a different lithium concentration. Such differences in composition may exist in the material as it is synthesized, or may occur during use, such as upon being lithiated or delithiated by chemical means or by electrochemical means in a storage battery.
• the amorphous phase or phases may have different alkali ion insertion and removal potentials compared to bulk crystalline or nanocrystalline phases.
• such amorphous or mixed amorphous- crystalline materials When combined with the characteristic of being nanoscale, such amorphous or mixed amorphous- crystalline materials may have the attributes of high alkali ion storage capacity and high rate capability. In particular, they are useful as the positive electrode material in lithium storage batteries.
• amorphous or partially amorphous nanoscale ion storage materials are provided in the as-prepared state (e.g., as-fired, or prior to use in a storage battery).
• such materials are prepared from highly homogeneous precursors at low temperatures.
• Suitable processes for producing the materials include, without limitation, wet-chemical processes, such as co-precipitation or sol-gel methods; physical vapor deposition; chemical vapor methods; mechanochemical methods, where chemical reaction is promoted by the application of mechanical energy, such as by grinding; heat treatment of solid-reactants; and combinations of such methods.
• amorphous or partially amorphous nanoscale ion storage materials are produced from an initially crystalline or predominantly crystalline nanoscale material by electrochemical lithiation or delithiation.
• a "predominantly crystalline" material may include at least about 50% by weight or volume of the active material. In some embodiments, the material includes at least about 75%, or at least about 90%, or at least about 95%, or at least about 99% by weight or volume of a crystalline phase.
• the initial crystalline nanoscale material is prepared as described in U.S. Patent Application No. 11/396,515.
• the initial crystalline material is an olivine material having the formula Li).
• x MP ⁇ 4 where M is one or more transition metals and 0 ⁇ x ⁇ l .
• M includes Fe.
• M comprises more than one transition metal, for example, Fe and another transition metal, such as Mn.
• At least about 5% by weight of the initially crystalline active material may become amorphous after charging or discharging. In other embodiments, at least about 10%, or at least about 20% by weight or volume of the initially crystalline active material becomes amorphous.
• the amorphous materials resulting upon lithiation or delithiation have significantly altered physical properties compared to the initial nanoscale, but crystalline, counterparts.
• such materials may have altered phase stability, including increased mutual solubility of lithium when the material comprises two or more coexisting phases, more isotropic and faster lithium ion diffusion, and higher electronic conductivity.
• phase stability including increased mutual solubility of lithium when the material comprises two or more coexisting phases, more isotropic and faster lithium ion diffusion, and higher electronic conductivity.
• a complete lithium solid solution may occur over a wider range of lithium concentration at any given temperature and particle size than is possible in the counterpart crystalline materials.
• a higher rate of lithium acceptance and removal is obtained, and/or decreased mechanical stresses and related mechanical failure events such as fracture and fatigue are achieved.
• an amorphous or partially amorphous nanoscale ion storage material is provided in a rechargeable battery by electrochemically disordering an initially substantially crystalline lithium storage compound. In some instances, the amorphous ion storage material remains permanently in the amorphous state.
• the amorphous material crystallizes over a time scale ranging from seconds to many days.
• Providing an amorphous material in this way is advantageous because it allows for production of a desirable but difficult-to- synthesize amorphous storage material from a crystalline material that is more easily produced.
• a highly lithiated olivine positive electrode material is often desirable as a starting material, since it generally provides the active lithium in a lithium ion cell.
• such compositions may crystallize easily, and for the reasons given earlier it may be desirable to have, in use, an amorphous active material.
• both objectives are met.
• the availability of the amorphous material even temporarily, may improve electrochemical storage properties, such as energy and power.
• this may occur by having a structurally disordered amorphous region separating the two crystalline phases at the particle level, and/or by having an entire particle transformed to an amorphous state while lithium is removed or inserted, after which the amorphous material crystallizes.
• composition and structure of the amorphous nanoscale materials described herein distinct from previously known ion storage materials, there are improvements in properties that enable performance in a lithium battery which are not available from the conventional, crystalline lithium metal phosphates or amorphous metal phosphates.
• the well-ordered olivine LiFePO 4 structure has one-dimensional lithium diffusion channels. It has been considered in the published literature that this aspect of the structure is detrimental to electrochemical performance, especially at high rates. For instance, it has been argued in published literature that disorder between Li and Fe in the ordered olivine structure is responsible for poor storage capacity and rate capability (e.g., Yang et al., Electrochem. Comm., 4:239 (2002)).
• amorphous materials such as those described herein have isotropic ion diffusion, thereby allowing a higher storage capacity at any particular charge-discharge rate.
• the electronic transport properties of crystalline lithium transition metal phosphates are highly sensitive to cation ordering.
• ordered olivine LiFePO 4 electronic transport properties are sensitive to both the Li and Fe ordering.
• electron localization in the crystalline structure limits electron mobility, and results in too low an electronic conductivity for practical use of the conventional olivine.
• the disordered, amorphous materials described herein have different, mostly disordered cation arrangements. Thus, these amorphous materials are reasonably expected to have different electronic structure and transport properties compared to commonly known crystalline materials.
• the present material does not form or retain this phase upon cooling to room temperature. Nor does it phase separate into the room-temperature equilibrium phases given by the phase diagram (the equilibrium phases being LiFePO 4 and FePO 4 ). Instead, the material comprises a mixture of crystalline LiFePO 4 , which by its X-ray diffraction pattern is distinguishable from conventional LiFePO 4 by having broadened peaks, and an amorphous phase.
• this class of materials useful for high energy and high power cathodes is clearly distinct from conventional crystalline LiFePO 4 or Lii_ x FePO 4 . It is a metastable phase assemblage enabled by having nanoscale dimensions and/or the method of processing and/or the particular composition used for these materials as described herein.
• the data presented in the Examples demonstrate that the nanoscale materials described herein exhibit a novel carbon-containing composition.
• the scanning transmission electron microscope data show that the materials studied here, despite having several percent carbon overall, do not have a surface coating of carbon, but instead have carbon detected throughout the material. (See, e.g., the elemental maps in Figures 5, 7, 9 and 1 1.)
• the X-ray composition maps show that wherever Fe, P and O have increased intensity due to greater sample thickness, the carbon signal is also increased. This shows that the carbon is distinctly not a surface layer, but is bulk carbon.
• the materials in question at least the amorphous phases but also the crystallized portions, have carbon in solid solution.
• the undoped materials these comprise Fe- P-O-C or Li-Fe-P-O-C; for the doped materials the dopant is also in solid solution. This is a distinct composition from any prior described amorphous transition metal phosphate used in a battery.
• Example 2 The results described in Example 2 below on an amorphous nanoscale FePO 4 sample having a carbon content of 4.68% show that the sample has an electrochemically active, amorphous/disordered Fe-P-O-C phase.
• This is a unique composition distinct from other known metal phosphate ion storage electrode materials.
• the results on the several other deliberately lithium-deficient Li] -x FePO 4 compositions show that such an amorphous phase is stable in the samples tested.
• the amorphous phase also can be deduced to contain lithium based on the crystalline olivine fraction seen by XRD relative to the overall composition.
• an amorphous/disordered Li-Fe-P-O-C phase is stable. This is also a unique composition distinct from known materials.
• an ion storage compound that contains carbon within the structure of the compound.
• the compound has a composition Li a C b M c N d X e O f , where M is one or more first-row transition metals, such as, for example, Ti, V, Cr, Mn, Fe, Co and Ni; N is an element from Groups HA, IIIA, IVA, VA, VIA, HB, UIB or VIIB of the periodic table; X is one or more of P, Si, Ge, As, S; O ⁇ a ⁇ l; 0.001 ⁇ b ⁇ 0.10; 0.8 ⁇ c ⁇ 1.2; 0 ⁇ d ⁇ 0.10; 0.9 ⁇ e ⁇ 2.2; and 3.6 ⁇ f ⁇ 8.8.
• the carbon-containing material is amorphous.
• the carbon-containing material is nanoscale.
• carbon-containing materials are prepared by wet- chemical processes, such as co-precipitation or sol-gel methods; physical vapor deposition; chemical vapor methods; mechanochemical methods, where chemical reaction is promoted by the application of mechanical energy, such as by grinding; heat treatment of solid-reactants; and combinations of such methods.
• the carbon is provided as a constituent of a starting reactant compound, or as a constituent of a precipitated compound, such compounds being exemplified by metal carbonates, alkoxides, and oxalates.
• the carbon is contained in the firing atmosphere, for example as carbon monoxide, carbon dioxide or hydrocarbon species.
• the carbon is provided by an added material that does not supply a substantial amount of the metal constituents, for example, by a liquid organic solvent, elemental carbon, or an organic compound that decomposes to carbon during firing (including, without limitation, sugars, aromatic compounds, and polymers, including those supplied by the containers or milling media used to prepare the compound).
• a liquid organic solvent, elemental carbon, or an organic compound that decomposes to carbon during firing including, without limitation, sugars, aromatic compounds, and polymers, including those supplied by the containers or milling media used to prepare the compound.
• Small particle size contributes to the ability of a material to form an amorphous phase, either in the as-prepared state or upon lithiation or delithiation.
• the nanoscale dimensions that realize the benefits as described herein can be characterized by several methods.
• Nanoscale refers to materials having a primary particle size with a smallest dimension that is about 500 ran or less, in some instances about 200 nm or less, or about 100 nm or less. If fabricated as a powder, the nanoscale materials have a specific surface area measured by the BET method of at least about 10 m 2 /g, and an equivalent spherical particle diameter calculated from the BET specific surface area of about 500 nm or less, in some instances about 200 nm or less, or about 100 nm or less.
• the nanoscale materials described herein have a BET specific surface area of at least about 10 m 2 /g. In some instances, the BET specific surface area is at least about 15 m 2 /g, at least about 20 m 2 /g, at least about 25 m 2 /g, at least about 30 m 2 /g, at least about 35 m 2 /g, at least about 40 m 2 /g, at least about 45 m 2 /g, or at least about 50 m 2 /g.
• the "BET” method refers to the method of Brunauer, Emmett and Teller, well-known to those skilled in the art of powder characterization, in which a gas phase molecule (such as N 2 ) is condensed onto the surfaces of a material at a temperature (such as 77 K) where the coverage of condensed gas per unit area is well- known, and the total amount of condensed gas on the sample is then measured upon being liberated by heating.
• a gas phase molecule such as N 2
• a temperature such as 77 K
• the equivalent spherical particle diameter is about 150 nm or less, for example, about 100 nm or less, about 75 nm or less, about 50 nm or less, or about 25 nm or less.
• the size of the primary particles can be determined by X-ray line-broadening methods well-known to those skilled in the art.
• the nanomaterials described herein have an average
• the unique properties of a nanomaterial may depend on the smallest cross- sectional dimension.
• Cross-sectional dimension is here understood to be that family of straight lines that can be drawn through the center of mass of an isolated or separable object. By assuming spherical morphology, the equivalent spherical particle size gives the largest average cross-sectional dimension of a particulate material.
• a very thin but continuous film, or a very thin but continuous fiber can exhibit nanoscale effects, even though the dimensions are far larger than nanoscale in the plane of the film or along the axis of the fiber.
• the smallest cross- sectional dimension namely the thickness of the film or the diameter of the fiber, is sufficiently small, nanoscale properties may be obtained.
• the specific surface area and the equivalent spherical particle size may not adequately define the characteristic dimension below which the nanomaterial will exhibit special properties. That is, for highly anisometric particle shapes, in some instances the BET surface area can be larger than the above- mentioned values, yet the material still will exhibit a smallest characteristic dimension sufficiently small to exhibit nanoscale properties as described herein.
• the primary particles of a nanoscale powder exhibit a smallest cross-sectional dimension that is, on a number-averaged basis to provide a mean value, about 500 nm or less, and in some cases about 200 nm or less.
• the smallest cross-sectional dimension is about 150 nm or less, for example, about 100 nm or less, about 75 nm or less, about 50 nm or less, or about 25 nm or less.
• a primary particle dimension is considered to be the characteristic spatial dimension that a BET surface area measurement would interrogate by adsorbing gas onto exposed surfaces of the material.
• the agglomerate may have an average particle size of less than about 800 nm, or less than about 600 nm, or less than about 500 nm, or less than about 300 nm.
• the nanoscale material is a thin film or coating, including a coating on a particle of any size, in which the film or coating has an average thickness of about 500 nm or less, in some cases about 200 nm or less, for example, about 150 nm or less, about 100 nm or less, about 50 nm or less, or about 25 nm or less.
• the thickness of the film or coating can be measured by various methods including transmission electron microscopy or other microscopy methods that can view the film or coating in cross-section.
• an ion storage material as described herein typically is formulated into an electrode by standard methods, including the addition of a few weight percent of a polymeric binder, and (e.g., if the material does not already include sufficient carbon) less than about 10 weight percent of a conductive additive, such as carbon.
• the electrodes typically are coated onto one or both sides of a metal foil, and optionally pressed to a coating thickness of between about 30 micrometers and about 200 micrometers, providing a charge storage capacity of between about 0.25 mAh/cm 2 and about 2 mAh/cm 2 .
• Such electrodes are suitable for use as the positive or negative electrode in a storage battery.
• an ion storage material as described herein is used as the positive electrode in a lithium battery.
• the electrodes are typically assembled into multilayer laminated cells of wound or stacked configuration, using lithium metal or an anode-active lithium storage electrode as the negative electrode.
• suitable negative electrode materials include lithium metal, carbon, an intermetallic compound, or a metal, metalloid or metal alloy that includes such lithium-active elements as Al, Ag, B, Bi, Cd, Ga, Ge, In, Pb, Sb, Si, Sn or Zn.
• the negative electrode material can be selected or designed for high capacity and high rate capability.
• the storage batteries thus assembled can employ a porous electronically insulating separator between the positive and negative electrode materials, and a liquid, gel or solid polymer electrolyte.
• the storage batteries employ electrode formulations and physical designs and constructions developed through methods well-known to those skilled in the art to provide low cell impedance, so that the high rate capability of the ion storage material as described herein is utilized.
• compositions of undoped Lio. 9 oFeP0 4 , Li 1.0 FePO 4 , and Li 0 ,9 5 FePO 4 were prepared from the starting raw materials Li 2 CO 3 , FeC 2 O 4 '2H 2 O, and (NH 4 )H 2 PO 4 .
• the starting raw materials were ball-milled using steel milling balls in a polypropylene jar with acetone solvent for 72 hours, then dried. The dried material was then fired in flowing nitrogen gas atmosphere, first at 35O 0 C for 10 hours, then at 600 0 C for 20 hours.
• the resultant samples were labeled A (Lio. 9 oFeP0 4 ), B (Li].
• Figures 2A, B and C are plots showing the capacity on charge and discharge for cycle 1 at C/50 rate for samples A (0.0900 mol Li 2 CO 3 ), B (0.1000 mol Li 2 CO 3 ), and C (0.0950 mol Li 2 CO 3 ), respectively. These results at low rates show an extended lower- voltage discharge "tail” indicating solid solution behavior.
• Figures 3A-B show dark field and bright field images, respectively, of sample B.
• Figures 4A-G show spectra at different locations of the sample. Table 1 summarizes the P content, Fe content, and phase results for each location. Table 1
• Figures 5A, B, C and D show, respectively, C, Fe, P and O elemental maps for the sample.
• Figure 6 shows another image of sample B.
• Figures 7A, B, C, D and E show, respectively, C, Fe, P, O and S elemental maps for the sample;
• Figure 8 shows an image of sample A.
• Figures 9 A, B, C and D show, respectively, C, Fe, P and O elemental maps for the sample.
• Figure 10 shows another image of sample A.
• Figures 1 IA, B, C and D show, respectively, C, Fe, P and O elemental maps for the sample.
• Figures 12A-E show spectra at different locations of the sample. Table 2 summarizes the P content, Fe content, and phase results for each location.
• Sample B and two different samples of 1% Nb-doped LiFePO 4 (designated samples D and E) were each mixed with 50 wt % crystalline silicon powder and X- rayed.
• Samples D and E were made by the same method as the undoped samples A-C, except that niobium oxalate was added as a starting raw material in the amount necessary to achieve the desired composition.
• the nanoscale phosphate powder whether doped or undoped, was seen to have much lower olivine peak intensities than the reference powder, showing a large if not dominant fraction of the material to be amorphous. Peak locations were similar in all of the powders, and only the peak intensities differed.
• the commercial powder had high peak intensities for every peak. (The three strongest peaks and the peak at about 69° in Figure 14 belonged to Si.)
• the sample had an electrochemically active, amorphous/disordered Fe-P-O-C phase.
• the results on the several other deliberately lithium-deficient Lii -x FePO 4 compositions showed that such an amorphous phase (which also can be deduced to contain lithium based on the crystalline olivine fraction seen by XRD relative to the overall composition) was stable in the samples tested.
• an amorphous/disordered Li-Fe-P-O-C phase is stable.
• An undoped predominantly crystalline nanoscale LiFePO 4 powder was prepared using the method of Example 1 , with final firing being carried out at 700 0 C for 5 hours.
• the powder was found to have a BET specific surface area of 39.8 m 2 /g, corresponding to an equivalent spherical particle size of 42 nm.
• Transmission electron microscopy (“TEM") showed the powder particles to be equiaxed, and TEM images and Rietveld refinement of X-ray diffraction data showed a crystallite size very similar to that inferred from the BET measurement.
• the powder was formulated into electrodes and tested in SwagelokTM type cells of the type described in Example 1.
• the assembled cell was charged and discharged for one full cycle at C/5 rate to determine the electrode capacity, and then charged to 50% state-of-charge (SOC) at a C/10 rate.
• SOC state-of-charge
• the cell was disassembled immediately, 0.5 mg of Si powder was placed on the surface of the electrode as a peak calibration standard, and X-ray diffraction was conducted. X-ray diffraction was then conducted again on the same electrode 48 hours after disassembly, and again 5 days after disassembly. Rietveld refinement was conducted on the X-ray diffraction patterns to obtain the lattice constants and amounts of the triphylite and heterosite phases in the electrode.
• the amorphous phase crystallizes over time at room temperature, and crystallizes a higher proportion of the heterosite (delithiated) phase. That is, the amorphous phase is rich in the heterosite composition. Aside from the crystallization of the amorphous phase, it is also possible that the charging process has produced equilibrium compositions of the triphylite phase. Namely, a solid solution forms that is more lithium deficient than the equilibrium composition, and as this phase evolves towards the equilibrium composition, more heterosite phase is formed.
• Table 3 also shows the unit cell dimensions of the heterosite and triphylite phases at each elapsed time. It is seen that the difference in unit cell volume was initially smaller, and increased over time. A smaller lattice misfit means that any phase transformation occurring between heterosite and triphylite or vice versa can occur more easily; and the rate of charge and discharge of the battery relies on the rate of this phase transformation.
• a smaller lattice misfit means that any phase transformation occurring between heterosite and triphylite or vice versa can occur more easily; and the rate of charge and discharge of the battery relies on the rate of this phase transformation.
• Meethong et al. "Strain accommodation during phase transformations in olivine-based cathodes as a materials selection criterion for high-power rechargeable batteries," Adv. Functional Mater., In press 2006; U.S. Patent Application No. 11/396,515.
• the charging (or discharging) process produces a material of smaller misfit and more facile phase transformation.
• Triphylite phase a (angstroms) 10.3075 10.2998 10.2997 b (angstroms) 5.9969 5.9931 5.9945 c (angstroms) 4.7003 4.6979 4.698 V (angstroms ⁇ 3) 290.53G3 289.9946 290.0623
• Heterosite phase ⁇ (angstroms) 9.855 9.828 9.834 b (angstroms) 5.815 5.811 5.807 c (angstroms) 4.785 4.792 4.785 V (angstroms ⁇ 3) 274.2322 273.6869 273.2917
• An undoped predominantly crystalline nanoscale LiFePO 4 powder was prepared using the method of Example 1 , with final firing being carried out at 600°C for 20 hours.
• the powder was found to have a BET specific surface area of 48.8 m 2 /g, corresponding to an equivalent spherical particle size of 34 nm.
• TEM showed the powder particles to be equiaxed, and TEM images and Rietveld refinement of X-ray diffraction data showed a crystallite size very similar to that inferred from the BET measurement.
• the powder was formulated into electrodes and tested in SwagelokTM type cells of the type described in Example 1.
• the assembled cell was charged and discharged for one full cycle at C/5 rate to determine the electrode capacity, and then charged to 50% state-of-charge (SOC) at a C/10 rate.
• SOC state-of-charge
• the cell was disassembled immediately, and X-ray diffraction was conducted. X-ray diffraction was then conducted again on the same electrode 27 hours after disassembly, and again 6 days after disassembly. Rietveld refinement was conducted on the X-ray diffraction patterns to obtain the lattice constants and amounts of the triphylite and heterosite phases in the electrode.
• the charging process has produced equilibrium compositions of the triphylite phase. Namely, a solid solution forms that is more lithium deficient than the equilibrium composition, and as this phase evolves towards the equilibrium composition, more heterosite phase is formed.
• Table 4 also shows the unit cell dimensions of the heterosite and triphylite phases at each elapsed time. It is seen that the difference in unit cell volume was initially smaller, and increased over time. A smaller lattice misfit means that any phase transformation occurring between heterosite and triphylite or vice versa can occur more easily; and the rate of charge and discharge of the battery relies on the rate of this phase transformation.
• a smaller lattice misfit means that any phase transformation occurring between heterosite and triphylite or vice versa can occur more easily; and the rate of charge and discharge of the battery relies on the rate of this phase transformation.
• Meethong et al. "Strain accommodation during phase transformations in olivine-based cathodes as a materials selection criterion for high-power rechargeable batteries," Adv. Functional Mater., In press 2006; U.S. Patent Application No. 11/396,515.
• the charging (or discharging) process produces a material of smaller misfit and more facile phase transformation.
• a predominantly crystalline nanoscale powder of composition Li 0 . 99 Nbo,oiMno .7 oFeo .30 P0 4 was prepared using the method of Example 1, with Nb oxalate and Mn carbonate as additional starting materials.
• the powder was found to have a BET specific surface area of 40.2 m 2 /g, and a carbon content of 2.44 wt%.
• Rietveld refinement of X-ray diffraction data showed a crystallite size very similar to that inferred from the BET measurement.
• the powder was formulated into electrodes and tested in SwagelokTM type cells of the type described in Example 1. This powder provided a high capacity even at high discharge rates, with the specific capacity at rates of C/5, C, 2C, 5C, 1OC and 2OC being 143, 141 , 138, 135, 134 and 130 mAh/g, respectively. Additional cells were then charged and discharged for one full cycle at C/5 rate to determine the electrode capacity, and then charged to various states-of-charge (SOC) at a C/10 rate.
• SOC states-of-charge
• the cell After charging to a desired SOC, the cell was disassembled, and X-ray diffraction was conducted within about 48 hours. Remarkably, it was found that the delithiated phase (corresponding to heterosite in the Fe-only endmember) did not form in detectable amounts until about 72% SOC. Even at 90% SOC, the ratio of the delithiated to lithiated phases (in wt%) was only 0.246, indicating that the majority of the delithiated material in the sample was not in the form of a crystallized form detectable by X-ray diffraction.
• a cell was then charged to 90% SOC and disassembled immediately, 0.5 mg of Si powder applied to the face of the electrode as a diffraction peak reference, and the electrode X-rayed. Then, the electrode was X-rayed again after 20 hours, and again after 3 days.
• Figure 20 shows the X-ray diffraction patterns after each elapsed time. Rietveld refinement was conducted on the X-ray diffraction patterns to obtain the lattice constants and amounts of the lithiated and delithiated phases in the electrode. Again, there is an initial broad background in the 2 ⁇ angle range from 15° to 30°, which has diminished considerably by 20 hours and even more so after 3 days.
• varying amounts of amorphous phase(s) can be produced in- situ by varying the initial composition and the particle size.
• Examples 3 and 4 show that the relative amounts of crystalline and amorphous material obtained upon electrochemical cycling are dependent on the particle size in the nanoscale regime (less than about 500 nm), as is the composition of the amorphous material and the relative amounts of the crystalline phases that may subsequently form from the amorphous material.
• Example 5 shows that this phenomenon (creation of an amorphous phase upon electrochemical cycling) also occurs for certain doped and mixed-transition-metal compositions.

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