EP2118949A2 - Matériaux de stockage d'ions à échelle nanométrique - Google Patents

Matériaux de stockage d'ions à échelle nanométrique

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Publication number
EP2118949A2
EP2118949A2 EP08782740A EP08782740A EP2118949A2 EP 2118949 A2 EP2118949 A2 EP 2118949A2 EP 08782740 A EP08782740 A EP 08782740A EP 08782740 A EP08782740 A EP 08782740A EP 2118949 A2 EP2118949 A2 EP 2118949A2
Authority
EP
European Patent Office
Prior art keywords
lithium
transition metal
iron phosphate
rate
composition
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP08782740A
Other languages
German (de)
English (en)
Other versions
EP2118949A4 (fr
Inventor
Yet-Ming Chiang
Antoni S. Gozdz
Martin W. Payne
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
A123 Systems LLC
Original Assignee
A123 Systems Inc
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Publication date
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First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=39739011&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=EP2118949(A2) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Priority claimed from US11/672,931 external-priority patent/US8323832B2/en
Application filed by A123 Systems Inc filed Critical A123 Systems Inc
Publication of EP2118949A2 publication Critical patent/EP2118949A2/fr
Publication of EP2118949A4 publication Critical patent/EP2118949A4/fr
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • 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 typically has crystal specific gravity values of about 3 g/cm 3 to about 5 g/cm 3 , and 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.
  • LiFePO 4 has been widely reported in the scientific literature to have an extremely limited range of solid solution at room temperature.
  • Nanoscale ion storage materials are provided that exhibit unique properties measurably distinct from their larger scale counterparts.
  • the disclosed nanoscale materials can exhibit increased electronic conductivity, improved electromechanical stability, increased rate of intercalation, and an extended range of solid solution.
  • a lithium transition metal phosphate material for use as an ion storage material including at least two co-existing phases, including a lithium- rich transition metal phosphate phase and a lithium-poor transition metal phosphate phase, wherein the percentage molar volume difference between the two phases is less than about 6.5%.
  • the percentage molar volume difference between the two phases of the lithium transition metal phosphate material is less than about 6.40%, or less than about 6.25%, or less than about 5.75%, or less than about 5.5%.
  • the at least two existing phases of the lithium transition metal phosphate material are crystalline and are defined by a unit cell having lattice parameters for each principal axis, and wherein the difference in lattice parameters for at least two principal axes of the unit cells are less than 3%.
  • the difference in lattice parameters for all principal axes of the unit cells are less than 4.7%, or the difference in lattice parameters for all principal axes of the unit cells are less than 4.5%, or the difference in lattice parameters for all principal axes of the unit cells are less than 4.0%, or the difference in lattice parameters for all principal axes of the unit cells are less than 3.5%.
  • the difference in the smallest product of lattice parameters for any two principal axes of lithium transition metal phosphate material is less than 1.6%, or the difference in the smallest product of lattice parameters for any two principal axes is less than 1.55%, or the difference in the smallest product of lattice parameters for any two principal axes is less than 1.5%, or the difference in the smallest product of lattice parameters for any two principal axes is less than 1.35%, or the difference in the smallest product of lattice parameters for any two principal axes is less than 1.2%, or the difference in the smallest product of lattice parameters for any two principal axes is less than 1.0%.
  • the difference in the largest product of lattice parameters for any two principal axes of lithium transition metal phosphate material is greater than 4.7%, or the difference in the largest product of lattice parameters for any two principal axes is greater than 4.8%, or the difference in the largest product of lattice parameters for any two principal axes is greater than 4.85%.
  • the nanoscale materials have a plane formed by any of the principal axes of the crystal along which the strain measured as a change in the area is less than about 1.6%, or less than about 1.5%, or less than about 1.4%. According to another embodiment, none of the planes formed by any of the principal axes of the crystal have such a strain exceeding 8%, or 7.5%, or 6%.
  • the lithium transition metal phosphate material has a specific surface area of at least about 20 m 2 /g, or at least about 35 m 2 /g, or at least about 50 ⁇ r/g.
  • the lithium transition metal phosphate material is selected from the group consisting of ordered or partially disordered structures of the olivine (A x MPO 4 ), NASICON (A x (M ⁇ M") 2 (PO 4 ) 3 ), VOPO 4 , LiVPO 4 F, LiFe(P 2 O 7 ) or Fe 4 (P 2 Ov) 3 structure types, wherein A is an alkali ion, and M, M' and M" are transition metals.
  • the lithium transition metal phosphate material has an overall composition of Lii_ x MPO 4 , where M comprises 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 from 0 to 1.
  • M can include Fe.
  • the material can exhibit a solid solution over a composition range of 0 ⁇ x ⁇ 0.3, or the material exhibits a stable solid solution over a composition range of x between 0 and at least about 0.15, or the material exhibits a stable solid solution over a composition range of x between 0 and at least about 0.07 or between 0 and at least about 0.05 at room temperature (22-25 0 C).
  • the material can also exhibit a stable solid solution at low lithium content; e.g., where l ⁇ x ⁇ 0.8 or where l ⁇ x ⁇ 0.9, or where Kx ⁇ 0.95.
  • the lithium-rich transition metal phosphate phase has the composition Li y MPO 4 and the lithium-poor transition metal phosphate phase has the composition Lii_ x MPO 4 , wherein 0.02 ⁇ y ⁇ 0.2 and 0.02>x>0.3 at room temperature (22-25°C).
  • the material can exhibit a solid solution over a composition range of 0 ⁇ x ⁇ 0.15 and 0.02 ⁇ y ⁇ 0.10.
  • the solid solution of the lithium transition metal phosphate material occupies a fraction of the compositional range of lithium defined as y + x.
  • the lithium transition metal phosphate material has an overall composition of Lii -x . z Mi -z PO 4 , where M comprises at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, where x is from 0 to 1 and z can be positive or negative. M includes Fe, z is between about 0.15 and -0.15.
  • the material can exhibit a solid solution over a composition range of 0 ⁇ x ⁇ 0.15, or the material exhibits a stable solid solution over a composition range of x between 0 and at least about 0.05, or the material exhibits a stable solid solution over a composition range of x between 0 and at least about 0.07 at room temperature (22-25 0 C).
  • the material may also exhibit a solid solution in the lithium-poor regime, e.g., where x>0.8, or x>0.9, or x>0.95.
  • the lithium transition metal phosphate material is of a form selected from the group consisting of particles, agglomerated particles, fibers and coatings.
  • the form has an average smallest cross-sectional dimension of about 75 ran or less, or about 60 nm or less, or about 45 nm or less.
  • the lithium transition metal phosphate material is in the form of dispersed or agglomerated particles and the average crystallite size as determined by x-ray diffraction is less than about 800 nm, or less than about 600 nm, or less than about 500 nm, or less than about 300 nm.
  • the form contains less than 3 wt% of a substantially non-lithium-storing conductive phase.
  • the lithium transition metal phosphate material is crystalline or amorphous.
  • a cathode includes a lithium transition metal phosphate material, for example, a lithium transition metal phosphate material having an overall composition of Lii -X MPO 4 , where M comprises 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 from 0 to 1.
  • the material can exhibit a solid solution over a composition range of 0 ⁇ x ⁇ 0.3 or over a range of 0 ⁇ x ⁇ 0.15.
  • An electrochemical cell containing the electrode is also provided.
  • a nanoscale crystalline lithium transition metal phosphate is provided that becomes disordered upon delithiation or lithiation having a specific surface area of at least about 25 m 2 /g.
  • a lithium deficient lithium transition metal phosphate is formed.
  • a lithium-deficient solid solution lithium transition metal phosphate is provided that is formed upon delithiation at a temperature below 150 0 C having a specific surface area of at least about 25 m 2 /g.
  • the lithium transition metal phosphate is an ordered olivine structure, and the deficiency occurs on the lithium or Ml sites of the ordered olivine, or the disorder occurs on the lithium or Ml sites of the ordered olivine.
  • a lithium transition metal phosphate that transforms upon first charge to disordered olivine having a lithium deficient solid solution and retains such solid solution at temperatures below 15O 0 C, or at temperatures below 100 0 C, or at temperatures below 50 0 C.
  • Still another aspect provides a high power storage battery.
  • the battery contains a cathode, an anode, an electrolyte in contact with and separating the anode and cathode, a cathode current collector in electronic communication with the cathode, and an anode current collector in electronic communication with the anode.
  • the storage battery exhibits specific power of at least about 500 W/kg (1000 W/L) at specific energy of at least about 100 Wh/kg (205 Wh/L), and in some cases exhibits specific power of at least about 1300 W/kg (2500 W/L) at specific energy of at least about 90 Wh/kg (180 Wh/L).
  • the battery cathode includes a nanoscale alkaline transition metal phosphate having a specific surface area of at least about 25 m 2 /g. In some embodiments, the cathode includes particles, fibers or coatings of a nanoscale alkaline transition metal phosphate having an average smallest cross-sectional dimension of about 75 nm or less. In specific embodiments, the cathode includes a composition of formula Lii_ x MPO 4 , where M is one or more transition metals. The composition has a specific surface area of at least about 25 m 2 /g, and exhibits a stable solid solution over a composition range of x between 0 and at least about 0.03, and in some embodiments up to about 0.15.
  • the cathode includes particles, fibers or coatings of a composition of formula IA ⁇ . X M?O ⁇ where M is one or more transition metals.
  • the particles, fibers or coatings have an average smallest cross-sectional dimension of about 75 nm or less, and the composition exhibits a stable solid solution at room temperature (22-25°C) over a composition range of x between 0 and at least about 0.03, and in some embodiments up to 0.15.
  • lithium transition metal phosphate powder having a specific surface area of at least 15 m 2 /g and having a lithium content at room temperature (23°C) that is at least 2 mole% less than the lithium content of a lithium transition metal phosphate of otherwise the same composition that is prepared in a bulk form or as a powder of specific surface area less than about 10 m 2 /g. It is understood that the powder may be used at any temperature, however, the difference in lithium content is determined relative to room temperature. [0031] In one or more embodiments, the powder has a specific surface area of at least 20 ⁇ flg, or at least 25 m 2 /g, or at least 30 m 2 /g.
  • the lithium transition metal phosphate has an olivine structure.
  • the lithium transition metal phosphate has a composition Lii -X MPO 4 , where M is one or more of first-row transition metals, and can be for example at least Fe.
  • a lithium iron phosphate composition forming a single crystalline phase of the olivine structure at room temperature having a solid solution composition
  • Lii -x FeP ⁇ 4 wherein x is greater than 0.01.
  • x is greater than 0.02, or greater than 0.03, or greater than 0.04, or greater than 0.05, or greater than 0.06, or greater than 0.07, or greater than 0.08, or greater than 0.09 or greater than 0.10.
  • the lithium iron phosphate has a specific surface area greater than 15 m 2 /g, or greater than 20 m 2 /g, or greater than 25 m 2 /g, or greater than 30 m 2 /g.
  • a partially lithiated iron phosphate composition of the olivine structure having at room temperature a single crystalline phase of the olivine structure and a solid solution composition O y FePO 4 wherein y is greater than 0.01.
  • y is greater than 0.02, or greater than 0.03, or greater than 0.04, or greater than 0.05, or greater than 0.06, or greater than 0.07, or greater than 0.08, or greater than 0.09 or greater than 0.10.
  • the lithium iron phosphate has a specific surface area greater than 15 m 2 /g, or greater than 20 m 2 /g, or greater than 25 m 2 /g, or greater than 30 m 2 /g.
  • a lithium transition metal phosphate compound characterized in that, when used as a lithium storage electrode in a standard electrochemical cell wherein the counterelectrode is lithium metal, the compound exhibits a continuously decreasing charging current upon charging in a potentiostatic intermittent titration (PITT) procedure at a constant overpotential of 5OmV above the open-circuit voltage of the cell, said open-circuit voltage being measured after charging to a 50% state of charge and holding for at least 12 hours.
  • PITT potentiostatic intermittent titration
  • the open-circuit voltage is measured after charging to a 50% state of charge and holding for at least 12 hours at 25 0 C. [0042] In one or more embodiments, the open-circuit voltage is measured after charging to a 50% state of charge and holding for at least 12 hours over a temperature range of about -
  • the compound is lithium transition metal phosphate
  • Lii_ x MP ⁇ 4 wherein M is one or more first-row transition metals and x has a value between zero and 1.
  • the lithium transition metal phosphate has an olivine structure.
  • the compound is Lii_ x FeP ⁇ 4 , wherein M is one or more first-row transition metals and x has a value between zero and 1.
  • a lithium transition metal phosphate compound characterized in that, when used as a lithium storage electrode in a standard electrochemical cell wherein the counterelectrode is lithium metal, the compound exhibits a continuously decreasing charging current upon discharging in a potentiostatic intermittent titration (PITT) procedure at a constant overpotential of 5OmV above the open-circuit voltage of the cell, said open-circuit voltage being measured after charging to a 50% state of charge and holding for at least 12 hours.
  • PITT potentiostatic intermittent titration
  • the open-circuit voltage is measured after charging to a 50% state of charge and holding for at least 12 hours at 25°C.
  • the open-circuit voltage is measured after charging to a 50% state of charge and holding for at least 12 hours over a temperature range of about -
  • the compound is lithium transition metal phosphate
  • Lii -X MPO 4 wherein M is one or more first-row transition metals and x has a value between zero and 1.
  • the lithium transition metal phosphate has an olivine structure.
  • the compound is Lii -x FePO 4 , wherein M is one or more first-row transition metals and x has a value between zero and 1.
  • the lithium transition metal phosphate compound may be used in a lithium ion storage device, such as a battery.
  • a method of storing electrical energy includes charging of the lithium storage battery as described according to one or more embodiments at a C-rate of at least 2C, said C- rate being the average C-rate for a current being applied over a period of at least 5 sec.
  • the method includes charging of the lithium storage battery as described according to one or more embodiments at a C-rate of at least 5C, or at least 1 OC, or at least 15C, or at least 2OC, or at a C-rate of at least 30C, or at least 4OC, or at a
  • C-rate is the average C-rate for a current being applied over a period of at least 10 sec, or at least 20 sec, or at least 30 sec.
  • a method of storing and delivering electrical energy includes charging of the lithium storage battery as described according to one or more embodiments at a C-rate of at least 2C, and discharging at a rate of at least 2C.
  • the method includes charging of the lithium storage battery as described according to one or more embodiments at a C-rate ranging from at least
  • the method includes discharging at a rate ranging from at least 5C up to at least 50C.
  • Figure 1 is a transmission electron microscope image of a nanoscale lithium iron phosphate ion storage material illustrating nanoscale dimensions.
  • Figures 2A-2B show bright-field and dark-field scanning transmission electron microscope images, respectively, of an aggregated nanoscale lithium iron phosphate material; and Figures 2C-F show Fe, P, O and C elemental maps taken on the sample in Figure 2B.
  • Figure 3 A is a composition-temperature phase diagram for a conventional
  • Li]- ⁇ FePO 4 ion storage material according to certain embodiments; and Figure 3B is a voltage vs composition graph for a conventional or coarsened Li]JFePO 4 material.
  • Figure 4A is a composition-temperature phase diagram for a nanoscale Li] JFePO 4 ion storage material according to certain embodiments of the invention demonstrating an extended region in which solid solution is formed; and
  • Figure 4B is a voltage vs composition graph for a conventional or coarsened Li] -x FePO 4 material; the nanocrystalline form behaves thermodynamically and electrochemically as a distinct material from the conventional or coarsened crystalline state.
  • Figure 5 is a plot of discharge capacity at various C-rates for the nanoscale lithium iron phosphate of Example 2; the plot includes the initial first charge capacity and illustrates that the first discharge capacity is more than 10% higher than the first charge capacity.
  • Figure 6 is a plot of discharge capacity at various C-rates for a conventional coarse grained lithium iron phosphate; the material exhibits conventional first charge and discharge behavior and the plot shows a decrease in first discharge capacity compared to first charge capacity.
  • Figure 7 is a plot illustrating the equilibrium or near-equilibrium electrical potential of a nanoscale Lii - ⁇ -FePO 4 ion storage material at a nearly fully lithiated composition, according to certain embodiments, relative to a standard or reference electrode in an electrochemical cell that allows electrochemical equilibration; an extended range of solid solution at room temperature in the nanoscale material is shown by a range of charge capacity, corresponding to regions of composition x, over which the open-circuit- voltage (OCV) varies continuously with composition, rather than being at a constant OCV.
  • OCV open-circuit- voltage
  • Figure 11 illustrates a PITT discharging experiment for the cell of Figure 9 in which the first voltage step was from a charge voltage of 3.8V to a voltage that is 5 mV above the open-circuit voltage of the cell, measured at a 50% state-of-charge; virtually no discharging of the cell is seen until the PITT voltage is about 20 mV below the OCV.
  • Figure 12 shows a charging PITT experiment on a nanoscale Li 0 95 FePO 4 material, in which substantial current flow, indicating charging, is seen well before the two-phase plateau voltage is reached.
  • Figure 13 shows the capacity measured for the cell of Figure 12 at each voltage step during the PITT charging experiment.
  • Figure 14 shows a PITT discharging experiment for the cell of Figure 12, in which the first voltage step was from a charge voltage of 3.8V to a voltage that is 5 mV above the open-circuit voltage of the cell, measured at a 50% state-of-charge; a substantial capacity of about 8 mAh/g is measured when the PIT voltage is still 5 mV above the OCV.
  • Figure 15 shows a powder X-ray diffraction pattern obtained from a conventional carbon-coated lithium iron phosphate material at 50% SOC.
  • Figure 16 shows the powder X-ray diffraction pattern obtained from a nanoscale
  • LiFePO 4 sample according to the invention measured at 67% SOC.
  • Figure 17 is a schematic illustration of the spatial distribution of space-charge defects in a nanoscale lithium storage material according to certain embodiments.
  • Figure 18 shows the specific capacity of the nanoscale lithium iron phosphate of
  • Example 1 as measured from a Swagelok cell.
  • Figure 19 shows test results from three lithium half-cells constructed using
  • Figure 20 shows the voltage and current traces upon discharging in a PITT measurement of the Aldrich sample described in Example 3 at 23 0 C.
  • Figure 21 shows the voltage and current traces upon charging in a PITT measurement of a nanoscale LiFePO 4 , 39.8 m /g, 23 0 C.
  • Figure 22 shows the voltage and current traces upon discharging in a PITT measurement of a nanoscale LiFePO 4 , 39.8 m Ig, 23°C
  • Figure 23 shows the voltage and current traces upon charging in a PITT measurement of a nanoscale LiFePO 4 , 48.8 m2/g, 23°C.
  • Figure 24 shows the voltage and current traces upon discharging in a PITT measurement of a nanoscale LiFePO 4 , 48.8 m2/g, 23°C.
  • Figure 25 shows the voltage and current traces upon charging in a PITT measurement of the Aldrich sample of Example 3 at 45°C.
  • Figure 26 shows the voltage and current traces upon discharging in a PITT measurement of the Aldrich sample of Example 3 at 45 0 C.
  • Figure 27 shows the voltage and current traces upon charging in a PITT measurement of a nanoscale LiFePO 4 , 49.8 m2/g, 45 0 C.
  • Figure 28 shows the voltage and current traces upon discharging in a PITT measurement of a nanoscale LiFePO 4 , 49.8 m2/g, 45 0 C charge.
  • Nanoscale ion storage materials and devices such as storage batteries, that use these materials are provided. It has been unexpectedly discovered that ion storage materials having sufficiently small size scale and correspondingly high surface to volume ratio or specific surface area provide fundamentally different physical properties compared to their conventional coarse-grained counterparts. In particular, despite having gross structural similarities such as crystal structure type and basic atomic arrangements, upon preparation or during use the nanoscale materials are compositionally and structurally distinct from, and provide different and improved electrochemical utility and performance compared to, the coarse-grained materials.
  • the nanoscale materials provide a very high rate capability, while providing a large fraction of the intrinsic charge capacity and energy density of the material.
  • the different properties can be exhibited, for example, in an as-prepared state, upon being thermally equilibrated or partially thermally equilibrated (for instance by heating), or upon equilibrating with a gas phase or condensed phase medium, or upon being assembled and used as a bipolar electrochemical device, including undergoing repeated charge-discharge cycles.
  • Nanoscale ion storage materials can be crystalline (i.e., nanocrystalline) or amorphous.
  • the unique properties discussed herein are believed to arise from the stresses created by free or internal surfaces or the behavior of the solid in the vicinity of a surface, and therefore the relevant nanoscale dimension is the separation between free or internal surfaces in the material.
  • the free surfaces define the cross-sectional dimensions that determine the nanoscale effects.
  • the free surfaces may again define the relevant cross-sectional dimensions, and if these are below the suitable size as described below, the material will exhibit nanoscale properties.
  • the overall particle or aggregate size may exceed these cross-sectional dimensions, yet a crystallite within the aggregate may nonetheless have cross-sectional dimensions defined by the separation between an internal surface (e.g., a grain boundary) and an external surface of the aggregate that are sufficiently small to provide nanoscale properties.
  • Such materials will be suitable for use in an electrochemical device wherein the crystallite has nanoscale properties and at least a portion of the crystallite has an external surface that is accessible to an electrolyte phase when the nanoscale material is used in the device.
  • thermodynamically, mechanically, and electrochemically distinct properties described herein reflect a fundamental difference in nature of the nanoscale materials compared to larger scale materials, as opposed to simple or "trivial" size-scaling effects that may have been recognized previously in the art of battery materials.
  • the rate- capability of electrode materials can be limited at least in part by solid-state diffusion of ions in the storage compound. Under such circumstances, an increased rate capability is expected from the use of smaller particles, or thinner films (in the case of thin film batteries), because diffusion times are shorter and charge/discharge rates correspondingly faster for a given transport coefficient or diffusion coefficient.
  • This simple effect of particle size is well-known in the battery field (see, e.g., U.S. Patent No.
  • transport in electrochemical systems can be limited by surface reaction rates.
  • a material having finer particle size and corresponding higher surface area will naturally have higher area available for surface reaction.
  • This simple relationship again does not suggest a fundamental change in physical properties occurring at a particular size scale.
  • the surface or interfacial chemistry of small scale materials can change due to their size, potentially causing a fundamental improvement in surface reaction rate that benefits rate capability apart from simple changes in available surface area. (See, e.g., Chiang, "Introduction and Overview: Physical Properties of Nano structured Materials," J.
  • Electroceramics, 1 :205 (1997), for a discussion of unexpected differences between nanoscale materials and their coarse counterparts, as opposed expected differences based on well- known size-scaling laws.) [0093] As described in more detail below, we have discovered unique behavior and phase composition at the nanoscale for ion storage materials based on alkali transition metal phosphates.
  • Examples include nanoscale ordered or partially disordered structures of the olivine (A x MPO 4 ), NASICON (A X (M',M") 2 (PO 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. Many such compounds have relatively low electronic conductivity and alkali ion conductivity when conventionally prepared, such that for electrochemical applications they benefit from unique properties arising from being in the nanoscale state.
  • the nanoscale ion storage material has the formula LiMPO 4 , where M is one or more transition metals.
  • the nanoscale material is an ordered olivine (Lii -X MXO 4 ), where M is one or more of V, Cr, Mn, Fe, Co and Ni, and x can range from zero to one, during lithium insertion and deinsertion reactions. In the as-prepared state, x is typically about one.
  • the special properties of nanoscale ion storage materials may be augmented by doping with foreign ions, such as metals or anions. Such materials are expected to exhibit similar behavior to that demonstrated herein for Lii_ ⁇ -FeP ⁇ 4 at the nanoscale, based on the scientific principles underlying such behavior. However, doping is not required for a material to exhibit special properties at the nanoscale.
  • the lithium transition metal phosphate material has an overall composition of Lii_ x _ z Mi JPO 4 , where M comprises at least one first row transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, where x is from 0 to 1 and z can be positive or negative.
  • M includes Fe, z is between about 0.15 and -0.15. The material can exhibit a solid solution over a composition range of 0 ⁇ x ⁇ 0.15.
  • Figure 1 is a transmission electron microscope image of a nanoscale lithium iron phosphate ion storage material exhibiting particle dimensions on these scales.
  • Figures 2A and 2B show bright-field and dark-field scanning transmission electron microscope images, respectively, of an aggregated nanoscale lithium iron phosphate material.
  • Figures 2C-2F show Fe, P, O and C elemental maps taken on the sample in Figure 2A, showing that the distribution of these elements is uniform, i.e. that there are not distinguishable phases or particles rich in one or another of these main constituents.
  • nanocrystalline form compositions will possess measurably distinct properties as described herein compared to their larger scale counterparts.
  • the nanoscale materials retain a greater extent of solid solution nonstoichiometry, namely, retain a higher defect content than the coarse-grained material.
  • Such properties are measurable by electrochemical and crystallographic methods well-known to those skilled in the art.
  • the nanoscale ion storage materials provide higher charge storage at higher rates of charge or discharge than comparable materials that are not nanoscale.
  • the nanoscale dimensions that realize the benefits as described herein can be characterized by several methods.
  • the size-dependent nonstoichiometry and related beneficial properties of nanoscale LiFePO 4 and other ion storage compounds increase as the particle size decreases. These properties are significant, measurable, and beneficial at particle sizes below that corresponding to a BET specific surface area of about 20 m 2 /g. In some instances, materials having a BET specific surface area of at least about 25 m 2 /g, for example, 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 are employed.
  • 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 size of crystallites or primary particles, when the materials of the invention are crystalline, can be determined by X-ray line-broadening methods well-known to those skilled in the art.
  • the nanomaterials described herein have an average (i.e., mean) diameter of about 100 nm or less. In some instances, the average diameter is about 75 nm or less, for example, about 70 nm or less, about 60 nm or less, about 50 nm or less, about 45 nm or less, about 40 nm or less, or about 35 nm or less.
  • 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.
  • 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.
  • nanoscale behavior will be observed if the primary particles of the powder exhibit a smallest cross-sectional dimension that is, on a number-averaged basis to provide a mean value, about 100 nm or less.
  • the smallest cross-sectional dimension about 75 nm or less, for example, about 70 nm or less, about 60 nm or less, about 50 nm or less, about 45 nm or less, about 40 nm or less, or about 35 nm or less.
  • These dimensions can be measured using various methods, including direct measurement with an electron microscope of the transmission or secondary-electron type, or with atomic force microscopy.
  • 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. In the instance of a substantially fully- dense polycrystalline aggregate, it is the dimension of that aggregate.
  • the agglomerate may have an average crystallite 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 100 nm or less, in some cases about 75 nm or less, for example, about 70 nm or less, about 60 nm or less, about 50 nm or less, about 45 nm or less, about 40 nm or less, or about 35 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.
  • the nanoscale ion storage materials described herein are prepared from conventional materials by size-reduction processes (e.g.
  • the materials also can be synthesized in the nanoscale state, by methods including, but not limited to, solid-state reactions between metal salts, wet-chemical methods, such as co-precipitation, spray-pyrolysis, mechanochemical reactions, or combinations thereof. Nanoscale materials with the desired particle sizes and specific surface areas are obtained by using homogeneous reactants, minimizing the reaction or crystallization temperature (in order to avoid particle coarsening), and avoiding formation of liquid phases in which the product is highly soluble (which also tends to lead to particle coarsening).
  • nanoscale ion storage materials are prepared by non- equilibrium, moderate temperature techniques, such as wet-chemical or low temperature solid-state reactions or thermochemical methods.
  • the materials thus prepared can acquire properties such as increased nonstoichiometry and disorder and increased solubility for dopants because they are synthesized in a metastable state or because kinetic pathways to the final product differ from those in conventional high temperature processes.
  • Such disorder in the nanoscale form can also be preserved substantially under electrochemical use conditions and provide benefits as described herein.
  • nanoscale ion storage materials would exhibit fundamentally different physical properties compared to their coarse-grained counterparts, nor was it known what measurable physical properties would differ, nor the size scale that would realize these differences.
  • Useful and advantageous characteristics of nanoscale ion storage materials according to certain embodiments include, but are not limited to, the following.
  • the materials can exhibit increased electronic conductivity, for example, due to the co-existence in solid solution of higher concentrations of mixed-valence transition metal ions, or changes in the electronic structure related to a closer separation between atomic orbitals providing higher electronic carrier mobility, or both. Typically, the improved electronic conductivity will have a value greater than about 10 " S/cm.
  • the materials can have improved electromechanical stability, such as improved resistance to fracture, due to suppressed or delayed phase transformations during use as a storage electrode. This can allow higher energy, higher rate capability, and longer life of the materials and electrochemical cells using the materials. When electrochemical cycling causes phase transformations, the materials also may exhibit smaller molar volume differences between phases, which contributes to more facile transformation between the phases upon insertion and deinsertion of lithium.
  • the nanoscale material can exhibit increased rate of intercalation, due to the existence of multiple paths out of the particle when there may be blocking immobile ions in the diffusion paths.
  • the diffusion coefficient should be a materials property, not size dependent unless something else changes such as structure or disorder. This phenomenon is illustrated as follows. A particle that is 100 unit cells wide in spatial dimension, assuming each unit cell contains one formula unit of the compound, can have 1% disorder and have only, on average, one disordered atom blocking a given diffusion channel. This will have little impact on diffusion of ions into and out of the particle, since the diffusion channel can be accessed from both ends.
  • the blocking ions will prevent access to the majority of the channel.
  • the specific value of the chemical diffusion coefficient of the transported ion e.g., Li in a lithium battery
  • the additional disorder of a nanoscale material typically to a value greater than about 10 ⁇ 16 cm 2 /sec.
  • Nanoscale ion storage materials as described herein differ from their larger scale counterparts in the composition range in which they can stably exist.
  • the nanoscale compound can exist in a state of extended solid solution compared to the coarse-grained compound at the same temperature.
  • the existence of solid- solution nonstoichiometry is important for improving ion and electron transport, as has been demonstrated in numerous ion-intercalation compounds
  • One aspect of the invention provides a nanocrystalline composition exhibiting a much wider range of solid solution or defect content at a given temperature than a bulk crystal or coarse powder of nominally similar composition and crystalline phase before phase-separating into two or more phases.
  • These features are described in particular detail for LiI-JFePO 4 , however, it will be apparent to those of skill in the art that application of these principals to other ion storage materials will provide similar results.
  • the conventional compound Li I- JFePO 4 is known to exhibit negligible solid solution nonstoichiometry x at room temperature, x being about 0.002 according to some published literature (Delacourt et al., "Two-phase vs.
  • the concentration of lithium that is tolerated in the delithiated compound Li ⁇ FePO 4 , with which Lii_JFePO 4 coexists, is even less.
  • These features are illustrated in the composition-temperature phase diagram for LiFePO 4 -FePO 4 , shown in Figure 3A.
  • the phase composition for an iron phosphate with varying levels of lithium will vary with temperature, and a solid solution exists over wider ranges of lithium concentration at elevated temperatures, e.g., above 150 0 C. Elevated temperatures are not practical for most ion storage applications and practical applications are constrained to be only slightly elevated above room temperature, e.g., less than about 100 0 C. Unless otherwise stated, we refer to compositions at a temperature below about 100 0 C and typically at room temperature (22-25 0 C).
  • FIG. 3 A shows that at this temperature range, the solid solution ranges are extremely limited.
  • An illustrative voltage vs. composition plot at room temperature for the ion storage material is shown in Figure 3B and demonstrates that the voltage curve is flat over most of the compositional range, indicating the presence of a two phase system over almost the entire lithium composition range.
  • Li I- JFePO 4 of a conventional coarse-grained form the absence of solid solution nonstoichiometry is manifested by decomposition of lithium deficient compositions into two highly stoichiometric compounds having a chemical composition approach that of the end group compositions, LiFePO 4 and FePO 4 .
  • nanocrystalline Li]-JFePO 4 and Li y FePO 4 having a specific surface area measured by the BET method of greater than about 20 m ⁇ /g, and in some instances greater than about 30 m 2 /g, has been found to exhibit x (and y) that are severalfold larger than in the conventional compound. Indeed at room temperature, Li].
  • x FePO 4 can exhibit x as large as 0.05, 0.07, 0.10, 0.15, 0.3 or even greater and y can be as large as 0.05 or 0.1 or 0.2.
  • the dashed lines shows the existence of a significant solid solution at temperatures of less than about 5O 0 C for Lii JFePO 4 and Li y FePO 4 .
  • FIG. 4B An illustrative voltage vs. composition plot at room temperature for the ion storage material is shown in Figure 4B.
  • the curve has a demonstrably smaller flat region, indicating that the compositional range of a two-phase system is limited.
  • the sloping regions that flank the flat region indicate the existence of a solid solution.
  • the solid solution end-limits for the two endmember phases coexisting in the nanoscale material are larger than for the conventional material. For instance, in LiFePO 4 this means having a large lithium deficiency x in the lithium-rich Lii.
  • the co-existing phases include a large extent of nonstoichiometry.
  • the higher degree of nonstoichiometry indicates a greater population of both Fe 2+ and Fe + at every point within the two-phase region, which provides higher electronic conductivity for the material.
  • the sloping voltage curve of the nanophosphate permits the functional advantage of allowing state-of-charge monitoring that is not possible or is more difficult and expensive to conduct with materials exhibiting a flat two-phase discharge voltage profiles.
  • the fundamentally different phase behavior applies to each of the components of the compositional system, although likely to different degrees.
  • Other aspects of atomic level disorder likely also are affected at nanoscale dimensions.
  • the site occupancy of the Ml and M2 sites of the ordered olivine structure, occupied solely by Li and Fe in the ideal crystal can vary in the nanoscale material.
  • solute cations (dopants) can be more soluble in the nanocrystalline material, or can occupy different sites than they do in the conventional material.
  • nonstoichiometry on the oxygen sublattice of the crystal structure also can occur.
  • nanoscale ion storage materials as described herein exhibit one or more of these variations in defect or solid solution behavior. However, as shown by experimental results presented herein, the presence of foreign metals or anions is not necessary to create or define the special properties of the nanocrystalline state. [0116] Differences in physical properties exhibited by the nanoscale materials according to one or more embodiments of the invention compared to their conventional coarse-grained counterparts are readily measurable by standard thermal and electrochemical techniques, such as calorimetry, cyclic voltammetry, galvanostatic intermittent titration (GITT), or potentiostatic intermittent titration (PITT).
  • GITT galvanostatic intermittent titration
  • PITT potentiostatic intermittent titration
  • the improved performance of the nanoscale materials in ion storage applications is also readily measurable, for example, by formulating the nanoscale material into an electrode coating, constructing a nonaqueous electrochemical cell, and performing charge-discharge tests at various current rates.
  • the state of extended solid solution in the nanoscale material can be confirmed using electrochemical methods.
  • a compound of nanocrystalline Lii -x FePO 4 can be tested in a nonaqueous electrochemical cell.
  • the nanocrystalline Lii -x FePO 4 serves as the positive electrode against a source of lithium having a total lithium content much greater than the lithium storage capacity of the nanocrystalline electrode, such as lithium foil.
  • This electrochemical cell construction is often referred to as a lithium half-cell by those skilled in the art of lithium-ion batteries.
  • the nanoscale ion storage material is formulated into an electrode, typically using a conductive additive, such as carbon, and a polymeric binder.
  • the nanoscale ion storage material electrode is separated from the lithium metal counterelectrode, typically by a microporous polymer separator.
  • the cell is then infused with a nonaqueous lithium-conducting liquid electrolyte. The charge and discharge rates of the electrode are sufficiently fast that the electrochemical behavior of the nanoscale material can be tested.
  • first discharge at C/5 rate is more than 11 % greater than initial capacity.
  • >90% discharge capacity is maintained up to 1OC, which represents a remarkably high capacity at high discharge rates.
  • the tests are conducted at a sufficiently slow rate upon both charge and discharge, and over a similar voltage range, that the observed results reflect the capabilities of the storage material itself, rather than polarization or kinetic limitations due to the cell construction. Methods to ensure that such is the case are well-known to those skilled in the art.
  • lithiated electrode material While it is generally desirable for a lithiated electrode material to have a higher initial extractable lithium content, in the present instance the ability of the nanoscale material to sustain a lithium-deficient solid solution confers various advantages as described herein, which may overcome the disadvantage of having slightly less lithium capacity.
  • the nanoscale materials of the invention can sustain a nonstoichiometry x and y in the coexisting phase that may be as large or larger than the nonstoichiometry present in the as-made material.
  • preparation in an initially nonstoichiometric state is not required of the materials of the invention, nor necessary in order to obtain the benefits described herein.
  • one aspect of the present nanoscale ion storage materials is the property, for an olivine compound that in bulk form has a very limited range of lithium solid solution in either its lithiated or delithiated form, to exhibit an increased solid solution range when produced in a nanoscale form. This is evidenced by the smaller first-charge capacity relative to the first- and subsequent discharge capacities of the material, e.g., as shown in Figures 5 and 19. In these instances, the lithium deficient solid solution clearly exists in the as-prepared material after heat treatment, and not only in the electrochemically cycled material, which as discussed previously also has an extended range of solid solution.
  • lithium metal phosphate material having an increased range of lithium nonstoichiometry in the as-synthesized state (prior to electrochemical use) due to the phenomenon of size-dependent nonstoichiometry.
  • lithium nonstoichiometry it is meant the extent to which a lithiated compound is deficient in lithium relative to the ideal composition, e.g., x in Lii_ x FePO4 where the ideal composition is LiFePO 4 , or the extent to which an as-prepared delithiated compound has an excess of lithium, e.g., Li ⁇ FePO 4 where the ideal composition is FePO 4 .
  • Such compounds may have the olivine structure or some other crystalline structure, or may be amorphous or partially amorphous.
  • the specific surface area of such a material may be at least 15 m /g, or more preferably at least 20 m /g, more preferably still at least 25 m 2 /g, or more preferably still at least 30 m 2 /g.
  • the extent to which the lithium nonstoichiometry x or y is greater than that which occurs in an as-prepared material of the same composition but having a lower surface area form, e.g. less than about 10 m 2 /g, may be at least 2 rnole%, more preferably at least 4 mole%, and more preferably still at least 6 mole%.
  • lithium nonstoichiometry can be measured by methods well- known to those skilled in the art including electrochemical titration measurements, X-ray or neutron diffraction measurements of lattice expansion and contraction due to the presence of nonstoichiometry, or chemical analyses.
  • electrochemical titration measurements X-ray or neutron diffraction measurements of lattice expansion and contraction due to the presence of nonstoichiometry, or chemical analyses.
  • the presence of lithium nonstoichiometry in the starting material benefits the electronic conductivity and phase transformation rate of the material, and thus its performance in a lithium storage battery.
  • FIG. 7 shows the cell voltage vs. specific capacity of the positive electrode active material for cells in which a lithium metal count erelectrode has been used, serving as a suitable reference.
  • Two nanoscale lithium iron phosphate materials of overall compositions LiFePO 4 and Lio .95 FeP0 4 are compared against a conventional, commercially available carbon-coated lithium iron phosphate. All three cells are tested at a slow C/50 rate permitting the near-equilibrium cell voltage to be observed.
  • the nanoscale materials are further known from separate tests to exhibit much faster relaxation to their equilibrium potentials than does the conventional sample. It is seen that the nanoscale materials exhibit a substantial charge capacity over which the voltage varies continuously, before reaching a relatively constant voltage plateau. In contrast, the cell voltage for the conventional material exhibits no such regime, instead reaching its voltage plateau nearly immediately after a small voltage overshoot.
  • Figure 8 shows the C/50 discharge curves for the same three samples.
  • the nanoscale materials both exhibit a capacity regime of continuously varying voltage, indicating the existence of a solid solution, that is essentially absent for the conventional material, and at the end of discharge, both nanoscale materials exhibit a wide capacity regime of continuously varying voltage indicating a solid solution.
  • These examples demonstrate the effect pictorially illustrated in Figures 3B and 4B for nanoscale and conventional lithium iron phosphate materials, respectively.
  • Other accepted electrochemical methods that can be used to show that the nanoscale materials of the invention possess regimes of extended solid solution include GITT and PITT.
  • the open-circuit-voltage (OCV) measured after allowing an electrochemical cell to approach equilibrium will exhibit a composition dependence (i.e., as a function of state-of-charge or charge capacity) that is measurably different between the conventional and nanocrystalline forms.
  • An extended range of solid solution in the nanoscale material is shown by regions of composition x over which the OCV varies continuously with composition, rather than being at a constant OCV. This indicates a constant chemical potential for lithium despite variation of x, corresponding to a multi-phase equilibrium.
  • Such measurements typically can be conducted to + 0.002V or better precision by those skilled in the art, allowing comparison of different materials to determine the value of x at which the boundary between a single-phase solid solution and multiple phases lies.
  • composition x For a nanoscale material, there is a wider range of composition x over which the single-phase solid solution can exist.
  • the wider range of solid solution in the nanoscale form can be attained for any one or more of the individual phases exhibited by the compound, including intermediate phases forming within the limits of lithiation discussed here.
  • the PITT method is also useful for not only determining the cell voltages at which electrochemical oxidation and reduction of an electrode-active compound occur, but also for providing information regarding the rate and mechanism of such reactions.
  • the cell voltage is stepped upwards or downwards incrementally, and the current flow is monitored as the cell spontaneously charges or discharges.
  • Figure 9 shows the voltage and current traces upon charging in a PITT measurement of a conventional carbon-coated lithium iron phosphate sample. With each incremental voltage step of 10 mV, the current is observed to flow as the cell undergoes charging. It is notable that virtually no capacity is recorded until a voltage plateau is reached.
  • FIG. 12 shows a charging PITT experiment on a nanoscale Lio .9 sFeP ⁇ 4 material, in which substantial current flow, indicating charging, is seen well before the two-phase plateau voltage is reached.
  • Figure 9 shows that the phase transformation forming the delithiated Li y FePO 4 phase is more facile in the nanoscale material.
  • Figure 13 shows the capacity measured for the cell at each voltage step during the PITT charging experiment. It is seen that there is substantial charging occurring below the plateau voltage.
  • a continuous solid solution between LiFePO 4 and FePO 4 would therefore show a continuous variation between the limiting values of the lattice constants as the lithium concentration varies between one and zero.
  • the lattice constants of the materials according to one or more embodiments of the invention may therefore be used to determine the corresponding nonstoichiometry of the coexisting phases. This was accomplished by carrying out careful X-ray diffraction measurement of the subject materials at different states of lithiation (different states of charge, SOC), from which lattice parameters and other crystallographic information was obtained using Rietveld refinement, a process for analyzing diffraction data that is well- known to those skilled in the art of battery materials synthesis and characterization.
  • Figure 15 shows a powder X-ray diffraction pattern obtained from a conventional carbon-coated lithium iron phosphate material (Aldrich Chemical) at 50% SOC. To this sample was added silicon powder to provide an internal standard for the X-ray peak positions. It is seen that the peaks for LiFePO 4 olivine are well aligned with the expected peak positions for this phase, based on the data in reference 01-081-1173 from the Joint Committee on Powder Diffraction Standards (JCPDS). The peaks for the olivine form of FePO 4 are also seen in Figure 15, and are somewhat displaced from the positions for a somewhat different composition listed by JCPDS.
  • JCPDS Joint Committee on Powder Diffraction Standards
  • Figure 16 shows the powder X-ray diffraction pattern obtained from a nanoscale LiFePO 4 sample according to the invention, measured at 67% SOC. It can be seen that numerous peaks for both the "LiFePO 4 " and “FePO 4 " phases are displaced from their corresponding positions in Figure 15. A precise determination of the lattice constants in these materials was made using the Rietveld refinement method, on powder X-ray diffraction spectra carefully obtained over a wide diffraction angle range (known to those skilled in the art as the "2-theta” range) of 15 degrees to 135 degrees.
  • nanoscale Lii -x FeP ⁇ 4 having smaller a and b lattice constants and a larger c lattice constant for than conventional LiFePO 4 are obtained.
  • the lithium deficient solid solution coexists with an Li ⁇ FePO 4 phase having the lattice parameters for a, b that are larger and c that is smaller than in conventional FePO 4 .
  • a reduction in the lattice parameter of the Lii_ ⁇ FePO 4 phase has the effect of bringing the multivalent transition metal ions closer together within the structure, which also increases the degree of orbital overlap thereby changing the electronic structure of the material so as to decrease the bandgap or increase carrier mobility, thereby increasing electronic conductivity.
  • the a, b lattice constants for the lithium deficient Li i JFePO 4 is less than that for LiFePO 4 and the a, b lattice constants for the lithium rich Li y FePO 4 is greater than that for FePO 4 . Therefore, the mismatch in lattice parameters and unit cell volume is decreased in the nanoscale materials of the invention, which may have a profound influence on the electrochemical performance of the material, particularly at high charge/discharge rates. This is because the facility with which one phase is formed from the other upon charging and discharging of the electrochemical cell is dependent on the mismatch in lattice parameters (if crystalline) and the relative volumes of the two co-existing phases.
  • the differences in the respective values of any lattice constant or unit cell volume is a percentage of the mean value between the two, as has been done in Table 2. That is, the percentage difference in the a lattice constant is the difference in a between any two materials divided by the arithmetic mean value of a for those two samples.
  • the percentage differences are computed in this manner.
  • the be plane is the most preferred orientation along which one phase will grow topotaxially upon the other (or vice versa). Comparing the nanoscale and conventional materials in Table 1, these differences are 7.43%, 2.62% and 1.32% respectively for the nanoscale material, and 8.79%, 3.19%, and 1.76% respectively for the conventional material. In the Aldrich material measured at 50% SOC these differences are 8.55%, 2.88% and 1.62% respectively.
  • the nanoscale materials of the invention are defined by having a plane formed by any of the principal axes of the crystal along which the strain measured as a change in the area is less than about 1.6%, or less than about 1.5%, or less than about 1.4%. According to another embodiment, none of the planes formed by any of the principal axes of the crystal have such a strain exceeding 8%, or 7.5%, or 6%.
  • the cycle life of a rechargeable battery is typically defined as the number of charge/discharge cycles, over a specified voltage range and at a specified current rate, over which the capacity of the battery decreases to a certain percentage of the initial value.
  • Conventional cathode-active materials and rechargeable batteries using these materials including LiFePO 4 olivine and its compositional derivatives, over a voltage range of about 2 V to 3.8 V and at a current rate of about 1C, typically show a cycle life of less than 1000 cycles before the capacity decreases to 80% of its initial value.
  • the materials and devices of the invention can undergo in excess of 1000, even in excess of 2000, and in some instances in excess of 5000 cycles before decreasing in capacity by this amount.
  • the behavior of the material during the very first cycle may not be as important as the behavior during subsequent cycling. Therefore the differences in unit cell parameters and lithium concentrations desirably are measured after at least one full intercalation and deintercalation cycle between the working voltage limits of the device, and after allowing said material to rest in its state-of-charge for at least 12 hours.
  • the extent of solid solution in each endmember phase may increase with electrochemical cycling, allowing the transformation from one phase to the other to become more facile with the use of the battery. This is manifested in, amongst other behavior, as a decrease in the impedance of the battery with charge/discharge cycling.
  • the formation of one phase from the other (and vice versa) upon electrochemical cycling is made much more facile in comparison to previous materials by the fact that the materials are nanoscale, and because they have been engineered to have smaller lattice parameter and unit cell mismatch between the two co-existing phases.
  • the advantages of minimizing the mismatch stresses in order to permit facile phase transitions and high rates of charge and discharge have not previously been recognized in the field of battery materials.
  • the cathode active material LiMn 2 O 4 has been used in high power lithium ion batteries, but frequently exhibits permanent capacity loss after use or storage, related to the dissolution of manganese in the electrolyte and/or protonation of the surface of the active material particles by residual acid in the liquid electrolytes used in such cells. Since these effects are exacerbated in high surface area materials, common knowledge teaches away from the use of nanocrystalline LiMn 2 O 4 . These observations suggest that nanoscale particle sizes could be undesirable with respect to certain properties. However, using the nanoscale ion storage materials described herein, such difficulties can be overcome while retaining energy density and power density advantages.
  • the surprisingly wider range of solid solution of the nanoscale materials of the invention compared to their conventional counterparts may be due to stress, both the stress exerted by the highly curved free surface combined with the surface tension of the material, and the stress induced when the two phases coexist and a region of each phase each exerts a stress on a region of the other phase.
  • differences in the properties of the nanoscale ion storage materials described herein compared to their conventional larger scale counterparts are also due to the formation of near-surface defect layers that alter the overall defect thermodynamic state of the material.
  • the differences in physical properties and structure between the nanoscale and conventional crystalline states can be likened to the difference between the crystalline and glassy forms of a single composition, which have such clearly different thermodynamic, structural and physical properties as to be considered different materials.
  • the following mechanisms may provide a basis for unique properties of the nanocrystalline materials according to one or more embodiments of the present invention.
  • iono-covalent compounds having a lattice discontinuity such as a free surface or grain boundary, due to differences in the free energies of formation of lattice defects, the surface can become enriched in one or more atomic species relative to others.
  • LiFePO 4 stoichiometric LiFePO 4 olivine compound that is then allowed to equilibrate its free surface with its surroundings.
  • the surface is likely to become enriched in the ion having the lowest defect formation energy and/or sufficient mobility to be removed preferentially to the surface.
  • this ion is energetically and kinetically most likely to be lithium.
  • Creation of a lithium-rich surface must leave a lithium- deficient interior, in which the deficiency corresponds to the presence of lithium vacancies.
  • the lithium deficiency is not likely to be distributed uniformly across the interior. Instead, the lithium vacancies may be preferentially concentrated near the surface in a space-charge layer.
  • the spatial extent of this layer depends at thermal equilibrium on the defect concentration, the dielectric constant of the material, and the temperature. If the system is not at equilibrium, the extent of the space- charge layer depends on transport kinetics of the ions and defects as well. [0146]
  • the spatial distribution of defects is shown schematically in Figure 17.
  • the spatial extent of the space-charge layer can be of the order of one to several nanometers.
  • the near-surface concentration of vacancies or other defects can be many times greater than the concentration that would be tolerated in a bulk crystal as a solid solution, i.e., without having precipitation or phase-separation.
  • the interior of the particle has a measurably higher lithium deficiency than a conventional particle.
  • the particle now behaves in a nonstoichiometric manner, especially if the Faradaic behavior of the Li + at the surface differs from that in the bulk. X-ray diffraction measurements and electrochemical tests can detect these differences compared to conventional materials.
  • the surface lithium ions can be reacted easily by surface reactions with adjacent media such as liquid electrolyte, or evaporated upon heating or reaction with the gas phase as a lithium oxide or lithium carbonate species.
  • the nanoparticle is left more lithium-deficient than a conventional particle or crystal, yet said defects giving rise to the nonstoichiometry remain as a solid solution rather than causing the nanoparticles to form new and separate phases as in a conventional material.
  • the Fe 3+ /Fe 2+ ratio also can vary spatially with distance from the surface, and provide not only greater electronic conductivity to the particle as a whole, but a greater electronic conductivity at the surface of the particle than in the interior.
  • the criteria for having high charge rate and high discharge rate capability necessarily include a temperature of use. While in actual use, the temperature of a storage battery may vary widely, and may for example rise due to resistive heating or vary due to external heating or cooling, it is nonetheless possible to define suitable materials according to their performance at a fixed ambient temperature using a standard test which can be appreciated and readily conducted by those skilled in the art.
  • PITT potentiostatic intermittent titration test
  • ⁇ 0.1V voltage
  • the rate of current flow can be used as a measure of the rate capability of the material.
  • the inherent rate capability of a material can be determined using a PITT measurement.
  • HEV hybrid electric vehicle
  • a battery that provides only a high discharge rate, but not a high charge rate is severely limited in its utility for HEVs.
  • a cellphone or laptop computer can benefit from a short charging time (fast charging rate).
  • the discharge rate is typically much slower since the device operates on battery power over a period of hours to days.
  • a battery that merely has high discharge rate capability but not high charge rate capability is limited in its utility.
  • the nanoscale ion storage materials described herein typically contain less than about 5 weight percent, or about 3 weight percent, of any additional phase that does not substantially store ions, but may provide added electrical conductivity.
  • additional phases include, for example, carbon, a metal, or an intermetallic phase, such as a metal phosphide, metal carbide, metal nitride, or mixed intermetallic compound, such as metal carbide-nitride or metal carbide-phosphide.
  • the nanoscale material typically is formulated into an electrode by standard methods, including the addition of a few weight percent of a polymeric binder, and 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 can be used as the positive or negative electrode in a storage battery.
  • Their performance can be evaluated, for example, using laboratory cells of the coin-cell or so-called Swagelok cell types, in which a single layer of electrode is tested against a counterelectrode (typically lithium metal when the nanoscale material is a lithium storage material) using galvanostatic (constant current) or potentiostatic (constant voltage) tests or some combination of the two. Under galvanostatic conditions, the current rate can be described as "C-rate,” in which the rate is CIn, and n is the number of hours required for substantially complete charge or discharge of the cell between a selected upper and lower voltage limit.
  • the electrodes when used as the positive electrode in a lithium battery, 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 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 can have electrode formulations and physical designs and constructions that are developed through methods well-known to those skilled in the art to provide low cell impedance, so that the high rate capability of the nanoscale ion storage material can be utilized.
  • the nanoscale ion storage materials described herein when tested in such laboratory cells or in storage batteries, will exhibit greatly improved capacity retention at high charge and discharge rates compared to their coarse-grained counterparts.
  • the discharge capacity measured at a 5C rate compared to the capacity measured at a low rate of C/5 or less i.e., the capacity retention
  • the capacity retention will be about 80% or greater, in some cases about 90% or greater, or about 95% or greater.
  • the capacity retention can be about 75% or greater, in some cases about 85% or greater, for example, about 90% or greater, or about 93% or greater.
  • the capacity retention can be about 60% or greater, in some cases about 70% or greater, for example, about 80% or greater, or about 85% or greater.
  • the capacity retention can be about 50% or greater, in some cases about 60% or greater, for example, about 75% or greater, or about 80% or greater.
  • the capacity retention can be about 30% or greater, in some cases about 40% or greater, for example, about 50% or greater, or about 60% or greater.
  • the nanoscale materials described herein when used in a complete wound or stacked multilayer cell having at least 5 Wh energy at a C/5 or lower discharge rate, can provide cells with the following levels of specific power (power density) and specific energy (energy density) for substantially complete discharge starting from a fully charged state (i.e., 100% depth of discharge).
  • the cells can exhibit, for example, specific power of at least about 500 W/kg (1000 W/L) at specific energy of at least about 100 Wh/kg (205 Wh/L), specific power of at least about 950 W/kg (2000 W/L) at specific energy of at least about 95 Wh/kg (190 Wh/L), specific power of at least about 1300 W/kg (2500 W/L) at specific energy of at least about 90 Wh/kg (180 Wh/L), and specific power of at least about 1600 W/kg (3200 W/L) at specific energy of at least about 85 Wh/kg (175 Wh/L). It is understood that for shallower depth of discharge, the specific power and power density can be significantly higher than those given above. [0154] The following non-limiting examples further illustrate certain embodiments. Example 1
  • LiFePO 4 LiFePO 4
  • Iron (II) oxalate (Alfa-Aesar, 99.999%) 3.598 g
  • the precursor was thoroughly dried and then heat treated in a tube furnace under flowing argon gas (grade 5.0), first at 35O 0 C for 10 h and then at 600 0 C for 20 h.
  • the specific surface area was measured using the BET method and found to be 38.6 m 2 /g, for which the equivalent spherical particle diameter was calculated to be 43.2 nm, assuming a crystal density of 3.6 g/cm 3 .
  • the carbon content was analyzed by the combustion method and found to be below 3 weight percent, such that the measured surface area can be predominantly attributed to the nanoscale phosphate phase.
  • transmission electron microscopy imaging such as in Figures 1 and 2 showed that the observed average particle diameter was close to the equivalent spherical particle size calculated from the BET specific surface area.
  • the fired powder was formulated into an electrode having the following composition:
  • Nanoscale lithium iron phosphate powder 3.95 g
  • the coating was dried in vacuum at 100-1 10 0 C, after which it was measured to have a thickness of about 100 micrometers, and punched into discs of 1-2 cm diameter as appropriate to fit Swagelok or coin cells.
  • the electrode coatings were assembled into lithium half-cells using Swagelok or coin cell hardware, using a microporous polymer separator, lithium foil as the negative electrode (total lithium content at least ten times greater than the theoretical storage capacity of the positive electrode), and a conventional nonaqueous lithium ion battery electrolyte containing LiPF 6 as the lithium salt.
  • Figure 18 shows the specific capacity of the nanoscale lithium iron phosphate as measured from a Swagelok cell.
  • the ability of the nanoscale material to deliver high capacities at high charge or discharge rates is remarkable.
  • the discharge capacity retention here is used to describe the percentage of the capacity measured at a particular C-rate, over the voltage range 2.0-3.8V, compared to the capacity observed at C/5 rate over the same voltage range, as shown in Figure 16.
  • the capacity retention was 95.9%; at 4.4C rate, the retention was 92.1%; at 9C rate, the retention was 88.1%; at 18C rate, it was 82.6%; at 31C rate, it was 75.6%; and at 44C rate, it was 69.1%.
  • a nanoscale ion storage material having overall composition 0 0.99 FePO 4 was synthesized and tested following procedures as described in Example 1 , except that a larger batch size was made and different sources of starting materials were used. The composition was made using the following proportions of starting materials:
  • the first-charge capacity was lower than the first-discharge capacity by 11.5%, both being measured at about a C/5 rate, showing that the initial nonstoichiometry of the sample may be about 11.5%.
  • outstanding capacity retention was observed.
  • the capacity retention was about 95%, at a 1OC rate, the capacity retention was about 90%, and at a 2OC rate, the capacity retention was in the range 66-72% for three cells tested.
  • Nanoscale ion storage materials having overall compositions LiFePO 4 and Lio 95 FePO 4 were synthesized and tested following procedures as described in Example 2, with the mass of lithium carbonate being adjusted so as to achieve the specified overall compositions.
  • the LiFePO 4 and Li 0 95 FePO 4 powders were measured by the BET method to have a specific surface areas of 39.78 m 2 /g and 46.2 m /g respectively, corresponding to equivalent spherical particle diameters of 41.9 nm and 36.1 nm respectively. Combustion analysis showed the two powders to both have residual carbon concentrations of 2.3 wt % and 3 wt % respectively.
  • Figures 7 and 8 show the C/50 charge and discharge curves for these two samples compared to a commercially purchased carbon-coated LiFePO 4 from Aldrich Chemical Company of several micrometer average particle size and markedly inferior rate capability. Due to the very high rate capability of these materials, see Figure 19, these low-rate charge/discharge curves show the near-equilibrium voltages of the cells. From these curves it is seen that during continuous charge and discharge, a lithium nonstoichiometry x of at least about 15%, andy of at least about 10% is obtained.
  • Figures 12-14 show PITT measurements of the nanoscale Lio 95 FePO 4 sample as described earlier.
  • Figure 16 and Tables 1 and 2 show X-ray powder diffraction measurements of the nanoscale Lii -x FePO 4 sample as described earlier. From the Rietveld refinement of this sample, a crystallite size of about 28 nm was determined, which is close to the calculated equivalent spherical particle size and shows that the high surface area of the sample is due to nanoscale crystallites of the lithium iron phosphate and not due to a high surface area impurity or additive phase.
  • Figure 19 shows test results from three lithium half-cells constructed using Swagelok hardware as in Example 2.
  • positive electrodes using a nanoscale ion storage materials for example, those of Examples 1 and 3 (having been well-characterized in their electrochemical performance over a wide range of C-rates), are used to construct a wound cylindrical lithium-ion cell.
  • a high-rate graphite anode is employed, such as one utilizing graphitized mesocarbon microbeads (MCMB, Osaka Gas Co.) of a few micrometers mean diameter.
  • MCMB graphitized mesocarbon microbeads
  • the performance of such cells including charge capacity and energy at various C- rates, can be modeled from the volumes and masses of the cell constituents when the density, thickness and performance of individual electrodes in prototype cells is known, as in the present case.
  • the model shows that such cells will exhibit specific power of at least about 500 W/kg (1000 W/L) at specific energy of at least about 100 Wh/kg (205 Wh/L), specific power of at least about 950 W/kg (2000 W/L) at specific energy of at least about 95 Wh/kg (190 Wh/L), specific power of at least about 1300 W/kg (2500 W/L) at specific energy of at least about 90 Wh/kg (180 Wh/L), and specific power of at least about 1600 W/kg (3200 W/L) at specific energy of at least about 85 Wh/kg (175 Wh/L). It is understood that for shallower depth of discharge, the specific power and power density can be significantly higher than these values.
  • the nanoscale ion storage material of composition LiFePO 4 and having a specific surface area of 39.8 m 2 /g described in Example 3 was used.
  • a sample having a specific surface area of 48.8 m /g was prepared by the same method, described in Example 2, with the exception that the final firing was carried out at 600 0 C.
  • the commercially-purchased carbon-coated LiFePO 4 from Aldrich Chemical Company having specific surface area of 14.8 m 2 /g described in Example 3 was used. All three materials were prepare into electrodes and tested in Swagelok cells using the procedures of Example 1. OCV measurements were taken with the cells at 50% state of charge, at the measurement temperature of interest, and after waiting at least 12 hours.
  • PITT measurements were conducted as described previously, starting from a fully discharged or charged state, and using voltage steps of 5 mV or 10 mV.
  • the Aldrich sample exhibits upon charging at room temperature (23 0 C), for an overpotential of 50 mV with respect to the OCV, a characteristic behavior wherein the charging current rises slowly over time, peaking at about 4 hours, before decaying again.
  • the discharge behavior at room temperature (23 0 C) is shown, for 5 mV voltage decrements.
  • FIGS 21-24 The corresponding PITT data for the nanoscale LiFePO 4 of 39.8 m 2 /g and 48.8 m 2 /g respectively are shown in Figures 21-24.
  • Figures 21 and 22 show the 23°C charging and discharging results for the sample of 39.8 m7g.
  • Figure 21 it is seen that on the voltage step where the greatest total amount of current flows, the current decreases essentially monotonically until the lower current limit of the PITT measurement is reached, and the voltage is stepped up again.
  • Figure 22 it is seen that during discharge, the current decreases more quickly with time, and also has large absolute values in general. This discharge curve behavior corresponds to a high discharge capacity at high rates, not shown but very similar to that in Figures 5 and 19.

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Abstract

L'invention concerne des matériaux de stockage d'ions à échelle nanométrique qui présentent des propriétés uniques qui se distinguent de manière mesurable de leurs homologues à échelle plus grande. Par exemple, ces matériaux à échelle nanométrique peuvent présenter une conductivité électronique accrue, une stabilité électromécanique améliorée, une vitesse d'intercalation accrue et/ou une plage étendue de solution solide. Des matériaux à échelle nanométrique comprennent des phosphates métalliques de transition alcalins, telle que LiMPO4, M représentant un ou plusieurs métaux de transition. Ces matériau de stockages à échelle nanométrique conviennent pour produire des dispositifs tels que des batteries de stockage de haute énergie et de haute puissance, des dispositifs hybrides condensateur-batterie, et des dispositifs électrochromiques à vitesse élevée.
EP08782740.8A 2007-02-08 2008-01-31 Matériaux de stockage d'ions à échelle nanométrique Pending EP2118949A4 (fr)

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JP2015038806A (ja) * 2010-03-30 2015-02-26 大日本印刷株式会社 電極活物質およびその製造方法
JP5539802B2 (ja) * 2010-07-12 2014-07-02 シャープ株式会社 非水電解質二次電池用正極活物質、非水電解質二次電池用正極および非水電解質二次電池
SG11201810610XA (en) 2016-06-08 2018-12-28 Solidenergy Systems Llc High energy density, high power density, high capacity, and room temperature capable "anode-free" rechargeable batteries
CN109817907B (zh) * 2019-01-03 2021-02-26 北京泰丰先行新能源科技有限公司 正极活性材料、含有该正极活性材料的正极和锂二次电池
KR20230095271A (ko) * 2021-12-22 2023-06-29 포스코홀딩스 주식회사 리튬 이차 전지용 양극 활물질, 이의 제조방법 및 이를 포함하는 리튬 이차 전지
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