Abstract
The invention relates to novel materials of the formula: A.sub.uM.sup.1.sub.vM.sup.2.sub.wM.sup.3.sub.XM.sup.4.sub.yM.sup.5.sub.ZO.sub.2 wherein A comprises one or more alkali metals selected from lithium, sodium and potassium; M.sup.1 is nickel in oxidation state +2 M.sup.2 comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium; M.sup.3 comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt; M.sup.4 comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium; M.sup.5 comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; further wherein U is in the range 1<U<2; V is in the range 0.25<V<1; W is in the range 0<W<0.75; X is in the range 0≦X<0.5; Y is in the range 0≦Y<0.5; Z is in the range 0≦Z<0.5; and further wherein (U+V+W+X+Y+Z)≦3. Such materials are useful, for example, as electrode materials in sodium and/or lithium ion battery applications.
Claims
1. A compound of the formula:
A.sub.UM.sup.1.sub.VM.sup.2.sub.WM.sup.3.sub.XM.sup.4.sub.YM.sup.5.sub.ZO.sub.2 wherein A is one or more alkali metals selected from sodium and potassium; M.sup.1 is nickel in oxidation state +2 M.sup.2 comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium; M.sup.3 comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt; M.sup.4 comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium; M.sup.5 comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; further wherein U is in the range 1<U<2; V is in the range 0.25<V<1; W is in the range 0<W<0.75; X is in the range 0<X<0.5; Y is in the range 0≦Y<0.5; Z is in the range 0≦Z<0.5; and further wherein U+V+W+X+Y+Z≦3.
2. A compound according to claim 1 wherein U is in the range 1<U<1.5; V is in the range 0.25<V<1; W is in the range 0<W<0.75; X is in the range 0<X≦0.25; Y is in the range 0≦Y≦0.25; Z is in the range 0≦Z≦0.25.
3. A compound according to claim 1 of the formula:
Na.sub.1.1Ni.sub.0.3Mn.sub.0.5Mg.sub.0.05Ti.sub.0.05O.sub.2; or Na.sub.1.05Ni.sub.0.4Mn.sub.0.5Mg.sub.0.025Ti.sub.0.025O.sub.2.
4. An electrode comprising an active compound according to claim 1.
5. An electrode according to claim 4 used in conjunction with a counter electrode and one or more electrolyte materials.
6. An electrode according to claim 5 wherein the electrolyte material comprises an aqueous electrolyte material.
7. An electrode according to claim 5 wherein the electrolyte material comprises a non-aqueous electrolyte.
8. An energy storage device comprising an electrode according to claim 4.
9. An energy storage device according to claim 8 suitable for use as one or more of the following: a sodium and/or lithium and/or potassium ion cell; a sodium metal and/or lithium metal and/or potassium metal ion cell; non-aqueous electrolyte sodium ion and/or lithium ion and/or potassium ion cell, an aqueous electrolyte sodium ion and/or lithium ion and/or potassium ion cell.
10. A rechargeable battery comprising an electrode according to claim 4.
11. An electrochemical device comprising an electrode according to claim 4.
12. An electrochromic device comprising an electrode according to claim 4.
13. A method of preparing the compounds according to claim 1 comprising the steps of: a) mixing starting materials together; b) heating the mixed starting materials in a furnace at a temperature of between 400° C. and 1500° C., for between 2 and 20 hours to give a reaction product; and c) allowing the reaction product to cool.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The present invention will now be described with reference to the following figures in which:
(2) FIG. 1(A) relates to a Na-ion Cell and shows the third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(3) FIG. 1(B) relates to a Na-ion Cell and shows the third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(4) FIG. 1(C) relates to a Na-ion Cell and shows the Charge-Discharge Voltage Profiles for first 4 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(5) FIG. 1(D) relates to a Na-ion Cell and shows the Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(6) FIG. 1E relates to a Cycle Discharge Voltage Profile of a further embodiment of the invention.
(7) FIG. 2(A) relates to a Na-ion Cell and shows the third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(8) FIG. 2(B) relates to a Na-ion Cell and shows the third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for a Hard Carbon//Na.sub.1.05/Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(9) FIG. 2(C) relates to a Na-ion Cell and shows the Charge-Discharge Voltage Profiles for first 4 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(10) FIG. 2(D) relates to a Na-ion Cell and shows Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(11) FIG. 3(A) relates to a Na-ion Cell and shows the third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(12) FIG. 3(B) relates to a Na-ion Cell and shows the third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(13) FIG. 3(C) relates to a Na-ion Cell and shows Charge-Discharge Voltage Profiles for first 4 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(14) FIG. 3(D) relates to a Na-ion Cell and shows Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 Cell;
(15) FIG. 4(A) relates to a Na-ion Cell and shows the third Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(16) FIG. 4(B) relates to a Na-ion Cell and shows the third Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2Cell;
(17) FIG. 4(C) relates to a Na-ion Cell and shows the Charge-Discharge Voltage Profiles for first 4 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(18) FIG. 4(D) relates to a Na-ion Cell and shows the Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 Cell;
(19) FIG. 5(A) relates to a Na-ion Cell and shows the First Cycle Discharge Voltage Profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 Cell;
(20) FIG. 5(B) relates to a Na-ion Cell and shows Second Cycle Differential Capacity Profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 Cell;
(21) FIG. 5(C) relates to a Na-ion Cell and shows Charge-Discharge Voltage Profiles for first 3 cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for a Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 Cell;
(22) FIG. 5(D) relates to a Na-ion Cell and shows Cycle Life Performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for a Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 Cell;
(23) FIG. 6(A) is an XRD of Na.sub.1.1Ni.sub.0.3Mn.sub.0.5Mg.sub.0.05Ti.sub.0.05O.sub.2 prepared according to Example 1 of the present invention; and
(24) FIG. 6(B) is an XRD of Na.sub.1.05Ni.sub.0.4Mn.sub.0.5Mg.sub.0.025Ti.sub.0.025O.sub.2 prepared according to Example 2 of the present invention.
DETAILED DESCRIPTION
(25) The materials according to the present invention are prepared using the following generic method:
(26) Generic Synthesis Method:
(27) The required amounts of the precursor materials are intimately mixed together and pressed into a pellet. The resulting mixture is then heated in a tube furnace or a chamber furnace using either an ambient air atmosphere, or a flowing inert atmosphere (e.g. argon or nitrogen), at a furnace temperature of between 400° C. and 1500° C. until reaction product forms. For some materials a single heating step is used and for others (as indicated below in Table 1) more than one heating step is used. When cool, the reaction product is removed from the furnace and ground into a powder.
(28) The above method was used to prepare a number of alkali-rich doped nickelates per Examples 1 to 4, as summarised below in Table 1:
(29) TABLE-US-00001 TABLE 1 STARTING FURNACE EXAMPLE TARGET COMPOUND MATERIALS CONDITIONS 1 Na.sub.1.1Ni.sub.0.3Mn.sub.0.5Mg.sub.0.05Ti.sub.0.05O.sub.2 Na.sub.2CO.sub.3, 1) Air/900° C., dwell NiCO.sub.3. time of 8 hours. MnO.sub.2 2) Air/900° C., dwell Mg(OH).sub.2 time of 8 hours. TiO.sub.2 3) Air/950° C., dwell time of 8 hours. 2 Na.sub.1.05Ni.sub.0.4Mn.sub.0.5Mg.sub.0.025Ti.sub.0.025O.sub.2 Na.sub.2CO.sub.3 1) Air/900° C., dwell NiCO.sub.3 time of 8 hours. Mg(OH).sub.2 2) Air/900° C., dwell TiO.sub.2 time of 8 hours. 3) Air/950° C., dwell time of 8 hours. 3 Na.sub.1.1Ni.sub.0.3Ti.sub.0.05Mg.sub.0.05Mn.sub.0.5O.sub.2 Na.sub.2CO.sub.3 Air/900° C., dwell NiCO.sub.3 time of 8 hours. Mg(OH).sub.2 MnO.sub.2 4 Na.sub.1.05Ni.sub.0.4Ti.sub.0.025Mg.sub.0.025Mn.sub.0.5O.sub.2 Na.sub.2CO.sub.3 Air/900° C., dwell NiCO.sub.3 time of 8 hours. MnO.sub.2 Mg(OH).sub.2 MnO.sub.2
Product Analysis Using XRD
(30) All of the product materials were analysed by X-ray diffraction techniques using a Siemens D5000 powder diffractometer to confirm that the desired target materials had been prepared, to establish the phase purity of the product material and to determine the types of impurities present. From this information it is possible to determine the unit cell lattice parameters.
(31) The operating conditions used to obtain the XRD spectra illustrated in FIGS. 1A, 2A, 3A, 4A, 5 and 6A are as follows:
(32) Slits sizes: 1 mm, 1 mm, 0.1 mm
(33) Range: 2θ=5°-60°
(34) X-ray Wavelength=1.5418 Å (Angstoms) (Cu Kα)
(35) Speed: 0.5 seconds/step
(36) Increment: 0.015°
(37) Electrochemical Results
(38) The target materials were tested either i) using a lithium metal anode test cell, or ii) using a Na-ion test cell using a hard carbon anode. It is also possible to test using a Li-ion cell with a graphite anode. Cells may be made using the following procedures:
(39) Generic Procedure to Make a Lithium Metal Electrochemical Test Cell
(40) The positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent. The conductive carbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf Atochem Inc.) is used as the binder, and acetone is employed as the solvent. The slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates. The electrode is then dried further at about 80° C. The electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder. Optionally, an aluminium current collector may be used to contact the positive electrode. Metallic lithium on a copper current collector may be employed as the negative electrode. The electrolyte comprises one of the following: (i) a 1 M solution of LiPF.sub.6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) in a weight ratio of 1:1; (ii) a 1 M solution of LiPF.sub.6 in ethylene carbonate (EC) and diethyl carbonate (DEC) in a weight ratio of 1:1; or (iii) a 1 M solution of LiPF.sub.6 in propylene carbonate (PC) A glass fibre separator (Whatman, GF/A) or a porous polypropylene separator (e.g. Celgard 2400) wetted by the electrolyte is interposed between the positive and negative electrodes.
(41) Generic Procedure to Make a Hard Carbon Na-Ion Cell
(42) The positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent. The conductive carbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf Atochem Inc.) is used as the binder, and acetone is employed as the solvent. The slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates. The electrode is then dried further at about 80° C. The electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder. Optionally, an aluminium current collector may be used to contact the positive electrode.
(43) The negative electrode is prepared by solvent-casting a slurry of the hard carbon active material (Carbotron P/J, supplied by Kureha), conductive carbon, binder and solvent. The conductive carbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf Atochem Inc.) is used as the binder, and acetone is employed as the solvent. The slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates. The electrode is then dried further at about 80° C. The electrode film contains the following components, expressed in percent by weight: 84% active material, 4% Super P carbon, and 12% Kynar 2801 binder. Optionally, a copper current collector may be used to contact the negative electrode.
(44) Generic Procedure to Make a Graphite Li-Ion Cell
(45) The positive electrode is prepared by solvent-casting a slurry of the active material, conductive carbon, binder and solvent. The conductive carbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf Atochem Inc.) is used as the binder, and acetone is employed as the solvent. The slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates. The electrode is then dried further at about 80° C. The electrode film contains the following components, expressed in percent by weight: 80% active material, 8% Super P carbon, and 12% Kynar 2801 binder. Optionally, an aluminium current collector may be used to contact the positive electrode.
(46) The negative electrode is prepared by solvent-casting a slurry of the graphite active material (Crystalline Graphite, supplied by Conoco Inc.), conductive carbon, binder and solvent. The conductive carbon used is Super P (Timcal). PVdF co-polymer (e.g. Kynar Flex 2801, Elf Atochem Inc.) is used as the binder, and acetone is employed as the solvent. The slurry is then cast onto glass and a free-standing electrode film is formed as the solvent evaporates. The electrode is then dried further at about 80° C. The electrode film contains the following components, expressed in percent by weight: 92% active material, 2% Super P carbon, and 6% Kynar 2801 binder. Optionally, a copper current collector may be used to contact the negative electrode.
(47) Cell Testing
(48) The cells are tested as follows using Constant Current Cycling techniques.
(49) The cell is cycled at a given current density between pre-set voltage limits. A commercial battery cycler from Maccor Inc. (Tulsa, Okla., USA) is used. On charge, sodium (lithium) ions are extracted from the active material. During discharge, sodium (lithium) ions are re-inserted into the active material.
(50) Results:
(51) The data shown in FIGS. 1A, 1B, 1C and 1D are derived from the constant current cycling data for a Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 active material in a Na-ion cell where this cathode material was coupled with a Hard Carbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 M solution of NaClO.sub.4 in propylene carbonate. The constant current data were collected at an approximate current density of 0.10 mA/cm.sup.2 between voltage limits of 1.50 and 4.00 V. To ensure that the Na-ion cell was fully charged, the cell was potentiostatically held at 4.0 V at the end of the constant current charging process until the current density dropped to 20% of the constant current value. The testing was carried out at room temperature. During the cell charging process, sodium ions are extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
(52) FIG. 1A shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. The cathode specific capacity in this cycle corresponds to 68 mAh/g.
(53) FIG. 1B shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. These symmetrical data demonstrate the excellent reversibility of the ion extraction-insertion reactions in this Na-ion cell.
(54) FIG. 1C shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. These data demonstrate that the level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes) is extremely small, indicating the excellent kinetics of the extraction-insertion reactions.
(55) FIG. 1D shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. The cell shows excellent reversibility with the delivered cathode specific capacity increasing over the first 20 cycles. The cathode specific capacity reaches around 96 mAh/g after 25 cycles.
(56) Referring to FIGS. 2A, 2B, 2C and 2D
(57) The data shown in FIGS. 2A, 2B, 2C and 2D are derived from the constant current cycling data for a Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 active material in a Na-ion cell where this cathode material was coupled with a Hard Carbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 M solution of NaClO.sub.4 in propylene carbonate. The constant current data were collected at an approximate current density of 0.10 mA/cm.sup.2 between voltage limits of 1.50 and 4.00 V. To charge the Na-ion cell fully it was potentiostatically held at 4.0 V at the end of the constant current charging process until the current density dropped to 20% of the constant current value. The testing was carried out at room temperature. During the cell charging process, sodium ions are extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
(58) FIG. 2A shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. The cathode specific capacity in this cycle corresponds to 88 mAh/g.
(59) FIG. 2B shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. These symmetrical data demonstrate the excellent reversibility of the ion extraction-insertion reactions in this Na-ion cell.
(60) FIG. 2C shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. These data demonstrate that the level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes) is extremely small, indicating the excellent kinetics of the extraction-insertion reactions.
(61) FIG. 2D shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. The cell shows good reversibility with the delivered cathode specific capacity reaching around 96 mAh/g after 8 cycles.
(62) Referring to FIGS. 3A, 3B, 3C and 3D
(63) The data shown in FIGS. 3A, 3B, 3C and 3D are derived from the constant current cycling data for a Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 active material in a Na-ion cell where this cathode material was coupled with a Hard Carbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 M solution of NaClO.sub.4 in propylene carbonate. The constant current data were collected at an approximate current density of 0.10 mA/cm.sup.2 between voltage limits of 1.50 and 4.00 V. To charge the Na-ion cell fully, it was potentiostatically held at 4.0 V at the end of the constant current charging process until the current density dropped to 20% of the constant current value. The testing was carried out at room temperature. During the cell charging process, sodium ions are extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
(64) FIG. 3A shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. The cathode specific capacity in this cycle corresponds to 75 mAh/g.
(65) FIG. 3B shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. These symmetrical data demonstrate the excellent reversibility of the ion extraction-insertion reactions in this Na-ion cell.
(66) FIG. 3C shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. These data demonstrate that the level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes) is extremely small, indicating the excellent kinetics of the extraction-insertion reactions.
(67) FIG. 3D shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//Na.sub.1.10Ni.sub.0.30Mn.sub.0.50Mg.sub.0.05Ti.sub.0.05O.sub.2 cell. The cell shows good reversibility.
(68) Referring to FIGS. 4A, 4B, 4C and 4D.
(69) The data shown in FIGS. 4A, 4B, 4C and 4D are derived from the constant current cycling data for a Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 active material in a Na-ion cell where this cathode material was coupled with a Hard Carbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 M solution of NaClO.sub.4 in propylene carbonate. The constant current data were collected at an approximate current density of 0.10 mA/cm.sup.2 between voltage limits of 1.50 and 4.00 V. To charge the Na-ion cell fully, it was potentiostatically held at 4.0 V at the end of the constant current charging process until the current density dropped to 20% of the constant current value. The testing was carried out at room temperature. During the cell charging process, sodium ions are extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
(70) FIG. 4A shows the third cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. The cathode specific capacity in this cycle corresponds to 84 mAh/g.
(71) FIG. 4B shows the third cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. These symmetrical data demonstrate the excellent reversibility of the ion extraction-insertion reactions in this Na-ion cell.
(72) FIG. 4C shows the first four charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. These data demonstrate that the level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes) is extremely small, indicating the excellent kinetics of the extraction-insertion reactions.
(73) FIG. 4D shows the cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//Na.sub.1.05Ni.sub.0.40Mn.sub.0.50Mg.sub.0.025Ti.sub.0.025O.sub.2 cell. The cell shows good reversibility.
(74) Referring to FIGS. 5A, 5B, 5C and 5D
(75) The data shown in FIGS. 5A, 5B, 5C and 5D are derived from the constant current cycling data for a Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 active material in a Na-ion cell where this cathode material was coupled with a Hard Carbon (Carbotron P/J) anode material. The electrolyte used is a 0.5 M solution of NaClO.sub.4 in propylene carbonate. The constant current data were collected at an approximate current density of 0.10 mA/cm.sup.2 between voltage limits of 1.50 and 4.00 V. To charge the Na-ion cell fully, it was potentiostatically held at 4.0 V at the end of the constant current charging process until the current density dropped to 20% of the constant current value. The testing was carried out at room temperature. During the cell charging process, sodium ions are extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions are extracted from the Hard Carbon and re-inserted into the cathode active material.
(76) FIG. 5A shows the first cycle discharge voltage profile (Na-ion Cell Voltage [V] versus Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 cell. The cathode specific capacity in this cycle corresponds to 77 mAh/g.
(77) FIG. 5B shows the second cycle differential capacity profiles (Differential Capacity [mAh/g/V] versus Na-ion Cell Voltage [V]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 cell. These symmetrical data demonstrate the excellent reversibility of the ion extraction-insertion reactions in this Na-ion cell.
(78) FIG. 5C shows the first three charge-discharge cycles (Na-ion Cell Voltage [V] versus Cumulative Cathode Specific Capacity [mAh/g]) for the Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 cell. These data demonstrate that the level of voltage hysteresis (i.e. the voltage difference between the charge and discharge processes) is extremely small, indicating the excellent kinetics of the extraction-insertion reactions.
(79) FIG. 5D shows the initial cycle life performance (Cathode Specific Capacity [mAh/g] versus Cycle Number) for the Hard Carbon//Na.sub.1.05Ni.sub.0.425Mn.sub.0.525O.sub.2 cell. The cell shows good reversibility.
