Abstract
The invention relates to a novel process for the preparation of metal-containing compounds comprising the steps of a) forming a mixture comprising i) elemental phosphorus and ii) one or more metal-containing precursor compounds, and b) heating the mixture to a temperature of at least 150 C. Materials made by such a process are useful, for example, as electrode materials in alkali metal-ion battery applications.
Claims
1. A process for the preparation of a metal-containing compound comprising the steps of: a) forming a mixture comprising: i) elemental phosphorus; and ii) one or more metal-containing precursor compounds, wherein the metal in each metal-containing precursor compound has an initial average oxidation state; and b) heating the mixture to a temperature of at least 300 C. to give a reaction product; wherein the one or more metal-containing precursor compounds comprise one or more metals selected from transition metals, non-transition metals and metalloids; wherein the initial average oxidation state of the one or more metals in the metal-containing precursor compounds is reduced during the reaction process; wherein at least a portion of the elemental phosphorous is oxidized and incorporated into the metal containing compound at an oxidation state higher than the oxidation state of elemental phosphorous; and further wherein the heating step b) is performed in the absence of a solvent, except optionally water.
2. The process according to claim 1 wherein the mixture further comprises one or more alkali metal-containing precursor compounds.
3. The process according to claim 1, wherein the metal-containing compound has the formula:
A.sub.aM.sub.b(X.sub.cY.sub.d).sub.eZ.sub.f wherein: A is an alkali metal selected from one or more of lithium, sodium and potassium; M comprises one or more metals selected from transition metals, non-transition metals, and metalloids; (X.sub.cY.sub.d).sub.e is at least one first anion; and Z is at least one second anion wherein a 0; b >0; c >0; d 0; e >0 and f 0; wherein a, b, c, d, e and f are chosen to maintain electroneutrality.
4. The process according to claim 3 wherein M is a metal selected from one or more of titanium, vanadium, niobium, tantalum, hafnium, chromium, molybdenum, tungsten, manganese, iron, osmium, cobalt, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, aluminium, scandium, yttrium, zirconium, technetium, rhenium, ruthenium, rhodium, iridium, mercury, gallium, indium, tin, lead, bismuth, magnesium, calcium, beryllium, strontium and barium, boron, silicon, germanium, arsenic, antimony and tellurium.
5. The process according to claim 3 wherein X comprises one or more elements selected from titanium, vanadium, chromium, arsenic, molybdenum, tungsten, niobium, manganese, aluminium, selenium, boron, oxygen, carbon, silicon, phosphorus, nitrogen, sulfur, fluorine, chlorine, bromine and iodine.
6. The process according to claim 3 wherein Y is selected from one or more halides, sulfur-containing groups, oxygen-containing groups and mixtures thereof.
7. The process according to claim 3 wherein Z is selected from one or more halides, hydroxide-containing groups and mixtures thereof.
8. The process according to claim 3 wherein X comprises phosphorus.
9. The process according to claim 8 wherein (X.sub.cY.sub.d).sub.e is a PO.sub.4 and/or P.sub.2O.sub.7 moiety.
10. The process according to claim 3 wherein X comprises sulfur.
11. The process according to claim 10 wherein (X.sub.cY.sub.d).sub.e is a SO.sub.4 moiety.
12. The process according to claim 3 wherein when a=0, (X.sub.cY.sub.d).sub.e is not a phosphide group.
13. The process according to claim 3, wherein the metal-containing compound is selected from one or more of the group consisting of LiFePO.sub.4, LiMnPO.sub.4, LiCoPO.sub.4, LiNiPO.sub.4, NaFePO.sub.4, NaMnPO.sub.4, NaCoPO.sub.4, NaNiPO.sub.4, LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4, Li.sub.3V.sub.2(PO.sub.4).sub.3, Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7, Na.sub.3V.sub.2(PO.sub.4).sub.3, LiMn.sub.0.5Fe.sub.0.5PO.sub.4, Na.sub.7V.sub.4(P.sub.2O.sub.7).sub.4PO.sub.4, Na.sub.7V.sub.3(P.sub.2O.sub.7).sub.4, Na.sub.2Fe(SO.sub.4).sub.2, NaVPO.sub.4F, LiVPO.sub.4F, Na.sub.3V(PO.sub.4).sub.2, Li.sub.3V(PO.sub.4).sub.2, NaVOPO.sub.4, LiVOPO.sub.4, LiV.sub.2O.sub.5, NaV.sub.2O.sub.5, NaVO.sub.2, VPO.sub.4, MoP.sub.2O.sub.7, MoOPO.sub.4, Fe.sub.3(PO.sub.4).sub.2, Na.sub.82xFe.sub.4+x(P.sub.2O.sub.7).sub.4, Na.sub.82xMn.sub.4+x(P.sub.2O.sub.7).sub.4, Na.sub.2MnP.sub.2O.sub.7, Na.sub.2FeP.sub.2O.sub.7, Na.sub.2CoP.sub.2O.sub.7, Na.sub.4Mn.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7, Na.sub.4Co.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7, Na.sub.4Ni.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7, NaFeSO.sub.4F, LiFeSO.sub.4F, NaMnSO.sub.4F, LiMnSO.sub.4F, Na.sub.2Fe.sub.2(SO.sub.4).sub.3, Li.sub.2Fe.sub.2(SO.sub.4).sub.3, Li.sub.2Fe(SO.sub.4).sub.2, Na.sub.2FePO.sub.4F, Na.sub.2MnPO.sub.4F, Na.sub.2CoPO.sub.4F and Na.sub.2NiPO.sub.4F.
14. The process according to claim 3, wherein the metal-containing compound has the formula: LiMPO.sub.4, where M is a metal selected from one or more of manganese, iron, cobalt, nickel, copper, zinc, magnesium and calcium.
15. The process according to claim 3, wherein the metal-containing compound is selected from one or more of Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, FePO.sub.4.xH.sub.2O, FePO.sub.4, Fe.sub.3(PO.sub.4).sub.2, FeSO.sub.4.xH.sub.2O, Fe(NO.sub.3).sub.3, Fe(CH.sub.3CO.sub.2).sub.2, C.sub.6H.sub.8O.sub.7xFe.sup.3+.yNH.sub.3 (ammonium iron (III) citrate), C.sub.6H.sub.5FeO.sub.7 (iron (III) citrate) and Fe(C.sub.5H.sub.7O.sub.2).sub.3 (iron (III) 2,4-petanedionate).
16. The process according to claim 1, wherein the mixture further comprises one or more conductive materials.
17. The process according to claim 3 wherein at least one conductive material is formed in situ during the heating step.
18. The process according to claim 1, wherein the mixture further comprises one or more compounds selected from LiH.sub.2PO.sub.4, Li.sub.2CO.sub.3, Li.sub.2HPO.sub.4, LiOH, LiOH.H.sub.2O, H.sub.3PO.sub.4, (NH.sub.4).sub.2HPO.sub.4and (NH.sub.4)H.sub.2PO.sub.4.
19. The process according to claim 1 wherein step b) is conducted under an atmosphere comprising a partial pressure of oxygen.
20. The process according to claim 1 wherein the elemental phosphorus comprises red phosphorus.
21. The process according to claim 16, wherein the at least one conductive material comprises one or more of a transition metal phosphide, a non-transition metal phosphide, or metalloid phosphide.
22. The process according to claim 1, wherein the reaction product comprises LiFePO.sub.4 and at least one conductive phosphide-containing compounds.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The present invention will now be described with reference to the following figures in which:
(2) FIG. 1A is an XRD profile for LiFePO.sub.4 active material produced according to Example 1 of the present invention;
(3) FIG. 1B shows the voltage profile (electrode potential versus cumulative specific io capacity) for LiFePO.sub.4 active material produced according to Example 1 of the present invention;
(4) FIG. 1C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4 active material produced according to Example 1 of the present invention;
(5) FIG. 2A is an XRD profile for LiFePO.sub.4 active material produced according to Example 2 of the present invention;
(6) FIG. 2B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4 active material produced according to Example 2 of the present invention;
(7) FIG. 2C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4 active material produced according to Example 2 of the present invention;
(8) FIG. 3A is an XRD profile for LiFePO.sub.4 active material produced according to Example 3 of the present invention;
(9) FIG. 3B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4 active material produced according to Example 3 of the present invention;
(10) FIG. 3C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4 active material produced according to Example 3 of the present invention;
(11) FIG. 4A is an XRD profile for LiFePO.sub.4 active material produced according to comparative Example 4;
(12) FIG. 4B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4 active material produced according to comparative Example 4;
(13) FIG. 4C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4 active material produced according to comparative io Example 4;
(14) FIG. 5A is an XRD profile for LiFePO.sub.4 active material produced according to comparative Example 5;
(15) FIG. 5B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4 active material produced according to Example 5;
(16) FIG. 5C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4 active material produced according to comparative Example 5;
(17) FIG. 6A is an XRD profile for Li.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 6 of the present invention;
(18) FIG. 6B shows the voltage profile (electrode potential versus cumulative specific capacity) for Li.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 6 of the present invention;
(19) FIG. 6C shows the differential capacity profile (differential capacity versus electrode potential) for Li.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 6 of the present invention;
(20) FIG. 7A is an XRD profile for LiMn.sub.0.5Fe.sub.0.5PO.sub.4 active material produced according to Example 7 of the present invention;
(21) FIG. 7B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiMn.sub.0.5Fe.sub.0.5PO.sub.4 active material produced according to Example 7 of the present invention;
(22) FIG. 7C shows the differential capacity profile (differential capacity versus electrode potential) for LiMn.sub.0.5Fe.sub.0.5PO.sub.4 active material produced according to Example 7 of the present invention;
(23) FIG. 8A is an XRD profile for LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4 active material produced according to Example 8 of the present invention;
(24) FIG. 8B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4 active material produced according to Example 8 of the present invention;
(25) FIG. 8C shows the differential capacity profile (differential capacity versus electrode potential) for LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4 active material produced according to Example 8 of the present invention;
(26) FIG. 9A is an XRD profile for Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 active material produced according to Example 9 of the present invention;
(27) FIG. 9B shows the voltage profile (electrode potential versus cumulative specific capacity) for Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 active material produced according to Example 9 of the present invention;
(28) FIG. 9C shows the differential capacity profile (differential capacity versus electrode potential) for Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 active material produced according to Example 9 of the present invention;
(29) FIG. 10A is an XRD profile for Na.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 10 of the present invention (asterisks denote peaks due to Na.sub.3V(PO.sub.4).sub.2 impurity);
(30) FIG. 10B shows the voltage profile (electrode potential versus cumulative specific capacity) for Na.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 10 of the present invention;
(31) FIG. 10C shows the differential capacity profile (differential capacity versus electrode potential) for Na.sub.3V.sub.2(PO.sub.4).sub.3 active material produced according to Example 10 of the present invention;
(32) FIG. 11A is an XRD profile for LiFePO.sub.4/Fe.sub.2P composite active material produced according to Example 11 of the present invention (asterisks denote peaks due to Fe.sub.2P);
(33) FIG. 11B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4/Fe.sub.2P composite active material produced according to Example 11 of the present invention;
(34) FIG. 11C shows the differential capacity profile (differential capacity versus electrode potential) for LiFePO.sub.4/Fe.sub.2P composite active material produced according to Example 11 of the present invention;
(35) FIG. 12 shows the basic schematic diagram of a sealed tube furnace as used in Example 12 of the present invention;
(36) FIG. 13A is an XRD profile for LiFePO.sub.4 produced according to Example 12 of the present invention (impurity peaks are denoted as *Fe.sub.2P, Li.sub.3PO.sub.4 and ^Fe.sub.2O.sub.3;
(37) FIG. 13B shows the voltage profile (electrode potential versus cumulative specific capacity) for LiFePO.sub.4 produced according to Example 12 of the present invention;
(38) FIG. 13C shows the first cycle differential capacity profile (Differential Capacity versus Electrode Voltage (V vs. Li)) for LiFePO.sub.4 prepared according to Example 12 of the present invention; and
(39) FIG. 13D shows the cycling performance (Cathode Specific Capacity (mAh/g) vs. Cycle Number) for LiFePO.sub.4 prepared according to Example 12 of the present invention.
DETAILED DESCRIPTION
(40) General Method
(41) 1) Intimately mix together the starting materials in the correct stoichiometric ratio and press into a pellet.
(42) 2) Heat the resulting mixture in a furnace under an inert atmosphere, at a furnace temperature of between 300 C. and 800 C. until reaction product forms.
(43) 3) Allow the product to cool before grinding it to a powder.
(44) The desired target reaction product is obtainable irrespective of the order in which the starting materials are mixed together. However, if a high-energy mixing process is used, then certain advantages may be obtained if the starting materials minus the elemental phosphorus are mixed with high energy first, before adding elemental phosphorus and mixing using a less vigorous mixing process.
(45) The starting materials and reaction conditions used in Examples 1 to 12 are summarised in Table 1 below:
(46) TABLE-US-00001 TABLE 1 REACTION EXAMPLE STARTING MATERIALS TARGET PRODUCT CONDITIONS 1 0.5 Li.sub.2CO.sub.3 LiFePO.sub.4 Mixing solvent: 1 FePO.sub.4 (sample X0851, Acetone. 0.2 Red phosphorus cell#210021) N.sub.2, 550 C., dwell time (0% excess reducing of 6 hours. power) [FePO.sub.4 prepd by heating FePO.sub.42H.sub.2O at 400 C., in air, for 16 h] 2 0.09 Li.sub.2CO.sub.3 LiFePO.sub.4 Mixing solvent: 0.82 LiH.sub.2PO.sub.4 (sample X0776, Acetone. 0.5 Fe.sub.2O.sub.3 Cell #209052) N.sub.2, 650 C., dwell time of 0.18 Red phosphorus (10% 8 hours. deficient reducing power) 3 0.12 Li.sub.2CO.sub.3 LiFePO.sub.4 Mixing solvent: None. 0.76 LiH.sub.2PO.sub.4 (sample X0686, N.sub.2, 650 C., dwell time of 0.50 Fe.sub.2O.sub.3 Cell #208052) 6 hours. 0.24 Red phosphorus (20% No carbon in the excess reducing power) precursor mix and no carbon in the electrode 4 1 LiH.sub.2PO.sub.4 LiFePO.sub.4 Mixing solvent: None. Comparative 1 Fe(C.sub.2O.sub.4)2H.sub.2O (sample X0650, N.sub.2, 750 C., dwell time of Cell # 207072) 8 hours. 5 1 LiH.sub.2PO.sub.4 LiFePO.sub.4 Mixing solvent: None. Comparative 0.5 Fe.sub.2O.sub.3 (sample X0649, N.sub.2, 750 C., dwell time of 0.625 C Cell #207071) 8 hours. 6 0.4 Li.sub.2CO.sub.3 Li.sub.3V.sub.2(PO.sub.4).sub.3 Mixing solvent: Acetone 2.2 LiH.sub.2PO.sub.4 (sample X0773, N.sub.2, 650 C., dwell time of 1 V.sub.2O.sub.5 Cell #209046) 8 hours. 0.8 Red phosphorus (0% excess reducing power) 7 0.12 Li.sub.2CO.sub.3 LiMn.sub.0.5Fe.sub.0.5PO.sub.4 Mixing solvent: Acetone 0.76 LiH.sub.2PO.sub.4 (sample X0703, N.sub.2, 650 C., dwell time of 0.25 Mn.sub.2O.sub.3 Cell # 208031) 6 hours. 0.25 Fe.sub.2O.sub.3 0.24 Red phosphorus (20% excess reducing power) 8 0.084 Li.sub.2CO.sub.3 LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4 Mixing solvent: Acetone 0.832 LiH.sub.2PO.sub.4 (sample X0771, N.sub.2, 600 C., dwell time of 0.25Mn.sub.2O.sub.3 Cell # 209045) 6 hours. 0.1 Fe.sub.2O.sub.3 0.3 Mg(OH).sub.2 0.168 Red phosphorus (20% excess reducing power) 0.875 C (added as a conductive additive) 9 1 Na.sub.4P.sub.2O.sub.7 Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 Mixing solvent: Acetone 3 FeC.sub.2O.sub.4H.sub.2O (sample X0761 N.sub.2, 300 C., dwell time of 1.4 NH.sub.4H.sub.2PO.sub.4 Cell # 209030) 4 hours 0.6 Red phosphorus N.sub.2, 500 C., dwell time of 3.75 C (added as a 6 hours conductive additive) 10 0.4 Na.sub.2CO.sub.3 Na.sub.3V.sub.2(PO.sub.4).sub.3 Mixing solvent: Acetone 2.2 NaH.sub.2PO.sub.4 (sample X0757 N.sub.2, 650 C., dwell time of 1 V.sub.2O.sub.5 Cell # 210042) 8 hours 0.8 Red phosphorus (0% excess reducing power) 11 0.14 Li.sub.2CO.sub.3 LiFePO.sub.4/Fe.sub.2P Mixing solvent: Acetone 0.72 LiH.sub.2PO.sub.4 Composite N.sub.2, 650 C., dwell time of 0.55 Fe.sub.2O.sub.3 (sample X0740 6 hours 0.28 Red phosphorus (40% Cell # 209008) excess reducing power) 12 0.5 Li.sub.2CO.sub.3 LiFePO.sub.4 Mixing solvent: Acetone 0.5 Fe.sub.2O.sub.3 (sample X1322 Sealed in Air, dwell 1.0 Red phosphorus Cell #305086) time of 4 hours
(47) The sources of the starting materials used in Examples 1 to 12 are listed in Table 2 below:
(48) TABLE-US-00002 TABLE 2 Chemical Supplier Order Code Li.sub.2CO.sub.3 Sigma Aldrich 62470 FePO.sub.42H.sub.2O Sigma Aldrich 436011 Red P Alfa Aesar 10281 LiH.sub.2PO.sub.4 Alfa Aesar A16987 Fe.sub.2O.sub.3 Alfa Aesar 12375 Fe(C.sub.2O.sub.4)2H.sub.2O Sigma Aldrich 307726 C TIMCAL Super P Li V.sub.2O.sub.5 Sigma Aldrich 223794 Mn.sub.2O.sub.3 Alfa Aesar 87791 Na.sub.4P.sub.2O.sub.7 Sigma Aldrich P8010 NH.sub.4H.sub.2PO.sub.4 Sigma Aldrich 216003 Na.sub.2CO.sub.3 Sigma Aldrich 223530 NaH.sub.2PO.sub.4 Sigma Aldrich S5011
Product Analysis using XRD
(49) Analysis by X-ray diffraction techniques was conducted 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.
(50) The general XRD operating conditions used to analyse the precursor electrode materials from Examples 1 to 10 are as follows:
(51) Slits sizes: 1 mm, 1 mm, 0.1 mm
(52) Range: 2=5-60
(53) X-ray Wavelength=1.5418 (Cu K)
(54) Speed: 1.0 second/step
(55) Increment: 0.025/step
(56) The XRD operating conditions used to analyse the precursor electrode material from Example 11 are as follows:
(57) Slits sizes: 1 mm, 1 mm, 0.1 mm
(58) Range: 2=30-60
(59) X-ray Wavelength=1.5418 (Cu Ka)
(60) Speed: 8.0 second/step
(61) Increment: 0.015/step
(62) The XRD operating conditions used to analyse the precursor electrode material from Example 12 are as follows:
(63) Slits sizes: 1 mm, 1 mm, 0.1 mm
(64) Range: 2=10-60
(65) X-ray Wavelength=1.5418 (Cu K)
(66) Speed: 8.0 second/step
(67) Increment: 0.015/step
(68) Electrochemical Results
(69) The target materials were tested in a metallic lithium half cell which can be made using the following procedure:
(70) Generic Procedure to Make a Lithium Metal Electrochemical Test Cell
(71) 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 (VVhatman, GF/A) or a porous polypropylene separator (e.g. Celgard 2400) wetted by the electrolyte is interposed between the positive and negative electrodes.
(72) Cell Testing
(73) The cells are tested as follows, using Constant Current Cycling techniques. The cell is cycled at a given current density between pre-set voltage limits. A commercial battery cycler from Maccor Inc. (Tulsa, Olka., USA) is used. On charge, sodium (lithium)-ions are extracted from the cathode active material. During discharge, lithium (sodium)-ions are re-inserted into the cathode active material.
EXAMPLE 1
(74) FIGS. 1B and C (Cell#210021) show the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0851, made using anhydrous FePO.sub.4 and Red P) measured in a metallic lithium half-cell. Specifically, FIG. 1B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 10 shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(75) The Open Circuit Voltage (OCV) of the as-made cell was 3.029 V vs. Li. Referring to FIG. 1B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 147 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 142 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(76) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 10.
EXAMPLE 2
(77) FIGS. 2B and C (Cell#209052) show the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0776, made using Fe.sub.2O.sub.3 and Red P) measured in a metallic lithium half-cell. FIG. 2B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 2C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(78) The Open Circuit Voltage (OCV) of the as-made cell was 3.231 V vs. Li. Referring to FIG. 2B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 155 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 145 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(79) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 2C.
EXAMPLE 3
(80) FIGS. 3B and C (Cell#208052) show the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0686, made using Fe.sub.2O.sub.3 and Red P) measured in a metallic lithium half-cell. In this test the electrode formulation contained no carbon io additive to improve electronic conductivity. FIG. 3B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 3C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(81) The Open Circuit Voltage (OCV) of the as-made cell was 3.259 V vs. Li. Referring to FIG. 3B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 124 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 111 mAh/g, thus indicating the general reversibility of the lithium-ion insertion reactions. This material performance derived from an electrode with no conductive additive is surprisingly good.
(82) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 3C.
EXAMPLE 4 (COMPARATIVE)
(83) FIGS. 4B and C (Cell#207072) show the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0650, made using iron oxalate, Fe(C.sub.2O.sub.4).2H.sub.2Oan Fe.sup.2+ precursor that requires no reducing agent) measured in a metallic lithium half-cell. FIG. 4B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 4C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(84) The Open Circuit Voltage (OCV) of the as-made cell was 3.177 V vs. Li. Referring to FIG. 4B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 63 mAh/g was obtained for the cathode active material. This is a relatively low material utilization. The subsequent re-insertion process corresponded to material specific capacity of 45 mAh/g indicating the relatively poor reversibility. FIG. 4C shows the corresponding differential capacity profile for this material which is indistinct and noisy indicating the poor electrochemical reversibility of the active material.
EXAMPLE 5 (COMPARATIVE)
(85) FIGS. 5B and C (Cell#207071) show the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0649, made using Fe.sub.2O.sub.3 by carbothermal reduction using Super P Carbon (Timcal) as the reducing agent and conductivity enhancer) measured in a metallic lithium half-cell. FIG. 5B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 5C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(86) The Open Circuit Voltage (OCV) of the as-made cell was 3.177 V vs. Li. Referring to FIG. 5B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 135 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 111 mAh/g indicating good reversibility.
(87) The symmetrical nature of the charge-discharge voltage profile further indicates the reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 5C.
EXAMPLE 6
(88) FIGS. 6B and C (Cell#209046) show the first cycle constant current data for the Li.sub.3V.sub.2(PO.sub.4).sub.3 cathode active material (X0773, made using V.sub.2O.sub.5 and Red P) measured in a metallic lithium half-cell. Specifically, FIG. 6B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 6C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 3.0 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(89) The Open Circuit Voltage (OCV) of the as-made cell was 3.286 V vs. Li. Referring to FIG. 6B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 107 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 92 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(90) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 6C.
EXAMPLE 7
(91) FIGS. 7B and C (Cell#208031) show the first cycle constant current data for the LiFe.sub.0.5Mn.sub.0.5PO.sub.4 cathode active material (X0703, made using Fe.sub.2O.sub.3, Mn.sub.2O.sub.3 and Red P) measured in a metallic lithium half-cell. Specifically, FIG. 7B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 7C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.4 V.
(92) The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(93) The Open Circuit Voltage (OCV) of the as-made cell was 3.114 V vs. Li. Referring to FIG. 7B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 121 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 98 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(94) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 7C.
EXAMPLE 8
(95) FIGS. 8B and C (Cell#209045) show the first cycle constant current data for the LiMn.sub.0.5Fe.sub.0.2Mg.sub.0.3PO.sub.4 cathode active material (X0771, made using Fe.sub.2O.sub.3, Mn.sub.2O.sub.3 and Red P) measured in a metallic lithium half-cell. FIG. 8B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 8C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 3.0 and 4.4 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(96) The Open Circuit Voltage (OCV) of the as-made cell was 3.042 V vs. Li. Referring to FIG. 8B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 122 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 87 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(97) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 8C.
EXAMPLE 9
(98) FIGS. 9B and C show the first cycle constant current data for the Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 cathode active material (XO761, made using Fe.sub.2O.sub.3 and Red P) measured in a metallic lithium half-cell. Specifically, FIG. 9B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 9C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.0 and 4.0 V. The electrolyte used was 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The testing was carried out at 25 C.
(99) The Open Circuit Voltage (OCV) of the as-made cell was 2.889 V vs. Li. Referring to FIG. 9B, it is assumed that sodium ions are extracted from the active material during the initial charging of the cell. During the sodium ion extraction process, a charge equivalent to a material specific capacity of 102 mAh/g was obtained for the cathode active material. It is expected from thermodynamic considerations that the sodium extracted from the Na.sub.4Fe.sub.3(PO.sub.4).sub.2P.sub.2O.sub.7 material during the initial charging process, enters the electrolyte, and is then displacement plated onto the lithium metal anode (i.e. releasing more lithium into the electrolyte). Therefore, during the subsequent discharging of the cell, it is assumed that a mix of lithium and sodium is re-inserted into the material. The re-insertion process corresponds to 104 mAh/g, indicating the reversibility of the ion insertion reactions.
(100) The symmetrical nature of the charge-discharge curves further indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile (for cycle #2) shown in FIG. 9C.
EXAMPLE 10
(101) FIGS. 10B and C show the first cycle constant current data for the Na.sub.3V.sub.2(PO.sub.4).sub.3 cathode active material (X0757, made using V.sub.2O.sub.5 and Red P) measured in a metallic lithium half-cell. Specifically, FIG. 10B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 10C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.1 V. The electrolyte used was 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The testing was carried out at 25 C.
(102) The Open Circuit Voltage (OCV) of the as-made cell was 2.719 V vs. Li. Referring to FIG. 10B, it is assumed that sodium ions are extracted from the active material during the initial charging of the cell. During the sodium ion extraction process, a charge equivalent to a material specific capacity of 97 mAh/g was obtained for the cathode active material. It is expected from thermodynamic considerations that the sodium extracted from the Na.sub.3V.sub.2(PO.sub.4).sub.3 material during the initial charging process, enters the electrolyte, and is then displacement plated onto the lithium metal anode (i.e. releasing more lithium into the electrolyte). Therefore, during the subsequent discharging of the cell, it is assumed that a mix of lithium and sodium is re-inserted into the material. The re-insertion process corresponds to 50 mAh/g, indicating the reversibility of the ion insertion reactions.
(103) The symmetrical nature of the charge-discharge curves further indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 10C.
EXAMPLE 11
(104) FIG. 11 (Cell#209008) shows the first cycle constant current data for the LiFePO.sub.4 cathode active material (X0740, made using Fe.sub.2O.sub.3 and Red P, using a 40% excess of Red P thereby producing a composite product of LiFePO.sub.4 and Fe.sub.2P) measured in a metallic lithium half-cell. FIG. 11B shows the voltage profile (electrode potential versus cumulative specific capacity) and FIG. 11C shows the differential capacity profile (differential capacity versus electrode potential). The constant current data shown in the figure were collected using a lithium metal counter electrode at a current density of 0.04 mA/cm.sup.2 between voltage limits of 2.5 and 4.2 V. The non-aqueous electrolyte used was a 1 M solution of LiPF.sub.6 in a 1:1 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical testing was carried out at a controlled temperature of 25 C.
(105) The Open Circuit Voltage (OCV) of the as-made cell was 3.187 V vs. Li. Referring to FIG. 11B, during the first lithium extraction process, a charge equivalent to a material specific capacity of 146 mAh/g was obtained for the cathode active material. The subsequent re-insertion process corresponded to material specific capacity of 137 mAh/g, indicating the general reversibility of the lithium-ion insertion reactions.
(106) The symmetrical nature of the charge-discharge voltage profile indicates the excellent reversibility of the system. This is further exemplified by the symmetrical nature of the differential capacity profile shown in FIG. 110.
EXAMPLE 12
(107) This Example was performed using a tube furnace such as that depicted in FIG. 12. In detail, FIG. 12 shows a schematic view of a tube furnace 10 which comprises a tubular furnace body 15 which has a cylindrical reaction cavity 20 for receiving an open ended non-porous ceramic tube 30, and heating elements (not shown) for heating the cylindrical reaction cavity 20. Two stainless steel ends 40, 50 are provided to seal against the open ends of the non-porous ceramic tube 30, aided by two rubber gaskets (not shown) and held in place by clamps (not shown). Furnace baffles 60, 70 inside the non-porous ceramic tube 30, provide heat insulation. Expansion vessels 80, 90 are also provided to accommodate a change in volume of the gaseous components in the non-porous ceramic tube 30, as it is heated during the reaction process. A crucible 100 is positioned within the non-porous ceramic tube 30 for containing the reactants during the reaction process.
(108) During the reaction process, an open ended non-porous ceramic tube 30 is placed within the cylindrical cavity 20 of the tubular furnace body 15 and a crucible 100 containing the starting materials and furnace baffles 60, 70 are all positioned inside the open ended non-porous ceramic tube 30 as shown in FIG. 12. The open ends of the open ended non-porous ceramic tube 30 are then sealed using the stainless steel ends 40, 50, under an atmosphere of air. The tubular furnace body 15 is then heated to the required reaction temperature and, as this proceeds, the pressure within the non-porous ceramic tube 30 is maintained at an approximately constant level by the expansion of the heated air being accommodated by the expansion vessels 80 and 90. After heating for the required reaction time, the tubular furnace body 15 is cooled sufficiently to allow removal of the crucible 100 from the non-porous ceramic tube 30, and recovery of the reaction products.
(109) FIG. 13(B) (cell #0 305086 ) shows the Electrode Voltage (V vs. Li) versus Cumulative Cathode Specific Capacity (mAh/g)) are derived from the first cycle constant current cycling data for the LiFePO.sub.4 (Sample X1322) active material in a metallic lithium half-cell. The electrolyte used was a 1.0 M solution of LiPF.sub.6in ethylene carbonate/diethyl carbonate. The constant current data were collected at a current density of 0.40 mA/cm.sup.2 between voltage limits of 2.50 and 4.20 V vs. Li. The testing was carried out at 25 C.
(110) During the cell charging process, lithium ions are extracted from the cathode active material. During the subsequent discharge process, lithium ions are re-inserted into the cathode active material. The first charge process corresponds to a cathode specific capacity of 102 mAh/g. The first discharge process corresponds to a cathode specific capacity of 80 mAh/g. These data demonstrate the reversibility of the lithium ion insertion reactions in the LiFePO.sub.4 active material.
(111) FIG. 13(C) (Cell#305086) shows the first cycle differential capacity profile (Differential Capacity (mAh/g/V) versus Electrode Voltage (V vs. Li)] for the LiFePO.sub.4 (Sample X 1322 ) derived from the constant current cycling data shown in FIG. 13(B). Differential capacity data have been shown to allow characterization of the reaction reversibility, order-disorder phenomenon and structural phase changes within the ion insertion system.
(112) The data presented in FIG. 13(C) for the LiFePO.sub.4 cathode confirm the reversible lithium-ion insertion behaviour as characterized by the generally symmetrical nature of the differential capacity peaks during cell charge and discharge.
(113) FIG. 13(D) (Cell#305086) shows the cycling performance (Cathode Specific Capacity (mAh/g) versus Cycle Number] for the LiFePO.sub.4 (Sample X 1322) derived from constant current cycling data on the active material carried out in a metallic lithium half-cell. The electrolyte used was a 1.0 M solution of LiPF.sub.6 in ethylene carbonate/diethyl carbonate. The constant current data were collected at a current density of 0.40 mA/cm.sup.2 between voltage limits of 2.50 and 4.20 V vs. Li. The testing was carried out at 25 C.
(114) The active material cycles at a cathode discharge specific capacity of around 80 mAh/g. These data again demonstrate the reversibility of the lithium ion insertion reactions in the LiFePO.sub.4 active material.
