TUNGSTEN DOPED MULTI-IONIC CATHODE

Abstract

The present invention discloses to tungsten doped mixed cationic cathodes for energy devices notably non-aqueous re-chargeable alkali-ion electrochemical cells and batteries and to the process of preparation thereof. More particularly, the present invention discloses to doped cathode active materials of Formula (I) that show a higher capacity and which can able to retains their structure during the entire charging-discharging cycles.

Claims

1. A tungsten doped mixed cation cathode active material of formula (I) comprising; ##STR00007## wherein, A comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; B comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; M1 is the transition metal in the oxidation state +2; M2 is the transition metal in the oxidation state +3; M3 is the transition metal in the oxidation state +4; W is tungsten in oxidation state +3; wherein, 0.67a1, preferably 0.85a1, further preferably 0.95a1; 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; 0c0.5, preferably 0c0.45, further preferably 0c0.333; 0d0.5, preferably 0d0.45, further preferably 0d0.333; 0e0.5, preferably 0e0.45, further preferably 0e0.333.

2. The tungsten doped cathode active material as claimed in claim 1, of formula (1A) comprising: ##STR00008## wherein, A comprises one or more alkali metals selected from Sodium, Lithium, or Potassium; B comprises one or more alkali metals selected from Sodium, Lithium, or Potassium; Ni is nickel in oxidation state +2; Fe is iron in oxidation state +3; Mn is manganese in oxidation state +4; W is tungsten in oxidation state +3; wherein, 0.67a1, preferably 0.85a1, further preferably 0.95a1; 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; 0c0.5, preferably 0c0.45, further preferably 0c0.333; 0d0.5, preferably 0d0.45, further preferably 0d0.333; 0e0.5, preferably 0e0.45, further preferably 0e0.333.

3. The tungsten doped cathode active material as claimed in claim 2, wherein c+d+e+f=1.

4. The tungsten doped mixed cation cathode active material of Formula (I) as claimed in any of the claims 1 to 3, comprises: i. Na.sub.0.95K.sub.0.05Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33 W.sub.0.01O.sub.2, ii. Na.sub.0.95K.sub.0.05Ni.sub.0.327Fe.sub.0.327Mn.sub.0.327 W.sub.0.02O.sub.2, and iii. Na.sub.0.95K.sub.0.05Ni.sub.0.316Fe.sub.0.316Mn.sub.0.316 W.sub.0.05 O.sub.2

5. A process for preparation of the cathode active material of Formula (I) comprising; i. Preparing separate solutions of the base metal C, D & E in their respective stoichiometric ratios, and the second solution of a mixture of 1% or 2% or 5% Tungstic acid dissolved in both NaOH and NH4OH solutions, wherein the second solution is further kept for vigorous stirring under an N2 atmosphere; ii. Mixing the above two solutions simultaneously drop wise into a fixed volume stirred reactor followed by aging (maturing) for a period of 12 hrs, under the stirring condition to allow homogenous particle formation, which is then washed, neutralized, and dried to form the ternary hydroxides; iii. Intimately mixing the obtained ternary hydroxides of step (ii) with stoichiometric quantities of A and B salts; iv. Heating the resulting mixture in a furnace under a suitable atmosphere over a temperature range of 450 C. to 900 C. until reaction product forms; and v. Allowing the product to cool before grinding it to a powder.

6. The process for preparation as claimed in claim 4, wherein, the base metals C, D & E are Ni, Fe & Mn respectively.

7. Use of the tungsten doped mixed cation active material as claimed in claim 1, in alkali ion-cell, in energy storage devices such as batteries, rechargeable batteries, electrochemical devices, and electrochemical devices.

8. A alkali-ion electrochemical cell comprising; i. the cathode consisting of tungsten doped mixed cation active material of the formula (I); ##STR00009## wherein, A comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; B comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; M1 is the transition metal in the oxidation state +2; M2 is the transition metal in the oxidation state +3; M3 is the transition metal in the oxidation state +4; W is tungsten in oxidation state +3; Wherein 0.67a1, preferably 0.85a1, further preferably 0.95a1, 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; 0c0.5, preferably 0c0.45, further preferably 0c0.333; 0d0.5, preferably 0d0.45, further preferably 0d0.333; 0e0.5, preferably 0e0.45, further preferably 0e0.333; ii. an anode selected from graphite, hard carbon, and silicon; iii. a separator; and iv. a non-aqueous electrolyte comprising 0.8M NaPF6-PC:EMC:FEC:PST:DDT composition.

9. The tungsten doped cathode material as claimed in any one of the preceding claims wherein said cathode material is stable, shows specific capacity of 130-150 mAh/gm with little or no fading on cycling and has higher energy density

10. A method of charging and discharging the electrochemical cell with the tungsten doped mixed cation cathode active material as claimed in claim 1.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

[0081] The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

[0082] FIG. 1: depict a schematic representation of cell voltage profile for the first 5 charge/discharge cycles of the a half-cell having sodium metal as anode material and Na Ni.sub.0.333 Fe.sub.0.333 Mn.sub.0.333 O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

[0083] FIG. 2: depict a schematic representation of cell voltage profile for the first 5 charge/discharge cycles of the a half-cell having sodium metal as anode material and Na Ni.sub.0.33 Fe.sub.0.33 Mn.sub.0.33 W.sub.0.01O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

[0084] FIG. 3: depict a schematic representation of cell voltage profile for the first 5 charge/discharge cycles of a half-cell having sodium metal as anode material and Na.sub.0.95K.sub.0.05 Ni.sub.0.33 Fe.sub.0.33Mn.sub.0.33 W.sub.0.01O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

DETAILED DESCRIPTION OF THE INVENTION

Abbreviations

[0085] EMC: Ethyl Methyl Carbonate [0086] PC: Propylene Carbonate [0087] FEC: Fluoroethylene Carbonate [0088] PP: Polypropylene [0089] DTD: Ethylene Sulfate (1,3,2-Dioxathiolane 2,2-dioxide) [0090] PST: prop-1-ene-1,3-sultone

[0091] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.

[0092] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of a, an, and the include plural references. The meaning of in includes in and on. Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.

[0093] The tables, figures and protocols have been represented where appropriate by conventional representations in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

[0094] As used herein, the term element, when used in the context of the present invention, refers to a member of the periodic table and has the suitable oxidation state when the element is used in combination with other members of the periodic table.

[0095] Accordingly, to accomplish the objectives of the present invention, the inventors propose a positive electrode material, suitable for preparing energy storage devices. Accordingly, the present invention provides a mixed cathode active material made up of layered transition metal oxides-based structure suitable for preparing rechargeable metal-ion batteries with higher capacity.

[0096] In an embodiment of the present invention, the mixed cathode material with optimized stoichiometry such that the O3 structure of the formed cathode is doped with larger alkali ions as well as tungsten ions (W) and results in enlarged interlayer spacing, providing larger channels for ion movement.

[0097] In another embodiment of the present invention, doping with tungsten (W) will greatly increase the structural stability of the mixed cathode material because of the formation energy. The greater the formation energy of metal oxide more stable the material will be. The formation energy of the intercalation of Alkali metal ion (Ef) is shown in Equation

[00001]$E_f=E_{t^{-}}{E}_{\mathrm{dil}}-E_{\mathrm{dilafter}}$ [0098] Where, Et is the total energy of the supercell, Edil is the deintercalation energy of alkali metal ion, and Edilafter is the energy after the deintercalation of alkali metal ion. The formation energy of WO is in the range 598 to 632 KJ/mol, compared to the Metal-O (Ni/Co/Mn) which is 391.6 kJ/mol, 397.48.7 KJ/mol, and 402 kJ/mol and thus helps in increasing the structural stability.

[0099] In still another embodiment of the present invention, the tungsten doped mixed cation cathode active material is represented by formula (I), comprising;

##STR00004## [0100] Wherein, [0101] A comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; [0102] B comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; [0103] M.sup.1 is the transition metal in the oxidation state +2; [0104] M.sup.2 is the transition metal in the oxidation state +3; [0105] M.sup.3 is the transition metal in the oxidation state +4; [0106] W is tungsten in oxidation state +3; [0107] Wherein [0108] 0.67a1, preferably 0.85a1, further preferably 0.95a1, [0109] 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; [0110] 0c0.5, preferably 0c0.45, further preferably 0c0.333; [0111] 0d0.5, preferably 0d0.45, further preferably 0d0.333; [0112] 0e0.5, preferably 0e0.45, further preferably 0e0.333;

[0113] In particular, the preferred cathode material have c+d+e+f=1

[0114] In yet another embodiment of the present invention, the tungsten doped mixed cation cathode active material is represented by formula (IA) comprising;

##STR00005## [0115] Wherein, [0116] A comprises one or more alkali metals selected from Sodium, Lithium, or Potassium; [0117] B comprises one or more alkali metals selected from Sodium, Lithium, or Potassium; [0118] Ni is nickel in oxidation state +2; [0119] Fe is iron in oxidation state +3; [0120] Mn is manganese in oxidation state +4; [0121] W is tungsten in oxidation state +3; [0122] Wherein, [0123] 0.67a1, preferably 0.85a1, further preferably 0.95a1; [0124] 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; [0125] 0c0.5, preferably 0c0.45, further preferably 0c0.333; [0126] 0d0.5, preferably 0d0.45, further preferably 0d0.333; [0127] 0e0.5, preferably 0e0.45, further preferably 0e0.333; [0128] Wherein the cathode material preferably have c+d+e+f=1.

[0129] In still another embodiment of the present invention, the doped cathode active material of Formula (I) comprises: [0130] i. Na.sub.0.95K.sub.0.05Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33 W.sub.0.01O.sub.2, [0131] ii. Na.sub.0.95K.sub.0.05Ni.sub.0.327Fe.sub.0.327Mn.sub.0.327 W.sub.0.02O.sub.2, and [0132] iii. Na.sub.0.95K.sub.0.05Ni.sub.0.316Fe.sub.0.316Mn.sub.0.316 W.sub.0.05 O.sub.2

[0133] In an embodiment of the present invention, the process for preparation of the cathode material of Formula (I) comprising co-precipitating a ternary/binary hydroxide of the base transition metal elements and further mixing with stoichiometric ratios of respective A, B, and W and calcination of the mixture to facilitate proper compound formation. Such a process may be conveniently performed in the presence of air, but it may also be performed under an inert atmosphere.

[0134] In another embodiment of the present invention, the process for the preparation of the cathode material of Formula (I) comprises the steps: [0135] i. Preparing separate solutions of the base metal C, D & E in their respective stoichiometric ratios, and the second solution of a mixture of 1% or 2% or 5% Tungstic acid dissolved in both NaOH and NH4OH solutions, the second solution is further kept for vigorous stirring under an N2 atmosphere; [0136] ii. Mixing the above two solutions simultaneously dropwise into a fixed volume stirred reactor followed by aging (mature) for a period of 12 hrs, under the stirring condition to allow homogenous particle formation, which is then washed, neutralized, and dried to form the ternary hydroxides; [0137] iii. Intimately mixing the obtained ternary hydroxides of step (ii) with stoichiometric quantities of A and B salts; [0138] iv. Heating the resulting mixture in a furnace under a suitable atmosphere and within a single temperature or over a range of temperatures between 450 C. and 900 C. until reaction product forms; [0139] v. Allowing the product to cool before grinding it to a powder.

[0140] In still another embodiment of the present invention, the base metals C, D & E are Ni, Fe & Mn respectively.

[0141] The Table 1 below lists the starting materials and experimental conditions used to prepare a known (comparative) composition (Example 1) and the Target Active Materials of the present invention (Examples 2 to 4).

TABLE-US-00001 TABLE 1 Sl. No Electrode Starting materials Experimental conditions 1. NaNi.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01O.sub.2 2M Ni Nitrate, Mn Nitrate, Fe 850 C., Oxygen Nitrate solution was drop wise Dwell: 12 Hrs added to 1% Tungstic acid Ramp Rate: 10 C./min Ammonia solution and Sodium hydroxide. (Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01)OH.sub.2 powder and Sodium carbonate were mixed in an appropriate molar ratio in a rotatory mixer for approx. 1 hr 2. Na.sub.0.95K.sub.0.05Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01O.sub.2 2M Ni Nitrate, Mn Nitrate, Fe 850 C., Oxygen Nitrate solution was drop wise Dwell: 12 Hrs added to 1% Tungstic acid Ramp Rate: 10 C./min Ammonia solution and Sodium hydroxide. (Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01)OH.sub.2 powder and Sodium carbonate, Potassium carbonate were mixed in appropriate molar ratio in a rotatory mixer for approx. 1 hr 3. Na.sub.0.95K.sub.0.05Ni.sub.0.327Fe.sub.0.327Mn.sub.0.327W.sub.0.02O.sub.2 2M Ni Nitrate, Mn Nitrate, Fe 850 C., Oxygen Nitrate solution was drop wise Dwell: 12 Hrs added to 2% Tungstic acid Ramp Rate: 10 C./min Ammonia solution and Sodium hydroxide. (Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01)OH.sub.2 powder and Sodium carbonate, Potassium carbonate were mixed in appropriate molar ratio in a rotatory mixer for approx. 1 hr 4. Na.sub.0.95K.sub.0.05Ni.sub.0.316Fe.sub.0.316Mn.sub.0.316W.sub.0.05O.sub.2 2M Ni Nitrate, Mn Nitrate, Fe 850 C., Oxygen Nitrate solution was drop wise Dwell: 12 Hrs added to 5% Tungstic acid Ramp Rate: 10 C./min Ammonia solution and Sodium hydroxide. (Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33W.sub.0.01)OH.sub.2 powder and Sodium carbonate, Potassium carbonate were mixed in appropriate molar ratio in a rotatory mixer for approx. 1 hr

[0142] In still another embodiment of the present invention, the doped cathode active material of Formula (I) is stable, shows an improvement in specific capacity with little or no fading on cycling and, therefore, the energy density of devices made from present cathode is higher over undoped cathodes.

[0143] In an embodiment, the tungsten doped cathode active material exhibits the specific capacity in the range of 130-150 mAh/gm at 4V.

[0144] In an embodiment of the present invention, the present cathode active material has a novel anionic stoichiometry suitable for preparing energy storage devices, accordingly, the active material of Formula (I) find application in alkali ion-cell, in energy storage devices such as batteries, rechargeable batteries, electrochemical devices, and electrochemical devices.

[0145] In another embodiment of the present invention, the active material of Formula (I) is used as an electrode preferably a positive electrode (cathode), in conjunction with a counter electrode and one or more electrolyte materials in alkali ion-cell and in energy storage devices or electrochemical cell.

[0146] In still another embodiment of the present invention, the alkali-ion electrochemical cell comprising; [0147] (i) the cathode consisting of tungsten doped mixed cation active material of the formula (I);

##STR00006## [0148] Wherein, [0149] A comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; [0150] B comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like; [0151] M.sup.1 is the transition metal in the oxidation state +2; [0152] M.sup.2 is the transition metal in the oxidation state +3; [0153] M.sup.3 is the transition metal in the oxidation state +4; [0154] W is tungsten in oxidation state +3; [0155] Wherein [0156] 0.67a1, preferably 0.85a1, further preferably 0.95a1, [0157] 0.01b0.25, preferably 0.01b0.1, further preferably 0.01b0.05; [0158] 0c0.5, preferably 0c0.45, further preferably 0c0.333; [0159] 0d0.5, preferably 0d0.45, further preferably 0d0.333; [0160] 0e0.5, preferably 0e0.45, further preferably 0e0.333. [0161] (ii) an anode selected from graphite, hard carbon, and silicon; [0162] (iii) a separator; and [0163] (iv) a non-aqueous electrolyte comprising 0.8M NaPF6-PC:EMC:FEC:PST:DDT composition.

[0164] In particular, the preferred cathode material have c+d+e+f=1

[0165] In yet another embodiment of the present invention, the cathode active material of Formula (I) in the alkali-ion electrochemical cell is arranged in series, parallel, or both.

[0166] In another embodiment of the present invention, during the cell charging process, host ions comprising the larger alkali metal ions migrate from the electrolyte and cathode and are inserted into the sodium anode, increasing the gallery height of the said carbon anode layers, thereby helping in unimpeded movement of the smaller host ions, leading to better capacity retention across multiple cycles in the cell comprising the said cathode, a standard anode, and an electrolyte. As the nickel ions are deintercalated from the cathode, they undergo oxidation from +2 to +4 oxidation states with a small contribution from Fe3+ to Fe4+ oxidation states. The capacity contribution of Manganese is insignificant and is only seen below 3V as a sloping curve. A subsequent discharge process extracts the host ions from sodium and reintroduces them into the cathode. In other words, during the charging process, the potential difference created makes the larger cation move towards the anode and intercalate into the structure and the reverse happens during discharging. The nature of the electrode intercalation material influences the resulting voltage of the battery since the voltage is the difference between the half-cell potentials at the cathode and anode.

[0167] In still another embodiment of the present invention, the charge-discharge profile of the present electrode active material of Formula (I) exhibits smooth discharging curve from 4V to 2V when used as the cathode in energy storage devices comprising sodium metal as the anode and 0.8M NaPF6-PC:EMC:FEC:PST:DDT as the electrolyte.

EXAMPLES

[0168] The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Comparative Example 1:Composites of NaNi.SUB.0.333 .Fe.SUB.0.333 .Mn.SUB.0.333.O.SUB.2

[0169] The composition NaNi.sub.0.333Fe.sub.0.333Mn.sub.0.333O.sub.2 is used as a cathode active material in the half cell format using sodium metal as anode. Further, 0.8M NaPF6-PC:EMC:FEC:PST:DDT is used as an electrolyte. The ratio of the carbonate is fixed to 4:6 and 2, 1, and 1 vol % of other additives were added. The cell was charged to 4V at 25 degrees at a 0.5 C rate.

[0170] FIG. 1 depict the schematic representation of cell voltage profile for the first 5 charge/discharge cycles of the half-cell having sodium metal as anode material and NaNi.sub.0.333Fe.sub.0.333Mn.sub.0.333O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

[0171] The half-cell having sodium metal as anode material and NaNi.sub.0.333Fe.sub.0.333Mn.sub.0.333O.sub.2 as cathode active material have a capacity of 110 mAh/g.

Example 1:Composites of Na Ni.SUB.0.33 .Fe.SUB.0.33 .Mn.SUB.0.33 .W.SUB.0.01.O.SUB.2

[0172] The composition Na Ni.sub.0.33 Fe.sub.0.33 Mn.sub.0.33 W.sub.0.01O.sub.2 is used as a cathode active material in the half cell format using sodium metal as anode. Further, 0.8M NaPF6-PC:EMC:FEC:PST:DDT is used as an electrolyte. The ratio of the carbonate is fixed to 4:6 and 2, 1, and 1 vol % of other additives were added. The cell was charged to 4V at 25 degrees at a 0.5 C rate.

[0173] FIG. 2 depict the schematic representation of cell voltage profile for the first 5 charge/discharge cycles of the half-cell having sodium metal as anode material and Na Ni.sub.0.33 Fe.sub.0.33 Mn.sub.0.33 W.sub.0.01O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

[0174] The W doped material achieved a high capacity of 130 mAh/g which is higher than comparative example of undoped material.

Example 2. Composites of Na.SUB.0.95.K.SUB.0.05 .Ni.SUB.0.33.Fe.SUB.0.33.Mn.SUB.0.33 .W.SUB.0.01.O.SUB.2

[0175] The composition Na.sub.0.95K.sub.0.05 Ni.sub.0.33Fe.sub.0.33Mn.sub.0.33 W.sub.0.01O.sub.2 is used as a cathode active material in the half cell format using sodium metal as anode. Further, 0.8M NaPF6-PC:EMC:FEC:PST:DDT is used as an electrolyte. The ratio of the carbonate is fixed to 4:6 and 2, 1, and 1 vol % of other additives were added. The cell was charged to 4V at 25 degrees at a 0.5 C rate.

[0176] FIG. 3 depict the schematic representation of cell voltage profile for the first 5 charge/discharge cycles of a half-cell having sodium metal as anode material and Na.sub.0.95K.sub.0.05 Ni.sub.0.33Fe.sub.0.33 Mn.sub.0.33 W.sub.0.01O.sub.2 as cathode active material which is charged up to 4V at 25 degrees using 0.8M NaPF6-PC:EMC:2% FEC:1% PST:1% DTD as electrolyte.

[0177] The composition with combination of K+ and W doping delivered higher capacity of 135 mAh/g compared to one Example 1 and comparative example both.

[0178] Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.