High-capacity high-rate multi-ionic cathodes

Abstract

The present invention pertains to doped cathode material that contains active material made up of layered transition metal oxides-based structure, for rechargeable metal-ion batteries. The present invention further provides a mixed cation doped cathode active material of layered transition metal oxides-based structure suitable for rechargeable metal-ion batteries with higher capacity.

Description

HIGH-CAPACITY HIGH-RATE MULTI-IONIC CATHODESFIELD OF THE INVENTION:

[0001] The present invention relates to a doped cathode material comprising active material of layered transition metal oxides-based structure, for rechargeable metal-ion batteries. The present invention further discloses a method of producing a doped cathode material having novel stoichiometry capable of preparing metalion batteries.BACKGROUND OF THE INVENTION:

[0002] With the ever-increasing energy consumption and demands on energy sources, renewable energy storage systems with low cost, high efficiency, long lifespan, and adequate safety are essential. Among all the energy storage techniques, rechargeable batteries are one of the most efficient technologies for storing electricity and powering electronic devices. The rechargeable battery is even the core component of electric vehicles (EVs), which requires high performance.

[0003] Critical battery characteristics such as specific capacity, cycling stability, and operation voltage largely depend on the intrinsic electrochemical properties of the electrode materials. The electrodes (mainly the cathode) are the limiting factors in terms of overall capacity, i.e. energy density, and cyclability, therefore, the main concern in the rechargeable battery system is to find suitable electrode materials, especially cathode materials, which, to a great extent, determine the energy density of a battery. Examples include metal oxide, polyanions, organic compounds, and others.

[0004] The most general formula used for describing transition metal oxides based on alkali metal ion cathode material is AxMCh, where M represents one or more metal ions having different oxidation states. The AxMCh usually adopts an 03-type stacking sequence. The 03 phase is composed of alternate alkali metalion layers and transition-metal (M) layers in the oxygen-ion framework, packed closely in the ABCABC pattern, in which alkali ions and M ions are respectively located in the octahedral sites. P2-phase is stacked in the ABBAABBA manner, with all the alkali ions occupying the trigonal prismatic sites of the alkali layers.

[0005] The exact position of the alkali metal ion defines what will be the structure of metal oxide i.e. octahedral, tetrahedral, or prismatic. These layered materials consist of MO6edge-sharing octahedral units forming (MO2) n sheets, in between which the sodium cation is coordinated octahedral (O), tetrahedral (T), or prismatic (P). O-type layered oxides comprise sodium ions in octahedral sites, while P-type materials accommodate the alkali ions in prismatic sites. The most common structures for layered transition metal oxides are 03, P2, and P3-type, whereby the number indicates the number of transition metal layers in the repeating cell unit. Transition metal layered oxides have attractive properties as cathode materials for rechargeable batteries, such as the ease of synthesis and the high feasibility and reversibility of the sodium shuttling process, thus, allowing a good overall electrochemical performance.

[0006] The most promising class of transition metal oxide material is the layered metal oxides. Layered transition metal oxides have gained considerable attention due to their simple structure, ease of synthesis, high operating potential, and feasibility for commercial production. The biggest challenges faced by this material include high capacity, cycle stability, high rate capacity, being environmentally friendly, and so on. Layered transition metal oxide cathodes have a higher theoretical capacity, faster sodium ion diffusion, and smaller electrode polarization. In addition, the structure of the layered metal oxide cathode is tailorable. By means of appropriate component modulation and process conditions, it is possible to prepare layered transition metal oxides with target structures. For example, little difference in transition metal element or Na content can result in a transition between P2- and 03- type structures. The synthesis methods of layered materials are generally the traditional solid-phase reactionmethods, co-precipitation, and sol-gel methods, which are relatively mature and simple, and therefore the preparation of layered transition metal oxide materials has certain industrial feasibility.

[0007] Metal doping is proven to be an important and reliable approach to stabilize the interslab spaces, reduce multiple phase transitions, and lead to enhancements in the long-term cycling and output voltage in the preparation of layered transition metal oxides. Research has been extended from AxMCh with a single transition metal to compounds with two, three, and even four or more metal ions by introducing different metals into the AxMCh framework, taking advantage of the unique characteristics and synergetic contributions of various metal elements.

[0008] KR102486386B1 discusses about a composite cathode active material and a secondary battery including the same. The negative electrode active material is selected from the group consisting of lithium metal, a metal alloyable with lithium, a transition metal oxide, a non-transition metal oxide, a material capable of doping and undoping lithium, and a carbon-based material.

[0009] EP3405988B1 discusses about a sodium ion battery material comprising the formula NaaLibNic-MndFeeTifOgwherein 0.70 < a < 1.0, 0.01 < b < 0.2, 0.10 < c < 0.37, 0.20 < d < 0.5, 0.00 < e < 0.3, 0.10 < f < 0.2, 1.85 < g < 2.2 and ((c+d+e+f) / g) <2.

[0010] US20220199982A1 discusses about a lithium metal composite oxide powder which has a layered structure and with a composition formula Li[Lim(Ni(i- n-p)XnMp)i.m]02 where -0.1<m<0.2, 0<n<0.6, 0<p<0.05, and n+p<0.6 and X is at least one element selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga and V and M is at least one element selected from the group consisting of B, Si, S and P.

[0011] CN115295787A discusses a positive electrode material of the sodium-ion battery is NaiNixFeyMnzMi.x-y-zO2 where M is one or more of Li, Mg, Zr, Al, Sn, Ti, Mo, Ba, Sr, Nb and Cr, i is more than 0.5 and less than or equal to 1.2, x is more than 0 and less than or equal to 0.7, y is more than 0 and less than or equal to 0.7, z is more than 0 and less than or equal to 0.7, the values of x + y + z are less than 1, i, x, y and z meet the charge balance of the chemical formula and the positive electrode material of the sodium-ion battery has a P2 / O3 phase composite layered structure.

[0012] W02020235909A1 discusses about a cathode active material for a sodium secondary battery represented by Na i-2x Cax[(NiyMzMni.yZ)]O2 where M includes at least one of Co and Fe and 0.001<x<0.1, 0<y<l and 0<z<l.

[0013] The non-patent literature “High Performance Nao.5[Nio.23Feo.i3Mno.63]02 Cathode for Sodium-ion Batteries” by Ivana Hasa et al. discusses about synthesizing layered cathode material, Nao.5[Nio.23Feo.i3Mno.63]02, and its characterization in terms of crystalline structure and electrochemical performance in a sodium cell.

[0014] The non-patent literature “Enhanced cathode materials for advanced lithium-ion batteries using nickel-rich and lithium / manganese-rich LiNixMnyCozCb” by Jeevanantham B et al. discusses about Lithium-ion batteries using LiNixMoyCozCb composite that offers high capacity and stability. Further, doping materials like Al, Mg, Cr, and F into the cathode makes the cathode stable and increases the lattice parameter size during cycling for Li+ ion diffusion.

[0015] The non-patent literature “Layered P2-NaxMn3 / 4Ni 1 / 402 Cathode Materials For Sodium-ion Batteries: Synthesis, Electrochemistry and Influence of Ambient Storage” by Pfeiffer et al discusses about a manganese-based, cobalt- free, layered NaxMn3 / 4Nii / 4O2 cathode active material for sodium-ion batteries.

[0016] The non-patent literature “Lithium Nickel Cobalt Manganese Oxide Synthesized Using Alkali Chloride Flux: Morphology and Performance As a Cathode Material for Lithium Ion Batteries” by Yongseon Kim discusses about synthesis of Li(Ni (0.8)Co(0.1)Mn(0.1))0(2) using alkali chlorides as a flux and analyzing the performance of the same for being a cathode material for lithium ion batteries.

[0017] On analyzing the literature pertaining to rechargeable batteries, there appears a need in the art to provide an improved cathode active material for energy storage devices or alkali-ion electrochemical cell which is capable of delivering high specific capacity with little or no fading on cycling, and yet being cost-effective.OBJECT OF THE INVENTION:

[0018] Accordingly, the main objective of the present invention is to provide a doped cathode material made up of layered transition metal oxides for rechargeable alkali ion batteries containing multiple cationic elements which allow increasing the rate and cycle life of batteries made utilizing this cathode.SUMMARY OF THE INVENTION:

[0019] Accordingly, the present invention discloses a cathode electrode material exhibiting a novel cationic stoichiometry, suitable for preparing energy storage devices. Accordingly, the present invention provides a mixed cation doped cathode active material of layered transition metal oxides-based structure suitable for rechargeable metal-ion batteries with high capacity.

[0020] In an aspect, a cathode active material comprising of a layered alkali- transition metal oxide represented by a Formula I:Aa Bb(M^ M2dM3e) 02(Formula I) 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;M1is the transition metal in the oxidation state +2,M2is the transition metal in the oxidation state +3,M3is the transition metal in the oxidation state +4, and wherein stoichiometric coefficients a, b, c, d and e are in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1;0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05;0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333;0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333; and 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333.

[0021] In an aspect, the preferred cathode material have c + d + e = 1.

[0022] In another aspect of the present invention, the cathode active material comprises of layered alkali-transition metal oxides-based structure represented by a Formula:AaBb (NicFea Mne) O2, wherein‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;‘B’ comprises another one or more alkali metal selected from Sodium, Lithium, Potassium and the like;M1is Nickel (Ni) in oxidation state +2;M2is Iron (Fe) in oxidation state +3;M3is Manganese (Mn) in oxidation state +4;wherein, stoichiometric coefficients a, b, c, d and e lies in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1;0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05;0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333;0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333; and 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333.

[0023] In an aspect, the preferred cathode material have c + d + e = 1.

[0024] In yet another aspect of the present invention, the mixed cation doped cathode active material of Formula (I) comprises: i. Na0.99K0.01Ni0.33Fe0.33Mn0.33O2, ii. Na0.95K0.05Ni0.33Fe0.33Mn0.33O2, and iii. Nao.9Ko.1Nio.33Feo.33Mno.33O2.

[0025] In an aspect of the present invention, the process for preparation of a cathode material of Formula (I) comprising co-precipitating a ternary / binary hydroxide of the base transition metal elements in their respective stoichiometric ratios and further mixing with stoichiometric ratios of respective A and B salts and calcination of the mixture to facilitate the compound formation for the cathode material. Such a process may be conveniently performed in the presence of air, but it may also be performed under an inert atmosphere.

[0026] In preferred aspect of the present invention, the process for preparation of a cathode material of Formula (I) comprises the steps: i. Preparing a first solution of the base transition metal M1, M2and M3, in their respective stoichiometric ratios, and the second solution of a mixture of sodium hydroxide (NaOH) and ammonium hydroxide (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, wherein A and B may be any alkali metal selected from the alkali metal group; 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 1000°C until a reaction product forms; v. Allowing the reaction product to cool before grinding it to a powder to form the cathode material.

[0027] In another preferred aspect of the present invention, the base metals M1, M2and M3may be any transition element selected from d-block of the periodic table. In an aspect, the transition base metal M1, M2and M3may be Nickel (Ni), Iron (Fe) and Manganese (Mn) respectively. Further, ‘A’ and B may comprise of one or more alkali metal selected from Sodium, Lithium, Potassium and the like.

[0028] In an aspect of the present invention, the doped cathode active material of Formula (I) find application in alkali ion-cell, in energy storage devices such as batteries, rechargeable batteries, electrochemical devices, energy accumulators, and electrochromic devices.

[0029] In an aspect, an alkali-ion electrochemical cell comprising:(i) a cathode comprising a layered alkali-transition metal oxide represented by a formula AaBb (M'cM2d M3e) O2, wherein A and B comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like and M1, M2and M3are transition metals in the oxidation state of +2, +3 and +4 respectively, wherein stoichiometric coefficients a, b, c, d and e lies in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1, 0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05,0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333,0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333, and0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333,(ii) an anode comprising carbon material; and(iii) an electrolyte.

[0030] In an aspect, the carbon material for anode is hard carbon.

[0031] In an aspect, the electrolyte comprises of an alkali salt dissolved in an organic solvent. In an another aspect, the alkali salts may be NaPFe, NaCIC , LiPFe and / or KPFe dissolved in an organic solvent like Ethyl Methyl Carbonate, Propylene Carbonate, Fluoroethylene Carbonate, Polypropylene, Dithiane Diol and / or prop-l-ene-1, 3-sultone.BRIEF DESCRIPTION OF DRAWINGS:

[0032] Figure 1 illustrates the Constant current cycling (CC / CV) of a full cell with hard carbon as anode material and NaiNio.333Feo.333Mno,33302 (NNFMO) in the voltage range 2 - 4V at 25°C in 0.5M NaPFe in EMC:PC:FEC and PP used as a separator.

[0033] Figure 2 illustrates the Constant current cycling (CC / CV) of a full cell with hard carbon as anode material and Na0.99K0.01Ni0.33Fe0.33Mn0.33O2 (NKNFM- 0.01) in the voltage range 2 - 4V at 25°C in 0.5M NaPFe and 0.3M KPFe in EMC:PC:FEC and PP used as a separator.

[0034] Figure 3 illustrates the Constant current cycling (CC / CV) of a full cell with hard carbon as anode material and Na0.95K0.05Ni0.33Fe0.33Mn0.33O2 (NKNFM-0.05) in the voltage range 2 - 4V at 25°C in 0.5M NaPFe and 0.3M KPFe in EMC:PC:FEC and PP used as a separator.

[0035] Figure 4 illustrates the Constant current cycling (CC / CV) of a full cell with hard carbon as anode material and Nao.9Ko.1Nio.33Feo.33Mno.33O2 (NKNFM- 0.1) in the voltage range 2 - 4V at 25°C in 0.5M NaPFe and 0.3M KPFe in EMC:PC:FEC and PP used as a separator.

[0036] Figure 5 illustrates the capacity retention of all the composites at various rates for a full cell with hard carbon as anode material and respective cathode materials in the voltage range 2 - 4V at 25°C in 0.5M NaPF6 and 0.3M KPF6 in EMC:PC:FEC and PP used as a separator.DETAILED DESCRIPTION OF THE INVENTION:Abbreviations:EMC: Ethyl Methyl CarbonatePC: Propylene CarbonateFEC: Fluoroethylene CarbonatePP: PolypropyleneDTD: Dithiane DiolPST: prop-l-ene-1, 3-sultone

[0037] 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.

[0038] 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.

[0039] Accordingly, to accomplish the objectives of the present invention, the inventors propose a cathode electrode material, suitable for preparing energy storage devices. Accordingly, the present invention provides a mixed cationic cathode active material made up of layered transition metal oxides-based structure suitable for preparing rechargeable metal-ion batteries with higher capacity.

[0040] In an embodiment of the present invention, the mixed cationic cathode material with optimized stoichiometry such that the 03 structure of the formed cathode is doped with larger alkali ions results in enlarged interlayer spacing, providing larger channels for ion movement.

[0041] In still another embodiment of the present invention, a cathode active material comprising of a layered alkali-transition metal oxide represented by a Formula I:AaBb(M3CM2dM3e) O2(Formula I)Wherein,‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;.‘B’ comprises another one or more alkali metal selected from Sodium, Lithium, Potassium and the like;M1is the transition metal in the oxidation state +2;M2is the transition metal in the oxidation state +3;M3is the transition metal in the oxidation state +4; and wherein stoichiometric coefficients a, b, c, d and e lies in the range: 0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1;0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05;0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333;0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333; and 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333;

[0042] In particular, the preferred cathode material may have c + d + e = 1.

[0043] In an embodiment, the transition base metals M1, M2and M3may be any transition element selected from d-block of the periodic table. In a preferred embodiment, the transition base metal M1, M2and M3may be Nickel (Ni), Iron (Fe) and Manganese (Mn) respectively.

[0044] In yet another embodiment of the present invention, the cathode active material comprises of layered alkali-transition metal oxides-based structure represented by a formula (IA),AaBb (NicFea Mne) O2 (Formula IA)Wherein,‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;‘B’ comprises another one or more alkali metal selected from Sodium, Lithium, Potassium and the like;M1is Nickel (Ni) in oxidation state +2;M2is Iron (Fe) in oxidation state +3;M3is Manganese (Mn) in oxidation state +4; wherein stoichiometric coefficients a, b, c, d and e lies in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1;0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05;0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333;0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333; and0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333.

[0045] In an embodiment, the preferred cathode material may have c + d + e = 1.

[0046] In yet another embodiment of the present invention, a mixed cation doped cathode active material of Formula (I) comprises: i. Na0.99K0.01Ni0.33Fe0.33Mn0.33O2, ii. Na0.95K0.05Ni0.33Fe0.33Mn0.33O2, and iii. Nao.9Ko.1Nio.33Feo.33Mno.33O2.

[0047] In an embodiment of the present invention, the process for the preparation of the cathode material of Formula (I) comprising co-precipitating a ternary / binary hydroxide of the base transition metal elements in their respective stoichiometric ratios and further mixing with stoichiometric ratios of respective A and B and calcination of the mixture to facilitate proper compound formation for the cathode material. Such a process may be conveniently performed in the presence of air, but it may also be performed under an inert atmosphere.

[0048] In another embodiment of the present invention, the process for the preparation of the cathode material of Formula (I) comprises the steps: i. Preparing a first solution of the base transition metal M1, M2and M3in their respective stoichiometric ratios, and a second solution of a mixture of sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH) solutions, 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 (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; iii. Intimately mixing the obtained ternary hydroxides of step (ii) with stoichiometric quantities of A and B salts, wherein A and B may be any alkali metal selected from the alkali metal group;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 1000°C until a reaction product forms; v. Allowing the reaction product to cool before grinding it to a powder.

[0049] In still another embodiment of the present invention, the base metals M1, M2and M3may be any transition element selected from d-block of the periodic table. In an aspect, the transition base metal M1, M2and M3may be Nickel (Ni), Iron (Fe) and Manganese (Mn) respectively. Further, A and B may preferably be Sodium (Na), Lithium (Li), Potassium (K), and the like.

[0050] In yet another embodiment of the present invention, an alkali-ion electrochemical cell comprising: a cathode comprising a layered alkali-transition metal oxide represented by a formula AaBb (C3cD2d E3e) O2, wherein A and B comprises of one or more alkali metals selected from Sodium, Lithium, Potassium and the like and C1, D2and E3are transition metals in the oxidation state of +2, +3 and +4 respectively and wherein stoichiometric coefficients a, b, c, d and e lies in the range: 0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1, 0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05, 0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333, 0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333, and 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, an anode comprising carbon material; and an electrolyte.

[0051] In an embodiment, the carbon material for anode is hard carbon.

[0052] In an embodiment of the present invention, the electrolyte comprises of an alkali salt dissolved in an organic solvent. The alkali salts may preferably be NaPFe, NaCICU, LiPFe and / or KPFe dissolved in an organic solvent like EthylMethyl Carbonate, Propylene Carbonate, Fluoroethylene Carbonate, Polypropylene, Dithiane Diol and / or prop-l-ene-1, 3-sultone.

[0053] In an embodiment of the present invention, the active material of Formula (I) finds application in alkali ion-cell, in energy storage devices such as batteries, rechargeable batteries, and electrochemical devices.

[0054] In still another embodiment of the present invention, the doped cathode active material of Formula (I) shows an improvement in specific capacity and, therefore, the energy density of devices made from them over undoped cathodes.

[0055] In another embodiment of the present invention, the active material of Formula (I) is used as an electrode preferably a cathode electrode in conjunction with a counter electrode and one or more electrolyte materials in alkali ion-cell and in energy storage devices or electrochemical cell.

[0056] 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.

[0057] 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 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, duringthe 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.

[0058] The following examples which include the preferred embodiments of the invention, 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 and are therefore not to be construed to be limiting the scope of the invention. The results obtained in the experimental examples are confirmed by way of analysis as depicted in the drawings, namely, figure 1 to figure 5. Examples:

[0059] The present invention and the advantages of the present invention are illustrated by way of experimental examples.Example 1: Composites of NaiNio.333Feo.333Mno.333Q2

[0060] The composite NaiNio.333Feo.333Mno,33302 is used as a cathode active material, along with hard carbon as anode material. Further, 0.5M solution of NaPFe in a mixture of ethyl methyl carbonate, propylene carbonate and fluoroethylene carbonate (EMC:PC:FEC) in a ratio of 1.2:0.8:0.1 is employed as electrolyte.

[0061] The cells were formed at 0.1C rate and post formation, were run at 0.5C rate. To ensure that the cell was fully charged, the cell was potentiostatically held at 4 V at the end of the constant current charging process for 1 hour during the formation cycling. For the rest of the tests after the formation cycling, cells were only held for 1 minute potentiostatically at 4V to ensure full desaturation of the cathode. The testing was carried out at 25°C.

[0062] During the cell charging process, sodium ions were extracted from the cathode active material, and inserted into the Hard Carbon anode. During the subsequent discharge process, sodium ions were extracted from the Hard Carbon and re-inserted into the cathode active material.

[0063] The constant current cycling graphs are plotted in Figure 1.

[0064] Figure 1 shows the constant current cycle life profile, i.e. the relationship between cathode specific capacity for discharge (mAh / g) and cycle number for hard carbon as anode material and NaiNio.333Feo.333Mno,33302 as cathode material. For the first cycle, the discharge specific capacity for the cathode is about 11 ImAh / g. For the twentieth cycle, the discharge specific capacity for the cathode is nearly 97 mAh / g. Therefore, it is evident that there occurs a capacity fade of about 12.6 % over 20 cycles, or an average of 0.63 % per cycle. The cathode material of this example demonstrates relatively poor capacity retention behavior.Example 2: Composites Nao.99Ko.oiNio.333Feo.333Mno.333Q2 as cathode material

[0065] In this example, the cathode active material composite is selected as Nao.99Ko.oiNio.333Feo.333Mno,33302 whereas the anode material is hard carbon. The electrolyte used is a 0.5M solution of NaPFe and 0.3M solution of KPFe in a mixture of Ethyl Methyl Carbonate, Propylene Carbonate and Fluoroethylene Carbonate (EMC:PC:FEC) in a ratio of 1.2:0.8:0.1. The cells were formed at 0.1C rate and post formation, were run at 0.5C rate. To ensure that the cell was fully charged, the cell was potentiostatically held at 4 V at the end of the constant current charging process for 1 hour during the formation cycle. For the rest of the tests after the formation cycle, cells were only held for 1 minute potentiostatically at 4 V to ensure full desaturation of the cathode. The testing was carried out at 25°C. During the cell charging process, host cations i.e., sodium and potassium are extracted from the cathode active material and inserted into the anode made of hard carbon. During the subsequent discharge process, said host ions are extracted from the hard carbon and re-inserted into the cathode active material.

[0066] Figure 2 shows the constant current cycle life profile, which is a graphical relationship between cathode specific capacity for discharge (mAh / g) and cycle number for the cell having composite as mentioned herein. For cycle 1, the discharge specific capacity for the cathode is nearly 125 mAh / g. For cycle 200,the discharge specific capacity for the cathode is nearly 121 mAh / g. This represents a capacity fade of about 3.2 % over 200 cycles or an average of 0.016% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.Example 3: Composites Nao.95Ko.osNio.333Feo.333Mno.33302 as cathode material

[0067] In this example, the cathode active material composite is selected as Nao.95Ko.o5Nio.333Feo.333Mno,33302 whereas the anode material is hard carbon. The electrolyte used is a 0.5M solution of NaPFe and 0.3M solution of KPFe in a mixture of Ethyl Methyl Carbonate, Propylene Carbonate and Fluoroethylene Carbonate (EMC:PC:FEC) in a ratio of 1.2:0.8:0.1. The cells were formed at 0.1C rate and post formation, were run at 0.5C rate. To ensure that the cell was fully charged, the cell was potentiostatically held at 4 V at the end of the constant current charging process for 1 hour during the formation cycle. For the rest of the tests after the formation cycle, cells were only held for 1 minute potentiostatically at 4 V to ensure full desaturation of the cathode. The testing was carried out at 25°C. During the cell charging process, host cations i.e., sodium and potassium are extracted from the cathode active material and inserted into the anode made of hard carbon. During the subsequent discharge process, said host ions are extracted from the hard carbon and re-inserted into the cathode active material.

[0068] Figure 3 shows the constant current cycle life profile, which is a graphical relationship between cathode specific capacity for discharge (mAh / g) and cycle number for the cell having composite as mentioned herein. For cycle 1, the discharge specific capacity for the cathode is nearly 125 mAh / g. For cycle 200, the discharge specific capacity for the cathode is nearly 123 mAh / g. This represents a capacity fade of about 1.6 % over 200 cycles or an average of 0.008% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.Example 4: Composites Nao.9Ko.iNio.333Feo.333Mno.333Q2 as cathode material

[0069] In this example, the cathode active material composite is selected as Nao.9Ko.iNio.333Feo.333Mno,33302 whereas the anode material is hard carbon. The electrolyte used is a 0.5M solution of NaPFe and 0.3M solution of KPFe in a mixture of Ethyl Methyl Carbonate, Propylene Carbonate and Fluoroethylene Carbonate (EMC:PC:FEC) in a ratio of 1.2:0.8:0.1. The cells were formed at 0.1C rate and post formation, were run at 0.5C rate. To ensure that the cell was fully charged, the cell was potentiostatically held at 4 V at the end of the constant current charging process for 1 hour during the formation cycle. For the rest of the tests after the formation cycle, cells were only held for 1 minute potentiostatically at 4 V to ensure full desaturation of the cathode. The testing was carried out at 25°C. During the cell charging process, host cations i.e., sodium and potassium are extracted from the cathode active material and inserted into the anode made of hard carbon. During the subsequent discharge process, said host ions are extracted from the hard carbon and re-inserted into the cathode active material.

[0070] Figure 4 shows the constant current cycle life profile, which is a graphical relationship between cathode specific capacity for discharge (mAh / g) and cycle number for the cell having composite as mentioned herein. For cycle 1, the discharge specific capacity for the cathode is nearly 120 mAh / g. For cycle 200, the discharge specific capacity for the cathode is nearly 118.2 mAh / g. This represents a capacity fade of about 1.5 % over 200 cycles or an average of 0.0075% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0071] ADVANTAGES OF THE INVENTION:• The present cathode active material has a novel cationic stoichiometry suitable for preparing energy storage devices.• The present cathode active material exhibits a high specific capacity with little or no fading on cycling. The incorporation of element B in the base compoundANFM reduces the strain on the cathode while cycling and thus allows for longer cycle life.• The present cathode active material allows for higher rate capability, delivered more capacity at elevated rates of charge and discharge. The incorporation of element B increases the inter-slab height and allows for faster intercalation and de-intercalation thus increasing the rate capability of the cathode.

Claims

We claim:

1. A cathode active material comprising of a layered alkali-transition metal oxide represented by a formula:Aa Bb CM^ M^ M3e) O2wherein‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;‘B’ comprises one or more another alkali metal selected from Sodium, Lithium, Potassium and the like;M1is a transition metal in the oxidation state +2;M2is a transition metal in the oxidation state +3;M3is a transition metal in the oxidation state +4; and wherein stoichiometric coefficients a, b, c, d and e are in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1, 0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05,0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333,0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333, and0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333.

2. A cathode active material as claimed in claim 1, wherein the layered alkali-transition metal oxide is represented by the formula:AaBb (NicFea Mne) O2, wherein‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;‘B’ comprises one or more another alkali metal selected from Sodium, Lithium, Potassium and the like;M1is Nickel in oxidation state +2;M2is Iron in oxidation state +3;M3is Manganese in oxidation state +4; and wherein the stoichiometric coefficients a, b, c, d and e lies in the range: 0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1, 0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05,0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333,0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333, and0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333.

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

4. The cathode active material as claimed in claim 2, wherein the cathode active material comprises of: Na0.99K0.01Ni0.33Fe0.33Mn0.33O2, Na0.95K0.05Ni0.33Fe0.33Mn0.33O2, or Nao.9Ko.1Nio.33Feo.33MnO.33O2.

5. The cathode active material as claimed in claim 1, wherein the cathode active material is used in an alkali ion-cell, any batteries, energy accumulators, electrochemical devices and / or electrochromic devices.

6. A method for preparing a cathode material, the method comprising steps of: step (a): co-precipitating a ternary or binary hydroxide of a base transition metal in their respective stoichiometric ratios; step (b): mixing product obtained from step (a) with one or more alkali salts in their respective stoichiometric ratios; and step (c): calcinating the mixture of step (b) to form the cathode material.

7. The method for preparing the cathode material as claimed in claim 6, wherein the method comprising steps of: step (i): preparing a first solution of base transition metal M1, M2& M3in their respective stoichiometric ratios and preparing a second solution which is a mixture of an alkali-hydroxide and ammonium hydroxide; step (ii): mixing above two solutions simultaneously followed by aging under stirring condition to allow homogenous particle formation to form a ternary hydroxide; step (iii): mixing the ternary hydroxides of step (ii) with stoichiometric quantities of A and B salts, where A and B are any alkali metals; step (iv): heating the mixture obtained in step (iii) within a single temperature or over a range of temperatures between 450°C and 1000°C until a final ternary oxide forms; and step (v): cooling the final ternary oxide as obtained from step (iv) before grinding it to a powder for forming the cathode material.

8. The method for preparing the cathode material as claimed in claim 7, wherein the alkali-hydroxide is Sodium Hydroxide (NaOH).

9. The method for preparing the cathode material as claimed in claim 7, wherein the cathode material may be prepared in the presence of air or in an inert atmosphere.

10. An alkali-ion electrochemical cell comprising: a cathode comprising a layered alkali-transition metal oxide represented by a formulaAaBb (M1cM2d M3e) O2wherein‘A’ comprises one or more alkali metal selected from Sodium, Lithium, Potassium and the like;‘B’ comprises one or more another alkali metal selected from Sodium, Lithium, Potassium and the like;M1is a transition metal in the oxidation state +2;M2is a transition metal in the oxidation state +3;M3is a transition metal in the oxidation state +4; and wherein stoichiometric coefficients a, b, c, d and e are in the range:0.67 < a < 1, preferably 0.85 < a < 1, further preferably 0.95 < a < 1,0.01 < b < 0.25, preferably 0.01 < b < 0.1, further preferably 0.01 < b < 0.05,0 < c < 0.5, preferably 0 < c < 0.45, further preferably 0 < c < 0.333,0 < d < 0.5, preferably 0 < d < 0.45, further preferably 0 < d < 0.333, and0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, an anode comprising carbon material; and an electrolyte.

11. The alkali-ion electrochemical cell as claimed in claim 10, wherein the electrolyte comprises of an alkali salt dissolved in an organic solvent.

12. The alkali-ion electrochemical cell as claimed in claim 11, wherein the alkali salts are NaPFe, NaCICh, LiPFe and / or KPFe dissolved in an organic solvent like Ethyl Methyl Carbonate, Propylene Carbonate, Fluoroethylene Carbonate, Polypropylene, Dithiane Diol and / or prop-1- ene-1, 3-sultone.

13. The alkali-ion electrochemical cell as claimed in claim 10, wherein the cathode is arranged in series, parallel, and / or both in the alkali-ion electrochemical cell.

14. The alkali-ion electrochemical cell as claimed in claim 10, wherein the cathode is used as a positive electrode along with a counter electrode and one or more electrolyte materials in the alkali ion electrochemical cell.

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