High-capacity mixed cation multi-ionic cathodes

Abstract

The present invention discloses a 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 discloses a method of producing a doped cathode material having novel stoichiometry capable of preparing alkali ion batteries.

Description

HIGH-CAPACITY MIXED CATION MULTI-IONIC CATHODESFIELD OF INVENTION:

[0001] The present invention relates to a doped cathode material that comprises of an active material made up 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 alkali ion 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 an03-type stacking sequence. The 03 phase is composed of alternate alkali metal ion 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 MOe edge-sharing octahedral units forming (M02)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 synthesismethods of layered materials are generally the traditional solid-phase reaction methods, 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] 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.

[0009] 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.

[0010] 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 areless 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.

[0011] On analyzing the literature pertaining to rechargeable batteries, there appears 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 INVENTION:

[0012] Accordingly, the main objective of the present invention is to provide a mixed cation 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 INVENTION:

[0013] Accordingly, the present invention provides 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 a layered transition metal oxides-based structure suitable for rechargeable metal-ion batteries with higher capacity.

[0014] In an aspect of the present invention, the cation doped mixed cationic cathode active material comprising of a layered alkali-transition metal oxide which is represented by Formula (I) comprising;AaBb(M^ M2dM3e)(i.f) M4fO2(Formula I) 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 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;M4is a transition metal in the oxidation state +2, +3 or +4; wherein stoichiometric coefficients a, b, c, d, e and flies 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, 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and 0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05.

[0015] In particular, M may be any transition metal selected from the d-block of the periodic table. In an aspect, transition metal M4is selected from Calcium (Ca), Strontium (Sr), Magnesium (Mg), Tin (Sn) and Titanium (Ti).

[0016] In particular, the preferred cathode material have c + d + e + f = 1.

[0017] In another aspect of the present invention, the mixed cationic cathode active material comprising of the layered alkali-transition metal oxide represented by a formula IA:AaBb (NicFea Mne) (i-p M4f O2 (Formula IA) 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 (Ni) in oxidation state +2;M2is Iron (Fe) in oxidation state 3+;M3is Manganese (Mn) in oxidation state 4+;M4is a transition metal in the oxidation state +2, +3 or +4; wherein stoichiometric coefficients a, b, c, d, e and flies 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 < 0.333,0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05.

[0018] In particular, M may be any transition metal selected from the d-block of the periodic table. In an aspect, transition metal M4is selected from Calcium (Ca), Strontium (Sr), Magnesium (Mg), Tin (Sn) and Titanium (Ti).

[0019] In particular, the preferred cathode material have c + d + e + f = 1.

[0020] In another aspect of the present invention, the mixed cation doped cathode active material of Formula (I) comprises: i. Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Cao.osCh, ii. Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sro.osCh, iii. Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Mgo.osCh, iv. Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sno.osCh, or v. Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Tio.osCh,

[0021] In an aspect 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 and further mixing with stoichiometric ratios of respective A, B and M4salts and calcination of the mixture to facilitate the compound formation. Such a process may be conveniently performed in the presence of air, but it may also be performed under an inert atmosphere.

[0022] In preferred aspect 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 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, B and M4salts; 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.

[0023] In another preferred aspect of the present invention, the base transition metals may be any transition metal selected from d-block of the periodic table. Preferably, the base metals M1, M2, M3and M4may be Nickel (Ni), Iron (Fe), Manganese (Mn) and elements like Calcium (Ca), Strontium (Sr), Magnesium (Mg), Tin (Sn) or Titanium (Ti) respectively.

[0024] In particular, the preferred cathode material have c + d + e + f = 1.

[0025] In an aspect, an alkali-ion electrochemical battery comprising: a cathode comprising a layered alkali-transition metal oxide represented by a formula:Aa Bb (M4CM2d M3e) (1-f) M4f 02wherein,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 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;M4is a transition metal in the oxidation state +2, +3 or +4; wherein, stoichiometric coefficients a, b, c, d, e and f 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 < 0.333,0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05, an anode comprising carbon material; and an electrolyte.

[0026] In another preferred aspect of the present invention, the base transition metals may be any transition metal selected from d-block of the periodic table. Preferably, the base metals M1, M2, M3and M4may be Nickel (Ni), Iron (Fe), Manganese (Mn) and elements like Calcium (Ca), Strontium (Sr), Magnesium (Mg), Tin (Sn) or Titanium (Ti) respectively.

[0027] In particular, the preferred cathode material have c + d + e + f = 1.

[0028] In an aspect, the carbon material for anode may be hard carbon.

[0029] In an aspect, the electrolyte comprises of an alkali salt dissolved in an organic solvent. In particular, the alkali salts are NaPFe, NaCICh, LiPFe and / orKPFe dissolved in an organic solvent like Ethyl Methyl Carbonate, Propylene Carbonate, Fluoroethylene Carbonate, Polypropylene, Dithiane Diol and / or prop- 1-ene-l, 3-sultone.

[0030] 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, and electrochromic devices.BRIEF DESCRIPTION OF DRAWINGS:

[0031] Figure 1 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and NaiNio.333Feo.333Mno,33302 in the voltage range 2 - 4V at 25°C in 0.5M NaPF6 in EMC:PC:FEC and PP used as a separator.

[0032] Figure 2 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and Na0.95K0.05Ni0.327Fe0.327Mn0.327Ca0.05O2 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.

[0033] Figure 3 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and Na0.95K0.05Ni0.327Fe0.327Mn0.327Sr0.05O2 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.

[0034] Figure 4 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and Na0.95K0.05Ni0.327Fe0.327Mn0.327Mg0.05O2 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.

[0035] Figure 5 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and Na0.95K0.05Ni0.327Fe0.327Mn0.327Sn0.05O2 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.

[0036] Figure 6 illustrates the Constant current cycling (CC / CV) of a present full cell with hard carbon as anode material and Na0.95K0.05Ni0.327Fe0.327Mn0.327Ti0.05O2 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-l,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] The common problems with 03 layered transition metal an oxide operating at high electrochemical potential is that they undergo phase transformation leading to irreversible capacity loss. To mitigate this, the current invention utilizes additional cationic elements that replace some portion of the cathode’s framework. The higher bond strength and dissimilar size of these elements allow for a more robust framework that is not prone to layers sliding or collapsing even after deintercalation.

[0040] 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 a layered transition metal oxides-based structure suitable for preparing rechargeable metal-ion batteries with higher capacity.

[0041] 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.

[0042] In still another embodiment of the present invention, the mixed cationic cathode active material is represented by Formula (I), comprising;AaBb(M^ M2dM3e)(i.f) M4fO2(Formula I) 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 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;M4is a transition metal in the oxidation state +2, +3 or +4, wherein stoichiometric coefficients a, b, c, d, e and flies 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; 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333; and 0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05;

[0043] In particular, M may be any transition metal selected from the d-block of the periodic table.

[0044] In particular, the preferred cathode material have c + d + e + f = 1.

[0045] In yet another embodiment of the present invention, the mixed cationic cathode active material is represented by Formula (IA) comprising;AaBb (NicFea Mne) (i-p M4f O2 (Formula IA) 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 (Ni) in oxidation state +2;M2is Iron (Fe) in oxidation state 3+;M3is Manganese (Mn) in oxidation state +4;M4is a transition metal in the oxidation state +2, +3 or +4; wherein stoichiometric coefficients a, b, c, d, e and flies 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;0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333; and0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05.

[0046] In particular, M may be any transition metal selected from d-block of the periodic table.

[0047] In particular, the preferred cathode material have c + d + e + f = 1.

[0048] In an embodiment, the mixed cationic cathode active material may comprise of:Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Cao.osCh,Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sro.osCh, Nao.95Ko.O5(Nio.33Feo.33Mno.33)o.95 Mg0.05O2, Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sno.osCh, or Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Tio.osCh.

[0049] 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 and further mixing with stoichiometric ratios of respective A, B and M4and 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.

[0050] In another embodiment of the present invention, the process for the preparation of the cathode material of Formula (I) comprises the steps of: i. Preparing a first solution of the base transition metal M1, M2M3and M4in their respective stoichiometric ratios, and a second solution of a mixture ofNaOH and 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 alkali metal salts and M4element; 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.

[0051] In an embodiment, the cathode material may be prepared in the presence of air or in an inert atmosphere.

[0052] In still another embodiment of the present invention, transition elements M1, M2and M3are the base metals C, D & E which are Ni, Fe & Mn respectively. Further, transition element M4may be selected from Calcium (Ca), Strontium (Sr), Magnesium (Mg), Tin (Sn) and Titanium (Ti).

[0053] Yet in another embodiment of the present invention, the alkali-ion electrochemical battery comprising; a cathode comprising a layered alkali-transition metal oxide represented by a formula:Aa Bb (M4c M2d M3e) (1-f) M4f 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 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;M4is a transition metal in the oxidation state +2, +3 or +4; wherein, stoichiometric coefficients a, b, c, d, e and f 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, 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and 0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05. an anode comprising carbon material; and an electrolyte.

[0054] In an embodiment, the carbon material for anode may be hard carbon.

[0055] In an embodiment, the electrolyte comprises of an alkali salt dissolved in an organic solvent. In particular, the alkali salts are 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- 1-ene-l, 3-sultone.

[0056] 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 6.Examples:

[0057] The present invention and the advantages of the present invention are illustrated by way of experimental examples.

[0058] Example 1: Composites of NaiNio.333Feo.333Mno.333Q2 as cathode materialThe composite NaiNio.333Feo.333Mno,33302is 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.

[0059] 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.

[0060] During the cell charging process, sodium ions were extracted from the cathode active material, and inserted into the Hard Carbon anode. During thesubsequent discharging process, sodium ions were extracted from the Hard Carbon and re-inserted into the cathode active material.

[0061] The constant current cycling graphs are plotted in Figure 1.

[0062] Figure 1 shows the constant current cyclelife 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 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.

[0063] Example 2: Composites Na0.95K0.05Ni0.327Fe0.327Mn0.327Ca0.05O2 as cathode materialIn this example, the cathode active material composite is selected as Na0.95K0.05Ni0.327Fe0.327Mn0.327Ca0.05O2 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.

[0064] 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 about 135 mAh / g. For cycle 200, the discharge specific capacity for the cathode is about 133 mAh / g. This represents a capacity fade of about 1.48 % over 200 cycles or an average of 0.0074% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0065] Example 3: Composites Na0.95K0.05Ni0.327Fe0.327Mn0.327Sr0.05O2 as cathode materialIn this example, the cathode active material composite is selected as Na0.95K0.05Ni0.327Fe0.327Mn0.327Sr0.05O2 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 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 about 140 mAh / g. For cycle 200, the discharge specific capacity for the cathode is about 136 mAh / g. This represents acapacity fade of about 2.85 % over 200 cycles or an average of 0.0142% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0067] Example 4: Composites Na0.95K0.05Ni0.327Fe0.327Mn0.327Mg0.05O2 as cathode materialIn this example, the cathode active material composite is selected as Na0.95K0.05Ni0.327Fe0.327Mn0.327Mg0.05O2 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 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 about 142 mAh / g. For cycle 200, the discharge specific capacity for the cathode is about 136.2 mAh / g. This represents a capacity fade of about 4.08 % over 200 cycles or an average of 0.0204% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0069] Example 5: Composites Na0.95K0.05Ni0.327Fe0.327Mn0.327Sn0.05O2 as cathode materialIn this example, the cathode active material composite is selected as Na0.95K0.05Ni0.327Fe0.327Mn0.327Sn0.05O2 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 5 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 about 136 mAh / g. For cycle 200, the discharge specific capacity for the cathode is about 133 mAh / g. This represents a capacity fade of about 2.20 % over 200 cycles or an average of 0.011% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0071] Example 6: Composites Na0.95K0.05Ni0.327Fe0.327Mn0.327Ti0.05O2 as cathode materialIn this example, the cathode active material composite is selected as Na0.95K0.05Ni0.327Fe0.327Mn0.327Ti0.05O2 whereas the anode material is hard carbon. The electrolyte used is a 0.5M solution of NaPFe and 0.3M solution of KPFe in amixture 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.

[0072] Figure 6 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 about 139 mAh / g. For cycle 200, the discharge specific capacity for the cathode is about 133 mAh / g. This represents a capacity fade of about 4.316 % over 200 cycles or an average of 0.021% per cycle. The cathode material under test clearly demonstrates relatively better capacity retention behavior.

[0073] 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 is higher than devices made from undoped cathodes.

[0074] 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.

[0075] In an 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.

[0076] 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.

[0077] 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 ions are deintercalated from the cathode, the nickel in the cathode undergoes 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.

[0078] The present invention conceives a mixed cationic cathode active material comprising of a layered alkali-transition metal oxide as a cathode active material in secondary batteries or alkali-metal ion batteries which may improve the cyclic properties of secondary batteries. Though the present invention may apply to secondary batteries, it may also be appreciated that the present invention may alsobe applicable to electrical energy accumulators or more commonly occurring rechargeable batteries.

[0079] 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.

[0080] 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 even at higher voltages and mitigates the cathode’s phase transformation. This benefit is attributed to the specific composite wherein the addition of element B and M4increases the stability of the cathode active material.

Claims

We claim:

1. A mixed cationic cathode active material comprising of a layered alkali- transition metal oxide represented by a formula:Aa Bb (M4CM2d M3e) (1-f) M4f 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 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;M4is a transition metal in the oxidation state +2, +3 or +4; wherein stoichiometric coefficients a, b, c, d, e and flies 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 < 0.333,0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05.

2. The mixed cationic cathode active material as claimed in claim 1, wherein the mixed cationic cathode active material is represented by a formula:AaBb (NicFea Mne) (i-i) M4f 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 (Ni) in oxidation state +2;M2is Iron (Fe) in oxidation state 3+;M3is Manganese (Mn) in oxidation state 4+;M4is a transition metal in the oxidation state +2, +3 or +4; wherein stoichiometric coefficients a, b, c, d, e and flies 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, 0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and 0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.05.

3. The mixed cationic cathode active material as claimed in claim 2, wherein the mixed cationic cathode active material comprises of: Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Cao.osCh, Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sro.osCh, Nao.95Ko.O5(Nio.33Feo.33Mno.33)o.95 Mg0.05O2, Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Sno.osCh, or Nao.95Ko.o5(Nio.33Feo.33Mno.33)o.95 Tio.osCh.

4. The mixed cationic cathode active material as claimed in claim 1, wherein c + d + e + f = 1.

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

6. The mixed cationic cathode active material as claimed in claim 5, wherein the energy storage devices are batteries like rechargeable batteries.

7. A method for preparing a cathode material, the method comprising steps of: step (a) co-precipitating a ternary or a 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 metals and one or more a transition metal in their respective stoichiometric ratios; and step (c) calcinating the mixture of step (b) to form a composite for the cathode material.

8. The method for preparing a cathode material as claimed in claim 7, wherein the method comprising steps of: step (i) preparing a first solution of base transition metals M1, M2, M3and M4in their respective stoichiometric ratios and preparing a second solution of a mixture of an alkali-hydroxide and ammonium hydroxide; step (ii) mixing the first and second solution 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 and one or more base transition metals, wherein 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 reaction product forms; and step (v) cooling the reaction product as obtained from step (iv) before grinding it to a powder for forming the cathode material.

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

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

11. The method as claimed in claim 8, wherein the second solution is vigorously stirred under Nitrogen (N2) atmosphere.

12. An alkali-ion electrochemical battery comprising: a cathode comprising a layered alkali-transition metal oxide represented by a formula:Aa Bb (M4CM2d M3e) (1-f) M4f 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 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;M4is a transition metal in the oxidation state +2, +3 or +4; wherein, stoichiometric coefficients a, b, c, d, e and f 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 < 0.333,0 < e < 0.5, preferably 0 < e < 0.45, further preferably 0 < e < 0.333, and0 < f < 0.2, preferably 0 < f < 0.1, further preferably 0 < f < 0.

05. an anode comprising carbon material; and an electrolyte.

13. The alkali-ion electrochemical cell as claimed in claim 12, wherein the electrolyte comprises of an alkali salt dissolved in an organic solvent.

14. The alkali-ion electrochemical cell as claimed in claim 13, wherein the alkali salts are 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.

15. The alkali-ion electrochemical battery as claimed in claim 12, wherein the alkali-ion electrochemical battery is arranged in series, parallel, or both.

16. The alkali-ion electrochemical battery as claimed in claim 12, wherein the cathode is used in conjunction with a counter electrode and one or more electrolyte materials in the alkali ion electrochemical battery or energy storage devices or electrochemical cells.

17. The alkali-ion electrochemical cell as claimed in claim 12, 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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