WO2023187798A1

WO2023187798A1 - Porous single crystal of metal oxide and preparation methods thereof

Info

Publication number: WO2023187798A1
Application number: PCT/IN2022/050784
Authority: WO
Inventors: Mani Vellaisamy; Laurel Simon Lobo; Rajesh MEKKAT
Original assignee: Ola Electric Mobility Private Limited
Priority date: 2022-03-31
Filing date: 2022-09-02
Publication date: 2023-10-05

Abstract

The present disclosure provides porous single crystal of a metal oxide for use as cathode material in lithium-ion batteries. The porous single crystal has a crystallite size of at least 8 microns and has plurality of pores uniformly distributed therein. The pores have an average dimension of 5 nm to 10 nm and a porosity of 8% to 10%. A method for preparing the same is also disclosed. The method comprises coprecipitation of metal hydroxide with doping metal ion and a pore creating agent. The metal hydroxide is subjected to double sintering to form the porous single crystal.

Description

POROUS SINGLE CRYSTAL OF METAL OXIDE AND PREPARATION METHODS THEREOF BACKGROUND FIELD OF THE DISCLOSURE Various embodiments of the disclosure relate generally to a single crystal layered metal oxide cathode material. More specifically, various embodiments of the disclosure relate to porous single crystal of a metal oxide, methods for preparing the same, and their use as a cathode material in alkali ion batteries. DESCRIPTION OF THE RELATED ART There is an ever-increasing demand for lithium-ion batteries (LIBs) having high-energy or high- power density fueled by their application in, for example, electric vehicle industry, electronic gadgets, and aerospace. Mixed metal oxides such as high-nickel metal oxides are promising candidates as cathode material for high-energy LIBs. Commercial layered metal oxides are typically prepared by a co-precipitation route that involves aggregation of nanometer-sized primary particles to form polycrystalline secondary particles. However, polycrystalline metal oxides are prone to pulverization that occurs during repeated charge-discharge cycles and is initiated by cracks on weak grain boundaries of the primary particles. The cracks lead to unwanted side reactions between the electrolyte and the electrode active material. This results in the reduction of the battery capacity and shortening of the cycle life of the battery. Single crystal cathode material with minimal grain boundaries has been proposed to overcome the problems associated with polycrystalline cathode material. A single crystal cathode material has good mechanical stability and cycle life compared to polycrystalline cathode material. Further, it has been observed that spherical, single crystal cathode material enhances the energy density of LIBs. The single crystals have typical crystallite size in the range of 3 microns - 5 microns which increases lithium diffusion path. As a result, in single crystal, lithium-ion diffusion rate decreases which in turn reduces the capacity of the battery. Heterostructure coating, namely, coating the surface of the single crystal with manganese-based metal-organic framework (Mn-MOF) has been disclosed. Though MOF improves the penetration of electrolytes and lithium-ion conductivity of the cathode material, the energy density of such heterostructure coatings requires further improvement. Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings. SUMMARY According to the embodiments of the present disclosure, a porous single crystal of a metal oxide is provided. The metal oxide is represented by the Formula (I), LiNi_1-xM1_xO_2,(I), wherein M1 is selected from the group consisting of one or more of Mn, Co, Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W, Mg, and Sn, where x varies from 0.05 to 0.4. The porous single crystal has a crystallite size of at least 8 microns. The porous single crystal has pores uniformly distributed therein having an average dimension of 5 nm to 10 nm and porosity in the range of 8% to 10%. In another embodiment, a method for preparing a porous, single crystal of a metal oxide represented by Formula (I), LiNi1-xM1xO2 (I) is provided. In the Formula (I), M1 is selected from the group consisting of one or more of Mn, Co, Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W, and Sn, and x varies from 0.05 to 0.4. At step (i), the method comprises providing at least one metal salt solution, a complexing agent solution, and a precipitating agent solution in a reactor. A metal hydroxide precursor solution is formed by co-precipitating with at least one metal from the at least one metal salt solution, a doping metal ion, and a pore creating agent in presence of the precipitating agent and the complexing agent, at step (ii). In one embodiment, forming the metal hydroxide precursor solution comprises providing a first aqueous solution comprising the doping metal ion and the pore creating agent at regular intervals in the reactor during co-precipitation. At step (iii), the metal hydroxide precursor solution undergoes aging to form aged metal hydroxide precursor solution comprising metal hydroxide particles. The metal hydroxide particles from the aged metal hydroxide precursor solution are separated at step (iv). At step (v), the metal hydroxide particles are mixed with a first lithium source and a first sintering process is performed under oxygen atmosphere to form metal oxide precursor particles. The metal oxide precursor particles are mixed with a second lithium source and a second sintering process is performed under oxygen atmosphere to form the porous, single crystal of the metal oxide, at step (vi). In yet another embodiment, a porous single crystal of a metal oxide having the Formula (I) LiNi_1- xM1xO2 (I) is provided. In the Formula (I), M1 is selected from the group consisting of one or more of Mn, Co, Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W, and Sn, and x varies from 0.05 to 0.4. The porous single crystal has a crystallite size of at least 8 microns and has pores uniformly distributed therein having an average dimension of 5 nm to 10 nm and a porosity in the range of 8% to 10%. The porous single crystal is prepared by a method comprising providing at least one metal salt solution, a complexing agent solution, and a precipitating agent solution in a reactor, at step (i). A metal hydroxide precursor solution is formed by co-precipitating at least one metal from the at least one metal salt solution with a doping metal ion and a pore creating agent in presence of the precipitating agent and the complexing agent, at step (ii). In one embodiment, forming the metal hydroxide precursor solution comprises providing a first aqueous solution comprising the doping metal ion and the pore creating agent at regular intervals in the reactor during co-precipitation. At step (iii), the metal hydroxide precursor solution undergoes aging to form aged metal hydroxide precursor solution comprising metal hydroxide particles. The metal hydroxide particles from the aged metal hydroxide precursor solution are separated at step (iv). At step (v), the metal hydroxide particles are mixed with a first lithium source and a first sintering process is performed under oxygen atmosphere to form metal oxide precursor particles. The metal oxide precursor particles are mixed with a second lithium source and a second sintering process is performed under oxygen atmosphere to form the porous, single crystal of the metal oxide, at step (vi). These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout. BRIEF DESCRIPTION OF DRAWINGS FIG.1 is a flow chart that illustrates a method for preparing a porous single crystal of a metal oxide, in accordance with an exemplary embodiment of the disclosure. Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure. DETAILED DESCRIPTION OF EMBODIMENTS The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure. The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained. As used herein, the term “lithium-ion battery” (LIB) refers to any conventional lithium-ion batteries having an anode and a cathode, or an anode-free battery, and includes lithium-ion polymer batteries, batteries with liquid electrolytes and also solid-state batteries. As used herein, the terms “cathode” and “anode” refer to the electrodes of a battery. During a charge cycle in a Li-ion battery, Li ions leave the cathode and move through an electrolyte to the anode. During the charge cycle, electrons leave the cathode and move through an external circuit to the anode. During a discharge cycle in the Li-ion battery, Li ions migrate towards the cathode through an electrolyte from the anode. During a discharge cycle, electrons leave the anode and move through an external circuit to the cathode. As used herein, the term “electrolyte” refers to a material that allows ions, e.g., Li⁺, to migrate therethrough, but which does not allow electrons to conduct therethrough. In one embodiment of the disclosure, a porous single crystal of a layered metal oxide represented by Formula (I), LiNi1-xM1xO2 (I), is provided. In the Formula (I), M1 is selected from the group of metals consisting of one or more of Manganese (Mn), Cobalt (Co), Titanium (Ti), Aluminum (Al), Magnesium (Mg), Chromium (Cr), Zirconium (Zr), Gadolinium (Gd), Niobium (Nb), Tantalum (Ta), Tungsten (W), and Tin (Sn). Here, x varies from 0.05 to 0.4. The porous single crystal has a crystallite size of at least 8 micrometers or microns and has pores uniformly distributed therein. The metal oxide as represented by Formula (I), in one embodiment, is a high-nickel metal oxide. LIBs based on high-nickel metal oxide cathode material are known for their high energy density and low cost. As used herein, the term “high-nickel oxide” refers to 1-x having a value of greater than or equal to 0.6 (1-x≥0.6) in the Formula (I). The metal oxide, in one embodiment, forms part of a cathode of a lithium-ion battery. The lithium in the Formula (I) may be replaced with other alkali metals like sodium or potassium. For example, for a sodium ion battery, lithium in the above formula may be replaced with sodium so as to form the metal oxide having formula NaNi_1-xM_xO₂. In one embodiment, M1 is selected from a combination of Mn and Co. When M1 is Mn and Co, the formula is represented by Formula (II), LiNi1-x-yMnx CoyO2. In Formula (II), x varies from 0.05 to 0.4, y varies from 0 to 0.4 and x+y is less than or equal to 0.4. (x+y≤0.4). In one example, x has the value 0.2 and y has a value 0.1, and the metal oxide has the formula LiNi0.7Mn0.2Co0.1O2. In another embodiment, M1 is selected from a combination of Mn, Co, and a third metal M2, where M2 is selected from a group of metals consisting of Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W, and Sn. The metal oxide, where M1 is selected from a combination of Mn, Co, and having a third metal M2 is represented by Formula (III), LiNi1-x-y-zMnxCoyM2zO2, where x varies from 0.05 to 0.4, y varies from 0 to 0.4, z varies from 0 to 0.04 and x+y+z is less than or equal to 0.4 (x+y+z≤0.4). It is an object of the present disclosure to provide a metal oxide cathode material having good tap density and mechanical strength associated with a single crystal cathode material while at the same time offer lithium-ion conductivity comparable to polycrystalline cathode material. A porous structured cathode material can provide enhanced surface area for interaction with the electrolyte as compared to a non-porous structure. It is an object of the disclosure to provide pores that are uniformly distributed in the single crystal, whereby the penetration of electrolyte is improved evenly. The porous structure reduces lithium-ion diffusion path length and enhances lithium-ion conductivity. Further, the porosity can be controlled to ensure that the tap density is not compromised. Accordingly, embodiments of the disclosure, provide a porous single crystal layered metal oxide prepared by fine tuning the porosity and pore size of the single crystal so as to optimize the tap density, lithium-ion conductivity to achieve high energy density. According to an embodiment of the disclosure, porosity of the single crystal is determined based on the required cathode material density. The required material density is determined based on the required energy density. It is known that the theoretical density of nickel, manganese, and cobalt based cathode material is approximately 4.6 g/cm³. Therefore, to achieve the required density of at least 4.2 g/cm³ in the cathode active material having plurality of pores, porosity of 8% to10% in the single crystal particle is created. In one embodiment, to maintain the mechanical and structural stability of the single crystal during electrode calendaring the crystal particle size or crystallite size is chosen to be of at least 8 micrometers (µm). For a crystal having at least 8 µm size, pore dimension or size is maintained in the range of 5 nm to10 nm to achieve porosity of 10%. The term, “tap density”, as used herein, is defined as the optimal packing density of the porous single crystal material. Several factors are favored to improve the tap density including compactness or fitting of particles, morphology, size, and porosity of the particle of the material. The metal oxide as represented by Formula (I) to (III) is a crystal having a crystallite size of at least 10 microns, more preferably in a range of 8 microns to 10 microns, and most preferably of at least 8 microns. An X-ray diffraction technique (XRD) can be used to determine the crystallite size of a crystal. The metal oxide as represented by Formula (I) to (III) is a porous crystal including plurality of pores in the crystal, where the average pore size is lower than 10 nm and the pores are uniformly distributed therein. In an embodiment, the pores of the single crystal have an average pore dimension in the range of 5 nm to 10 nm. As used herein, the term “average pore size”, refers to summation of individual pore sizes averaged over the number of pores. The porous single crystal has a porosity in the range of 8% to 10%. The term, “porosity” can be defined as the ratio of the volume of pores to the volume of bulk. The porosity and other pore parameters such as distribution of pores and pore dimension can be determined using conventional techniques such as small-angle scattering techniques (X-ray or neutrons), gas physisorption (mostly with nitrogen), or through mercury intrusion porosimetry (MIP). Additionally, imaging methods such as SEM or TEM may be employed. The porous single crystal is spherical. FIG.1 is a flow chart that illustrates a method 100 for preparing a porous single crystal of a metal oxide, in accordance with embodiments of the present disclosure. At step 102, at least one metal salt solution, a complexing agent solution, and a precipitating agent solution are provided in a reactor. The at least one metal solution is prepared by dissolving one or more metal salts in distilled water. In one embodiment, the at least one metal of the metal salt is selected from Mn, Co, Ti, Al, Cr, Zr, Gd, W, Sn or any combinations thereof. The salts are sulfates, carbonates, oxalates, chlorides, and nitrates of the respective metal. In one embodiment, nickel salt may be chosen from nickel sulfate, nickel carbonate, nickel nitrate, nickel chloride, and nickel oxalate. Manganese salt may be chosen from manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, and manganese oxalate. Cobalt salt may be chosen from cobalt sulfate, cobalt carbonate, cobalt nitrate, cobalt chloride, and cobalt oxalate. In a preferred embodiment, metal salts are sulfate salts of the metals, namely, nickel, cobalt, and manganese. The precipitating agent solution is prepared by dissolving the precipitating agent in water. The precipitating agent comprises sodium hydroxide, sodium oxalate, or sodium bicarbonate. The complexing agent solution is prepared by dissolving complexing agent in water. The complexing agent comprises ammonium hydroxide or carbonate or oxalate. In a preferred embodiment, sodium hydroxide is used as the precipitating agent and ammonium hydroxide is used as the complexing agent. The reactor, as used herein, refers to any process vessel that is commonly used for performing a chemical reaction. The reactor may be a batch reactor, a continuous stirred-tank reactor (CSTR), or a plug flow tubular reactor (PFR). In one embodiment, the reactor is a CSTR reactor. Additionally, the reactor may be fitted with agitators or stirrers for uniform mixing during a reaction. In one embodiment, providing the at least one metal salt solution, the complexing agent solution, and the precipitating agent solution comprises flowing into the reactor each of these solutions at a set flow rate. At step 104, a metal hydroxide precursor solution is formed by co-precipitating at least one metal from the at least one metal salt solution with a doping metal ion and a pore creating agent in presence of the precipitating agent and the complexing agent. The doping metal ion is selected from the group of metals that forms strong metal-oxygen bonds. In an embodiment, the doping metal ion is chosen from ions of Ti, Al, Zr, Nb, Ta, W, Cr, Mg, and any combinations thereof. In a preferred embodiment, the doping metal ion is Ti. Doping metal ion reduces phase transition, cation mixing and oxygen loss thus stabilizing the mechanical and thermal properties of the resultant oxide precursor prepared at step 110. The pore creating agents are selected based on their solubility in water and high decomposition temperature. The high decomposition temperature, for example, 550 ºC, of the pore creating agent is beneficial by being stable at a lower sintering temperature and decomposing at a higher temperature thus creating stable pores in the particle. The solubility of pore creating agents in water facilitates co-precipitation. The pore creating agent is chosen from the group of water- soluble polyimides having the functional group of amines; water soluble functionalized carbon nanotubes (CNT), amine-functionalized CNT, hydroxide-functionalized CNT, carboxylic acid- functionalized CNT water soluble polymer-grafted CNT, saccharide-functionalized CNT, and chitosan. In the case of functionalized CNT, the hydrophilic nature of the functional group like carboxylic, hydroxyl, water soluble polymer, or a saccharide group renders the functionalized- CNT water soluble. In one embodiment, the pore creating agent is functionalized CNT which forms a suspension in water. During co-precipitation, the suspended CNT is co-precipitated along with the at least one metal and doping metal ion which is facilitated by the precipitating agent. The concentration of the pore creating agent is decided based on the required pore size, particle size of the primary particle, and morphology of the pore. The step 104 of forming the metal hydroxide precursor solution comprises providing a first aqueous solution comprising the doping metal ion and the pore creating agent at regular intervals in the reactor during co-precipitation. In one embodiment, regular intervals constitute addition at every 5 minutes for a co-precipitation reaction that lasts an hour. The first aqueous solution is prepared by adding a desired amount of the doping metal ion and the pore creating agent in water. It is known that the precipitating agent and the complexing agent can precipitate the at least one metal of the at least one metal salt solution as a metal hydroxide. The rate of precipitation reaction can be controlled by factors including the flow rate of the reactants and the stirring rate. In the inventive process, the doping metal ion, the pore creating agent, and the at least one metal of metal salt solution are coprecipitated. The term, co-precipitation, refers to simultaneous precipitation of multiple species from a solution. The co-precipitation reaction is critical to achieve desired single crystal morphology, porosity, and pore size. This is because the primary particles formed, i.e., the metal hydroxide particles formed at this step determine the crystallite size, morphology, uniform distribution of pores, and porosity of the single crystal of metal oxide. In one embodiment, primary particle growth during co- precipitation is achieved by the addition of doping metal ion and the pore creating agent at regular intervals resulting in uniform distribution of the doping metal and the pore creating agent in the metal hydroxide. During co-precipitation, the reactor temperature is maintained at 40 ºC - 60 ºC, and the pH is in the range of 10 – 12 with continuous stirring in the range of 1000 rotations per minute (rpm) – 3000 rpm. The reactor is maintained in nitrogen and/or oxygen atmosphere. The nitrogen and oxygen atmosphere during the co-precipitation reaction reduces cation disorder at the precursor level. The cation disorder is a structural disorder as a result of Ni²⁺/Li⁺exchange in octahedral sites. This effect becomes critical in nickel rich cathode material, as the cation disorder could result in reduced lithium-ion diffusivity, cycling stability, first-cycle efficiency, and overall electrode performance. At step 106, the metal hydroxide precursor solution is aged to form aged metal hydroxide precursor solution comprising metal hydroxide particles. The aging of the metal hydroxide precursor solution helps in forming the metal hydroxide particles of desired size. The size of the particles can be controlled by varying the duration for which aging is performed. In one embodiment, aging is carried out for a time period in a range of 6 hours to 24 hours to get metal hydroxide particles having a dimension or diameter in the range of 13 micrometers to 15 micrometers. In one embodiment, the size of the particles that are being formed through aging is monitored by a light scattering technique and once the desired size is realized aging is stopped thus preventing further growth in particle size. At step 108, the metal hydroxide particles are separated from the aged metal hydroxide precursor solution. In one embodiment, the aged metal hydroxide particles are filtered to obtain a filtrate comprising the metal hydroxide particles. In one embodiment, the filtrate is washed with water and dried in vacuum at 100 ºC for 12 hours to 18 hours. In yet another embodiment, the filtrate is washed with water and dried, followed by crushing and sieving. At step 110, the metal hydroxide particles are mixed with a first lithium source and is subjected to a first sintering process under oxygen atmosphere. In one embodiment, mixing the metal hydroxide particles and the first lithium source comprises mixing in a ball mill. In one embodiment, the first portion of lithium source is 35% to 40% of the total lithium source utilized for the metal oxide preparation. Further, an excess of 6% to 10% of the first lithium source is added to compensate for the lithium loss during sintering. In an embodiment, the first lithium source comprises lithium hydroxide, lithium acetate, lithium carbonate, lithium oxalate, or lithium nitrate. In a preferred embodiment, the lithium source is lithium hydroxide. The first sintering is performed in oxygen atmosphere at temperatures ranging from 400 ºC to 500 ºC for a time in the range of 6 hours to 10 hours. The first sintering step results in metal oxide precursor particles. The metal oxide precursor particles are composed of partially oxidized metal hydroxide where the pore creating agent and the doping metal ion are uniformly dispersed therein. At step 112, the metal oxide precursor particles are mixed with a second lithium source and subjected to a second sintering process. In an embodiment, the second lithium source is 55% to 60% of the total lithium source required for the metal oxide preparation. Further, an excess of 6% to 10% of lithium source is added to compensate for the lithium loss during sintering. The second lithium source is same as the first lithium source except for the quantity used. For high-nickel cathode material formation, nickel being sensitive to temperature the sintering can be done at comparatively lower temperature compared to low nickel content cathode material. The nickel-sensitivity to temperature can be addressed by two-step sintering. Two-step sintering is advantageous for uniform distribution of lithium in the metal oxide material and hence an ordered, layered structure may be obtained. Further, two-step sintering avoids agglomeration and offers better control of spherical morphology. In an embodiment, the second sintering is performed in an oxygen atmosphere at temperatures ranging from 750 °C to 950 ºC with a ramp rate of 1-5 ºC/min for 6 hours to 24 hours. In a preferred embodiment, the second sintering process is performed in two stages. At stage one, sintering is performed at 750 ºC for 6 hours to 18 hours in an oxygen atmosphere. The temperature is increased to 900 ºC, at stage 2, and sintering is continued for another 6 hours to 18 hours at a heating ramp rate of 3 ºC/min. At 750 °C, pore creating agents are decomposed forming uniform pores in the particle. The decomposition of pore creating agents at higher temperature (≥750 ℃) results in decomposition components and or decomposition products. In one embodiment, the decomposition component comprises carbon that remains in the particle as residual carbon. Carbon is known to enhance electrochemical performance of the cathode material by forming a conducting network and additionally imparts mechanical stability to the cathode material. During the second sintering, the pore creating agent decomposes to create pores in the structure. The metal oxide precursor particles fuse to form layered metal oxide and the process is enhanced by increased mobility of lithium ion at high temperature. The lithium ion stabilizes the formation of ordered layered structure. After the second sintering process, the porous single crystal is typically cooled at the same ramp rate as the heating cycle to prevent cracking or any morphology change to obtain porous single crystal of the metal oxide. Embodiments of the present disclosure provide a lithium-ion battery comprising an anode, a cathode, and an electrolyte interposed between the anode and the cathode. The anode may be any conventional anode employed in a lithium-ion battery and can comprise an anode active material and an anode collector. Example anode active materials include graphite, hard carbon, carbonaceous materials like carbon nanotubes (CNTs), reduced graphene oxide (rGO), lithium titanate (LTO), a tin/cobalt alloy, silicon, and silicon/carbon composites, all alloying and conversion anodes. In certain embodiments, the anode may comprise an anode collector. Standard anode collector materials include but are not limited to aluminium, copper, nickel, stainless steel, carbon, carbon paper, and carbon cloth. The electrolyte can be a solid or a liquid electrolyte. Non-limiting examples of the electrolyte include LiPF6, LiAsF6, LiBOB, LiClO4, LiBF4, and LiPF6. The cathode may comprise a cathode active material and a cathode current collector. The cathode active material comprises the porous single crystal of the metal oxide prepared according to the embodiments of the present disclosure. Non-limiting examples of cathode current collector include copper, aluminum, and stainless steel. Example 1 Preparation of porous single crystal of LiNi0.85Mn0.7Co0.05Ti0.03O2 using chitosan as pore creating agent: A 2 litre (L) metal salt solution consisting of nickel sulfate, cobalt sulfate and manganese sulfate was prepared in distilled water, in a beaker with the total ion concentration of 5 mol/L according to the molar ratio of the metals in the formula LiNi0.85Mn0.7Co0.05Ti0.03O2. In a separate beaker, a first aqueous solution comprising doping metal ion and pore creating agent was prepared by dissolving ammonium bis(oxalato)oxotitanate(IV) hydrate (5mol/L) in the same molar concentration and molar ratio of ‘Ti’ metal in the formula along with pore creating agent chitosan in distilled water (0.1mol/L). The metal salt solution, ammonium hydroxide at a molar concentration of 1 mol/L and sodium hydroxide at molar concentration of 2 mol/L were flowed into a reaction kettle in a concurrent flow manner for co-precipitation reaction. The temperature of the reactor was maintained at 50 ºC using a water bath, with pH at 11 and with stirring at a speed of 1000 rpm under a mixture of nitrogen/oxygen atmosphere. At regular intervals, the first aqueous solution comprising titanium doping ion and chitosan was added to the kettle, to form a metal hydroxide precursor solution. The metal hydroxide precursor solution was aged till metal hydroxide precursor particles attained a size in the range of 13 µm to 15 µm. The metal hydroxide precursor solution is then filtered, washed and dried, crushed and sieved to obtain a powder comprising the metal hydroxide precursor particles. The doping titanium ion and chitosan are uniformly distributed in the metal hydroxide precursor particles. Lithium hydroxide salt was taken at a stoichiometric ratio with metal hydroxide precursor particles. About 40% of the lithium hydroxide was added to the metal hydroxide precursor particles and ball milled. The mixture of lithium hydroxide and metal hydroxide precursor particles was sintered at a temperature of 600℃ at a ramp rate of 2 ºC/minute under oxygen atmosphere for a time period of 6 hours to obtain a powder comprising metal oxide precursor particles. The obtained powder comprising the metal oxide precursor particles was cooled to room temperature at a cooling rate of -2 ℃/min, and then was crushed and sieved. This was then added to the remaining 60% of the lithium hydroxide and ball milled. The addition of lithium hydroxide at both the stages was taken in excess of 6% to accommodate lithium loss during sintering. A second sintering was performed in two stages. The metal oxide precursor particles mixed with lithium source was sintered at 800 ºC at a ramp rate of 2 ℃/min for 9 hours in oxygen atmosphere at flow rate of 2m³/min, then the temperature was increased to 950 ºC and continued for 15 hours. After sintering, it was then cooled at the ramp rate of -1 ℃/min to obtain the LiNi_0.85Mn_0.7Co_0.05Ti_0.03O₂ porous, single crystal cathode material with uniformly distributed pores. Example 2 Preparation of porous single crystal of LiNi0.85Mn0.7Co0.05Al0.3O2 using water soluble polyimide as pore creating agent: A 2 litre (L) metal salt solution was prepared by sequential addition of nickel sulfate, cobalt sulfate and manganese sulfate in a beaker according to the molar ratio of the metals in the formula LiNi0.85Mn0.7Co0.05Al0.3O2, and water was added into it to obtain total ion concentration of 5 mol/L In a separate beaker, a first aqueous solution comprising doping metal ion and pore creating agent was prepared by dissolving aluminum sulphate (5mol/L) along with pore creating agent polyimide containing the functional group of amino acid-derived building block, 4,4′-diamino-α-truxillate dianion in distilled water (0.1mol/L). The metal salt solution, ammonium hydroxide at a molar concentration of 1 mol/L and sodium hydroxide at molar concentration of 2 mol/L were flowed into a reaction kettle in a concurrent flow manner for co-precipitation reaction. The temperature of the reactor was maintained at 50 ºC using a water bath, with pH at 11 and with stirring at a speed of 1000 rpm under a mixture of nitrogen/oxygen atmosphere. At regular intervals, the first aqueous solution comprising aluminum doping ion and polyimide was added to the kettle, to form a metal hydroxide precursor solution. The metal hydroxide precursor solution was aged till metal hydroxide precursor particles attained a size in the range of 13 microns to 15 microns. The metal hydroxide precursor solution is then filtered, washed and dried, crushed, and sieved to obtain a powder comprising the metal hydroxide precursor particles. The doping aluminum ion and polyimide are uniformly distributed in the metal hydroxide precursor particles. Lithium hydroxide salt was taken at a stoichiometric ratio with metal hydroxide precursor particles. About 40% of the lithium hydroxide was added to the metal hydroxide precursor particles and ball milled. The mixture of lithium hydroxide and metal hydroxide precursor particles was sintered at a temperature of 600 at a ramp rate of 2 ºC/minute under oxygen atmosphere for a time period of 6 hours to obtain a powder comprising metal oxide precursor particles. The obtained powder comprising the metal oxide precursor particles was cooled to room temperature at a cooling rate of -2 ℃/min, and then was crushed, and sieved. This was then added to the remaining 60% of the lithium hydroxide and ball milled. The addition of lithium hydroxide at both the stages was taken in excess of 6% to accommodate lithium loss during sintering. A second sintering was performed in two stages. The metal oxide precursor particles mixed with lithium source was sintered at 800 ºC at a ramp rate of 2 ℃/min for 9 hours in oxygen atmosphere at flow rate of 2m³/min, then the temperature was increased to 950 ºC and continued for 15 hours. After sintering, it was then cooled at the ramp rate of -1 ℃/min to obtain the LiNi0.85Mn0.7Co0.05Al0.3O2 porous, single crystal cathode material with uniformly distributed pores. Example 3 Preparation of porous single crystal of LiNi0.85Mn0.7Co0.05Ti0.3O2 using functionalized carbon nanotubes as pore creating agent: A 2 litre (L) metal salt solution was prepared by sequential addition of nickel sulfate, cobalt sulfate and manganese sulfate in a beaker according to the molar ratio of the metals in the formula LiNi_0.85Mn_0.7Co_0.05Ti_0.3O₂ , and water was added into it to obtain total ion concentration of 5 mol/L In a separate beaker, a first aqueous solution comprising doping metal ion and pore creating agent was prepared by dissolving ammonium bis(oxalato)oxotitanate (IV) hydrate (5mol/L) along with pore creating agent, water soluble amine functionalized carbon nanotube (CNT) in distilled water (0.5 mg/L). The metal salt solution, ammonium hydroxide at a molar concentration of 1 mol/L and sodium hydroxide at molar concentration of 2 mol/L were flowed into a reaction kettle in a concurrent flow manner for co-precipitation reaction. The temperature of the reactor was maintained at 50 ºC using a water bath, with pH at 11 and with stirring at a speed of 1000 rpm under a mixture of nitrogen/oxygen atmosphere. At regular intervals, the first aqueous solution comprising titanium doping ion and functionalized CNT was added to the kettle, to form a metal hydroxide precursor solution. The metal hydroxide precursor solution was aged till metal hydroxide precursor particles attained a size in the range of 13 microns to 15 microns. The metal hydroxide precursor solution is then filtered, washed and dried, crushed, and sieved to obtain a powder comprising the metal hydroxide precursor particles. The doping titanium ion and functionalized CNT are uniformly distributed in the metal hydroxide precursor particles. Lithium hydroxide salt was taken at a stoichiometric ratio with metal hydroxide precursor particles. About 40% of the lithium hydroxide was added to the metal hydroxide precursor particles and ball milled. The mixture of lithium hydroxide and metal hydroxide precursor particles was sintered at a temperature of 600 ºC at a ramp rate of 2 ºC/minute under oxygen atmosphere for a time period of 6 hours to obtain a powder comprising metal oxide precursor particles. The obtained powder comprising the metal oxide precursor particles was cooled to room temperature at a cooling rate of -2 ℃/min, and then was crushed and sieved. This was then added to the remaining 60% of the lithium hydroxide and ball milled. The addition of lithium hydroxide at both the stages was taken in excess of 6% to accommodate lithium loss during sintering. A second sintering was performed in two stages. The metal oxide precursor particles mixed with lithium source was sintered at 800 ºC at a ramp rate of 2 ℃/min for 9 hours in oxygen atmosphere at flow rate of 2m³/min, then the temperature was increased to 950 ºC and continued for 15 hours. After sintering, it was then cooled at the ramp rate of -1 ℃/min to obtain the LiNi0.85Mn0.7Co0.05Ti0.3O2 porous, single crystal cathode material with uniformly distributed pores. It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.

Claims

CLAIMS We claim, 1. A porous single crystal of a metal oxide represented by Formula (I) LiNi_1-xM1_xO₂ (I) wherein M1 is selected from the group consisting of one or more of Mn, Co, Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W and Sn, wherein x varies from 0.05 to 0.4, wherein the porous single crystal has a crystallite size of at least 8 microns, and wherein the porous single crystal has pores uniformly distributed therein having porosity in the range of 8 % to 10%.

2. The porous single crystal as claimed in claim 1, wherein the pores have an average dimension in the range of 5 (nanometers) nm to 10 nm.

3. The porous single crystal as claimed in claim 1, wherein the metal oxide is represented by Formula (II) LiNi1-x-yMnx CoyO2 (II) wherein x varies from 0.05 to 0.4, wherein y varies from 0 to 0.4, and wherein x+y ≤ 0.4. 4. The porous single crystal as claimed in claim 1, wherein the metal oxide is represented by Formula (III) LiNi1-x-y-zMnxCoyM2zO2 (III) wherein M2 is selected from the group consisting of one or more of Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W and Sn, wherein x varies from 0.05 to 0.4, wherein y varies from 0 to 0.4, wherein z varies from 0 to 0.04, and x+y+z≤0.

4.

5. The porous single crystal as claimed in claim 1, wherein the porous single crystal forms part of a cathode of a lithium-ion battery.

6. A method for preparing a porous, single crystal of a metal oxide represented by Formula (I) LiNi1-xM1xO2 (I) wherein M1 is selected from the group consisting of one or more of Mn, Co, Ti, Al, Mg, Cr, Zr, Gd, Nb, Ta, W and Sn, and wherein x varies from 0 to 0.4, the method comprising: i) providing at least one metal salt solution, a complexing agent solution and a precipitating agent solution in a reactor; ii) forming a metal hydroxide precursor solution by co-precipitating at least one metal from the at least one metal salt solution with a doping metal ion and a pore creating agent in presence of the precipitating agent and the complexing agent, wherein forming the metal hydroxide precursor solution comprises providing a first aqueous solution comprising the doping metal ion and the pore creating agent at regular intervals in the reactor during co-precipitation; iii) aging the metal hydroxide precursor solution to form aged metal hydroxide precursor solution comprising metal hydroxide particles; iv) separating the metal hydroxide particles from the aged metal hydroxide precursor solution; v) mixing the metal hydroxide particles with a first lithium source and performing a first sintering process under oxygen atmosphere to form metal oxide precursor particles; and vi) mixing the metal oxide precursor particles with a second lithium source and performing a second sintering process under oxygen atmosphere to form the porous, single crystal of the metal oxide.

7. The method as claimed in claim 6, wherein the at least one metal salt comprises sulphate, carbonate, nitrate, chloride, or oxalate salts of a metal selected from Mn, Co, Ti, Al, Cr, Zr, Gd, W, Sn or any combinations thereof.

8. The method as claimed in claim 6, wherein the doping metal ion is selected from ions of Ti, Al, Mg, Zr, Nb, Ta, W, Cr and any combinations thereof.

9. The method as claimed in claim 6, wherein the pore creating agent comprises water-soluble polyimides, water soluble functionalized carbon nanotubes (CNT), amine-functionalized CNT, hydroxide-functionalized CNT, carboxylic acid-functionalized CNT, water soluble polymer-functionalized CNT, saccharide-functionalized CNT, chitosan or any combinations thereof.

10. The method as claimed in claim 6, wherein the precipitating agent comprises sodium hydroxide, sodium oxalate, or sodium bicarbonate.

11. The method as claimed in claim 6, wherein the complexing agent comprises ammonium hydroxide, ammonium carbonate or ammonium oxalate.

12. The method as claimed in claim 6, wherein forming the metal hydroxide precursor solution comprises co-precipitating at a pH in the range of 10 to 12 and at a temperature in the range of 40 ℃ to 60 ℃ with constant stirring.

13. The method as claimed in claim 6, wherein aging is continued for a time period so as to form the metal hydroxide particles having a diameter in the range of 13 microns to 15 microns.

14. The method as claimed in claim 6, wherein the metal hydroxide particles are spherical and the doping metal ion and the pore creating agent are uniformly dispersed therein.

15. The method as claimed in claim 6, wherein mixing the metal hydroxide particles or mixing the metal oxide precursor particles comprises mixing in a ball mill.

16. The method as claimed in claim 6, wherein the first lithium source has a lithium concentration which is 35% to 40% of combined concentration of the first and the second lithium source.

17. The method as claimed in claim 6, wherein the first sintering process is performed at a temperature in the range of 400 ℃ to 500 ℃ and for a time in the range of 6 hours to 10 hours.

18. The method as claimed in claim 6, wherein the second sintering process is performed at a temperature in the range of 750 ℃ to 950 ℃ and for a time in the range of 6 hours to 24 hours.

19. The method as claimed in claim 6, wherein the porous, single crystal of the metal oxide comprises decomposition components of pore creating agent uniformly dispersed therein.

20. A porous single crystal of a metal oxide represented by Formula (I) LiNi_1-xM1_xO₂ (I) wherein M1 is selected from the group consisting of one or more of Mn, Co, Ti, Mg, Al, Cr, Zr, Gd, Nb, Ta, W and Sn, wherein x varies from 0.05 to 0.4, wherein the porous single crystal has a crystallite size of at least 8 microns, wherein the porous single crystal has pores uniformly distributed therein having an average dimension of 5 nm to 10 nm and a porosity in the range of 8% to 10%, and wherein the porous single crystal is prepared by a method comprising: i) providing at least one metal salt solution, a complexing agent solution and a precipitating agent solution in a reactor; ii) forming a metal hydroxide precursor solution by co-precipitating at least one metal from the at least one metal salt solution with a doping metal ion and a pore creating agent in presence of the precipitating agent and the complexing agent, wherein forming the metal hydroxide precursor solution comprises providing a first aqueous solution comprising the doping metal ion and the pore creating agent at regular intervals in the reactor during co-precipitation; iii) aging the metal hydroxide precursor solution to form aged metal hydroxide precursor solution comprising metal hydroxide particles; iv) separating the metal hydroxide particles from the aged metal hydroxide precursor solution; v) mixing the metal hydroxide particles with a first lithium source and performing a first sintering process under oxygen atmosphere to form metal oxide precursor particles; and vi) mixing the metal oxide precursor particles with a second lithium source and performing a second sintering process under oxygen atmosphere to form the porous, single crystal of the metal oxide.