A process of preparing spherical metal phosphates, and implementations thereof

Abstract

The present disclosure provides a process of preparing spherical metal phosphate, comprising a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to 220 °C, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate. The present disclosure also provides a lithium manganese iron phosphate (LMFP) composite comprising the spherical metal phosphate; and a cathode material prepared using the LMFP.

Description

A PROCESS OF PREPARING SPHERICAL METAL PHOSPHATES, AND IMPLEMENTATIONS THEREOFFIELD OF INVENTION

[0001] The present disclosure broadly relates to the field of battery. Particularly, the present disclosure relates to a process of preparing spherical metal phosphates, and a cathode prepared using an electrode composite comprising the spherical metal phosphate.BACKGROUND OF INVENTION

[0002] The development of lithium-ion batteries (LIB), a technology that is revolutionizing the way of life, while first used in portable electronics, is now increasingly used in diverse applications including electric vehicles, medical devices, smart watches, and satellites. The positive electrode of the lithium-ion battery is composed of lithium-based compounds, such as lithium iron phosphate (LiFePCU) and lithium manganese oxide. Lithium iron phosphate (LFP) is the most preferred cathode material for large scale applications, such as hybrid electric vehicles. However, LFP suffers from limitations like low theoretical energy density (578 Wh / Kg) and lower operating voltages. Hence manganese was introduced in the LFP system to enhance the energy density and high operation voltage. Lithium Manganese Iron Phosphate (LMFP), as a cathode material ensures high energy density, high thermal stability, and high safety, when compared to LFP cathode materials. However, LMFP is generally irregular in shape resulting in low tap density, and compact density. Therefore, there is a need to develop regular shaped LMFP material with improved tap density and better conductivity to enhance the high temperature performance of lithium-ion batteries (LIB).SUMMARY OF THE INVENTION

[0003] In a first aspect of the present disclosure, there is provided a process of preparing spherical metal phosphate, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to220 °C, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate.

[0004] In a second aspect of the present disclosure, there is provided a lithium manganese iron phosphate (LMFP) composite comprising the spherical metal phosphate as disclosed herein with lithium and carbon.

[0005] In a third aspect of the present disclosure, there is provided a process of preparing the LMFP composite as disclosed herein, the process comprising: a) preparing spherical metal phosphate by the process as disclosed herein; b) providing a Lithium (Li) source to the spherical metal phosphate followed by grinding to obtain a lithiated precursor; and c) mixing a carbon source with the lithiated precursor and calcinating at a temperature in a range of 600 to 750 °C for a duration in a range of 6 to 12 hours to obtain the LMFP composite.

[0006] In a fourth aspect of the present disclosure, there is provided a cathode comprising the LMFP composite as disclosed herein or obtained by the process as disclosed herein.

[0007] In a fifth aspect of the present disclosure, there is provided an electrochemical cell comprising: i) an anode; ii) a cathode as disclosed herein; and iii) an electrolyte.

[0008] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

[0009] In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure wherein:

[0010] Figure 1 depicts the X-Ray Diffraction (XRD) based structural analysis of LMFP / C composite-sample L2 Cal, in accordance with an embodiment of the present disclosure.

[0011] Figure 2 depicts the particle size distribution (PSD) analysis of spherical metal phosphate samples A) LI; B) L2; C) L3; D) L4; and E) L5, in accordance with an embodiment of the present disclosure.

[0012] Figure 3 depicts the scanning electron microscopy (SEM) images of spherical metal phosphate samples: (a) & (b) LI; (c) & (d) L2; (e) & (f) L3; (g) & (h) L4; and (i) & (j) L5, wherein different spheres chosen for sphericity measurements are denoted with circle codes as A, B, C, and D in the SEM images of the samples, in accordance with an embodiment of the present disclosure.

[0013] Figure 4 depicts the scanning electron microscopy (SEM) images of LMFP composites: L2 (a) & (b); L3 (c) & (d); and L5 ( e) & (f), wherein different spheres chosen for sphericity measurements are denoted with circle codes A, and B in the SEM images of the LMFP composites, in accordance with an embodiment of the present disclosure.

[0014] Figure 5 depicts the initial charge and discharge profiles of the LMFP composite-sample L5 Cal at 0.1 C-rate at 45 °C, in accordance with an embodiment of the present disclosure.

[0015] Figure 6 depicts the cyclic stability data of the LMFP composite at 1 C-rate at 45 °C, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0016] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features. Definitions

[0017] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. Thesedefinitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0018] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0019] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0020] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of element or steps.

[0021] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0022] The term “w / w” means the percentage by weight, relative to the weight of the total composition, unless otherwise specified.

[0023] The term "at least one" is used to mean one or more and thus includes individual components as well as mixtures / combinations.

[0024] The term “active material” refers to the active constituent of an electrode, which comprises the particles that undergo oxidation or reduction, resulting in reversible ion storage. Examples of active material in the present disclosure includes but not limited to natural graphite, synthetic graphite, silicon, siliconcarbon composites as anode materials, and layered oxide cathode materials such as olivine materials like lithium iron phosphate (LFP), and lithium iron manganese phosphate (LMFP).

[0025] The term “spherical metal phosphates”, as used herein refers to the precursor metal phosphate spheres comprising metal precursors and phosphate precursors used for the fabrication of LMFP cathode materials post lithiation and calcination.Examples of metal precursors include but are not limited to nitrates of iron, such as Iron III nitrate nonahydrate ((Fe(NO3)3.9H2O), and nitrates of manganese, such as Manganese (II) nitrate hydrate (Mn(NO3)3 H2O). Examples of phosphate precursors include but are not limited to ammonium dihydrogen phosphate (NH4H2PO4), or phosphoric acid (H3PO4).

[0026] The term “sphericity”, as used herein refers to the form or shape of a particle that ranges from mere spherical to complete spherical in shape in a given particle. Sphericity of the LMFP particles are calculated using the formula proposed by Riley et al (1941)Sphericity = d(in) / DWherein, d(in) - diameter of a circle inscribed in a particle projectionD - diameter of circle circumscribed in the particle projectionWhen the particle is completely spherical in shape the sphericity values will be 1.

[0027] The term “structure directing agent”, as used herein refers to substances that dictate the overall shape specific morphology of the LMFP composites. Examples of structure directing agent include but are not limited to single walled carbon nanotubes (SWCNT) and carboxymethyl cellulose (CMC). According to the present disclosure, SWCNT dispersed in CMC reduces the surface tension and influences the driving force for the formation of spherical metal phosphate metal phosphate precursors by hydrothermal reaction.

[0028] The term “hydrothermal treatment” as used herein refers to a process of treating an aqueous solution at high temperature and high vapor pressure. According to the present disclosure an aqueous slurry of metal precursors and phosphate precursors is subjected to hydrothermal treatment at a temperature in a range of 170 °C to 220 °C at a pressure in the range of 0 to 15 bar, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate in the presence of structure directing agents as described herein.

[0029] The term “particle size distribution (D50)” as used herein refers to the particle size corresponding to the cumulative distribution at 50%. It is also known as the median diameter or the medium value of the particle size distribution. Further,the terms “particle size distribution (D90)” and “particle size distribution (DIO)” as used herein refer to particle size values corresponding to cumulative distribution at 90% and 10%, respectively.

[0030] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, weight percentage in the range of 10% to 20% should be interpreted to include not only the explicitly recited limits of 10% to 20% but also to include sub-ranges, such as 11% to 18%, 15% to 19% and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 12.8%, 13.5%, and 17.55%.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.

[0032] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products, compositions, formulations, and methods are clearly within the scope of the disclosure, as described herein.

[0033] As discussed in the background, there is a need in the art to develop spherical lithium manganese iron phosphates-based cathode material with good tap density, better conductivity, and high temperature performance. Conventionally prepared LMFP based cathode material have poor conductivity IO-10S cm-1owing to the irregular morphology of LMFP, which therefore shows poor tap density and further reflects in low volumetric energy density. The present disclosure provides a process for obtaining LMFP with spherical morphology by fine tuning thehydrothermal synthesis parameters to improve the tap density of the cathode material drastically. Specifically, the disclosed process comprises the use of structure directing agents, such as single walled carbon nanotubes and carboxymethyl cellulose, which are essential for attaining the spherical morphology of lithium manganese iron phosphates (LMFP).

[0034] Accordingly, in an embodiment of the present disclosure, there is provided a process of preparing spherical metal phosphate, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to 220 °C, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate.

[0035] In an embodiment of the present disclosure, the spherical metal phosphate has a sphericity in the range of 0.87 to 0.99.

[0036] In an embodiment of the present disclosure, the tap density of the spherical metal phosphate is in a range of 1.3 to 1.4 g / cc.

[0037] In an embodiment of the present disclosure, the structure directing agent comprises a mixture of single walled carbon nanotubes (SWCNT) and carboxymethyl cellulose (CMC) in an aqueous solution.

[0038] In an embodiment of the present disclosure, the structure directing agent comprises SWCNT and CMC in a weight ratio of 2:3.

[0039] In an embodiment of the present disclosure, the structure directing agent in the slurry comprises 0.004 to 0.008 (w / w)% of SWCNT and 0.005 to 0.01 (w / w)% of CMC. In another embodiment of the present disclosure, the structure directing agent in the slurry comprises 0.005 to 0.007 (w / w)% of SWCNT and 0.007 to 0.009 (w / w)%.

[0040] In an embodiment of the present disclosure, the metal precursors are selected from Iron III nitrate nonahydrate (Fe(NO3)3.9H2O), Manganese (II) nitrate hydrate (Mn(NO3)3.H2O), or mixtures thereof.

[0041] In an embodiment of the present disclosure, the metal precursors are in a mole range of 0.3 to 1.1. In another embodiment of the present disclosure, the metal precursors are in a mole range of 0.4 to 0.7.

[0042] In an embodiment of the present disclosure, the metal precursors comprises Manganese and Iron in a mole ratio of 0.6:0.4.

[0043] In an embodiment of the present disclosure, the phosphate precursor is selected from ammonium dihydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), or mixtures thereof.

[0044] In an embodiment of the present disclosure, the phosphate precursor is ammonium dihydrogen phosphate; and the phosphate precursor is in a mole range of 1.0 to 1.05.

[0045] In an embodiment of the present disclosure, the phosphate precursor and the metal precursors are in equimolar ratio [ M:P=1 : 1 where M is the total amount OF metal precursors],

[0046] In an embodiment of the present disclosure, the metal precursors and phosphate precursors are used in an equimolar ratio in the disclosed process.

[0047] In an embodiment of the present disclosure, the hydrothermal treatment is carried out at a pressure in a range of 0 to 15 bar. In an embodiment of the present disclosure, there is provided a process of preparing spherical metal phosphate, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to 220 °C at a pressure in a range of 0 to 15 bar, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate; wherein the structure directing agent is an aqueous solution comprising 0.004 to 0.008 (w / w)% of SWCNT and 0.005 to 0.01 (w / w)% of CMC in water to obtain the solution of structure directing agent; wherein the metal precursors are selected from Iron III nitrate nonahydrate ((Fe(NO3)3.9H2O), Manganese (II) nitrate hydrate (Mn(NO3)3.H2O), or mixtures thereof; and wherein the phosphate precursor is selected from ammonium dihydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), or mixtures thereof.

[0048] In an embodiment of the present disclosure, there is provided a process of preparing spherical metal phosphate, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to220 °C at a pressure in a range of 0 to 15 bar, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate. In another embodiment of the present disclosure, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 180 °C to 210 °C at a pressure in a range of 0 to 15 bar, for a time period in a range of 8 to 15 hours to obtain the spherical metal phosphate.

[0049] In an embodiment of the present disclosure, the spherical metal phosphate has a particle size distribution (D50) in the range of 4 to 16 pm. In another embodiment of the present disclosure, the spherical metal phosphate has a particle size distribution (D50) in the range of 12 to 15 pm.

[0050] In an embodiment of the present disclosure, there is provided a lithium manganese iron phosphate (LMFP) composite comprising the spherical metal phosphate as disclosed herein with lithium and carbon.

[0051] In an embodiment of the present disclosure, the composite is LiM .xFexPO4, where x ranges from 0.2 to 0.4. In another embodiment of the present disclosure, the composite is LiMni-xFexPO4, where x ranges from 0.3 to 0.4.

[0052] In an embodiment of the present disclosure, there is provided a process of preparing the LMFP composite as disclosed herein, the process comprising: a) preparing spherical metal phosphate by the process as disclosed herein; b) providing a Lithium (Li) source to the spherical metal phosphate followed by grinding to obtain a lithiated precursor; and c) mixing a carbon source with the lithiated precursor and calcinating at a temperature in a range of 600 to 750 °C for a duration in a range of 6 to 12 hours to obtain the LMFP composite.

[0053] In an embodiment of the present disclosure, the Li source is selected from lithium hydroxide (LiOH), Lithium carbonate (Li2CC>3), Lithium acetate (LiCFLCOO). or mixtures thereof; and the Li source is in a mole range of 1.0 to 1.05.

[0054] In an embodiment of the present disclosure, the Li source is in an equimolar ratio with the metal phosphate [ Li: Metal Phosphate = (1-1.05): 1],

[0055] In an embodiment of the present disclosure, the carbon source is selected from sucrose, glucose, citric acid, ascorbic acid, tartaric acid, or mixtures thereof.

[0056] In an embodiment of the present disclosure, the carbon source is in an amount in the range of 10 to 20 (w / w)%. In another embodiment of the present disclosure, the carbon source is in an amount in the range of 13 to 18 (w / w)%.

[0057] In an embodiment of the present disclosure, the calcination in step (iii) is carried out in the presence of an inert gas.

[0058] In an embodiment of the present disclosure, there is provided a process of preparing the LMFP composite as disclosed herein, the process comprising: a) preparing spherical metal phosphate by the process as disclosed herein; b) providing a Lithium (Li) source to the spherical metal phosphate followed by grinding to obtain a lithiated precursor; and c) mixing a carbon source with the lithiated precursor and calcinating at a temperature in a range of 600 to 750 °C for a duration in a range of 6 to 12 hours to obtain the LMFP composite; wherein the Li source is selected from lithium hydroxide (LiOH), Lithium carbonate (Li2CC>3), Lithium acetate (LiCFLCOO). or mixtures thereof; and the Li source is in molar amount 9 In another embodiment of the present disclosure, there is provided a process of preparing the LMFP composite as disclosed herein, the process comprising: a) preparing spherical metal phosphate by the process as disclosed herein; b) providing a Lithium (Li) source to the spherical metal phosphate followed by grinding to obtain a lithiated precursor; and c) mixing a carbon source with the lithiated precursor and calcinating at a temperature in a range of 650 to 750 °C for a duration in a range of 7 to 10 hours to obtain the LMFP composite; wherein the Li source is selected from lithium hydroxide (LiOH), Lithium carbonate (Li2CO3), Lithium acetate (LiCftCOO) or mixtures thereof; and Li source is taken in an equimolar ratio with respect to metal phosphate.

[0059] In an embodiment of the present disclosure, there is provided a cathode comprising the LMFP composite as disclosed herein or obtained by the process as disclosed herein.

[0060] In an embodiment of the present disclosure, the tap density of the cathode is in a range of 1.00 to 1.10 g / cm3.

[0061] In an embodiment of the present disclosure, the sphericity of the LMFP particles ranges from 0.8 to 0.99.

[0062] In an embodiment of the present disclosure, there is provided an electrochemical cell comprising: i) an anode; ii) a cathode as disclosed herein; and iii) an electrolyte.

[0063] In an embodiment of the present disclosure, the anode comprises an active material selected from graphite; a conductive carbon selected from Super P, and a binder selected from polyvinylidene fluoride (PVDF), vinylidene fluoride (VDF) or mixture thereof.

[0064] In an embodiment of the present disclosure the cathode comprises LMFP composite as active material; a conductive carbon selected from Super P, multiwalled carbon nanotube (MWCNT); and a binder selected from polyvinylidene fluoride (PVDF), vinylidene fluoride (VDF) or mixture thereof.

[0065] In an embodiment of the present disclosure, the electrolyte comprises Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) in IM LiPF6.EXAMPLES

[0066] The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply.Materials and Methods

[0067] The various chemicals and solvents used in the present disclosure are as follows:Metal precursors- Nitrate precursor of Iron and Manganese were procured from Sigma Aldrich.Structure directing agent - SWCNT and CMC were procured from OCSiAl.Phosphate precursors- Ammonium hydrogen phosphate was procured from Sigma AldrichLithium source was procured from Sigma Aldrich.EXAMPLE 1Preparation and characterization of LMFP composites

[0068] Requisite molar amount of Iron III nitrate nonahydrate (Fe(NO3)3.9H2O), Manganese (II) nitrate hydrate (Mn(NO3)3.H2O) (metal precursors) were dissolved in distilled-water medium; the molar amount of iron precursor is 0.4, and the molar amount of manganese precursor is 0.6. Requisite amount of SWCNT dispersed in aqueous solution of CMC was added as a structure directing agent to the solution of metal precursors (Table 1). Equimolar ratio of ammonium dihydrogen phosphate (phosphate precursor) dissolved in aqueous medium was then added dropwise to the above solution and stirred at 300 rpm for 30 minutes to obtain a slurry (600 mL). The phosphorus precursor and the total amount of metal precursors were taken in equimolar ratio [1:1].

[0069] The slurry was subjected to hydrothermal reaction at 180-220 °C for 9-18 hours to prepare spherical phosphates corresponding to samples LI to L5 as provided in Table l.The sphericity of the spherical metal phosphate samples LI to L5 were calculated using the following formulae, based on selective spheres of the samples labelled with the sample codes A to D in the SEM images (Figure 3 and Figure 4).Sphericity = d(in) / D

[0070] Wherein d(in) - diameter of a circle inscribed in a particle projection and D - diameter of circle circumscribed in the particle projection.

[0071] The obtained spherical metal phosphates (MFP) were mixed with requisite amount [(1-1.05) mol ] of lithium hydroxide (Li-source) and grinded to obtain alithiated precursor. The Li source is in an equimolar ratio with the spherical metal phosphate [1 : 1].

[0072] The prepared lithiated precursor was uniformly mixed with 15 wt% of sucrose (carbon source), and then sintered for 6-12 hours under the protection of nitrogen gas at 650-700°C (calcinating), to obtain LiMno.eFeo^PO C composite (LMFP composite) in the form of spherical particles, corresponding to samples L2 Cal, L3 Cal and L5 Cal as listed in Table 4.

[0073] The prepared samples of (LI to L5) of spherical metal phosphates and the corresponding LMFP composites (L2 Cal, L3 Cal, and L5 Cal ) were characterized using X-ray Diffraction (XRD) with a 2-theta range of 10 to 80 degrees and Scanning Electron Microscopy (SEM) with a magnification range of 5000 to 50000 x.Observation and Results

[0074] After hydrothermal reaction, the metal phosphate samples were analyzed using XRD to determine their particle size distribution and further SEM analysis was performed for determining their morphological characteristics.

[0075] From the XRD analysis it was evident that the spherical metal phosphates exhibited good phase purity with only minor impurity phases (Figure 1 and Table 2). From the PSD analysis the prepared spherical metal phosphates exhibited PSD (D50) in a range of 4 to 15 pm, specifically sample L2 exhibited a median PSD of 4.8 pm (Figure 2B) , sample L3 exhibited a median PSD of 12.4 pm (Figure 2C) and sample L5 exhibited a median PSD of 14.3 pm (Figure 2E). Sample LI exhibited a non-uniform spherical morphology with a median PSD of 13.4 pm (Figure 2A; Figure 3a and 3b) and sample L4 exhibited an agglomerated morphology with a median PSD of 15.27 pm (Figure 2D; Figure 3g and 3h) owing to the lower and higher SWCNT concentration, respectively. Further, the sample L5 exhibited a sphericity value in the range of 0.87 to 0.97, the sphericity values of other samples were in the range 0.77 to 0.89. The sphericity values were calculated as an average sphericity value of selected spheres from the SEM images of each spherical metal phosphate samples, as listed in Table 3a-3e. Therefore, samples L2 (Figure 3c and 3d), L3 (Figure 3e and 3f), and L5 (Figure 3i and 3j) with betterspherical morphology owing to optimum SWCNT concentration were taken forward for the preparation of corresponding LMFP composites.Table 1: Samples LI to L5 of spherical metal phosphates prepared using different hydrothermal reaction conditionsTable 2: XRD analysis

[0076] Table 2 descriptions: a, b, c are lattice cell parameters in x, y, z direction respectively. V is the cell volume. GOF is goodness of fit and wR is the weighted factors.Table 3a: Sphericity calculation of Sample LITable 3b: Sphericity calculation of Sample L2Table 3c: Sphericity calculation of Sample L3Table 3d: Sphericity calculation of Sample L4Table 3e: Sphericity calculation of Sample L5

[0077] After lithiation and calcination, LMFP composite sample L5 Cal exhibited perfect sphere morphology with a sphericity value of 0.91 (Figure 4e and 4f; Table 4d) with a tap density of 1.10 g / cm3(Table 4), when compared to the samples L2 Cal (Figure 4a and 4b) and L3 Cal (Figure 4c and 4d), which exhibited distorted irregular spheres and non-uniform spheres, respectively.Table 4a: Samples L2 Cal, L3 Cal, and L5 Cal of LMFP composites prepared using different calcination conditionsTable 4b: Sphericity values of L2 CalTabel 4c: Sphericity values of L3 CalTable 4d: Sphericity values of L5 Cal

[0078] The LMFP composite L5 Cal was used as a cathode material with Li metal ion as an anode in a coin cell preparation, wherein the IM LiPFe electrolyte and EC / EMC / DMC solvent combinations were used.

[0079] The L5 Cal exhibited a specific capacity of 138 mAh / g at O.lC-rate (Figure 5) when compared to samples L3 Cal (115.8 mAh / g) and L2 Cal (102.1mAh / g) at 45°C. Specifically, the grain boundaries of LMFP particles were not distinct after calcination in case of samples L3 Cal and L2 Cal, which resulted in their poor electrochemical performances.

[0080] It was also observed from figure 6, that the prepared spherical LMFP / C composite has a good cyclic stability at higher temperature with a capacity retention of 96% after 30 cycles at 1 C-rate.

[0081] Overall, the process comprising specific hydrothermal reaction conditions and specific calcination conditions resulted in spherical LMFP, which further resulted in improved capacity of the electrochemical cell .ADVANTAGES OF THE PRESENT DISCLOSURE

[0082] The present disclosure provides an efficient process to obtain spherical LMFP. The obtained LMFP composites exhibited a uniform spherical morphology, which is attributable to the fine tuning of the hydrothermal reaction parameters,along with the use of SWCNT in CMC as structure directing agent. The spherical morphology improved the tap density, and volumetric energy density of the composites along with better high temperature performance.

Claims

I / We Claim:

1. A process of preparing spherical metal phosphate, the process comprising: a) preparing a slurry comprising a structure directing agent, metal precursors, and a phosphate precursor; and b) hydrothermal treatment of the slurry at a temperature in a range of 170 °C to 220 °C, for a time period in a range of 7 to 18 hours to obtain the spherical metal phosphate.

2. The process as claimed in claim 1, wherein the spherical metal phosphate has a sphericity in the range of 0.87 to 0.99.

3. The process as claimed in claim 1, wherein the tap density of the spherical metal phosphate is in a range of 1.3 to 1.4 g / cc.

4. The process as claimed in claim 1, wherein the structure directing agent comprises a mixture of single walled carbon nanotubes (SWCNT) and carboxymethyl cellulose (CMC) in an aqueous solution.

5. The process as claimed in claim 4, wherein the structure directing agent comprises SWCNT and CMC in a weight ratio of 2:3.

6. The process as claimed in claim 1, wherein the structure directing agent in the slurry comprises 0.004 to 0.008 (w / w)% of SWCNT and 0.005 to 0.01 (w / w)% of CMC.

7. The process as claimed in claim 1, wherein the metal precursors are selected from Iron III nitrate nonahydrate ((Fe(NO3)3.9H2O), Manganese (II) nitrate hydrate (Mn(NO3)3.H2O), or mixtures thereof.

8. The process as claimed in claim 1, wherein the metal precursors are in a mole range of 0.3 to 0.9.

9. The process as claimed in claim 1, wherein the phosphate precursor is selected from ammonium dihydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), or mixtures thereof.

10. The process as claimed in claim 1, wherein the phosphate precursor is ammonium dihydrogen phosphate; and the phosphate precursor is in a mole range of 1.0 to 1.05.

11. The process as claimed in claim 1, wherein the hydrothermal treatment is carried out at a pressure in a range of 0 to 15 bar.

12. The process as claimed in claim 1, wherein the spherical metal phosphate has a particle size distribution (D50) in the range of 4 to 16 pm.

13. A lithium manganese iron phosphate (LMFP) composite comprising the spherical metal phosphate as claimed in claim 1 with lithium and carbon.

14. The LMFP composite as claimed in claim 13, wherein the composite is LiMni-x FexPO4, where x ranges from 0.2 to 0.4.

15. A process of preparing the LMFP composite as claimed in claim 13, the process comprising:(i) preparing spherical metal phosphate by the process as claimed in claim 1;(ii) providing a Lithium (Li) source to the spherical metal phosphate followed by grinding to obtain a lithiated precursor; and(iii) mixing a carbon source with the lithiated precursor and calcinating at a temperature in a range of 600 to 750 °C for a duration in a range of 6 to 12 hours to obtain the LMFP composite.

16. The process as claimed in claim 15, wherein the Li source is selected from lithium hydroxide (LiOH), Lithium carbonate (Li2CCh), Lithium acetate (LiCFLCOO) or mixtures thereof; and the Li source is in a mole range of 1.0 to 1.05.

17. The process as claimed in claim 15, wherein the carbon source is selected from sucrose, glucose, citric acid, ascorbic acid, tartaric acid, or mixtures thereof.

18. The process as claimed in claim 15, wherein the carbon source is in an amount in the range of 10 to 20 (w / w)%.

19. The process as claimed in claim 154, wherein the calcination in step (iii) is carried out in the presence of an inert gas.

20. A cathode comprising the LMFP composite as claimed in claim 13 or obtained by the process as claimed in claim 15.

21. The cathode as claimed in claim 20, wherein the tap density of the cathode active material is in a range of 1.00 to 1.10 g / cm3.

22. An electrochemical cell comprising: i) an anode; ii) a cathode as claimed in claim 20; and iii) an electrolyte.

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