Description:A METHOD FOR PRODUCING A STRUCTURALLY LAYERED POSITIVE ELECTRODE ACTIVE MASS MATERIAL

[001] The present disclosure relates to a design of high voltage positive electrode material in lithium ion cell that provides a high discharge capacity and which is capable of achieving high energy densities. More particularly, the present invention relates to carbon coating methods of O3-type layered materials for improving the capacity and stability for lithium ion cells.
BACKGROUND OF THE INVENTION
[002] Background description includes information that may be useful in understanding the present invention.
[003] Concerns about petroleum fuels have put attention towards the alternative development of sustainable and renewable energy storage for backup systems. Lithium-ion batteries (LIB) are the current energy storage device used in most electronic appliances viz., mobile phones, laptops, electric vehicles, energy storage grids, etc. The feasibility and performance of LIB, mainly depend on its potential components; cathode, anode, and electrolytes used for the design of LIB cells.
[004] Among numerous cathode materials, LiCoO2, LiNiO2, LiFePO4, LiNixCoyMn1-x-yO2, (NCM), etc. are considered as promising cathodes for LIB with an average voltage of ~ 3.8 V (vs Li+ /Li). In recent years, layered oxide cathode materials having high voltage and capacity are focused on the rational design and development of lithium-ion energy storage cells. In this direction, Ni-rich oxides are considered for high reversible capacity. However, due to structural transformation, stacking faults, decomposition of electrolyte, undesirable side reactions at electrode/electrolyte interface, low electrode stability during cycling, etc. inhibit their electrochemical response.
[005] Nowadays, synthesis and studies of new layered oxides of alkali and transition metals with honeycomb-based crystal structure A+3M2+2X5+O6 (A = Li, Na; M is transition metal, X = Bi, Sb, Te, etc.) are focused due to their electrode material applications, electronic and magnetic properties. There are two type of crystal structure based on ABCABC stacking and A+ in octahedral sites; called O3-type structure and other one is P2-type structure in which A+ in prismatic sites consisting ABBA stacking.
[006] As X having high oxidation state would maximize the M2+ content as positive electrode materials for energy storage cells. Analogous to A+3M2+2X5+O6 O3-type materials, D. Yuan et al. [Adv. Mater. 26 (2014) 6301-6306] studied honeycomb layered Na3Ni2SbO6 cathode material that demonstrated high capacity of 117 mAhg-1 with remarkable cyclability of 70% capacity retention over 500 cycles at a 2C rate. Thus, in O3-type family, Li3Co2SbO6 can be considered as potential electrode material for lithium ion cells. The honeycomb structure of Li3Co2SbO6 is generated by 2:1 ordering of Co2+ and Sb5+.
[007] In the theoretical evaluation of Li3Co2SbO6, there is the possibility of full de-lithiation from the structure without any structural deformation and phase transition. Such type of layered structures has displayed to be feasible hosts for the reversible insertion of lithium even though their insulating nature. The theoretical capacity of Li3Co2SbO6 has been found to be 225 mAh/g on full de-lithiation of lithium from the host. In case of pristine Li3Co2SbO6, the electrical conductivity is very poor (~10-9 S/cm) which restrict it electrochemical response. Similar electrical conductivity was found in case of pristine LiFePO4 as an active electrode material.
[008] Recently, A. J. Brown et.al. [Inorg. Chem. 58 (2019) 13881-13891] prepared Li3Co2SbO6 for lithium ion storage cells that show relatively poor electrochemical performance as lithium-ion battery cathode materials and capacities falls off rapidly after few cycles which extremely hinders its potential applications in energy storage systems. The pristine Li3Co2SbO6 synthesized by the present invention shows poor capacity that can be attributed to low electronic conductivity of the material. Several techniques have been used to improve the electrical conductivity of materials viz. carbon coating, doping, composites with other materials etc.
[009] Thus, in the present disclosure, process of carbon coated Li3Co2SbO6 as active cathode material for lithium ion energy storage cells is being achieved. The fabricated cell using optimal composition of active mass, with respect to Li demonstrated the discharge capacity of 110 mAh/g with good capacity retention and stability features.

OBJECTS OF THE INVENTION
[010] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.
[011] It is an object of the present subject matter to disclose a method for producing carbon coating process of a structurally layered positive electrode active mass material.
[012] It is another object of the present subject matter to disclose a lithium ion cell.
[013] These and other objects and advantages will become more apparent when reference is made to the following description and accompanying drawings.

SUMMARY OF THE INVENTION
[014] This summary is provided to introduce concepts related to a method for producing a carbon coating process of structurally layered positive electrode active mass material and related to a lithium ion cell. The concepts are further described below in the detailed description. 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.
[015] The present invention discloses a method for producing a structurally layered positive electrode active mass material, the method comprising the steps of preparing a solution by agitating, in a solvent, a predetermined amounts of a carbon source necessary for forming carbon coating of structurally layered positive electrode active mass material represented by Li3Co2SbO6. It then includes adding and agitating the compound represented by the formula (1) in a predetermined quantity in the solution. Further, the method includes drying the solution obtained after the addition of the compound Li3Co2SbO6 at a predefined temperature in an air medium to obtain a powder. Finally, the method concludes by calcinating the powder to obtain a carbon coated layered oxide active mass material.
[016] In an aspect of the present disclosure, agitating the carbon source and the compound Li3Co2SbO6 is done by mechanical stirring or by sonication followed by calcination.
[017] In another aspect of the present disclosure, the solvent comprises of deionized water and the predetermined carbon source comprises of an appropriate stoichiometry (5-20 times) of sucrose.
[018] In yet another aspect of the present disclosure, the predetermined quantity of the compound Li3Co2SbO6 is 200-500 mg.
[019] In yet another aspect of the present disclosure, the step of drying the solution includes heating the solution at a temperature of 100 0C for 2 hours, cooling the obtained mixture, and grinding the mixture.
[020] In yet another aspect of the present disclosure, the grinding of the mixture is done using mechanical mixing for a duration commensurate with volume.
[021] In yet another aspect of the present disclosure, the step of subjecting the powder to a calcinating treatment includes placing the powder in an alumina crucible and reacting at temperature of 750 0C in air at a heating rate of 2 0C/min for 6 hours.
[022] Further, the present invention discloses a lithium ion cell, wherein the cell comprises of a cathode comprising carbon coated electrode active mass having the formula Li3Co2SbO6. Furthermore, the lithium ion cell comprises of an anode comprising of an alkali metal, a microporous membrane separator and an electrolyte.
[023] In an aspect of the present disclosure, the anode comprising of an alkali metal is made up of lithium.
[024] In yet another aspect of the present disclosure, the electrolyte comprises of Lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ethyl methyl carbonate in a 50:50 volume ratio.
[025] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[026] The illustrated embodiments of the subject matter will be understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of methods of carbon coating of layered material, systems and devices that are consistent with the subject matter as claimed herein, wherein:
[027] Figure 1 illustrates an image depicting a carbon coating process by mechanical stirring for Li3Co2SbO6 sample and an image depicting a carbon coating process by sonication method for Li3Co2SbO6 sample, in accordance with an embodiment of the present disclosure;
[028] Figure 2 illustrates a graphical representation depicting an X-ray diffraction of Li3Co2SbO6 and carbon coated Li3Co2SbO6 samples calcined at temperatures 750 ºC and an image depicting interlayer spacing and Li+ diffusion path, in accordance with an embodiment of the present disclosure;
[029] Figure 3 illustrates images depicting a transmission electron microscopy analysis of pristine Li3Co2SbO6, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present disclosure;
[030] Figure 4(a) illustrates a graphical representation of a vibrational FTIR spectra for pristine and carbon coated Li3Co2SbO6 samples, in accordance with an embodiment of the present disclosure;
[031] Figure 4(b) illustrates a graphical representation of a Raman spectra for pristine and carbon coated Li3Co2SbO6 samples, in accordance with an embodiment of the present disclosure;
[032] Figure 5 illustrates a graphical representation depicting a complex impedance spectroscopy analysis result of a pristine Li3Co2SbO6, calcined carbon coated Li3Co2SbO6, and mechanical carbon coated Li3Co2SbO6 at room temperature in accordance with an embodiment of the present invention;
[033] Figure 6 illustrates graphical representation of cyclic voltammetry curves of pristine Li3Co2SbO6 electrode compositions, in accordance with an embodiment of the present invention;
[034] Figure 7 illustrates a graphical representation depicting a voltage time plots of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention;
[035] Figure 8 illustrates a graphical representation depicting a voltage capacity plots of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6, and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention; and
[036] Figure 9 illustrates a graphical representation of an EIS measurements before and after charge-discharge tests of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention.
[037] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
[038] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[039] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[040] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
[041] Active material used in the present disclosure may be synthesized using the conventional solid state reaction method. All the starting precursors may have been analytical grade and may have been used without further purification. Initially, the starting materials Li2CO3, CoCO3 and Sb2O3 may be dried at 100 °C prior to avoid moisture impurity. Relevant stoichiometric ratios of precursors may be mixed together with ethanol and ground using an agate mortar and pestle for 3 h to get a homogeneous physical mixture of precursors. The ready physical mixture may be heated up with 2 °C/min heating rate on ambient air atmosphere at 1100 °C for 12 h dwell time. After natural cooling, the resulting materials (Li3Co2SbO6) may be collected and reground by an agate mortar. Carbon coating of the prepared sample may be done by using three different approaches using sucrose as a carbon source.
[042] In an embodiment of the present disclosure, the present disclosure may be configured to disclose a process for carbon coating. Sucrose (5-20 times) may be added with Li3Co2SbO6 (200-500 mg) and mixed by an agate mortar for 3 h. The resulting mixture of Li3Co2SbO6 and sucrose may be then placed in muffle furnace with 2 °C/min heating ramp rate for 750 °C under air for 6 h. After natural cooling, the final reaction product may be collected and ground into a powder form named as calcined carbon coated Li3Co2SbO6.
Exemplary Implementations
[043] Figure 1 illustrates an image 102 depicting carbon coating process by mechanical stirring and an image 104 depicting carbon coating process by sonication method for Li3Co2SbO6 sample, in accordance with an embodiment of the present disclosure. Referring to the image 102, the present invention discloses a process for preparing carbon coating of Li3Co2SbO6 using mechanical stirring method. In the process, an appropriate stoichiometry (5-20 times) of sucrose may be dissolved in deionized water (DI) by mechanical stirring for 15 min. After the mechanical stirring, 200-500 mg of synthesized Li3Co2SbO6 may be added in reaction solution and stirred for another 2 h. The solution may then be heated at a temperature of 100 °C for 2 h. The resulting mixture of sucrose and Li3Co2SbO6 may be cooled to room temperature and then may be grinded using an agate mortar to get a fine powder. After this, the fine powder may be placed in alumina crucible and then may be reacted at a temperature of 750 °C with heating rate of 2 °C/min for 6 h. When cooled, the product may be removed from the furnace and ground into a powder.
[044] Further, referring to the image 104, an appropriate stoichiometry of sucrose and Li3Co2SbO6 may be sonicated alternatively for 2h. The sonication assisted mixture of sucrose and Li3Co2SbO6 may be dried at a temperature of 100 °C for 2h. When cooled, the mixture may be then grinded using an agate mortar and to get a fine powder. The resulting physical mixture may be kept in a crucible and may be reacted with a heating rate of 2 °C/min at 750 °C for 6 h. After cooling, the product may be removed from the furnace and may be ground into a powder.
[045] Figure 2 Illustrates a graphical representation 202, depicting an X-ray diffraction of Li3Co2SbO6 and carbon coated Li3Co2SbO6 samples calcined at temperatures 750 ºC and an image 204, 206 depicting interlayer spacing and Li+ diffusion path, in accordance with an embodiment of the present disclosure. Referring to the graphical representation 202, all the prepared products in the present disclosure may be analysed by X-ray diffraction techniques using an ARL ™ EQUINOX 100 X-ray powder diffractometer using Cu-Ka radiation generated at 40 kV, 30 mA for confirmation of phase purity and structure. Phase formation of pristine Li3Co2SbO6 may be confirmed by well crystalline single monoclinic structural phase having space group C2/m related to the A3M2SbO6 honeycomb-layered oxide phases.
[046] Carbon coating of Li3Co2SbO6 may be confirmed by the X-ray diffraction. The XRD patterns of carbon coated Li3Co2SbO6 sample may have broader background between 20-30º suggesting the presence of amorphous carbon. The carbon coated Li3Co2SbO6 prepared according to other examples demonstrate the single monoclinic structural phase related to C2/m honeycomb-layered oxide phase.
[047] Further, figure 2 illustrates an image 204 and an image 206 respectively depicting interlayer spacing and Li+ diffusion paths, in accordance with an embodiment of the present disclosure. Referring to the image 204, the crystal structure of Li3Co2SbO6 consists of the alternating Co2SbO6 slabs and Li-layers. The honeycomb layers are well separated by interlayer spacing of ~ 5.153 Å by layers of Li atoms. Referring to the image 206, two-diffusion path in the crystal structure of Li3Co2SbO6, along b-axis with diffusion length of 2.941 A? and along a-axis with diffusion length of 2.95 A?. Moreover, diffusion path along c-axis is blocked.
[048] Figure 3 illustrates an image 302, 304, 306, 308 depicting a transmission electron microscopy analysis of pristine Li3Co2SbO6, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present disclosure. Figure 3 illustrates an image 302 depicting a transmission electron microscopy analysis of pristine Li3Co2SbO6, in accordance with an embodiment of the present disclosure. The structure features and elemental compositions of prepared example materials may be visually observed in transmission electron microscopy as shown by the image 302.
[049] The image 302 displays the layered structure with crystalline features. Crystalline feature is also confirmed by selected area electron diffraction pattern as display the image 302 (ii). The image 302 (iii) inset demonstrates the elemental mapping approaching to its constituent elements.
[050] Further, the figure 3 illustrates an image 304 depicting a transmission electron microscopy analysis of calcined carbon coated Li3Co2SbO6, in accordance with an embodiment of the present disclosure. By looking at the image 304 (i), the carbon coating may be observed in the edge of layered structure and this may also be verified by selected area electron diffraction pattern in the image 304 (ii) by ring pattern at the edge of the material. The image 304 (i) depicts that an amorphous carbon layer overlays on the surface of the Li3Co2SbO6, which may facilitate electron migration during electrochemical reactions. Further, the image 304 (iii) depicts the elemental analysis by elemental mapping and EDS spectra. It is clear that the image 304 (iii) covers the Co, Sb, O along with C.
[051] Further, the figure 3 illustrates an image 306 depicting a transmission electron microscopy analysis of mechanical carbon coated Li3Co2SbO6, in accordance with an embodiment of the present disclosure. The image 306 (i) display the carbon coating of layered structure with the amorphous carbon as displayed in inset of the image 306 (ii). The elemental mapping may be evaluated as shown in the image 306 (iii). The presence of carbon with Co, Sb and O suggests carbon coating.
[052] Furthermore, the figure 3 illustrates an image 308 depicting a transmission electron microscopy analysis of the sonication carbon coated Li3Co2SbO6, in accordance with an embodiment of the present disclosure. The image 308 (i) shows the carbon coating in which a thin layer of carbon is surrounded to the layered structure of prepared sample. When observed, the selected area electron diffraction pattern at the edge, a circle pattern is founded as shown in inset of the image 308 (ii). However, the existence of carbon in the structure may be confirmed by elemental mapping and EDS spectra as demonstrated in the image 308 (iii).
[053] Figure 4(a) illustrates a graphical representation 402, 404, 406, 408 of a vibrational FTIR for pristine and carbon coated Li3Co2SbO6 samples, in accordance with an embodiment of the present disclosure. The bands found in between 500 and 700 cm-1 are related to the deformational (bending) mode of the MO6 polyhedra. The main absorption peaks of functional groups are bending vibration of d (O-Co-O) at 432 cm-1, stretching of Co-O bands in v (CoO6) octahedron (592 cm-1) and stretching of SbO6 octahedron (654 cm-1) that are present in the example samples. Furthermore, peaks at 1631 mainly belonging to the C=C stretching confirmed the coating of the examples.
[054] Figure 4(b) illustrates a graphical representation 410, 412, 414, 416 of Raman spectra pattern for pristine and carbon coated Li3Co2SbO6 samples, in accordance with an embodiment of the present disclosure. In the graphical representation 404, there are distinct peaks at ?165, ?194 and ?474 belonging to symmetric bending vibration of O-Li-O bond (F2g(3) symmetry), lattice vibration of SbO6 octahedra and CoO6 octahedra (Eg symmetry) mainly belonging to the signature peak of Li3Co2SbO6. Further, the presence of D band and G band approximately at ~1350 cm-1 and ~1580 cm-1 in the examples confirms carbon coating.
[055] Figure 5 illustrates a graphical representation 502, 504, 506 depicting a complex impedance spectroscopy analysis result of a pristine Li3Co2SbO6, calcined carbon coated Li3Co2SbO6, and mechanical carbon coated Li3Co2SbO6 at room temperature in accordance with an embodiment of the present invention. The DC electrical conductivity of the prepared products may be estimated by complex impedance spectroscopy measurements using pellets of Examples with applied AC signal of 5 mV in the frequency range of 1 mHz to 100 kHz. Referring to the graphical representation 502, appearance of semicircle in the CIS spectra indicates that electrical properties of Li3Co2SbO6 system arise due to single relaxation process of bulk material and the tail shows the blocking electrode nature of silver paste against Li+ ions.
[056] The high frequency semicircle may be accredited to the parallel combination of the bulk resistance (Rb) and capacitance (Cb) of the material. The value of estimated bulk resistance of Li3Co2SbO6 is the order of 106 O. Electrical conductivity of pristine Li3Co2SbO6 at room temperature is measured to be 7.87 × 10-8 S/cm which is better than the first reported conventional electrode material LiFePO4 (~10-9 S/cm).
[057] Further, the figure 5 illustrates a graphical representation 504 depicting a complex impedance spectroscopy analysis result of calcined carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention. Referring to the graphical representation 504, a vertical straight line is present in CIS spectra of carbon coated Li3Co2SbO6 sample and no semicircle is found. The following confirm that carbon coated Li3Co2SbO6 sample has only resistive nature. Further, the bulk resistance of carbon coated Li3Co2SbO6 sample may be found to be 785 O that reflect improved electrical conductivity. The calcined carbon coated Li3Co2SbO6 as depicted by the graphical representation 504, the DC electrical conductivity is improved and measured to be 4.2 × 10-4 S/cm which is four order enhanced in comparison to pristine Li3Co2SbO6 prepared.
[058] Furthermore, the figure 5 illustrates a graphical representation 506 depicting a complex impedance spectroscopy analysis result of mechanical carbon coated Li3Co2SbO6 at room temperature, in accordance with an embodiment of the present invention. Referring to the graphical representation 506, the bulk resistance of carbon coated Li3Co2SbO6 sample is found to be order of kO that indicates improved electrical conductivity. The DC electrical conductivity at room temperature is measured to be 3.6 × 10-5 S/cm which is three order greater than the pristine Li3Co2SbO6 prepared in as per the graphical representation 502.
[059] In another aspect of the present disclosure, the present disclosure provides a composition for cathode material prepared as per the above examples. The working electrode slurry may be prepared by mixing cathode active mass material, conducting carbon Super-P and polymeric (resin /PVDF) binder in different weight ratio (65:30:5, 65:25:10, 70:20:10 and 85:10:5) in N-methyl-2-pyrrolidinone (NMP) followed by vigorous stirring for 12 h. Then, the slurry was casted on aluminium (Al) foil using a mini-coater and dried at 100 °C for 12 h.
[060] The coated Al foil was calendared using the hot twin roller and may be cut into disks with a diameter of 16 mm and dried at 80 °C for 12 h in a vacuum oven. In an argon-filled glovebox (H2O and O2 level = 0.1 ppm), the coin-type half cells CR2016 may be fabricated using calendared Al-foil as the working electrode, Lithium foil as the counter electrode, porous poly(propylene) membrane as separator with 1 M LiPF6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (1:1 wt%) electrolyte.
[061] In yet another aspect of the present disclosure, the selected composition may be 70:20:10 for making a slurry of carbon coated Li3Co2SbO6 cathode, super P carbon and binder PVDF in NMP solvent. The homogeneous slurry may be casted on Al-foil and may be dried in the oven. After calendaring, the sheet may be cut into disk form for lithium ion electrochemical cell CR2016 assembly. A lithium ion cell may comprise a working electrode, the counter electrode of lithium foil, separator polypropylene film, and 1 M LiPF6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (1:1 wt%) electrolyte was used which was fabricated inside the argon environmental in the glove box (H2O and O2 level = 0.1 ppm).
[062] All the electrochemical features of lithium ion cell may be tested using CHI760D electrochemical workstation (CH Instruments). The cyclic voltammetry (CV) curve may be tested at scan rate of 0.1 mV/s and electrochemical impedance spectroscopy (EIS) may be performed in the frequency range of 100 kHz to 1 Hz at an AC signal of 5 mV/s using CH Instruments. The charge discharge measurements may be obtained at constant current density of 10 mA/g in the voltage range of 3.0 to 4.5 V using Neware battery tester.
[063] Figure 6 illustrates a graphical representation 602, 604, 606, 608 of cyclic voltammetry curves of pristine Li3Co2SbO6 electrode compositions, in accordance with an embodiment of the present invention. Referring to the figure 6, the cyclic voltammetry curves of a Li//Li3Co2SbO6 cells for different composition ratios of electrode composition; active mass material (Li3Co2SbO6): conductive carbon: PVDF binder, the graphical representation 602, 65:30:5, the graphical representation 604, 65:25:10, the graphical representation 606, 70:20:10, and the graphical representation 608, 85:10:5 are tested at 0.1 mV/s scan rate in a voltage range of 3 to 4 V and 3 to 4.5 V in which an oxidation and reduction peaks appeared as illustrated in Figure 6. The oxidation peak at around 3.53 V and reduction peak at 3.37 V may be observed due to the redox reaction assigned to the Co2+/Co3+ redox couple with insertion/extraction of Li+ form structure of Li3Co2SbO6 system.
[064] The voltage diffrence of anodic and cathodic peaks are 0.24, 0.22, 0.11 and 0.15 V signifying good electrochemical reversibility as well as lower interfacial polarization by the surface coating for 65:30:5, 65:25:10, 70:20:10 and 85:10:5 composition ratio cells. In case of 70:20:10 composition cell the lowest potential differencce indicates improved electrochemical performance. In the layered oxide materials, multiple phase transition may be reported in CV curves of A3M2XO6 due to phase transformations during Li+/Na+ (de)intercalation reactions and Li/Na ordering and transition metal gliding.
[065] But in case of Li3Co2SbO6 system only one redox peak may be seen in CV curves which suggest that after removal of Li from the lattice, its structure is stable and multiple phase transition will not allow. It may be interesting to note down that for 2nd cycle, positions of the redox peaks remain altered, implying good kinetic behaviour of the Li3Co2SbO6 electrode in case of 70:20:10 ratio combination. Based on the results presented in Table 1, may be advisable to use a 70:20:10 ratio composition ratio for electrochemical response with the prepared examples for Lithium ion cell invention.

Table 1. Electrochemical performance of pristine Li3Co2SbO6 electrode composition in coin cell (Li // LiPF6 in EC/EMC // Li3Co2SbO6 composite) configuration.

[066] Figure 7 illustrates a graphical representation 702, 704, 706 and 708 depicting a voltage time plots of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6, respectively in accordance with an embodiment of the present invention Thus, the voltage-time plots for all the prepared examples at current density of ~10 mA/g are illustrated. It is advantageous over the example as depicted by the graphical representation 702, relative over the example as depicted by the graphical representation 704, over the example as depicted by the graphical representation 706 and over the example as depicted by the graphical representation 708 of carbon coating on electrochemical cell response of the prepared material with respect pristine that make it possible to enhanced the cell features. In particular, the example as depicted by the graphical representation 702 has lower discharging time in comparison to rest of the examples that further indicates the improved electrochemical cell response. By looking at the graphical representation 702, 704, 706, 708, it was clear that in the present invention, example as depicted by graphical representation 704 has maximum discharging time and electrochemical features.
[067] Figure 8 illustrates a graphical representation 802, 804, 806 and 808 depicting a voltage capacity plots of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention. Taking into account the prepared examples, show the first reversible capacity of 44, 110, 69 and 60 mAh/g at same current density ~10 mAh/g. It is important to note that calculated reversible capacity is nearly identical or more to its theoretical capacity during one lithium extraction from the host of the Li3Co2SbO6 lattice.
[068] However, in case of in case of LiFePO4, almost 0.7 lithium is extracted. Thus it is evident that after the carbon coating of Li3Co2SbO6, no phase transition occurs. It may be very interesting that during initial discharge, the obtained capacity indicates that, almost more than one Li+ ions per formula are extracted in case of example illustrated by graphical representation 804. However, during the fourth discharge the capacity drops down to ~84 mAh/g. It may happen that, as during the reinsertion of Li+ ions, those ions could not return at their initial lattice sites and during discharging it may be possible that diffusion paths of Li+ ion are blocked.
[069] Figure 9 illustrates a graphical representation 902, 904, 906 and 908 of EIS measurements, before and after charge-discharge test of pristine, calcined carbon coated Li3Co2SbO6, mechanical carbon coated Li3Co2SbO6 and sonication carbon coated Li3Co2SbO6 in accordance with an embodiment of the present invention The EIS analysis of all the prepared examples are done at 5 mV alternating sine wave signal and corresponding Nyquist plots before and after 100 charge-discharge cycles are demonstrated in the graphical representations. The Nyquist plot of the prepared examples show a solid electrolyte interface (SEI) resistance (Rs), semicircle at high frequency side (charge transfer resistance; Rct) and a straight line at low frequency in the Warburg region (controlled by mass transfer; Warburg constant (w)), constant phase element CPEp and some other circuit elements.
[070] The estimated fitting equivalent circuit component parameters are given in the Table 2 (as given below) for before and after 100 charge discharge cycles. After 100 change discharge measurement the value of both the resistance (Rs and Rct) are changed due to the polarization effect. From EIS response of the prepared examples, it is clear that, the semi-circular loop increases prominently upon 100 charge discharge cycling, signifying lowered ion transport into/from Li3Co2SbO6 electrode structure.
[071] However, in all the prepared examples, example depicted by the graphical representation 904 has low value of Rs and Rct. This indicates improved electrochemical performance. The high value of Rct of example depicted by the graphical representation 902, Li3Co2SbO6 implies that it has poor electron transportation. The high value of Rct may prevent the full extraction of Li+ ion and suppress the reversible capacity of electrode material. The results, described in Table 2, show the electrochemical response of the prepared materials with its effectiveness in case of lithium ion cells for a new material with carbon coating modifications.
Table 2. Electrochemical performance of carbon coated Li3Co2SbO6 electrode in coin cell (Li // LiPF6 in EC/EMC // carbon coated Li3Co2SbO6 configuration).
[072] It will be further appreciated that functions or structures of a number of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
, Claims:1) A method for producing a structurally layered positive electrode active mass material, the method comprising the steps of:
preparing a solution by agitating, in a solvent, a predetermined amounts of a carbon source necessary for forming the structurally layered positive electrode active mass material, represented by a following formula (1);
adding and agitating the compound represented by the formula (1) in a predetermined quantity in the solution;
drying the solution obtained after the addition of the compound represented by the formula (1) at a predefined temperature in an air medium to obtain a powder;
calcinating the powder to obtain a carbon coated lithium containing composite oxide;
wherein the positive electrode active mass is represented by the formula (1): Li3Co2SbO6.
2) The method as claimed in claim 1, wherein agitating the carbon source and the compound represented by the formula (1) is done by direct calcination or mechanical stirring or by sonication followed by calcination.
3) The method as claimed in claim 1, wherein the solvent comprises of deionized water and the predetermined carbon source comprises of an appropriate stoichiometry (5-20 times) of sucrose.
4) The method as claimed in claim 1, wherein the predetermined quantity of the compound represented by the formula (1) is 200-500 mg.
5) The method as claimed in claim 1, wherein the step of drying the solution includes heating the solution at a temperature of 100 °C for 2 hours, cooling the obtained mixture, grinding and pestling the mixture.
6) The method as claimed in claim 5, wherein the grinding of the mixture is done using mechanical mixing for a duration commensurate with volume.
7) The method as claimed in claim 1, wherein the step of subjecting the powder to a calcinating treatment includes placing the powder in an alumina crucible and reacting at temperature of 750 °C in air at a heating rate of 2 °C/min for 6 h.
8) A lithium ion cell, the cell comprising:
a cathode comprising carbon coated electrode represented by a following formula (1);
an anode comprising of an alkali metal;
a microporous membrane separator;
an electrolyte;
wherein the carbon coated electrode is represented by the formula (1): Li3Co2SbO6.
9) The lithium ion cell as claimed in claim 8, wherein the anode comprising of an alkali metal is made up of lithium.
10) The lithium ion cell as claimed in claim 8, wherein the electrolyte comprises of Lithium hexafluorophosphate (LiPF6) in ethylene carbonate/ethyl methyl carbonate in a 50:50 volume ratio.