Synthesizing high energy density cathode material

Abstract

A method for synthesizing a high energy density cathode material for lithium-ion batteries are disclosed. The method includes obtaining a solution comprising a ferrous salt, a manganese salt, and a source of carboxylic acid in de-ionized water. Thereafter, a source of phosphate and a source of lithium are added to form a precursor solution. Thereafter, source of glycol is added to the precursor solution. Once the source of glycol is added, a hydrothermal synthesis process of the precursor solution is performed at a predetermined temperature for a predetermined period to crystallize plurality of LMFP primary particles into secondary particles. The secondary particles possess a spherical morphology, contributing to a high tap density and high energy density of the cathode material.

Description

SYNTHESIZING HIGH ENERGY DENSITY CATHODE MATERIALBACKGROUND

[0001] Batteries are typically used in variety of electrical and mechanical devices to power different components of these devices. Such batteries include a pair of electrodes and an electrolyte between the two electrodes. The performance of these batteries is largely dependent on the materials used for the cathode and anode, as well as the electrolyte. Among these, the material used for cathode is the most important to enhance the reliability and efficiency of the battery. A common cathode material is LFP material which comes with a manganese doping to form a lithium manganese iron phosphate (LMFP) material to improve its energy density. There are several structural attributes, such as type of morphology, tap density, and particle size, of the LMFP material which needs to be optimized to such a value that it may results in improved performance of the battery.BRIEF DESCRIPTION OF DRAWINGS

[0002] The detailed description is provided with reference to the accompanying figures, wherein:

[0003] FIG. 1 illustrates a method for synthesizing a cathode material having high energy density, in accordance with one example of the present subject matter;

[0004] FIG. 2 illustrates a table summarizing an experimental design of experiments for the synthesis of LiMm-xFexPO4 with 20% citric acid, in accordance with an example of the present subject matter;

[0005] FIG. 3 illustrates scanning electron microscope (SEM) images showing the experimental results of LiMm-xFexPO4 at different synthesis conditions, in accordance with an example of the present subject matter;

[0006] FIG. 4 illustrates a table summarizing experimental findings for the synthesis of LiMm-xFexPO4 with details on synthesis conditions and outcomes, in accordance with an example of the present subject matter;

[0007] FIG. 5 illustrates scanning electron microscope (SEM) images showing the effects of varying concentrations of ethylene glycol and citric acid on the morphology of synthesized particles, in accordance with an example of the present subject matter;

[0008] FIG. 6A illustrates a graph plotting relationship between the percentage of citric acid used, the pH and tap density of the synthesized material, in accordance with an example of the present subject matter;

[0009] FIG. 6B illustrates a graph plotting relationship between the percentage volume of Ethylene Glycol and Particle Size Distribution (PSD) values of the synthesized material, in accordance with an example of the present subject matter;

[0010] FIG. 7A-7B illustrates two X-ray diffraction patterns depicting crystallographic structure analysis related to synthesis of LiMm-xFexPO4, in accordance with an example of the present subject matter;

[0011] FIG. 8 illustrates SEM images highlighting the synthesis of LiMm- xFexPO4 particles, in accordance with an example of the present subject matter; and

[0012] FIG. 9 illustrates two graphs analysing the PSD as part of the synthesis of LiMm-xFexPO4, in accordance with an example of the present subject matter.

[0013] It may be noted that throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and / or implementations consistent with the description; however, the description is not limited to the examples and / or implementations provided in the drawings.DETAILED DESCRIPTION

[0014] A rechargeable battery or secondary cell is a type of electrical battery which may be charged, discharged into a load, and recharged again.This is opposed to a disposable or primary battery, which is for one time use only as it comes charged and discharged permanently after use. Rechargeable batteries accumulates and stores energy through a reversible electrochemical reaction. Several different combinations of electrode materials and electrolytes are used in formation of such rechargeable batteries for providing efficient battery characteristics. Examples of such materials include, but are not limited to, lead-acid, zinc air, nickel-cadmium (NiCd), nickel-metal hydride (NiMH), lithium-ion (Li ion), lithium iron phosphate (LiFePO4), and lithium-ion polymer (Li-ion polymer).

[0015] Among these, lithium-ion batteries are most efficient which operate on the principle of lithium ions moving from the negative electrode to the positive electrode during discharge and comes back during charging. The performance of these batteries is largely dependent on the materials used for the cathode and anode, as well as the electrolyte. The cathode material, in particular, plays a pivotal role in determining the energy density, power density, safety, and life cycle of the battery.

[0016] Lithium Iron Phosphate (LFP) is one of the commonly used cathode materials in lithium-ion batteries. LFP is known for its robustness, safety, and long cycle life. However, it has a relatively low energy density and potential window, which limits its application in high energy density batteries. This limitation has led to the exploration of various strategies to enhance the energy density of LFP. One such strategy is the introduction or doping of other metal ions into the LFP structure. For instance, manganese (Mn) has been introduced into the LFP structure to form LMFP. The introduction of Mn improves the energy density and potential window of the cathode material, thereby enhancing the overall performance of the battery.

[0017] The synthesis of LMFP material may be performed using various synthesis process. One of these processes is hydrothermal synthesis process. The synthesis of LMFP involves several steps, including the preparation of a precursor solution and the hydrothermal synthesis process.The precursor solution typically includes a ferrous salt, a manganese salt, and other additives. The hydrothermal synthesis process involves heating the precursor solution at a predetermined temperature for a predetermined period of time. This process is carefully controlled to ensure the desired properties of the final product.

[0018] The ionic diffusion of the lithium ions in the LMFP along with the morphology and tap density of the synthesized LMFP particles are the factors that may affect the performance of the cathode material. The morphology of the particles may be controlled by adjusting the synthesis conditions, such as the temperature and duration of the hydrothermal synthesis process and the concentration of different additives in the precursor solution. The tap density of the particles, which is a measure of the packing efficiency of the particles, may also be improved by controlling the synthesis conditions. These factors are carefully optimized to achieve the desired performance characteristics of the cathode material.

[0019] However, conventionally used additives and subsequent hydrothermal synthesis process conditions are not such devised which led to low ionic diffusion of Lithium ions of the LMFP which subsequently leads to irregular morphological structure of LMFP particles and lower tap density. With these important features of the cathode material being non-optimized, the efficiency and reliability of the batteries suffers. Therefore, there is a need to explore new additives along with specific hydrothermal synthesis conditions which combinedly helps in achieving or obtaining an optimized LMFP cathode material.

[0020] Method for synthesizing a cathode material having high energy density are described. As would be known, the cathode material is used to produce a cathode which is to be installed within a battery. In an example, there are number of characteristics of a good-quality rechargeable battery, e.g., voltage value, discharge curve, capacity, energy density, specific energy density, power density, etc. Among all of these characteristics,energy density is one of the main characteristics representing operational longevity of the battery.

[0021] The cathode material is synthesized through a series of steps, which involve the preparation of a precursor solution followed by performing a hydrothermal synthesis process on the precursor solution. The method includes obtaining a first solution by dissolving a ferrous salt, a manganese salt, and a source of carboxylic acid in the de-ionized (DI) water. In an example, the concentration of carboxylic acid in the first solution is in a range of about 15-20%. Various constituents of the first solution may be obtained and added from different sources. For example, the ferrous salt is one of ferrous sulphate, ferric nitrate, ferrous chloride, and ferric phosphate. The manganese salt is one of hydrated manganese sulphate, manganese nitrate, manganese chloride, and manganese phosphate. Further, the carboxylic acid is sourced from one of citric acid, ascorbic acid, and tartaric acid. It may be noted that above disclosed sources of various constituents of first solution is exemplary and any other chemical solution providing similar constituent may also be used without deviating from the scope of the present subject matter.

[0022] Returning to the present example, the first solution is then titrated by adding 1 molar (M) concentration of a source of phosphorous to form a second solution. Subsequently, 2M to 3M concentration of a source of lithium is added into the second solution to form a third solution which is a precursor solution, wherein the addition of the source of lithium is to start off the nucleation process. Thereafter, a predefined volume of source of glycol is added to the precursor solution, wherein the addition of source of glycol helps in controlling the morphology of the particles thus formed. Different chemical solution added to form the precursor solution acts as a source for each of the metal ion for the LiMm-xFexPC (LMFP) cathode material, wherein 'x’ ranges from 0.2 to 0.5.

[0023] In an example, the source of phosphorous is one of ammonium dihydrogen phosphate and phosphoric acid. The source of lithium is one oflithium phosphate, lithium hydroxide, lithium nitrate, and lithium chloride. Further, the source of glycol is one of ethylene glycol, diethylene glycol, and propylene glycol. It may be noted that above disclosed sources of various constituents of precursor solution is exemplary and any other chemical solution providing similar constituent may also be used without deviating from the scope of the present subject matter.

[0024] Subsequently, the precursor solution is subjected to hydrothermal reaction which involves heating the precursor solution at a predetermined temperature for a predetermined holding period. Generally, this process crystallizes a plurality of LMFP primary particles to form a plurality of secondary particles and such secondary particles possess a spherical morphology, which is advantageous for achieving a high tap density. In an example, the tap density of the particles is a measure of the packing efficiency of the particles, which may be improved by controlling the synthesis conditions. In an example, the morphology of the particles may also be controlled by adjusting the synthesis conditions, such as the concentration of the additives in the precursor solution and the temperature and duration of the hydrothermal synthesis process.

[0025] Various additives have been used in the synthesis of LMFP to control the morphology and tap density of the particles. For instance, source of carboxylic acid has been used to chelate the metal ions and control the primary particle nucleation. Further, the source of glycol has been used to control the secondary particle growth. It may be noted that, the synergistic effect of these additives may control the Ostwald ripening and crystal growth, which reduces the diffusion path length and control the morphology of the particles. In an example, the concentration of source of carboxylic acid and the volume of source of glycol in the precursor solution may be adjusted to achieve the desired morphology and tap density of the particles. Further, some specific hydrothermal synthesis conditions, such as specific temperature and holding time, also helps in achieving desired structural attributes of the LMFP secondary particles.

[0026] The above aspects are further described in conjunction with the figures, and in associated description below. It should be noted that the description and figures merely illustrate principles of the present subject matter. Therefore, various method steps that encompass the principles of the present subject matter, although not explicitly described or shown herein, may be devised from the description and are included within its scope.

[0027] FIG. 1 illustrates a method 100 for synthesizing a cathode material having high energy density, in accordance with one example of the present subject matter. The order in which the above-mentioned method is described is not intended to be construed as a limitation, and some of the described method blocks may be combined in a different order to implement the method, or an alternative method.

[0028] To this end, at block 102, a first solution including a ferrous salt, a manganese salt and a source of carboxylic acid is obtained. For example, by dissolving certain amount of ferrous salt, manganese salt and source of carboxylic acid in the de-ionized water, the first solution is obtained. In an example, the manganese salt may have concentration in the range of 0.5 to 0.8 mole in the first solution and the ferrous salt may have concentration in the range of 02. to 0.5 mole in the first solution, which specifically is 0.4 mole. Further, the source of carboxylic acid which is added to the DI water have concentration in the range of about 15-20%. It may be noted that, the source of carboxylic acid serves as a chelating agent to chelate the metal ions, which eventually control the primary particle nucleation.

[0029] In an example, the ferrous salt is one of ferrous sulphate, ferric nitrate, ferrous chloride, and ferric phosphate and the manganese salt is one of hydrated manganese sulphate, manganese nitrate, manganese chloride, and manganese phosphate. Further, the carboxylic acid is sourced from one of citric acid, ascorbic acid, and tartaric acid. It may be noted that above disclosed sources of various constituents of first solution is exemplary and any other chemical solution providing similar constituentmay also be used without deviating from the scope of the present subject matter.

[0030] At block 104, a source of phosphorous having 1 M concentration is added into the first solution to form a second solution. In an example, the source of phosphorous is added slowly into the first solution to control the size of primary particles . The rate of addition of source of phosphorous into the first solution to obtain the second solution is in the range of 3-7 mL / min which may range between 4-6 mL / min in specific cases. The source of phosphorous is one of ammonium dihydrogen phosphate and phosphoric acid.

[0031] At block 106, a source of lithium having 2M to 3M concentration is added into the second solution to form a third solution which is referred to as a precursor solution. Similar to the addition of source of phosphorous, the source of lithium is also added slowly into the second solution to control the oxidation of the metal precursors. The rate of addition of source of lithium hydroxide into the second solution is in the range of 2-6 mL / min which may be fixed at 5 mL / min in specific cases. In an example, the source of lithium and source of phosphorous acts as a metal ion source providing lithium ion and phosphate ion in the LMFP material.

[0032] At block 108, a predefined volume of source of glycol is added to the precursor solution. In an example, the source of glycol serves to control the secondary particle growth. In some cases, the predefined volume of source of glycol may be 30 to 40% of the precursor solution. The precursor solution thus prepared contains a plurality of LMFP primary particles.

[0033] At block 1 10, a hydrothermal synthesis is performed with the precursor solution at a predetermined temperature for a predetermined holding period. In an example, the predetermined temperature is in a range of about 160-200°C. Further, the predetermined holding period is in a range of about 9-20 hours. Such synthesis of precursor solution leads to the crystallization of plurality of LMFP primary particles to form a plurality of secondary particles. The secondary particles thus formed through thisprocess possess a spherical morphology, which is advantageous for achieving a high tap density. As would be known, the tap density of the particles is a measure of the packing efficiency of the particles, which may be improved by controlling the synthesis conditions.

[0034] In a specific example, as per the experimental resultsthe hydrothermal synthesis process is performed at a temperature of about 180°C for a holding period of about 12 hours, with 15-20% concentrated citric acid and 30-40% of ethylene glycol, which results in spherical morphology of the secondary particles, tap density ranging between 1 to 1 .2 g / cc and 2.7 to 3.6 pm particle size. It may be noted that, the predetermined temperature and holding period are carefully chosen to ensure the formation of secondary particles with the desired morphology and tap density. The temperature and holding period may be adjusted based on the specific requirements of the cathode material. For instance, a higher temperature or a longer holding period may be used to achieve a higher tap density or a different particle morphology.

[0035] Using the above-described method, at specific hydrothermal synthesis conditions with specific concentration of additives and the sequence of addition, a cathode material including a plurality of secondary particles having spherical morphology with higher tap density is synthesized. In an example, the tap density of the plurality of secondary particles ranges between 1 to 1.2 g / cc. Further, the diameter of the secondary particle is in the range of about 3 pm to 4 pm. This cathode material is further used to manufacture a battery cathode which is to be placed inside a battery.

[0036] FIG. 2 illustrates a table 200 summarizing an experimental design of experiments for the synthesis of LiMnl -xFexPO4 with 20% citric acid, in accordance with an example of the present subject matter. The table 200 displays various synthesis conditions and their corresponding tap density (Tap) and PSD results. Each row in the table represents a different experimental condition with varying amounts of lithium (Li), synthesistemperature (Temp in °C), holding time (in hours), and the ratio of water (H2O) to ethylene glycol (EG).

[0037] For instance, experiment 1 with 3 moles of Li, conducted at 180°C for 12 hours with a water to ethylene glycol ratio of 1 :2, resulted in a tap density of 1.09 g / cc and a PSD of 0.97 pm. This experiment demonstrates the effect of the synthesis conditions on the tap density and PSD of the synthesized particles. The tap density is a measure of the packing efficiency of the particles, which may be improved by controlling the synthesis conditions. The PSD provides information about the size distribution of the particles, which may also be controlled by adjusting the synthesis conditions. It may be noted that, although with such conditions we have achieved higher tap density, i.e., 1.09, however, the PSD is way to small which is not desirable.

[0038] Further, experiment 2 with 2 moles of Li, conducted at 180°C for 12 hours with a water to ethylene glycol ration of 1 :2, resulted in a tap density of 0.95 g / cc and a PSD of 3.6. This experiment yields higher tap density with desired PSD under specific synthesis conditions. This experiment demonstrates the effect of various synthesis conditions on the tap density and PSD of the synthesized particles. By adjusting various synthesis conditions, the morphology and tap density of the particles may be controlled, thereby improving the performance of the cathode material.

[0039] FIG. 3 illustrates scanning electron microscope (SEM) images showing the experimental results of LiMnl -xFexPO4, wherein x ranges from 0.2 to 0.5, at different synthesis conditions, in accordance with an example of the present subject matter. The SEM images provide a visual representation of the morphology of the synthesized particles under different conditions, thereby offering insights into the impact of synthesis conditions on the particle morphology.

[0040] As shown in FIG. 3, top left image 302 which is labelled as “3Li” exhibits a densely packed morphology of small particles when synthesized at 160°C with 10% citric acid. This image illustrates the effect of a lowersynthesis temperature on the morphology of the particles. At this temperature, the particles tend to be smaller and more densely packed. However, when the same 3M Li is synthesized with 20 % citric acid, the secondary particle are distorted in shape which is provided in image labelled as 310 which may affect the tap density and energy density of the cathode material. Further, the top right image 304 which is labelled as “2Li” displays a distinct spherical morphology achieved at the optimum temperature of 180°C with 10 % citric acid. This image shows particles with a disc-like shape, indicating a controlled growth of the particles at this temperature. Further when LMFP was synthesized with 2M Li and 20% citric acid it resulted in nearly spherical morphology. This near spherical morphology of the particles is advantageous for achieving a high tap density, which in turn improves the performance of the cathode material.

[0041] Further, the bottom images (306, 308) illustrate the change in particle morphology at different temperatures, labelled as "160°C" and "200°C" respectively. These images (306, 308) show irregular flake-like structures, indicating less controlled particle formation outside the optimum synthesis temperature. This observation underscores the impact of the synthesis temperature on the morphology of the particles. Below and above 180°C, irregular flakes are observed, suggesting that the control over the particle morphology is less effective at these temperatures.

[0042] However, at 180°C with 2M lithium precursor, the desired disclike morphology is achieved, as shown in the image labelled "2 Li" i.e., image 304 This image demonstrates the effect of the concentration of lithium on the morphology of the particles. With a precursor solution comprising 20% carboxylic acid concentration and a predefined volume of ethylene glycol synthesized at 180°C for about 12 hours, the secondary particles achieve a spherical morphology, a tap density between 1 and 1 .2 g / cc, and a particle size ranging from 2.7 to 3.6 pm. These results highlight the synergistic effect of the synthesis conditions on the morphology and tap density of the particles.

[0043] FIG. 4 illustrates a table 400 summarizing experimental findings for the synthesis of LiMnl -xFexPO4 with details on synthesis conditions and outcomes, in accordance with an example of the present subject matter. Each entry in the table represents a different set of synthesis conditions, including the amount of lithium (Li) used, the synthesis temperature (Temp), the holding time, the ratio of water to ethylene glycol (H2O:EG), and the citric acid percentage (Cit acid (%)). The resulting solution pH, morphology description (S), tap density (Tap), and particle size distribution (PSD) are also provided for each set of conditions.

[0044] For instance, in the highlighted row 4, the optimized conditions of 2M Li, a temperature of 180°C, a 12-hour hold time, a 2:1 ratio of H2O:EG, and 15% citric acid are used. These conditions yield a tap density of 1.09 g / cc and a PSD of 2.17 pm. The morphology of the particles transitions from disc to spherical under these conditions. This transition in morphology is advantageous for achieving a high tap density, which in turn improves the performance of the cathode material. The spherical morphology also contributes to the structural attributes of the secondary particles, which include a type of morphology, a particle size, and a tap density.

[0045] The table in FIG. 4 provides a systematic approach to investigate the effect of various synthesis conditions on the tap density and PSD of the synthesized particles. By analysing the results presented in the table, the optimum synthesis conditions for achieving the desired tap density and PSD may be determined.

[0046] FIG. 5 illustrates SEM images showing the effects of varying concentrations of ethylene glycol and citric acid on the morphology of synthesized particles, in accordance with an example of the present subject matter. Each image corresponds to a different concentration, as indicated by the labels 2.5%, 5%, 10%, 15%, 20%, and 30%. These labels describe the increasing percentages of citric acid used during the synthesis process.

[0047] For example, SEM images (502, 504, and 506) display irregular and less defined particle morphologies at lower citric acid concentrations (i.e., 2.5%, 5%, 10%). This observation suggests that at lower concentrations of citric acid, the control over the primary particle nucleation and secondary particle growth is less effective. As a result, the particles formed under these conditions tend to have irregular shapes and less defined structures.

[0048] On the other hand, SEM images (508, 510, and 512) display a clear transition to more uniform and spherical particles at progressively higher citric acid concentrations (i.e., 15%, 20%, 30%). This transition is highlighted by the green measurement labels which indicate the sizes of individual particles. The spherical morphology of the particles is advantageous for achieving a high tap density, which in turn improves the performance of the cathode material.

[0049] The images collectively illustrate the synergistic effect of EG and CA on the morphology, demonstrating substantial changes in particle shape and uniformity as the concentration of citric acid increases. The use of citric acid in a range of 15-20% in the precursor solution plays a pivotal role in controlling the primary particle nucleation. The EG, on the other hand, controls the secondary particle growth. The synergistic effect of EG and CA controls the Ostwald ripening and crystal growth, which may decrease the diffusion path length and control the morphology of the particles. By adjusting the concentrations of EG and CA in the precursor solution, the morphology and tap density of the particles may be controlled, thereby improving the performance of the cathode material.

[0050] FIG. 6A illustrates a graph 600A plotting relationship between the percentage of citric acid used, the pH and tap density of the synthesized material, in accordance with an example of the present subject matter. The graph has two y-axes and one x-axis. The left vertical axis 602 represents pH values which are indicated by diamonds connected by a line, right vertical axis 604 represents tap density in grams per cubic centimetre (g / cc)which are depicted by circles connected by a line, and a horizontal axis 606 represents the citric acid concentration percentage ranging from 0 to 30%.

[0051] Firstly, the graph between pH value (602) and citric acid (606) shows a decreasing trend in pH values as the percentage of citric acid increases. This trend suggests that the acidity of the precursor solution increases with the concentration of citric acid, which may influence the chelation of the metal ions and the primary particle nucleation.

[0052] Secondly, the graph between tap density (604) and citric acid (606) shows a general increase in tap density with higher concentrations of citric acid. This trend suggests that the tap density of the synthesized particles may be improved by increasing the concentration of citric acid in the precursor solution. The tap density of the particles is a measure of the packing efficiency of the particles, which may be improved by controlling the synthesis conditions. In some cases, the tap density of the plurality of secondary particles is between 1 and 1 .2 g / cc, which is advantageous for achieving a high energy density of the cathode material.

[0053] For example, as depicted in FIG. 6A, at 20% concentration of source of carboxylic acid, the tap density of the LMFP material increases to a maximum value of 1.1 g / cc which results in higher packing efficiency of the particles. The graph provides a visual representation of the synergistic effect of citric acid on the pH and tap density of the synthesized material. By adjusting the concentration of citric acid in the precursor solution, the pH and tap density of the synthesized particles may be controlled, thereby improving the performance of the cathode material.

[0054] FIG. 6B illustrates a graph 600B showing the relationship between the percentage volume / volume of Ethylene Glycol and Particle Size Distribution (PSD) values. The graph has a y-axis 608 represents PSD values in micrometres which are indicated by square connected by a line and a horizontal axis 610 represents the percentage ethylene glycol.

[0055] The graph illustrates a trend where the initial PSD value 1.5 corresponds to the lowest concentration of Ethylene Glycol, and as theconcentration increases, the PSD values rise sequentially to the low concentration PSD value 2.1 , increased concentration PSD value 2.36, further increased concentration PSD value 2.45, and high concentration PSD value 7.3, culminating in the peak concentration PSD value 8.3 at the highest Ethylene Glycol concentration depicted. This progression indicates that the PSD values are directly related to the Ethylene Glycol concentration, with higher concentrations resulting in larger PSD values.

[0056] FIG. 7A-7B illustrates two X-ray diffraction patterns depicting crystallographic structure analysis related to synthesis of LiMnl -xFexPO4, in accordance with an example of the present subject matter. Each pattern displays a series of peaks with varying intensities on the y-axis against 2 Theta degrees on the x-axis. The presence and intensity of these peaks provide valuable information about the crystalline structures within the LMFP samples. The XRD patterns provide a comprehensive understanding of the crystallographic structure of the synthesized LMFP particles. By analysing these patterns, the synthesis conditions may be optimized to achieve the desired crystallographic structure, which in turn may improve the performance of the cathode material in lithium-ion batteries.

[0057] Important peaks in the XRD patterns are labelled with their corresponding crystal planes such as (200) and (31 1 ). These labels indicate the specific crystallographic planes of the LMFP structure that are responsible for the observed diffraction peaks. The intensity of the peaks is a measure of the degree of crystallinity and the orientation of the crystalline structures within the LMFP samples. A higher peak intensity indicates a higher degree of crystallinity and a preferred orientation of the crystalline structures along the corresponding crystal plane.

[0058] Further, such pattern shows that the channel length in the

[0010] direction is a pivotal factor for Li diffusion. The

[0010] direction corresponds to the Y-direction in the crystallographic structure of LMFP, which is the primary direction for Li-ion diffusion. The length of the diffusion path in this direction may affect the Li-ion diffusion rate and, consequently, theperformance of the cathode material. The high intensity of the peak at the 200 plane shows that the diffusion length is smaller in 010 direction.

[0059] FIG. 8 illustrates SEM image 800 highlighting the synthesis of LiMn1 -xFexPO4 particles, in accordance with an example of the present subject matter. The main image showcases an array of LMFP secondary particles, with individual particles marked by green labels indicating their sizes, such as 847.7 nm, 1.597 pm, and 2.188 pm. These labels provide a visual representation of the particle size distribution of the synthesized particles. The particle size distribution is a measure of the size range of the particles, which may be controlled by adjusting the synthesis conditions. In some cases, the diameter (or the particle size distribution) of the secondary particle ranges from 3 pm to 4 pm, which is advantageous for achieving a high energy density of the cathode material.

[0060] A highlighted secondary particle is encircled in yellow with an enlarged inset at the top right corner, providing a detailed view of the surface texture. This detailed view offers insights into the morphology of the secondary particles, which is a pivotal factor affecting the performance of the cathode material. The morphology of the particles may be controlled by adjusting the synthesis conditions, such as the concentration of the additives in the precursor solution and the temperature and duration of the hydrothermal synthesis process. In some cases, with a precursor solution comprising 20% citric acid concentration and a predefined volume of ethylene glycol synthesized at 180°C for about 12 hours, the plurality of secondary particles achieves the spherical morphology, the tap density is between 1 g / cc and 1 .2 g / cc and the particle size ranging from 2.7 to 3.6 pm.

[0061] This diagram provides a visual representation of the three- dimensional structure of the synthesized particles, which contributes to the structural attributes of the secondary particles. The structural attributes of the secondary particles include a type of morphology, a particle size, and a tap density. These attributes may be controlled by adjusting the synthesisconditions, thereby improving the performance of the cathode material in lithium-ion batteries.

[0062] FIG. 9 illustrates two histograms analysing the PSD as part of the synthesis of LiMnl -xFexPO4, in accordance with an example of the present subject matter. Specifically, FIG. 9A depicts a graph representing the distribution of particle sizes in a sample having 20% source of carboxylic acid or specifically citric acid which managed to achieve tap density of 0.513 g / cc and PSD of 1.49 micron. The horizontal axis is labelled "Size (pm)" indicating the size of particles in micrometres, while the left vertical axis is labelled "% Passing" showing the cumulative percentage of particles that pass through a channel of a given size. The right vertical axis is labelled "% Channel" indicating the percentage of channels that correspond to a particular particle size. The graph includes a histogram with bars representing "% Channel" and a curve representing "% Passing." The bars show the frequency distribution of particle sizes, while the curve indicates the cumulative distribution, allowing for the analysis of particle size distribution within the sample.

[0063] Further, FIG. 9B depicts another graph representing the relationship between particle size distribution and the corresponding channels in a sample having 20% source of carboxylic acid and 33% of source of glycol. The graph illustrates a histogram with bars indicating the percentage of channels of various sizes and a curve showing the cumulative percentage of particles passing through these channels. The histogram bars correspond to the “% Channel” and are plotted against the right vertical axis, while the curve represents the “% Passing” and is plotted against the left vertical axis. The horizontal axis" measures “the size of particles in micrometres (pm), demonstrating the distribution of particle sizes within the sample. The bars and curve intersect at various points, indicating the proportion of particles that pass through channels of corresponding sizes, which is essential for analysing the sample’s particle size distribution. It may be noted that, with addition of carboxylic acid and glycol, higher tap densityand PSD is achieved, i.e., tap density as 1 .1 g / cc and PSD as 2.44 micron. The two graphs illustrate the variation in particle size and tap density under different synthesis conditions or with different formulations of the LMFP material.

[0064] The particle size distribution of the secondary particles is a measure of the size range of the particles, which may be controlled by adjusting the synthesis conditions. In some cases, the diameter of the secondary particle may range from 3 pm to 4 pm. This range is advantageous for achieving a high energy density of the cathode material. The finer median particle size of 3.6 pm, as indicated in the histogram at the bottom, corresponds to a higher tap density of 1 .1 g / cc. This suggests that a finer particle size may lead to a higher tap density, thereby improving the performance of the cathode material.

[0065] The variation in particle size and tap density under different synthesis conditions or with different formulations of the LMFP material, as illustrated by the two graphs, provides valuable insights into the synthesis process of the cathode material. By understanding this variation, the synthesis conditions may be optimized to achieve the desired particle size distribution and tap density, thereby improving the performance of the cathode material in lithium-ion batteries.

[0066] One of the pivotal factors that determine the performance of the battery cathode is the energy density of the synthesized cathode material. The energy density is a measure of the amount of energy that may be stored in a given system or region of space per unit volume. In the context of lithium-ion batteries, the energy density of the cathode material is a measure of the amount of energy that may be stored in the cathode material per unit volume. A higher energy density implies that more energy may be stored in the cathode material, thereby enhancing the performance of the battery cathode.

[0067] In some cases, the energy density of the synthesized cathode material, which is synthesized using the method as described above, is inthe range of about 560 to 580 Wh / Kg. This range of energy density is advantageous for achieving a high performance of the battery cathode. The energy density of the cathode material may be controlled by adjusting the synthesis conditions, such as the concentration of the additives in the precursor solution and the temperature and duration of the hydrothermal synthesis process. By optimizing these synthesis conditions, a cathode material with a high energy density may be synthesized, thereby improving the performance of the battery cathode.

[0068] In some cases, the battery cathode comprises a cathode material which is synthesized in accordance with the method described above. The cathode material comprises a plurality of secondary particles having a spherical morphology with a higher tap density. The spherical morphology of the secondary particles is advantageous for achieving a high tap density, which in turn improves the performance of the cathode material. The tap density of the particles is a measure of the packing efficiency of the particles, which may be improved by controlling the synthesis conditions. The morphology of the particles may also be controlled by adjusting the synthesis conditions, such as the concentration of the additives in the precursor solution and the temperature and duration of the hydrothermal synthesis process. By synthesizing the cathode material in accordance with the method described above, a battery cathode with a high performance may be achieved.

[0069] It may be noted that, although, the explanation of the above figures are described with some specific solutions such as citric acid and ethylene glycol, etc., however, other solutions having similar properties may also be used without deviating from the scope of the present subject matter.

[0070] Although aspects and other examples have been described in a language specific to structural features and / or methods, the present subject matter is not necessarily limited to such specific features or elements as described. Rather, the specific features are disclosed as examples and should not be construed to limit the scope of the present subject matter.

Claims

I / We Claim:1 . A method for synthesizing a high energy density cathode material, wherein the method comprises: obtaining a first solution, wherein the first solution comprises a ferrous salt, a manganese salt, and a source of carboxylic acid in de-ionized (DI) water, wherein the concentration of the source of carboxylic acid is in a range of about 15-20%; subsequently adding 1 molar (M) concentration of a source of phosphorous into the first solution to form a second solution; adding 2M to 3M concentration of a source of lithium into the second solution to form a precursor solution; adding a predefined volume of a source of glycol to the precursor solution; and performing hydrothermal synthesis of the precursor solution at a predetermined temperature for a predetermined holding period to crystallize a plurality of LiMm-xFexPC (LMFP) primary particles to form a plurality of LMFP secondary particles, wherein the secondary particles possess a spherical morphology.

2. The method as claimed in claim 1 , wherein the manganese salt is one of hydrated manganese sulphate, manganese nitrate, manganese chloride, manganese phosphate having 0.5 to 0.8 mole of concentration in the first solution and ferrous salt is one of hydrated ferrous sulphate, ferric nitrate, ferrous chloride, and ferric phosphate having 0.2 to 0.5 mole of concentration in the first solution.

3. The method as claimed in claim 1 , wherein the predefined volume of ethylene glycol is 30% to 40% of the precursor solution which is subjected to the hydrothermal synthesis.

4. The method as claimed in claim 1 , wherein the source of phosphorous is one of ammonium dihydrogen phosphate and phosphoric acid and is added to control the size of plurality of LMFP primary particles.

5. The method as claimed in claim 1 , wherein the source of lithium is one of lithium phosphate, lithium hydroxide, lithium nitrate, and lithium chloride and is added to control the oxidation of the metal precursors.

6. The method as claimed in claim 1 , wherein the rate of addition of source of phosphorous into the first solution to obtain the second solution is in the range of 3-7 mL / min .

7. The method as claimed in claim 1 , wherein the rate of addition of source of lithium into the second solution to obtain the precursor solution is in the range of 2-6 mL / min.

8. The method as claimed in claim 1 , wherein the predetermined temperature is in a range of about 160-200 °C.

9. The method as claimed in claim 8, wherein the temperature at which the spherical morphology of the secondary particles is achieved is 180 °C.

10. The method as claimed in claim 1 , wherein the energy density of the synthesized cathode material is in the range of about 560 to 580 Wh / Kg.1 1 . The method as claimed in claim 1 , wherein the predetermined holding period is in a range of about 9-24 hours, wherein the holding period to achieve spherical morphology is 12 hours.

12. A cathode material comprising a plurality of secondary LiMm-xFexPC (LMFP) particles having spherical morphology with higher tap density, wherein x is in the range of 0.2 to 0.5, wherein the cathode material is synthesized in accordance with method as claimed in any one of claims 1 - 1 1.

13. The cathode material as claimed in claim 12, wherein the tap density of the plurality of secondary LMFP particles is in the range of 1 g / cc to 1 .2 g / cc.

14. The cathode material as claimed in claim 12, wherein the particle size distribution of the plurality of secondary LMFP particles is in the range between 3 pm to 4 pm.

15. A battery cathode comprising a cathode material as claimed in claim 12 which is synthesized in accordance with method as claimed in any one of claims 1 -11.

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