Description:FIELD OF INVENTION
[0001] The present invention relates to a process for preparing a synthetic anode material from coal tar, and more particularly to the process of preparing synthetic anode material from coal tar pitch for a lithium ion battery application.

BACKGROUND
[0002] Over the past few decades, tremendous efforts have been made in developing alternative technologies to store sustainable clean energy. Different kinds of energy storage systems were developed, of which rechargeable lithium-ion battery was found to be the best energy storage system due to its lower energy density. Lithium-ion batteries have many advantages such as high voltage, large specific energy, long life and no memory effect. In recent years, they have been widely used in 3C products, electric bicycles, energy storage systems, especially electric vehicles.
[0003] Lithium-ion battery includes an anode (negative electrode), a cathode (positive electrode) and an electrolyte. The two electrodes (anode and cathode) are capable of reversibly hosting lithium in ionic form. Common candidates for the cathode are lithiated metal oxides and carbonaceous materials for the anode. Presently, carbonaceous material such as graphite is being used as anode material for intercalating lithium ions in rechargeable LIB due to its well defined layered structure, low operating potential, and remarkable interfacial stability. Graphite anode exhibits excellent cycle performance, high capacities of 350–370 mAh g-1, and coulombic efficiencies higher than 90%. Due to the rapid market growth of lithium-ion batteries, demand for anode materials is increasing 2-3 folds every year. As availability of natural grade graphite is limited, preparation of synthetic anode materials has gained importance to cater to the market demand.
[0004] The synthetic carbonaceous anode materials utilized for lithium ion batteries are classified into two different types, non-graphitizable carbon (hard carbon), and graphitizable carbon (soft carbon). Due to their high aromatics petroleum residue or coal tar are used as raw materials in processing of the non-graphitizable carbon (hard carbon) and graphitizable carbon (soft carbon). As, natural coal reserves are far more abundant than petroleum resources. The usage of coal resources has garnered practical important significance for protection of environment, energy conservation and emission reduction, and sustainable economic development.
[0005] Coal tar is one of the by-products of coke making and huge quantities of coal tar is produced internationally. Distillation of coal tar produces different organic solvents and residue, known as coal tar pitch which is conventionally discarded. Studying the use of coal tar or coal tar pitch as raw materials to produce high-quality anode materials with high added value can significantly increase the added value of downstream products in the deep processing of coal, which is conducive to adjusting the industrial structure of enterprises.

OBJECTIVE OF INVENTION
[0006] It is an object of the invention to solve the aforementioned problems of the prior art and to provide a process to prepare a synthetic anode material such as soft carbon material or needle coke from coal tar or coal tar pitch and evaluate its properties for its application as anode in lithium-ion batteries.
[0007] Another objective of the present invention is to develop synthetic anode materials having high capacity, enhanced lithium-ion diffusion, long cycling life, high cycling stability, and no safety issues for replacing conventional graphite anodes.
[0008] Another objective of present invention to utilize pitch obtained from coal tar distillation as it has an advantage over other available precursor materials in terms of high aromaticity, high softening point, low cost, market availability etc.
[0009] It is further another objective of the present invention meet the latest requirement of market to product further.
SUMMARY OF INVENTION
[0010] This summary is provided to introduce concepts related to a process for preparing synthetic anode material from coal tar or coal tar pitch for lithium ion battery application. 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.
[0011] In one aspect of the present invention, a process for preparing a lithium ion battery synthetic anode material from coal tar is provided. The process comprises distilling coal tar to produce coal tar pitch. The process also comprises heating the said coal tar pitch to obtain a meso-phase pitch. The process further comprises graphitizing the said meso-phase pitch in an inert atmosphere to obtain pre-final product. The process comprises cooling the said pre-final product to obtain a cooled pre-final product. The process also comprises grinding or pulverizing the cooled pre-final product to obtain the soft carbon product of predetermined size.
[0012] In an embodiment, the coal tar is distilled at a temperature of 280-340oC under vacuum of 50-150 torr. In an embodiment, the coal tar pitch is heated at a temperature of 450-550oC for 6-12 hours.
[0013] In an embodiment, the meso-phase pitch is graphitized at a temperature in the range of 1100-1400oC. In an embodiment, the meso-phase pitch is graphitized for 30-120 minutes.
[0014] In an embodiment, meso-phase structure within the meso-phase pitch is improved by addition of at least one of iron or graphite powder or graphitized pitch as catalyst.
[0015] In an embodiment, the soft carbon product is grinded to a size of 150µ. In an embodiment, the said meso-phase pitch shows a carbon layer d-spacing of 0.344 nm.
[0016] In an embodiment, the anode made of the soft carbon product shows a carbon layer d-spacing of 0.338 nm, specific capacitance of 210-250 mAh/g and stable cycle performance at a charging rate of 0.1C and 0.5C.
[0017] In another aspect of the present invention, a process for preparing a lithium ion battery synthetic anode material from coal tar is provided. The process comprises distilling coal tar to produce coal tar pitch. The process also comprises heating the said coal tar pitch to raise the temperature. The process further comprises coking the pre-heated coal tar pitch to obtain green coke. The process comprises calcining the said green coke in an inert atmosphere to obtain needle coke.
[0018] In an embodiment, the coal tar is distilled at a temperature in between 280-340oC under vacuum of 50-150 torr. In an embodiment, the coking is performed at a temperature range of 430-520oC.
[0019] In an embodiment, the coking is performed at a pressure between atmospheric pressure to 10 bar pressures. In an embodiment, the coking is performed for a duration of 12-24 hours.
[0020] In an embodiment, the calcining is performed at a temperature in the range of 1000 – 1400oC. In an embodiment, the calcining is performed for a duration of 30 minutes to 2 hours.
[0021] In an embodiment, the needle coke is grinded or pulverized to a size of 150µ. In an embodiment, the anode made of needle coke shows a specific capacitance of 140-250 mAh/g and stable cycle performance at different charging rates of 0.1C, 0.5 C and 1C.
[0022] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 is a flowchart which illustrates the process of preparing soft carbon anode material from coal tar, according to an embodiment of the present invention;
[0024] Figure 2 is a flowchart which illustrates the process of preparing needle coke anode material from coal tar, according to an embodiment of the present invention;
[0025] Figure 3 is a graph showing the relationship between charge/discharge capacity and the number of cycles of a lithium ion battery anode electrode made of soft carbon material at a charge/discharge rate of 0.1 C, 0.5 C, and 1 C, according to an embodiment of the present invention; and
[0026] Figure 4 is a graph showing the relationship between charge/discharge capacity and the number of cycles of a lithium ion battery anode electrode material made of needle coke at a charge/discharge rate of 0.1 C, 0.5 C, and 1 C, according to an embodiment of the present invention.
[0027] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.

DETAILED DESCRIPTION
[0028] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein 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.
[0029] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0031] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0032] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0033] Figures 1 and 2, illustrate an exemplary process (100, 200) for preparing a lithium ion battery synthetic anode material from coal tar. The synthetic anode material is at least one of a soft carbon material or a needle coke.
[0034] Referring to Figure 1, the process (100) for preparing a soft carbon anode material from coal tar is illustrated. At step (102), coal tar is distilled to produce coal tar pitch (coal tar pitch formation step). At step (104), the coal tar pitch obtained in the coal tar pitch formation step is heated to obtain meso-phase pitch (heating step). At step (106), the meso-phase pitch obtained in the meso-phase pitch formation step is graphitized in an inert atmosphere to obtain a pre-final product (graphitizing step). At step (108), the pre-final product obtained during the pre-final product formation step is cooled to obtain a cooled pre-final product (cooling step). At step (110), the cooled pre-final product obtained in the cooled pre-final product step is grinded or pulverized to obtain a soft carbon product (soft carbon anode material) of predetermined size (grinding and pulverizing step).
[0035] < Coal tar pitch formation step >
[0036] In the coal tar pitch formation step, coal tar is distilled to produce coal tar pitch. More particularly, the coal tar is distilled at a temperature of 280-340oC under vacuum of 50-150 torr to produce coal tar pitch. In the preferred embodiment, the coal tar used to produce the coal tar pitch has density in between 1.12 to 1.18 g/cc and preferably in between 1.14 to 1.16 g/cc. In the preferred embodiment, the coal tar used has viscosity in between 150 to 480 cP at room temperature and preferably in between 160 to 470 cP at room temperature. In the preferred embodiment, the coal tar has a softening point in between 70 to 100 °C, preferably between 90 to 100 °C. In the preferred embodiment, the coal tar has an atomic ratio of carbon to hydrogen less than three, preferably in between 1.9 to 2.7. In the preferred embodiment, the coal tar has a pitch yield in between 40 to 60 % and preferably 55 - 60 % under same distillation condition.
[0037]
[0038] In the heating step, the coal tar pitch formed in the coal tar pitch formation step is heated to obtain a meso-phase pitch. In preferred embodiment, the coal tar pitch is heated in a temperature range of 450-550oC for 6-12 hours. Meso-phase structure within the meso-phase pitch helps in obtaining layer-layer carbon structure. The meso-phase pitch obtained shows a carbon layer d-spacing of 0.344 nm. In the preferred embodiment, the meso-phase structure within the meso-phase pitch may be improved by addition of at least one of iron or graphite powder or graphitized pitch as catalyst.
[0039]
[0040] In the graphitizing step, the meso-phase pitch obtained in the heating step is graphitized in an inert atmosphere to obtain a pre-final product. In the preferred embodiment, the meso-phase pitch is graphitized at a temperature in the range of 1100-1400oC for 30-120 minutes to obtain the pre-final product. In the preferred embodiment, the inert gas is nitrogen gas. In the preferred embodiment, the gas flow rate is in the range of 3 to 5 L/min. In another embodiment, the inert gas may be argon, without any limitations.
[0041]
[0042] The pre-final product obtained in the graphitizing step is cooled to obtain cooled pre-final product. In the preferred embodiment, the pre-final product is cooled to room temperature to obtain cooled pre-final product.
[0043]
[0044] The cooled pre-final product obtained in the cooling step is the grinded or pulverized to obtain a soft carbon material of predetermined size. In the preferred embodiment, the size of the soft carbon material is 150µ.
[0045] In the preferred embodiment, the soft carbon material obtained from the above process (100) is used to make an anode used for lithium ion battery applications. Alternatively, the soft carbon material obtained from the above process (100) may be used to make an anode for other applications such as electric arc furnace etc., without limiting the scope of the invention.
[0046] Electrochemical performance test
[0047] To test the capacity and the efficiency performance of the soft carbon material obtained in the process (100), test was carried out by the half-cell test method using the anode made from the soft carbon material. The battery performance was tested at charge/discharge rates of 0.1C, 0.5C, 1C. The results of half-cell tests are depicted in Figure 3. The anode of the battery made of the soft carbon material shows good charge/discharge performance with a specific capacitance in the range of 170-250 mAh g-1 at a charging/discharging rate of 0.1C and 0.5C. The performance was found to be stable for 60 charge/discharge cycles at lower charging rates of 0.1C and 0.5C. At higher charging rates, the performance deteriorated.
[0048] Example 1
[0049] Coal tar pitch was obtained by distilling coal tar at 340°C under vacuum of 120 torr. The coal tar pitch was then heated at 500°C for 6 hrs to obtain a meso-phase pitch having meso-phase structure. The meso-phase pitch was then graphitized at 1400°C in the presence of nitrogen gas for 120 minutes and the pre-final product was obtained. The pre-final product was then cooled to room temperature and then grinded or pulverized to obtain the soft carbon material of size 150µ. The material was then used for half-cell test which exhibited a good charge/discharge performance with a specific capacitance of 240 mAh g-1 at a charge/discharge rate of 0.1C and a specific capacitance of 170 mAh g-1 at charge/discharge rate of 0.5C.
[0050] Referring to Figure 2, the process (200) for preparing a needle coke anode material from coal tar is illustrated. At step (202), coal tar is distilled to produce coal tar pitch (coal tar pitch formation step). At step (204), the coal tar pitch obtained in the coal tar pitch formation step is heated to obtain pre-heated coal tar pitch (heating step). At step (206), the pre-heated coal tar pitch obtained in the heating step is coked to obtain green coke (coking step). At step (208), the green coke obtained during the coking step is calcined in an inert atmosphere to obtain a pre-final product (calcining step). At step (210), the pre-final product obtained in the calcining step is grinded or pulverized to obtain a needle coke product (needle coke anode material) of predetermined size (grinding and pulverizing step).
[0051]
[0052] In the coal tar pitch formation step, coal tar is distilled to produce coal tar pitch. More particularly, the coal tar is distilled at a temperature of 280-340oC under vacuum of 50-150 torr to produce coal tar pitch. In the preferred embodiment, the coal tar used to produce the coal tar pitch has density in between 1.12 to 1.18 g/cc and preferably in between 1.14 to 1.16 g/cc. In the preferred embodiment, the coal tar used has viscosity in between 150 to 480 cP at room temperature and preferably in between 160 to 470 cP at room temperature. In the preferred embodiment, the coal tar has a softening point in between 70 to 100°C, preferably between 90 to 100°C. In the preferred embodiment, the coal tar has an atomic ratio of carbon to hydrogen less than three, preferably in between 1.9 to 2.7. In the preferred embodiment, the coal tar has a pitch yield in between 40 to 60 % and preferably 55 -60 % under same distillation condition.
[0053]
[0054] In the heating step, the coal tar pitch formed in the coal tar pitch formation step is heated in a series of heaters to increase the temperature to obtain a pre-heated coal tar pitch.
[0055]
[0056] In the coking step, the pre-heated coal tar pitch obtained in the heating step is fed into a coker unit and coked to obtain green coke. In the preferred embodiment, the coker unit is externally electrically heated. In the preferred embodiment, the coking of the pre-heated coal tar pitch in the coker unit is performed at a temperature in between 430 - 520oC at atmospheric pressure to 10 bar pressures for a duration of 12-24 hours.
[0057]
[0058] In the calcining step, the green coke obtained in the coking step is calcined in an inert atmosphere to obtain a pre-final product. In the preferred embodiment, the green coke is calcined at a temperature in the range of 1000-1400oC for 30-120 minutes to obtain the pre-final product. In the preferred embodiment, the inert gas is nitrogen gas.
[0059]
[0060] The pre-final product obtained in the calcining step is grinded or pulverized to obtain a needle coke material of predetermined size. In the preferred embodiment, the size of the needle coke material is 150µ.
[0061] In the preferred embodiment, the needle coke material obtained from the above process (200) is used to make an anode used for lithium ion battery applications. Alternatively, the needle coke material obtained from the above process (200) may be used to make an anode for other applications such as electric arc furnace etc., without limiting the scope of the invention.
[0062] Electrochemical performance test
[0063] To test the capacity and the efficiency performance of the needle coke material obtained in the process (200), test was carried out by the half-cell test method using the anode made from the needle coke material. The battery performance was tested at charge-discharge rates of 0.1C, 0.5C, 1C. The results of half-cell tests are depicted in Figure 4. The anode of the battery made of the needle coke material shows good charge discharge performance with a specific capacitance in the range of 140-240 mAh g-1 at a charging rate of 0.1C, 0.5C and 1C. The performance was found to be stable for different charging rates of 0.1C, 0.5 C and 1C.
[0064] Example 2
[0065] Coal tar pitch was obtained by distilling coal tar at 340°C under vacuum of 120 torr. The coal tar pitch was then heated to raise the temperature of the coal tar pitch. The pre-heated coal tar pitch was then placed in the coker unit and coking was done at 520°C and 10 bar pressures for 24 hours and the green coke was obtained. The green coke was calcined at a temperature of 1400°C in the presence of nitrogen gas for 120 minutes and the pre-final product was obtained. The pre-final product was then grinded or pulverized to obtain the needle coke material 150µ size. The material was then used for half-cell test which exhibited a good charge/discharge performance with a specific capacitance of 240 mAh g-1 at a charge/discharge rate of 0.1C, a specific capacitance of 170 mAh g-1 at charge/discharge rate of 0.5C, and a specific capacitance of 140 mAh g-1 at charge/discharge rate of 1C.
[0066] The present invention relates to the process (100, 200) for preparing synthetic anode material from coal tar. By means of procedures such as distilling, heating, graphitizing, cooling and grinding or pulverizing, the soft carbon anode material of predetermined size is prepared from coal tar. By means of procedures such as distilling, heating, coking, calcining and grinding or pulverizing, the needle coke anode material of predetermined size is prepared from coal tar. As the anodes made from soft carbon material and needle coke have high capacity, enhanced lithium-ion diffusion, long cycling life, high cycling stability, and no safety issues, these anodes are suitable for replacing conventional graphite anodes. Further as coal tar (which is a by-product) is being used to make these anode material, protection of environment, energy conservation and emission reduction, and sustainable economic development can be achieved.
[0067] Furthermore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0068] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0069] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

Claims:1. A process (100) for preparing a lithium ion battery synthetic anode material from coal tar, the process (100) comprising:
distilling coal tar to produce coal tar pitch;
heating the said coal tar pitch to obtain a meso-phase pitch;
graphitizing the said meso-phase pitch in an inert atmosphere to obtain pre-final product;
cooling the said pre-final product to obtain a cooled pre-final product; and
grinding or pulverizing the cooled pre-final product to obtain a soft carbon material of predetermined size.
2. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the coal tar is distilled at a temperature of 280-340oC under vacuum of 50-150 torr.
3. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the coal tar pitch is heated at a temperature of 450-550oC for 6-12 hours.
4. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the meso-phase pitch is graphitized at a temperature in the range of 1100-1400oC.
5. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the meso-phase pitch is graphitized for 30-120 minutes.
6. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein meso-phase structure within the meso-phase pitch is improved by addition of at least one of iron or graphite powder or graphitized pitch as catalyst.
7. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein size of the soft carbon material obtained after grinding or pulverizing is 150µ.
8. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the said meso-phase pitch shows a carbon layer d-spacing of 0.344 nm.
9. The process (100) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 1, wherein the anode made of the soft carbon material shows a specific capacitance of 170-240 mAh/g and stable cycle performance at a charging rate of 0.1C and 0.5C.
10. A process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 1, the process (200) comprising:
distilling coal to produce coal tar pitch;
heating the said coal tar pitch to raise the temperature to obtain a pre-heated coal tar pitch;
coking the pre-heated coal tar pitch to obtain green coke; and
calcining the said green coke in an inert atmosphere to obtain pre-final product; and
grinding or pulverizing the pre-final product to obtain a needle coke material of predetermined size.
11. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in the claim 10, wherein the coal tar is distilled at a temperature in between 280-340oC under vacuum of 50-150 torr.
12. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the coking is performed at a temperature range of 430-520oC.
13. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the coking is performed at a pressure between atmospheric pressure to 10 bar pressures.
14. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the coking is performed for a duration of 12-24 hours.
15. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the calcining is performed at a temperature in the range of 1000 – 1400oC.
16. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the calcining is performed for a duration of 30 minutes to 2 hours.
17. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the size of the needle coke obtained after grinding or pulverizing is 150µ.
18. The process (200) for preparing a lithium ion battery synthetic anode material from coal tar as claimed in claim 10, wherein the anode made of needle coke shows a specific capacitance of 140-240 mAh/g and stable cycle performance at different charging rates of 0.1C, 0.5 C and 1C. ,