Claims:CLAIMS
We claim:
1. A battery (100) comprising:
a cathode (102);
an anode (104), wherein the anode (104) and the cathode (102) disposed on opposite sides of a separator (106) are soaked with an electrolyte (108); and
an electrolyte-permeable microporous interlayer (110) disposed between the separator (106) and the cathode (102), wherein the interlayer (110) is glass micro fiber paper coated with carbonized synthetic carbon material.
2. The battery (100) as claimed in the claim 1, wherein the carbonized synthetic carbon material is coal tar pitch obtained from coal tar.
3. The battery (100) as claimed in the claim 1, wherein the interlayer (110) is a carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper.
4. The battery (100) as claimed in the claim 1, wherein the cathode (102) is a sulfur-based cathode made by loading sulfur into carbon material.
5. The battery (100) as claimed in the claim 4, wherein the carbon material is selected from any one of mesoporous carbon, graphene, carbon fiber, active carbon, carbon nanotube, carbon sphere, or carbon derived from green coke, polymeric materials, petroleum coke.
6. The battery (100) as claimed in the claims 4 and 5, wherein a process (200) for fabricating the sulfur-based cathode comprises:
mixing sulfur, carbon black and polyvinylidene difluoride (PVDF) to obtain an admixture;
grounding the admixture in a mortar pestle for 1 hour;
adding N-Methyl-2-pyrrolidone (NMP) solution to obtain a slurry;
coating the slurry onto aluminum foil using doctor blade; and
drying the slurry coated aluminum foil in an oven under vacuum at 60 oC for 12 hours to obtain sulfur-based cathode.
7. The battery (100) as claimed in the claim 6, wherein sulfur, carbon black and polyvinylidene difluoride (PVDF) are mixed in a weight percentage of 70:20:10 respectively.
8. The battery (100) as claimed in the claim 1, wherein the anode is a metal anode selected from any of Lithium (Li), Sodium (Na), Potassium (K), Iron (Fe), Silicon (Si), Magnesium (Mg), Manganese (Mn), Aluminium (Al), Zinc (Zn), a combination of these metals or other metals and their compounds.
9. The battery (100) as claimed in the claim 1, wherein the anode is lithium metal anode or lithium alloy anode.
10. The battery (100) as claimed in the claim 1, wherein the electrolyte is selected from any one of a liquid state electrolyte comprising solvent and metal-salt compound or metal-ion conductor organic and inorganic solid electrolyte (SSE).
11. The battery (100) as claimed in the claim 10, wherein the electrolyte is made of LiTFSI in a mixture of 1,3 dioxolane and dimethoxy ethane with LiNO3 additive.
12. The battery (100) as claimed in the claim 10, wherein the electrolyte is selected from any of LiF, LiCl, LiI, Li2O, Li2S, Li3N, Li3P, LGPS, Li3.5Ge0.25PS4, Li3PS4, Li6PS5Cl, Li7P2S8I, LiPON, LLZO, LLTO, LATP, LAGP, LISICON and/or any mixtures thereof.
13. The battery (100) as claimed in the claim 3, the battery (100) with the carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper as an interlayer (110) shows capacity of around 900-1600 mAh g-1 with the high columbic efficiency above 95% and excelled rate capability for a stable long cycle life more than 250 cycles
14. The battery (100) as claimed in the claim 1, wherein the electrolyte-permeable microporous interlayer (110) is formed as a coating on a surface of the separator (106).
15. The battery (100) as claimed in the claim 1, wherein the carbonized synthetic carbon material is selected from any one of green coke, carbon derived from polymeric materials, petroleum coke.
16. A method (300) of preparing an interlayer (110) from coal tar pitch, the method (300) comprising:
stirring coal tar pitch with a NMP (N-Methyl-2-pyrrolidone) solution for a first predetermined time at a first predetermined temperature to obtain an intermediate solution;
pouring the intermediate solution onto a glass micro fiber paper;
drying the intermediate solution and the glass micro fiber paper for a second predetermined time at a second predetermined temperature; and
calcining the dried intermediate solution and the glass micro fiber paper for a third predetermined time at a third predetermined temperature to obtain carbonized coal tar pitch-glass micro fiber paper (CCTP-GF) which is used as the interlayer (110).
17. The method (300) as claimed in the claim 16, wherein the first predetermined time is in the range of 0.5 hours and 2 hours.
18. The method (300) as claimed in the claim 17, wherein the first predetermined time is 1 hr.
19. The method (300) as claimed in the claim 16, wherein the first predetermined temperature is in the range of 25 and 50 oC.
20. The method (300) as claimed in the claim 19, wherein the first predetermined temperature is room temperature.
21. The method (300) as claimed in the claim 16, wherein the second predetermined time is in the range 0.5 hours and 2 hours.
22. The method (300) as claimed in the claim 21, wherein the second predetermined time is 1 hour.
23. The method (300) as claimed in the claim 16, wherein the second predetermined temperature is in the range of 60 and 120 oC.
24. The method (300) as claimed in the claim 23, wherein the second predetermined temperature is 70o C.
25. The method (300) as claimed in the claim 16, wherein the third predetermined time is in the range of 0.5 hours and 2 hours.
26. The method (300) as claimed in the claim 25, wherein the third predetermined time is 1 hour.
27. The method (300) as claimed in the claim 16, wherein the third predetermined temperature is in the range of 600 and 900 oC.
28. The method (300) as claimed in the claim 27, wherein the third predetermined temperature is 700o C.
29. The method (300) as claimed in the claim 16, wherein the coal tar pitch is distilled from coal tar.
30. A lithium-sulfur battery (100) comprising:
a sulfur-based cathode (102);
a lithium anode (104), wherein the lithium anode (104) and the sulfur-based cathode (102) are disposed on opposite sides of a separator (106) soaked with an electrolyte (108); and
an electrolyte-permeable microporous interlayer (110) disposed between the separator (106) and the sulfur-based cathode (102), wherein the interlayer (110) is a carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper.
31. The lithium-sulfur battery (100) as claimed in the claim 30, wherein the sulfur-based cathode (102) is made by loading sulfur into carbon material.
32. The lithium-sulfur battery (100) as claimed in the claim 31, wherein carbon material is selected from any one of mesoporous carbon, graphene, carbon fiber, active carbon, carbon nanotube, carbon sphere, or carbon derived from green coke, polymeric materials, petroleum coke.
33. The lithium-sulfur battery (100) as claimed in the claims 31 and 32, wherein the sulfur-based cathode (102) is fabricated by:
mixing sulfur, carbon black and polyvinylidene difluoride (PVDF) to obtain an admixture;
grounding the admixture in a mortar pestle for 1 hour;
adding N-Methyl-2-pyrrolidone (NMP) solution to obtain a slurry;
coating the slurry onto aluminum foil using doctor blade; and
drying the slurry coated aluminum foil in an oven under vacuum at 60 oC for 12 hours to obtain sulfur-based cathode.
34. The lithium-sulfur battery (100) as claimed in the claim 33, wherein sulfur, carbon black and polyvinylidene difluoride (PVDF) are mixed in a weight percentage of 70:20:10 respectively.
35. The lithium-sulfur battery (100) as claimed in the claims 30 to 34, wherein the Li-S battery with the carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper as an interlayer (110) shows capacity of around 900-1600 mAh g-1 with the high columbic efficiency above 95% and excelled rate capability for a stable long cycle life more than 250 cycles.

Dated this 25th day of June 2021
Signature:
Name: Sridhar R
To: Of K&S Partners, Bangalore
The Controller of Patents Agent for the Applicant
The Patent Office, at Kolkata IN/PA No. 2598
, Description:FIELD OF INVENTION
[0001] The present invention relates to an interlayer for a battery, and more particularly to a method of preparing the interlayer using coal tar pitch.

BACKGROUND
[0002] Over the past few decades, with the development of portable electronic devices such as mobiles, laptops etc., electric grids and zero emission electric vehicles, the need for batteries with long cycle life, high capacity, and low self-discharge is continuously increasing. Tremendous efforts have been made in developing different kinds of energy storage systems, such as metal-ion batteries to provide effective energy storage. Metal-ion batteries, particularly lithium-ion batteries have been racing ahead as the power source of choice. However, for high energy applications such as powering an electric vehicle, or grid energy storage, the Li-ion batteries having an energy density in the range of 180 to 220 Wh kg-1, may not be suitable. Moreover, the transition metal oxides (LiCoO2/LiNiO2/LiMn2O4/LiFePO4) which are being used as cathodes in the lithium-ion batteries are hazardous to the environment and are on verge of scarcity.
[0003] To meet the energy requirements, metal batteries such as Li-S, Li-air and other metal batteries are being developed, of which rechargeable lithium-sulfur batteries (LSB) with theoretical specific energy of 2600 Wh/kg offers great potential to meet many of the needs. Also, the materials needed to produce LSBs are light, energetic, inexpensive, and readily available. In contrast with most cathode materials, sulfur which is being used as a cathode in LSB is relatively non-toxic, making these batteries relatively safe for human contact.
[0004] Even though they have above mentioned advantages, the LSBs have failed to achieve commercial success for several reasons. The reasons include: (1) Shuttling and dissolution of higher-order lithium polysulfide formed in the electrochemical reaction. (2) Insulating nature of sulfur which exhibit poor electronic conductivity and forms sluggish kinetic process with poor utilization of active material. (3) The volume expansion in electrode causing material to fracture or pulverize. This, in turn, leads to a loss of capacity, low columbic efficiency and limited charge-discharge cycle life of Li-S battery.
[0005] Recent studies have demonstrated that utilization of an interlayer within the battery has provided an effective solution for solving the above-mentioned challenges. The interlayer is typically regarded as a device which hinders polysulfide crossover and helps to accommodate the high order Li-polysulfides generated during cycling. Even though different types of interlayers made of carbon-based materials such as, porous carbon fiber paper, CoS2/carbon fiber fabric, Ti4O7/carbon fibers, and PPY coated carbon fibers are being used in LSBs. There is a requirement of an interlayer, which is cost effective and has better electrolyte retaining property to provide better electrochemical performance of LSBs.
OBJECTIVE OF INVENTION
[0006] It is an objective of the invention to provide an interlayer having properties such as optimum surface area, porosity, conductivity, microstructure/morphology, voids, and defects etc., which facilitate in improving the electrochemical performance of a battery.
[0007] Another objective of the present invention is to develop a method of preparing the interlayer from coal tar pitch obtained from coal tar and evaluate its properties for application for lithium-sulfur batteries.
SUMMARY OF INVENTION
[0008] This summary is provided to introduce concepts related to an interlayer for battery and a method of preparing the interlayer using coal tar pitch. 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.
[0009] In one aspect of the present invention, a battery is provided. The battery comprises cathode and an anode. The anode and the cathode disposed on opposite sides of a separator are soaked with an electrolyte. The battery also comprises an electrolyte-permeable microporous interlayer disposed between the separator and the cathode. The interlayer is glass micro fiber paper coated with carbonized synthetic carbon material.
[0010] In an embodiment, the carbonized synthetic carbon material is coal tar pitch obtained from coal tar.
[0011] In an embodiment, the interlayer is a carbonized coal tar pitch-glass micro fiber paper.
[0012] In an embodiment, the cathode is a sulfur-based cathode made by loading sulfur into carbon material.
[0013] In an embodiment, the carbon material is selected from any one of mesoporous carbon, graphene, carbon fiber, active carbon, carbon nanotube, carbon sphere, or carbon derived from green coke, polymeric materials, petroleum coke.
[0014] In an embodiment, a process for fabricating the sulfur-based cathode is provided. The process comprises mixing sulfur, carbon black and polyvinylidene difluoride to obtain an admixture. The process also comprises grounding the admixture in a mortar pestle for 1 hour. The process further comprises adding N-Methyl-2-pyrrolidone solution to obtain a slurry. The process comprises coating the slurry onto aluminum foil using doctor blade. The process further comprises drying the slurry coated aluminum foil in an oven under vacuum at 60 oC. for 12 hours to obtain sulfur-based cathode.
[0015] In an embodiment, sulfur, carbon black and polyvinylidene difluoride are mixed in a weight percentage of 70:20:10 respectively.
[0016] In an embodiment, the anode is a metal anode selected from any of Lithium, Sodium, Potassium, Iron, Silicon, Magnesium, Manganese, Aluminium, Zinc, a combination of these metals or other metals and their compounds.
[0017] In an embodiment, the anode is lithium metal anode or lithium alloy anode.
[0018] In an embodiment, the electrolyte is selected from any one of a liquid state electrolyte comprising solvent and metal-salt compound or metal-ion conductor organic and inorganic solid electrolyte.
[0019] In an embodiment, the electrolyte is selected from any of LiF, LiCl, LiI, LiPON, Li2O, Li2S, Li3N, Li3P, LGPS, Li3.5Ge0.25PS4, Li3PS4, Li6PS5Cl, Li7P2S8I, LLZO, LLTO, LATP, LAGP, LISICON and/or any mixtures thereof.
[0020] In an embodiment, the electrolyte-permeable microporous interlayer is formed as a coating on a surface of the separator.
[0021] In an embodiment, the carbonized synthetic carbon material is selected from any one of green coke, carbon derived from polymeric materials, petroleum coke.
[0022] In another aspect of the present invention a method of preparing an interlayer from coal tar pitch is provided. The method comprises stirring coal tar pitch with a NMP solution for a first predetermined time at a first predetermined temperature to obtain an intermediate solution. The method also comprises pouring the intermediate solution onto a glass micro fiber paper. The method further comprises drying the intermediate solution and the glass micro fiber paper for a second predetermined time at a second predetermined temperature. The method comprises calcining the dried intermediate solution and the glass micro fiber paper for a third predetermined time at a third predetermined temperature to obtain carbonized coal tar pitch-glass micro fiber paper which is used as the interlayer.
[0023] In an embodiment, the first predetermined time is in the range of 0.5 hours and 2 hours. More preferably, the first predetermined time is 1 hr.
[0024] In an embodiment, the first predetermined temperature is in the range of 25 and 50 oC. More preferably, the first predetermined temperature is room temperature.
[0025] In an embodiment, the second predetermined time is in the range 0.5 hours and 2 hours. More preferably, the second predetermined time is 1 hour.
[0026] In an embodiment, the second predetermined temperature is in the range of 60 and 120 oC. More preferably, the second predetermined temperature is 70 oC.
[0027] In an embodiment, the third predetermined time is in the range of 0.5 hours and 2 hours. More preferably, the third predetermined time is 1 hour.
[0028] In an embodiment, the third predetermined temperature is in the range of 600 and 900 oC. More preferably, the third predetermined temperature is 700 oC.
[0029] In an embodiment, the coal tar pitch is distilled from coal tar.
[0030] In yet another aspect of the present invention, a lithium-sulfur battery is provided. The lithium-sulfur battery comprises a sulfur-based cathode and a lithium anode. The lithium anode and the sulfur-based cathode are disposed on opposite sides of a separator soaked with an electrolyte. The lithium-sulfur battery also comprises an electrolyte-permeable microporous interlayer disposed between the separator and the sulfur-based cathode. The interlayer is a carbonized coal tar pitch-glass micro fiber paper.
[0031] In an embodiment, the sulfur-based cathode is made by loading sulfur into carbon material.
[0032] In an embodiment, carbon material is selected from any one of mesoporous carbon, graphene, carbon fiber, active carbon, carbon nanotube, carbon sphere, or carbon derived from green coke, polymeric materials, petroleum coke.
[0033] In an embodiment, the sulfur-based cathode is fabricated by mixing sulfur, carbon black and polyvinylidene difluoride to obtain an admixture; grounding the admixture in a mortar pestle for 1 hour; adding N-Methyl-2-pyrrolidone solution to obtain a slurry; coating the slurry onto aluminum foil using doctor blade; and drying the slurry coated aluminum foil in an oven under vacuum at 60 oC. for 12 hours to obtain sulfur-based cathode.
[0034] In an embodiment, sulfur, carbon black and polyvinylidene difluoride are mixed in a weight percentage of 70:20:10 respectively.
[0035] In an embodiment, the Li-S battery with the carbonized coal tar pitch-glass micro fiber paper as an interlayer shows capacity of around 900-1600 mAh g-1 with the high columbic efficiency above 95% and excelled rate capability for a stable long cycle life more than 250 cycles.
[0036] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0037] In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:
[0038] Figure 1 illustrates a schematic configuration of a battery having an interlayer, according to an embodiment of the present invention.
[0039] Figure 2, illustrates a schematic configuration of a battery without an interlayer, as disclosed in the prior art.
[0040] Figure 3 illustrates a flow chart of a process of fabricating a sulfur-based cathode of the battery, according to an embodiment of the present invention.
[0041] Figure 4 illustrates a flow chart of a method of preparing the interlayer of the battery using coal tar pitch, according to an embodiment of the present invention.
[0042] Figure 5 illustrates a graph showing cyclic voltammetry curves of the battery with interlayer, according to an embodiment of the present invention.
[0043] Figure 6 illustrates a graph depicting the rate capability of the battery with interlayer, according to an embodiment of the present invention.
[0044] Figure 7 illustrates a graph depicting charge-discharge curves (voltage profile) of the battery with interlayer, according to an embodiment of the present invention.
[0045] Figure 8 illustrates a graph depicting cycle life of battery with and without the interlayer, according to an embodiment of the present invention.
[0046] 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
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] Referring to Figure 1, a schematic view of a battery (100), according to embodiment of the present invention is illustrated. The battery (100) is a secondary battery which converts stored chemical energy into electrical energy during discharge and, converts electrical energy into stored chemical energy during recharge. The battery (100) described herein embodies an electrochemical cell (herein after alternatively referred to as electrochemical cell (100)). Plurality of these batteries (100) may be connected in series or parallel or any combination thereof to produce a greater voltage output and current, without limiting the scope of the invention.
[0053] The battery (100) comprises a cathode (102), an anode (104), a separator (106), an electrolyte (108), and an electrolyte-permeable microporous interlayer (110). The battery (100) may further include additional components such as casing, terminals, tabs etc. know in the art, that are generally associated with batteries, without limiting the scope of the invention.
[0054] The battery (100) is connected to a load device (122) via an interruptible external circuit (120) that connects the anode (102) and the cathode (102). The battery (100) supports a load device (122) that is operatively connected to the external circuit (120). The load device (122) receives electrical energy from the battery (100) during the discharge cycle. The load device (122) may be electric motor, a laptop, a phone, a light bulb etc. The load device (122) may also be a power-suppling or power-generating apparatus which charges the battery (100), without any limitations.
[0055] The anode (104) is selected from materials, including, but not limited to, Lithium (Li), Sodium (Na), Potassium (K), Iron (Fe), Silicon (Si), Magnesium (Mg), Manganese (Mn), Aluminium (Al), Zinc (Zn), a combination of these metals and/or their compounds. In the preferred embodiment, the anode (104) is a metal anode of lithium (herein after alternatively referred to as lithium anode (104)). Alternatively, the anode (104) may be lithium alloy anode such as lithium silicon alloy, lithium tin alloy, lithium silver alloy etc., without limiting the scope of the invention.
[0056] In the illustrated example. the cathode (102) is a sulfur-based cathode (herein after alternatively referred to as the sulfur-based cathode (102)) made by loading sulfur into carbon material. The carbon material used is selected from any one of carbon black, mesoporous carbon, graphene, carbon fiber, active carbon, carbon nanotube, carbon sphere, or carbon derived from green coke, polymeric materials, and petroleum coke etc., without limiting the scope of the invention. In the illustrated example, as the anode (104) is lithium anode and the cathode (102) is sulfur-based cathode, the battery (100) is alternatively referred to as a lithium-sulfur battery (100).
[0057] Referring to Figure 3, an exemplary process (200) for fabrication of the sulfur-based cathode (102) is illustrated. At step (202), predetermined weight percentage of sulfur, carbon black and polyvinylidene difluoride (PVDF) are mixed together to obtain an admixture. In the preferred example, the sulfur, carbon black and polyvinylidene difluoride (PVDF) are mixed in a weight percentage of 70:20:10 respectively. At step (204), the admixture obtained is ground in a mortar pestle for a time of 1 hr. At step (206), N-Methyl-2-pyrrolidone (NMP) solution is added to the ground admixture to obtain a slurry. At step (208), the slurry obtained is coated onto the aluminum foil using doctor blade. At step (210), the slurry coated aluminum foil is dried in an oven under vacuum at 60 oC for 12 hours to obtain sulfur-based cathode which is used in the battery (100).
[0058] Referring to Figure 1, the anode (104) and the cathode (102) are disposed on opposite sides of a separator (106). The separator (106) may be made with nonwoven fabrics, cellulose natural fibers, or one or more synthetic fibers selected from the group consisting of polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), Glass fiber (GF) and polyvinylidene fluoride (PVDF), without limiting the scope of the invention.
[0059] Each of the anode (104), the cathode (102), and the separator (106) are soaked with an electrolyte (108). The electrolyte (108) is configured to conduct ions between the anode (104) and the cathode (102). The electrolyte (108) may be selected from any one of a liquid state electrolyte comprising solvent and metal-salt compound, or metal-ion conductor organic and inorganic solid electrolyte (SSE). In the illustrated example, the electrolyte is made of LiTFSI in a mixture of 1,3 dioxolane and dimethoxy ethane with LiNO3 additive. Other examples include, but not limited to LiF, LiCl, LiI, Li2O, Li2S, Li3N, Li3P, LGPS, Li3.5Ge0.25PS4, Li3PS4, Li6PS5Cl, Li7P2S8I, LiPON, LLZO, LLTO, LATP, LAGP, LISICON and/or any mixtures thereof.
[0060] Referring further to Figure 1, the battery (100) comprises the electrolyte-permeable microporous interlayer (110). In the illustrated example, the interlayer (110) is disposed between the separator (106) and the cathode (102). Alternatively, the interlayer (110) may be coated onto surface of the separator (106), without limiting the scope of the invention. In the illustrated example, a glass micro fiber paper coated with carbonized synthetic carbon material is used as the interlayer (110). The carbonized synthetic carbon material may be selected from any one of green coke, carbon derived from polymeric materials, petroleum coke. In the preferred embodiment, the carbonized synthetic carbon material is coal tar pitch obtained from coal tar, and the interlayer (110) is a carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper.
[0061] Referring to Figure 4, an exemplary method (300) of preparing an interlayer (110) from coal tar pitch is illustrated. At step (302), coal tar pitch is stirred with a NMP (N-Methyl-2-pyrrolidone) solution for a first predetermined time at a first predetermined temperature to obtain an intermediate solution (Stirring step). At step (304), the intermediate solution obtained in the stirring step is poured onto a glass micro fiber paper (Pouring step). At step (306), the intermediate solution poured onto the glass micro fiber paper in the pouring step is dried for a second predetermined time at a second predetermined temperature (Drying step). At step (308), the dried intermediate solution and the glass micro fiber paper obtained in the drying step is calcined for a third predetermined time at a third predetermined temperature to obtain carbonized coal tar pitch-glass micro fiber paper (CCTP-GF) which is used as an interlayer (110) (Calcining step).
[0062]
[0063] In the stirring step, coal tar pitch obtained from distillation of coal tar is mixed with NMP (N-Methyl-2-pyrrolidone) solution and is stirred for the first predetermined time at the first predetermined temperature to obtain intermediate solution. In the preferred embodiment, the first predetermined time is in the range of 0.5 hours and 2 hours. More preferably, the first predetermined time is 1 hr. In preferred embodiment, the first predetermined temperature is in the range of 25 and 50 oC. More preferably, the first predetermined temperature is room temperature.
[0064]
[0065] The intermediate solution obtained in the stirring step, is poured onto a glass micro fiber paper.
[0066]
[0067] The intermediate solution along with the glass micro fiber paper is dried for second predetermined time at second predetermined temperature. In the preferred embodiment, the second predetermined time is in the range of 0.5 hours and 2 hours. More preferably, the second predetermined time is 1 hr. In preferred embodiment, the second predetermined temperature is in the range of 60 and 120 oC. More preferably, the second predetermined temperature is 70 oC.
[0068]
[0069] The dried intermediate solution and the glass micro fiber paper obtained in the drying step is calcined for a third predetermined time at a third predetermined temperature to obtain carbonized coal tar pitch-glass micro fiber paper (CCTP-GF) which is used as an interlayer (110). In the preferred embodiment, the third predetermined time is in the range of 0.5 hours and 2 hours. More preferably, the third predetermined time is 1 hr. In preferred embodiment, the third predetermined temperature is in the range of 600 and 900 oC. More preferably, the second predetermined temperature is 700 oC.
[0070] During the carbonation of the coal tar pitch from room temperature to 700 oC, the coal tar pitch passes through the mesophase at around 350 to 450 oC, which is the liquid crystalline state. On further increasing the temperature the liquid mesophase it converts to solid carbonized material. On reaching to mesophase temperature the highly aromatic substances undergo thermolysis forming spherules and these spherules coalesce to form highly connecting macroscopic structures with voids. Therefore, the carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper interlayer (110) grown on the porous micro glass fiber paper has agglomerate primary particles with many voids giving the sorbent configuration which has high efficiency of adsorbing the Li-polysulfides, accommodating the electrolyte and improving the conductivity. These factors help in achieving the excellent electrochemical performance which can be evidenced from rate capability, cycle life.
[0071] The battery (100) with the carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper as an interlayer (110) shows capacity of around 900-1600 mAh g-1 with the high columbic efficiency above 95% and excelled rate capability for a stable long cycle life more than 250 cycles.
[0072] To further illustrate the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the present disclosure
[0073] Two batteries (coin cells) were prepared. Each of the batteries were composed of a lithium metal anode, a porous separator, and a sulfur-based cathode. The sulfur-based cathode in both batteries were fabricated by mixing the sulfur [99%, Sigma Aldrich] carbon black [Super P conductive, Alfa Aesar, 99%] and PVDF [Sigma Aldrich, 99%] in the weight percentage of 70:20:10. The mixture was ground in mortar pestle for 1hr and NMP is added to it for making slurry followed by coating onto the aluminium foil using Doctor blade with 25 µm thickness. Then it is dried in oven under vacuum at 60 oC for 12 hrs. The dried electrode is punched into circular disc of 10 mm.
[0074] It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the invention. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

[0075] Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present invention, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein.
[0076] Example 1
[0077] The first battery (no interlayer) (shown in Figure 2) included a lithium metal anode, a porous separator, and a sulfur-based cathode. The first battery was fabricated in Argon filled glove box by using sulfur-based cathode as working electrode, circular Lithium metal disc [Sigma Aldrich, 99%] as counter and reference electrode, electrolyte made of 1M LiTFSI in a mixture of 1,3 dioxolane and dimethoxy ethane [1:1v/v] with 0.1M LiNO3[Sigma Aldrich 99%] additive.
[0078] Example 2
[0079] The second battery (CCTP-GF-IL) (shown in Figure 1) included a lithium metal anode, a porous separator, a sulfur-based cathode, and carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper interlayer.
[0080] The carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper interlayer was fabricated using a glass microfiber filter paper (WhatmanTM with model number 1823-025 and grade GF/D) having pore size of 2.7 µm, thickness 675 µm and diameter of 2cm. Coal tar pitch [TATA steel] was used as such without further purification. 2 mg of coal tar pitch was added into the 5 ml of NMP and stirred for 1hr at room temperature and then poured onto the GF/D glass fiber paper having diameter of 2cm. Then it was dried at 70 oC for 1hr followed by calcination at 700 oC for 1hr. The as obtained carbonized coal tar pitch-glass fiber (CCTP-GF) paper was used as interlayer between sulfur cathode and separator.
[0081] The second battery was fabricated in Argon filled glove box by using sulfur cathode as working electrode, circular Lithium metal disc [Sigma Aldrich, 99%] as counter and reference electrode, electrolyte made of 1M LiTFSI in a mixture of 1,3 dioxolane and dimethoxy ethane [1:1v/v] with 0.1M LiNO3[Sigma Aldrich 99%] additive, and (CCTP-GF) paper introduced between the sulfur cathode and the separator.
[0082] Electrochemical tests of the first battery and the second battery were performed using 2032- type cells. During the electrochemical performance tests of the first battery and the second battery (i.e., Li-S batteries without and with CCTP-GF-IL respectively, Figure 8), cyclic voltammetry [CV] (shown in Figure 5) analysis of the second battery recorded the cathodic peak at 2.35 V and anodic peak at 2.08 V. The cathodic peak at 2.35 V corresponds to the reduction of elemental sulfur to high order Li-polysulfide [S = 8, 6, 4], and anodic peak at 2.08 V corresponds to formation of low order lithium sulfides [S = 2, 1]. Whereas the anodic peaks at 2.26 and 2.41 V designates the reversible formation of elemental sulfur form lithium sulfides. The CV curves (Figure 5) show stable peaks without much deviation in their intensities and peak positions for three cycles, suggesting the stability and reversibility of the Li-S battery by the introduction of CCTP-GF-IL.
[0083] The rate capability (Figure 6) of the second battery delivered discharge capacities of 1110 mAh g-1 [C/5], 920 mAh g-1 [C/2], 810 mAh g-1 [1C] and 490 mAh g-1 at 5C. The high capacity at different rates is due to improved conductivity by the introduction of CCTP-GF-IL. The voltage profile [charge-discharge curves] of the secondary battery are shown in Figure 7. The two discharge plateaus are clearly distinguished in the voltage ranges from 2.4 to 2.1 V [formation of Li-polysulfides] and 2.1 to 1.8V [formation of Lithium sulfides]. This discharge plateaus can be correlated well with the cathodic peaks in the CV curves. The initial discharge capacity Li-S battery with CCTP-GF-IL attained at C/10 is 1264 mAh g-1. Also, Li-S battery with CCTP-GF-IL is showing excellent cycle life (Figure 8) at 1C having discharge capacity of 600 mAhg-1 at 270th cycle with the capacity retention of 74 percent compared to Li-S battery without interlayer which showed the poor discharge capacity and capacity retention and showed rapid capacity fade till 43rd cycle.
[0084] The present invention relates to the CCTP-GF interlayer (110) used in the battery (100) and the method (300) of preparing the CCTP-GF interlayer (110) using coal tar pitch. The disclosed method (300) of preparing the interlayer (110) is a simple and effective method to fabricate porous carbon structure with 3D interlace arrangement made by carbonizing the coal tar pitch on glass micro fiber paper. The disclosed CCTP-GF interlayer (110) has properties including, but not limited to optimum surface area, porosity, conductivity, voids, defects, and microstructure/morphology etc., which facilitate in improving the electrochemical performance of the battery (100).
[0085] The disclosed interlayer (110) is an environmental friendly and cost-effective solution, as the CCTP-GF interlayer (110) is prepared from coal tar which is a by-product in coke making process. The carbonized coal tar pitch-glass micro fiber (CCTP-GF) paper interlayer (110) grown on the porous micro glass fiber paper has agglomerate primary particles with many voids giving the sorbent configuration which has high efficiency of adsorbing the Li-polysulfides, accommodating the electrolyte and improving the conductivity. These factors help in achieving the excellent electrochemical performance which can be evidenced from rate capability, cycle life.
[0086] Furthermore, the terminology used herein is for describing 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.
[0087] 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.
[0088] 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.