WO2019017846A1

WO2019017846A1 - Hexaazatriphenylene derivative and graphene oxide composites

Info

Publication number: WO2019017846A1
Application number: PCT/SG2018/050359
Authority: WO
Inventors: Yugen Zhang; Jinquan Wang
Original assignee: Agency For Science, Technology And Research
Priority date: 2017-07-20
Filing date: 2018-07-20
Publication date: 2019-01-24

Abstract

The present invention generally relates to composites comprising hexaazatnnaphthalene (HATN) or its derivatives and a conductive carbon material, which are suitable for use as cathode materials in lithium ion batteries. The HATN derivatives may contain groups that are capable of forming hydrogen bonds. The conductive carbon material is preferably graphene oxide (GO). The present invention also relates to a method of preparing said composites, comprising steps of heating a cydoketone with an amine, and mixing the produced compound with a conductive carbon material.

Description

Hexaazatriphenylene Derivative and Graphene

Oxide Composites

Cross- Reference to Related Applications

This application claims priority to Singapore patent application 10201705961W filed 20 July 2017, the contents of which are incorporated by reference.

Technical Field

The present invention generally relates to a composite comprising an organic molecule and a carbon conductive material, and a method of preparing said composite. The present invention also relates to a cathode material comprising a composite as defined herein and a method of preparing said cathode.

Background Art

The demand for environmentally friendly low-cost electrode material is growing in pace with deployment of large-scale applications such as electric vehicles and energy storage systems. Redox active electrodes made from organic compounds have received great attention as materials for rechargeable batteries due to their green, sustainable, versatile and low-cost nature. However, the dissolution of such small organic molecules in non-aqueous electrolyte leads to the fast fading of electrochemical capacity, representing one of the main challenges for its potential practical applications.

Hexaazatrinaphthalene (HATN), with its structure reproduced below, is a derivative of hexaazatriphenylene (HAT). HATN is also an electron deficient, rigid and planar aromatic discotic system which can be easily synthesized from low-cost chemicals.

HATN has been studied as organic cathode material in lithium ion batteries, and possesses a high theoretical capacity of up to 418 mAh g^"1. However, due to the high solubility of HATN in electrolyte solution, poor cycling stability was observed. A highly conjugated framework with HATN core and 1,4-bisethynylbenzene linker was also developed and tested as organic cathode material in lithium ion battery. Although these conjugated porous polymers possess high porosity and highly stable structures, these materials only exhibit a moderate cycling stability, such as 62% capacity retention after 50 cycles.

Graphene oxide (GO) plays an important role in materials science due to its unique structural and morphological features, relatively easy chemical modifications, as well as excellent electrical, mechanical, and thermal properties. GO composites have been utilized for different applications in various fields due to its ability to form non-covalent bonding composites with organic molecules via hydrogen bonding, π-π interactions and Van der Waals forces.

Therefore, there is a need to provide a composite cathode material that overcomes, or at least ameliorates, one or more of the disadvantages described above.

Summary

According to a first aspect, there is provided a composite comprising a compound of Formula (I)

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material.

Advantageously, composites as defined herein have low solubility. These composites as defined herein may be used as cathode materials. When used, said cathodes may exhibit high specific capacity, good rate capability, and/or excellent long-term cycling stability.

Therefore, advantageously, the composites as defined herein have great potential as green cathode materials for energy storage devices.

In another aspect, there is provided a method of preparing a composite comprising a compound of Formula (I)

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material, comprising the steps of:

(a) mixing a cycloketone and an amine to form a reaction mixture;

(b) heating the reaction mixture of step (a), to produce the compound of Formula (I); and

(c) mixing the compound of Formula (I) produced from step (b) with the conductive carbon material.

Advantageously, the method used to prepare the composites as described herein is a wet chemical process under mild and simple conditions. Hence, the method may be scaled-up in a straightforward approach.

In another aspect, there is provided a cathode comprising a composite, wherein said composite comprises a compound of Formula (I)

In another aspect, there is provided a method for preparing a cathode comprising the steps of: (a) preparing a composite comprising a compound of Formula (I)

(R₃)z

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material; and (b) mixing the composite of step (a) with a binder.

Definitions

The following words and terms used herein shall have the meaning indicated:

The term "hydrogen bonding" refers to an attractive interaction between a hydrogen (H) atom from a molecule or a molecular fragment X-H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.

"Aryl" as a group or part of a group denotes (i) an optionally substituted monocyclic, or fused polycyclic, aromatic carbocycle (ring structure having ring atoms that are all carbon) preferably having from 5 to 12 atoms per ring. Examples of aryl groups include phenyl, naphthyl, and the like; or (ii) an optionally substituted partially saturated bicyclic aromatic carbocyclic moiety in which a phenyl and a C₅_₇ cycloalkyl or C₅_₇ cycloalkenyl group are fused together to form a cyclic structure, such as tetrahydronaphthyl, indenyl or indanyl. The group may be a terminal group or a bridging group. Typically an aryl group is a C₆-C₁₈ aryl group.

The word "substantially" does not exclude "completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Detailed Disclosure of Embodiments

Exemplary, non-limiting embodiments of a composite comprising a compound of Formula (I) and a conductive carbon material will now be disclosed.

The composite may comprise a compound of Formula (I)

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4 (such as 1, 2, 3, or 4); and a conductive carbon material.

The groups R_{l 5} R₂ and R₃ may be the same or may be different.

The composite may comprise a compound of Formula (I), wherein R_{l 5} R₂ and R₃ are H, and x, y and z are 4, and graphene oxide as the conductive carbon material. This compound is represented by structure (la) as shown below.

(Ia),

wherein the interactions between this compound of Formula (la) and graphene oxide is substantially π-π interactions.

The composite may comprise a compound of Formula (I), wherein R_{l 5} R₂ and R₃ are -COOH, and x, y and z are 1, and graphene oxide as the conductive carbon material. This compound is represented by structure (lb) as shown below.

(lb),

wherein the interactions between this compound of Formula (lb) and graphene oxide is substantially hydrogen bonding and/or π-π interactions

Exemplary, non-limiting embodiments of a method to produce the composite comprising a compound of Formula (I) and a conductive carbon material as defined herein, will now be disclosed.

The composite described in the disclosure may be prepared by mixing a cycloketone and an amine to form a reaction mixture. The reaction mixture may then be heated to produce the compound of Formula (I). The produced compound of Formula (I) may then be mixed with a conductive carbon material to produce the composite.

The cycloketone used in the above reaction to produce the compound of Formula (I) may be hexaketocyclohexane octahydrate.

The amine used in the above reaction to produce the compound of Formula (I) may be an aryl group having at least two substituents, such as two or three substituents. On the aryl group, two of the substituents are amine groups. The amine may be selected from the following amines:

The compound described herein may be synthesized in the presence of an acid known in the art or a combination of two or more acids. The acid used may be an organic acid, an inorganic acid, a weak acid, a strong acid, a monoprotic acid, a polyprotic acid or other suitable acids. Non- limiting examples of such acids include acetic acid, malic acid, citric acid, formic acid, carbonic acid, lactic acid, phosphoric acid, oxalic acid or methanoic acid. The acid used in the above reaction may be acetic acid. The heating of the reaction mixture in the above reaction may proceed for about 4 hours to 10 hours, about 5 hours to 10 hours, about 6 hours to 10 hours, about 7 hours to 10 hours, about 8 hours to 10 hours, about 9 hours to 10 hours, about 4 hours to 9 hours, about 4 hours to 8 hours, about 4 hours to 7 hours, about 4 hours to 6 hours, about 4 hours to 5 hours, about 5 hours to 9 hours, about 6 hours to 8 hours, about 6 hours to 7 hours, about 7 hours to 8 hours, or any range or value therein, preferably 5 hours.

Upon completion of the above heating step, the reaction mixture may be cooled, such as to room temperature.

Any solid form of the compound may be separated from the reaction mixture by a suitable separation technique known in the art. Non-limiting examples of such separation technique include filtration, centrifugation, extraction and decantation. The separation technique used in the above reaction may be filtration. The resulting solid compound may be subjected to washings with suitable solvents. Such solvents may be aqueous or organic solvents known in the art. Non-limiting examples of such solvent include water, ethanol or acetone. The mixing of the compound with the conductive carbon material in the above reaction may be performed by a suitable mixing technique known in the art. Non-limiting examples of such mixing technique include sonicating, stirring, vortexing and ball-milling. The mixing technique used in the above reaction may be sonicating.

Non-limiting examples of conductive carbon material include graphene oxide, reduced graphene oxide, graphene, graphite and graphite oxide. The conductive carbon material used in the above reaction may be graphene oxide.

The mixing of the compound with the conductive carbon material in the above reaction may be performed in the presence of a solvent known in the art or a combination of two or more solvents. Non-limiting examples of such solvent include ethanol, acetone, acetonitrile, t- butyl alcohol, methanol, 1-propanol and 2-propanol. The solvent used in the above reaction may be ethanol.

The mixing of the compound with the conductive carbon material in the above reaction may proceed for about 1 hour to 24 hours, about 1 hour to 21 hours, about 1 hour to 18 hours, about 1 hour to 15 hours, about 1 hour to 12 hours, about 1 hour to 9 hours, about 1 hour to 6 hours, about 1 hour to 3 hours, about 3 hours to 24 hours, about 6 hours to 24 hours, about 9 hours to 24 hours, about 12 hours to 24 hours, about 15 hours to 24 hours, about 18 hours to 24 hours, about 21 hours to 24 hours, about 3 hours to 21 hours, about 6 hours to 18 hours, about 9 hours to 15 hours, about 12 hours to 15 hours, about 9 hours to 12 hours, or any range or value therein, preferably for about 6 hours.

Upon completion of the above mixing step, the solid form of the composite may be obtained by removing the solvent under reduced pressure.

Once the composite above is recovered, the composite may be subjected to material characterization. Non-limiting examples of such characterization include Fourier transform infrared (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), and suitable methods to evaluate the electrochemical properties of the composite described herein. In the present disclosure, there is provided exemplary conditions for synthesizing the composite as defined above. These exemplary conditions are provided for illustrative purposes only and it is to be understood that the conditions are not limited to these exemplary conditions.

Exemplary condition 1

When hexaketocyclohexane octahydrate and

are mixed at a mole ratio of

1 :3.3, added to acetic acid and followed by heating to reflux for about 5 hours, a compound of Formula (I), wherein R_{l 5} R₂ and R₃ are H, and x, y and z are 4, may be formed and may be represented by the following structure (la):

(la).

When the compound of structure (la) and graphene oxide are sonicated at a weight ratio of 5:4 in ethanol for about 6 hours, a composite may be formed.

Exemplary condition 2

When hexaketocyclohexane octahydrate and

are mixed at a mole ratio of 1 :3.3, added to acetic acid and followed by heating to reflux for about 5 hours, a compound of Formula (I), wherein R_{l 5} R₂ and R₃ are -COOH, and x, y and z are 1, may be formed and may be represented by the following structure (lb):

(lb).

When the compound of structure (lb) and graphene oxide are sonicated at a weight ratio of 5:4 in ethanol for about 6 hours, a composite may be formed.

As seen from the exemplary conditions and the examples provided in the present disclosure, the method for preparing the composite as described herein is performed using mild and simple conditions. Hence, this method may be scaled-up in a straightforward approach.

Exemplary, non-limiting embodiments of a cathode comprising the composite disclosed herein and method of making said cathode will now be disclosed.

There is provided a cathode comprising the composite, wherein the composite comprises a compound of Formula (I) and a conductive carbon material as described herein.

The cathode comprising the composite which comprises a compound of Formula (I) and a conductive carbon material may be prepared by mixing the composite with a binder in a suitable ratio. It may be desirable that a higher ratio of composite is used.

The method of mixing the composite and the binder stated above may involve mixing these materials in the presence of a solvent, and the thus -obtained paste may be coated on a metal sheet, such as aluminium sheet, using a coater. The solvent may then be removed under vacuum at about 60°C, about 65 °C, about 70°C, about 75 °C, about 80°C, about 85 °C, about 90°C, about 95°C, about 100°C, about 105°C, about 110°C, or about 115°C for about 6 to 16 hours, about 6 to 9 hours, about 6 to 12 hours, about 9 to 12 hours, about 9 to 16 hours, preferably for about 12 hours.

The cathode material as described herein may be assembled in a hermetically sealed two- electrode cell or system, and this cell is used for electrochemical experiments to further evaluate the electrochemical performance of the cathode comprising the composite as described herein. The cathode may be separated from the lithium anode by a film known in the art such as polyethylene porous film imbibed with an equimolar LiPF₆/EC+DEC (ethylene carbonate and diethyl carbonate). The layers obtained from the assembly above may be pressed between two current collectors, one in contact with the cathodic material and the other in contact with a lithium disk. All cells are preferably assembled in a substantially oxygen-free environment such as an argon-filled glovebox. As mentioned above, when used, the cathodes comprising the composites as described herein may exhibit high specific capacity, good rate capability, and/or excellent long-term cycling stability. Therefore, advantageously, the composites as defined herein may potentially be used as green cathode materials for energy storage devices.

Brief Description of Drawings

The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

Fig. 1

[Fig. 1] shows scanning electron microscope (SEM) images acquired from characterization of the composites synthesized in examples 1 and 2; where (a) shows the SEM image for the composite of example 1 ; (b) shows the SEM image for the composite of example 2; (c) shows the scanning transmission electron microscope (STEM) image and energy dispersive X-ray spectroscopy (EDX) line-scan profile of oxygen element for the nano-rod of (a); and (d) shows the SEM image for the composite of example 1 after undergoing 600 cycles of charge -discharge at 500 mA g ¹.

Fig. 2

[Fig. 2] is a Fourier transform infrared (FT-IR) spectra acquired from characterization of the composites synthesized in examples 1 and 2; where (a) shows the FT-IR spectrum for the composite of example 1 ; and (b) shows the FT-IR spectrum for the composite of example 2.

Fig. 3

[Fig. 3] is a number of charge-discharge profile, coulombic efficiency and cycling stability curves acquired from the composites synthesized in examples 1 and 2; where (a) shows the charge-discharge profile curve (voltage vs. specific capacity) at a current density of 0.05 A g ¹ for the composite of example 1 ; (b) shows the coulombic efficiency and cycling stability (specific capacity vs. cycle number) for the composite of example 1 ; (c) shows the charge- discharge profile curve (voltage vs. specific capacity) at a current density of 0.05 A g ¹ for the composite of example 2; and (d) shows the coulombic efficiency and cycling stability (specific capacity vs. cycle number) for the composite of example 2. Fig. 4

[Fig. 4] shows cyclic voltammetry (CV) curves acquired from the composites synthesized in examples 1 and 2 when measured with a scan rate of 0.2 mV s ¹; where (a) shows the CV curve (current vs. potential) for the composite of example 1 ; and (b) shows the CV curve (current vs. potential) for the composite of example 2.

Fig. 5

[Fig. 5] is a number of specific capacity vs. cycle number curves at different current densities for rate capability evaluation of the composites synthesized in examples 1 and 2; where (a) shows the specific capacity vs. cycle number curves at different current densities for the composite of example 1 ; and (b) shows the specific capacity vs. cycle number curves at different current densities for the composite of example 2.

Fig. 6

[Fig. 6] is a number of Nyquist plots acquired from electrochemical impedance spectroscopy (EIS) measurements of the composites synthesized in examples 1 and 2; where (a) shows the Nyquist plots (-Z" vs. Z') for the composite of example 1 ; and (b) shows the Nyquist plots (-Z" vs. Z') for the composite of example 2.

Fig. 7

[Fig. 7] is a number of coulombic efficiency and long-term cycling stability curves acquired at a current density of 0.5 A g ¹ from the composites synthesized in examples 1 and 2; where (a) shows the coulombic efficiency and long-term cycling stability (specific capacity vs. cycle number) for the composite of example 1 ; and (b) shows the coulombic efficiency and long-term cycling stability (specific capacity vs. cycle number) for the composite of example 2.

Examples

Non-limiting examples of the invention will be further described in greater detail below, which should not be construed as in any way limiting the scope of the invention.

Example 1: Preparation of HATN/GO

Hexaketocyclohexane octahydrate (0.78 g, 2.50 mmol, purchased from Scientific Resources Pte. Ltd. of Singapore) and 1 ,2-phenylenediamine (0.89 g, 8.25 mmol, purchased from Scientific Resources Pte. Ltd. of Singapore) were added to 50 mL of acetic acid (AcOH, purchased from Scientific Resources Pte. Ltd. of Singapore). The solution was then heated to reflux for 5 hours. The resultant dark green suspension was next cooled to room temperature and filtered off, and washed with water, ethanol and acetone to obtain moss green needles of hexaazatrinaphthalene (HATN) in 94% yield (0.90 g) (refer to the reaction scheme provided below).

HATN (25 mg) and graphene oxide (GO) sheet (20 mg, Staudenmaier method, purchased from Scientific Resources Pte. Ltd. of Singapore) were sonicated in 10 mL of ethanol for 6 hours. The composite from HATN and GO was then obtained after ethanol was removed under reduced pressure.

Example 2: Preparation of HATNTA/GO

Hexaketocyclohexane octahydrate (0.78 g, 2.50 mrnol, purchased from Scientific Resources Pte. Ltd. of Singapore) and 3,4-diaminobenzoic acid (1.25 g, 8.25 mrnol, purchased from Scientific Resources Pte. Ltd. of Singapore) were added to 50 mL of acetic acid (AcOH, purchased from Scientific Resources Pte. Ltd. of Singapore). The solution was then heated to reflux for 5 hours. The resultant dark green suspension was next cooled to room temperature and filtered off, and washed with water, ethanol and acetone to obtain green solids of hexaazatrinaphthalene tricarboxylic acid (HATNTA) in 98% yield (refer to the reaction scheme provided below).

HATNTA (25 mg) and graphene oxide (GO) sheet (20 mg, Staudenmaier method, purchased from Scientific Resources Pte. Ltd. of Singapore) were sonicated in 10 mL of ethanol for 6 hours. The composite from HATNTA and GO was then obtained after ethanol was removed under reduced pressure.

Example 3: Material Characterizations

a. Scanning electron microscope (SEM)

The composites of examples 1 and 2 were characterized by scanning electron microscope (SEM, performed on a field emission SEM (JEOL JSM-7400F) operated at an accelerating voltage of 5 keV) (Fig. 1). In the SEM images, it can be observed that the HATN/GO composite has core- shell nano-rods structure with HATN as the core and covered with GO shell. It was found that HATN has nano-rods structure with diameters of about 100 nm after sonication in ethanol. Hence, this suggests that when HATN was co-sonicated with GO, the strong interactions between HATN and GO induced the rolling process to form the core-shell nano-rods of HATN/GO composite. Furthermore, the core-shell nano-rods structure in the cathode comprising the HATN/GO composite was observed to disappear after the cycling performance test. On the other hand, it can be observed that when HATNTA was sonicated with GO, HATNTA was homogeneously dispersed on GO to form HATNTA/GO composite. This suggests that HATNTA has a much better solubility in ethanol and also has stronger interactions with GO.

b. Fourier transform infrared (FT-IR)

The composites of examples 1 and 2 were characterized by Fourier transform infrared (FT- IR, performed on a Perkin Elmer Spectrum 100) (Fig. 2). In the FT-IR spectrum of the HATN/GO composite (Fig. 2a), a blue shift of C=C stretch from 1628 cm ¹ (GO) to 1643 cm ¹ (HATN/GO) indicates strong π-π interactions between GO and HATN. In the FT-IR spectrum of HATNTA/GO composite (Fig. 2b), a blue shift of C=C stretch from 1630 cm ¹ (GO) to 1641 cm ¹ (HATNTA/GO) indicates the π-π interactions between GO and HATNTA. Additionally, a red shift of C=0 stretch from 1723 cm ¹ (HATNTA) to 1719 cm^"1 (HATNTA/GO) indicates the strong hydrogen bonding interactions between HATNTA and GO.

Example 4: Preparation of Cathode

The synthesized composites were evaluated as cathode materials for lithium ion battery. Cathodes were prepared by mixing the composite synthesized in examples 1 and 2, with polyvinylidene fluoride (PVDF) as a binder (ratio: 9/1 in weight). These materials were mixed with N-methyl-2-pyrrolidone (NMP) as a solvent, and the thus-obtained paste was coated on aluminium foil using a coater. NMP was then removed under vacuum at 80 °C for 12 hours. Hermetically sealed two-electrode cells (CR2032) were used for electrochemical experiments. The cathode was separated from the lithium anode by the polyethylene porous film (purchased from Celgard of Charlotte, North Carolina of the United States of America) imbibed with an equimolar LiPF₆/EC+DEC (ethylene carbonate and diethyl carbonate, purchased from Zhangjiagang Guotai-Huarong New Chemical Materials Co., Ltd. of China). The three layers were pressed between two current collectors, one in contact with the cathodic material and the other in contact with a lithium disk. All cells were assembled in an argon-filled glovebox. The cyclic voltammetry (CV) measurements were performed using a CHI 760C electrochemical workstation (purchased from CH Instruments, Inc. of Texas of the United States of America). The battery testing system (CT2001A, purchased from Wuhan LAND electronics Co., Ltd. of China) was used to evaluate the electrochemical performance. The battery capacities and C-rates were calculated based on the active material in the cathode. The capacity contribution of blank GO is around 25 mAh g \ which was tested under current conditions at 50 mA g^"1. Example 5: Electrochemical Performance

a. Charge-Discharge Profile, Coulombic efficiency and Short-term Cycling stability

The charge-discharge profiles of synthesized composites were measured at current density of 0.05 A g ¹ in the working voltage range of 1.5-4.0 V, and shown in Fig. 3a and Fig. 3c. The initial discharge capacities of HATN/GO and HATNTA/GO composites were found to be 410 and 226 mAh g^~\ respectively. Indeed, HATN/GO and HATNTA/GO composites achieved the capacities of 98% and 73 % of their theoretical capacities.

The coulombic efficiency and short-term cycling stability of synthesized composites at cut- off voltage of 1.5-4.0 V, are shown in Fig. 3b and Fig. 3d. The initial coulombic efficiency was found to be 88% for HATN/GO composite and 98% for HATNTA/GO composite.

After 90 cycles, the specific capacity of HATN/GO composite decreased to 226 mAh g \ which corresponds to 55% of the initial specific capacity. This suggests an obvious deterioration of the cycling performance of the HATN/GO composite as compared to that of HATNTA/GO composite whereby the specific capacity of HATNTA/GO composite decreased to 193 mAh g ¹ after 90 cycles, corresponding to 85% of the initial specific capacity. b. Cyclic voltammetry

Cyclic voltammetry measurements of synthesized composites were performed at a scan rate of 0.2 mV s ¹ in the working voltage range of 1.5-4.0 V, and shown in Fig. 4. It can be observed that these composite materials display multiple broad peaks, suggesting the multi- electron redox capability during the lithiation and delithiation processes, and the multi- electron redox reaction of hexaazatriphenylene (HAT) unit.

c. Rate Capability

The rate capability of synthesized composites was evaluated by cycling at different current densities and shown in Fig. 5. For HATN/GO composite, the reversible capacity is 270 mAh g ¹ at a current density of 0.1 A g \ and the capacity retention is 84%, 78%, 69%, 62% and 34% at a current density of 0.2, 0.3, 0.4, 0.5 and 1 A g \ respectively. For HATNTA/GO composite, the reversible capacity is 215 mAh g ¹ at a current density of 0.1 A g \ and the capacity retention is 90%, 85%, 79%, 62% and 53% at a current density of 0.2, 0.3, 0.4, 0.5 and 1 A g^~\ respectively. These results indicate that HATNTA/GO composite has a much better rate capability as compared with HATN/GO composite.

d. Electrochemical Impedance Spectroscopy

It is known in the art that factors determining rate capability are mainly due to charge and solid-state ion transportation resistances of materials with similar redox reaction. The electrochemical impedance spectroscopy (EIS) results for the composites of HATN/GO and HATNTA/GO are shown in the form of Nyquist plots in Fig. 6. The semicircles in the high frequency range represent the charge transfer resistance, and the straight lines in the low frequency range correspond to the Warburg impedance, owing to the ion diffusion- controlled process. The resistance of ion transportation and charge transfer of HATNTA/GO composite are comparatively much smaller than that of HATN/GO composite. The low charge transfer resistance and diffusion resistance of HATNTA/GO composite are related to the structure of HATNTA and its strong interactions with GO, which are in accordance with its better rate capability (Fig. 5).

e. Long-term Cycling stability and Coulombic efficiency

The long-term cycling stability and coulombic efficiency of these organic composite cathodes were tested at a current density of 0.5 A g ¹ and shown in Fig. 7. These composites demonstrate excellent long-term cycling stability. The composite of HATN/GO exhibits a discharge capacity of 130 mAh g ¹ after 600 cycles, corresponding to capacity retention of 90% of its initial capacity. The composite of HATNTA/GO exhibits a discharge capacity of 119 mAh g ¹ after 600 cycles, corresponding to capacity retention of 94% of its initial capacity. Additionally, the coulombic efficiency is close to 98% during the 600 cycles for these composites.

The HATNTA/GO composite as cathode demonstrated better electrochemical performance than that of HATN/GO composite in the aspects of specific capacity, rate capability and long term cycling stability. These results are related to their different composite nano-structures. For HATN, it has conjugated planar molecular structure which has strong π-π interactions and can easily assembly to form stable crystalline structure. It was found that HATN itself formed nano- rods structure under sonication. Hence, when HATN was sonicated with GO together, a core- shell nano-rod morphology was formed. However, while such type of composite structure may have good electric conductivity, ionic transportation will be challenging for this core (HATN)- shell (GO) nano-rods structure. Furthermore, volumetric changes during redox reaction could also destroy the core-shell structure. It was found that the core-shell nano-rods in cathode disappeared after the cycling performance test (Fig. Id). On the other hand, HATNTA molecule possesses three carboxylic acid groups which apparently weaken its intermolecular π-π interactions. Hence, when HATNTA was sonicated with GO, it was easily dispersed homogeneously onto GO surface. The strong hydrogen bonding interactions and π-π interactions between HATNTA and GO make the HATNTA/GO composite material stable, and HATNTA/GO composite displays excellent charge conductivity as well as ionic conductivity, as shown in the Nyquist plots (Fig. 6). Therefore, the better electrochemical performance of HATNTA/GO composite is related to its homogeneous structure and the stronger interactions between HATNTA and GO, which remarkably suppressed the dissolution and enhanced its charge and ionic conductivity. Furthermore, lower capacity and poor stability were observed when GO was replaced with reduced-GO or other carbon conductive materials. Industrial Applicability

The composites described in the present disclosure can be used as cathode materials. Since these composites are shown to exhibit low solubility, high specific capacity, good rate capability, and/or excellent long-term cycling stability; they therefore allow a broader application of lithium ion battery using the cathode comprising the composite as described herein. The application of the present technology will allow the use of lithium ion battery in many applications such as electronics in the fields of communication, healthcare and transportation. In addition, these new composites have great potential as green cathode materials for energy storage devices. The lithium ion batteries which use the cathode comprising the composite as described in the present disclosure may be employed as high density power sources for a plethora of applications ranging from automobiles (electric vehicles including electric cars, hybrid vehicles, electric bicycles, personal transporters and advanced electric wheelchairs, radio-controlled models, model aircraft and aircraft), portable devices (mobile phones or smartphones, laptops, tablets, digital cameras and camcorders), power tools (cordless drills, sanders and saws), to healthcare (portable medical equipment such as monitoring devices, ultrasound equipment and infusion pumps).

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

1. A composite comprising a compound of Formula (I)

(R

2. The composite according to claim 1 wherein the conductive carbon material is graphene oxide, reduced graphene oxide, graphene, graphite or graphite oxide.

3. The composite according to claim 2, where the conductive carbon material is graphene oxide.

4. The composite according to any one of claims 1-3, wherein at least one of R_l5 R₂ or R₃ is H.

5. The composite according to claim 4, wherein R_{l 5} R₂ and R₃ is H.

6. The composite according to any one of claims 1-3, wherein at least one of R_l5 R₂ or R₃ is independently -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding.

7. The composite according to claim 6, wherein at least one of R_{l 5} R₂ or R₃ is -COOH.

8. The composite according to claim 7, wherein R_{l 5} R₂ and R₃ is -COOH.

9. The composite according to any one of claims 1-3, wherein R_l5 R₂ and R₃ are the same; and wherein x, y and z are independently integers of value of 1 or 2.

10. A method of preparing a composite comprising a compound of Formula (I)

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material, comprising the steps of:

(a) mixing a cycloketone and an amine to form a reaction mixture;

11. The method according to claim 9, wherein the cycloketone is hexaketocyclohexane octahydrate.

12. The method according to any one of claims 9-10, wherein the amine is selected from the group comprising of

13. The method according to any one of claims 9 to 11, wherein step (a) further comprises mixing the cycloketone and the amine in an acid to form the reaction mixture; wherein the acid is acetic acid, malic acid, citric acid, formic acid, carbonic acid, lactic acid, phosphoric acid, oxalic acid, methanoic acid or combinations thereof.

14. The method according to any one of claims 9 to 12, wherein step (b) further comprises heating the reaction mixture of step (a) for a period of time; wherein the period of time is at least 4 hours.

15. The method according to any one of claims 9 to 13, wherein the method of mixing the compound of step (b) with the conductive carbon material is sonication.

16. The method according to any one of claims 9 to 14, wherein the conductive carbon material is graphene oxide, reduced graphene oxide, graphene, graphite or graphite oxide.

17. The method according to any one of claims 9 to 15, wherein step (c) further comprises mixing the compound of step (b) with the conductive carbon material in a solvent.

18. The method according to any one of claims 9 to 16, wherein step (c) further comprises mixing the compound of step (b) with the conductive carbon material for a period of time; wherein the period of time is at least 1 hour.

19. A cathode comprising a composite, wherein said composite comprises a compound of Formula (I)

Formula (I); wherein R R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH

forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material.

20. A method for preparing a cathode comprising the steps of:

(a) preparing a composite comprising a compound of Formula (I)

Formula (I); wherein R_l5 R₂ and R₃ are independently H, -COOH, -OH, -CHO, -NH₂, or a group capable of forming hydrogen bonding; and wherein x, y and z are independently integers of value from 1 to 4; and a conductive carbon material; and

(b) mixing the composite of step (a) with a binder.

21. The method according to claim 19, wherein the binder is polyvinylidene fluoride.