Compound q-CTF-oh having covalent triazine framework and method of making the same, method of preparing cathode of metal ion battery and metal ion battery

Abstract

A method of preparing a compound Q-CTF-OH having covalent triazine framework is disclosed. The method comprises steps of: reacting a 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer with a ZnCl 2under vacuum to obtain a solid reactant, wherein a reaction condition comprises heating the 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer and the ZnCl 2from room temperature to

Description

Technical Field

[0001] This invention relates to a positive electrode material for a battery. More particularly, it relates to a method for preparing a compound Q-CTF-OH having a covalent triazine framework, the compound Q-CTF-OH obtained therefrom, a method for preparing a positive electrode for a metal-ion battery, and a metal-ion battery. Prior Technology

[0002] Sustainable organic electrode materials have great potential to replace traditional non-renewable inorganic electrode materials. Among them, framework materials assembled by covalent bonds have many advantages, including highly flexible structural design, redox tunability, high stability, and low-carbon processes.

[0003] Covalent triazine frameworks are a class of non-crystalline porous materials. Their porous structure allows ions to easily pass through, and the bipolar triazine centers can interact with both anions and cations simultaneously, creating high-efficiency energy storage performance. Benzoquinone has a high redox potential and can undergo redox reactions to transfer two electrons, making it suitable for cathode materials. However, given that a pair of cyano groups is required to synthesize triazine, the selectivity of monomer molecules suitable for synthesizing covalent triazine framework cathode materials containing benzoquinone structures is extremely limited. Furthermore, to allow benzoquinone and cyano groups to coexist in the structure, it is usually necessary to extend the monomer molecule length; too many redox-inactive structures result in limited final electrochemical energy storage efficiency.

[0004] Therefore, there is a need to improve the conventional covalent triazine framework cathode material. Summary of the Invention

[0005] To address the problems of the prior art, the present invention aims to provide a method for preparing a compound Q-CTF-OH with a covalent triazine framework (CTF) to increase the redox site density of the obtained compound, thereby improving its electrochemical energy storage efficiency when applied as a cathode material in batteries.

[0006] To achieve the above objectives, in one embodiment of the present invention, a method for preparing a compound Q-CTF-OH having a covalent triazine skeleton is provided, the compound Q-CTF-OH being shown in formula (1) below: Equation (1), The method includes the following steps: S10: reacting 1,4-dicyano-2,3,5,6-tetrahydroxybenzene (LH4) monomer with zinc chloride (ZnCl2) under vacuum to obtain a solid reactant, wherein the molar ratio of the 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer to the zinc chloride is 1:0.5 to 1:10, wherein the reaction conditions are: heating from room temperature to 300 to 500°C and holding at that temperature for 10 to 48 hours to obtain a solid reactant.

[0007] In one embodiment of the present invention, the method further comprises the following steps: S20: cooling the solid reactant to room temperature; S30: grinding the solid reactant to obtain a crude product; S40: washing the crude product with water for the first time; S50: stirring the crude product after the first wash in an acid solution, optionally in a 0.8 to 1.5 M hydrochloric acid solution; S60: washing the crude product with water and tetrahydrofuran for the second time; and S70: drying the crude product after the second wash to obtain the compound Q-CTF-OH.

[0008] In one embodiment of the present invention, in step S10, the heating rate is 1 to 5°C / min.

[0009] In one embodiment of the present invention, in step S40, the crude product is first washed with water under ultrasonic conditions.

[0010] In one embodiment of the present invention, in step S50, the stirring time is 10 to 48 hours.

[0011] In one embodiment of the present invention, in step S70, the drying temperature is 50 to 180°C.

[0012] In one embodiment of the present invention, in step S70, the drying time is 10 to 48 hours.

[0013] To achieve the above objectives, in another embodiment of the present invention, a compound Q-CTF-OH prepared by the method described above is provided, as shown in formula (1). Equation (1), The compound Q-CTF-OH contains a covalent triazine skeleton.

[0014] To achieve the above objective, in another embodiment of the present invention, a method for preparing a positive electrode of a metal-ion battery is provided, comprising the steps of: S01: co-grinding a compound Q-CTF-OH prepared by the method described in claim 1, a conductive carbon additive, and a fluoropolymer to obtain a mixture, wherein the ratio of the compound Q-CTF-OH, the conductive carbon additive, and the polyvinylidene fluoride is 3:6:1 to 8:1:1, and the fluoropolymer comprises polyvinylidene fluoride or polytetrafluoroethylene; S02: adding water, ethanol, or N-methyl-2-pyrrolidone to the mixture to form a slurry; and S03: coating the slurry onto a current collector layer and drying it under vacuum at 90 to 110°C, optionally for 8 to 48 hours, to obtain the positive electrode of the metal-ion battery.

[0015] In one embodiment of the present invention, the current collector layer is a conductive carbon substrate.

[0016] To achieve the above objectives, in another embodiment of the present invention, a metal-ion battery is provided, comprising: a positive electrode, an insulating layer, a negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode as described above, the negative electrode is separated from the positive electrode by the insulating layer, and the negative electrode is a metal or an alloy thereof, the electrolyte is disposed between the positive electrode and the negative electrode, wherein the electrolyte is an ethylene carbonate / diethyl carbonate electrolyte solution containing lithium hexafluorophosphate.

[0017] In one embodiment of the present invention, the concentration of lithium hexafluorophosphate in the ethylene carbonate / diethyl carbonate electrolyte solution is 0.5 to 2 M.

[0018] The beneficial effects of this invention are as follows: The method for preparing a compound Q-CTF-OH with a covalent triazine skeleton according to this invention yields Q-CTF-OH, which contains a benzoquinone skeleton and has all hydrogen atoms replaced by hydroxyl groups. The polar hydroxyl groups can stably allow lithium ions to enter the pores, which is beneficial for extremely high-efficiency electrochemical performance. In lithium-ion batteries, Q-CTF-OH exhibits a capacity as high as 689 mAh g⁻¹ at a current density of 200 mA g⁻¹, and retains 118 mAh g⁻¹ after 2000 cycles at a high charge-discharge rate of 20 A g⁻¹, with a capacity retention of 97%. The Q-CTF-OH of this invention outperforms general organic porous cathode materials in all charge-discharge performance aspects. Furthermore, the porous nature and redox reactions of the organic functional groups in Q-CTF-OH of this invention allow for applications in various types of post-lithium-ion batteries, such as sodium, potassium, magnesium, and zinc ions, making it more widely applicable and sustainable than general inorganic electrodes. Simple Explanation of the Diagram

[0019] Figure 1 is a flowchart of the method for preparing the compound Q-CTF-OH with a covalent triazine skeleton according to the present invention. Figure 2 shows the structure of Q-CTF-OH synthesized by ionothermal trimerization of aromatic nitrile LH4 monomer. Figure 3 is a flowchart of the method for preparing the positive electrode of a metal-ion battery according to the present invention. Figure 4a shows the Fourier-transform infrared spectroscopy (FTIR) spectra of LH4 and Q-CTF-OH; Figure 4b shows the solid-state 13C nuclear magnetic resonance (NMR) spectra of Q-CTF-OH and model compounds 1 and 2; Figure 4c shows the O 1s X-ray photoelectron spectroscopy (XPS) spectra of Q-CTF-OH; Figure 4d shows the 77K N2 adsorption / desorption isotherms and pore size distribution of Q-CTF-OH; Figure 4e shows the Raman spectra of Q-CTF-OH; and Figure 4f shows the high-resolution transmission electron microscopy (HR-TEM) image of the layered structure of Q-CTF-OH and the measured spacing. Figure 5a shows the constant current discharge / charge curves of Q-CTF-OH at a current density of 200 mA / g, where the positive electrode compound Q-CTF-OH: Ketjenblack:polyvinylidene difluoride (PVDF) = 3:6:1; Figures 5b, c, and d show the voltage curves (Figure 5b), rate capability (Figure 5c), and long-term cycling performance (Figure 5d) of Q-CTF-OH at 100 mA / g (Figure 5b), where the positive electrode compound Q-CTF-OH: Ketjenblack:PVDF = 6:3:1; Figure 5e shows the cyclic voltammetry of Q-CTF-OH at 0.5 mV / s. Figures 6a and 6b show the electrochemical results of lithium-ion batteries (Q-CTF-OH: Ketjenblack:PVDF = 6:3:1) synthesized at different temperatures using Q-CTF-OH. Figure 7 shows the capacity retention of the lithium-ion battery (Q-CTF-OH: Ketjenblack:PVDF = 3:6:1) at current densities of 200, 500 and 1000 mA g⁻¹. Figure 8 shows the capacity retention of the lithium-ion battery (Q-CTF-OH: Ketjenblack:PVDF = 3:6:1) at current densities of 3, 5, 10 and 20 A g⁻¹. Figure 9 shows the capacity retention of the lithium-ion battery (Q-CTF-OH: Ketjenblack:PVDF = 6:3:1) at current densities of 100, 200 and 500 mA g⁻¹. Figure 10 shows the capacity retention of lithium-ion batteries with different contents of active material Q-CTF-OH at a current density of 500 mA g⁻¹ (PVDF kept constant at 10 wt%). Figures 11a and 11b compare the electrochemical performance of the full cell (graphite / Q-CTF-OH) and the half cell (Li / Q-CTF-OH) at a current density of 500 mA / g⁻¹ and a voltage range of 1.0 to 4.3 V. For the full cell, the graphite anode (graphite: Ketjen black: PVDF = 8:1:1) was pre-lithiated at a current density of 100 mA g⁻¹ in the voltage range of 0 to 3.0 V, while the Q-CTF-OH cathode was prepared with an active material ratio of Q-CTF-OH: Ketjen black: PVDF = 6:3:1. Figure 12 shows the XPS of Q-CTF-OH synthesized at different temperatures. Implementation

[0020] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can understand other advantages and effects of the present invention from the content disclosed in this specification. However, the illustrative embodiments disclosed in this invention are for illustrative purposes only and should not be considered as limiting the scope of the invention. In other words, the present invention can also be implemented or applied through other different embodiments, and the details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0021] Referring to Figures 1 and 2, a method for preparing a compound Q-CTF-OH having a covalent triazine framework (CTF) according to one embodiment of the present invention is described, wherein the compound Q-CTF-OH is shown in formula (1) below: Equation (1), the method includes the following steps:

[0022] Step S10: 1,4-Dicyano-2,3,5,6-tetrahydroxybenzene monomer (LH4) is reacted with zinc chloride (ZnCl2) under vacuum to obtain a solid reactant, wherein the molar ratio of the 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer to the zinc chloride is 1:0.5 to 1:10, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9. The reaction ratio is 1:10, wherein the reaction conditions are: heating from room temperature to 300 to 500°C (e.g., 300, 350, 400, 450, 500°C) and holding at that temperature for 10 to 48 hours (e.g., 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 hours). Specifically, in this step, the heating rate is 1 to 5°C / min, for example, 1, 2, 3, 4, 5°C / min.

[0023] Step S20: Cool the solid reactant to room temperature.

[0024] Step S30: Grind the solid reactant, for example, by grinding it in a mortar to obtain a coarse product. Preferably, grind the solid reactant thoroughly so that the coarse product is a uniform powder.

[0025] Step S40: Perform a first wash with water on the coarse product. Preferably, the wash is performed under ultrasonic conditions to improve the cleaning precision.

[0026] Step S50: The crude product after the first washing is stirred in an acid solution, for example, in a hydrochloric acid solution of 0.8 to 1.5 M (e.g., 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5 M), for a stirring time of 10 to 48 hours; for example, 10 to 40 hours; for example, 10 to 30 hours; for example, 10 to 20 hours.

[0027] Step S60: The crude product is washed a second time with water, and the remaining ZnCl2 is removed using tetrahydrofuran (THF).

[0028] Step S70: The crude product after the second washing is dried to obtain the compound Q-CTF-OH, which has a covalent triazine skeleton. Specifically, in this step, the drying time can be from 10 to 48 hours (e.g., 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48 hours), for example, 22, 23, 24, 25, or 26 hours; and the drying temperature can be from 50 to 180°C, for example: 500, 60, 70, 80, 90, 100, 120, 140, 160, or 180°C.

[0029] Referring to FIG3, a method for preparing a positive electrode of a metal-ion battery according to another embodiment of the present invention includes the following steps.

[0030] Step S01: The compound Q-CTF-OH prepared by the method described above, the conductive carbon additive, and the fluoropolymer are co-ground to obtain a mixture, wherein the ratio of the compound Q-CTF-OH, the conductive carbon additive, and the polyvinylidene fluoride is 3:6:1 to 8:1:1. Optionally, the fluoropolymer comprises polyvinylidene fluoride or polytetrafluoroethylene, and the conductive carbon additive can be conductive carbon black, such as Ketjen black series superconducting carbon black. Optionally, Ketjen black can be Ketjen black EC-300J, Ketjen black EC-600JD, Ketjen black ECP-600JD, VXC72, Black Pearls 2000, PRINTEX XE2-B, PRINTEX L6, or HIBLAXK 40B2. Optionally, the conductive carbon additive can be Super-P, KS-4, Super C65, or Acetylene Black. Step S02: Add water, ethanol or N-methyl-2-pyrrolidinone (NMP) to the mixture to form a slurry.

[0031] Step S03: Coat the slurry onto a current collector layer (e.g., a conductive carbon substrate) and dry it in a vacuum environment at 90 to 110°C (e.g., 90, 95, 100, 105, or 110°C) for 8 to 48 hours (e.g., 8, 10, 20, 30, 40, 42, 44, 46, or 48 hours) to obtain the positive electrode of the metal-ion battery.

[0032] According to another embodiment of the present invention, a metal-ion battery comprises: a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode is as described above, the negative electrode is separated from the positive electrode by the separator, and the negative electrode is a metal or an alloy thereof, the electrolyte is disposed between the positive electrode and the negative electrode, wherein the electrolyte is an ethylene carbonate / diethyl carbonate (EC / DEC) electrolyte solution containing lithium hexafluorophosphate. Specifically, the volume ratio of ethylene carbonate to diethyl carbonate can be 1:1, the concentration of lithium hexafluorophosphate in the ethylene carbonate / diethyl carbonate electrolyte solution can be from 0.5 to 2 M (e.g., 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.4, 1.6, 1.8, or 2 M), and the metal can be selected from the group consisting of lithium, sodium, potassium, magnesium, and zinc.

[0033] Unless otherwise stated herein, the singular forms “a” and “the” used in the specification and the appended claims include the numerals. Unless otherwise stated herein, the term “or” used in the specification and the appended claims includes the meaning of “and / or”.

[0034] Synthesis of Q-CTF-OH in this invention

[0035] Example 1

[0036] First, in a glove box, 19 mg (0.1 mmol) of 1,4-dicyano-2,3,5,6-tetrahydroxybenzene (LH₄) monomer and 68 mg (0.5 mmol) of ZnCl₂ were placed into a Pyrex glass tube. The Pyrex glass tube was then evacuated and sealed, and heated from room temperature to 400°C at a rate of 3°C / min, and held at that temperature for 24 hours. After cooling the Pyrex glass tube to room temperature, it was opened, and the resulting black solid was thoroughly ground in a mortar to obtain a crude product. The crude product was washed with water under ultrasonication, stirred in 1 M HCl solution for 24 hours, washed again with water, and the remaining ZnCl₂ was removed using tetrahydrofuran (THF). Finally, it was dried in a vacuum oven at 120°C for 24 hours to obtain pure Q-CTF-OH (8 mg, yield 43%).

[0037] Example 2

[0038] First, in a glove box, 19 mg (0.1 mmol) of 1,4-dicyano-2,3,5,6-tetrahydroxybenzene (LH₄) monomer and 68 mg (0.5 mmol) of ZnCl₂ were placed into a Pyrex glass tube. The Pyrex glass tube was then evacuated and sealed, and heated from room temperature to 300°C at a rate of 3°C / min, and held at that temperature for 24 hours. After cooling the Pyrex glass tube to room temperature, it was opened, and the resulting black solid was thoroughly ground in a mortar to obtain a crude product. The crude product was washed with water under ultrasonication, stirred in 1 M HCl solution for 24 hours, washed again with water, and the remaining ZnCl₂ was removed using tetrahydrofuran (THF). Finally, it was dried in a vacuum oven at 120°C for 24 hours to obtain pure Q-CTF-OH (7 mg, yield 38%).

[0039] Example 3

[0040] First, in a glove box, 19 mg (0.1 mmol) of 1,4-dicyano-2,3,5,6-tetrahydroxybenzene (LH4) monomer and 68 mg (0.5 mmol) of ZnCl2 were placed into a Pyrex glass tube. The Pyrex glass tube was then evacuated and sealed, and heated from room temperature to 500°C at a rate of 3°C / min, and held at that temperature for 24 hours. After cooling the Pyrex glass tube to room temperature, it was opened, and the resulting black solid was thoroughly ground in a mortar to obtain a crude product. The crude product was washed with water under ultrasonication, stirred in 1 M HCl solution for 24 hours, washed again with water, and the remaining ZnCl2 was removed using tetrahydrofuran (THF). Finally, it was dried in a vacuum oven at 120°C for 24 hours to obtain pure Q-CTF-OH (10 mg, yield 54%).

[0041] Lithium-ion battery manufacturing:

[0042] Example 4:

[0043] The negative electrode material uses lithium metal, the electrolyte is 1 M LiPF6 ethylene carbonate / diethyl carbonate (EC / DEC, volume ratio 1:1), and a Celgard membrane positive electrode is used. The positive electrode comprises a positive electrode material mixture, which, based on a total weight of 100 wt%, contains 60 wt% of Q-CTF-OH active material (Example 1), 30 wt% black conductive carbon (Ketjen Black), and 10 wt% polyvinylidene fluoride (PVDF). The Q-CTF-OH, black conductive carbon, and PVDF are co-milled to obtain the positive electrode material mixture. Then, N-methyl-2-pyrrolidone (NMP) is added to the positive electrode material mixture to form a slurry. This slurry is coated onto a carbon paper (MGL280) current collector (i.e., the current collector layer) and dried overnight in a vacuum at 100°C to obtain the positive electrode.

[0044] Example 5:

[0045] The negative electrode material uses lithium metal, the electrolyte is 1 M LiPF6 ethylene carbonate / diethyl carbonate (EC / DEC, volume ratio 1:1), and a Celgard membrane positive electrode is used. The positive electrode comprises a positive electrode material mixture, which, based on 100 wt% of the total weight of the mixture, contains 30 wt% of Q-CTF-OH active material (Example 1), 60 wt% of black conductive carbon (Ketjen Black), and 10 wt% polyvinylidene fluoride (PVDF). The Q-CTF-OH, black conductive carbon, and PVDF are co-milled to obtain the positive electrode material mixture. Then, N-methyl-2-pyrrolidone (NMP) is added to the positive electrode material mixture to form a slurry. This slurry is coated onto a carbon paper (MGL280) current collector (i.e., current collector layer) and dried overnight in a vacuum at 100°C to obtain the positive electrode.

[0046] Referring to Figure 4a, Fourier-transform infrared spectroscopy (FT-IR) was used to detect LH4 and Q-CTF-OH of Example 1, confirming the successful formation of the triazine ring. It can be seen that, at any temperature, the characteristic peak at 2245 cm⁻¹ attributed to the stretching of the nitrile group of the LH4 monomer did not appear in the spectrum of Q-CTF-OH. Instead, two additional peaks were observed at 1581 and 1329 cm⁻¹, corresponding to the presence of C=N and CN on the triazine ring, indicating that the nitrile group had undergone cyclization. It was also found that the C=O signal at 1657 cm⁻¹ was broad and overlapped with the C=N signal (see the enlarged view in Figure 4a).

[0047] Referring to Figure 4b, the structure of Q-CTF-OH was studied using solid-state 13C nuclear magnetic resonance (NMR). The resonance peak of C=N in Q-CTF-OH at 172.5 ppm confirmed the successful formation of a triazine center through trimerization of the nitrile group, which is consistent with the results of FT-IR.

[0048] Referring to Figure 4c, the O 1s XPS data provides further detailed information about the quinone center. Two distinct components were observed at 531.9 and 533.2 eV, in a 1:1 ratio, corresponding to C=O and ‒OH, respectively.

[0049] Referring to Figure 4d, nitrogen adsorption / desorption experiments were conducted at 77 K to determine the porosity of Q-CTF-OH. It was found that the Brunauer–Emmett–Teller (BET) surface area of ​​Q-CTF-OH is 438 m²g⁻¹, and the main pore size is approximately 8 to 12 Å (inset in Figure 4d).

[0050] Referring to Figure 4e, the Raman spectrum of Q-CTF-OH shows two prominent peaks at 1346 and 1591 cm⁻¹, corresponding to the D band attributed to the edges and defects of the 2D structure and the G band indicating the presence of conjugated carbon material, respectively. Furthermore, the broad peak at 2865 cm⁻¹ indicates a graphite-like layered structure. Referring to Figure 4f, the microstructure of Q-CTF-OH was probed using high-resolution transmission electron microscopy (HR-TEM), revealing that Q-CTF-OH possesses fairly uniformly distributed pores and some visible two-dimensional stacked structures, consistent with the Raman spectroscopy results. Referring to the inset in Figure 4f, the measured interlayer spacing is 0.364 nanometers, a typical characteristic of π-stacking.

[0051] Electrochemical characteristics analysis:

[0052] The electrochemical performance of Q-CTF-OH in lithium batteries was investigated using a 1:1 (v / v) ethylene carbonate / diethyl carbonate (containing 1 M LiPF6) as the electrolyte and constant current charge / discharge cycling was performed using a Neware battery cycler. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on a VMP3 (BioLogic) system, with a voltage range of 1.1 to 4.4 V vs. Li / Li+. EIS measurements were performed in the frequency range of 10 kHz to 10 mHz. The battery was allowed to stand for at least 30 minutes before measurement.

[0053] Referring to Figure 5a, the results show that the discharge capacity increases with continued cycling. At the 11th cycle, the lithium battery of Example 5 (Example 1: Q-CTF-OH: Ketjen Black:PVDF = 3:6:1) reaches a maximum capacity of 689 mAh g⁻¹ at a current density of 200 mA g⁻¹. After deducting the capacity contribution of conductive carbon, this capacity is equivalent to 7 electron transfers per repeating unit of Q-CTF-OH, which is highly consistent with the expected theoretical capacity (3 Li⁺ ions stored on the triazine ring, 3 Li⁺ ions stored on the carbonyl group, and PF₆⁻ stored on the triazine). This high capacity essentially originates from the structure of Q-CTF-OH, which has the highest density of redox active sites among all covalent triazine backbones.

[0054] Referring to Figure 5b, the electrochemical performance of Q-CTF-OH in a lithium-ion battery was also investigated using Example 4 (i.e., Example 1: Q-CTF-OH: Ketjen Black: PVDF = 6:3:1) with different component ratios of the cathode material mixture. At a current density of 100 mA g⁻¹, the maximum discharge capacity of Q-CTF-OH was 441 mAh g⁻¹ (31st cycle). In this experiment, the capacity decrease was due to the relatively low proportion of conductive additives used in the electrode, a phenomenon also observed in other organic electrode materials.

[0055] The rate capability of the lithium battery in Example 4 was tested by changing the current density from 0.2 to 20 A g⁻¹ and then back to 0.2 A g⁻¹. As shown in Figure 5c, a highly reversible rate capability curve was obtained. The output capacity was 278, 254, 232, 204, 151, 105, 84, and 73 mAh g⁻¹ at current densities of 0.2, 0.5, 1, 2, 5, 10, 15, and 20 A g⁻¹, respectively. When the current density was switched back to 0.2 A g⁻¹, a capacity of 331 mAh g⁻¹ was obtained.

[0056] To further test long-term cycle stability, the lithium battery of Example 4 was subjected to 2000 discharge / charge cycles. Referring to Figure 5d, the results show that at extremely high rates of 10 and 20 A g⁻¹, the lithium battery can provide reversible capacities of up to 134 and 118, respectively, and after 2000 cycles, the capacity retention rates reached 92% and 97%, respectively.

[0057] The above results indicate that the Q-CTF-OH of this invention exhibits excellent electrochemical performance in lithium batteries, particularly high cycle stability at high rates. Furthermore, based on a discharge capacity of 441 mAh g⁻¹ at 100 mA g⁻¹ and an average discharge potential of 2.02 V, the mass energy density of the Q-CTF-OH of this invention can be estimated to be 891 Wh kg⁻¹.

[0058] Cyclic voltammetry (CV) was performed on the Q-CTF-OH of this invention at a scan rate of 0.5 mV s⁻¹. As shown in Figure 5e, the results show two broad anodic peaks centered at 2.59 and 3.74 V, and two broad cathode peaks centered at 2.20 and 3.60 V. This indicates the presence of multiple redox centers in the Q-CTF-OH of this invention, consistent with the characterization results mentioned above. Notably, these broad CV characteristics are common in CTF-based materials.

[0059] In summary, the Q-CTF-OH of this invention, when applied to lithium batteries, can provide a capacity of up to 689 mAh g⁻¹ at 200 mA g⁻¹, a reversible capacity of 118 mAh g⁻¹ at 20 A g⁻¹, and maintain a retention rate of 97% after 2000 cycles.

[0060] Figures 6a and 6b show the electrochemical results of the compound Q-CTF-OH obtained by reacting at 300°C, 400°C, and 500°C in a lithium battery (Q-CTF-OH: Ketjen Black: PVDF = 6:3:1). Figure 6a shows the voltage curve, while Figure 6b shows the capacity retention at 200 mA g⁻¹. The results show that the charge-discharge performance of Q-CTF-OH obtained by reacting at 400°C and 500°C is similar.

[0061] Figure 7 shows the capacity retention of the lithium battery (Q-CTF-OH: Ketjenblack:PVDF = 3:6:1) of Example 5 at current densities of 200, 500, and 1000 mA g⁻¹. The results show that this lithium battery has excellent reversible capacity, with capacities of 483, 392, and 372 mAh g⁻¹ after 100 cycles at current densities of 200, 500, and 1000 mA g⁻¹, respectively.

[0062] Figure 8 shows the capacity retention of the lithium battery (Q-CTF-OH: Ketjen Black:PVDF = 3:6:1) of Example 5 at current densities of 3, 5, 10, and 20 A g⁻¹. The results show that for long-term cycling, after 1000 cycles, the lithium battery achieves reversible capacities of 242, 224, 217, and 180 mAh g⁻¹ at current densities of 3, 5, 10, and 20 A g⁻¹, respectively, corresponding to retention rates of 74%, 85%, 100%, and 99%.

[0063] Figure 9 shows the capacity retention of the lithium battery (Q-CTF-OH: Ketjenblack:PVDF = 6:3:1) in Example 4 at current densities of 100, 200, and 500 mA g⁻¹. The results show that the electrode material composed of a higher proportion of Q-CTF-OH exhibits fairly stable charge-discharge performance.

[0064] Figure 10 shows the capacity retention of lithium batteries with different contents (80 wt%, 60 wt%, 30 wt%) of active material Q-CTF-OH at a current density of 500 mA g⁻¹ (PVDF kept constant at 10 wt%).

[0065] Figures 11a and 11b compare the electrochemical performance of the full cell (graphite / Q-CTF-OH) and the half cell (Li / Q-CTF-OH) at a current density of 500 mA / g⁻¹ and a voltage range of 1.0 to 4.3 V. For the full cell, the graphite anode (graphite: Ketjen black: PVDF = 8:1:1) was pre-lithiated at a current density of 100 mA g⁻¹ in the voltage range of 0 to 3 V, while the Q-CTF-OH cathode was prepared with an active material ratio of Q-CTF-OH: Ketjen black: PVDF = 6:3:1. The results show that the charge-discharge performance of the half cell and the full cell is similar.

[0066] Referring to Figure 12, X-ray photoelectron spectroscopy analysis was performed on Q-CTF-OH synthesized at 300°C, 400°C, and 500°C. The results showed that Q-CTF-OH obtained at 400°C had more and more complete triazine structures.

[0067] Although the present invention has been disclosed with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art may make various modifications and alterations without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0068] S10 to S70: Steps of the method for preparing the compound Q-CTF-OH having a covalent triazine skeleton according to the present invention S01 to S03: Steps of the method for preparing the positive electrode of a metal-ion battery according to the present invention

Claims

1. A method for preparing a compound Q-CTF-OH having a covalent triazine skeleton, the compound Q-CTF-OH being represented by the following formula (1): Formula (1), the method comprising the steps of: S10: reacting 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer with zinc chloride under vacuum to obtain a solid reactant, wherein the molar ratio of the 1,4-dicyano-2,3,5,6-tetrahydroxybenzene monomer to the zinc chloride is 1:0.5 to 1:10, wherein the reaction conditions are: heating from room temperature to 300 to 500°C and holding at that temperature for 10 to 48 hours to obtain a solid reactant.

2. The method as described in claim 1 further comprises the following steps: S20: cooling the solid reactant to room temperature; S30: grinding the solid reactant to obtain a crude product; S40: washing the crude product with water for the first time; S50: stirring the crude product after the first wash in an acid solution; S60: washing the crude product with water and tetrahydrofuran for the second time; and S70: drying the crude product after the second wash to obtain the compound Q-CTF-OH.

3. The method as described in claim 1, wherein in step S10, the heating rate is 1 to 5°C / min.

4. The method as described in claim 2, wherein in step S40, the crude product is first washed with water under ultrasonic conditions.

5. The method as described in claim 2, wherein in step S50, the stirring time is 10 to 48 hours.

6. The method as described in claim 2, wherein in step S70, the drying temperature is 50 to 180°C.

7. The method as described in claim 2, wherein in step S70, the drying time is 10 to 48 hours.

8. A compound Q-CTF-OH prepared by the method described in claim 1, as shown in formula (1), wherein the compound Q-CTF-OH comprises a covalent triazine skeleton.

9. A method for preparing a positive electrode of a metal-ion battery, comprising the steps of: S01: co-grinding a compound Q-CTF-OH prepared by the method described in claim 1, a conductive carbon additive, and a fluoropolymer to obtain a mixture, wherein the ratio of the compound Q-CTF-OH, the conductive carbon additive, and the fluoropolymer is 3:6:1 to 8:1:1, and the fluoropolymer comprises polyvinylidene fluoride or polytetrafluoroethylene; S02: adding water, ethanol, or N-methyl-2-pyrrolidone to the mixture to form a slurry; and S03: coating the slurry onto a current collector layer and drying it under vacuum at 90 to 110°C to obtain the positive electrode of the metal-ion battery.

10. The method as described in claim 9, wherein the current collector layer is a conductive carbon substrate.

11. A metal-ion battery comprising: a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the positive electrode is a positive electrode prepared by the method described in claim 9, the negative electrode is separated from the positive electrode by the separator and is a metal or an alloy thereof, and the electrolyte is disposed between the positive electrode and the negative electrode, wherein the electrolyte is an ethylene carbonate / diethyl carbonate electrolyte solution containing lithium hexafluorophosphate.

12. The metal-ion battery as claimed in claim 11, wherein the concentration of lithium hexafluorophosphate in the ethylene carbonate / diethyl carbonate electrolyte solution is from 0.5 to 2 M.

13. The metal-ion battery as claimed in claim 11, wherein the metal is selected from the group consisting of lithium, sodium, potassium, magnesium and zinc.

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