High-conductivity conjugated coordination polymer, preparation thereof and application of high-conductivity conjugated coordination polymer in low-temperature battery

Abstract

The invention belongs to the field of electrochemical energy storage materials, and discloses a high-conductivity conjugated coordination polymer as well as preparation and application thereof in a low-temperature battery. According to the polymer, 5, 8-dihydroxy-1, 4-naphthoquinone is taken as an organic ligand, transition metal ions are taken as a metal center, and a pi-d conjugated structure with a plane is formed by removing coordinated water, so that the polymer shows high intrinsic conductivity. As an electrode active material, the material can effectively solve the problem that the capacity of a secondary battery is suddenly reduced due to lattice shrinkage of an electrode material and reaction kinetics hysteresis in a low-temperature environment. The material has rapid charging capability and super-long cycle life, and an organic battery assembled by the material can still keep over 80% of capacity at an extremely low temperature of-40 DEG C. The invention provides a key material solution for developing energy storage equipment with wide temperature range and high performance.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, and more specifically, relates to a highly conductive conjugated coordination polymer, its preparation, and its application in low-temperature batteries. Background Technology

[0002] With the rapid development of renewable energy and the widespread adoption of electric vehicles, the development of low-cost, highly safe, and environmentally adaptable electrochemical energy storage systems has become an urgent need. Among various battery technologies, alkali metal ion batteries (such as lithium-ion, sodium-ion, and potassium-ion batteries) have already taken a dominant position or show great promise. However, many potential applications, such as grid energy storage and equipment operating in high-latitude or high-altitude regions, require batteries to have reliable operating capabilities in low-temperature environments.

[0003] Currently, commercial lithium-ion batteries suffer from severe performance degradation at low temperatures; for example, at -40°C, their chargeable capacity is less than 12% of that at room temperature (C.-K. Huang, JS Sakamoto., J. Wolfenstine, S. Surampudi. The Limits of Low‐Temperature Performance of Li-Ion Cells. J. Electrochem. Soc.2000, 147 (8), 2893). This challenge also exists in emerging sodium-ion and potassium-ion batteries. At low temperatures, the reaction kinetics inside the battery are generally sluggish. On the one hand, the increased viscosity of the electrolyte leads to a decrease in its ionic conductivity; on the other hand, the lattice of the electrode material also shrinks at low temperatures, causing the diffusion channels of ions in the solid phase to narrow, the diffusion barrier to increase, and the charge transfer process to become difficult, ultimately leading to a sharp decline in battery capacity. For sodium ions (1.02 Å) and potassium ions (1.38 Å), which have larger ionic radii, their intrinsic solid-phase diffusion in electrode materials is slower than that of lithium ions (0.76 Å), making the kinetic challenges they face at low temperatures more severe.

[0004] To address these challenges, organic electrode materials possessing structural flexibility and sustainability have attracted widespread attention. However, these materials generally suffer from low intrinsic electronic conductivity, heavy reliance on conductive additives, and the dissolution of active materials in electrolytes, which limits their practical applications. Conjugated coordination polymers, through strong coordination bonds, construct extended π-d conjugated systems, theoretically capable of simultaneously achieving high conductivity and excellent structural stability, demonstrating great potential.

[0005] Therefore, developing a conjugated coordination polymer that combines a well-defined structure, high intrinsic conductivity, and excellent low-temperature stability is of great significance for promoting the development of high-performance alkali metal ion batteries with a wide temperature range. Summary of the Invention

[0006] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method for preparing a novel conjugated coordination polymer and its application. The purpose is to obtain a material with a well-defined molecular structure, high intrinsic conductivity, and the ability to effectively maintain efficient ion transport and charge transfer at low temperatures, so as to be suitable for constructing high-performance, wide-temperature-range alkali metal ion batteries.

[0007] To achieve the above objectives, in a first aspect of the present invention, a highly conductive conjugated coordination polymer is provided, which has a planar π-d conjugated structure and is free of coordinating water; the polymer has the general structural formula M-DHNQ, where M is a transition metal ion and DHNQ is a deprotonated 5,8-dihydroxy-1,4-naphthoquinone ligand; the structure of the polymer is shown in Formula 1: Equation 1.

[0008] Preferably, the transition metal ion is selected from Mn. 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ One or more of the following; preferably, the transition metal ion is Ni. 2+ .

[0009] In a second aspect of the present invention, a method for preparing a highly conductive conjugated coordination polymer as described in any of the preceding claims is provided, characterized by comprising the following steps: (1) The precursor M-DHNQ with coordinated water molecules was prepared by hydrothermal synthesis by mixing an aqueous solution of transition metal salt with a solution of 5,8-dihydroxy-1,4-naphthoquinone ligand. (2) The precursor M-DHNQ with coordinated water molecules is subjected to heat treatment to remove the coordinated water molecules.

[0010] Preferably, in step (1), the preparation is specifically carried out through the following steps: an aqueous solution of a transition metal salt is added dropwise to a solution of 5,8-dihydroxy-1,4-naphthoquinone ligand to obtain a mixed solution; then the mixed solution is heated so that the transition metal ions coordinate with the deprotonated 5,8-dihydroxy-1,4-naphthoquinone and water molecules to obtain the precursor M-DHNQ with coordinated water molecules.

[0011] Preferably, in step (1), the molar ratio of the transition metal salt to the 5,8-dihydroxy-1,4-naphthoquinone ligand is 1 to 2; the concentration of the transition metal salt solution is 0.02 to 2 mol / L; and the solvent in the 5,8-dihydroxy-1,4-naphthoquinone ligand solution is selected from one or more of water, ethanol, N,N-dimethylformamide, or dimethyl sulfoxide.

[0012] Preferably, in step (1), the heating temperature in the hydrothermal synthesis method is 60~120℃ and the heating time is 24~72 h.

[0013] Preferably, the heat treatment is carried out under a vacuum or inert atmosphere, and the temperature of the heat treatment is 130~200℃, and the time is 12~24 h.

[0014] In a third aspect of the present invention, a positive electrode for a secondary battery is provided, comprising: dispersing a highly conductive conjugated coordination polymer, a conductive additive and a binder as described in any one of the preceding claims uniformly in a solvent and coating them onto a current collector, and drying the mixture to obtain the positive electrode for the secondary battery.

[0015] Preferably, the mass ratio of the highly conductive conjugated coordination polymer, the conductive additive, and the binder is (1~9):(8~0.5):(1~0.5). The conductive additive is selected from one or more of Ketjen black, conductive carbon black, carbon nanotubes, and graphene. The adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0016] In a third aspect of the invention, a secondary battery is provided, comprising a secondary battery positive electrode as described in any of the preceding claims.

[0017] Preferably, the battery is a lithium-ion, sodium-ion, potassium-ion battery or a dual-ion battery.

[0018] Preferably, the battery retains at a capacity of not less than 80% at -40°C.

[0019] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. The polymer provided by this invention has the structure shown in Formula 1, with the general structural formula M-DHNQ, where M is a transition metal ion and DHNQ is a deprotonated 5,8-dihydroxy-1,4-naphthoquinone ligand. It possesses a planar conjugated structure, forming a long-range π-d conjugated system with the ligand, and contains no coordinating water, significantly improving the intrinsic conductivity of the material and greatly promoting rapid charge transport. Furthermore, this conjugated coordination polymer exhibits structural stability at an extreme low temperature of -40℃, with minimal lattice shrinkage.

[0020] 2. The transition metal ions of this invention are selected from Mn. 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ One or more of these transition metals, which have similar ionic radii and are all divalent ions, can also form structurally similar products through the same method. Ni is the preferred material in this invention. 2+ With unique d 8 Electronic configuration and coordination characteristics make it easier to form long-range ordered coordination structures, which can greatly improve the degree of electronic delocalization of materials and endow them with excellent structural stability.

[0021] 3. By selecting specific ligands and metal ions and combining them with hydrothermal reactions, this invention can easily obtain crystalline materials with well-defined structures. By further removing coordination water, a planar π-d conjugated system is induced to form at the metal center, thereby increasing the intrinsic conductivity of the material and promoting charge transport.

[0022] 4. This invention preferably involves heat treatment under a vacuum or inert atmosphere, which effectively prevents the precursor from being oxidized by air during the removal of coordinated water molecules at high temperatures. This condition ensures that the material accurately forms the predetermined planar π-d conjugated structure, avoiding the destruction of the conjugated system, decrease in conductivity, and loss of electrochemical activity caused by oxidation, thereby ensuring that the final product has high purity and excellent performance.

[0023] 5. The polymer of the present invention, as a positive electrode material for batteries, has a stable flexible polymer structure and anhydrous properties, which effectively prevent structural collapse and dissolution and loss of active materials during cycling. At the same time, it exhibits an ultra-long cycle life (e.g., a capacity retention rate of up to 86% after 5000 cycles) and a fast charging capability (e.g., it can be charged to 52% state of charge within 90 seconds).

[0024] 6. Because the conjugated coordination polymer exhibits structural stability and minimal lattice shrinkage at extreme low temperatures of -40°C, its robust structure and open channels ensure that alkali metal ions maintain a high diffusion coefficient even at low temperatures. Batteries based on this material retain at least 80% of their capacity at -40°C, effectively overcoming the industry challenge of rapid capacity drop at low temperatures. Attached Figure Description

[0025] Figure 1 Fourier transform infrared spectrum (left) and powder XRD pattern (right) of the conjugated coordination polymer prepared for Example 1 of this invention.

[0026] Figure 2The XRD patterns (left) and conductivity variation curves (right) of the conjugated coordination polymer powder prepared in Example 1 of this invention were measured at different temperatures.

[0027] Figure 3 The image shows a SEM image of the Zn-DHNQ·2H2O precursor microcrystal sample obtained in Comparative Example 1 of this invention.

[0028] Figure 4 This is a schematic diagram of the structure of the Zn-DHNQ·2H2O precursor obtained in Comparative Example 1 of the present invention.

[0029] Figure 5 The powder XRD pattern (at room temperature) of the Zn-DHNQ·2H2O precursor obtained in Comparative Example 1 of this invention is shown; the single-crystal simulation data in the figure were obtained by calculation using the crystal's space group.

[0030] Figure 6 The powder XRD patterns of the Ni-DHNQ·2H2O precursor and the Zn-DHNQ·2H2O precursor obtained in Comparative Example 2 and Comparative Example 1 of this invention are shown.

[0031] Figure 7 The present invention provides charge-discharge curves and rate performance diagrams for a sodium-ion cathode half-cell, as shown in Embodiment 2 of this invention; wherein... Figure 7 The left figure shows the conjugated coordination polymer powder prepared in Example 1 at 100 mA g. -1 The right figure shows the charge-discharge curves at different current densities. The right figure shows the cycle performance of the conjugated coordination polymer prepared in Example 1 after it is assembled into a battery.

[0032] Figure 8 The sodium-ion positive electrode half-cell provided in Embodiment 2 of the present invention is in 1 A g -1 Cyclic performance at current density.

[0033] Figure 9 The charge-discharge curve of the sodium-ion positive electrode half-cell provided in Example 2 of the present invention at a low temperature of -40°C.

[0034] Figure 10 This is a comparison chart of the cycle performance of the sodium-ion cathode full cell provided in Example 5 of the present invention at different temperatures (25°C and -40°C).

[0035] Figure 11 The image shows the XRD pattern of the amorphous product in Comparative Example 1 of this invention.

[0036] Figure 12 The graph shows the cycle performance of the aqueous precursor in Comparative Example 4 of this invention after it is assembled into a battery at different current densities.

[0037] Figure 13The aqueous precursor in Comparative Example 5 of this invention was assembled into a battery at 0.1 A g. -1 Cyclic performance at current density. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] In the following embodiments, all instruments and other equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise specified, all methods described are conventional methods, and all raw materials are available from publicly available commercial sources.

[0040] To achieve the above objectives, according to a first aspect of the present invention, a highly conductive conjugated coordination polymer is provided, which has a planar π-d conjugated structure and does not contain coordinated water molecules, and is represented by the general formula M-DHNQ, wherein M represents a transition metal ion and DHNQ is a deprotonated 5,8-dihydroxy-1,4-naphthoquinone ligand, the structure of which is shown in Formula 1: Equation 1.

[0041] Preferably, the transition metal ion is selected from Mn. 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ One or more of the following; more preferably, the transition metal ion is Ni. 2+ .

[0042] The highly conductive conjugated coordination polymer provided by this invention, through the selection of specific ligands and synthetic pathways, can yield a well-defined crystalline material. Furthermore, by removing coordination water to induce the formation of a planar π-d conjugated system, its intrinsic conductivity is significantly improved, greatly promoting rapid charge transport. In addition, this material possesses both a stable flexible polymer structure and anhydrous properties, effectively preventing structural collapse and dissolution of active materials during cycling, thereby contributing to improved fast charging capability and cycle life of secondary batteries. Particularly noteworthy is the polymer's structural stability and minimal lattice shrinkage at extreme low temperatures, ensuring a high diffusion coefficient for alkali metal ions. This allows batteries based on this material to maintain high capacity at low temperatures, effectively overcoming the technical challenge of rapid capacity drop in secondary batteries at low temperatures.

[0043] According to a second aspect of the present invention, a method for preparing a highly conductive conjugated coordination polymer is provided. The method includes: (1) mixing an aqueous solution of a transition metal salt with a 5,8-dihydroxy-1,4-naphthoquinone ligand solution to obtain a precursor M-DHNQ·nH2O with coordinated water molecules, 1≤n≤2, by hydrothermal synthesis; (2) subjecting the precursor M-DHNQ·nH2O with coordinated water molecules to heat treatment to remove the coordinated water molecules, thereby obtaining a conjugated coordination polymer. Wherein, due to different types of transition metal salts, precursors M-DHNQ·nH2O with different amounts of coordinated water can be formed (1≤n≤2), which is mainly determined by the number of coordinated water molecules required for different metal ions to form their stable coordination structures. Different metal ions have their characteristic coordination geometry preferences: for ions that tend to form a six-coordinate octahedral structure (such as Mn...), ... 2+ Fe 2+ Co 2+ Ni 2+ Zn 2+ After coordinating with the DHNQ ligand, the axial position is occupied by two water molecules, thus forming a precursor with n=2; for ions that readily form five-coordinate tetragonal pyramids due to factors such as the Jahn-Teller effect (e.g., Cu), 2+ ), with only one water molecule coordinated along its axis, forming a precursor with n=1.

[0044] In the embodiment, step (1) specifically includes: slowly adding an aqueous solution of a transition metal salt to a 5,8-dihydroxy-1,4-naphthoquinone ligand solution to obtain a mixed solution; then heating the mixed solution to allow the transition metal ion (M) to coordinate with the deprotonated 5,8-dihydroxy-1,4-naphthoquinone (DHNQ) and water molecules to obtain the precursor M-DHNQ·nH2O.

[0045] In the embodiments, in step (1), the solvent in the 5,8-dihydroxy-1,4-naphthoquinone ligand solution is selected from one or more of water, ethanol, N,N-dimethylformamide or dimethyl sulfoxide.

[0046] In the embodiments, in step (1), the molar ratio of the transition metal salt to the 5,8-dihydroxy-1,4-naphthoquinone ligand is 1 to 2; the concentration of the transition metal salt solution is 0.02 to 2 mol / L.

[0047] In the embodiment, in step (1), the temperature in the hydrothermal synthesis method is 60~120℃ and the heating time is 24~72 h.

[0048] In the embodiment, in step (2), the heat treatment is carried out under vacuum or inert atmosphere at a temperature of 130~200℃ for 12~24 h.

[0049] According to a third aspect of the present invention, a positive electrode for a secondary battery is provided, comprising the aforementioned conjugated coordination polymer, conductive additive and binder, which are uniformly dispersed in a solvent and coated onto a current collector, and then dried to obtain the positive electrode of the secondary battery.

[0050] In the embodiments, the mass ratio of the conjugated coordination polymer, the conductive additive and the binder is (1~9):(8~0.5):(1~0.5).

[0051] In the embodiments, the conductive additive is selected from one or more of Ketjen black, conductive carbon black, carbon nanotubes, and graphene.

[0052] In the embodiments, the adhesive is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, and sodium carboxymethyl cellulose.

[0053] According to a fourth aspect of the present invention, a secondary battery is provided, comprising the aforementioned positive electrode.

[0054] In the embodiments, the secondary battery is a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, or a dual-ion battery.

[0055] In this embodiment, the battery retains at a capacity of no less than 80% at -40°C.

[0056] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0057] Example 1: Based on the present invention, the method for preparing the conjugated coordination polymer Ni-DHNQ by removing coordination water through hydrothermal method and heat treatment as shown in this embodiment includes the following steps: (1) Weigh 0.2 mmol (38 mg) of 5,8-dihydroxy-1,4-naphthoquinone ligand and suspend it in 10 mL of distilled water.

[0058] (2) Dissolve 0.22 mmol (55 mg) of Ni(OAc)2·4H2O in 10 mL of distilled water and slowly add it dropwise to the above ligand suspension.

[0059] (3) The mixed solution was stirred at 85°C for 72 hours. After the reaction was completed, it was cooled to room temperature to obtain the precipitate.

[0060] (4) After the reaction was completed, the precipitate was collected by filtration and washed successively with N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and deionized water. Finally, it was dried in a vacuum drying oven at 80°C to obtain Ni-DHNQ·2H2O precursor with a yield of 52 mg and a yield of 93%.

[0061] (5) The blue powder of the precursor Ni-DHNQ·2H2O was placed in a vacuum oven and heat-treated at 130°C for 24 hours in a vacuum environment to remove coordinated water molecules.

[0062] (6) After heat treatment, the product color changed from blue to brown, and Ni-DHNQ powder was obtained. It was quickly transferred to an argon glove box with oxygen and moisture content of less than 1.0 ppm for storage to prevent reabsorption of water.

[0063] The powder sample obtained in Example 1 was analyzed by infrared and XRD, and the results are as follows: Figure 1 As shown, from Figure 1 The infrared spectrum in the middle left image shows that the region after removing coordinated water molecules is located in the 3000-3700 cm⁻¹ range. -1 The water peak disappeared, while other infrared absorption peaks did not change significantly. The X-ray powder diffraction pattern of Ni-DHNQ is shown below. Figure 1 As shown in the right figure, the diffraction peaks changed significantly after removing the coordinated water; the strongest diffraction peak was located at 13.208. o The corresponding pore spacing is 6.69 Å, while the diffraction peak corresponding to the interlayer spacing is located at 25.048 Å. o The stability of the powder sample obtained in Example 1 was tested at low temperature. The X-ray powder diffraction pattern of the powder sample obtained in Example 1 at -40°C was measured, and the results are as follows: Figure 2 As shown in the left figure, the crystal structure of the material remains stable at a low temperature of -40℃, with the diffraction peaks corresponding to the channel spacing and the interlayer spacing shifting by 0.24. o and 0.29 o These changes correspond to lattice shrinkages of only 1.78% and 1.13%, respectively.

[0064] The conductivity of the powder sample obtained in Example 1 was tested at low temperature. For the powder sample obtained in Example 3, its conductivity at different temperatures was tested, and the results are as follows: Figure 2 As shown in the right figure, even at a low temperature of -40°C, the material still exhibits a high strength of 1.91 × 10⁻⁶. -2 S m -1 The conductivity is 4.16 × 10⁻⁶ at room temperature. -2 S m -1 Only minor changes.

[0065] It is evident that the conjugated coordination polymer in this invention has great application potential as a low-temperature secondary battery.

[0066] Comparative Example 1: Based on this invention, the preparation of the precursor Zn-DHNQ·2H2O shown in this example includes the following steps: (1) Weigh 0.2 mmol (38 mg) of 5,8-dihydroxy-1,4-naphthoquinone ligand and suspend it in 10 mL of distilled water.

[0067] (2) Dissolve 0.22 mmol (40 mg) of Zn(OAc)2 in 10 mL of distilled water and slowly add it dropwise to the above ligand suspension.

[0068] (3) The mixed solution was stirred at 85°C for 72 hours. After the reaction was completed, it was cooled to room temperature to obtain the precipitate.

[0069] (4) After the reaction was complete, the precipitate was collected by filtration and washed sequentially with N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and deionized water. Finally, it was dried in a vacuum drying oven at 80°C to obtain the Zn-DHNQ·2H2O precursor, with a yield of 51 mg and a yield of 89%. The powder could be further processed by optical microscopy to select crystalline samples (crystals up to several micrometers in length, for example...). Figure 3 The crystal sample shown can be over 4 micrometers in length.

[0070] The precursor can be structurally characterized using low-temperature rotating scanning electron diffraction (RSD) to obtain accurate structural information. Crystal structure analysis confirms that the coordination polymer crystallizes in an orthorhombic crystal system. P2 1 2 1 2 In the space group, its cell parameters are a = 11.130(2) Å, b = 5.0600(10) Å, and c = 8.1600(16) Å. Figure 4 This is a schematic diagram of the results for the precursor Zn-DHNQ·2H2O, as shown below. Figure 4 As shown, in the coordination unit of the Zn-DHNQ·2H2O precursor, Zn 2+ The two carbonyl oxygens and two deprotonated hydroxyl oxygens of the two ligands are coordinated via coordinate bonds and coordinated with two water molecules at axial positions, forming a six-coordinate octahedral configuration. This three-dimensional coordination environment disrupts the coplanarity of the ligand units, preventing the formation of an effective planar π-d conjugated system between the metal center and the organic ligands. Furthermore, adjacent molecular chains exhibit a typical herringbone arrangement.

[0071] Figure 5 The X-ray powder diffraction pattern of the Zn-DHNQ·2H2O precursor powder is shown. The powder diffraction pattern of the prepared precursor is consistent with the X-ray pattern simulated by crystal data, which confirms that the synthesized precursor is a pure Zn-DHNQ·2H2O phase with the above-mentioned octahedral non-planar coordination structure.

[0072] Comparative Example 2: Based on this invention, the preparation of the precursor Ni-DHNQ·2H2O shown in this example includes the following steps: (1) Weigh 0.2 mmol (38 mg) of 5,8-dihydroxy-1,4-naphthoquinone ligand and suspend it in 10 mL of distilled water.

[0073] (2) Dissolve 0.22 mmol (55 mg) of Ni(OAc)2·4H2O in 10 mL of distilled water and slowly add it dropwise to the above ligand suspension.

[0074] (3) The mixed solution was stirred at 85°C for 72 hours. After the reaction was completed, it was cooled to room temperature to obtain the precipitate.

[0075] (4) After the reaction was completed, the precipitate was collected by filtration and washed successively with N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and deionized water. Finally, it was dried in a vacuum drying oven at 80°C to obtain Ni-DHNQ·2H2O precursor with a yield of 52 mg and a yield of 93%.

[0076] Figure 6 The X-ray powder diffraction pattern of the Ni-DHNQ·2H2O precursor powder is shown. The X-ray powder diffraction pattern of the prepared Ni-DHNQ·2H2O precursor is consistent with that of the prepared Zn-DHNQ·2H2O precursor, indicating that the Ni-DHNQ·2H2O precursor has the same crystal structure as the Zn-DHNQ·2H2O precursor and also has high purity.

[0077] Example 2: The conjugated coordination polymer of this invention can be used in low-temperature secondary batteries. Taking the conjugated coordination polymer obtained in Example 1 as an example of its application to the positive electrode of a sodium-ion battery, the following operations can be performed: The conjugated coordination polymer, conductive additive (Ketjen black), and binder (polyvinylidene fluoride) described in Example 1 were mixed in a mass ratio of 7:2:1 and ground thoroughly. A small amount of dispersant (N-methylpyrrolidone) was added, and the mixture was ground again into a uniform slurry. The slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 12 hours. The slurry was then transferred to a glove box and cut into discs with a diameter of 14 mm to obtain the positive electrode of the secondary battery.

[0078] 2032 type button cells were used, employing the aforementioned positive electrode, metallic sodium as the negative electrode, glass fiber as the separator, and 1M NaPF6 DME solution (room temperature) or 1M NaPF6 G2 solution (-40℃) as the electrolyte. Encapsulation was carried out in a glove box with a water and oxygen content of less than 1.0 ppm, with an active material loading of approximately 1.0~2.0 mg. Constant current charge-discharge tests were conducted on a Blue Battery testing system, with a voltage range of 1.0-3.0 V vs. Na / Na. + .

[0079] Figure 7 The left figure shows the conjugated coordination polymer powder prepared in Example 1 at 100 mA g. -1 The charge / discharge curves at current densities show that, within a voltage window of 1.0–3.0 V, this conjugated coordination polymer exhibits high charge / discharge capacity (208 / 215 mAh g⁻¹). -1 This demonstrates that the conjugated coordination polymer in Implementation Case 3 exhibits excellent sodium storage performance when used as a cathode material for sodium-ion batteries.

[0080] Figure 7 The right figure shows the cycling performance of this conjugated coordination polymer assembled into a battery at different current densities. Even at current densities as high as 5.0 A g, this battery demonstrates excellent performance. -1 and 8.0 A g -1 The amplification specific capacity at high current density can reach 123 and 104 mAh g, respectively. -1 The results show that the conjugated coordination polymer in Example 1 has excellent fast charge and discharge capabilities when used as a cathode material for sodium-ion batteries, corresponding to a state of charge of 62% in 144 s and a state of charge of 52% in 90 s.

[0081] Figure 8 After assembling this conjugated coordination polymer into a battery, at 1.0 A g... -1 Cyclic performance at current densities of 1.0 A g. -1 After 5000 cycles at a current density, it still retains 145 mAh g. -1 The discharge specific capacity has a corresponding capacity retention rate of up to 86%, demonstrating excellent cycle stability.

[0082] Figure 9 The conjugated coordination polymer powder was subjected to a temperature of -40°C at 100 mA g. -1 The charge / discharge curves at current densities show that, within a voltage window of 1.0–3.0 V, this conjugated coordination polymer still exhibits high charge / discharge capacity (148 / 151 mAh g⁻¹) even at a low temperature of -40°C. -1This indicates that the conjugated coordination polymer in Implementation Case 1 has excellent low-temperature electrochemical performance when used as a cathode material for sodium-ion batteries.

[0083] Example 3: Based on the present invention, this embodiment demonstrates the application of the conjugated coordination polymer in the assembly of an all-organic pouch cell and its performance verification at extreme low temperatures.

[0084] (1) Preparation of positive electrode: The conjugated coordination polymer, conductive additive (Ketjen Black), and binder (polytetrafluoroethylene) prepared in Example 1 were ground and mixed in an agate mortar at a mass ratio of 7:2:1. After adding an appropriate amount of ethanol to adjust the viscosity, the mixture was rolled into a self-supporting film and pressed onto a 6 cm × 10 cm stainless steel mesh current collector to obtain a positive electrode sheet with an active material areal density of approximately 8 mg / cm³. -2 .

[0085] (2) Anode preparation: Sodium 4,4′-stilbene dicarboxylate (SSDC) was used as the anode active material. A self-supporting thin film anode was prepared by referring to the same dry process. The anode loading was controlled so that the N / P ratio was about 3.

[0086] (3) Negative electrode pre-sodiumization: The SSDC negative electrode prepared in step (2) is assembled with a sodium metal sheet into a half-cell, and then subjected to 0.1 Ag... -1 The battery was subjected to 5 charge-discharge cycles at a current density of 0.01 V (vs. Na / Na). + The SSDC cathode is fully discharged under a voltage of 0.5, so that it is in a fully sodium-intercalated state.

[0087] After pre-sodiumization, the above half-cells are disassembled in a glove box. The pre-treated negative electrode is taken out, gently rinsed with electrolyte to remove residual sodium salts, and then dried for later use.

[0088] (4) Assembly of soft-pack battery: In an argon glove box, the above-mentioned pre-sodium treated negative electrode, glass fiber separator (Whatman, GF / A) and positive electrode are stacked in sequence, and 1 M NaPF6 G2 electrolyte is injected. The battery is vacuum sealed in an aluminum-plastic packaging bag to obtain an organic sodium-ion soft-pack battery.

[0089] (5) Electrochemical performance testing: Room temperature performance test: First, the packaged pouch cell was placed at 25°C and subjected to a 0.1 A g test. -1 Charge-discharge tests were conducted at a current density (voltage window: 1.0-3.0 V) to determine its room temperature discharge capacity.

[0090] Low-temperature performance testing: Subsequently, the same battery was placed in a -40°C low-temperature test chamber and left to stand for 5 hours to reach thermal equilibrium, and then subjected to the same current density (0.1 A g).- ¹) Charge and discharge tests were conducted under the voltage window to determine its low-temperature discharge capacity.

[0091] Figure 10 The cycling performance of the all-organic pouch cell at different temperatures is shown. Even at an extreme low temperature of -40°C, the pouch cell retains 87% of its room temperature capacity during discharge, demonstrating excellent low-temperature capacity retention. This result verifies the wide temperature range adaptability of the conjugated coordination polymer described in this invention in practical battery devices, fully demonstrating its enormous potential in energy storage applications.

[0092] Comparative Example 3: This comparative example is used for polymer precursors prepared using organic solvents, specifically: Weigh 0.2 mmol (38 mg) of 5,8-dihydroxy-1,4-naphthoquinone ligand and dissolve it in 10 mL of DMF. Simultaneously, dissolve 0.22 mmol (55 mg) of Ni(OAc)₂·4H₂O in 10 mL of DMF. Under stirring, the DMF solution of the metal salt is slowly added dropwise to the ligand solution to obtain a mixed solution. The mixture is then stirred continuously at 85 °C for 72 hours. After the reaction is complete, cool to room temperature, filter and collect the precipitate, and wash successively with N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and deionized water. Finally, dry in a vacuum oven at 80 °C.

[0093] from Figure 11 As can be seen, the obtained product is a dark amorphous powder, and its X-ray powder diffraction pattern only shows broadened diffuse peaks without any sharp crystalline diffraction peaks. This is in stark contrast to the well-crystallized Ni-DHNQ·2H2O precursor obtained in aqueous phase in Comparative Example 2 of this invention.

[0094] This comparative example demonstrates that water, as a poor reaction solvent, is a crucial and irreplaceable condition for achieving the growth of high-quality crystal precursors. Using organic solvents such as DMF cannot guide the orderly self-assembly of molecules, resulting only in amorphous products with disordered structures. Consequently, it is impossible to obtain the conjugated coordination polymer with a planar π-d conjugated structure protected by claim 1 of this invention through subsequent heat treatment.

[0095] Comparative Example 4: This comparative example uses the aqueous precursor Zn-DHNQ·2H2O for secondary batteries, specifically: Zn-DHNQ·2H2O precursor powder prepared according to the method of Comparative Example 1 was used as the active material and mixed with conductive additive Ketjen black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1. The mixture was then coated onto an aluminum foil current collector to prepare the positive electrode. Using metallic sodium as the counter electrode, a CR2032 type button cell was assembled in an argon glove box, with a 1 M NaPF6 DME solution as the electrolyte.

[0096] Cyclic performance tests were conducted on Zn-DHNQ·2H2O-assembled batteries at different current densities within a voltage window of 1.0–3.0 V at room temperature. The test results are as follows: Figure 12 As shown, this material exhibits poor rate performance. Its discharge capacity decreases sharply with increasing current density, reaching a minimum at 5.0 A g. -1 and 8.0 A g -1 At high rates, the capacity is only 33mAh g. -1 and 22 mAh g -1 This is far lower than the performance of the dehydrated Ni-DHNQ material of this invention under the same conditions (123 mAh g⁻¹, respectively). -1 and 104 mAh g -1 ).

[0097] These results clearly demonstrate that the presence of coordinated water severely hinders rapid charge transport, resulting in extremely poor rapid charge-discharge capability of the material at room temperature. This inherent defect of slow charge transport is amplified dramatically at low temperatures, inevitably leading to a sharp decline in its low-temperature performance. This comparative example proves that directly using the aqueous Zn-DHNQ·2H2O precursor cannot achieve practically valuable electrochemical performance, nor can it guarantee the effective operation of the battery at low temperatures.

[0098] Comparative Example 5: This comparative example uses the aqueous precursor Ni-DHNQ·2H2O for secondary batteries, specifically: The Ni-DHNQ·2H2O precursor powder prepared according to the method of Comparative Example 2 was used as the active material and mixed with the conductive additive Ketjen black and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1. The mixture was then coated onto an aluminum foil current collector to prepare the positive electrode. Using metallic sodium as the counter electrode, a CR2032 type button cell was assembled in an argon glove box, with a 1 M NaPF6 DME solution as the electrolyte.

[0099] The cycle performance of the Ni-DHNQ·2H2O assembled battery was tested at room temperature within a voltage window of 1.0–3.0 V. The test results are as follows: Figure 13 As shown, although the material at 0.1 A g -1It exhibits an initial discharge capacity of approximately 184 mAh g⁻¹ at a given current density, but its cycling stability is extremely poor, with rapid capacity decay; after 300 cycles, the capacity retention is only about 39%. In stark contrast, the dehydrated Ni-DHNQ of this invention exhibits a capacity of 1.0 A g⁻¹ at a given current density. -1 After 5000 cycles under high current, the capacity retention rate is still as high as 86%. This severe capacity decay is caused by side reactions triggered by coordination water in the material.

[0100] This comparative example demonstrates that directly using the aqueous Ni-DHNQ·2H2O precursor will lead to rapid degradation of battery performance due to its inherent instability, failing to meet the requirements for long cycle life. This highlights the criticality and indispensability of the heat treatment step for removing coordination water in this invention.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments given to fully illustrate this invention, and their scope of protection is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on this invention are all within the scope of protection of this invention.

Claims

1. A highly conductive conjugated coordination polymer, characterized in that, The polymer has a planar π-d conjugated structure and does not contain coordinated water; the polymer has a general structure of M-DHNQ, wherein M is a transition metal ion, and DHNQ is a deprotonated 5,8-dihydroxy-1,4-naphthoquinone ligand; the structure of the polymer is shown as formula 1: , Formula 1.

2. The high conductive conjugated coordination polymer of claim 1, wherein, The transition metal ion is selected from one or more of Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ ; preferably, the transition metal ion is Ni 2+ .

3. A method of producing a high-conductivity conjugated coordination polymer as claimed in any one of claims 1-2, characterized by, The method comprises the following steps: (1) mixing an aqueous solution of a transition metal salt with a solution of a 5,8-dihydroxy-1,4-naphthoquinone ligand to obtain a precursor M-DHNQ having coordinated water molecules by a hydrothermal synthesis method; (2) performing heat treatment on the precursor M-DHNQ having coordinated water molecules to remove the coordinated water molecules.

4. The method of claim 3, wherein the high conductive conjugated coordination polymer is prepared by the reaction of a transition metal salt and a ligand in a solvent. In step (1), the aqueous solution of the transition metal salt is added dropwise into the solution of the 5,8-dihydroxy-1,4-naphthoquinone ligand to obtain a mixed solution; and then the mixed solution is heated to allow the transition metal ion to coordinate with the deprotonated 5,8-dihydroxy-1,4-naphthoquinone and water molecules to obtain the precursor M-DHNQ having coordinated water molecules.

5. The method of claim 3, wherein the high conductive conjugated coordination polymer is prepared by the reaction of a transition metal salt and a ligand in a solvent. In step (1), the molar ratio of the transition metal salt to the 5,8-dihydroxy-1,4-naphthoquinone ligand is 1-2; the concentration of the solution of the transition metal salt is 0.02-2 mol / L; the solvent in the solution of the 5,8-dihydroxy-1,4-naphthoquinone ligand is selected from one or more of water, ethanol, N,N-dimethylformamide or dimethyl sulfoxide.

6. The method for preparing the highly conductive conjugated coordination polymer according to claim 3, characterized in that, In step (1), the heating temperature in the hydrothermal synthesis method is 60-120℃, and the heating time is 24-72 h.

7. The method for preparing the highly conductive conjugated coordination polymer according to claim 3, characterized in that, The heat treatment is performed in a vacuum or an inert atmosphere, and the heat treatment is performed at a temperature of 130-200℃ for 12-24 h.

8. A positive electrode of a secondary battery, characterized by comprising: The method comprises: dispersing the high-conductivity conjugated coordination polymer, the conductive additive and the binder in a solvent and applying them on a current collector to obtain a positive electrode of a secondary battery after drying.

9. A secondary battery characterized by comprising: The secondary battery comprises the positive electrode of claim 8; and the secondary battery is a lithium ion battery, a sodium ion battery, a potassium ion battery or a dual-ion battery.

10. The secondary battery according to claim 9, characterized by The capacity retention rate of the battery at -40℃ is not less than 80%.

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