Preparation and application of iron-based metal-organic assembly type lithium ion battery negative electrode material

Abstract

Iron-based metal organic assembly, its preparation method and application as negative material of lithium ion battery. The chemical formula of the iron-based metal organic assembly is {[Fe(Hpyzdc)2]·2H2O} n , wherein Hpyzdc ‑ is pyrazine-2,3-dicarboxylic acid ion; the preparation method is to add pyrazine-2,3-dicarboxylic acid and ferrous sulfate into deionized water, and then the target product is obtained after stirring. The iron-based metal organic assembly synthesized by the application can be used as the negative material of lithium ion battery and assembled into CR2032 lithium ion button cell. The synthesis method is simple, the raw material is cheap and easy to obtain, the yield is high, and the cost is low. When the iron-based metal organic assembly is directly used in the negative material of lithium ion battery, the volume expansion effect in the alloying process can be effectively alleviated, the discharge specific capacity of the complex is maintained at 1109 mAh g ‑1 after 150 cycles when the charge and discharge current density is 100 mA g ‑1 , and the complex also shows good stability and excellent electrochemical performance in the rate test.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode materials, specifically to the synthesis of a novel iron-based metal-organic assembly with good stability, a lithium-ion battery negative electrode sheet, and a method for preparing lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as recyclable energy storage devices, rely on the dynamic migration of lithium ions between the positive and negative electrodes for their core operating mechanism. During the repeated cycles of charging and discharging, lithium ions act like messengers, shuttling between the electrodes and utilizing the insertion and extraction mechanisms of the negative electrode material to achieve energy storage and supply. The choice of negative electrode material is undoubtedly a key factor determining the overall battery performance and a significant driving force for battery technology innovation. For a long time, graphite has been widely used as a negative electrode material due to its excellent stability. However, with the rapid development of technology and the increasing market demand, the pursuit of higher energy density and longer lifespan batteries has prompted the scientific community to continuously explore and experiment with new negative electrode materials. New materials such as silicon-based materials, metal oxides, and even lithium metal, with their potential for high energy density and possible safety improvements, are gradually becoming the focus of research. Although these emerging materials show promising prospects, they also face significant challenges, such as stability issues during cycling, bottlenecks in improving charge and discharge efficiency, and the need for further optimization of compatibility with electrolytes. Therefore, the research and optimization of anode materials has become a core issue in battery science, and it has immeasurable value in promoting the leapfrog development of energy storage technology. Iron-based anode materials, due to their abundant reserves, high theoretical specific capacity, and stable structural characteristics, have become strong candidates for anode materials. However, the volume changes and lithium dendrite growth they face during charging and discharging threaten battery stability and lifespan. Researchers have mitigated these problems through morphology control, elemental doping, heterostructure construction, defect engineering, and composite materials, but new challenges such as reduced active sites, interface incompatibility, and increased costs remain. Completely eliminating volume changes is still a challenge, and innovative synthesis methods and the development of economical and efficient new iron-based anode materials have become research hotspots and challenges. Metal-organic assemblies are a class of ordered structures formed by the assembly of metal ions and organic ligands through coordination bonds. In recent years, metal-organic assemblies have attracted significant attention from scientists due to their rich and varied chemical structures, simple synthesis, and low cost, and have been widely used in gas storage and separation, heterogeneous catalysis, magnetic materials, fluorescent probes, catalysis, and energy storage. In the field of energy storage, metal-organic assemblies have been used as electrode materials for lithium-ion batteries due to their abundant lithium storage active sites and structural stability. Therefore, considering both cost reduction and mitigation of the volume expansion effect of iron, it is feasible to construct metal-organic assemblies by combining metallic iron with active organic ligands. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems in the prior art and provide a simple and low-cost iron-based metal-organic assembly, which can be used as an active material in the anode of lithium-ion batteries. This strategy effectively suppresses the volume expansion effect of iron, resulting in the iron-based metal-organic assembly material exhibiting higher capacity properties and better cycle stability in the anode of lithium-ion batteries.

[0004] An iron-based metal-organic assembly, characterized by having the chemical formula {[Fe(Hpyzdc)2]·2H2O} n In the formula: Hpyzdc - It is a pyrazine-2,3-dicarboxylic acid ion; this iron-based metal-organic assembly consists of Fe 2+ Ions and organic ligands form a one-dimensional chain structure through coordination bonds, wherein the organic ligand is pyrazine-2,3-dicarboxylic acid; the one-dimensional chain structure is constructed into a three-dimensional supramolecular structure through hydrogen bonding between ligands.

[0005] A method for preparing an iron-based metal-organic assembly, characterized by using ferrous sulfate (FeSO4) as the metal salt, pyrazine-2,3-dicarboxylic acid (H2pyzdc) as the ligand, and water as the solvent, the synthesis steps are as follows:

[0006] 1) Place the mixture of ferrous sulfate (FeSO4) and pyrazine-2,3-dicarboxylic acid (H2pyzdc) in a container, add deionized water, and stir until homogeneous to obtain a mixed solution;

[0007] 2) Place the above mixture at 80℃ for 12-24 hours to obtain purplish-black crystals;

[0008] 3) Wash the obtained crystals with deionized water and anhydrous ethanol, and let them air dry naturally.

[0009] The method for preparing the iron-based metal-organic assembly is characterized in that: the molar ratio of ferrous sulfate (FeSO4) and pyrazine-2,3-dicarboxylic acid (H2pyzdc) in the mixture is 1:1; and the volume ratio of ferrous sulfate (FeSO4) to deionized water is 0.1 mmol: 6-10 mL.

[0010] 1) Weigh out the dry iron-based metal-organic assembly, Ketjen black, and polyvinylidene fluoride in a mass ratio of 7:2:1, add N-methylpyrrolidone, grind and mix evenly into a slurry, coat it on copper foil, vacuum dry it, and cut it into circular electrode sheets.

[0011] 2) Using lithium sheets as the counter electrode, Celgard 2400 membrane as the separator, and a 1 mol / L lithium hexafluorophosphate (LiPF6) ethylene carbonate (EC) / diethyl carbonate (DEC) solution with a volume ratio of 1:1 as the electrolyte, the electrode sheets obtained in the previous step are used as the negative electrode to assemble a CR2032 lithium-ion button battery.

[0012] The test was conducted at room temperature, and the voltage range during the constant current charge-discharge test was 0.01-3 V.

[0013] The test current density was 100 mA g. -1 Constant current charge-discharge performance and cycle performance at high current density of 500 mA g -1 Under normal cyclic performance;

[0014] At current densities of 100, 200, 300, 500, 1000, and 2000 mA g -1 Rate performance at that time.

[0015] A novel iron-based metal-organic assembly with a simple chemical synthesis method was successfully prepared and applied to lithium-ion battery anode materials. This material effectively mitigates the volume expansion effect during charge and discharge, achieving optimal performance at a charge / discharge current density of 100 mA g / g. -1 After 150 cycles, the specific capacity of the metal-organic assembly remained at 1109 mAh g⁻¹. -1 It also exhibits good stability and excellent electrochemical performance during rate testing, which is conducive to enhancing and improving the performance of iron-based electrode materials and is expected to advance the research progress of iron-based metal-organic assemblies. Attached Figure Description

[0016] Figure 1 It is {[Fe(Hpyzdc)2]·2H2O} n A one-dimensional structural diagram of a crystal.

[0017] Figure 2 It is {[Fe(Hpyzdc)2]·2H2O} n A diagram of the three-dimensional supramolecular structure of a crystal.

[0018] Figure 3 It is {[Fe(Hpyzdc)2]·2H2O} n X-ray powder diffraction pattern of the crystal.

[0019] Figure 4 It is {[Fe(Hpyzdc)2]·2H2O} n Crystals as a negative electrode material for lithium-ion batteries at 100 mA g -1 The constant current charge and discharge diagram.

[0020] Figure 5 It is {[Fe(Hpyzdc)2]·2H2O} n Crystals as a negative electrode material for lithium-ion batteries at 100 mA g -1 The charge / discharge cycle diagram.

[0021] Figure 6 It is {[Fe(Hpyzdc)2]·2H2O} n When crystals are used as anode materials for lithium-ion batteries, at 500 mA g -1 The charge / discharge cycle diagram.

[0022] Figure 7 It is {[Fe(Hpyzdc)2]·2H2O} n When crystals are used as anode materials for lithium-ion batteries, at 2000 mA g -1 The charge / discharge cycle diagram.

[0023] Figure 8 It is {[Fe(Hpyzdc)2]·2H2O} n Rate performance diagram of crystals as negative electrode materials for lithium-ion batteries. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Example

[0025] 1) Weigh out a mixture of ferrous sulfate (76 mg, 0.5 mmol) and pyrazine-2,3-dicarboxylic acid (84 mg, 0.5 mmol) and place it in a glass bottle. Then add 40 mL of deionized water and stir until homogeneous to obtain a mixed solution.

[0026] 2) Place the above-mentioned well-mixed solution in a 90 ℃ oven for 12 hours to obtain purplish-black crystals;

[0027] 3) Wash the obtained crystals with deionized water and anhydrous ethanol, and let them air dry to obtain iron-based metal-organic assemblies. Example

[0028] 1) Weigh out a mixture of ferrous sulfate (76 mg, 0.5 mmol) and pyrazine-2,3-dicarboxylic acid (84 mg, 0.5 mmol) and place it in a glass bottle. Then add 40 mL of deionized water and stir until homogeneous to obtain a mixed solution.

[0029] 2) Place the above-mentioned well-mixed solution in an 80 ℃ oven for 16 hours to obtain purplish-black crystals;

[0030] 3) Wash the obtained crystals with deionized water and anhydrous ethanol, and let them air dry to obtain iron-based metal-organic assemblies. Example

[0031] 1) Weigh out a mixture of ferrous sulfate (76 mg, 0.5 mmol) and pyrazine-2,3-dicarboxylic acid (84 mg, 0.5 mmol) and place it in a glass bottle. Then add 40 mL of deionized water and stir until homogeneous to obtain a mixed solution.

[0032] 2) Place the above-mentioned well-mixed solution in a 75 ℃ oven for 24 hours to obtain purplish-black crystals;

[0033] 3) Wash the obtained crystals with deionized water and anhydrous ethanol, and let them air dry to obtain iron-based metal-organic assemblies.

[0034] The crystals obtained in the above embodiments were placed on a glass slide. Suitable crystals were selected under a microscope and tested on a Supernova X-ray single-crystal diffractometer. Mo-Kα rays (λ=0.71073 Å) monochromated by a graphite monochromator were used as the incident radiation source. Diffraction points were collected using an ω-φ scanning method. Their coordinates and anisotropy parameters were corrected using the least squares method. The positions of hydrogen atoms were obtained theoretically by adding hydrogen. All calculations were performed using SHELXL-97 and the SHELXL-97 software package. Crystal structure analysis was performed using Olex-2 software, combined with elemental analysis and thermogravimetric analysis. The final structural formula of the metal-organic assembly was determined to be {[Fe(Hpyzdc)2]·2H2O}. n H2pyzdc is pyrazine-2,3-dicarboxylic acid. This organometallic assembly belongs to the monoclinic crystal system, space group I 1 2 / a 1, with cell parameters a=14.9219(19) Å, b=8.4923(7) Å, c=13.0852(17) Å, α=γ=90°, β=118.145(17) °, and a cell volume of 1462.1(4) Å. 3 Z=4, Dc=1.936 g / cm³ 3 This iron-based metal-organic assembly consists of Fe 2+ It forms a three-dimensional supramolecular structure with an organic ligand via coordination bonds, wherein the organic ligand is pyrazine-2,3-dicarboxylic acid; Fe 2+ Through Hpyzdc - Bridges are formed to create a polymer structure with an infinite number of chains; then, hydrogen bonds between the chains are used to construct a three-dimensional supramolecular structure. The structural diagram of the metal-organic assembly was drawn using Diamond software. Figure 1 It is {[Fe(Hpyzdc)2]·2H2O} nA one-dimensional structure diagram of a crystal. Figure 2 It is {[Fe(Hpyzdc)2]·2H2O} n A three-dimensional supramolecular structure diagram of a crystal.

[0035] A large quantity of iron-based metal-organic assemblies was collected, yielding purplish-black crystals. To further characterize the purity of the synthesized iron-based metal-organic assemblies, we analyzed their X-ray diffraction patterns. Please refer to [link to relevant documentation]. Figure 3 As can be seen from the figure, the diffraction patterns of the synthesized samples are consistent with the X-ray diffraction patterns obtained by simulation through crystal data, indicating that the synthesized iron-based metal-organic assemblies have high purity.

[0036] This invention also provides a method for preparing lithium-ion battery electrode sheets using iron-based metal-organic assemblies as negative electrode materials. The specific steps are as follows: The iron-based metal-organic assembly crystals collected in the above examples are dried in a vacuum oven at 80°C for 8 hours. Iron-based metal-organic assemblies, Ketjen Black, and polyvinylidene fluoride are weighed out in a mass ratio of 7:2:1, and N-methylpyrrolidone is added. The mixture is then ground and mixed evenly into a slurry, coated onto copper foil, dried under vacuum at 80°C for 12 hours, and cut into circular electrode sheets with a diameter of 12 mm.

[0037] A CR2032 lithium-ion button battery was assembled using a lithium sheet as the counter electrode, a Celgard 2400 membrane as the separator, and a 1 mol / L lithium hexafluorophosphate (LiPF6) solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio 1:1) as the electrolyte.

[0038] Constant current charge-discharge tests were performed on the Blue Electric test system (25°C), with the voltage range set to 0.01-3.0 V. Please refer to [link / reference]. Figure 4 It is a constant current charge-discharge diagram of a lithium-ion battery prepared from the lithium battery negative electrode material of the present invention, at a current density of 100 mA g. ‒1 At that time, the initial discharge capacity was 2875 mAh g. ‒1 The first week's charging capacity is 998 mAh g. -1 It has a low charge / discharge platform. Please refer to [link / reference]. Figure 5 At a current density of 100 mA g ‒1 After 150 charge-discharge cycles, its specific capacity remains stable at 1109 mAh g⁻¹. ‒1 Around [value missing], the coulombic efficiency is relatively high, exhibiting good electrochemical performance. Please refer to [link missing]. Figure 6 At 500 mAg ‒1 At that time, after 500 cycles, the capacity is 548 mAh g. ‒1 Please refer to the left and right sides. Figure 7, at 2000 mA g ‒1 At that time, after 1500 cycles, the capacity was 192 mAh g. ‒1 The left and right sides remain stable, reflecting the principle of {[Fe(Hpyzdc)2]·2H2O}. n It exhibits good cyclic stability and has promising application prospects.

[0039] Please see Figure 8 It is {[Fe(Hpyzdc)2]·2H2O} n Rate performance diagram when used as a negative electrode material in lithium-ion batteries. At current densities of 100, 200, 300, 500, 1000, and 2000 mA g. -1 After 10 cycles, the capacities were approximately 682, 556, 537, 440, 334, and 221 mAh g, respectively. -1 When the current density returns to 100 mA g -1 When the battery capacity recovers to its initial value, it indicates that the metal-organic assembly has good cycle stability and rate performance under high current, showing great potential as a negative electrode material for lithium-ion batteries.

[0040] The above are preferred embodiments and do not constitute a limitation on the implementation of the patent content. Any substantially equivalent substitutions, process optimizations, changes, modifications, or mergers of conditions are all within the scope of patent protection. The use of a small number of necessary terms in the description and explanation does not constitute a limitation on the invention.

Claims

1. An iron-based metal-organic assembly, characterized in that, The chemical formula is {[Fe(Hpyzdc)2]·2H2O} n In the formula: Hpyzdc - It is a pyrazine-2,3-dicarboxylic acid ion; this iron-based metal-organic assembly consists of Fe 2+ Ions and organic ligands form a one-dimensional chain structure through coordination bonds, wherein the organic ligand is pyrazine-2,3-dicarboxylic acid; the one-dimensional chain structure is constructed into a three-dimensional supramolecular structure through hydrogen bonding between ligands.

2. The iron-based metal-organic assembly according to claim 1, characterized in that: This metal-organic assembly belongs to the monoclinic crystal system, space group I 1 2 / a 1, with cell parameters a=14.9219(19) Å, b=8.4923(7) Å, c=13.0852(17) Å, α=γ=90°, β=118.145(17) °, and a cell volume of 1462.1(4) Å. 3 Z=4, Dc=1.936 g / cm³ 3 .

3. A method for preparing the iron-based metal-organic assembly according to claim 1, characterized in that: The synthesis steps are as follows: using ferrous sulfate (FeSO4) as the metal salt, pyrazine-2,3-dicarboxylic acid (H2pyzdc) as the ligand, and water as the solvent: 1) Place the mixture of ferrous sulfate (FeSO4) and pyrazine-2,3-dicarboxylic acid (H2pyzdc) in a container, add deionized water, and stir until homogeneous to obtain a mixed solution; 2) Place the above mixture at 80℃ for 12-24 hours to obtain purplish-black crystals; 3) Wash the obtained crystals with deionized water and anhydrous ethanol, and let them air dry naturally.

4. The method for preparing the iron-based metal-organic assembly according to claim 3, characterized in that: The molar ratio of ferrous sulfate (FeSO4) to pyrazine-2,3-dicarboxylic acid (H2pyzdc) in the mixture is 1:1; the volume ratio of ferrous sulfate (FeSO4) to deionized water is 0.1 mmol: 6-10 mL.

5. The application of the iron-based metal-organic assembly of claim 1 as a negative electrode material for lithium-ion batteries, characterized in that: The method for directly using iron-based metal-organic assemblies as anode materials for lithium-ion batteries is as follows: 1) Weigh out the dry iron-based metal-organic assembly, Ketjen black, and polyvinylidene fluoride in a mass ratio of 7:2:1, add N-methylpyrrolidone, grind and mix evenly into a slurry, coat it on copper foil, vacuum dry it, and cut it into circular electrode sheets. 2) Using lithium sheets as the counter electrode, Celgard 2400 membrane as the separator, and a 1 mol / L lithium hexafluorophosphate (LiPF6) ethylene carbonate (EC) / diethyl carbonate (DEC) solution with a volume ratio of 1:1 as the electrolyte, the electrode sheets obtained in the previous step are used as the negative electrode to assemble a CR2032 lithium-ion button battery.

6. The application of the iron-based metal-organic assembly according to claim 4 as a negative electrode material for lithium-ion batteries, characterized in that: The assembled lithium-ion button batteries were tested on the Blue Battery Testing System. The test was conducted at room temperature, and the voltage range during the constant current charge-discharge test was 0.01-3 V. The test current density was 100 mA g. -1 Constant current charge-discharge performance and cycle performance at high current densities of 500 and 2000 mA g -1 Under normal cyclic performance; At current densities of 100, 200, 300, 500, 1000, and 2000 mA g -1 Rate performance at that time.

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