Lithium iron phosphate-containing electrode material for lithium ion battery and preparation method of lithium iron phosphate-containing electrode material

Abstract

The invention relates to the technical field of electrode materials, in particular to a lithium iron phosphate-containing electrode material for a lithium ion battery and a preparation method of the lithium iron phosphate-containing electrode material. The electrode material comprises the following raw materials: a lithium iron phosphate material, acetylene black, polyvinylidene fluoride and N-methyl pyrrolidone. Polypyrrole or poly (9-vinylcarbazole) is modified and then complexed with the copper salt, so that the conductivity of the composite aerogel can be remarkably improved; the composite aerogel is prepared from a polypyrrole complex and / or a poly (9-vinylcarbazole) complex and carboxymethyl cellulose and / or sodium polyacrylate, so that the cycling stability of the lithium ion battery is improved; lithium iron phosphate is synthesized in the cavity of the composite aerogel in situ, so that the transmission distance of lithium ions is shortened, and the diffusion rate of the lithium ions is remarkably increased; and the nitrogen-copper co-doped carbon composite coating layer constructed on the surface of the lithium iron phosphate is utilized, so that the conductivity of the material is greatly improved, and the durability of the structure of the material is enhanced.

Description

Technical Field

[0001] This application relates to the technical field of electrode materials, and particularly relates to an electrode material for a lithium-ion battery containing lithium iron phosphate and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in various electronic products and power drive systems due to their high energy density, long cycle life and other characteristics. However, traditional lithium-ion battery electrode materials have problems such as low charge and discharge efficiency and poor cycle stability, especially performing poorly under high power output and extreme environments. Currently, the mainstream electrode materials for lithium-ion batteries mainly include graphite, lithium cobaltate, lithium manganate, lithium nickel cobalt manganate and lithium nickel cobalt aluminate, as well as lithium iron phosphate (LiFePO4) which has received much attention in recent years.

[0003] With the rapid expansion of the electric vehicle and energy storage markets, the demand for batteries with high energy density, fast charge and discharge capabilities and good cycle stability is becoming increasingly strong. Although LiFePO4 has received attention due to its good safety and low price, its low electronic and ionic conductivities limit the overall performance of lithium-ion batteries, especially the prominent problem of capacity decay under high-rate charge and discharge. Summary of the Invention

[0004] In order to solve the problem of capacity decay of lithium iron phosphate under high-rate charge and discharge, this application provides an electrode material for a lithium-ion battery containing lithium iron phosphate. The composite aerogel prepared from the polypyrrole complex and / or poly(9-vinylcarbazole) complex and carboxymethyl cellulose and / or sodium polyacrylate helps to prevent the aerogel from collapsing or deforming in the process of charge and discharge, thereby improving the cycle stability of the lithium-ion battery.

[0005] In a first aspect, this application provides a preparation method for an electrode material for a lithium-ion battery containing lithium iron phosphate, adopting the following technical solution: A preparation method for an electrode material for a lithium-ion battery containing lithium iron phosphate, comprising the following steps: Add 70-90 parts of lithium iron phosphate material, 15-25 parts of acetylene black and 10-20 parts of polyvinylidene fluoride into N-methylpyrrolidone solvent, stir evenly to form a paste, and obtain the electrode material; The preparation method of the lithium iron phosphate material comprises the following steps: Premixing: Dissolve the iron source, phosphorus source and lithium source in deionized water, after uniform mixing, adjust the pH value to 7-8 with ammonia water to obtain a premixed solution; Mixing: Ultrasonically disperse the composite aerogel in deionized water to form a dispersion liquid, then add the premixed solution, and ultrasonically disperse to obtain a mixed liquid; Reaction heating: Perform hydrothermal reaction on the mixed solution. After the reaction, wash the product and then dry it under vacuum to obtain the lithium iron phosphate precursor. Heat the lithium iron phosphate precursor again to obtain the lithium iron phosphate material. The preparation method of the composite aerogel comprises the following steps: Place carboxymethyl cellulose and / or sodium polyacrylate in deionized water, stir evenly, add polypyrrole complex and / or poly(9-vinylcarbazole) complex, raise the temperature and stir to collect the product, and subject the product to freeze-drying treatment to obtain the composite aerogel. The preparation method of the polypyrrole complex or poly(9-vinylcarbazole) complex comprises the following steps: Modification: Ultrasonically disperse polypyrrole or poly(9-vinylcarbazole) in N-methylpyrrolidone, add citric acid and a basic catalyst, mix evenly, raise the temperature and stir, and perform rotary evaporation to obtain modified polypyrrole or modified poly(9-vinylcarbazole). Complexation: After adding an ethanol aqueous solution to the modified polypyrrole and / or modified poly(9-vinylcarbazole) and mixing evenly, add a copper salt, heat and mix, and discharge after cooling to obtain a polypyrrole complex or a poly(9-vinylcarbazole) complex.

[0006] By adopting the above technical scheme, by ultrasonically dispersing polypyrrole and / or poly(9-vinylcarbazole) in N-methylpyrrolidone and adding citric acid and a basic catalyst for modification, the conductivity and stability of the polymer are improved. Complex the modified polypyrrole and / or poly(9-vinylcarbazole) with a copper salt to form a complex with a special structure. The polypyrrole complex and / or poly(9-vinylcarbazole) complex can further improve the conductivity and stability of the electrode material, and at the same time increase the active sites of the electrode material, which is beneficial to the rapid transmission and reaction of lithium ions.

[0007] Functional groups (such as carboxyl groups, hydroxyl groups, etc.) on the molecular chains of carboxymethyl cellulose and / or sodium polyacrylate interact with functional groups (such as nitrogen atoms, aromatic rings, etc.) in the polypyrrole complex and / or poly(9-vinylcarbazole) complex, such as hydrogen bonds, van der Waals forces or π-π stacking, etc. These interactions help to "anchor" the polypyrrole complex and / or poly(9-vinylcarbazole) complex on the polymer network to form a stable composite. As the solvent evaporates or the temperature decreases, the polymer solution gradually concentrates to form a three-dimensional network structure. The polypyrrole complex and / or poly(9-vinylcarbazole) complex are wrapped in this network to form a composite aerogel.

[0008] As conductive polymers, polypyrrole complexes and / or poly(9-vinylcarbazole) complexes can significantly improve the conductivity of composite aerogels. This is beneficial to the transport of electrons in the aerogel, thereby improving the charge-discharge performance of lithium-ion batteries. As polymer matrices, carboxymethyl cellulose and / or sodium polyacrylate can enhance the mechanical strength and stability of the aerogel. This helps prevent the structural collapse or deformation of the aerogel during charge and discharge, thus improving the cycle stability of lithium-ion batteries.

[0009] By in-situ synthesizing lithium iron phosphate in the cavities of the composite aerogel, the unique pore structure of the aerogel is used to control the particle size distribution of lithium iron phosphate, shorten the lithium-ion transport distance, and significantly improve the diffusion rate of lithium ions. More importantly, through the subsequent sintering process, a stable nitrogen-copper co-doped carbon composite coating layer is constructed on the surface of lithium iron phosphate, greatly improving the conductivity of the material and enhancing the durability of its structure.

[0010] In this application, polypyrrole or poly(9-vinylcarbazole) is modified and then complexed with copper salts to obtain polypyrrole complexes or poly(9-vinylcarbazole) complexes, which can significantly improve the conductivity of composite aerogels; preparing composite aerogels from polypyrrole complexes and / or poly(9-vinylcarbazole) complexes and carboxymethyl cellulose and / or sodium polyacrylate helps prevent the structural collapse or deformation of the aerogel during charge and discharge, thus improving the cycle stability of lithium-ion batteries; by in-situ synthesizing lithium iron phosphate in the cavities of the composite aerogel, the lithium-ion transport distance is shortened, and the diffusion rate of lithium ions is significantly improved; the use of a nitrogen-copper co-doped carbon composite coating layer constructed on the surface of lithium iron phosphate greatly improves the conductivity of the material and enhances the durability of its structure.

[0011] Preferably, in the preparation method of the polypyrrole complex or poly(9-vinylcarbazole) complex, in the modification step, the temperature range of the heating and stirring is 50 - 60 °C, and the time is 4 - 8 h.

[0012] By adopting the above technical solution, within the temperature range of 50 - 60 °C, the modification reaction of polypyrrole or poly(9-vinylcarbazole) can proceed at a relatively moderate rate. If the temperature is too low, the reaction rate will slow down, resulting in incomplete modification, which affects the subsequent complexation effect and the performance of the final product. If the temperature is too high, side reactions may be triggered, such as the degradation of the polymer, which will all damage the structure of the polymer and reduce its conductivity and stability.

[0013] Within the time range of 4 - 8 hours, the modification reaction can proceed sufficiently to ensure that the functional groups on the polymer chain are fully modified, providing sufficient active sites for the subsequent complexation reaction. If the time is too short, the reaction may be incomplete, affecting the performance of the final product. If the time is too long, over-reactions may occur, such as the cross-linking or degradation of the polymer, which will also reduce the performance of the product.

[0014] Preferably, in the preparation method of the polypyrrole complex or poly(9-vinylcarbazole) complex, in the complexation step, the temperature range for the heating and mixing is 50 - 70°C, and the time is 12 - 24 h.

[0015] By adopting the above technical solution, within the temperature range of 50 - 70°C, the complexation reaction between the modified polypyrrole or poly(9-vinylcarbazole) and the copper salt can proceed at a relatively moderate rate. If the temperature is too low, the reaction rate will slow down, resulting in incomplete complexation and affecting the performance of the final product. If the temperature is too high, side reactions may be accelerated, such as the degradation of the polymer or the decomposition of the copper salt, which will destroy the structure of the complex and reduce its conductivity and stability.

[0016] Within the time range of 12 - 24 hours, the complexation reaction can proceed sufficiently to ensure that the functional groups on the modified polymer chain are fully combined with the copper salt to form a stable complex structure. If the time is too short, the reaction may be incomplete, resulting in poor performance of the complex. If the time is too long, over-reaction may occur, such as excessive deposition of the copper salt, which will affect the performance and stability of the complex.

[0017] Preferably, in the preparation method of the composite aerogel, a mixture of carboxymethyl cellulose and sodium polyacrylate is placed in deionized water, and the mass ratio between carboxymethyl cellulose and sodium polyacrylate is 1:1 - 2.

[0018] By adopting the above technical solution, both carboxymethyl cellulose and sodium polyacrylate are water-soluble polymers, and they can dissolve in water to form a colloidal solution. When they are added simultaneously, interactions such as hydrogen bonds and van der Waals forces will occur, and these interactions contribute to the formation of a more stable and uniform network structure. This interaction can also enhance the mechanical strength and stability of the aerogel, preventing its structural collapse or deformation during charge and discharge. Adding carboxymethyl cellulose and sodium polyacrylate simultaneously can form a more complex and uniform porous structure. This porous structure is beneficial to the penetration of the electrolyte and the transport of lithium ions, thereby improving the performance of the lithium-ion battery.

[0019] When their mass ratio is within the range of 1:1 - 2, a better balance state is achieved for the interaction between carboxymethyl cellulose and sodium polyacrylate. They can form a tight and stable network structure, which can resist the destruction of external stress and improve the mechanical strength and stability of the aerogel.

[0020] Preferably, in the preparation method of the composite aerogel, a mixture of the polypyrrole complex and the poly(9-vinylcarbazole) complex is added, and the mass ratio between the polypyrrole complex and the poly(9-vinylcarbazole) complex is 1:1 - 1.5.

[0021] By adopting the above technical solutions, the polypyrrole complex has excellent electrochemical redox reversibility, which means that it can maintain high efficiency and stability during the charge and discharge processes. When it is added simultaneously with the poly(9-vinylcarbazole) complex, the two can form a synergistic effect to jointly improve the electrochemical performance of the aerogel. The poly(9-vinylcarbazole) complex has high conductivity, which helps the rapid transmission of electrons in the aerogel. After combining with the polypyrrole complex, the electron transport path can be further optimized, and the charge and discharge rate and energy density of the battery can be increased.

[0022] The polypyrrole complex also has high conductivity and high tensile strength. These properties enable it to form a tough network structure in the aerogel, improving the mechanical strength and stability of the aerogel. The poly(9-vinylcarbazole) complex has high thermal stability and antioxidant properties, which help the aerogel maintain stable performance in high-temperature or oxidative environments. Adding these two polymers simultaneously can further enhance the heat resistance and antioxidant properties of the aerogel.

[0023] When the mass ratio of the polypyrrole complex to the poly(9-vinylcarbazole) complex is in the range of 1:1 - 1.5, the electrochemical performance and physical properties can be balanced. If the proportion of the polypyrrole complex is too high, it may lead to insufficient mechanical strength of the aerogel; conversely, if the proportion of the poly(9-vinylcarbazole) complex is too high, the electrochemical performance may be reduced. Within this ratio range, a balance between the two can be ensured. Within this mass ratio range, the polypyrrole complex and the poly(9-vinylcarbazole) complex can form a more compact and uniform network structure. This network structure not only facilitates the transmission of electrons and the diffusion of lithium ions but also improves the mechanical strength and stability of the aerogel.

[0024] Preferably, in the preparation method of the composite aerogel, the temperature range of the heating and stirring is 45 - 55°C, and the time is 5 - 7 h.

[0025] By adopting the above technical solutions, within the temperature range of 45 - 55°C, heating and stirring can ensure that the movement between reactant molecules is accelerated, thus promoting the reaction. This temperature range is neither too high to cause the reaction to be too violent nor too low to result in an overly slow reaction rate. If the temperature is too high, adverse reactions such as the decomposition of reactants and the degradation of polymers may occur, affecting the structure and performance of the aerogel. If the temperature is too low, the reaction rate will be significantly reduced, leading to incomplete reactions and affecting the preparation efficiency and final performance of the aerogel.

[0026] Within the time range of 5 - 7 hours, heating with stirring can ensure sufficient contact and reaction time between reactant molecules, thus forming a stable aerogel structure. If the time is too short, the reaction may not be complete, resulting in an unstable aerogel structure and poor performance. If the time is too long, it may lead to overreaction, such as the degradation of polymers, which will also affect the performance of the aerogel.

[0027] Preferably, in the preparation method of the lithium iron phosphate material, in the step of reaction heating, the temperature range of the hydrothermal reaction is 170 - 180 °C, and the time is 5 - 10 h.

[0028] By adopting the above technical solution, within the temperature range of 170 - 180 °C, the movement between reactant molecules is accelerated, which is conducive to the progress of the reaction. This temperature range can ensure a moderate reaction rate, neither too violent nor too slow, thus being conducive to the production of high-quality lithium iron phosphate materials. If the temperature is too high, it may lead to too fast a reaction rate, generating too much heat and gas, making the reaction system unstable and even causing danger. In addition, too high a temperature may also cause the decomposition or phase change of the lithium iron phosphate material, affecting its performance. If the temperature is too low, the reaction rate will be significantly reduced, resulting in an incomplete reaction and affecting the performance of the lithium iron phosphate material.

[0029] An appropriate temperature is conducive to the formation of a stable crystal structure of the lithium iron phosphate material. Within the temperature range of 170 - 180 °C, the crystal structure of lithium iron phosphate can be effectively controlled, thus ensuring its good electrochemical performance. Too high or too low a temperature may have an adverse effect on the crystal structure of lithium iron phosphate, resulting in a decline in the performance of the material.

[0030] Within the time range of 5 - 10 hours, there is sufficient contact and reaction time between reactant molecules, which can ensure the full progress of the reaction and the production of high-quality lithium iron phosphate materials. If the time is too short, the reaction may not be complete, resulting in unreacted reactants remaining in the lithium iron phosphate material or generating other impurities, affecting its performance. If the time is too long, it may lead to overreaction, such as the aggregation or grain growth of the lithium iron phosphate material, which will also affect its performance.

[0031] Preferably, in the preparation method of the lithium iron phosphate material, in the step of reaction heating, the temperature range for reheating the lithium iron phosphate precursor is 650 - 850 °C, and the time is 1 - 3 h.

[0032] By adopting the above technical solution, within the temperature range of 650 - 850 °C, the lithium iron phosphate precursor can undergo solid-phase reaction to form the lithium iron phosphate phase. This temperature range ensures that the reaction has sufficient driving force to proceed, while avoiding side reactions caused by excessively high temperatures. If the temperature is too low, the reaction rate will decrease significantly, resulting in incomplete reaction and affecting the purity and performance of lithium iron phosphate. Specifically, if the temperature is lower than 650 °C, the crystal structure of lithium iron phosphate may not be fully formed, leading to poor electrochemical performance of the material. If the temperature is too high, it may cause decomposition, phase change or excessive sintering of the lithium iron phosphate material, all of which will damage the crystal structure of the material and reduce its electrochemical performance.

[0033] An appropriate temperature is beneficial to the formation of a stable crystal structure of the lithium iron phosphate material, thus ensuring its good electrochemical performance. Within the temperature range of 650 - 850 °C, a lithium iron phosphate material with high crystallinity, high purity and excellent electrochemical performance can be obtained. Too high or too low temperature may have an adverse effect on the crystal structure of lithium iron phosphate, resulting in a decrease in the cycle stability, energy density and rate performance of the material.

[0034] Within the time range of 1 - 3 hours, the lithium iron phosphate precursor has sufficient reaction time to undergo solid-phase reaction to form the lithium iron phosphate phase. This time range ensures the sufficiency of the reaction, while avoiding overreaction caused by too long time. If the time is too short, the reaction may be incomplete, resulting in unreacted precursors remaining in the lithium iron phosphate material or the formation of other impurities, affecting its performance. If the time is too long, it may cause agglomeration, grain growth or excessive sintering of the lithium iron phosphate material, all of which will reduce the electrochemical performance of the material. In addition, too long time will also increase production costs and energy consumption.

[0035] Preferably, the electrode material for lithium-ion batteries containing lithium iron phosphate further comprises adding 1 - 3 parts of NiO and / or MnO₂, together with the lithium iron phosphate material, acetylene black and polyvinylidene fluoride, into the N-methylpyrrolidone solvent.

[0036] By adopting the above technical solution, NiO and MnO₂ as additives can be embedded into the crystal structure of lithium iron phosphate to form a stable solid solution or composite structure. This structure can effectively prevent lattice distortion or structure collapse of lithium iron phosphate during charge and discharge processes, thereby improving the structural stability of the material. During the charge and discharge processes of lithium-ion batteries, the active substances in the electrode material may fall off due to volume expansion or contraction, resulting in a decrease in battery performance. The addition of NiO and MnO₂ can enhance the binding force between the electrode material and the current collector, effectively inhibit the shedding of active substances, and thus improve the cycle stability of the battery.

[0037] Although NiO and MnO2 are not conductive materials themselves, the network structure formed by them together with components such as lithium iron phosphate, acetylene black, and polyvinylidene fluoride can optimize the transport paths of electrons and lithium ions. This optimization helps improve the conductivity of the electrode material, thereby enhancing the charge-discharge performance and energy density of the battery. When NiO and MnO2 are added simultaneously, a synergistic effect may occur between them, further enhancing the stability of the electrode material. This synergistic effect may stem from their combined stabilizing effect on the crystal structure of lithium iron phosphate and their combined improvement of the conductivity and cycle stability of the electrode material.

[0038] In a second aspect, the present application provides an electrode material for a lithium-ion battery containing lithium iron phosphate, adopting the following technical solution: An electrode material for a lithium-ion battery containing lithium iron phosphate, which is prepared by the preparation method of the above-mentioned electrode material for a lithium-ion battery containing lithium iron phosphate.

[0039] In summary, the present application has the following beneficial effects: 1. Since the present application modifies polypyrrole or poly(9-vinylcarbazole), and then complexes with a copper salt to obtain a polypyrrole complex or a poly(9-vinylcarbazole) complex, it can significantly improve the conductivity of the composite aerogel; preparing a composite aerogel from the polypyrrole complex and / or the poly(9-vinylcarbazole) complex and carboxymethyl cellulose and / or sodium polyacrylate helps prevent the aerogel from collapsing or deforming during charge and discharge, thereby improving the cycle stability of the lithium-ion battery; in-situ synthesizing lithium iron phosphate in the cavities of the composite aerogel shortens the lithium-ion transport distance and significantly enhances the diffusion rate of lithium ions; using the nitrogen-copper co-doped carbon composite coating layer constructed on the surface of lithium iron phosphate greatly improves the conductivity of the material and enhances the durability of its structure; 2. By using NiO and MnO2 as additives in the present application, they can be embedded into the crystal structure of lithium iron phosphate to form a stable solid solution or composite structure; the addition of NiO and MnO2 can enhance the bonding force between the electrode material and the current collector, effectively inhibit the shedding of the active material, thereby improving the cycle stability of the battery; NiO and MnO2 can optimize the transport paths of electrons and lithium ions. Specific Embodiments

[0040] The raw materials in the present application include the following parts: Polypyrrole: A commercially available product with a CAS number of 30604-81-0; Poly(9-vinylcarbazole): A commercially available product with a CAS number of 25067-59-8; N-methylpyrrolidone: A commercially available product with a CAS number of 872-50-4; Citric acid: A commercially available product with a CAS number of 77-92-9; Alkaline catalyst: Sodium hydroxide, potassium hydroxide, etc. can be used. In this application, a commercially available sodium hydroxide product with a CAS number of 1310-73-2 is used; Ethanol: A commercially available product with a CAS number of 64-17-5 is used; Copper salt: Copper acetate, copper sulfate pentahydrate, copper nitrate, etc. can be used. In this application, a commercially available copper acetate product with a CAS number of 6046-93-1 is used; Carboxymethyl cellulose: A commercially available product with a CAS number of 9000-11-7 is used; Sodium polyacrylate: A commercially available product with a CAS number of 9003-04-7 is used; Iron source: Ferrous chloride, iron nitrate, ferrous oxalate, etc. can be used. In this application, a commercially available ferrous chloride product with a CAS number of 7758-94-3 is used; Phosphorus source: Sodium dihydrogen phosphate, ammonium phosphate, triethyl phosphate, etc. can be used. In this application, a commercially available sodium dihydrogen phosphate product with a CAS number of 7558-80-7 is used; Lithium source: Lithium carbonate, lithium nitrate, lithium hydroxide, etc. can be used. In this application, a commercially available lithium carbonate product with a CAS number of 554-13-2 is used; Ammonia water: A commercially available product with a CAS number of 1336-21-6 is used; Acetylene black: A commercially available product with a CAS number of 1333-86-4 is used; Polyvinylidene fluoride: A commercially available product with a CAS number of 24937-79-9 is used; Deionized water: A commercially available product with a CAS number of 7732-18-5 is used; NiO: A commercially available product with a CAS number of 1313-99-1 is used; MnO2: A commercially available product with a CAS number of 1313-13-9 is used; The present application will be further described in detail below with reference to examples and comparative examples.

[0041] Example 1 The preparation method of the polypyrrole complex or poly(9-vinylcarbazole) complex includes the following steps: Modification: 6 g of polypyrrole or 6 g of poly(9-vinylcarbazole) is ultrasonically dispersed in 18 g of N-methylpyrrolidone, 1.8 g of citric acid and 0.1 g of sodium hydroxide are added, and after mixing, the temperature is raised and stirred at 55 °C for 6 h, and rotary evaporation is carried out to obtain modified polypyrrole or modified poly(9-vinylcarbazole); Complexation: After adding 50 wt% aqueous ethanol solution to 6 g of modified polypyrrole or 6 g of modified poly(9-vinylcarbazole) and mixing evenly, 3 g of copper acetate was added and then heated and mixed at a temperature of 65 °C, stirred at 200 rpm for 18 h. After the material was naturally cooled, it was discharged to obtain polypyrrole complex or poly(9-vinylcarbazole) complex.

[0042] The preparation method of the composite aerogel includes the following steps: 15 g of the mixture of carboxymethyl cellulose and sodium polyacrylate was placed in deionized water and stirred evenly. The mass ratio of carboxymethyl cellulose to sodium polyacrylate was 1:1.5. 15 g of the mixture of polypyrrole complex and poly(9-vinylcarbazole) complex was added, and the mass ratio of polypyrrole complex to poly(9-vinylcarbazole) complex was 1:1.3. The temperature was raised and stirred to collect the product at 50 °C for 6 h. The product was freeze-dried, and the treatment conditions were to store at -20 °C for 6 h first, and then freeze-dry at -50 °C for 18 h to obtain the composite aerogel.

[0043] The preparation method of the lithium iron phosphate material includes the following steps: Premixing: 0.3 g of ferrous chloride, 0.04 g of sodium dihydrogen phosphate, and 0.008 g of lithium carbonate were dissolved in deionized water. After being evenly mixed, the pH value was adjusted to 7.5 (pH within the range of 7 - 8 was acceptable) with ammonia water to obtain a premixed solution; Mixing: 2 g of the composite aerogel was ultrasonically dispersed in deionized water to form a dispersion, and then the premixed solution was added, and ultrasonically dispersed at 70 KHz for 3 h to obtain a mixed solution; Reaction heating: The mixed solution was subjected to hydrothermal reaction under nitrogen protection at a temperature of 175 °C, stirred at 600 rpm for 8 h. The reaction product was washed and then vacuum dried to obtain a lithium iron phosphate precursor; the lithium iron phosphate precursor was heated again at a temperature of 750 °C for 2 h to obtain the lithium iron phosphate material.

[0044] The preparation method of the electrode material for a lithium ion battery containing lithium iron phosphate includes the following steps: 80 g of the lithium iron phosphate material, 20 g of acetylene black, and 15 g of polyvinylidene fluoride were added to 350 g of N-methylpyrrolidone solvent, stirred evenly at a rotation speed of 80 rpm, and adjusted to a paste to obtain the electrode material.

[0045] Examples 2 - 3 Based on the preparation method of Example 1, in Examples 2 - 3, the contents of each component of the electrode material were adjusted, and the specific adjustments are shown in Table 1.

[0046] Comparative Example 1 80 g of commercially available lithium iron phosphate, 20 g of acetylene black, and 15 g of polyvinylidene fluoride were added to 350 g of N-methylpyrrolidone solvent, stirred evenly at a rotation speed of 80 rpm, and adjusted to a paste to obtain the electrode material. Note: The commercially available lithium iron phosphate was purchased from Hubei Xinyuhong Biomedical Technology Co., Ltd.

[0047] Table 1 Component contents of the electrode materials in Examples 1-3 and performance test table with Comparative Example 1

[0048] Performance detection test Examples 1-3 and Comparative Example 1 were subjected to the following performance detections, and the detection results are shown in Table 1.

[0049] The prepared electrode material was evenly coated on the surface of aluminum foil, placed in a vacuum drying oven at 100 °C for 10 h, and then the aluminum foil was made into a positive electrode sheet with a diameter of 10 mm. A metal lithium sheet was used as the counter electrode, and the electrolyte was 1 mol / L LiPF6. The positive electrode sheet, electrolyte, PP separator, and metal lithium sheet were assembled into a conventional lithium battery using a CR2032-type housing in a glove box protected by pure argon. After standing in a constant temperature oven at 25 °C for 24 h, a CH1600D-type electrochemical workstation was used to perform cyclic voltammetry testing on the positive electrode of the assembled lithium battery, and the capacity retention rate was calculated.

[0050] Referring to Table 1, by comparing Examples 1-3 and Comparative Example 1, it can be seen that the prepared lithium batteries have good rate performance and cycle stability; the lithium battery prepared in Comparative Example 1 has a lower discharge specific capacity at a 10C rate. After 50 cycles at a 10C rate, the capacity retention rate is less than 90%. Compared with the examples, the rate performance and cycle stability of the lithium battery are both poor. This shows that in-situ synthesis of lithium iron phosphate in the cavities of the composite aerogel shortens the lithium ion transmission distance and significantly improves the lithium ion diffusion rate. By constructing a nitrogen-copper co-doped carbon composite coating layer on the surface of lithium iron phosphate, the conductivity of the material is greatly improved and the durability of its structure is enhanced.

[0051] After comprehensive comparison, the performance of Example 1 is the best, and Example 1 is preferred.

[0052] Examples 4-7 Based on the preparation method of Example 1, for the preparation methods of polypyrrole complex or poly(9-vinylcarbazole) complex, in the modification step, the temperature and time of heating and stirring were adjusted, and the specific adjustments are shown in Table 2.

[0053] The electrode materials of Examples 4-7 were subjected to the above performance detections, and the test results are shown in Table 2.

[0054] Table 2 Temperature and time of heating and stirring in Example 1 and Examples 4-7, and performance test table

[0055] Referring to Table 2, by comparing Example 1 and Examples 4-7, it can be seen that when the temperature of heating and stirring continuously increases, the discharge specific capacity and capacity retention rate at 10C rate show a trend of first increasing and then decreasing. This may be because when the temperature of heating and stirring continuously increases, the reaction rate increases, the modification becomes gradually sufficient, improving the complexation effect in the subsequent process and the rate performance and cycle stability of the final product. When exceeding a certain range, side reactions may be triggered. For example, the degradation of the polymer will damage the structure of the polymer, reducing its conductivity and stability.

[0056] When the time of heating and stirring continuously increases, the discharge specific capacity and capacity retention rate at 10C rate show a trend of first increasing and then decreasing. This may be because when the time of heating and stirring continuously increases, the modification reaction can proceed sufficiently, ensuring that the functional groups on the polymer chain are fully modified, providing sufficient active sites for the subsequent complexation reaction, improving the complexation effect in the subsequent process and the rate performance and cycle stability of the final product. When exceeding a certain range, overreaction may occur. For example, the degradation of the polymer will damage the structure of the polymer, reducing the rate performance and cycle stability of the final product.

[0057] Examples 8-11 Based on the preparation method of Example 1, for the preparation methods of polypyrrole complex or poly(9-vinylcarbazole) complex in Examples 8-11, in the complexation step, the temperature and time of heating and mixing are adjusted, and the specific adjustments are shown in Table 3.

[0058] The electrode materials of Examples 8-11 are subjected to the above performance tests, and the test results are shown in Table 3.

[0059] Table 3 Temperature and time of heating and mixing in Example 1 and Examples 8-11, and performance test table

[0060] Referring to Table 3, by comparing Example 1 and Examples 8-11, it can be seen that when the temperature of heating and mixing continuously increases, the discharge specific capacity and capacity retention rate at 10C rate show a trend of first increasing and then decreasing. This may be because when the temperature of heating and mixing continuously increases, the reaction rate increases, the complexation reaction becomes gradually sufficient, improving the rate performance and cycle stability of the final product. When exceeding a certain range, side reactions may be triggered. For example, the degradation of the polymer or the decomposition of copper salt will damage the structure of the polymer, reducing its conductivity and stability.

[0061] When the heating and mixing time continuously increases, the discharge specific capacity and capacity retention rate at the 10C rate show a trend of first increasing and then decreasing. This may be because when the heating and mixing time continuously increases, the complexation reaction can proceed sufficiently, ensuring that the functional groups on the modified polymer chain are fully combined with the copper salt to form a stable complex structure, improving the subsequent complexation effect and the rate performance and cycle stability of the final product. When it exceeds a certain range, it may lead to overreaction, such as excessive deposition of the copper salt, which affects the performance and stability of the complex, reducing the rate performance and cycle stability of the final product.

[0062] Examples 12 - 15 Based on the preparation method of Example 1, in the preparation method of the composite aerogel, the mass ratio of carboxymethyl cellulose and sodium polyacrylate was adjusted, and the specific adjustment is shown in Table 4.

[0063] Based on the preparation method of Example 1, in the preparation method of the composite aerogel, 15 g of the mixture of carboxymethyl cellulose and sodium polyacrylate was replaced with 15 g of carboxymethyl cellulose, and other conditions remained unchanged.

[0064] Based on the preparation method of Example 1, in the preparation method of the composite aerogel, 15 g of the mixture of carboxymethyl cellulose and sodium polyacrylate was replaced with 15 g of sodium polyacrylate, and other conditions remained unchanged.

[0065] The electrode materials of Examples 12 - 15 were subjected to the above performance tests, and the test results are shown in Table 4 respectively.

[0066] Table 4 Mass ratio and performance test table of carboxymethyl cellulose and sodium polyacrylate in Example 1 and Examples 12 - 15

[0067] Referring to Table 4, by comparing Example 1 with Examples 12 - 15, it can be seen that when carboxymethyl cellulose and sodium polyacrylate are added simultaneously, the rate performance and cycle stability of the final product are better than when the two substances are added separately. This may be because when they are added simultaneously, interactions such as hydrogen bonds and van der Waals forces will occur. These interactions help to form a more stable and uniform network structure. This interaction can also enhance the mechanical strength and stability of the aerogel, preventing its structural collapse or deformation during charge and discharge. Adding carboxymethyl cellulose and sodium polyacrylate simultaneously can form a more complex and uniform porous structure. This porous structure is beneficial to the penetration of the electrolyte and the transport of lithium ions, thus improving the performance of lithium-ion batteries.

[0068] When their mass ratio is within the range of 1:1 - 2, the interaction between carboxymethyl cellulose and sodium polyacrylate reaches a better balance state. They can form a tight and stable network structure, which can resist the destruction of external stress and improve the mechanical strength and stability of the aerogel.

[0069] Examples 16 - 19 Based on the preparation method of Example 1, in the preparation method of the composite aerogel, the mass ratio of the polypyrrole complex and the poly(9-vinylcarbazole) complex was adjusted, and the specific adjustment is shown in Table 5.

[0070] Based on the preparation method of Example 1, in the preparation method of the composite aerogel, 15 g of the mixture of the polypyrrole complex and the poly(9-vinylcarbazole) complex was replaced with 15 g of the polypyrrole complex, and other conditions remained unchanged.

[0071] Based on the preparation method of Example 1, in the preparation method of the composite aerogel, 15 g of the mixture of the polypyrrole complex and the poly(9-vinylcarbazole) complex was replaced with 15 g of the poly(9-vinylcarbazole) complex, and other conditions remained unchanged.

[0072] The electrode materials of Examples 16 - 19 were subjected to the above performance tests, and the test results are shown in Table 5 respectively.

[0073] Table 5 Mass ratio and performance test table of the polypyrrole complex and the poly(9-vinylcarbazole) complex in Example 1 and Examples 16 - 19

[0074] Referring to Table 5, by comparing Example 1 and Examples 16 - 19, it can be seen that when the polypyrrole complex and the poly(9-vinylcarbazole) complex are added simultaneously, the rate performance and cycle stability of the final product are better than those when the two substances are added separately. This may be because when they are added simultaneously, the two can form a synergistic effect to jointly improve the electrochemical performance of the aerogel, further optimize the electron transport path, and improve the charge and discharge rate and energy density of the battery.

[0075] When the mass ratio of the polypyrrole complex to the poly(9-vinylcarbazole) complex is in the range of 1:1 - 1.5, the electrochemical properties and physical properties can be balanced. If the proportion of the polypyrrole complex is too high, it may lead to insufficient mechanical strength of the aerogel; conversely, if the proportion of the poly(9-vinylcarbazole) complex is too high, the electrochemical properties may be reduced. Within this ratio range, a balance between the two can be ensured. Within this mass ratio range, the polypyrrole complex and the poly(9-vinylcarbazole) complex can form a more compact and uniform network structure. This network structure not only facilitates electron transfer and lithium-ion diffusion but also improves the mechanical strength and stability of the aerogel.

[0076] Examples 20 - 23 Based on the preparation method of Example 1, in the preparation method of the composite aerogel, the temperature and time of heating with stirring were adjusted. The specific adjustments are shown in Table 6.

[0077] The electrode materials of Examples 20 - 23 were subjected to the above performance tests, and the test results are shown in Table 6.

[0078] Table 6 Temperature and time of heating with stirring and performance test table of Example 1 and Examples 20 - 23

[0079] Referring to Table 6, by comparing Example 1 and Examples 20 - 23, it can be seen that when the temperature of heating with stirring continuously increases, the discharge specific capacity and capacity retention rate at a 10C rate show a trend of first increasing and then decreasing. This may be because when the temperature of heating with stirring continuously increases, the reaction rate increases, promoting the reaction and improving the rate performance and cycle stability of the final product; when it exceeds a certain range, it may lead to adverse reactions such as decomposition of reactants and degradation of polymers, thus affecting the structure and performance of the aerogel and reducing its conductivity and stability.

[0080] When the time of heating with stirring continuously increases, the discharge specific capacity and capacity retention rate at a 10C rate show a trend of first increasing and then decreasing. This may be because when the time of heating with stirring continuously increases, it ensures sufficient contact and reaction time between reactant molecules, thus forming a stable aerogel structure and improving the rate performance and cycle stability of the final product; when it exceeds a certain range, it may lead to overreaction, such as degradation of polymers, which will destroy the polymer structure and reduce the rate performance and cycle stability of the final product.

[0081] Examples 24 - 27 Based on the preparation method of Example 1, in the preparation method of the lithium iron phosphate material, in the step of reaction heating, the temperature and time of the hydrothermal reaction were adjusted. The specific adjustments are shown in Table 7.

[0082] The electrode materials of Examples 24-27 were subjected to the above performance tests, and the test results are shown in Table 7.

[0083] Table 7 Temperature and time of the hydrothermal reaction and performance test table of Example 1 and Examples 24-27

[0084] Referring to Table 7, by comparing Example 1 and Examples 24-27, it can be seen that when the temperature of the hydrothermal reaction continuously increases, the discharge specific capacity and capacity retention rate at the 10C rate show a trend of first increasing and then decreasing. This may be because when the temperature of the hydrothermal reaction continuously increases, the reaction rate increases, promoting the progress of the reaction, improving the rate performance and cycle stability of the final product; when exceeding a certain range, it may cause the reaction rate to be too fast, generating too much heat and gas, making the reaction system unstable, and reducing its conductivity and stability.

[0085] When the time of the hydrothermal reaction continuously increases, the discharge specific capacity and capacity retention rate at the 10C rate show a trend of first increasing and then decreasing. This may be because when the time of the hydrothermal reaction continuously increases, it can ensure the full progress of the reaction, generate high-quality lithium iron phosphate materials, and improve the rate performance and cycle stability of the final product; when exceeding a certain range, it may lead to overreaction, such as the agglomeration or grain growth of the lithium iron phosphate material, which will also affect its performance and reduce the rate performance and cycle stability of the final product.

[0086] Examples 28-31 Based on the preparation method of Example 1, in the preparation method of the lithium iron phosphate material of Examples 28-31, in the step of reaction heating, the temperature and time of reheating were adjusted, and the specific adjustments are shown in Table 8.

[0087] The electrode materials of Examples 28-31 were subjected to the above performance tests, and the test results are shown in Table 8.

[0088] Table 8 Temperature and time of reheating and performance test table of Example 1 and Examples 28-31

[0089] Referring to Table 8, by comparing Example 1 and Examples 28-31, it can be seen that when the temperature of reheating continuously increases, the discharge specific capacity and capacity retention rate at the 10C rate show a trend of first increasing and then decreasing. This may be because when the temperature of reheating continuously increases, the reaction rate increases, promoting the progress of the reaction, improving the rate performance and cycle stability of the final product; when exceeding a certain range, it may cause the lithium iron phosphate material to decompose, undergo a phase change or sinter excessively, all of which will damage the crystal structure of the material and reduce its conductivity and stability.

[0090] When the reheating time continuously increases, the discharge specific capacity and capacity retention rate at the 10C rate show a trend of first increasing and then decreasing. This may be because when the reheating time continuously increases, it can ensure the full progress of the reaction, generate a high-quality lithium iron phosphate phase, and improve the rate performance and cycle stability of the final product. When it exceeds a certain range, it may lead to overreaction, such as the agglomeration or grain growth of the lithium iron phosphate material, which will also affect its performance and reduce the rate performance and cycle stability of the final product.

[0091] Examples 32 - 35 Based on the preparation method of Example 1, in Example 32, 3 g of NiO, 80 g of lithium iron phosphate material, 20 g of acetylene black, and 15 g of polyvinylidene fluoride were added to the N-methylpyrrolidone solvent, and the other conditions remained unchanged.

[0092] Based on the preparation method of Example 1, in Example 33, 1 g of MnO2, 80 g of lithium iron phosphate material, 20 g of acetylene black, and 15 g of polyvinylidene fluoride were added to the N-methylpyrrolidone solvent, and the other conditions remained unchanged.

[0093] Based on the preparation method of Example 1, in Example 34, a mixture composed of 1 g of NiO and 1 g of MnO2 was added to 80 g of lithium iron phosphate material, 20 g of acetylene black, and 15 g of polyvinylidene fluoride in the N-methylpyrrolidone solvent, and the other conditions remained unchanged.

[0094] Based on the preparation method of Example 1, in Example 35, a mixture composed of 1.5 g of NiO and 1.5 g of MnO2 was added to 80 g of lithium iron phosphate material, 20 g of acetylene black, and 15 g of polyvinylidene fluoride in the N-methylpyrrolidone solvent, and the other conditions remained unchanged.

[0095] The electrode materials of Examples 32 - 35 were subjected to the above performance tests, and the test results are shown in Table 9.

[0096] Table 9 Additive types, addition amounts, and performance test table of Example 1 and Examples 32 - 35

[0097] Referring to Table 9, by comparing Example 1 with Examples 32 - 35, it can be seen that when NiO and / or MnO₂ are added together with lithium iron phosphate material, acetylene black, and polyvinylidene fluoride into N-methylpyrrolidone solvent to prepare the electrode material, the discharge specific capacity and capacity retention rate at 10C rate can be further improved. This may be because NiO and MnO₂, as additives, can be embedded into the crystal structure of lithium iron phosphate to form a stable solid solution or composite structure. This structure can effectively prevent lattice distortion or structural collapse of lithium iron phosphate during charge and discharge processes, thereby improving the structural stability of the material.

[0098] NiO and MnO₂ themselves are not conductive materials, but the network structure formed by them together with components such as lithium iron phosphate, acetylene black, and polyvinylidene fluoride can optimize the transmission paths of electrons and lithium ions. This optimization helps to improve the conductivity of the electrode material, and further enhance the charge and discharge performance and energy density of the battery.

[0099] When NiO and MnO₂ are added simultaneously, it is superior to adding them separately. This may be due to the synergistic effect between the two, which further enhances the stability of the electrode material. This synergistic effect may stem from their common stabilizing effect on the crystal structure of lithium iron phosphate, as well as their common improvement of the conductivity and cycle stability of the electrode material.

[0100] Examples 36 - 39 Based on the preparation method of Example 1, in the preparation method of the composite aerogel of Example 36, 15 g of carboxymethyl cellulose was placed in deionized water and stirred evenly, and then 15 g of polypyrrole complex was added, with other conditions remaining unchanged.

[0101] Based on the preparation method of Example 1, in the preparation method of the composite aerogel of Example 37, 15 g of carboxymethyl cellulose was placed in deionized water and stirred evenly, and then 15 g of poly(9-vinylcarbazole) complex was added, with other conditions remaining unchanged.

[0102] Based on the preparation method of Example 1, in the preparation method of the composite aerogel of Example 38, 15 g of sodium polyacrylate was placed in deionized water and stirred evenly, and then 15 g of polypyrrole complex was added, with other conditions remaining unchanged.

[0103] Based on the preparation method of Example 1, in the preparation method of the composite aerogel of Example 39, 15 g of sodium polyacrylate was placed in deionized water and stirred evenly, and then 15 g of poly(9-vinylcarbazole) complex was added, with other conditions remaining unchanged.

[0104] The electrode materials of Examples 36 - 39 were subjected to the above performance tests, and the test results are shown in Table 10.

[0105] Table 10 Performance Test Table of Example 1 and Examples 36 - 39

[0106] Referring to Table 10, by comparing Example 1 and Examples 36 - 39, it can be seen that the preparation of the composite aerogel using a mixture of carboxymethyl cellulose and sodium polyacrylate, as well as a mixture of polypyrrole complex and poly(9 - vinylcarbazole) complex is superior to the combination of two substances out of the four. It can give full play to the synergistic effect of carboxymethyl cellulose and sodium polyacrylate, as well as the synergistic effect of the mixture of polypyrrole complex and poly(9 - vinylcarbazole) complex, thereby improving the rate performance and cycle stability of the final product.

[0107] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A preparation method of an electrode material for a lithium-ion battery containing lithium iron phosphate, characterized in that, It includes the following steps: Add 70 - 90 parts of lithium iron phosphate material, 15 - 25 parts of acetylene black, and 10 - 20 parts of polyvinylidene fluoride into 350 parts of N - methylpyrrolidone solvent, stir evenly to form a paste, and obtain the electrode material; The preparation method of the lithium iron phosphate material includes the following steps: Premixing: Dissolve the iron source, phosphorus source, and lithium source in deionized water, after uniform mixing, adjust the pH value to 7 - 8 with ammonia water to obtain a premixed solution; Mixing: Ultrasonically disperse the composite aerogel in deionized water to form a dispersion liquid, then add the premixed solution, and ultrasonically disperse to obtain a mixed solution; Reaction heating: Carry out hydrothermal reaction on the mixed solution, wash the reaction product and then vacuum dry to obtain the lithium iron phosphate precursor; Heat the lithium iron phosphate precursor again to obtain the lithium iron phosphate material; The preparation method of the composite aerogel includes the following steps: Put carboxymethyl cellulose and / or sodium polyacrylate into deionized water, stir evenly, add polypyrrole complex and / or poly(9 - vinylcarbazole) complex, raise the temperature and stir to collect the product, and subject the product to freeze - drying treatment to obtain the composite aerogel; The preparation method of the polypyrrole complex or poly(9 - vinylcarbazole) complex includes the following steps: Modification: Ultrasonically disperse polypyrrole or poly(9 - vinylcarbazole) in N - methylpyrrolidone, add citric acid and a basic catalyst, mix evenly and then raise the temperature and stir, and rotary evaporate to obtain modified polypyrrole or modified poly(9 - vinylcarbazole); Complexation: After adding an ethanol aqueous solution to the modified polypyrrole or modified poly(9 - vinylcarbazole) and mixing evenly, add a copper salt and heat and mix, and discharge after cooling to obtain the polypyrrole complex or poly(9 - vinylcarbazole) complex.

2. The preparation method of the electrode material for lithium ion batteries containing lithium iron phosphate according to claim 1, characterized in that: In the preparation method of the polypyrrole complex or poly(9 - vinylcarbazole) complex, in the modification step, the temperature range of the temperature - raising stirring is 50 - 60°C, and the time is 4 - 8 h.

3. The preparation method of the electrode material for lithium ion batteries containing lithium iron phosphate according to claim 2, characterized in that: In the preparation method of the polypyrrole complex or poly(9 - vinylcarbazole) complex, in the complexation step, the temperature range of the heating and mixing is 50 - 70°C, and the time is 12 - 24 h.

4. The preparation method of the electrode material for lithium ion battery containing lithium iron phosphate according to claim 1, characterized in that: In the preparation method of the composite aerogel, put the mixture of carboxymethyl cellulose and sodium polyacrylate into deionized water, and the mass ratio between carboxymethyl cellulose and sodium polyacrylate is 1:1 - 2.

5. The preparation method of the electrode material for lithium ion battery containing lithium iron phosphate according to claim 1, characterized in that: In the preparation method of the composite aerogel, add the mixture of the polypyrrole complex and the poly(9 - vinylcarbazole) complex, and the mass ratio between the polypyrrole complex and the poly(9 - vinylcarbazole) complex is 1:1 - 1.

5.

6. The preparation method of the electrode material for lithium ion battery containing lithium iron phosphate according to claim 1, characterized in that: In the preparation method of the composite aerogel, the temperature range of the temperature - raising stirring is 45 - 55°C, and the time is 5 - 7 h.

7. The preparation method of the electrode material for lithium-ion batteries containing lithium iron phosphate according to claim 1, characterized in that: In the preparation method of the lithium iron phosphate material, in the reaction heating step, the temperature range of the hydrothermal reaction is 170 - 180°C, and the time is 5 - 10 h.

8. The preparation method of the electrode material for a lithium-ion battery containing lithium iron phosphate according to claim 7, characterized in that: In the preparation method of the lithium iron phosphate material, in the reaction heating step, the temperature range for reheating the lithium iron phosphate precursor is 650 - 850°C, and the time is 1 - 3 h.

9. The preparation method of the electrode material for lithium ion battery containing lithium iron phosphate according to claim 1, wherein: It also includes adding 1-3 parts of NiO and / or MnO2, together with lithium iron phosphate material, acetylene black and polyvinylidene fluoride, into N-methylpyrrolidone solvent.

10. An electrode material for a lithium-ion battery containing lithium iron phosphate, characterized in that: It is prepared by the preparation method of the lithium iron phosphate-containing electrode material for lithium-ion battery according to any one of claims 1-9.

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