A composite cathode material for lithium ion batteries and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a composite positive electrode material for a lithium ion battery and a preparation method thereof, the lithium ion battery composite positive electrode material comprises the following raw materials: a lithium iron manganese phosphate composite material, a conductive material, polyvinylidene fluoride and N-methyl-2-pyrrolidone; the lithium iron manganese phosphate composite material is prepared; on one hand, the active sites are increased, the transmission resistance of lithium ions is reduced, the diffusion rate and the transmission rate of the lithium ions are improved, the conductivity, the rate performance and the specific capacity of the lithium ion battery composite positive electrode material are effectively improved; on the other hand, the lithium iron manganese phosphate particle size can be dispersed and controlled; the structure and the volume can be effectively prevented from being changed and destroyed in the charging and discharging process; the corrosion by electrolyte and other chemical substances and the probability of occurrence of a side reaction are reduced; and the cycle stability of the lithium ion battery composite positive electrode material is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and specifically to a composite cathode material for lithium-ion batteries and its preparation method. Background Technology

[0002] With social development and technological progress, the energy crisis has become increasingly severe. Finding low-carbon, environmentally friendly, and economical new energy sources has become a focus of attention and research. Lithium-ion batteries, as a new type of energy, have advantages such as being pollution-free, highly safe, and having a long cycle life, and are widely used in transportation, electronic equipment, and medical fields. Cathode materials, as one of the core components of lithium-ion batteries, are crucial to their performance. Currently, common lithium-ion battery cathode materials include lithium manganese oxide, nickel-cobalt-manganese oxide layered materials, and lithium iron phosphate. Lithium iron phosphate cathode materials are environmentally friendly, have less impact on the environment, and exhibit good stability and a long cycle life. As a mainstream lithium-ion battery cathode material, lithium manganese iron phosphate is an optimized version of lithium iron phosphate, offering higher energy density and voltage platform compared to lithium iron phosphate. However, lithium manganese iron phosphate also has shortcomings. Its low conductivity and ion mobility result in poor cycle performance, rate performance, and capacity retention, severely limiting the development and application of lithium-ion batteries. Therefore, modification of lithium manganese iron phosphate cathode materials is essential.

[0003] Patent CN109650367A discloses a method for preparing lithium manganese iron phosphate. The method involves mixing elemental iron, manganese dioxide, and an aqueous solution of phosphoric acid to obtain a mixture. This mixture is then ball-milled to obtain ferromanganese hydrogen phosphate. Ferromanganese hydrogen phosphate, lithium carbonate, and glucose are mixed and milled until the product particle size (D25) is 0.2 μm-1 μm. The resulting product is then dried and calcined to obtain lithium manganese iron phosphate. This method produces lithium manganese iron phosphate, which, as a cathode material for lithium-ion batteries, improves the discharge specific capacity. The method is simple in equipment and process, requires minimal environmental pressure, and is easy to industrialize. However, the conductivity, cycle performance, and rate performance of the prepared lithium manganese iron phosphate material have not been effectively improved. Therefore, this invention provides a composite cathode material for lithium-ion batteries with excellent rate performance, cycle stability, and discharge specific capacity, showing broad application prospects. Summary of the Invention

[0004] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a composite cathode material for lithium-ion batteries and a method for preparing the same.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 70-85 parts of lithium manganese iron phosphate composite material, 10-15 parts of conductive material, and 10-15 parts of polyvinylidene fluoride.

[0007] Furthermore, the conductive material is any one of carbon black, carbon nanotubes, or acetylene black.

[0008] Furthermore, the preparation method of the lithium manganese iron phosphate composite material includes the following steps:

[0009] Step A: Add phosphorus source, manganese source, iron source, lithium source and complexing agent to deionized water, stir at 100-200 r / min for 40-60 min to obtain a mixture;

[0010] Step B: Add the modified composite aerogel to the mixture and ultrasonically disperse it at a frequency of 80-100KHz for 1-3 hours at a temperature of 50-70℃. Transfer the system to a reaction vessel, raise the temperature to 200-220℃, stir and react for 8-10 hours, centrifuge and wash, and vacuum dry to obtain the precursor.

[0011] Step C: The precursor is placed in a crucible, protected by argon gas, and sintered at high temperature in a vacuum tube furnace. After cooling to room temperature, the lithium manganese iron phosphate composite material is obtained.

[0012] Further, in step A, the phosphorus source is any one of phosphoric acid, sodium dihydrogen phosphate, or diammonium hydrogen phosphate; the manganese source is any one of manganese acetate, manganese chloride, or manganese nitrate; the iron source is any one of ferrous acetate, ferric nitrate, ferric chloride, or ferrous nitrate; the lithium source is any one of lithium hydroxide, lithium acetate, lithium carbonate, or lithium chloride; and the complexing agent is any one of citric acid, tartaric acid, malic acid, or succinic acid.

[0013] Further, in step B, the preparation method of the modified composite aerogel includes the following steps:

[0014] Step T1: Add sodium alginate to deionized water and stir thoroughly. Add sodium periodate solution and stir the reaction in the dark for 1-2 hours. Then add ethylene glycol to stop the reaction, separate the product, precipitate, freeze dry, and obtain aldehyde-modified sodium alginate.

[0015] Step T2: Add aldehyde-modified sodium alginate to N,N-dimethylformamide, mix well, add L-methionine alcohol and catalyst, raise the temperature to 45-55℃, and react for 2-4 hours to obtain modified sodium alginate.

[0016] Step T3: Add modified sodium alginate to deionized water to prepare a solution. Slowly add the solution to anhydrous ethanol, stir for 8-10 hours, let stand for 30-50 minutes, and freeze dry to obtain modified composite aerogel.

[0017] By adopting the above technical solution, the hydroxyl groups in sodium alginate are oxidized to aldehyde groups using sodium periodate solution to obtain aldehyde-modified sodium alginate. Under the action of a catalyst, the aldehyde group in the aldehyde-modified sodium alginate structure can undergo a Schiff base reaction with the amino group in the L-methionine alcohol structure to obtain modified sodium alginate. After freeze-drying, modified composite aerogel is obtained.

[0018] Furthermore, in step T1, the concentration of the sodium periodate solution is 10-20%.

[0019] Furthermore, in step T2, the catalyst is sodium carbonate or triethylamine.

[0020] Furthermore, in step C, the high-temperature sintering is performed at a heating rate of 4-6℃ / min, with the temperature rising to 600-800℃ for 1-3 hours.

[0021] A method for preparing a composite cathode material for lithium-ion batteries includes the following steps:

[0022] Step 1: Weigh out each ingredient by weight and set aside.

[0023] Step 2: Add the lithium manganese iron phosphate composite material, conductive material and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place it on a magnetic stirrer and stir at 300-600 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

[0024] The beneficial effects of this invention are:

[0025] A lithium manganese iron phosphate composite material was prepared by hydrothermal reaction and sintering of a mixture of phosphorus, manganese, iron, and lithium sources with a modified composite aerogel. On one hand, the modified composite aerogel forms nitrogen-sulfur doped carbon, altering the structure of the carbon material and increasing active sites, thereby improving electronic conductivity. Simultaneously, it reduces lithium-ion transport resistance, increases the diffusion and transport rates of lithium ions, and enhances the rate performance of the lithium-ion battery composite cathode material, ensuring stable electrochemical performance even at high rates. On the other hand, using the modified composite aerogel as a carbon substrate can disperse and control the particle size of lithium manganese iron phosphate, inhibiting excessive growth and forming an interconnected conductive network, significantly improving conductivity and electrochemical performance. Furthermore, it effectively prevents changes in material structure and volume during charging and discharging, avoiding structural damage. This results in good stability for the lithium manganese iron phosphate composite material, reducing the probability of corrosion by electrolytes and other chemicals and side reactions, improving the cycle stability of the lithium-ion battery composite cathode material, and extending battery life.

[0026] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The infrared spectrum of the modified composite aerogel prepared in this invention is shown. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The preparation method of the lithium manganese iron phosphate composite material in the following examples is shown below:

[0031] I. Preparation of Modified Composite Aerogels

[0032] Step T1: Add 3.2g of sodium alginate to deionized water and stir thoroughly. Add 16g of 20% sodium periodate solution and stir for 2 hours in the dark. Then add 3g of ethylene glycol to stop the reaction. Separate the product, precipitate, freeze dry, and obtain aldehyde-modified sodium alginate.

[0033] Step T2: Add 3g of aldehyde-modified sodium alginate to N,N-dimethylformamide, mix well, then add 2g of L-methionine and 0.5g of triethylamine, raise the temperature to 50℃, and react for 3 hours to obtain modified sodium alginate.

[0034] Step T3: Add 2.8g of modified sodium alginate to deionized water to prepare a 1wt% solution. Slowly add the solution to anhydrous ethanol, stir for 10h, let stand for 40min, and freeze dry to obtain the modified composite aerogel.

[0035] Samples were prepared using the potassium bromide pellet method, and the modified composite aerogel was analyzed using Fourier transform infrared spectroscopy. Figure 1 As shown in the figure, analysis reveals that 3422cm -1 An absorption peak of hydroxyl group OH appeared at 1678 cm⁻¹. -1 An absorption peak for the C=O group in the carboxyl group appeared at 1618 cm⁻¹. -1 A Schiff base C=N absorption peak appeared at 1175 cm⁻¹. -1A CSC absorption peak appeared at 1086 cm⁻¹. -1 An absorption peak for COC appeared at that location.

[0036] II. Preparation of Lithium Manganese Iron Phosphate Composite Materials

[0037] Step A: Add 1.22g sodium dihydrogen phosphate, 0.77g manganese chloride, 0.71g ferrous acetate, 0.38g lithium carbonate and 2g citric acid to deionized water, stir at 200r / min for 50min to obtain a mixture;

[0038] Step B: Add 3g of modified composite aerogel to the mixture, and ultrasonically disperse it at 90KHz for 2h at 65℃. Transfer the system to a reaction vessel, raise the temperature to 220℃, stir and react for 8h, centrifuge and wash, and vacuum dry to obtain the precursor.

[0039] Step C: The precursor is placed in a crucible, protected by argon gas, and sintered at high temperature in a vacuum tube furnace at a heating rate of 5℃ / min, with the temperature rising to 700℃ for 2 hours. After cooling to room temperature, the lithium manganese iron phosphate composite material is obtained.

[0040] The lithium manganese iron phosphate composite material and commercially available lithium manganese iron phosphate material (purchased from Shenzhen Liyou New Energy Technology Co., Ltd., particle size distribution D90) were ground and sieved using agate, and then resistivity was tested using a powder resistivity meter. The results are as follows:

[0041] Table 1 - Resistivity Test Results

[0042] Resistivity (Ω·cm) Lithium manganese iron phosphate composite material 0.95 Commercially available lithium manganese iron phosphate materials 2.13

[0043] As shown in Table 1, the lithium manganese iron phosphate composite material prepared by this invention has low resistivity and excellent conductivity, while commercially available lithium manganese iron phosphate materials have high resistivity and poor conductivity. This is because commercially available lithium manganese iron phosphate materials are unmodified, have few active sites, high lithium-ion diffusion resistance, and low lithium-ion diffusion and transport rates.

[0044] Example 1

[0045] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 70g lithium manganese iron phosphate composite material, 10g conductive carbon nanotubes, and 10g polyvinylidene fluoride; the preparation method of this lithium-ion battery composite cathode material includes the following steps:

[0046] Step 1: Weigh out each ingredient by weight and set aside.

[0047] Step 2: Add lithium manganese iron phosphate composite material, conductive carbon nanotubes and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place on a magnetic stirrer and stir at 300 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

[0048] Example 2

[0049] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 75g lithium manganese iron phosphate composite material, 12g conductive carbon nanotubes, and 12g polyvinylidene fluoride; the preparation method of this lithium-ion battery composite cathode material includes the following steps:

[0050] Step 1: Weigh out each ingredient by weight and set aside.

[0051] Step 2: Add lithium manganese iron phosphate composite material, conductive carbon nanotubes and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place on a magnetic stirrer and stir at 400 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

[0052] Example 3

[0053] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 80g of lithium manganese iron phosphate composite material, 14g of conductive carbon nanotubes, and 13g of polyvinylidene fluoride; the preparation method of this lithium-ion battery composite cathode material includes the following steps:

[0054] Step 1: Weigh out each ingredient by weight and set aside.

[0055] Step 2: Add lithium manganese iron phosphate composite material, conductive carbon nanotubes and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place on a magnetic stirrer and stir at 500 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

[0056] Example 4

[0057] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 85g lithium manganese iron phosphate composite material, 15g conductive carbon nanotubes, and 15g polyvinylidene fluoride; the preparation method of this lithium-ion battery composite cathode material includes the following steps:

[0058] Step 1: Weigh out each ingredient by weight and set aside.

[0059] Step 2: Add lithium manganese iron phosphate composite material, conductive carbon nanotubes and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place on a magnetic stirrer and stir at 600 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

[0060] Comparative Example 1

[0061] A composite cathode material for lithium-ion batteries comprises the following raw materials in parts by weight: 80g of commercially available lithium manganese iron phosphate, 14g of conductive carbon nanotubes, and 13g of polyvinylidene fluoride; the preparation method of this lithium-ion battery composite cathode material includes the following steps:

[0062] Step 1: Weigh out each ingredient by weight and set aside.

[0063] Step 2: Add commercially available lithium manganese iron phosphate material (purchased from Shenzhen Liyou New Energy Technology Co., Ltd., with a particle size distribution of D90), conductive carbon nanotubes, and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place them on a magnetic stirrer and stir at 500 r / min until they are mixed evenly to obtain a paste-like substance, which is the composite cathode material.

[0064] Performance testing

[0065] The composite cathode materials prepared in Examples 1-4 and Comparative Example 1 were coated onto aluminum foil current collectors and dried in a vacuum oven at 90°C for 8 hours to form cathode sheets. The cathode sheets were then cut into 10mm circular pieces using a stamping machine. Lithium foil was used as the anode. The electrolyte was 1 mol / L LiPF6 dissolved in an EC / DMC / EMC solvent (volume ratio 1:1:1). The cathode sheets, electrolyte, PP separator, and lithium metal foil were assembled to obtain a button lithium-ion battery. Cyclic voltammetry was used for testing, and the results are as follows:

[0066] Cyclic stability was tested under a current density of 0.2 A / g, and the results are shown in Table 2.

[0067] Table 2 - Discharge specific capacity and cycle stability test results

[0068] Discharge specific capacity (mAh / g) Capacity retention rate (%) after 1000 cycles Example 1 191.1 91.3 Example 2 191.9 91.8 Example 3 192.4 92.1 Example 4 191.4 91.5 Comparative Example 1 153.2 66.4

[0069] As shown in Table 2, the lithium-ion battery composite cathode materials prepared in Examples 1-4 of this invention have high specific capacity and excellent cycle stability. However, the lithium-ion battery composite cathode material prepared in Comparative Example 1 has poor cycle stability because the lithium manganese iron phosphate material is unmodified. During cycling, it undergoes volume changes, is corroded by contact with electrolytes and other chemicals, and may undergo side reactions, resulting in poor cycle stability.

[0070] Table 3 - Ratio Performance Test Results

[0071]

[0072] As shown in Table 3, the lithium-ion battery composite cathode materials prepared in Examples 1-4 of this invention have excellent rate performance, with a maximum capacity retention of 74% from 0.5C to 3C. In contrast, the lithium-ion battery composite cathode material prepared in Comparative Example 1, which is unmodified lithium manganese iron phosphate material, has a capacity retention of only 43.6% from 0.5C to 3C, indicating poor rate performance.

[0073] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A composite cathode material for lithium-ion batteries, characterized in that, The raw materials include the following parts by weight: 70-85 parts lithium manganese iron phosphate composite material, 10-15 parts conductive material, and 10-15 parts polyvinylidene fluoride. The preparation method of the lithium manganese iron phosphate composite material includes the following steps: Step A: Add phosphorus source, manganese source, iron source, lithium source and complexing agent to deionized water, stir at 100-200 r / min for 40-60 min to obtain a mixture; Step B: Add the modified composite aerogel to the mixture and ultrasonically disperse it at a frequency of 80-100KHz for 1-3 hours at a temperature of 50-70℃. Transfer the system to a reaction vessel, raise the temperature to 200-220℃, stir and react for 8-10 hours, centrifuge and wash, and vacuum dry to obtain the precursor. Step C: The precursor is loaded into a crucible, protected by argon gas, and sintered at high temperature in a vacuum tube furnace. After cooling to room temperature, the lithium manganese iron phosphate composite material is obtained. The preparation method of the modified composite aerogel includes the following steps: Step T1: Add sodium alginate to deionized water and stir thoroughly. Add sodium periodate solution and stir the reaction in the dark for 1-2 hours. Then add ethylene glycol to stop the reaction, separate the product, precipitate, freeze dry, and obtain aldehyde-modified sodium alginate. Step T2: Add aldehyde-modified sodium alginate to N,N-dimethylformamide, mix well, add L-methionine alcohol and catalyst, raise the temperature to 45-55℃, and react for 2-4 hours to obtain modified sodium alginate. Step T3: Add modified sodium alginate to deionized water to prepare a solution. Slowly add the solution to anhydrous ethanol, stir for 8-10 hours, let stand for 30-50 minutes, and freeze dry to obtain modified composite aerogel.

2. The composite cathode material for lithium-ion batteries according to claim 1, characterized in that, The conductive material is any one of carbon black, carbon nanotubes, or acetylene black.

3. The composite cathode material for lithium-ion batteries according to claim 1, characterized in that, In step A, the phosphorus source is any one of phosphoric acid, sodium dihydrogen phosphate, or diammonium hydrogen phosphate; the manganese source is any one of manganese acetate, manganese chloride, or manganese nitrate; the iron source is any one of ferrous acetate, ferric nitrate, ferric chloride, or ferrous nitrate; the lithium source is any one of lithium hydroxide, lithium acetate, lithium carbonate, or lithium chloride; and the complexing agent is any one of citric acid, tartaric acid, malic acid, or succinic acid.

4. The composite cathode material for lithium-ion batteries according to claim 1, characterized in that, In step T1, the concentration of the sodium periodate solution is 10-20%.

5. The composite cathode material for lithium-ion batteries according to claim 1, characterized in that, In step T2, the catalyst is sodium carbonate or triethylamine.

6. The composite cathode material for lithium-ion batteries according to claim 1, characterized in that, In step C, the high-temperature sintering is performed at a heating rate of 4-6℃ / min, with the temperature rising to 600-800℃ for 1-3 hours.

7. A method for preparing a composite cathode material for lithium-ion batteries as described in claim 1, characterized in that, Includes the following steps: Step 1: Weigh out each ingredient by weight and set aside. Step 2: Add the lithium manganese iron phosphate composite material, conductive material and polyvinylidene fluoride to N-methyl-2-pyrrolidone, place it on a magnetic stirrer and stir at 300-600 r / min to mix evenly to obtain a paste-like substance, which is the composite cathode material.

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