Composite sodium-ion positive electrode material and preparation method and application thereof

Abstract

The application discloses a composite sodium ion positive electrode material and a preparation method and application thereof, and belongs to the technical field of electrode material preparation of sodium ion batteries. In the application, polymethyl methacrylate as a polymer can effectively isolate the sodium ion positive electrode material from contacting carbon dioxide and moisture in the air to react, meanwhile, the polymethyl methacrylate has good ion transmission performance and does not affect the performance of the positive electrode main material. Due to the compounding of the polymethyl methacrylate, the combination of the positive electrode material and the binder can be effectively improved, and the stability of the positive electrode coating can be improved. The composite material has good storage property, and deterioration of the material in the storage and transportation process can be inhibited.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery electrode material preparation technology, and in particular relates to a composite sodium-ion cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and lack of memory effect, have been widely used in various portable electronic products and devices. Especially under the dual pressures of the energy crisis and environmental degradation, human society's reliance on lithium-ion batteries will increase, leading to a surge in demand for lithium. However, the uneven distribution of lithium in the Earth's crust, coupled with the difficulty in meeting such high demand, has resulted in continuously rising lithium prices, failing to meet the needs of societal development. Therefore, there is an urgent need to develop a new generation of energy storage battery systems with excellent overall performance.

[0003] Compared to lithium, sodium is more abundant, more widely distributed, cheaper, and easier to extract. Furthermore, sodium belongs to the same group as lithium and has very similar electrochemical properties. Therefore, sodium-ion batteries have attracted considerable attention from researchers. Currently, commonly used sodium-ion cathode materials mainly fall into three categories: layered transition metal oxides, polyanionic compounds, and Prussian blue analogues. Layered transition metal oxides are similar to ternary lithium-ion battery materials, polyanionic compounds are closer to the structure of lithium iron phosphate, and Prussian blue represents a new approach for sodium-ion batteries. Prussian blue compounds have low synthesis costs, high specific capacity (approximately 170 mAh / g), and excellent fast-charging performance, but the water of crystallization in their structure is difficult to remove, posing certain safety risks. A common characteristic of these materials is their poor air stability; when the material comes into contact with air, Na... + It will be released from the crystal lattice and react with substances such as H2O and CO2 in the air to produce substances such as NaOH and NaCO3, collectively known as residual alkali. This will not only cause Na... + A decrease in the number of inserted elements leads to a reduction in material capacity, deterioration in cycling performance, and also affects the positively charged Na+. + The shielding effect weakens, the repulsive force between adjacent oxide layers increases, the interlayer spacing widens, and even particle cracking occurs. In addition, the material's hygroscopic deterioration reduces its compatibility with binders, resulting in decreased slurry dispersibility and stability, which is detrimental to subsequent coating processes.

[0004] Therefore, there is an urgent need in the field to develop a more effective method that can improve the cycle stability of sodium batteries while isolating the positive electrode material from harmful gases in the environment, without affecting the conductivity of sodium ions, and extending the storage life of the material.

[0005] Polymethyl methacrylate (PMMA) is lightweight, inexpensive, and easy to mold. It dissolves in organic solvents such as anisole, forming good thin films and exhibiting excellent dielectric properties. It can be used as the dielectric layer in organic field-effect transistors. Therefore, in batteries, PMMA is often used in the preparation of separators or electrolytes (CN110438798A). Currently, there is no literature on the composite of PMMA with cathode materials, and even fewer reports on the use of such composite materials as cathode materials for sodium batteries. Summary of the Invention

[0006] Therefore, this invention proposes a method for preparing a PMMA composite sodium ion cathode material, which has good cycle performance and storage properties.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0008] A method for preparing a composite sodium-ion cathode material includes the following steps:

[0009] (1) Dissolve the polymer in an organic solvent, then add sodium ion cathode material and disperse evenly to obtain a dispersion;

[0010] (2) First, add a portion of the initiator to the dispersion obtained in step (1) to carry out the polymerization reaction and obtain the reaction solution;

[0011] (3) Add the remaining initiator to the reaction solution obtained in step (2) to carry out a polymerization reaction to obtain the composite sodium ion cathode material;

[0012] In step (1), the polymer is polymethyl methacrylate; in step (2), a portion of the dosage accounts for 40% to 60% of the total mass of the initiator.

[0013] Specifically, in step (1), the solid content of the polymer dissolved in the organic solvent is 20%-30%; the organic solvent is at least one of acetone, N-methylpyrrolidone, N,N-dimethylformamide, toluene, and styrene.

[0014] Preferably, since excessive polymer will affect the performance of the main material, the mass ratio of polymer to sodium ion cathode material is 1:1.5 to 2.

[0015] Preferably, the sodium ion cathode material is a nickel-iron-manganese ternary sodium ion cathode material or a sodium iron pyrophosphate cathode material.

[0016] More preferably, the nickel-iron-manganese ternary sodium ion cathode material is Na. a Ni x Fey Mn z O2, 0.86≤a≤1.01, 0.22≤x≤1 / 3, 0.3≤y≤1 / 3, 1 / 3≤z≤0.45;

[0017] The sodium ferric pyrophosphate cathode material is Na. b Fe m (PO4) q (P2O7) n , 3≤b≤4, 2.19≤m≤2.84, 1.16≤q≤1.38, 0.81≤n≤1.55.

[0018] In an embodiment of the present invention, the example sodium-ion cathode material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na 0.86 Ni 0.22 Fe 0.3 Mn 0.45 O2, Na3Fe 2.19 (PO4) 1.38 (P2O7) 0.81 Na4Fe 2.84 (PO4) 1.06 (P2O7) 1.55 Or Na 1.01 Ni 0.30 Fe 0.33 Mn 0.35 O2.

[0019] Specifically, the mass ratio of the added polymer to the initiator is 100:1 to 10;

[0020] The initiator is at least one of azobisisobutyronitrile, benzoyl oxide, sodium bisulfite, ammonium persulfate, sodium persulfate, potassium persulfate, ammonium bisulfite, and potassium bisulfite.

[0021] Specifically, in step (2), the polymerization reaction is as follows: the temperature is increased to 60-90℃ at a heating rate of 1℃-5℃ / min, and the reaction is maintained at this temperature for 1-6 hours.

[0022] In step (3), the polymerization reaction is carried out at a temperature of 60-90°C for 6-24 hours.

[0023] Adding the polymer in batches is to control the polymerization rate, prevent the polymer from reacting too quickly and causing explosive polymerization, and improve safety during the process.

[0024] In step (3), after the polymerization reaction, the composite sodium ion cathode material is obtained by filtration, washing and drying; the washing solvent is chloroform, and the drying temperature is 80-120℃.

[0025] The present invention also provides a composite sodium ion cathode material prepared by the aforementioned preparation method.

[0026] This invention also provides the application of composite sodium-ion cathode materials in the preparation of sodium-ion batteries.

[0027] The present invention also provides a sodium-ion battery, comprising the aforementioned composite sodium-ion cathode material.

[0028] The present invention has the following beneficial effects:

[0029] 1. In this invention, polymethyl methacrylate (PMMA) is a polymer that can effectively prevent sodium ion cathode material from reacting with carbon dioxide and moisture in the air. At the same time, PMMA has good ion transport performance and does not affect the function of the cathode material.

[0030] 2. Due to the composite of polymethyl methacrylate, the bonding between the cathode material and the binder can be effectively improved, thereby enhancing the stability of the cathode coating;

[0031] 3. The composite material prepared by this invention has good storage properties, which inhibits the deterioration of the material during storage and transportation. Attached Figure Description

[0032] Figure 1 The graph shows the rate performance test results of the PMMA composite sodium ion cathode material prepared in Example 1 and the untreated sodium ion cathode material in Comparative Example 1 at a current density of 0.2C.

[0033] Figure 2 The graph shows the cycle performance test results of the PMMA composite sodium ion cathode material prepared in Example 1 and the untreated sodium ion cathode material in Comparative Example 1 at a current density of 1C.

[0034] Figure 3 This is a comparison of transmission electron microscopy (TEM) results of the cathode materials in Example 1; where A represents the untreated NaNi nano-cathode material without polymethyl methacrylate (PMMA) composite treatment. 1 / 3 Fe1 / 3Mn 1 / 3 O2 and B are PMMA composite sodium ion cathode materials. Detailed Implementation

[0035] Example 1

[0036] S1: Prepare 100g of acetone dispersion (polymethyl methacrylate (PMMA) solid content 20%), and add 30g of NaNi nano cathode material. 1 / 3 Fe 1 / 3 Mn 1 / 3O2 (Beijing Dangsheng Materials Technology Co., Ltd., SFM-K3) was added to the dispersion, and then placed in a three-necked flask and ultrasonically dispersed for 30 min at a working frequency of 50 kHz.

[0037] S2: Place the three-necked flask in a water bath and add 1g of sodium persulfate. Heat the flask to 80℃ at a rate of 3℃ / min and stir for 5 hours.

[0038] S3: Then add the remaining 1g of sodium persulfate and stir at a constant temperature of 80℃ for 12 hours;

[0039] S4: The reaction product is filtered, washed three times with chloroform, and dried under vacuum at 90°C to obtain a PMMA composite cathode material.

[0040] Example 2

[0041] S1: Prepare 100g of acetone dispersion (PMMA solid content is 25%), and add 40g of nano-cathode material Na... 0.86 Ni 0.22 Fe 0.3 Mn 0.45 O2 (Ningbo Ronbay New Energy Technology Co., Ltd., YNL2-B) was added to the dispersion, and then placed in a three-necked flask and ultrasonically dispersed for 30 min at a working frequency of 50 kHz.

[0042] S2: Place the three-necked flask in a water bath and add 1g of sodium persulfate. Heat the flask to 80℃ at a rate of 4℃ / min and stir for 6 hours.

[0043] S3: Then add the remaining 1g of sodium persulfate and stir at a constant temperature of 90℃ for 10 hours;

[0044] S4: The reaction product is filtered, washed three times with chloroform, and dried under vacuum at 90°C to obtain a PMMA composite cathode material.

[0045] Example 3

[0046] S1: Prepare 100g of toluene dispersion (PMMA solid content 25%), and add 40g of nano-cathode material Na3Fe. 2.19 (PO4) 1.38 (P2O7) 0.81 (Shenzhen Jiana Energy Technology Co., Ltd., JNP-1) was added to the dispersion, and then placed in a three-necked flask and ultrasonically dispersed for 30 min at a working frequency of 50 kHz.

[0047] S2: Place the three-necked flask in a water bath and add 1g of azobisisobutyronitrile. Heat the flask to 80℃ at a rate of 4℃ / min and stir for 6 hours.

[0048] S3: Then add the remaining 1g of azobisisobutyronitrile and stir at a constant temperature of 90℃ for 10 hours;

[0049] S4: The reaction product is filtered, washed three times with chloroform, and dried under vacuum at 90°C to obtain a PMMA composite cathode material.

[0050] Example 4

[0051] S1: Prepare 100g of toluene dispersion (PMMA solid content 20%), and add 40g of nano-cathode material Na4Fe. 2.84 (PO4) 1.16 (P2O7) 1.55 (YNL2-B) was added to the dispersion and then placed in a three-necked flask. The mixture was ultrasonically dispersed for 30 minutes at a working frequency of 50 kHz.

[0052] S2: Place the three-necked flask in a water bath and add 0.08 g of benzoyl oxide dropwise. Heat the flask to 80 °C at a rate of 4 °C / min and stir for 6 hours.

[0053] S3: Then add the remaining 0.12g of benzoyl oxide and stir at a constant temperature of 90℃ for 10 hours;

[0054] S4: The reaction product is filtered, washed three times with chloroform, and dried under vacuum at 90°C to obtain a PMMA composite cathode material.

[0055] Example 5

[0056] S1: Prepare 100g of toluene dispersion (PMMA solid content 30%), and add 50g of nano-cathode material Na... 1.01 Ni 0.3 Fe 0.33 Mn 0.35 O2 (Ningbo Ronbay New Energy Technology Co., Ltd., YNL1-C) was added to the dispersion, and then placed in a three-necked flask and ultrasonically dispersed for 30 min at a working frequency of 50 kHz.

[0057] S2: Place the three-necked flask in a water bath and add 1.32g of benzoyl oxide dropwise. Heat the flask to 90℃ at a rate of 4℃ / min and stir for 5 hours.

[0058] S3: Then add the remaining 0.88g of benzoyl oxide and stir at a constant temperature of 90℃ for 10 hours;

[0059] S4: The reaction product is filtered, washed three times with chloroform, and dried under vacuum at 90°C to obtain a PMMA composite cathode material.

[0060] Comparative Example 1

[0061] The nano-cathode material NaNi used in Example 1 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (Beijing Dangsheng Materials Technology Co., Ltd., SFM-K3) has not undergone polymethyl methacrylate (PMMA) composite treatment.

[0062] Test Example 1

[0063] 1. Moisture test

[0064] The PMMA composite sodium ion cathode materials from Examples 1-5 and the uncomposite nano cathode material NaNi from Comparative Example 1 were compared. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was exposed to air for different number of days, and the moisture content of the material was tested during this period. The test data are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from the data in Table 1, after being exposed to air for 15 days, the untreated NaNi nano-cathode material in Comparative Example 1 showed... 1 / 3 Fe 1 / 3 Mn 1 / 3 The moisture content of O2 is 4 to 5 times that of the PMMA composite sodium ion cathode materials in Examples 1 to 5, indicating that the PMMA composite sodium ion cathode materials can effectively isolate moisture in the air.

[0068] 2. Electrochemical performance testing

[0069] The PMMA composite sodium ion cathode material from Example 1 and the uncomposite nano cathode material NaNi from Comparative Example 1 were used. 1 / 3 Fe 1 / 3 Mn 1 / 3 The sodium-ion battery prepared with O2 was subjected to electrochemical performance testing. The preparation steps are as follows:

[0070] S1: PMMA composite sodium ion cathode material or nano cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 exposure to air for 8 hours;

[0071] S2: PMMA composite sodium ion cathode material or nano-cathode material NaNi are respectively added to the cathode material. 1 / 3 Fe 1 / 3 Mn 1 / 3O2, SP, and PVDF are mixed and slurried in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1 to obtain the positive electrode slurry;

[0072] S3: Then, the positive electrode slurry is evenly coated onto the aluminum foil using a 200μm coating scraper. It is dried in a vacuum environment at 110℃ for 16 hours. After cooling, the aluminum foil is removed and cut into round sheets using a sheet-making machine to obtain the standby positive electrode sheet.

[0073] S4: Using a sodium metal sheet as the negative electrode, sodium perchlorate as the electrolyte, and polyethylene material as the separator, a CR2032 button sodium-ion battery was assembled in a glove box under inert gas protection. After being placed for 12 hours, the electrical performance was tested at a voltage of 2.0-4.0V.

[0074] Test results show that the PMMA composite sodium-ion cathode material prepared in Example 1 and the uncomposite nano-cathode material NaNi in Comparative Example 1 are significantly different. 1 / 3 Fe 1 / 3 Mn 1 / 3 After exposure to air for 8 hours, the discharge capacities of O2 at room temperature and a current density of 0.2C were 131.6 mAh / g and 123 mAh / g, respectively. Figure 1 The retention rates after 200 cycles at 1C were 91.2% and 79.4%, respectively. Figure 2 It can be seen that the composite cathode material of the present invention has good cycle performance. The PMMA composite sodium ion cathode material prepared in Example 1 has a uniform coating layer under transmission electron microscopy, with a thickness of approximately 11.37 nm. Figure 3 ).

Claims

1. A method for preparing a composite sodium-ion cathode material, characterized in that, Includes the following steps: (1) Dissolve the polymer in an organic solvent, then add sodium ion cathode material and disperse evenly to obtain a dispersion; the mass ratio of polymer to sodium ion cathode material is 1:1.5~2; (2) First, add a portion of the initiator to the dispersion obtained in step (1) to carry out the polymerization reaction and obtain the reaction solution; the polymerization reaction is: heating to 60-90℃ at a heating rate of 1℃-5℃ / min and keeping the temperature for 1-6h. (3) Add the remaining initiator to the reaction solution obtained in step (2) to carry out a polymerization reaction to obtain the composite sodium ion cathode material; the polymerization reaction temperature is 60-90℃ and the reaction time is 6-24h; In step (1), the polymer is polymethyl methacrylate; the polymer dissolves in the organic solvent at a mass-volume percentage of 20%-30%. In step (2), a portion of the dose accounts for 40% to 60% of the total mass of the initiator.

2. The method for preparing the composite sodium-ion cathode material as described in claim 1, characterized in that, In step (1), the organic solvent is at least one of acetone, N-methylpyrrolidone, N,N-dimethylformamide, toluene, and styrene.

3. The method for preparing the composite sodium-ion cathode material as described in claim 1, characterized in that, The sodium ion cathode material is a nickel-iron-manganese ternary sodium ion cathode material or a sodium iron pyrophosphate cathode material.

4. The method for preparing the composite sodium-ion cathode material as described in claim 3, characterized in that, The nickel-iron-manganese ternary sodium ion cathode material is Na. a Ni x Fe y Mn z O2, 0.86≤a≤1.01, 0.22≤x≤1 / 3, 0.3≤y≤1 / 3, 1 / 3≤z≤0.45; The sodium ferric pyrophosphate cathode material is Na. b Fe m (PO4) q (P2O7) n , 3≤b≤4, 2.19≤m≤2.84, 1.16≤q≤1.38, 0.81≤n≤1.

55.

5. The method for preparing the composite sodium-ion cathode material as described in claim 1, characterized in that, The mass ratio of the added polymer to the initiator is 100:1~10; The initiator is at least one of sodium persulfate, benzoyl peroxide, sodium bisulfite, ammonium persulfate, azobisisobutyronitrile, potassium persulfate, ammonium bisulfite, and potassium bisulfite.

6. The composite sodium ion cathode material prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the composite sodium-ion cathode material as described in claim 6 in the preparation of sodium-ion batteries.

8. A sodium-ion battery, characterized in that, Including the composite sodium ion cathode material as described in claim 6.

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