Sodium ferrous sulfate positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of sodium ion battery positive electrode materials, and discloses a sodium ferrous sulfate positive electrode material and a preparation method thereof, and the preparation method of the sodium ferrous sulfate positive electrode material comprises the following steps: step 1, preparing a ferrous sulfate precursor; 2, mixing the ferrous sulfate precursor with a sodium source, iron-containing sulfate, an M source and a carbon source, and then sintering and crushing to obtain a sodium ferrous sulfate positive electrode material; wherein the specific method of the step 1 is as follows: an iron source and a hydrophilic modified carbon material are added into deionized water and stirred to obtain uniform slurry, then the slurry is subjected to spray drying to obtain a ferrous sulfate precursor, and the mass ratio of the iron source to the hydrophilic modified carbon material is (9-19): 1; the M source is a Mn source or a mixture formed by the Mn source and at least one of a Mg source, a Ti source and a Zn source; the chemical general formula of the sodium ferrous sulfate positive electrode material is NaxFeyMz (SO4) x / 2 + y + z, wherein x is greater than or equal to 1 and less than or equal to 3, y is greater than or equal to 0.1 and less than or equal to 2, and z is greater than or equal to 0.1 and less than or equal to 1. According to the invention, the morphology of the obtained sodium ferrous sulfate positive electrode material is controlled by firstly preparing the ferrous sulfate precursor, so that the electrical performance is improved.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery cathode materials technology, specifically to a sodium ferrous sulfate cathode material and its preparation method. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have a wider range of sodium sources, which can effectively reduce their cost. Simultaneously, sodium-ion batteries exhibit excellent thermal stability, making them safer and allowing them to operate over a wider temperature range. Therefore, sodium-ion batteries have been extensively researched and applied. The main cathode materials for sodium-ion batteries include three types: transition metal layered oxides, polyanionic compounds, and Prussian blue analogues. Among these, sodium ferrous sulfate cathode materials, a type of polyanionic compound, possess excellent cycle stability, high voltage, and low cost, showing broad application prospects in large-scale energy storage power stations and electric vehicles. However, the material itself has low conductivity, is sensitive to water and oxygen in the air, and its low compaction density and relatively low capacity limit its further development. Currently, researchers are using carbon coating to reduce the surface impedance of sodium ferrous sulfate materials, enhancing electron transport between particles and improving its electronic conductivity. Simultaneously, the carbon coating forms a stable protective layer on the surface of the sodium ferrous sulfate material, isolating it from water and oxygen in the air, which is beneficial for storage and transportation, thereby further reducing the material's cost.

[0003] Prior art 1: Chinese patent application 202410909379.1 discloses a carbon-coated sodium ferrous sulfate cathode material and its preparation method. Specifically, it describes the synthesis of a sodium ferrous sulfate cathode material with a sodium to iron molar ratio of 1:1 to 2:1 without the need for a dispersant, followed by coating.

[0004] The aforementioned patent relates to a method for synthesizing and coating a polyanionic cathode material for sodium-ion batteries. The specific method is as follows: spray-drying a mixed aqueous solution of anhydrous sodium sulfate, ferrous sulfate heptahydrate, and an antioxidant, followed by drying and dehydration to obtain a precursor; mixing and granulating the precursor and carbon materials to obtain a mixed particulate material; and sintering and pulverizing the mixed particulate material to obtain the cathode material.

[0005] The aforementioned patent employs a liquid-phase spray drying combined with solid-phase coating method to achieve carbon coating of sodium ferrous sulfate cathode material, thereby improving the conductivity of the sodium ferrous sulfate cathode material. At the same time, it isolates water and oxygen in the air, thereby increasing the energy storage capacity. This avoids the problem that general carbon materials have poor dispersibility in aqueous solutions, requiring the addition of dispersants and introducing impurities. It can serve as an important reference scheme for further research and development of sodium ferrous sulfate cathode materials.

[0006] Meanwhile, prior art 2: Chinese patent application 202111543146.7 discloses a sodium-ion battery composite cathode material and its preparation method, specifically sodium ferrous sulfate, ferrous sulfate, and carbon nanotubes, with the following mass ratios: sodium ferrous sulfate: 90~99%, ferrous sulfate: 0.1~9.9%, and carbon nanotubes: 0.1~9.9%. This effectively solves the problems of easy oxidation and deterioration of polyanionic sodium ferrous sulfate cathode materials.

[0007] The preparation method of the composite sodium ferrous sulfate cathode material involved in the above patent is as follows: 1. First, vacuum dry the heptahydrate ferrous sulfate material to remove the water of crystallization in the material to obtain anhydrous ferrous sulfate; 2. Mix the anhydrous ferrous sulfate, sodium ferric sulfate and carbon nanotubes by ball milling under nitrogen protection to obtain a composite precursor; 3. Sinter and pulverize the composite precursor to obtain a composite cathode material.

[0008] The aforementioned patent utilizes solid-phase carbon coating technology to avoid the problem of organic residues in in-situ organic carbon source coating methods at sintering temperatures below 400℃. It also improves the specific capacity and cycle stability of sodium ferrous sulfate cathode materials and, to some extent, overcomes the technical challenge of sodium ferrous sulfate's susceptibility to deterioration. This provides a valuable reference for the future development of sodium-ion battery cathode materials.

[0009] The aforementioned prior art 1 and prior art 2 improve the electrochemical performance of sodium ferrous sulfate cathode materials through different methods. However, both materials have poor crystallinity and their morphology has not been further controlled, which in turn affects the battery's electrochemical performance. Summary of the Invention

[0010] One of the objectives of this application is to provide a method for preparing sodium ferrous sulfate cathode material, which controls the morphology of sodium ferrous sulfate cathode material by first preparing a ferrous sulfate precursor, thereby improving the battery's electrical performance.

[0011] Another objective of this application is to provide a sodium ferrous sulfate cathode material that, when used in a battery, can produce further improvements in electrical performance.

[0012] To achieve the above objectives, this application provides a method for preparing sodium ferrous sulfate cathode material, comprising the following steps:

[0013] Step 1: Preparation of ferrous sulfate precursor;

[0014] Step 2: Mix the ferrous sulfate precursor with a sodium source, an iron sulfate, an M source, and a carbon source, and then sinter and crush to obtain sodium ferrous sulfate cathode material;

[0015] The specific method of step 1 is as follows: an iron source and a hydrophilic modified carbon material are added to deionized water and stirred to obtain a uniform slurry. The slurry is then spray-dried to obtain a ferrous sulfate precursor. The mass ratio of the iron source to the hydrophilic modified carbon material is 9-19:1.

[0016] The M source is an Mn source or a mixture of an Mn source with at least one of a Mg source, a Ti source, and a Zn source; the general chemical formula of the sodium ferrous sulfate cathode material is Na. x Fe y M z (SO4) x / 2+y+z , where 1≤x≤3, 0.1≤y≤2, 0.1≤z≤1.

[0017] The spray drying described in step 1 of this application can be achieved through conventional technical settings. More preferably, the inlet air temperature is 170~230 ℃ and the outlet air temperature is 70~130 ℃.

[0018] Preferably, the hydrophilic modified carbon material can be obtained by purchasing commercially available products. More preferably, the preparation method of the hydrophilic modified carbon material is as follows: immersing carbon nanotubes in hydrogen peroxide solution and heating and refluxing at 60-80°C for 1-5 hours to obtain the hydrophilic modified carbon material.

[0019] Furthermore, the specific operation of step 2 is as follows: the ferrous sulfate precursor is mixed with sodium source, ferric sulfate, M source and carbon source to obtain a mixture, the mixture is sintered at a sintering temperature of 220-280℃ for 1-4h under an inert atmosphere, and then sintered at a sintering temperature of 300-450℃ for 10-20h.

[0020] Furthermore, the sodium source is one of anhydrous sodium sulfate, sodium sulfate heptahydrate, sodium sulfate decahydrate, and anhydrous sodium carbonate.

[0021] Furthermore, the iron-containing sulfate is at least one of ferrous sulfate heptahydrate, ferric sulfate, ferric ammonium sulfate, and ferrous ammonium sulfate.

[0022] Furthermore, when the M source is a mixture formed by Mn source and at least one of Mg source, Ti source and Zn source, the mass percentage of Mn source in the mixture is 6-90 wt%.

[0023] Furthermore, the specific operation of the mixing is as follows: the ferrous sulfate precursor, sodium source, ferric sulfate, M source and carbon source are placed in a ball mill under an inert gas atmosphere, the ball-to-material ratio is controlled at 5:1 and zirconia balls are added, and the ball milling is carried out at a general speed of 800 r / min and a self speed of 400 r / min for 5 h. After the ball milling is completed, a mixture is obtained.

[0024] Preferably, the carbon source is one of polyaniline, carbon nanotubes, graphene, carbon fiber, activated carbon, conductive carbon black, and organic carbon.

[0025] More preferably, the carbon source is polyaniline. This application found that when preparing sodium ferrous sulfate cathode material using the ferrous sulfate precursor of this application, manganese doping and polyaniline coating can chelate manganese ions to stabilize divalent iron ions, thereby improving capacity performance.

[0026] This application also provides a sodium ferrous sulfate cathode material, which is prepared using the above-described method for preparing sodium ferrous sulfate cathode materials.

[0027] Beneficial effects

[0028] Compared with the prior art, this application provides a method for preparing sodium ferrous sulfate cathode material, which controls the morphology of the obtained sodium ferrous sulfate cathode material by first preparing a ferrous sulfate precursor, thereby improving the electrical performance. Detailed Implementation

[0029] The present application will be further described below with reference to embodiments, but this does not constitute any limitation on the present application. Any limited modifications made within the scope of the claims of the present application shall still be within the scope of the claims of the present application.

[0030] To illustrate the technical content of this application in detail, the following description is provided in conjunction with the embodiments.

[0031] In the following examples and comparative examples, the preparation method of the hydrophilic modified carbon material is as follows: carbon nanotubes are immersed in a 20% hydrogen peroxide solution and heated under reflux at 70±5℃ for 3 hours to obtain the hydrophilic modified carbon material.

[0032] Example 1

[0033] A sodium ferrous sulfate cathode material is prepared using the following steps:

[0034] Step 1: Add ferrous sulfate heptahydrate and hydrophilic modified carbon material to deionized water at a mass ratio of 13:1 and stir to obtain a uniform slurry. Then spray dry the slurry to obtain the ferrous sulfate precursor.

[0035] Step 2: Add 0.25 mol of anhydrous sodium sulfate, 1 mol of ferrous sulfate precursor, 0.25 mol of manganese carbonate and 0.19 mol of graphene to a ball mill under a nitrogen atmosphere. Add zirconia balls to the ball mill. The ball-to-material ratio is 5:1. The ball milling speed is 800 r / min and the rotation speed is 400 r / min. The ball milling time is 5 h to obtain a mixture.

[0036] Step 3: Place the mixture into a nitrogen-protected box furnace for heat treatment. Heat the mixture to 250℃ and hold for 1 hour, then heat it to 350℃ and hold for 12 hours. Crush and sieve to obtain sodium ferrous sulfate cathode material with a particle size D50 of 6μm.

[0037] Example 2

[0038] It is largely the same as Example 1, except that graphene is replaced with polyaniline.

[0039] Example 3

[0040] It is largely the same as Example 1, except that graphene is replaced with carbon nanotubes.

[0041] Example 4

[0042] The process is largely the same as in Example 2, except that step 2 is modified as follows: 0.75 mol of anhydrous sodium sulfate, 0.75 mol of ferrous sulfate precursor, 0.5 mol of manganese carbonate and 0.19 mol of graphene are added to a ball mill under a nitrogen atmosphere. Zirconia balls are added to the ball mill, the ball-to-material ratio is 5:1, the ball milling speed is 800 r / min, the rotation speed is 400 r / min, and the ball milling time is 5 h to obtain a mixture.

[0043] Example 5

[0044] The process is largely the same as in Example 2, except that step 2 is modified as follows: 0.25 mol of anhydrous sodium sulfate, 0.75 mol of ferrous sulfate precursor, 0.5 mol of manganese carbonate and 0.19 mol of graphene are added to a ball mill under a nitrogen atmosphere. Zirconia balls are added to the ball mill, the ball-to-material ratio is 5:1, the ball milling speed is 800 r / min, the rotation speed is 400 r / min, and the ball milling time is 5 h to obtain a mixture.

[0045] Example 6

[0046] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.01 mol of manganese carbonate and 0.24 mol of zinc carbonate.

[0047] Example 7

[0048] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.25 mol of manganese sulfate.

[0049] Example 8

[0050] The process is largely the same as in Example 2, except that step 3 is changed to: placing the mixture in a nitrogen-protected box furnace for heat treatment, heating it to 350°C and holding it for 13 hours, then crushing and sieving to obtain sodium ferrous sulfate cathode material with a particle size D50 of 6 μm.

[0051] Example 9

[0052] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.05 mol of manganese carbonate and 0.2 mol of zinc carbonate.

[0053] Example 10

[0054] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.05 mol of manganese carbonate and 0.2 mol of titanium carbonate.

[0055] Example 11

[0056] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.2 mol of manganese carbonate and 0.05 mol of zinc carbonate.

[0057] Comparative Example 1

[0058] The process is largely the same as in Example 2, except that step 1 is changed to: adding ferrous sulfate heptahydrate and carbon nanotubes to deionized water at a mass ratio of 13:1 and stirring to obtain a uniform slurry, and then spray drying the slurry to obtain the ferrous sulfate precursor.

[0059] Comparative Example 2

[0060] A sodium ferrous sulfate cathode material is prepared using the following steps:

[0061] Step 1: Add 0.25 mol of anhydrous sodium sulfate, 1 mol of ferrous sulfate heptahydrate, hydrophilic modified carbon material, 0.25 mol of manganese carbonate, and 0.19 mol of polyaniline to a ball mill under a nitrogen atmosphere. Add zirconia balls to the ball mill. The ball-to-material ratio is 5:1. The ball mill's rotational speed is 800 r / min, its rotational speed is 400 r / min, and the milling time is 5 h to obtain a mixture. The mass ratio of ferrous sulfate heptahydrate to hydrophilic modified carbon material is 13:1.

[0062] Step 2: Place the mixture into a nitrogen-protected box furnace for heat treatment. Heat the mixture to 250℃ and hold for 1 hour, then heat it to 350℃ and hold for 12 hours. Crush and sieve to obtain sodium ferrous sulfate cathode material with a particle size D50 of 6μm.

[0063] Comparative Example 3

[0064] It is largely the same as Example 2, except that 0.25 mol of manganese carbonate is replaced with 0.25 mol of titanium carbonate.

[0065] Performance testing

[0066] I. Compacted density test

[0067] Test method: Weigh the sample to be tested and place it in the sample slot of the ST-2722 powder resistance tester, and smooth the sample; rotate the knob counterclockwise to make the compression column slowly descend; make real-time adjustments and data readings according to the required compaction value, and record the data.

[0068] The sodium ferrous sulfate cathode materials of Examples 1-3 and Comparative Examples 1-3 were tested according to the above method, and the results are shown in Table 1.

[0069] Table 1 Compacted density test results

[0070] <![CDATA[Compaction density (g / cm 3 )]]> Example 1 2.36 Example 2 2.40 Example 3 2.30 Comparative Example 1 1.92 Comparative Example 2 2.00 Comparative Example 3 2.35

[0071] According to the results in Table 1:

[0072] Based on the comparison of data from Example 2 and Comparative Example 1, it can be seen that the compaction density of the sodium ferrous sulfate cathode material in Comparative Example 1 decreased significantly. It is speculated that the reason is that when the carbon nanotubes are not hydrophilically modified, the morphology of the ferrous sulfate precursor prepared in step 1 is difficult to control, which affects the morphology of the subsequent sodium ferrous sulfate cathode material and leads to a decrease in compaction density.

[0073] A comparison of the data from Example 2 and Comparative Example 2 shows that Comparative Example 2 did not prepare a ferrous sulfate precursor first, but directly prepared a sodium ferrous sulfate cathode material, which resulted in a significant decrease in the compaction density of the sodium ferrous sulfate cathode material. This proves that the preparation step of the ferrous sulfate precursor in this application is important, as it can effectively improve the compaction density of the sodium ferrous sulfate cathode material.

[0074] A comparison of the data from Example 2 and Comparative Example 3 shows that the change in doping elements has almost no effect on the compaction density, indicating that the control of material morphology is crucial for the regulation of compaction density.

[0075] II. Button performance test

[0076] Electrochemical performance tests were conducted on Examples 1-11 and Comparative Examples 1-3 using a button cell test cabinet. The specific test methods are as follows:

[0077] Capacity testing method: Blue Electric test cabinet, constant current and constant voltage charging and discharging at a rate of 0.1C, voltage range of 2.0~4.5V.

[0078] Cyclic testing method: Blue Electric test cabinet, constant current and constant voltage charge and discharge cycle for 100 cycles at 1C rate, voltage range of 2.0~4.5 V.

[0079] The test results are shown in Table 2.

[0080] Table 2. Performance test results of coin cells in Examples 1-11 and Comparative Examples 1-3

[0081] 0.1C discharge specific capacity (mAh / g) First-time Coulomb efficiency (%) 1C100-cycle retention rate (%) Example 1 101.6 98.20 89.2 Example 2 110.5 99.52 93.5 Example 3 100.2 98.00 88.2 Example 4 106.3 98.80 90.6 Example 5 105.5 98.65 91.2 Example 6 99.8 97.60 88.5 Example 7 104.6 99.10 90.3 Example 8 103.7 99.00 91.7 Example 9 102.3 99.13 90.6 Example 10 104.1 99.05 90.2 Example 11 103.8 98.95 89.9 Comparative Example 1 94.00 97.3 86.3 Comparative Example 2 93.45 97.5 87.5 Comparative Example 3 86.63 97.0 85.6

[0082] According to the results in Table 2:

[0083] As can be seen from the data in Examples 1-11, the sodium ferrous sulfate cathode materials prepared by the technical solution of this application all exhibit good electrical performance, with a 0.1C discharge specific capacity of 99.8 mAh / g or higher, an initial coulombic efficiency of 98% or higher, and a 1C 100-cycle retention rate of 88% or higher.

[0084] The sodium ferrous sulfate cathode material prepared in Example 2 exhibited the best electrical performance. A comparison between Example 2 and Examples 1 and 3 shows that when polyaniline is used as the carbon source, the 0.1C discharge specific capacity, initial coulombic efficiency, and 1C 100-cycle retention rate of the sodium ferrous sulfate cathode material are significantly improved. This is presumably due to the N-doped carbon layer formed by the decomposition of polyaniline, which can achieve:

[0085] 1. Improve the overall electronic conductivity of the material;

[0086] 2. The N site can interact with Mn. 2+ Formation of chelates, inhibiting Mn 2+ The oxidation of Fe is further inhibited. 2+ Oxidation of polyaniline with Mn 2+ This resulted in a synergistic effect in improving the electrical performance of sodium ferrous sulfate cathode materials.

[0087] However, a comparison of the data from Examples 2 and 6 shows that when the M source is changed from manganese carbonate to a mixture of manganese carbonate and zinc carbonate, the 0.1C discharge specific capacity, initial coulombic efficiency, and 1C 100-cycle retention rate of the sodium ferrous sulfate cathode material all decrease significantly compared to Example 2, further verifying the above hypothesis: polyaniline and Mn 2+ This resulted in a synergistic effect in improving the electrical performance of sodium ferrous sulfate cathode materials.

[0088] Meanwhile, based on the data comparison of Examples 2, 10, 11 and Comparative Example 3, it was found that the amount of manganese carbonate in the M source has a very significant impact on the electrical performance of the sodium ferrous sulfate cathode material. In particular, when the amount of manganese carbonate in Comparative Example 3 was 0, the 0.1C discharge specific capacity, first coulombic efficiency and 1C 100-cycle retention rate of the sodium ferrous sulfate cathode material showed a huge decrease.

[0089] Based on the comparison between Examples 2 and 7, it can be seen that when manganese carbonate is replaced with manganese sulfate, although both are manganese elements, the electrical properties are different. It is speculated that the reason is that manganese sulfate fails to decompose sufficiently at this temperature, which affects the effective doping of manganese ions and the generation of sodium manganese sulfate impurity phase.

[0090] According to the data comparison between Example 2 and Comparative Examples 1 and 2, the preparation of ferrous sulfate precursor is also a key factor affecting the electrical performance of sodium ferrous sulfate cathode material.

[0091] The embodiments presented herein are merely selected implementations based on combinations of all possible embodiments. The appended claims should not be limited to the embodiments described herein. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A method for preparing a sodium ferrous sulfate cathode material, characterized in that, Includes the following steps: Step 1: Preparation of ferrous sulfate precursor; Step 2: Mix the ferrous sulfate precursor with a sodium source, an iron sulfate, an M source, and a carbon source, and then sinter and crush to obtain sodium ferrous sulfate cathode material; The specific method of step 1 is as follows: an iron source and a hydrophilic modified carbon material are added to deionized water and stirred to obtain a uniform slurry. The slurry is then spray-dried to obtain a ferrous sulfate precursor. The mass ratio of the iron source to the hydrophilic modified carbon material is 9-19:

1. The M source is an Mn source or a mixture of an Mn source with at least one of a Mg source, a Ti source, and a Zn source; the general chemical formula of the sodium ferrous sulfate cathode material is Na. x Fe y M z (SO4) x / 2+y+z , where 1≤x≤3, 0.1≤y≤2, 0.1≤z≤1.

2. The method for preparing sodium ferrous sulfate cathode material according to claim 1, characterized in that, The preparation method of the hydrophilic modified carbon material is as follows: carbon nanotubes are immersed in hydrogen peroxide solution and heated under reflux at 60-80℃ for 1-5 h to obtain the hydrophilic modified carbon material.

3. The method for preparing sodium ferrous sulfate cathode material according to claim 1, characterized in that, The specific operation of step 2 is as follows: the ferrous sulfate precursor is mixed with sodium source, ferric sulfate, M source and carbon source to obtain a mixture, the mixture is sintered at a sintering temperature of 220-280℃ for 1-4h under an inert atmosphere, and then sintered at a sintering temperature of 300-450℃ for 10-20h.

4. The method for preparing sodium ferrous sulfate cathode material according to claim 1 or 3, characterized in that, The sodium source is one of anhydrous sodium sulfate, sodium sulfate heptahydrate, sodium sulfate decahydrate, and anhydrous sodium carbonate.

5. The method for preparing sodium ferrous sulfate cathode material according to claim 1 or 3, characterized in that, The iron-containing sulfate is at least one of ferrous sulfate heptahydrate, ferric sulfate, ferric ammonium sulfate, and ferrous ammonium sulfate.

6. The method for preparing sodium ferrous sulfate cathode material according to claim 1 or 3, characterized in that, When the M source is a mixture formed by Mn source and at least one of Mg source, Ti source and Zn source, the mass percentage of Mn source in the mixture is 6-90 wt%.

7. The method for preparing sodium ferrous sulfate cathode material according to claim 1 or 3, characterized in that, The specific operation of the mixing is as follows: ferrous sulfate precursor, sodium source, ferric sulfate, M source and carbon source are placed in a ball mill under an inert gas atmosphere, and zirconia balls are added with a ball-to-material ratio of 5:

1. The ball milling is carried out at a general speed of 800 r / min and a self-speed of 400 r / min for 5 h. After the ball milling is completed, a mixture is obtained.

8. The method for preparing sodium ferrous sulfate cathode material according to claim 1 or 3, characterized in that, The carbon source is one of polyaniline, carbon nanotubes, graphene, carbon fiber, activated carbon, conductive carbon black, or organic carbon.

9. A sodium ferrous sulfate cathode material, characterized in that, It was prepared using the method for preparing sodium ferrous sulfate cathode material as described in any one of claims 1-8.