A sodium iron manganese magnesium phosphate positive electrode material and a preparation method thereof

Abstract

The application relates to a sodium iron manganese magnesium phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of sodium batteries. The preparation method comprises the following steps: (1) under the stirring state, magnesium sulfate solution, ferrous sulfate solution, manganous sulfate solution and sodium carbonate solution are added into a reaction kettle; (2) the slurry is filtered and washed, the filter cake after washing is added with water to prepare a slurry, then phosphoric acid, sodium bicarbonate solution and sucrose are added into the reaction kettle, and then the slurry is reacted under the action of an alternating current field and a magnetic field for 3-6 hours; (3) the slurry after reaction is filtered, washed and dried to obtain sodium iron manganese magnesium phosphate; (4) rapid sintering and mechanical crushing are carried out to obtain the sodium iron manganese magnesium phosphate positive electrode material. The material prepared by the application has higher crystallinity and better carbon coating effect, so that the synthesized material has higher capacity, more excellent rate performance and longer cycle life compared with the material synthesized without adding an electric field and a magnetic field.

Description

Technical Field

[0001] This invention relates to the technical field of sodium batteries, specifically to a sodium iron manganese magnesium phosphate cathode material and its preparation method. Background Technology

[0002] In recent years, sodium-ion batteries have gradually developed due to their low cost and readily available raw materials. This is thanks to the fact that sodium is much cheaper than lithium, typically costing only one-tenth of the price of lithium. There are three main types of cathode materials used in sodium-ion batteries: ternary sodium nickel cobalt manganese oxide, Prussian series materials, and polyanionic materials. Among these three, ternary sodium-ion battery materials have relatively high costs due to the need for relatively expensive cobalt and nickel, and there are certain safety concerns. Prussian series materials, because their raw materials and products are cyanides, have a certain degree of toxicity, are not environmentally friendly and pose safety risks during preparation. Polyanionic sodium-ion battery cathode materials have received widespread attention due to their low cost, non-toxicity to humans, environmental friendliness, and long cycle life. Among polyanionic materials, sodium iron manganese phosphate combines the advantages of sodium iron phosphate and sodium manganese phosphate, exhibiting high electrochemical activity, low cost, and good rate and low-temperature performance, making it a key research focus for research and industrialization.

[0003] The existing methods for preparing polyanionic sodium cathode materials include the following:

[0004] (1) Patent CN116741975A discloses a method for preparing sodium vanadium iron manganese phosphate material, which uses iron, manganese, sodium, vanadium and phosphorus sources and prepares sodium vanadium iron manganese phosphate material by sol-gel method and high temperature sintering. However, the sol-gel method has a long preparation cycle, and the gelation time is several days. In order to avoid cracking of the material, the drying process also needs to be slow, resulting in low overall production efficiency, which is difficult to meet the needs of large-scale industrial production and the cost is also high. In addition, the prepared sodium vanadium iron manganese phosphate material has low electrical performance, with a 0.1C discharge capacity of only 104 mAh / g, which is far lower than its theoretical discharge capacity of 154 mAh / g.

[0005] (2) Patent CN114436235A discloses a method for preparing sodium iron manganese phosphate material. This method uses ferrous sulfate, a byproduct of titanium dioxide, as a raw material. After purification, a ferrous sulfate solution is obtained. Then, a soluble permanganate is added to react and prepare a mixture of ferric hydroxide and manganese hydroxide. After filtration and drying, a mixed powder of ferric hydroxide and manganese hydroxide is obtained. This powder is then ball-milled with sodium dihydrogen phosphate and sintered at a high temperature of 800-900℃ to obtain sodium iron manganese phosphate material. The above method has a long preparation process and easily generates impurities such as iron hydroxide during preparation. These impurities may reduce the charge / discharge capacity and service life of the product. Furthermore, the sintering temperature during preparation is high, resulting in high energy consumption. In addition, the prepared sodium iron manganese phosphate product has a low capacity, with a 1C capacity of only 75 mAh / g, far below its theoretical discharge capacity of 154 mAh / g.

[0006] In summary, there is a need to develop a high-capacitance polyanionic sodium cathode material. Summary of the Invention

[0007] To address the technical problem of low capacitance in existing polyanionic sodium cathode materials, this invention proposes a method for preparing sodium iron manganese magnesium phosphate cathode material to solve the aforementioned problem.

[0008] The technical solution of this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a sodium iron manganese magnesium phosphate cathode material, comprising the following steps:

[0010] (1) While stirring, magnesium sulfate solution, ferrous sulfate solution, manganese sulfate solution and sodium carbonate solution are added to the reaction vessel to generate a slurry;

[0011] (2) Slurry filtration and washing: The washed filter cake is mixed with water to make slurry, which is then added to the reaction vessel and heated to 80℃~100℃. Phosphoric acid, sodium bicarbonate solution and sucrose are then added to the reaction vessel and reacted for 3~6 hours under the action of alternating electric field and magnetic field.

[0012] (3) The slurry after the reaction is filtered, washed and dried to obtain sodium iron manganese magnesium phosphate;

[0013] (4) The sodium iron manganese magnesium phosphate obtained in step (3) is rapidly sintered, and the sintered sodium iron manganese magnesium phosphate is mechanically crushed to obtain sodium iron manganese magnesium phosphate cathode material.

[0014] Furthermore, the molar ratio of magnesium sulfate, ferrous sulfate, manganese sulfate, sodium carbonate, sodium bicarbonate, phosphoric acid, and sucrose is: (0.1~0.2):(0.1~0.3):(0.7~0.9):(1.1~1.5):(1.1~1.5):(1.0~1.5):(0.01~0.02).

[0015] Furthermore, in step (1), the purity of magnesium sulfate is >98%, ferrous sulfate is treated with ferrous sulfate powder, a byproduct of titanium dioxide, to remove impurities, and the purity of ferrous sulfate after impurity removal is 99%, the purity of manganese sulfate is >98%, and the purity of sodium carbonate is >98%.

[0016] Furthermore, in step (1), the stirring speed is 50~200 rpm and the addition time is 3~5 h.

[0017] Furthermore, in step (2), during slurry filtration and washing, the filter cake is washed until the conductivity of the filtrate is <3000μs / cm.

[0018] Furthermore, in step (2), the phosphoric acid concentration is 40%~85%; the AC electric field frequency is 20~50Hz, the voltage is 5~10V, the electric field strength is 100~500V / m, and the magnetic field strength is 20~50mT.

[0019] Furthermore, in step (3), the filter cake is washed until the conductivity of the filtrate is <1000μs / cm; the drying is carried out by centrifugal drying, with a centrifugal speed of 1000~3000rpm and a drying time of 1~3h.

[0020] Furthermore, in step (4), the rapid sintering is carried out by blower sintering, that is, the blower blows the material up and rapidly sintersects and calcines it at high temperature. The blower frequency is 35Hz, the sintering temperature is 600℃~700℃, the outlet temperature is 200℃~400℃, and the sintering time is 10~40min.

[0021] Secondly, the present invention provides a sodium iron manganese magnesium phosphate cathode material obtained by the above method.

[0022] The beneficial effects of this invention are as follows:

[0023] The method for preparing sodium iron manganese magnesium phosphate cathode material provided by this invention first generates manganese iron manganese magnesium carbonate, which is then filtered and washed to remove impurities. Phosphoric acid, sodium carbonate, and sucrose are then added to the washed manganese iron manganese magnesium carbonate material to initiate a crystallization reaction and carbon coating. Simultaneously, an electric field and a magnetic field are applied during the synthesis of the sodium iron manganese magnesium phosphate material, resulting in higher crystallinity and better carbon coating. This leads to a material with higher capacity, superior rate performance, and longer cycle life compared to materials synthesized without the application of electric and magnetic fields. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 These are XRD comparison images of the products prepared in Example 3, Comparative Example 1, and Comparative Example 2 of this invention.

[0026] Figure 2 This is a SEM image of the sodium iron manganese magnesium phosphate material prepared in Example 3 of this invention.

[0027] Figure 3 XPS of sodium iron manganese magnesium phosphate material prepared in Example 3 of this invention Figure 1 .

[0028] Figure 4 XPS of sodium iron manganese magnesium phosphate material prepared in Example 3 of this invention Figure 2 . Detailed Implementation

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

[0030] Example 1

[0031] A method for preparing a sodium iron manganese magnesium phosphate cathode material includes the following steps:

[0032] (1) Prepare 1L of 0.1mol / L magnesium sulfate solution, 1L of 0.3mol / L ferrous sulfate solution, 1L of 0.7mol / L manganese sulfate solution, and 1L of 1.1mol / L sodium carbonate solution. The reactor is filled with water, and the stirring speed is controlled at 100rpm. The magnesium sulfate solution, ferrous sulfate solution, manganese sulfate solution, and sodium carbonate solution are added to the reactor simultaneously through four pipes to generate a slurry.

[0033] (2) Slurry filtration: The filter cake was washed until the conductivity of the filtrate was <3000 μs / cm. Then, water was added to the filter cake until the slurry concentration was 1 mol / L. 116 g of 85% phosphoric acid, 1 L of 1.2 mol / L sodium bicarbonate solution, and 3.5 g of sucrose were added. The reaction system was heated to 90℃. An electric field and a magnetic field were applied to the reaction system. The frequency of the alternating electric field was 20 Hz, the voltage was 5 V, the electric field strength was 100 V / m, and the magnetic field strength was 20 mT. The reaction was carried out for 4 h under the action of the alternating electric field and magnetic field.

[0034] (3) After the reaction was completed, the filter cake was washed until the conductivity of the filtrate was <1000μs / cm. The filter cake was dried by centrifugation at 3000rpm for 2h to obtain sodium iron manganese magnesium phosphate.

[0035] (4) The sodium iron manganese magnesium phosphate obtained in step (3) is rapidly sintered by blowing air, that is, blowing air to lift the material and rapidly sintering and calcining at high temperature. The blowing frequency is 35Hz, the sintering temperature is 600℃, the outlet temperature is 200℃, and the sintering time is 30min, resulting in 148g of sodium iron manganese magnesium phosphate material.

[0036] Example 2

[0037] A method for preparing a sodium iron manganese magnesium phosphate cathode material includes the following steps:

[0038] (1) Prepare 10L of 0.1mol / L magnesium sulfate solution, 10L of 0.3mol / L ferrous sulfate solution, 10L of 0.7mol / L manganese sulfate solution, and 10L of 1.1mol / L sodium carbonate solution. The reactor is filled with water, and the stirring speed is controlled at 100rpm. The magnesium sulfate solution, ferrous sulfate solution, manganese sulfate solution, and sodium carbonate solution are added to the reactor simultaneously through four pipes to generate a slurry.

[0039] (2) Slurry filtration: The filter cake is washed until the conductivity of the filtrate is <3000μs / cm. Then, water is added to the filter cake until the slurry concentration is 1mol / L. 1160g of 85% phosphoric acid, 10L of 1.2mol / L sodium bicarbonate solution, and 35g of sucrose are added. The reaction system is heated to 90℃. An electric field and a magnetic field are applied to the reaction system. The frequency of the alternating electric field is 50Hz, the voltage is 10V, the electric field strength is 500V / m, and the magnetic field strength is 50mT. The reaction is carried out for 4h under the action of the alternating electric field and magnetic field.

[0040] (3) After the reaction was completed, the filter cake was washed until the conductivity of the filtrate was <1000μs / cm. The filter cake was dried by centrifugation at 3000rpm for 2h to obtain sodium iron manganese magnesium phosphate.

[0041] (4) The sodium iron manganese magnesium phosphate obtained in step (3) is rapidly sintered by blowing air, that is, blowing air to blow the material up and rapidly sintering and calcining at high temperature. The blowing frequency is 35Hz, the sintering temperature is 700℃, the outlet temperature is 400℃, and the sintering time is 30min, resulting in 1.47kg of sodium iron manganese magnesium phosphate material.

[0042] Example 3

[0043] A method for preparing a sodium iron manganese magnesium phosphate cathode material includes the following steps:

[0044] (1) Prepare 100L of 0.1mol / L magnesium sulfate solution, 100L of 0.3mol / L ferrous sulfate solution, 100L of 0.7mol / L manganese sulfate solution, and 100L of 1.1mol / L sodium carbonate solution. The reactor is filled with water, and the stirring speed is controlled at 150rpm. The magnesium sulfate solution, ferrous sulfate solution, manganese sulfate solution, and sodium carbonate solution are added to the reactor simultaneously through four pipes to generate a slurry.

[0045] (2) Slurry filtration: The filter cake is washed until the conductivity of the filtrate is <3000μs / cm. Then, water is added to the filter cake until the slurry concentration is 1mol / L. 11.6kg of 85% phosphoric acid, 100L of 1.2mol / L sodium bicarbonate solution, and 350g of sucrose are added. The reaction system is heated to 90℃. An electric field and a magnetic field are applied to the reaction system. The frequency of the alternating electric field is 35Hz, the voltage is 7V, the electric field strength is 300V / m, and the magnetic field strength is 35mT. The reaction is carried out for 4h under the action of the alternating electric field and magnetic field.

[0046] (3) After the reaction was completed, the filter cake was washed until the conductivity of the filtrate was <1000μs / cm. The filter cake was dried by centrifugation at 3000rpm for 2h to obtain sodium iron manganese magnesium phosphate.

[0047] (4) The sodium iron manganese magnesium phosphate obtained in step (3) is rapidly sintered by blowing air, that is, blowing air to blow the material up and rapidly sintering and calcining at high temperature. The blowing frequency is 35Hz, the sintering temperature is 650℃, the outlet temperature is 300℃, and the sintering time is 30min, resulting in 14.9kg of sodium iron manganese magnesium phosphate material.

[0048] Comparative Example 1

[0049] A method for preparing sodium iron manganese phosphate cathode material is the same as that in Example 3, except that magnesium sulfate solution is not added in step (1).

[0050] Comparative Example 2

[0051] A method for preparing a sodium iron manganese magnesium phosphate cathode material is the same as that in Example 3, except that no electric field or magnetic field is applied in step (2).

[0052] Test case

[0053] The products prepared in Example 3, Comparative Example 1, and Comparative Example 2 were subjected to XRD analysis. The results are detailed in [link to XRD analysis]. Figure 1 .from Figure 1 As can be seen, the XRD pattern of Comparative Example 2 contains a large peak of amorphous state and several peaks of crystalline state. After refinement, the crystallinity was measured to be only 52.4%, indicating low crystallinity and incomplete crystallization. Comparative Example 1 is a sodium iron manganese phosphate product prepared by applying electric and magnetic fields but without magnesium doping. Figure 1 As can be seen, after applying electric and magnetic fields to Comparative Example 1, compared to Comparative Example 2, no amorphous peaks appeared; the peaks were sharp and all were diffraction peaks of the crystalline state. This indicates that the crystallinity was greatly improved after applying electric and magnetic fields, and the crystallinity was calculated to be 99.3% after refinement. Example 3 is a product of sodium iron manganese magnesium phosphate prepared by applying electric and magnetic fields and performing magnesium doping treatment. Figure 1 As can be seen, the XRD spectrum of the product prepared in Example 3 is in excellent agreement with the standard PDF card (04-011-6740), indicating that it is a pure-phase sodium iron manganese magnesium phosphate material, and no peaks of other impurity phases were found. The only difference between Example 3 and Comparative Example 2 is that the sodium iron manganese magnesium phosphate product prepared by applying electric and magnetic fields was different. Figure 1 The XRD results showed that the crystallinity increased significantly after applying electric and magnetic fields, from 52.4% without electric and magnetic fields to 99.59%.

[0054] The sodium iron manganese magnesium phosphate prepared in Example 3 was analyzed by SEM. Figure 2 It can be seen that the sodium iron manganese magnesium phosphate material consists of near-spherical particles with a primary particle size of 50-300 nm.

[0055] XPS analysis was performed on the sodium iron manganese magnesium phosphate prepared in Example 3. Figure 3 It can be seen that the binding energy peaks of elements such as Na, Mg, Fe, Mn, P, and O are all visible in the XPS total spectrum, indicating that the substance synthesized in Example 3 is sodium iron manganese magnesium phosphate. From... Figure 4 It can be seen that the peak position of the Mg binding energy is at 1304.5 eV, proving that Mg has been doped into the bulk phase of sodium iron manganese phosphate.

[0056] The products prepared in Examples 1-3 and Comparative Examples 1-2 were tested for compaction density, and then fabricated into coin cells under the same conditions. Their electrical performance was then tested under the same conditions using conventional methods in the art. The electrical performance test results are shown in Tables 1 and 2 below:

[0057] Table 1 - Test Results of Product Compacted Density and 0.1C Charge / Discharge Capacity

[0058]

[0059] As shown in Table 1, the sodium iron manganese magnesium phosphate prepared by Examples 1-3 exhibits good compaction and electrical properties. The compaction density of Examples 1-3 reaches over 2.60 g / cc, indicating high compaction density. The 0.1C charging capacity of the samples from Examples 1-3 reaches 150-154 mAh / g, close to the theoretical capacity of 154 mAh / g, and the 0.1C discharging capacity reaches 148-151 mAh / g, also showing high capacity. The prepared sodium iron manganese magnesium phosphate products possess high compaction and high capacity, thus exhibiting high energy density. Comparative Example 1, the sodium iron manganese phosphate sample without magnesium doping, has a slightly lower compaction density and 0.1C charge / discharge capacity than Examples 1-3, indicating that magnesium doping is beneficial for improving compaction density and charge / discharge capacity. Comparative Example 2 shows the sodium iron manganese magnesium phosphate product prepared without the application of an electric or magnetic field. It can be seen that its compaction density and capacity are lower than those of Examples 1-3, with a compaction density 0.3-0.4 g / cc lower and a discharge capacity 10-14 mAh / g lower. Therefore, its energy density (energy density = compaction density * discharge capacity * voltage) is 20%-30% lower than that of Examples 1-3. If this material is applied to electric vehicles, the sodium iron manganese magnesium phosphate material prepared without the application of an electric or magnetic field will have a driving range 100-200 kilometers less than that prepared with the application of an electric or magnetic field. Therefore, applying an electric or magnetic field during the preparation process significantly improves the performance of the prepared material.

[0060] Table 2 - Comparison of Product Rate Performance (mAh / g)

[0061]

[0062] As can be seen from the comparison results of rate performance in Table 2, the materials prepared by applying electric and magnetic fields in Examples 2 and 3, as well as Comparative Example 1, all exhibit excellent rate performance. However, the sodium iron manganese magnesium phosphate material prepared in Comparative Example 2 has poor rate performance because no electric or magnetic field was applied during its preparation. For example, in Example 3, at a high rate of 20C, its capacity can still reach 92.53 mAh / g, while in Comparative Example 2 it is only 56.49 mAh / g, which is only 61% of that in Example 3. If converted to the driving range of an electric vehicle, the electric vehicle prepared with the material in Example 3 (at 20C) has a driving range of 500 kilometers, while the electric vehicle prepared with the material in Comparative Example 2 (at 20C) has a driving range of only 305 kilometers, a significant reduction in driving range.

[0063] Table 3 - Comparison of Product Cycle Life (1C)

[0064]

[0065] Note: CR = Capacity retention

[0066] Comparing the cycle life results at 1C rate in Table 3, after 200 cycles, Examples 2 and 3, as well as Comparative Example 1 (with applied electric and magnetic fields), still retain 96%~98.5% of their capacity, while Example 2 (without applied electric and magnetic fields) retains only 85.67%. After 400 cycles, Examples 2 and 3, as well as Comparative Example 1 (with applied electric and magnetic fields), still retain 94%~96.3% of their capacity, while Example 2 (without applied electric and magnetic fields) retains only 45.78%. If the electric vehicle battery prepared using the material of Example 3 has a lifespan of 10 years, then the electric vehicle battery prepared using the material of Example 2 has a lifespan of only 4.7 years, which is halved. Therefore, in summary, the electric vehicle power battery prepared using sodium iron manganese magnesium phosphate material prepared by simultaneously applying electric and magnetic fields during the preparation process will have higher compaction and capacity, superior rate performance, longer driving range, and longer lifespan, resulting in a better user experience for electric vehicles.

[0067] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing a sodium iron manganese magnesium phosphate cathode material, characterized in that, Includes the following steps: (1) While stirring, magnesium sulfate solution, ferrous sulfate solution, manganese sulfate solution and sodium carbonate solution are added to the reaction vessel to generate a slurry; (2) Slurry filtration and washing: The washed filter cake is mixed with water to make slurry, which is then added to the reaction vessel and heated to 80℃~100℃. Phosphoric acid, sodium bicarbonate solution and sucrose are then added to the reaction vessel and reacted for 3~6 hours under the action of alternating electric field and magnetic field. (3) The slurry after the reaction is filtered, washed and dried to obtain sodium iron manganese magnesium phosphate; (4) The sodium iron manganese magnesium phosphate obtained in step (3) is rapidly sintered, and the sintered sodium iron manganese magnesium phosphate is mechanically crushed to obtain sodium iron manganese magnesium phosphate cathode material. The molar ratios of magnesium sulfate, ferrous sulfate, manganese sulfate, sodium carbonate, sodium bicarbonate, phosphoric acid, and sucrose are: (0.1~0.2):(0.1~0.3):(0.7~0.9):(1.1~1.5):(1.1~1.5):(1.0~1.5):(0.01~0.02). In step (2), the frequency of the alternating electric field is 20~50Hz, the voltage is 5~10V, the electric field strength is 100~500V / m, and the magnetic field strength is 20~50mT. In step (4), the sintering temperature is 600℃~700℃ and the sintering time is 10~40min.

2. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (1), the purity of magnesium sulfate is >98%, ferrous sulfate is treated with ferrous sulfate powder, a byproduct of titanium dioxide, to remove impurities, and the purity of ferrous sulfate after impurity removal is 99%, the purity of manganese sulfate is >98%, and the purity of sodium carbonate is >98%.

3. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (1), the stirring speed is 50~200 rpm and the addition time is 3~5 h.

4. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (2), during slurry filtration and washing, the filter cake is washed until the conductivity of the filtrate is <3000μs / cm.

5. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (2), the phosphoric acid concentration is 40%~85%.

6. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (3), the filter cake is washed until the conductivity of the filtrate is <1000μs / cm; the drying is carried out by centrifugal drying, with a centrifugal speed of 1000~3000rpm and a drying time of 1~3h.

7. The method for preparing a sodium iron manganese magnesium phosphate cathode material as described in claim 1, characterized in that, In step (4), rapid sintering is carried out using forced air sintering with a forced air frequency of 35Hz and an outlet temperature of 200℃~400℃.

8. A sodium iron manganese magnesium phosphate cathode material obtained using the preparation method described in claim 1.

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