A Prussian blue-based sodium-ion battery cathode material, its preparation method and application

Abstract

This invention provides a Prussian blue-based sodium-ion battery cathode material, its preparation method, and its application. The preparation method includes: subjecting a first mixture containing activated S-doped g-C3N4 and a Prussian blue precursor to a first ball milling process to obtain the Prussian blue-based sodium-ion battery cathode material. The Prussian blue-based material prepared by the above method exhibits good conductivity and structural stability, and its use as a cathode material in sodium-ion batteries enables sodium-ion batteries to possess excellent rate performance and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a Prussian blue sodium-ion battery cathode material, its preparation method and application, and a sodium-ion battery. Background Technology

[0002] Electrochemical energy storage, characterized by low cost, no pollution, high efficiency, long cycle life, and flexible power configuration, is a key focus of research in various energy storage fields. Lithium-ion battery technology is considered the most promising due to its high gravimetric and volumetric energy density. However, currently, with the continuous increase in global demand for lithium-ion batteries, the price of lithium is rising steadily, and LIBs are facing a severe resource shortage problem.

[0003] Sodium is the sixth most abundant element in the Earth's crust and is widely distributed, providing a solid raw material foundation for the development of low-cost sodium-ion batteries. While sodium-ion batteries operate on similar principles to lithium-ion batteries, they offer significant resource and cost advantages, making them a promising candidate for large-scale application in energy storage. Furthermore, the similar manufacturing processes of sodium-ion and lithium-ion batteries allow for compatibility with existing lithium-ion battery production equipment during industrialization, reducing technological bottlenecks and further lowering production costs. Therefore, sodium-ion batteries hold a very broad application prospect as energy storage devices for low-cost, high-safety, large-scale energy storage power stations.

[0004] Prussian blue compounds are three-dimensional framework materials that enable reversible insertion and extraction of sodium ions, making them a high-capacity cathode material for sodium-ion batteries. However, the poor conductivity of Prussian blue compounds prevents sodium-ion batteries from reaching their full potential, resulting in poor rate performance. Furthermore, common Prussian blue compounds undergo phase transitions and ion dissolution during charge and discharge due to sodium ion insertion and extraction, leading to structural collapse, which significantly limits their applications. Therefore, improving the cycle performance and conductivity of Prussian blue cathode materials is a pressing issue. Summary of the Invention

[0005] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0006] One objective of this invention is to provide a method for preparing a Prussian blue-based sodium-ion battery cathode material. The method includes: subjecting a first mixture containing activated S-doped g-C3N4 and a Prussian blue precursor to a first ball milling process to obtain the Prussian blue-based sodium-ion battery cathode material.

[0007] On the one hand, the S-doped g-C3N4 in this invention can improve the conductivity of the cathode material. The incorporation of sulfur atoms into carbon nitride changes the electronic structure and energy level distribution of carbon nitride, forming new charge transfer pairs and increasing the electron density of carbon nitride, thereby improving its conductivity. As a coating layer, it can significantly improve the conductivity of Prussian blue. On the other hand, sulfur-doped carbon nitride can optimize the structure of the cathode material, improve its stability, improve the distortion and element dissolution problems during charge and discharge, and improve the rate performance and cycle performance of the material.

[0008] In some embodiments, in the first ball milling process, the ball milling speed is 600-1000 rpm, and / or the ball milling time is 2-6 h, and / or the mass ratio of the first mixture to the milling beads is 1:5-10, and / or the ball milling temperature is 25°C-100°C.

[0009] In some embodiments, the mass ratio of Prussian blue precursor to S-doped g-C3N4 in the first mixture is 9.5:0.5 to 8:2. Within this mass ratio range, the cathode material can achieve high capacity and rate capability, while also exhibiting good cycle performance. If the mass ratio of Prussian blue precursor to S-doped g-C3N4 is low, excessive coating results in low capacity and high cost; conversely, if the mass ratio is high, insufficient coating leads to minimal improvement in rate capability and poor cycle performance.

[0010] In some embodiments, the sulfur doping amount in the S-doped g-C3N4 is 0.15–5 wt%. Compared to ordinary g-C3N4 materials, sulfur-containing g-C3N4 can improve structural stability and conductivity, thereby enhancing battery rate performance and cycle performance.

[0011] In some embodiments, the method for preparing S-doped g-C3N4 includes: calcining thiourea in an oxygen-containing atmosphere, followed by a second ball milling treatment of the calcined product to obtain S-doped g-C3N4.

[0012] In some embodiments, the calcination temperature is 450°C to 650°C, and / or the calcination time is 4 to 10 hours, and / or the oxygen-containing atmosphere includes air.

[0013] In some embodiments, during the second ball milling process, the rotation speed is 400–800 rpm, and / or the milling time is 1–5 h, and / or the mass ratio of S-doped g-C3N4 to milling beads is 1:10–20. The second ball milling process is to pulverize the calcined agglomerated S-doped g-C3N4 into uniform, fine particles, which is beneficial for coating the Prussian blue precursor.

[0014] In some embodiments, after the second ball milling treatment, the S-doped g-C3N4 is placed in a solution with an acid concentration of 0.05–2 mol / L and sonicated for 5–30 min to achieve activation treatment of the S-doped g-C3N4. The acid activation treatment of the coating material in this invention can increase the adhesion and wear resistance of the S-doped g-C3N4 surface, and improve its mechanical strength and chemical stability. The acid activation treatment can also introduce hydrophilic functional groups into the S-doped g-C3N4 surface, which facilitate the binding of g-C3N4 and the Prussian blue precursor, thereby further improving the stability of the coating layer.

[0015] In some embodiments, the acid includes one or more of hydrochloric acid, nitric acid, perchloric acid, and sulfuric acid, but is not limited thereto.

[0016] In some embodiments, after the activation treatment is completed, the obtained activated S-doped g-C3N4 is washed and dried, and then the activated S-doped g-C3N4 with a size of less than 400 mesh is sieved out and mixed with Prussian blue precursor to form the first mixture.

[0017] Furthermore, the washing includes washing the activated S-doped g-C3N4 with water multiple times, and / or the drying includes vacuum drying at a temperature of 80–120°C for 12–24 hours, and / or the sieving includes sieving with a sieve of 400 mesh or less.

[0018] In some embodiments, the method for preparing the Prussian blue precursor includes: subjecting a second mixture containing sodium ferrocyanide and a transition metal salt to a third ball milling process to obtain the Prussian blue precursor. The third ball milling process is performed, for example, at room temperature.

[0019] In some embodiments, the molar ratio of sodium ferrocyanide to transition metal salt in the second mixture is 1:0.8 to 1.5.

[0020] In some embodiments, the transition metal salt includes one or more combinations of compounds containing Mn, Fe, Co, V, Cr, Zn, and Cu.

[0021] In some preferred embodiments, the transition metal salt includes one or more combinations of compounds containing Mn, Fe, and Co. Compared to other transition metal salts, transition metal salts containing Mn, Fe, and Co can form two-electron-active Prussian blue precursors, providing higher specific capacity during charge and discharge.

[0022] In some embodiments, during the third ball milling process, the rotation speed is 800–1200 rpm, and / or the milling time is 2–6 hours, and / or the mass ratio of the first material to the milling beads is 1:5–15. The milling beads are zirconium beads, and there are three types of milling beads: large, medium, and small, with a mass ratio of 5:3:2.

[0023] The second objective of this invention is to provide a Prussian blue sodium-ion battery cathode material prepared according to the preparation method described in any of the above technical solutions.

[0024] The third objective of this invention is to provide a Prussian blue-based sodium-ion battery cathode material with the chemical formula s-C3N4-Na. X M[Fe(CN)6] Y .nH2O, wherein 1.65≤X≤1.95, 0.90≤Y≤0.98, and M includes one or more combinations of Mn, Fe, Co, V, Cr, Zn, and Cu.

[0025] In some embodiments, the cathode material includes Prussian blue and S-doped g-C3N4, wherein the S-doped g-C3N4 is coated onto the surface of the Prussian blue by ball milling.

[0026] In some embodiments, the S-doped g-C3N4 content in the cathode material is 5-20 wt% of the Prussian blue.

[0027] In some embodiments, the sulfur doping amount in the S-doped g-C3N4 is 0.15–5 wt%.

[0028] In some embodiments, M includes one or more of Mn, Fe, and Co.

[0029] The fourth objective of this invention is to provide the application of the Prussian blue sodium-ion battery cathode material described in any of the above technical solutions in the preparation of sodium-ion battery cathodes or sodium-ion batteries.

[0030] The fifth objective of this invention is to provide a sodium-ion battery, which includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode active material includes the Prussian blue sodium-ion battery positive electrode material described in the above technical solution.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] This invention provides a method for preparing sulfur-doped g-C3N4-coated Prussian blue materials by ball milling. The method physically coats a Prussian blue precursor with sulfur-doped g-C3N4 through ball milling without introducing additional moisture, resulting in low crystal water content in the Prussian blue and thus good cycle stability of the obtained Prussian blue-based material. Furthermore, the use of sulfur-containing g-C3N4 to coat the Prussian blue-based material enhances the conductivity and structural stability of the g-C3N4 coating layer, thereby enabling sodium-ion batteries containing the sulfur-doped g-C3N4-coated Prussian blue composite material to exhibit high rate performance and cycle performance.

[0033] The sodium-ion battery containing the Prussian blue-type cathode material provided by this invention can achieve an initial discharge specific capacity of over 127.6 mAh / g at a 0.1C rate (100 mAh / g); the capacity retention rate after 500 charge-discharge cycles at a 1C rate can reach over 80%, even reaching 82.72%; and the capacity retention rate at a 30C rate compared to a 0.1C rate can reach over 70%, even reaching 77.31%. Detailed Implementation

[0034] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be construed as limiting, but are merely intended to form the basis of the claims and to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0035] Example 1

[0036] Thiourea was calcined at 550℃ for 5 hours under air atmosphere to obtain S-doped g-C3N4. Then, the S-doped g-C3N4 was placed in a 1 mol / L sulfuric acid solution and ultrasonically vibrated for 30 minutes to activate it. After activation, it was dried. The activated S-doped g-C3N4 was added to a ball mill jar and ball milled at 800 rpm for 5 hours. The mass ratio of the ball milling beads to the S-doped g-C3N4 was 1:10. After ball milling, it was sieved through a 400-mesh sieve.

[0037] Weigh out 0.01 mol of sodium ferrocyanide, 0.01 mol of manganese sulfate, and 65.3 g of ball milling beads. Ball mill at 1000 rpm for 6 h to obtain the Prussian blue precursor.

[0038] Take 9.5g of the Prussian blue precursor obtained above and 0.5g of the S-doped g-C3N4 prepared above and place them in a ball mill jar. Then add 100g of ball milling beads and ball mill for 3 hours at 25°C and 700rpm to obtain Prussian blue material coated with S-doped g-C3N4.

[0039] The preparation of a sodium-ion battery positive electrode using the S-doped g-C3N4-coated Prussian blue material obtained above includes: mixing the S-doped g-C3N4-coated Prussian blue material, conductive carbon (Super P), and binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, grinding, adding an appropriate amount of 1-methyl-2-pyrrolidone (NMP) solvent, placing it in a homogenizer and vibrating for 10 minutes to uniformly coat the slurry onto carbon-coated aluminum foil, drying it, and then using a slicing machine to punch the aluminum foil coated with black slurry into a circular electrode sheet with a diameter of 14 mm. Then, a pressing machine is used to apply a certain pressure to the electrode sheet for pressing, and finally, the electrode sheet is placed in a vacuum oven and vacuum dried at 120°C for 12 hours to obtain the sodium-ion battery positive electrode sheet.

[0040] The prepared sodium-ion battery positive electrode was used as the working electrode, and metallic sodium was used as the counter electrode. A 1 mol / L NaClO4 / PC∶EMC∶FEC (49∶49∶2) organic electrolyte was used, and the cells were assembled into coin cells in a glove box filled with argon atmosphere. The relevant performance of the cells prepared in this embodiment is shown in Table 1.

[0041] Example 2

[0042] The only difference from Example 1 is that 9.5g of Prussian blue precursor and 0.5g of S-doped g-C3N4 were placed in a ball mill jar, and 50g of milling beads were added. The mixture was ball-milled for 2 hours at 25°C and 600 rpm to obtain Prussian blue material coated with S-doped g-C3N4. The rest of the process was the same as in Example 1.

[0043] Example 3

[0044] The only difference from Example 1 is that 9.5g of Prussian blue precursor and 0.5g of S-doped g-C3N4 were placed in a ball mill jar, and 80g of milling beads were added. The mixture was ball-milled for 6 hours at 25°C and 1000rpm to obtain Prussian blue material coated with S-doped g-C3N4. The rest of the process was the same as in Example 1.

[0045] Example 4

[0046] The only difference from Example 1 is that 8g of Prussian blue precursor and 2g of S-doped g-C3N4 coating material were placed in a ball mill jar and ball-milled to obtain S-doped g-C3N4 coated Prussian blue material. The rest of the process was the same as in Example 1.

[0047] Example 5

[0048] The only difference from Example 1 is that 8.5g of the Prussian blue precursor obtained above and 1.5g of S-doped g-C3N4 coating material are placed in a ball mill jar to obtain S-doped g-C3N4 coated Prussian blue material. The rest is the same as in Example 1.

[0049] Example 6

[0050] The only difference from Example 1 is that 0.01 mol of sodium ferrocyanide, 0.01 mol of cobalt sulfate, and 65.3 g of ball milling beads were weighed and ball milled at 700 rpm for 1 h to obtain the Prussian blue precursor.

[0051] Example 7

[0052] The only difference from Example 1 is that 0.01 mol of sodium ferrocyanide, 0.01 mol of ferrous sulfate, and 65.3 g of ball milling beads were weighed and ball milled at 1300 rpm for 7 h to obtain the Prussian blue precursor.

[0053] Comparative Example 1

[0054] The only difference between Comparative Example 1 and Example 1 is that 0.01 mol of sodium ferrocyanide, 0.01 mol of manganese sulfate, and 65.3 g of ball milling beads were weighed and ball milled at 1000 rpm for 6 hours. After washing, centrifugation, and drying, uncoated Prussian blue material was obtained. The rest of the process was the same as in Example 1.

[0055] Comparative Example 2

[0056] The only difference from Example 1 is that thiourea is replaced with urea for calcination to obtain S-free g-C3N4. This g-C3N4 is used to replace the S-doped g-C3N4 coating material in Example 1. The rest is the same as in Example 1.

[0057] Comparative Example 3

[0058] Prepare a 0.1 mol / L Na₄Fe(CN)₆ aqueous solution and a 0.1 mol / L manganese sulfate aqueous solution;

[0059] 1 L of Na4Fe(CN)6 aqueous solution was added to the reactor, and 1.65 g of S-doped g-C3N4 powder prepared in Example 1 was added to the reactor. The mixture was stirred at 50 °C and 300 rpm.

[0060] The manganese sulfate aqueous solution was pumped into the reactor at a rate of 5 ml / min, and the feeding was stopped after 200 min.

[0061] The material was centrifuged, washed, and dried at 120°C to obtain S-doped g-C3N4-coated Prussian blue sodium material.

[0062] Comparative Example 4

[0063] The only difference between this comparative example and Example 1 is that 9.7g of Prussian blue precursor and 0.3g of S-doped g-C3N4 coating material were placed in a ball mill jar, and 100g of milling beads were added. The mixture was milled at 700rpm for 3 hours. The rest of the process was the same as in Example 1.

[0064] Comparative Example 5

[0065] The only difference between this comparative example and Example 1 is that 7g of the Prussian blue precursor obtained above and 3g of S-doped g-C3N4 coating material were placed in a ball mill jar, and 100g of milling beads were added. The mixture was then milled at 700 rpm for 3 hours. The rest of the process was the same as in Example 1.

[0066] Comparative Example 6

[0067] The only difference from Example 1 is that the S-doped g-C3N4 is not activated with a 1 mol / L sulfuric acid solution; the rest of the procedures are the same as in Example 1.

[0068] The relevant performance of sodium-ion batteries prepared in the embodiments and comparative examples of this invention is shown in Table 1.

[0069] Table 1 shows the similar performance of sodium-ion batteries prepared in the examples and comparative examples.

[0070]

[0071]

[0072] As shown in Table 1, the S-doped g-C3N4-coated Prussian blue composite material of Example 1 showed a decrease in discharge specific capacity from 138.6 mAh / g to 114.6 mAh / g after 500 cycles at 1C, with a capacity retention rate of 82.72%. The discharge specific capacity at 30C was 109.2 mAh / g, representing a capacity retention rate of 77.31% compared to 0.1C. The S-doped g-C3N4-coated Prussian blue composite material of Example 2 showed a capacity retention rate of 80.42% after 500 cycles at 1C, with a capacity retention rate of 70.93% at 30C compared to 0.1C. The S-doped g-C3N4-coated Prussian blue composite material of Example 3 showed a capacity retention rate of 80.42% after 500 cycles at 1C, with a capacity retention rate of 70.93% at 30C compared to 0.1C. The capacity retention rate was 63.93% after cycling at 1C, and 78.91% after cycling at 30C compared to 0.1C. In Example 4, the S-doped g-C3N4-coated Prussian blue composite material retained 88.17% of its capacity after 500 cycles at 1C, and 82.64% after cycling at 30C compared to 0.1C. In Example 5, the S-doped g-C3N4-coated Prussian blue composite material retained 85.66% of its capacity after 500 cycles at 1C, and 82.06% after cycling at 30C compared to 0.1C. In Example 6, the S-doped g-C3N4-coated Prussian blue composite material retained 51.18% of its capacity after 500 cycles at 1C. The capacity retention rate at 30C was 60.09% compared to 0.1C; the S-doped g-C3N4-coated Prussian blue composite material in Example 7 retained 34.36% of its capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 65.32% compared to 0.1C; the uncoated Prussian blue material in Comparative Example 1 retained 32.70% of its capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 54.95% compared to 0.1C; the g-C3N4-coated Prussian blue composite material in Comparative Example 2 retained 75.27% of its capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 72% compared to 0.1C. 17%; Comparative Example 3, the S-doped g-C3N4-coated Prussian blue composite material synthesized by water bath method, retained 68.02% capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 76.45% compared to 0.1C; Comparative Example 4, the S-doped g-C3N4-coated Prussian blue composite material, retained 54.13% capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 68.56% compared to 0.1C; Comparative Example 5, the S-doped g-C3N4-coated Prussian blue composite material, retained 89.41% capacity after 500 cycles at 1C, and the capacity retention rate at 30C was 85.21% compared to 0.1C.The S-doped g-C3N4-coated Prussian blue composite material of Comparative Example 6 retained 73.21% capacity after 500 cycles at 1C, and achieved a capacity retention of 63.58% at 30C compared to 0.1C. This demonstrates that the S-doped g-C3N4-coated Prussian blue composite material synthesized using the method of this invention exhibits excellent electrochemical cycling and rate performance, showing promising application prospects.

[0073] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0074] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0075] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing a Prussian blue-based sodium-ion battery cathode material, characterized in that, include: Thiourea was calcined in an oxygen-containing atmosphere, and then the calcined product was subjected to a second ball milling treatment to obtain S-doped g-C3N4; the S-doped g-C3N4 was placed in a solution with an acid concentration of 0.05~2 mol / L and sonicated for 5~30 min to activate the S-doped g-C3N4. A second mixture containing sodium ferrocyanide and transition metal salts was subjected to a third ball milling process to obtain the Prussian blue precursor. A first mixture containing activated S-doped g-C3N4 and Prussian blue precursor is subjected to a first ball milling treatment, wherein the mass ratio of Prussian blue precursor to S-doped g-C3N4 is 9.5:0.5~8:2, to obtain a Prussian blue sodium-ion battery cathode material.

2. The preparation method according to claim 1, characterized in that: In the first ball milling process, the ball milling speed is 600~1000 rpm, and / or the ball milling time is 2~6 h, and / or the mass ratio of the first mixture to the ball milling beads is 1:5~10, and / or the ball milling temperature is 25℃~100℃.

3. The preparation method according to claim 1, characterized in that: In the S-doped g-C3N4, the sulfur doping amount is 0.15~5wt%.

4. The preparation method according to claim 1, characterized in that: The calcination temperature is 450~650℃, and / or the calcination time is 4~10h, and / or the oxygen-containing atmosphere includes air.

5. The preparation method according to claim 1, characterized in that: In the second ball milling process, the rotation speed is 400~800 rpm, and / or the ball milling time is 1~5 h, and / or the mass ratio of S-doped g-C3N4 to the ball milling beads is 1:10~20.

6. The preparation method according to claim 1, characterized in that, Also includes: After the activation treatment is completed, the obtained activated S-doped g-C3N4 is washed and dried, and then the activated S-doped g-C3N4 with a size of less than 400 mesh is screened out and mixed with Prussian blue precursor to form the first mixture.

7. The preparation method according to claim 1, characterized in that: In the second mixture, the molar ratio of sodium ferrocyanide to transition metal salt is 1:0.8~1.

5.

8. The preparation method according to claim 1, characterized in that: The transition metal salts include one or more combinations of compounds containing Mn, Fe, Co, V, Cr, Zn, and Cu.

9. The preparation method according to claim 8, characterized in that: The transition metal salts include one or more combinations of compounds containing Mn, Fe, and Co elements.

10. The preparation method according to claim 1, characterized in that: In the third ball milling process, the rotation speed is 800~1200 rpm, and / or the ball milling time is 2~6 h, and / or the mass ratio of the first material to the milling beads is 1~5:

15.

11. The Prussian blue sodium-ion battery cathode material obtained by the preparation method according to any one of claims 1-10.

12. The Prussian blue sodium-ion battery cathode material according to claim 11, characterized in that, Its chemical formula is s-C3N4-Na X M[Fe(CN)6] Y .nH2O, wherein 1.65≤X≤1.95, 0.90≤Y≤0.98, and M includes one or more combinations of Mn, Fe, Co, V, Cr, Zn, and Cu.

13. The use of the Prussian blue sodium-ion battery cathode material according to claim 11 or 12 in the preparation of sodium-ion battery cathodes or sodium-ion batteries.

14. A sodium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that: The positive electrode active material includes the Prussian blue sodium-ion battery positive electrode material as described in claim 11 or 12.

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