Sodium ion poly-cathode and anode material synthesized by solid phase method and preparation method of sodium ion poly-cathode and anode material

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a sodium ion poly-cathode and anode material synthesized by a solid phase method and a preparation method thereof. The sodium ion polycathode and anode material is sodium ferric fluorophosphate (NFPF), the chemical composition of the sodium ferric fluorophosphate (NFPF) is Na < 4 + x > Fe < 3 + y > P4O15 + zF gamma, and x is greater than or equal to-0.1 and less than or equal to 0.1; y is in the range of-0.1 < = y < = 0.1; z is greater than or equal to-1 and less than 0; 0 < gamma < = 2. The sodium ion polycathode and anode material-sodium ferric fluorophosphate (NFPF) prepared by the solid phase method has the advantages of high ion and electron conductivity, structural stability, easiness in synthesis of a pure phase and the like, is favorable for improving the performance of a battery and reducing the production cost, and has a wide application prospect.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a sodium-ion polycathode material synthesized by solid-state method and its preparation method. Background Technology

[0002] Lithium-ion batteries possess numerous advantages such as high energy density, high energy conversion efficiency, and long cycle life, and have been widely used in consumer electronics and power storage. However, lithium is relatively rare in the Earth's crust, and its distribution is extremely uneven (70% is located in South America). Sodium-ion batteries operate on a similar principle to lithium-ion batteries, and sodium is 400 times more abundant than lithium in the Earth's crust, with a very wide distribution (found in large quantities underground, in salt lakes, and in the ocean). Sodium-ion batteries also have mature development technologies. Compared to lithium-ion batteries, sodium-ion batteries have significant potential advantages in cost, safety performance, charge / discharge rate, and environmental adaptability, and have broad application prospects in energy storage and small-scale power applications.

[0003] Sodium-ion cathode materials are the core materials of sodium-ion batteries, determining their key performance indicators. Compared with layered oxide materials and Prussian blue cathode materials, polyanionic materials have comprehensive advantages such as higher safety, lower cost, and longer lifespan, and have attracted widespread attention. Among them, sodium iron pyrophosphate composites with abundant and widely available sodium, iron, and phosphorus as chemical components and a NASICON crystal structure have suitable operating voltage (3.1V vs. Na+ / Na), high theoretical capacity (up to about 129mAh / g), open three-dimensional framework, and safety and non-toxicity, and are considered to have the greatest application potential.

[0004] However, composite sodium iron phosphate (NFPP, conventionally Na4Fe3(PO4)2P2O7) suffers from defects such as low intrinsic conductivity and impurity phases during synthesis, resulting in low rate performance and poor cycling performance, which severely restricts its commercial application. Current research mainly focuses on introducing crystal defects and improving carbon coating to address these issues. Authors: Cao Yuliang, Zhao Along, Yuan Tianci, Zhou Xi, Ai Xinping, Yang Hanxi. Title: A Na4Fe 3-x(PO4)2P2O7 / C sodium-ion battery cathode material, its preparation method, and application are disclosed. This paper discloses the synthesis of NFPP with different proportions of iron defects through non-stoichiometric design, which improves the material's conductivity and further reduces the proportion of impurity phases, thus improving the material's rate performance. Authors: Zhang Ye'an, Sun Xuewen, Lai Yanqing, Wang Taosheng, Zhang Kai, Hong Bo, Li Jie. Title: A fluorine-doped carbon-coated sodium iron pyrophosphate@mesoporous carbon composite material, its preparation, and its application in sodium-ion batteries are disclosed. This paper discloses the method of uniformly coating the surface of NFPP with a layer of fluorine-doped carbon through simple ball milling and solid-state sintering. The fluorine-doped carbon coating effectively improves the stability of the NFPP material, thereby enhancing its cycle performance.

[0005] However, even with the above methods such as introducing defects and modifying the carbon coating, the rate capability and cycling performance of NFPP materials still cannot fully meet the requirements for large-scale applications, and the problem of impurity phases in the synthesis process still exists. Summary of the Invention

[0006] The purpose of this application is to address the shortcomings of current technologies by providing a solid-state synthesis method for sodium-ion polycathode cathode materials and its preparation method. Compared to NFPP, the solid-state synthesis method of sodium-ion polycathode cathode material—sodium iron fluorophosphate (NFPF)—is easier to synthesize into a pure phase, and the material formation reaction is more readily carried out. Therefore, the preparation method of this application employs a solid-state method to prepare high-purity NFPF. Furthermore, the PF structure in NFPF can effectively reduce the crystal band gap, thereby increasing the probability of electronic transitions and improving its rate performance. Simultaneously, the interaction between F and Fe can enhance structural stability and improve its cycle performance.

[0007] Firstly, this application provides a sodium-ion polycathode cathode material synthesized by a solid-state method, employing the following technical solution: a sodium-ion polycathode cathode material synthesized by a solid-state method, wherein the sodium-ion polycathode cathode material is sodium ferric fluorophosphate (NFPF), and the chemical composition of the sodium ferric fluorophosphate (NFPF) is: Na... 4+x Fe 3+y P4O 15+z F γ , where the range of x is -0.1≤x≤0.1; the range of y is -0.1≤y≤0.1; the range of z is -1≤z<0; and the range of γ is 0<γ≤2.

[0008] By adopting the above technical solution, the sodium-ion polyanion cathode material synthesized by solid-state method in this application—sodium iron fluorophosphate (NFPF)—is comparable to the current Na4Fe... 3-x P4O 15 Compared to (NFPP) polyanionic cathode materials, its anionic groups are polyhedral anionic groups composed of phosphorus and oxygen. NFPF uses (PO) 4-x F x) m n- and (P2O) 7-x F x ) m n- The two components share corners or edges, forming a stable polyanionic framework. Compared to NFPP sodium-ion cathode materials, NFPF introduces electronic polarization of chemical bonds, inducing an inductive effect that allows sodium ions to conduct rapidly within the open framework during electrochemical processes, resulting in a higher redox potential for NFPF. Therefore, the NFPF prepared in this application exhibits high ionic and electronic conductivity. Furthermore, the interaction between F and Fe enhances structural stability and improves its cycling performance.

[0009] Preferably, the composite stabilizer is composed of modified naphthiourea, chromium chloride and thiodipropionic acid in a mass ratio of 5:1:2-4.

[0010] Secondly, this application provides a method for preparing sodium-ion polycathode cathode materials synthesized by solid-state method, using the following technical solution: As a general technical concept, this application also provides a method for preparing the sodium-ion polycathode cathode material synthesized by solid-state method, comprising the following steps: Sodium fluorophosphate (NFPF) is prepared by uniformly mixing sodium source compound, iron source compound, phosphorus source compound, fluorine source compound and carbon source compound according to the element ratio in the chemical composition of sodium fluorophosphate (NFPF), adding solvent and mixing evenly, grinding to a specified particle size, spray drying and calcining in a protective atmosphere.

[0011] By employing the above technical solution, the sodium-ion polyanionic cathode material—sodium iron fluorophosphate (NFPF)—prepared by the solid-phase method in this application has polyhedral anionic groups composed of phosphorus and oxygen. NFPF uses (PO4) as its anionic group. 4-x F x ) m n- and (P2O) 7- x F x ) m n-The two components share corners or sides, forming a stable polyanionic framework. Compared to NFPP sodium-ion cathode materials, NFPF introduces electronic polarization of chemical bonds, inducing an inductive effect that allows sodium ions to conduct rapidly within the open framework during electrochemical processes, resulting in a higher redox potential for NFPF. Therefore, the NFPF prepared in this application exhibits high ionic and electronic conductivity. Furthermore, the interaction between F and Fe enhances structural stability, facilitates the synthesis of a pure phase, and makes the material formation reaction easier. The solid-state synthesis method for sodium-ion polyanionic cathode materials in this application is suitable for large-scale production applications.

[0012] Preferably, the sodium source compound is selected from one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium nitrate, sodium fluoride, sodium fluorophosphate, sodium trifluoroacetate, sodium oxalate, sodium acetate, sodium persulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and sodium alginate.

[0013] Preferably, the iron source compound is selected from one or more of reduced iron powder, iron(II,III) oxide, iron oxide, ferrous oxide, ferric nitrate, ferric chloride, ferric sulfate, ferric phosphate, ferric oxalate, ferrous oxalate, ferric acetate, ferric citrate, and ferric fluoride.

[0014] Preferably, the phosphorus source compound is selected from one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, phosphoric acid, ammonium dihydrogen phosphate, and triammonium phosphate.

[0015] Preferably, the fluorine source compound is selected from one or more of fluorophosphoric acid, hydrofluoric acid, sodium monofluorophosphate, sodium difluorophosphate, sodium fluoride, ammonium fluoride, ammonium monofluorophosphate, ammonium difluorophosphate, trifluoroacetic acid, sodium trifluoroacetate, and iron fluoride.

[0016] Preferably, the carbon source compound is selected from one or more of glucose, sucrose, citric acid, malic acid, polyaniline, polyethylene glycol, adipic acid, phenolic resin, polypyrrole, ascorbic acid, chitosan, and soluble starch.

[0017] Preferably, the solvent is selected from one or both of water and ethanol, and more preferably, the solvent is a solution of ethanol and water in a molar ratio of 1:1.

[0018] Preferably, the grinding to the specified particle size is achieved by wet grinding with a sand mill to a particle size of 0-400 nm; more preferably, the particle size is 150 nm.

[0019] Preferably, the protective atmosphere is one of an inert gas and an argon-hydrogen mixture, wherein the hydrogen volume content in the argon-hydrogen mixture is 5%; the calcination process conditions are a temperature of 400-600℃, preferably 500℃, and a calcination time of 8-12h.

[0020] In summary, the beneficial technical effects of this application are as follows: 1. High ionic and electronic conductivity: By introducing electronic polarization of chemical bonds, an inductive effect is triggered, enabling sodium ions to conduct rapidly within an open framework during electrochemical processes. This characteristic gives NFPF a high redox potential, thereby improving the energy density and power density of the battery.

[0021] 2. Structural stability: The interaction between F and Fe can enhance structural stability, enabling the material to maintain its structure well during cycling, thereby extending the battery's lifespan.

[0022] 3. Easy to synthesize pure phase: The solid-state preparation method of this application makes it easy to synthesize pure phase of NFPF, which reduces production costs and is conducive to large-scale production and application.

[0023] 4. Environmental friendliness: Compared with traditional lithium-ion batteries, sodium-ion batteries have better environmental performance. Sodium resources are abundant and inexpensive, and sodium-ion batteries do not produce toxic or harmful substances during use, making them environmentally friendly.

[0024] 5. Safety: Sodium-ion batteries offer higher safety compared to lithium-ion batteries. Sodium ions have a larger radius, making them less likely to embed between graphite layers, thus reducing the risk of short circuits. Furthermore, sodium-ion batteries have a relatively lower risk of thermal runaway under abnormal conditions such as overcharging and over-discharging.

[0025] 6. Easy for large-scale production: The solid-state synthesis process of this application is simple, easy to control, and suitable for large-scale production applications. This method does not require complex equipment and conditions, reducing production costs and improving the feasibility of industrial applications. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below: Figure 1 The charge-discharge curves are shown for the batteries assembled from sodium-ion polycathode cathode materials synthesized by solid-state method as prepared in Comparative Example 1 and Examples 1-3. Detailed Implementation

[0027] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0028] Example 1 A sodium-ion polycathode cathode material Na4Fe synthesized by solid-state method 2.92 P4O 14.6 F 0.08 The preparation method includes the following steps: Weigh 0.4 mol sodium bicarbonate, 0.292 mol ferric nitrate, 0.4 mol ammonium dihydrogen phosphate, 0.008 mol ammonium fluoride, and 0.02 mol glucose according to the specified proportions, and dissolve these materials in a water / ethanol solution (ethanol and water molar ratio of 1:1); transfer the raw materials to a sand mill and wet-mill at a speed of 2000 r / min for 3 hours (particle size 150 nm), then spray-dry to obtain a solid powder; place the solid powder in a tube furnace with a hydrogen-argon mixed gas atmosphere (hydrogen volume content of 5%) and sinter at 550℃ for 10 hours. The obtained solid product is the sodium-ion polycathode cathode material synthesized by the solid-phase method.

[0029] Example 2 A sodium-ion polycathode cathode material Na4Fe synthesized by solid-state method 1.46 P4O 14.6 F 0.08 The preparation method includes the following steps: Weigh 0.4 mol sodium bicarbonate, 0.146 mol iron oxide, 0.4 mol ammonium dihydrogen phosphate, 0.008 mol ammonium fluoride, and 0.02 mol glucose according to the specified proportions, and dissolve these materials in a water / ethanol solution (ethanol and water molar ratio of 1:1); transfer the raw materials to a sand mill and wet-mill at a speed of 2000 r / min for 3 hours (particle size 150 nm), then spray-dry to obtain a solid powder; place the solid powder in a tube furnace with a hydrogen-argon mixed gas atmosphere (hydrogen volume content of 5%) and sinter at 550℃ for 10 hours. The obtained solid product is the sodium-ion polycathode cathode material synthesized by the solid-phase method.

[0030] Example 3 A sodium-ion polycathode cathode material Na4Fe synthesized by solid-state method 1.46 P4O 14.7 F 0.06 The preparation method includes the following steps: Weigh 0.4 mol sodium bicarbonate, 0.146 mol iron oxide, 0.4 mol ammonium dihydrogen phosphate, 0.006 mol ammonium fluoride, and 0.02 mol glucose according to the specified proportions, and dissolve these materials in a water / ethanol solution (ethanol and water molar ratio of 1:1); transfer the raw materials to a sand mill and wet-mill at a speed of 2000 r / min for 3 hours (particle size 150 nm), then spray-dry to obtain a solid powder; place the solid powder in a tube furnace with a hydrogen-argon mixed gas atmosphere (hydrogen volume content of 5%) and sinter at 550℃ for 10 hours. The obtained solid product is the sodium-ion polycathode cathode material synthesized by the solid-phase method.

[0031] Example 4 Similar to Example 3, except that the solid powder was placed in a tube furnace with a hydrogen-argon mixture (hydrogen volume content of 5%) and sintered at 400°C for 12 hours.

[0032] Example 5 Similar to Example 3, except that the solid powder was placed in a tube furnace with a hydrogen-argon mixture (hydrogen volume content of 5%) and sintered at 600°C for 8 hours.

[0033] Comparative Example 1 A sodium-ion polycathode cathode material Na4Fe synthesized by solid-state method 2.92 P4O 15 The preparation method includes the following steps: Weigh 0.4 mol sodium bicarbonate, 0.292 mol ferric nitrate, 0.4 mol ammonium dihydrogen phosphate, and 0.02 mol glucose according to the specified proportions, and dissolve these materials in a water / ethanol solution (ethanol and water molar ratio of 1:1); transfer the raw materials to a sand mill and wet-mill at a speed of 2000 r / min for 3 hours (particle size 150 nm), then spray-dry to obtain a solid powder; place the solid powder in a tube furnace with a hydrogen-argon mixed gas atmosphere (hydrogen volume content of 5%) and sinter at 550℃ for 10 hours. The obtained solid product is the sodium-ion polycathode cathode material synthesized by the solid-phase method.

[0034] Performance testing The sodium-ion polycathode cathode materials prepared by solid-state method in Examples 1, 3 and Comparative Example 1 were sampled and tested as follows. The test results are shown in Table 1.

[0035] The particle size of the above sodium ion polycathode cathode material was tested using a laser particle size analyzer (DLS), and the specific surface area was tested using a Bestar Instruments BSD-BET400 fully automatic nitrogen adsorption BET specific surface area analyzer. Battery performance test: The sodium-ion polycathode materials synthesized by solid-state method in Examples 1, 3, and Comparative Example 1 were respectively used to prepare sodium-ion batteries as follows: Sodium-ion polycathode cathode material, conductive agent Super P, and carboxymethyl cellulose were mixed with water in a ratio of 8:1:1 to form a slurry. The mixture was stirred for 24 hours, then coated onto carbon-coated aluminum foil and dried in an oven at 80℃ for 24 hours. The dried electrode was cut into 12mm round pieces with a loading of 1-1.4 mg / cm³. 2 Sodium-ion batteries were fabricated using sodium foil as the counter electrode. Charge / discharge test conditions: constant current charge / discharge at 1C rate, voltage range 0.01V to 3.70V. Test results are shown in Table 1 and... Figure 1 As shown.

[0036] Table 1 Performance Tests Analyzing the data in Table 1, we can see that: The performance test results of the sodium-ion polycathode cathode materials synthesized by the solid-state method in Examples 1-3 show that, compared with NFPP, the sodium-ion polycathode cathode material synthesized by the solid-state method in this application—sodium iron fluorophosphate (NFPF)—is easier to synthesize into a pure phase, and the material formation reaction is easier to carry out. Therefore, the preparation method of this application adopts the solid-state method to prepare high-purity NFPF. At 1C rate, the discharge specific capacity reaches more than 105 mAh / g after 5000 cycles, and the capacity retention rate reaches more than 90.7%.

[0037] The performance comparison analysis of the sodium-ion polycathode cathode materials synthesized by solid-state method in Example 3 and Comparative Example 1 shows that the PF structure in NFPF can effectively reduce the crystal band gap of the material, thereby increasing the probability of electronic transition and thus improving its rate performance. At the same time, the interaction between F and Fe can enhance the structural stability and improve its cycle performance.

[0038] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this invention. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A solid-state synthesized sodium-ion polyanionic cathode material, characterized in that, The sodium ion polyanion cathode material is sodium iron fluorophosphate (NFPF), and the chemical composition of the sodium iron fluorophosphate (NFPF) is: Na 4+x Fe 3+y P4O 15+z F γ wherein, the range of x is -0.1≤x≤0.1; the range of y is -0.1≤y≤0.1; the range of z is -1≤z<0; and the range of γ is 0<γ≤2.

2. A method for preparing the sodium-ion polyanionic cathode material synthesized by the solid-phase method according to claim 1, characterized in that, According to the element ratio in the chemical composition of the sodium iron fluorophosphate (NFPF), the sodium source compound, the iron source compound, the phosphorus source compound, the fluorine source compound and the carbon source compound are mixed uniformly, then a solvent is added and mixed uniformly, and then sand grinding is performed to a specified particle size, and then spray drying is performed, and then calcination is performed in a protective atmosphere to obtain the sodium iron fluorophosphate (NFPF).

3. The solid-state synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The sodium source compound is selected from one or more of sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium nitrate, sodium fluoride, sodium fluorophosphate, sodium trifluoroacetate, sodium oxalate, sodium acetate, sodium persulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate and sodium alginate.

4. The solid-state synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The iron source compound is selected from one or more of reduced iron powder, magnetite, iron oxide, ferrous oxide, ferric nitrate, ferric chloride, ferric sulfate, ferric phosphate, ferric oxalate, ferrous oxalate, ferric acetate and ferric citrate, and ferric fluoride.

5. The solid-state synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The phosphorus source compound is selected from one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, phosphoric acid, ammonium dihydrogen phosphate and ammonium triphosphate.

6. The solid phase synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The fluorine source compound is selected from one or more of fluorophosphoric acid, hydrofluoric acid, sodium monofluorophosphate, sodium difluorophosphate, sodium fluoride, ammonium fluoride, ammonium monofluorophosphate, ammonium difluorophosphate, trifluoroacetic acid, sodium trifluoroacetate and ferric fluoride.

7. The solid phase synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The carbon source compound is selected from one or more of glucose, sucrose, citric acid, malic acid, polyaniline, polyethylene glycol, adipic acid, phenol formaldehyde resin, polypyrrole, ascorbic acid, chitosan and soluble starch.

8. The solid phase synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The solvent is selected from one or both of water and ethanol.

9. The solid phase synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The sand grinding to a specified particle size is wet grinding to a particle size of 0-400 nm using a sand mill.

10. The solid phase synthesized sodium-ion polyanionic cathode material of claim 2, wherein, The protective atmosphere is one of an inert gas and argon-hydrogen mixed gas, the hydrogen gas content of the argon-hydrogen mixed gas is 5%, and the calcination process conditions are a temperature of 400-600°C and a calcination time of 8-12 h.

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