Doped sodium iron fluorosulfate compound, positive electrode material, preparation method thereof and sodium ion battery

Abstract

The application discloses a doped sodium iron fluorosulfate compound, a positive electrode material and a preparation method thereof and a sodium ion battery. y M z (SO4)2F, wherein y+z=1, 0 The doped sodium iron fluorosulfate compound of the application not only reduces the gas production, but also has relatively high gram capacity performance and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a doped sodium ferric fluorosulfate compound, a cathode material, a method for preparing the same, and a sodium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles, lithium-ion power batteries, as a core component of these vehicles, are about to enter the TWh era. The demand for lithium-ion batteries is high, while the abundance of lithium in the Earth's crust is only about 0.0065%. In recent years, the shortage of lithium resources has increased the cost of lithium-ion batteries, limiting their application in large-scale energy storage devices. Therefore, sodium, with its abundant and inexpensive raw materials, has once again attracted the interest of scientists. In the periodic table, sodium and lithium are in the same group and have similar physicochemical properties. Sodium resources on Earth are very abundant, with an elemental content of approximately 23,000 ppm (compared to only about 17 ppm for lithium), ranking 6th in abundance, and distributed globally, completely unrestricted by resources or location. Therefore, in terms of resources, sodium-ion batteries have a greater advantage than lithium-ion batteries.

[0003] Compared to lithium-ion batteries, sodium-ion batteries have a larger radius and atomic mass, making ion diffusion more difficult and resulting in inferior theoretical capacity and reaction kinetics. Specifically, sodium-ion batteries experience greater difficulty and slower electrode insertion / extraction, and are more prone to morphological damage to the cathode material, thus significantly impacting the specific capacity, lifespan, and safety performance of sodium-ion batteries.

[0004] Unlike lithium-ion batteries, where the cathode technology route is largely established, there are currently over 100 types of cathode materials related to sodium-ion batteries, and the technology route is still evolving. Based on composition, mainstream sodium-ion battery cathode materials can be divided into transition metal oxides, polyanionic compounds, and Prussian blue-based compound systems. Transition metal oxides, based on their microstructure, can be further divided into layered metal oxides and tunnel-type transition metal oxides. Due to the low initial sodium-ion content of tunnel-type oxides, they have received less market attention. Currently, each of the three types of sodium-ion battery cathode materials has its advantages and disadvantages, and competition among these three types of cathode materials is expected to continue in the future.

[0005] Polyanionic compounds exhibit diverse and stable three-dimensional structures, with olivine-type crystal structures similar to lithium iron phosphate being the most common. During the insertion and extraction of sodium ions, polyanionic compounds show minimal volume change and few phase transitions, resulting in good long-term cycling stability and high safety. The cycle life of polyanionic compounds is mostly above 4000 cycles. The main disadvantage of polyanionic compounds lies in their relatively low specific capacity, currently around 100 mAh / g. There are many types of polyanionic compounds, with sodium ferric sulfate, sodium vanadium fluorophosphate, and sodium vanadium phosphate being among the most studied.

[0006] Sodium ferric sulfate, as the lowest-cost polyanionic material, has attracted widespread attention. However, due to the hygroscopic nature of sodium ferric sulfate, its water of crystallization is difficult to remove, leading to severe gas production, sodium precipitation, and impaired circulation performance. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a doped sodium ferric sulfate compound, a cathode material, a preparation method thereof, and a sodium-ion battery. The invention uses sodium fluoride, which has low hygroscopicity, as the sodium source, and by doping to replace part of the easily hygroscopic sodium sulfate and ferrous sulfate, it not only reduces the gas production, but also has relatively high specific capacity and cycle performance.

[0008] To achieve the above objectives, the first technical solution of the present invention is as follows:

[0009] A doped sodium ferric fluoride compound, characterized in that its chemical structural formula is Na3Fe y M z (SO4)2F, where y+z=1, 0<z≤0.5, and M is selected from Mn, Cu, Ni, Co, Cr, V or Ti.

[0010] The second technical solution of the present invention is as follows:

[0011] A positive electrode material comprising a conductive agent and a doped sodium ferric fluorosulfate compound as described above.

[0012] The third technical solution of the present invention is as follows:

[0013] A method for preparing the above-mentioned positive electrode material includes the following steps:

[0014] Sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and a conductive agent are mixed and then sintered to obtain the positive electrode material.

[0015] The fourth technical solution of the present invention is as follows:

[0016] A sodium-ion battery comprising the positive electrode material as described above.

[0017] Implementing the embodiments of the present invention will have the following beneficial effects:

[0018] The hygroscopicity of sodium ferric sulfate is due to the strong water absorption of sodium sulfate and ferrous sulfate themselves. In this embodiment of the invention, a new doped sodium ferric sulfate compound is obtained by replacing part of the easily hygroscopic sodium sulfate with sodium fluoride, which has low hygroscopicity, and by replacing part of the easily hygroscopic ferrous sulfate with M sulfate. This not only reduces the gas production, but also has relatively high specific capacity and circulation performance.

[0019] The cathode material of this invention solves the problem of poor electronic conductivity of polyanionic compounds by doping with conductive agents, making it suitable for use in sodium-ion batteries and as a power supply for electrical devices, exhibiting good battery utilization and cycle life.

[0020] The preparation method of the present invention is simple to operate, mild under mild conditions, and easy to prepare on a large scale. Attached Figure Description

[0021] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] in:

[0023] Figure 1 This is a scanning electron microscope image of the cathode material prepared in Example 6 of the present invention.

[0024] Figure 2 This is a diagram of the experimental apparatus used in the test example of the present invention to test the gas production volume using the water displacement method. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention discloses a doped sodium ferric fluoride compound with the chemical structural formula Na3Fe. y M z (SO4)2F, where y+z=1, 0<z≤0.5, and M is selected from Mn, Cu, Ni, Co, Cr, V or Ti.

[0027] In a preferred embodiment, the chemical structural formula of a doped sodium ferric fluorosulfate compound is Na3Fe. y Ni z (SO4)2F, where y+z=1, 0<z≤0.2.

[0028] The present invention also discloses a positive electrode material comprising a conductive agent and the above-mentioned doped sodium ferric fluorosulfate compound.

[0029] In one specific embodiment, the mass percentage of the conductive agent to the positive electrode material is 0.1% to 10%.

[0030] Furthermore, conductive agents may include carbon-based electronic conductive agents and / or metallic conductive agents.

[0031] Carbon-based electronic conductive agents may include one or more of the following: amorphous carbon, Superp, carbon nanotubes (e.g., multi-walled carbon nanotubes, single-walled carbon nanotubes, etc.), VGCF (vapor-grown carbon fiber reinforcement), graphene, Ketjen black, acetylene black, C65 carbon black, and conductive graphite (e.g., KS6, etc.).

[0032] Metallic conductive agents may include one or more of Ni powder, Cu powder, Ag powder, and Al powder.

[0033] In one specific embodiment, the particle size of the conductive agent is 1 nm to 10 μm.

[0034] This invention also discloses a method for preparing the above-mentioned cathode material, comprising the following steps:

[0035] Sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and a conductive agent are mixed and then sintered to obtain the positive electrode material.

[0036] In one specific embodiment, the sintering temperature is 250°C to 500°C; the sintering time is 2 hours to 24 hours. Preferably, the sintering is carried out under an inert atmosphere.

[0037] In one specific embodiment, prior to sintering, a process is further included in refining sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and a conductive agent, wherein the particle size D50 of the refined sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and conductive agent is 0.02 μm to 20 μm.

[0038] Specifically, the refining process can be achieved using any of the following methods: ball milling, sand milling, and air jet milling.

[0039] In one specific embodiment, sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and a conductive agent are ball-milled and mixed, and then sintered at 250°C to 500°C under an inert atmosphere for 2 to 24 hours to obtain the positive electrode material. Preferably, the ball milling and mixing are also carried out under an inert atmosphere.

[0040] Preferably, before refining, the process also includes drying sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride and conductive agent separately to avoid water vapor in the cathode material and to avoid increasing the gas production.

[0041] Specifically, drying can be achieved through methods such as vacuum drying and baking.

[0042] The present invention also discloses a sodium-ion battery comprising the above-described positive electrode material.

[0043] The following are specific examples.

[0044] Example 1

[0045] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0046] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours, and then refined separately;

[0047] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.5:0.5:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0048] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.5 Ni 0.5 (SO4)2F cathode material.

[0049] Example 2

[0050] The only difference between Example 2 and Example 1 is the sodium ferric fluorosulfate compound; the preparation method, conductive agent, and its content are the same. Details are as follows:

[0051] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0052] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0053] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.6:0.4:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0054] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.6 Ni 0.4 (SO4)2F cathode material.

[0055] Example 3

[0056] Example 3 differs from Example 1 only in the sodium ferric fluorosulfate compound; the preparation method, conductive agent, and its content are all the same. Details are as follows:

[0057] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0058] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0059] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.7:0.3:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0060] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.7 Ni 0.3 (SO4)2F cathode material.

[0061] Example 4

[0062] Example 4 differs from Example 1 only in the sodium ferric fluorosulfate compound; the preparation method, conductive agent, and its content are all the same. Details are as follows:

[0063] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0064] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0065] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.8:0.2:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0066] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.8 Ni 0.2 (SO4)2F cathode material.

[0067] Example 5

[0068] Example 5 differs from Example 1 only in the sodium ferric fluorosulfate compound; the preparation method, conductive agent, and its content are all the same. Details are as follows:

[0069] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0070] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0071] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.9:0.1:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0072] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.9 Ni 0.1 (SO4)2F cathode material.

[0073] Example 6

[0074] Example 6 differs from Example 1 only in the sodium ferric fluorosulfate compound; the preparation method, conductive agent, and its content are all the same. Details are as follows:

[0075] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0076] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0077] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0078] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0079] The scanning electron microscope image of the cathode material prepared in Example 6 is shown below. Figure 1 , Figure 1 It can be seen from the data that the particle size of the prepared sample is 2-7 μm.

[0080] Example 7

[0081] The only difference between Example 7 and Example 1 is the composition of the conductive agent. Specifically:

[0082] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0083] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0084] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent was added to the mixture at a weight ratio of 95:5, wherein the conductive agent was a mixture of carbon nanotubes and nickel powder in a weight ratio of 4:1. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0085] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0086] Example 8

[0087] The only difference between Example 8 and Example 1 is the composition of the conductive agent. Specifically:

[0088] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0089] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0090] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent was added to the mixture at a weight ratio of 95:5, wherein the conductive agent was a mixture of carbon nanotubes and nickel powder in a weight ratio of 3:2. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0091] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0092] Example 9

[0093] The only difference between Example 9 and Example 1 is the composition of the conductive agent. Specifically:

[0094] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0095] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0096] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent was added to the mixture at a weight ratio of 95:5, wherein the conductive agent was a mixture of carbon nanotubes and nickel powder in a weight ratio of 1:1. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0097] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0098] Example 10

[0099] The only difference between Example 10 and Example 1 is the composition of the conductive agent. Specifically:

[0100] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0101] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0102] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent was added to the mixture at a weight ratio of 95:5, wherein the conductive agent was a mixture of carbon nanotubes and nickel powder in a weight ratio of 2:3. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0103] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0104] Example 11

[0105] The only difference between Example 11 and Example 1 is the composition of the conductive agent. Specifically:

[0106] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0107] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours, and then refined separately.

[0108] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent was added to the mixture at a weight ratio of 95:5, wherein the conductive agent was a mixture of carbon nanotubes and nickel powder in a weight ratio of 1:4. The mixture was then ball-milled under an inert atmosphere to obtain the cathode material precursor.

[0109] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0110] Example 12

[0111] The only difference between Example 12 and Example 1 is the composition of the conductive agent. Specifically:

[0112] This embodiment provides a method for preparing a cathode material based on doped sodium ferric fluorosulfate compound, comprising the following steps:

[0113] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0114] S2, a mixture is prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent (nickel powder) is added to the mixture at a weight ratio of 95:5, and the mixture is then ball-milled under an inert atmosphere to obtain a positive electrode material precursor.

[0115] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Ni 0.001 (SO4)2F cathode material.

[0116] Example 13

[0117] The difference between Example 13 and Example 6 is that nickel sulfate is replaced with manganese sulfate, as detailed below:

[0118] S1, anhydrous sodium sulfate, ferrous sulfate, manganese sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0119] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, manganese sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0120] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Mn 0.001 (SO4)2F cathode material.

[0121] Example 14

[0122] The difference between Example 14 and Example 6 is that nickel sulfate is replaced with copper sulfate, as detailed below:

[0123] S1, anhydrous sodium sulfate, ferrous sulfate, copper sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0124] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, copper sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0125] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Cu 0.001 (SO4)2F cathode material.

[0126] Example 15

[0127] The difference between Example 15 and Example 6 is that nickel sulfate is replaced with cobalt sulfate, as detailed below:

[0128] S1, anhydrous sodium sulfate, ferrous sulfate, cobalt sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0129] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, cobalt sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0130] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Co 0.001 (SO4)2F cathode material.

[0131] Example 16

[0132] The difference between Example 16 and Example 6 is that nickel sulfate is replaced with vanadium(II) sulfate, as follows:

[0133] S1, anhydrous sodium sulfate, ferrous sulfate, vanadium sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0134] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, vanadium sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0135] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 V 0.001 (SO4)2F cathode material.

[0136] Example 17

[0137] The difference between Example 17 and Example 6 is that nickel sulfate is replaced with titanium sulfate (Ti(SO)), as follows:

[0138] S1, anhydrous sodium sulfate, ferrous sulfate, titanium sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0139] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, titanium sulfate, and sodium fluoride in a molar ratio of 1:0.998:0.002:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0140] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.998 Ti 0.001 (SO4)2F cathode material.

[0141] Example 18

[0142] The difference between Example 18 and Example 6 is that nickel sulfate is replaced with chromium sulfate (Cr(SO)), as follows:

[0143] S1, anhydrous sodium sulfate, ferrous sulfate, chromium sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours, and then refined separately;

[0144] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, chromium sulfate, and sodium fluoride in a molar ratio of 1:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0145] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric sulfate compound Na3Fe. 0.999 Cr 0.001 (SO4)2F cathode material.

[0146] Comparative Example 1

[0147] Comparative Example 1 is the prior art. Compared with Examples 1-6, sodium fluoride and nickel sulfate were not used in the raw materials, as detailed below:

[0148] S1, anhydrous sodium sulfate and ferrous sulfate were dried under vacuum at 150°C for 12 hours, and then refined separately;

[0149] S2, a mixture is prepared by mixing anhydrous sodium sulfate and ferrous sulfate in a molar ratio of 1:1. A conductive agent, consisting of carbon nanotubes, is added to the mixture at a weight ratio of 95:5. The mixture is then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0150] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain the cathode material of sodium iron sulfate compound Na2Fe(SO4)2.

[0151] Comparative Example 2

[0152] Comparative Example 2, compared to Examples 1-6, was not doped with nickel sulfate, as detailed below:

[0153] S1, anhydrous sodium sulfate, ferrous sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours, and then refined separately;

[0154] S2, a mixture is prepared by mixing anhydrous sodium sulfate, ferrous sulfate and sodium fluoride in a molar ratio of 1:1:1.05. A conductive agent is added to the mixture in a weight ratio of 95:5, wherein the conductive agent is carbon nanotubes. The mixture is ball-milled under an inert atmosphere to obtain a precursor for the cathode material.

[0155] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain the cathode material of sodium ferric sulfate compound Na3Fe(SO4)2F.

[0156] Comparative Example 3

[0157] Compared to Example 6, Comparative Example 3 changed the content of anhydrous sodium sulfate, as follows:

[0158] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0159] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 0.5:0.9999:0.0001:1.05. A conductive agent, specifically carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0160] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain Na2Fe, a doped sodium ferric sulfate compound. 0.999 Ni 0.001 (SO4) 1.5 F is the positive electrode material.

[0161] Comparative Example 4

[0162] Compared to Example 6, Comparative Example 4 changed the content of anhydrous sodium sulfate, as follows:

[0163] S1, anhydrous sodium sulfate, ferrous sulfate, nickel sulfate and sodium fluoride were dried under vacuum at 150°C for 12 hours and then refined separately;

[0164] S2, a mixture was prepared by mixing anhydrous sodium sulfate, ferrous sulfate, nickel sulfate, and sodium fluoride in a molar ratio of 1.5:0.999:0.001:1.05. A conductive agent, consisting of carbon nanotubes, was added to the mixture at a weight ratio of 95:5. The mixture was then ball-milled under an inert atmosphere to obtain the precursor for the cathode material.

[0165] S3, under an inert atmosphere, the cathode material precursor is sintered at 350°C for 12 hours to obtain a doped sodium ferric fluorosulfate compound, Na4Fe. 0.999 Ni 0.001 (SO4) 2.5 F is the positive electrode material.

[0166] Test case

[0167] The positive electrode materials of Examples 1-12 and Comparative Examples 1-4 were assembled into sodium-ion 2016 coin cells, and the performance of the sodium-ion cells could be tested. The solid electrolyte was 1M NaPF6 with EMC / DEC / PC = 5:3:2, and the negative electrode was a hard carbon negative electrode, resulting in a 1Ah pouch cell.

[0168] The cycle performance and rate performance testing methods are as follows: At room temperature, the battery is left to rest for 5 minutes, then charged at a constant current rate of 0.1C to 4.5V, then charged at a constant voltage rate until the current is less than or equal to 0.05C, then left to rest for 5 minutes, and then discharged at a constant current rate of 0.1C to 1.5V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as the charge-discharge capacity of the sodium-ion secondary battery in the first cycle. The battery is cycled 100 times according to the above method, and the charge-discharge capacity of each cycle is recorded. The battery capacity retention rate (%) = discharge capacity of the 100th cycle / discharge capacity of the 1st cycle × 100%. The results of 0.1C specific capacity utilization and 100-cycle battery capacity retention rate are shown in Table 1.

[0169] The gas production rate is tested using the water displacement method. The specific testing method is as follows:

[0170] During cell formation and thermal instability testing, a large amount of gas is generated. Therefore, quantitative analysis of this gas is crucial. The water displacement method is based on the ideal gas law:

[0171] PV = nRT (1)

[0172] By maintaining uniform pressure inside and outside the battery cell, the amount of gas can be determined by measuring the volume change of the cell. The volume change can be measured using Archimedes' displacement method. (Test diagram follows.) Figure 2 As shown.

[0173] The density of the liquid is ρ.

[0174] F_buoyancy = ρgV (2)

[0175] When the battery cell is in equilibrium and at rest, the balance reading is m1:

[0176] F_weight = F_tension + F_buoyancy (3)

[0177] F_pull = m1g (4)

[0178] When the battery cell produces gas, its volume expands by ΔV. At this time, the balance reading is m2. Since the overall mass of the battery cell remains unchanged, the weight F remains constant. Therefore:

[0179] ΔF_pull = ΔF_buoyancy = ρgΔV = g(m1-m2) (5)

[0180] so:

[0181] ΔV=(m1-m2) / ρ (6)

[0182] The specific gas production can then be obtained using formula (1). This method is suitable for testing pouch cells and can be used to study the gas production during formation, aging, and cycling. The key point of this method is to reserve sufficient gas space in the cell to ensure that the gas pressure inside and outside the cell is consistent. The test results are shown in Table 1.

[0183] Table 1: Test results of the cathode materials prepared in Examples 1-12 and Comparative Examples 1-4

[0184]

[0185]

[0186] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A positive electrode material, characterized by, comprising an electrically conductive agent and a doped sodium iron fluorosulfate compound, wherein the doped sodium iron fluorosulfate compound has a chemical structure of Na3Fe y M z (SO4)2F, wherein y+z = 1, 0.001 < z < 0.1, M is selected from Mn, Cu, Ni, Co, Cr, V, or Ti; The conductive agent is a carbon-based electronic conductive agent.

2. The positive electrode material of claim 1, wherein, The mass percentage of the conductive agent in the positive electrode material is 0.1% to 10%.

3. The positive electrode material of claim 2, wherein, The carbon-based electronic conductive agent includes one or more of amorphous carbon, Super p, carbon nanotube, VGCF, graphene, Ketjen black, acetylene black, C65 carbon black, and conductive graphite.

4. A method for producing the positive electrode material according to any one of claims 1 to 3, characterized by, The process includes: The sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and conductive agent are weighed according to the molar ratio Na:Fe:M:S:F = 3:y:z:2:1, mixed, and sintered to obtain the positive electrode material.

5. The method for preparing the cathode material according to claim 4, characterized in that, The sintering temperature is 250°C to 500°C; the sintering time is 2h to 24h; and the sintering is performed in an inert atmosphere.

6. The method for preparing the cathode material according to claim 5, characterized in that, The process further includes a step of refining the sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and conductive agent before sintering, and the particle size D50 of the refined sodium sulfate, ferrous sulfate, M sulfate, sodium fluoride, and conductive agent is 0.02μm to 20μm.

7. A sodium-ion battery, characterized in that, The positive electrode material as claimed in any one of claims 1 to 3.

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